Solution Manual & Test Bank for Java Software Solutions, Global Edition, 9th Edition by John Lewis

Solution Manual & Test Bank for Java Software Solutions, Global Edition, 9th Edition by John Lewis

Java Software Solutions, 9e (Lewis/Loftus) Chapter 1 Introduction TRUE/FALSE 1. All information is stored in the computer using binary numbers.

ANS: T The computer is a digital device meaning that it stores information in one of two states using binary.

We must determine then how to represent meaningful information (such as a name or a program instruction or an image) in binary.

2. Java is an object-oriented programming language.

ANS: T Java is classified as a high-level programming language but it is also classified as an object-oriented programming language because it allows the programmer to implement data structures as classes.

3. System.out.print is used in a program to denote that a documentation comment follows.

ANS: F Documentation comments follow // marks or are embedded between */ and */.

System.out.print is an instruction used to output a message to the screen (the Java console window).

4. Java byte codes are directly executable whereas Java source code is not.

ANS: F Neither Java source code nor Java byte codes are executable. Both must be compiled or interpreted into machine code. Java byte codes are useful however in that they are machine-independent but semi-compiled code that allows your Java code to be transmitted over the Internet and executed on another computer even if that other computer is a completely different type.

5. The Java compiler is able to find all programmer errors.

ANS: F The Java compiler can find syntax errors but cannot find either logical errors (errors that are caused because of poor logic in writing the program) or run-time errors (errors that arise during the execution of the program).

6. Java is a case-sensitive language which means Current, CURRENT, and current will all reference the same identifier.

ANS: F

Java is case sensitive which means that Current, CURRENT, and current will all be recognized as different identifiers. This causes problems with careless programmers who do not spell an identifier consistently in terms of upper and lower case characters.

7. Code placed inside of comments will not be compiled and, therefore, will not execute.

ANS: T The compiler discards comments; therefore, any code inside a comment is discarded and is not compiled. Your executable program consists only of the code that is compiled.

8. The word Public is a reserved word.

ANS: F public is a reserved word, but since Java is case sensitive, Public differs from public and therefore Public is not a reserved word.

9. Reserved words in Java can be redefined by the programmer to mean something other than their original intentions.

ANS: F Java reserved words cannot be redefined.

10. In a Java program, dividing by zero is a syntax error.

ANS: F Dividing by 0 is not detected at compile time, and because a computer cannot divide by 0, this is a runtime error.

11. In a Java program, dividing by zero is a syntax error.

ANS: F Dividing by 0 is not detected at compile time, and because a computer cannot divide by 0, this is a runtime error.

12. During translation, the compiler puts its output (the compiled Java program) into ROM. ANS: F ROM stands for read-only-memory. The compiled output (the byte codes) may be placed into RAM (writable random access memory) or into a file (on your hard drive, for example).

13. Objects are defined by a class that describes the characteristics common to all instances of the class.

ANS: T An object is an instance of a class. And, the purpose of a class is to describe these common characteristics.

14. Inheritance is a form of software reuse.

ANS: T Inheritance allows us to capitalize on the similarities among various kinds of classes that have a common base (parent) class. Thus we reuse the base class each time a class inherits from it.

15. Polymorphism is the idea that we can refer to multiple types of related objects in consistent ways.

ANS: T Polymorphism allows us to use the same name for similar behaviors that occur among diverse and possibly unrelated objects. For example, to "open" may refer to a file, or to a device, or to a communications line, etc. The same term, "open," is being used even though the objects that are being opened are quite different.

16. In Java, identifiers may be of any length up to a limit determined by the compiler.

ANS: F Java (and Java compilers) do not limit the length of the identifiers you use. Identifiers may be as long as you wish. Good programming practice, however, will limit the lengths of the identifiers you create.

MULTIPLE CHOICE 1. A Java program is best classified as a. b. c. d. e.

hardware software storage processor input

ANS: B Programs are classified as software to differentiate them from the mechanisms of the computer (hardware). Storage and the processor are two forms of hardware while input is the information that the program processes.

2. Six bits can be used to represent a. b. c. d. e.

distinct items or values.

6 20 24 32 64

ANS: E With n bits, we can represent 2^n different values. 2^6 = 64.

3. When executing a program, the processor reads each program instruction from a. secondary memory (storage) b. the Internet

c. registers stored in the processor d. main memory e. Any of these ANS: D The program is first loaded from secondary memory into main memory before it is executed so that the processor is not slowed down by reading each instruction. This idea of executing programs stored in memory is called the Stored Program Computer and was pioneered by John Von Neumann in the 1940s.

4. Which memory capacity is the largest? a. b. c. d. e.

1,500,000,000,000 bytes 100 gigabytes 3,500,000 kilobytes 10 terabytes 12,000,000 megabytes

ANS: E We convert each of these capacities to bytes (rounding off) to compare them. The value in A remains the same, 1 1/2 trillion bytes. The value in B is 100 billion bytes. The value in C is 3 1/2 billion bytes. The value in D is 10 trillion bytes. The answer in E is 12 trillion bytes.

5. Binary numbers are composed entirely of a. b. c. d. e.

0s 1s 0s and 1s any digits between 0 and 9 0s, 1s, and 2s

ANS: C Binary is base 2. In Mathematics, numbers in base n are composed entirely of digits between 0 and n1.

6. Volatility is a property of a. b. c. d. e.

RAM ROM disk software computer networks

ANS: A

Volatility means that the contents of memory are lost if the electrical power is shut off. This is true of RAM (Random Access Memory), but not ROM (Read Only Memory) or disk.

Software and computer networks are not forms of memory.

7. The ability to directly obtain a stored item by referencing its address is known as a. b. c. d.

random access sequential access read-only access fetch access

e. volatility ANS: A Random access is meant to convey the idea that accessing any item is equally easy, and that any item is retrievable based solely on its address. Random access is the form of access used by both RAM and ROM memory. Disk access, called direct access, is a similar idea, and direct and random access are sometimes referred to synonymously. Sequential access is used by tape.

8. Which phase of the fetch-decode-execute cycle might use a circuit in the arithmetic-logic unit? a. b. c. d. e.

fetch decode execute during fetch or execute, but not decode any of the phases

ANS: C The fetch phase retrieves (fetches) the next program instruction from memory. The decode phase determines which circuit(s) needs to be used to execute the instruction. The instruction is executed during the execute phase. If the instruction is either an arithmetic operation (like add or multiply) or a logical operation (like comparing two values), then it is carried out by the ALU. 9. In order for a computer to be accessible over a computer network, the computer needs its own a. b. c. d. e.

MODEM communication line network address packet router

ANS: C In order to differentiate between the computers on a network, each is given its own, unique, network address. In this way, a message intended for one computer can be recognized by that computer through the message's destination address. A MODEM is a device that is used to allow a computer to communicate to another computer over a telephone line. A communication line is the network media itself. A packet is a collection of data that is sent over a network. A router is a hardware device used to take a message from one network and move it to another based on the message's destination address.

10. For a computer to communicate over the Internet, it must use a. b. c. d. e.

the TCP protocol the IP protocol the combined TCP/IP protocol the Ethernet protocol the ARPANET protocol

ANS: C IP is the Internet Protocol, but the TCP (Transmission Control Protocol) also must be used because it handles such problems as how to piece together packets of the same message that arrive out of order.

Ethernet is a LAN protocol, which might be used in addition to TCP/IP in some networks, but it is not needed to communicate over the Internet. There is no such thing as the ARPANET protocol.

11. A URL (Uniform Resource Locator) specifies the address of a a. computer on any network

b. c. d. e.

computer on the Internet local area network (LAN) on the Internet a document or other type of file on the Internet a Java program on the Internet

ANS: D URLs are used to locate documents (or other types of files such as an image or sound file) anywhere on the Internet. A URL contains the address of the LAN or WAN and the specific computer from which the file is to be retrieved; it specifies the file's address, not just the computer's address.

12. It is important to dissect a problem into manageable pieces before trying to solve the problem because a. most problems are too complex to be solved as a single, large activity b. most problems are solved by multiple people and it is easy to assign each piece to a separate person c. ir is easier to integrate small pieces of a program into one program than it is to integrate one big chunk of code into one program d. the first solution may not solve the problem correctly e. All of these ANS: A Any interesting problem will be too complex to solve easily as a single activity. By decomposing the problem, we can build small solutions for each piece and then integrate the pieces. Answer D is true, but it is not the reason why we will break a problem into pieces.

13. Once we have implemented a solution, we are not done with the problem because a. b. c. d.

the solution may not be the best (most efficient) the solution may have errors and need testing and fixing the solution may, at a later date, need revising to handle new specifications the solution may, at a later date, need revising because of new programming language features e. All of these ANS: E A program should not be considered as a finished product until we are reasonably assured that it is efficient and error-free. Further, it is common that programs require modification in the future because of a change to specifications or a change to the language or computer running the program.

14. Java is an example of a(n) a. b. c. d. e.

machine language Assembly language high-level language fourth generation language both high-level and fourth generation language

ANS: E While Java was created during the fourth generation, it is clearly also a high-level language. Machine language is the executable language of a machine, with programs written in 1s and 0s only. Assembly language uses mnemonics. Fourth generation languages are tools wrapped inside of programs so that the user has the flexibility to write some code to executed from within the program.

15. Of the following, which statement is not true regarding Java as a programming language? a. Java is a relatively recent language; it was introduced in 1995. b. Java is a language whose programs do not require translating into machine language before they are executed. c. Java is an object-oriented language. d. Java is a language that embraces the idea of writing programs to be executed with the World Wide Web. e. All of these are true ANS: B All languages require translation into machine language. The other statements are all true about Java.

16. Comments should a. b. c. d. e.

rephrase all the code to explain it in English be insightful and explain the intention of an instruction or block of code only be included with code that is difficult to understand be used to define variables that have hard to understand names All of these

ANS: B Comments should not rephrase in English what an instruction says, but instead should explain what that instruction is doing in relation to the program. Introductory programmers often have difficult explaining their code and wind up stating the obvious in their comments. While answer D is partially correct, it is not entirely true even though all variables should have comments that explain their use.

17. The main method for a Java program is defined by a. b. c. d. e.

public static main() public static main(String[] args); public static main(String[] args) private static main(String[] args) The main method could be defined by all of these except B

ANS: C In A, the parameter is missing. The parameters are defined later in the text, but in effect, they allow the user to run the program and include some initial arguments if the program calls for it. In B, the semicolon at the end of the statement is not allowed. In D, private instead of public would make the program non-executable by anyone and thus makes the definition meaningless.

18. What does the following line of Java code do? //System.out.println("Hello"); a. b. c. d. e.

nothing cause Hello to be output cause a syntax error cause ("Hello") to be output There is no way to tell without executing the code.

ANS: A The characters // denote the beginning of a comment. The comment is not compiled and so, nothing would happen when this code is executed.

19. What comment might be added to explain the following instruction?

System.out.println("Hello World"); a. b. c. d. e.

// prints "Hello World" to the screen //prints a message //used to demonstrate an output message // // meaningless instruction

ANS: C Comments in A and B state the obvious while the comments in D and E are meaningless. The comment in C explains why the instruction appears in the program.

20. Which character belowis not allowed in an identifier? a. b. c. d. e.

$ _ 0 1 ^

ANS: E Java identifiers can consist of any letter, digit, $ or _ as long as the identifier starts with a letter or _. ^ is not a legal character.

21. Which of the following is not syntactically legal in Java? a. b. c. d. e.

System.out.println("Hi"); public class Foo s t a t i c main(String[] args) {} only A is legally valid; all the others are illegal

ANS: C The Java compiler would not recognize "s t a t i c" as "static" because the Java compiler treats white space (blanks) as separators between entities. The other statements are all legal, including "{}" which is a block that happens to have no statements within it.

22. Which of the following is a legal Java identifier? a. b. c. d. e.

i class 1likeclass! idon'tlikeclass i-like-class

ANS: A Java identifiers cannot have the characters !, ' or - in them so answers C, D and E are wrong. The word class is a reserved word in Java and cannot be used as an identifier. The identifier i is perfectly legal although it is not necessarily a good identifier since it is not descriptive of its use.

23. A unique aspect of Java that allows code compiled on one machine to be executed on a machine with a different hardware platform is Java's

a. b. c. d. e.

bytecodes syntax use of objects use of exception handling All of these

ANS: A The translation process for a Java program is to first compile it into bytecodes, which are architecturally neutral (that is, they can be used no matter what the architectural platform is). To execute the program, the bytecodes must be further compiled by a Java compiler or interpreted by a Java Virtual Machine.

24. Java is similar in syntax to which of the following high-level languages? a. b. c. d. e.

Pascal Ada C++ FORTRAN BASIC

ANS: C The creators of Java decided to use syntax similar to C++ so that C++ programmers could easily learn Java. Variable declarations, assignment statements, loops, selection statements and comments are among the features that have nearly identical syntax. There are many differences however, so don't assume that any C or C++ programmer will easily or instantly be able to program in Java.

25. An error in a program that results in the program outputtinh $100 instead of the correct answer, $250, is a a. b. c. d. e.

compiler error syntax error run-time error logical error snafu

ANS: D While this is an error, programmers classify the type of error in order to more easily solve the problem.

Syntax errors are caught by the compiler and the program cannot run without fixing all syntax errors.

Run-time errors arise during program execution and cause the program to stop running. Logical errors are errors whereby the program can run to completion, but gives the wrong answer. If the result should have been $250, then the logic of the program is wrong since it output $100. A snafu is a term expressing a messed up situation in combat and should not be used by respectable programmers!

26. Which of the following is true regarding Java syntax and semantics? a. A Java compiler can determine if you have followed proper syntax but not proper semantics. b. A Java compiler can determine if you have followed proper semantics but not proper syntax. c. A Java compiler can determine if you have followed both proper syntax and proper semantics. d. A Java compiler cannot determine if you have followed either proper syntax or proper semantics.

e. A Java compiler can determine if you have followed proper syntax but not proper semantics only if you follow the Java naming convention rules.

ANS: A Compilers for all languages have the ability to detect syntax errors because improper use of the syntax leads to situations where the compilers cannot translate the code properly. However, compilers are unable to follow the semantics of a program because this requires a degree of understanding what the program is intended to do and computers have no sense of understanding (at least at this point).

27. Using Java naming convention, which of the following would be a good variable name for the current value of a stock? a. b. c. d. e.

curstoval theCurrentValueOfThisStock currentStockVal csv current

ANS: C Java allows long variable names but the programmer must find a good compromise between an excessive long name (as with B) and names too short to understand their use (A and D). The name current possibly might be reasonable if there are no other "current" values being referenced in the program.

28. Which of the following is a legal Java identifier? a. b. c. d. e.

1ForAll oneForAll one/4/all 1_4_all 1forall

ANS: B Java identifiers cannot start with a number (so the answers in A, D and E are illegal) and cannot include the / character, so the answer in C is illegal.

29. A color image is broken down into individual pixels (points), each of which is represented by a. b. c. d.

a 1 for white and a 0 for black 3 values denoting the intensity of red, green, and blue in the image a single number indicating the intensity of color between white and black two numbers, where one indicates where the color is between white and black and the other denotes the brightness e. None of these; it is not possible to represent color ANS: B Black and white images are stored using 0s and 1s while color images are stored using three values, one each for the degree of red, the degree of blue, and the degree of green.

30. Which of the following characters does not need to have an associated closing character in a Java program? a. { b. (

c. [ d. < e. All of these require closing characters ANS: D { is used to open a block, and so } is needed to close the block. ( is used to open an expression and so ) is needed to close an expression. [ is used to start an array index so ] is needed to close the array index. < is "less than" and > is "greater than" and these are not needed together, so < requires no closing character.

31. Mistyping println as printn will result in a. b. c. d. e.

a syntax error a run-time error a logical error no error the statement being converted to a comment

ANS: A If the Java compiler cannot make sense of a command, the compiler cannot convert it and responds with a syntax error. While println is recognized as a command, printn is not, and so the compiler provides a syntax error.

PROBLEM 1. What is wrong with the following class definition? public class Program1 { public static void main(String[ ] args) { System.out.println("My first Java program") } } ANS: The one executable statement in the main method is missing a ";" at the end of the line. Executable statements end with ";".

2. What is wrong with the following class definition? public class Program2 public static void main(String[] args) { System.out.println("My second Java program"); } ANS: The definition of a class is placed within {} statements, which are missing here.

3. Given the following class definition, what are the reserved words and what are the identifiers? public class Program3

{ public static void main(String[] args) { System.out.println("My third Java program"); } } ANS: The reserved words are public, class, static, void. The identifiers are main, String, System.out, Program3, and args. main is the name of a method defined within the Program3 class. string and System.out are classes already defined in Java and println is a method of System.out. Program3 is a class, defined here, and args is a variable.

4. Provide a brief explanation of the role of main memory, the control unit, the arithmetic logic unit, and registers. (Refer to figure 1.13 in the text) ANS: Main memory is used to store the currently executing processes along with their data. The control unit performs the fetch-decode-execute cycle, which fetches an instruction from memory, decodes it and determines how it is to be executed. The arithmetic logic unit comprises a number of circuits that execute arithmetic and logic instructions. Registers are used to store values in the CPU temporarily while the current instruction(s) need them.

5. What is the output of the following code when the main method is executed? public class Question4 { public static void main(String[] args) { System.out.println("hi there"); System.out.println(" "); System.out.println("how are you doing } }

today?

");

ANS: hi there how are

you doing

today?

Notice that while the Java compiler ignores "white space", blanks that appear in a println statement inside of quote marks are retained and output in that manner.

6. What is wrong with the following println statement?

System.out.println("My fourth Java Program); ANS: It is missing a closing ". The compiler will look for a second " before the end of the statement. So, like {}, (), and [], an initial " must have a corresponding closing ".

7. Provide identifier names that would be used to represent a person's social security number, income tax withheld, and net pay.

ANS: socialSecurityNumber, or ssn, incomeTaxWithheld or incomeTax, and netPay all would be reasonable.

8. There are a number of reserved words in Java that have no current meaning (denoted with an * in figure 1.18 in the text). Why? ANS: Java language designers anticipate introducing these statements in future versions, but have not yet implemented them because they are lower priority, or it has not been decided how they will be implemented or precisely what they will mean.

9. A document of text is 15 pages long. Each page contains approximately 200 words and the average length of each word is 5 characters. Also assume one blank space between each word and no punctuation. How many bytes will it take to store this document in memory or on disk using ASCII? ANS: A character is stored in ASCII using 8 bits or 1 byte. Therefore, 5 characters per word plus 1 blank space between words take 6 bytes per word (except for the first). Each page stores 200 words and there are 15 pages. So we need 15 * 200 * 6 - 1 (no blank space to start the text) = 17,999 bytes which is 17.58 kilobytes, or nearly 18 Kbytes.

10. Provide a brief description of the roles of the following hardware elements (that is, what each is used for): a) CPU b) Main memory c) Secondary memory devices d) Input/Output devices ANS: a) The CPU is the processor. It executes all program instructions. It does this through the fetchdecode-execute cycle where the next program instruction is fetched from memory, decoded in the CPU, and then executed by one or more circuits. b) Main memory is stored on chips on the motherboard and is used for quick access to the currentprogram for the fetch-decode-execute cycle and to store data being used by this program. c) Secondary memory devices are storage devices, used to store programs and data not currently being used. Storage devices, such as the hard disk, also are used to store things for permanence and archives. d) Input/Output devices are used to communicate with the computer. Input devices, like the keyboard, take commands and data from the user and output devices, like the monitor, display the results of the process/computation.

11. Examine figure 1.7 before answering this question. What 8-bit value comes immediately before and what 8-bit value comes immediately after 10010111?

ANS: 10010110 comes immediately before 10010111 and 10010100 comes immediately after 10010111.

12. Rewrite the following comment so that is can appear over multiple lines. // This is one really enormously long comment that might run off the page ANS: We can do this in two ways, preceding each line with // or by enclosing the comment in /* and */. /* This is one really enormously long comment that might run off the page */ or // This is one really enormously // long comment that might run // off the page 13. Rewrite the following program with better formatting to make it easier to read. public class MyProgram { public static void main( String[] args) { System.out.println( "Wow, this is messed up!" ); } } ANS: There are many ways this program might appear. The following would be very acceptable: public class MyProgram { public static void main(String[] args) { System.out.println("Wow, this is messed up!"); } } 14. Write a Java program that will output on two separate lines the names of the authors of this textbook.

ANS: public class OutputNames { public static void main(String[] args) { System.out.println("John Lewis"); // 1st author's name System.out.println("William Loftus");// 2nd author's name } }

15. Correct all the syntax errors in the following program.

Public Class Program \\ A problem program ( Public static voided main[Strings() args] { system.out.println('This program'); \* oh, my... *\ system.out.println('has several syntax errors'); \* lots of errors *\ } ) ANS: public class Program // A problem program { public static void main(String[] args) { System.out.println("This program"); /* oh, my... */ System.out.println("has several syntax errors"); /* lots of errors */ } } 16. Write a Java program that will display the following three lines when it is run: * * * * * * * * * ANS: public class Stars { public static void main(String[] args) { System.out.println(" *"); System.out.println(" * * *"); System.out.println("* * * * *"); } }

17. Name five of the fundamental terms which encompass object-oriented programming.

ANS:

There are seven terms to choose from: object, attribute, method, class, encapsulation, inheritance, and polymorphism.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 2 Data and Expressions TRUE/FALSE 1. If x is a String, then x = new String("OH"); and x = "OH"; will accomplish the same thing.

ANS: T In Java, to instantiate (assign a value to) an object, you must use new and the class's constructor.

However, since Strings are so common in Java, they can be instantiated in a way similar to assigning primitive types their values. So, both of the above assignment statements will accomplish the same task.

2. If x is the String "Hi There", then x.toUpperCase().toLowerCase(); will return the original value of x.

ANS: F x.toUpperCase() returns x as all capital letters, while x.toLowerCase()will return x as all lower case letters. So, this code will first convert x to all upper case letters and then convert the new version to all lower case characters.

3. If String name = "George W. Bush"; then the instruction name.length(); will return 14.

ANS: T There are 14 characters between the quote marks including two blanks and a period.

4. If String a = "ABCD" and String b = "abcd" then a.equals(b); returns false but a.equalsIgnoreCase(b); returns true.

ANS: T Since "ABCD" is not the same as "abcd", the equals method returns false, but by ignoring case in equalsIgnoreCase, the two are considered to be the same.

5. Unlike the String class where you must pass a message to an object (instance) of the class, as in x.length(), in order to use either the Scanner or Math classes, you pass messages directly to the class name, as in Math.abs()or scan.nextInt().

ANS: T The Math and Scanner classes use methods known as static methods (or class methods) which are invoked by passing a message directly to the class name itself rather than to an object of the class.

6. In order to generate a random number, you must use Math.random().

ANS: F There is also a Random class available in java.util. This class can generate random int, float, and double values. This is a better mechanism for generating random numbers because you can instantiate several different random number generators.

7. A double is wider than a float and a float is wider than an int.

ANS: T Wider types are larger in size or can store a greater range of values. The double is 64 bits whereas the float is 32 bits and the float, because of the way it is stored, can store a significantly larger range of values than the int.

8. A variable of type boolean will store either a 0 or a 1.

ANS: F A boolean variable can store only one of two values, but these values are the reserved words true and false. In C, C++, and C# booleans are implemented as int variables that store only a 0 or a 1, but in Java, the authors of the language opted to use the boolean literals true and false as this is considered to be semantically more understandable (and is much safer).

9. In Java, 'a' and 'A' are considered to be different values.

ANS: T Characters values are stored using ASCII, and 'a' and 'A' have different ASCII values as well as different Unicode values.

10. You cannot cast a String to be a char and you cannot cast a String which stores a number to be an int, float, or double.

ANS: T There is no mechanism available to cast a String to one of the primitive types, but there are methods available to perform a similar action and return a character at a given location (CharAt) or to return the int, float, or double value equivalent to the number stored in the String.

11. The values of (double)5/2 and (double)(5/2) are identical.

ANS: F In the first expression, the (double) cast applies to theint 5, changing it to the double value, 5.0. Then 5.0/2 is calculated, yielding the double value, 2.5. In the second expression the int division is performed first, yielding the value 2. 2 is then changed to a double, yielding the double value, 2.0.

12. There are three ways that data conversion may occur: by assignment, by promotion, and by casting.

ANS: T Assignment conversion occurs when a value on the right side of the assignment operator is converted prior to being stored in the variable on the left. Promotion occurs within an expression when values of differing widths are combined. Casting is a programmer's explicit way to control the data conversion process.

13. As explained in the Software Failure section in the text, the Mars Lander most likely crash landed when its descent engines cut off too high over the Mars surface.

ANS: T The software on board the lander mistook the vibrations caused by the deployment of the lander's legs for the vibration caused by actually landing on the planet's surface.

MULTIPLE CHOICE Example Code Ch 02-1 public class Questions1_4 { public static void main(String[] args) { System.out.print("Here"); System.out.println("There " + "Everywhere"); System.out.println("But not" + "in Texas"); } } 1. Refer to the class definition in Example Code Ch 02-1. The program will print the word "Here" and then print a. b. c. d. e.

"There Everywhere" on the line after "Here" "The" on the line after "Here" and "Everywhere" on the line after "There" "There Everywhere" on the same line as "Here" "ThereEverywhere" on the same line as "Here" "ThereEverywhere" on the line after "Here"

ANS: C System.out.print will output the word Here but will leave the cursor at that point rather than starting a new line. The next statement will output There Everywhere immediately after the word Here. Since there is a blank space within the quote marks for There, there is a blank space inserted between There and Everywhere.

2. Refer to the class definition in Example Code Ch 02-1. The final println command will output a. b. c. d. e.

"But not in Texas" "But notin Texas" "But not" on one line and "in Texas" on the next line "But not+in Texas" "But not + in Texas"

ANS: B

The + performs String concatenation, so that But not and in Texas are concatenated together.

Notice that there is no blank space after not or before in so that when they are concatenated, they are placed together without a blank space.

3. Refer to the class definition in Example Code Ch 02-1. How many lines of output are provided by this program? a. b. c. d. e.

1 2 3 4 5

ANS: B There will be one line of output for the first two statements combined because the print statement does not return the cursor to start a new line. And since the second statement is a println, it returns the cursor and the last println outputs its message on a separate line.

4. Refer to the class definition in Example Code Ch 02-1. A reasonable documentation comment for this program might be a. //a program that demonstrates the differences between print, println, and how + works b. //a program that outputs a message about Texas c. //a program that demonstrates nothing at all d. //a program that outputs the message "Here There Everywhere But not in Texas e. //a program that contains three output statements ANS: A Remember that comments should not state the obvious (ruling out D and E) but instead should explain what the program is doing or why. This program demonstrates print and println and +.

5. The following statement will output

lines of text.

System.out.println("1 big bad wolf\t8 the 3 little pigs\n4 dinner\r2night"); a. b. c. d. e.

1 2 3 4 5

ANS: B The \t escape sequence inserts a tab, but leaves the cursor on the same line. The \n escape sequence causes a new line to be produced so that 4 dinner is output on the next line. The escape sequence \r causes the carriage to return (that is, the cursor to be moved back to the left margin) but because it does not start a new line, 2night is output over 4 dinn resulting in a second line that looks like 2nighter.

6. If you want to output the text "hi there" including the quote marks, which of the following would you use?

a. b. c. d. e.

System.out.println("hi there"); System.out.println(""hi there""); System.out.println("\"hi there"); System.out.println("\"hi there\""); None of these; it is not possible to output a quote mark because it is used to mark the beginning and end of the String to be displayed.

ANS: D \" is an escape sequence used to place a quote mark in a String, so it is used here to output the quote marks with the rest of the String.

7. The word println is a(n) a. b. c. d. e.

method reserved word variable class String

ANS: A The word println is passed as a message to the System.out object, and so println is a method.

8. A Java variable is the name of a a. numeric data value stored in memory b. data value stored in memory that cannot change during the program's execution c. data value stored in memory that can change its value but cannot change its type during the program's execution d. data value stored in memory that can change both its value and its type during the program's execution e. data value or a class stored in memory that can change both its value and its type during the program's execution ANS: C A variable can change its value as long as it is within the same type, but the variable cannot change type. A constant is similar to a variable but it cannot change its value. Variables can be numeric but are not restricted to being numeric, they can also be boolean, char, or an object of any class.

9. Of the following types, which one cannot store a numeric value? a. b. c. d. e.

int double float char All of these can store numeric values

ANS: D int and byte are used to store whole numbers (integers) and float is used to store a real or floating point value (value with a decimal point). A char stores a single character including letters, punctuation marks and digits. However, storing the numeric digit '5' is not the same as storing the number 5.

10. What is the value of z after the following assignment statement is executed? float z = 5/10; a. b. c. d. e.

0.0 0.5 5.0 0.05 None of these; a run-time error will occur because z is a float and 5/10 is an int.

ANS: A 5 and 10 are both int values, so 5 / 10 is an integer division. The result is 0. Even though z is a float and can store the real answer, 0.5, it only gets 0 because of the integer division. In order to get 0.5, we would have to first cast 5 or 10 as a float.

11. Which of the following situations would require a cast? a. b. c. d. e.

using charAt to take an element of a String and store it in a char storing an int in a float storing a float in a double storing a float in an int All of these require casts

ANS: D For A, charAt returns a char, so there is no problem. In B and C, the situations are widening operations taking a narrower type and storing the value in a wider type. Only in D is there a situation where a wider type is being stored in a narrower type, so a cast is required.

12. If x is an int and y is a float, which of the following statements is not a legal assignment statement? a. b. c. d. e.

y = x; x = y; y = (float)x; x = (int)y; All of these are legal assignment statements

ANS: B Since x is an int, it cannot except a float unless the float is cast as an int. There is no explicit cast in the assignment statement in B. In A, a cast is not necessary because a float (y) can accept an int value (x), and in C and D, explicit casts are present making them legal.

13. What will be the result of the following assignment statement, given that b = 5 and c = 10? int a = b * (-c + 2)/2; a. b. c. d. e.

30 -30 20 -20 -6

ANS: D The unary minus is applied first giving -c + 2 = -8. Next, the * is performed giving 5*-8=40, and finally the / is performed giving -40/2 = -20.

14. Which of the following is true regarding the mod operator, %? a. b. c. d. e.

It can only be performed on int values and its result is a double.

It can only be performed on int values and its result is an int.

It can only be performed on float or double.values and its result is an int.

It can only be performed on float or double.values and its result is a double.

It can be performed on any numeric values and its result is always numeric.

ANS: E Mod, or modulo, returns the remainder that results from a division. The remainder is always is numeric. Although usually integer values are used, the % operator may be used on all kinds of numeric data.

15. Assume that x, y, and z are all ints equal to 50, 20, and 6 respectively. What is the result of: x / y / z a. b. c. d. e.

0 12 16 this would cause a syntax error this would cause a run-time error because it is a division by zero

ANS: A This division is performed left to right, so first 50/20 is performed. Since 50 and 20 are ints, this results in 2. Next, 2/6 is performed which is 0. Notice that if the division were performed right to left, the evaluation would instead be 50/(20/6) = 50/3 = 16.

16. Assume that x and y are ints equal to 10 and 5 respectively. What is the output of the following statement?

System.out.println(x + y); a. b. c. d. e.

15 105 10 5 x + y this would cause an error since neither x nor y is a String

ANS: A Java first computes x+y and then casts it as a String to be output. x+y= 10 + 5 = 15, so the statement outputs 15.

17. Assume that x and y are ints equal to 10 and 5 respectively. What is the output of the following statement?

System.out.println("" + x + y); a. b. c. d. e.

15 105 10 5 x + y this would cause an error since neither x nor y is a String

ANS: B The "" causes the rest of the expression to be treated as a String, and so the two + signs are used as String concatenation. Therefore x+y becomes x concatenated with y, or 105.

18. If you want to store the value "Harry Potter" in the String variable name, which of the following statements could you use? a. b. c. d. e.

String name = "Harry Potter"; String name = new String("Harry Potter"); String name = "Harry" + " " + "Potter"; String name = new String("Harry" + " " + "Potter"); Any of these would work

ANS: E There are two ways to store a character string into a String variable, by constructing a new String using new String(string value); or by using an assignment statement, so either A or B will work. In C and D, we have variations where the String concatenation operator is used. So all four approaches will work.

19. Given three String variables, a, b, and c, which of the following statements could you use to achieve the same thing as: c = a + b; a. b. c. d. e.

c = a.length() + b.length(); c = (int)a + (int)b; c = a.concat(b); c = b.concat(a); c = a.plus(b);

ANS: C The statement c = a + b uses the concatenation operator (not to be confused with numeric addition). The same result can be achieved by passing a the concat message with b as the parameter.

Answer D will set c to be b + a rather than a + b.

20. If the String major = "Computer Science", what is returned by major.charAt(1)? a. b. c. d. e.

'C' 'o' 'm' "C" "Computer"

ANS: B Neither D nor E would be correct because charAt returns a char (single character) whereas these answers are Strings. So, the question is, which character is returned? In Java, the first character of a String is numbered 0. So charAt(1) returns the second character of the String, or 'o'.

21. Which of the following would return the last character of the String x? a. x.charAt(0); b. x.charAt(last); c. x.charAt(length(x));

d. x.charAt(x.length()-1); e. x.charAt(x.length()); ANS: D Since last is not defined, B is syntactically invalid. The 0th character is the first in the String, so A is true only if the String has a single character. The answer in C is syntactically invalid as length can only be called by passing the message to x. Finally, D and E are syntactically valid, but since length returns the size of the String, and since the first character starts at the 0th position, the last character is at x.length()-1, so E would result in a run-time error.

22. Given String name = "Arleen Crabtree". What will the following instruction return? name.toUpperCase().replace('R', 'Z'); a. b. c. d. e.

"ARLEEN CRABTREE" "AZLEEN CZABTREE" "Azleen Czabtree" "Arleen Crabtree" "ArZleen CrZabtree"

ANS: B The toUpperCase method returns the String as all upper case characters, or "ARLEEN CRABTREE". The replace method will replace each instance of R with Z. 23. Which library package would you import to use NumberFormat and DecimalFormat? a. b. c. d. e.

java.beans java.io java.lang java.text java.util

ANS: D Both of these classes are used for "text processing", that is, to handle values like Strings. Such classes are found in java.text. You might think these would be in java.io, but this library has classes related to input and sending output to locations other than the monitor.

24. Which library package would you import to use the class Random? a. b. c. d. e.

java.beans java.io java.lang java.text java.util

ANS: E This is a Java numeric utility, and so is found in the java.util package.

25. The Random class has a method, nextFloat() which returns a random float value between a. b. c. d.

-1 and +1 0 and 1 0 and 99 1 and 100

e. -2,147,483,648 and +2,147,483,647 ANS: B The method nextFloat() returns a float value between 0 and 1 so that it may be used as a probability.

26. If you want to output a double so that at least one digit appears to the left side of the decimal point and exactly one digit appears to the right side, which pattern would you give a DecimalFormat variable when you instantiate it? a. b. c. d. e.

"0.0" "0.#" "0.0#" "0.##" "#.#"

ANS: A The pattern "0.0" says to output all of the digits to the left of the decimal point or a 0 if there are none (you want at least 1 digit to the left, including a 0 if there are no digits) and exactly one digit to the right of the decimal point, even if the digit is 0. The patterns "0.#" and "#.#" would not output any digits to the right side of the decimal point if the value had no decimal portion (e.g., 39.0).

The patterns in C and D can output up to 2 values to the right of the decimal point.

27. Given the double likelihood = 0.013885 and given DecimalFormat dformatter = DecimalFormat("0.00##"); What would be the output if you execute the following: System.out.println(df.format(likelihood)); a. b. c. d. e.

0.013885 0.0139 0.0145 .0138 .014

ANS: B The format "0.00##" means that at least 1 digit should appear to the left of the decimal point, even if it is 0, that at least two digits should appear to the right of the decimal point even if they are zeros, and if there are two additional digits to the right, they should also be printed, rounding the value off as needed. So, this gives 0.0139 since the number, 0.013885 will be rounded up to 0.0139.

28. Using getCurrencyInstance() formats a variable, automatically inserting a. b. c. d. e.

a decimal point for cents a dollar sign a percent sign all three of these a decimal point for cents and a dollar sign but not a percent sign

ANS: E getCurrencyInstance will format a double or float variable so that it has 2 digits to the right of the decimal point and a dollar sign preceding the value. getPercentInstance is used to format a double or float to be output with a percent sign.

29. What will be the value of z after the following statement is executed? int z = 50 /10.00; a. b. c. d. e.

5 5.0 50 10 None of thse; a run-time error will occur because z is an int and 50/10.00 is not

ANS: E Because 10.00 is not an int, the division produces a double precision value which cannot be stored in the int z. For this to work, the result of the division must be cast as an int before being stored in z, or the value 10.00 would have to first be cast as an int before the division takes place.

30. Since you cannot take the square root of a negative number, which of the following could you use to find the square root of the variable x? a. b. c. d. e.

Math.sqrt(x*x); Math.sqrt((int)x); Math.sqrt(Math.abs(x)); Math.abs(Math.sqrt(x)); Math.sqrt(-x);

ANS: C Math.abs returns the absolute value of x. If x is negative, Math.sqrt(x)causes a run-time error, but Math.sqrt(Math.abs(x))does not since x is first converted to its positive equivalent before the square root is performed. Answer A returns x (square root of x^2 is x). In answer B, casting x to an int will not resolve the problem if x is negative. In answer D, the two Math functions are performed in opposite order and so if x is negative, it still generates a run-time error.

Answer E only will work if x is not positive and so if x is positive, it now generates a run-time error.

31. Given x is a double and has the value 0.362491. To output this value as 36%, you could use the NumberFormat class with: NumberFormat nf = NumberFormat.getPercentInstance(); Which of the following statements then would output x as 36%? a. b. c. d. e.

System.out.println(x); System.out.println(nf); System.out.println(nf.format(x)); System.out.println(nf.x); System.out.println(format(x));

ANS: C nf is an object and so must be passed a message to use it. The method to format a float or double is called format and the value to be formatted is the parameter passed to format.

Therefore, the proper way to do this is nf.format(x). The answer in A merely outputs 0.362491 while the answers to B, C, and E are syntactically invalid.

Example Code Ch 02-2 import java.util.Scanner;

public class Questions33_34 { public static void main(String[] args) { int x, y, z; double average; Scanner scan = new Scanner(System.in); System.out.println("Enter an integer value"); x = scan.nextInt(); System.out.println("Enter another integer value"); y = scan.nextInt(); System.out.println("Enter a third integer value"); z = scan.nextInt(); average = (x + y + z) / 3; System.out.println("The result of my calculation is " + average); } } 32. Refer to Example Code Ch 02-2. This code computes a. b. c. d. e.

The correct average of x, y, and z as a double The correct average of x, y, and z as an int The average of x, y, and z as a double but the result may not be accurate The sum of x, y, and z as an int The remainder of the sum of x, y, and z divided by 3

ANS: C Because the division is an int division, even though the result is stored in a double, the resulting double may not be accurate. For instance, if x, y and z are 1, 2, and 4, the double average should be 2.33333 but average will instead be 2.00000.

33. Refer to Example Code Ch 02-2. What is the output if x = 0, y = 1, and z = 1? a. b. c. d. e.

0 0.0 0.6666666666666666 0.6666666666666667 0.67

ANS: B The division is performed as an int division since x, y, z, and 3 are all ints. Therefore, average gets the value 0.0. It is output as 0.0 instead of 0 because average is a double, which outputs at least one decimal digit unless specified otherwise using the DecimalFormat class.

34. In order to create a constant, which of the following Java reserved words is used? a. b. c. d. e.

private static int final class

ANS: D

The reserved word final indicates that this is the final value that will be stored in this variable, thus making it unchangeable, or constant. While constants can be of type int, constants can be of any other type as well. It is the final reserved word that makes the value unchangeable.

35. Given three int variables with the values a = 5, b = 7, and c = 12, what is the value of z after the following statement is executed? int z = (a * b - c) / a; a. b. c. d. e.

0 4 5 -5 23

ANS: B (a * b - c) / a = (5 * 7 - 12) / 5 = (35 - 12) / 5 = 23 / 5, and since 23 and 5 are int values, the division is performed as an int division, or 23 / 5 = 4.

36. Java is a strongly typed language. What is meant by "strongly typed"? a. Every variable must have an associated type before it can be used. b. Variables can be used without declaring their types. c. Every variable has a single type associated with it throughout its existence in the program and the variable can only store values of that type. d. Variables are allowed to change type during their existence in a program so long as the value a variable currently stores is of the type it currently declared to be. e. Variables are allowed to change types during their existence in a program but only if the change is to a narrower type.

ANS: C Strong typing is a property of a programming language whereby the variable's type does not change during the variable's existence, and any value stored in that variable is of that type. The reason that strong typing is important is it guarantees that a program that was successfully compiled will not have run-time errors associated with the misuse of types for the variables declared.

37. As presented in the Software Failure section of the text, the root cause of the Mars Climate Orbiter problem was a. b. c. d. e.

the cost of the project an inability to track the orbiter at long distances atmospheric friction a communication issue between subsystems None of these

ANS: D The cause was determined to be an embarrassing communication issue between subsystems. The navigation subsystem used imperial units of measure (pound-force) and the spacecraft's software itself expected data in metric units (newtons).

PROBLEM

1. Write a set of instructions to prompt the user for an int value and input it using the Scanner class into the variable x and prompt the user for a float value and input it using the Scanner class into the variable y.

ANS: Scanner scan = Scanner.create(System.in); System.out.println("Enter an integer"); int x = scan.nextInt(); System.out.println("Enter a float"); float y = scan.nextFloat(); 2. Provide an example of how you might use a boolean, a float, a char, a String, and an

int.

ANS: Answers may vary. Samples: boolean to store whether a person is of voting age or not float: to store someone's GPA char: to store someone's middle initial String: to store someone's social security number int: to store someone's age 3. Explain what the following statement computes: int z = (int)Math.ceil(Math.sqrt(x)/Math.sqrt(y)); ANS: The integer value which bounds sqrt(x)/sqrt(y)where bounds means it is equal to the result of the division or the next int larger than the result of the division if the result has a remainder.

4. Given four int values, x1, x2, y1, y2, write the code to compute the distance between the two points (x1, y1) and (x2, y2), storing the result in the double distance.

ANS: double distance = Math.sqrt(Math.pow(x1 - y1, 2) + Math.pow(x2 y2,2)); 5. Write an assignment statement to compute the gas mileage of a car where the int values milesTraveled and gallonsNeeded have already been input. The variable gasMileage needs to be declared and should be a double.

ANS: double gasMileage = (double)milesTraveled/gallonsNeeded; The reason that the value milesTraveled is cast as a double is to ensure that the division is performed as a double and not an int.

6. Write the paint method for an applet so that it contains 4 concentric circles (each circle is inside the previous circle), where the largest circle is bounded by a 400x400 box and the smallest is bounded by a 100x100 box. Each circle is centered on an applet that is 400x400. Make each circle a different color of your choice.

ANS: public void paint(Graphics page) { page.setColor(Color.white); page.fillOval(0, 0, 400, 400); page.setColor(Color.yellow); page.fillOval(50, 50, 300, 300); page.setColor(Color.orange); page.fillOval(100, 100, 200, 200); page.setColor(Color.red); page.fillOval(150, 150, 100, 100); } 7. Given two points in an applet represented by the four int variables x1, y1, x2 and y2, write a paint method to draw a line between the two points and write the location of the two points next to the two points.

ANS: public void paint(Graphics page) { page.setColor(Color.blue); page.drawLine(x1, y1, x2, y2); page.drawString("" + x1 + ", " + y1, x1, y1); page.drawString("" + x2 + ", " + y2, x2, y2); } 8. An employer has decided to award a weekly pay raise to all employees by taking the square root of the difference between his weight and the employee's weight. For instance, an employee who weighs 16 pounds less than the employer will get a $4 per week raise. The raise should be in whole dollars (an int). Assume that employerWeight and employeeWeight are both int variables that have been input. Write an assignment statement to compute the int value for raise.

ANS: raise = (int) Math.sqrt(Math.abs(employerWeight - employeeWeight)); The absolute value of the difference must be taken in case the employee weighs more than the employer, which would then result in an attempt to take the square root of a negative number. So Math.abs is used. After computing the absolute value of the difference, the square root is taken and the result (a double) is cast as an int to be stored in raise.

9. Using the various String methods, manipulate a String called current to be the last character of current followed by the remainder of its characters in order, placing the result in a String called rearranged.

ANS:

String rearranged = current.charAt(current.length() - 1) + current.substring(0, current.length() - 2); The last character, which is found at charAt(current.length() - 1) is the first item in rearranged, followed by the substring of current starting at 0 (the first character) and going to current.length() - 2 (the second to last character).

10. How many ways are there to test to see if two String variables, a and b, are equal to each other if we ignore their case (for instance, "aBCd" would be considered equal to "ABcd")?

ANS: There are at least 10 ways that this can be done: a.toLowerCase().equals(b.toLowerCase()); b.toLowerCase().equals(a.toLowerCase()); a.toUpperCase().equals(b.toUpperCase()); b.toUpperCase().equals(a.toUpperCase()); a.equalsIgnoreCase(b); b.equalsIgnoreCase(a); a.equalsIgnoreCase(b.toLowerCase()); a.equalsIgnoreCase(b.toUpperCase()); b.equalsIgnoreCase(a.toLowerCase()); b.equalsIgnoreCase(a.toUpperCase()); 11. How do the statements "import java.util.*;" and "import java.util.Random;"

differ from each other?

ANS: In the former, all of the classes defined in the java.util library are imported whereas in the latter, only the Random class is imported from the java.util library. The former approach is easier but more time consuming and wasteful of memory, so the latter approach is more appropriate if you only want to use a single class from a given library.

12. Assume that a = "1", b = "2", y = 3, and z = 4. How do the following two statements differ?

System.out.println(a + b + y + z); System.out.println(y + z + a + b); ANS: In the first statement, since a and b are Strings, a + b + c + d is treated as String concatenation and the statement outputs 1234. In the second statement, y + z is treated as int addition, which is then cast as a String to be concatenated with y + z, giving 712 instead of 3412 as you might expect.

13. Write a program which will input an int value, x, and compute and output the values of 2^x and x^10 as int values.

ANS: import java.util.Scanner;

public class Compute14 { public static void main(String[] args) { Scanner scan = Scanner.create(System.in); System.out.println("Enter an integer value"); int x = scan.nextInt(); int twoToTheX = (int) Math.pow(2, x); int xToThe10th = (int) Math.pow(x, 10); System.out.println("The results are " + twoToTheX + " and " + xToThe10th); } } 14. What is wrong with the following assignment statement? Assume x and y are both String objects.

String z = x.equals(y); ANS: The equals method returns a boolean value, not a String. The values true and false are not the same as the values "true" and "false.

15. Write a program that will input some number of cents (less than 100) and output the number of quarters, dimes, nickels and pennies needed to add up to that amount.

ANS: import java.util.Scanner; public class Change { public static void main(String[] args) { Scanner scan = Scanner.create(System.in); System.out.println("Enter the amount of change"); int amount = scan.nextInt(); System.out.println("The change for " + amount " cents is: "); int quarters = amount / 25; System.out.println(" " + quarters + " quarters"); amount = amount - quarters * 25; int dimes = amount / 10; System.out.println(" " + dimes + " dimes"); amount = amount - dimes * 10; int nickels = amount / 5; System.out.println(" " + nickels + " nickels"); amount = amount - nickels * 5; int pennies = amount; System.out.println(" " + pennies + " pennies"); } } 16. Write an output statement which will output the following characters exactly as shown: / ' \" / ' \

ANS: System.out.println("/ \ ' \ \ \" / \ ' \ \ ");

17. Provide three examples of code using assignment statements where one assignment statement would result in a syntax error, one would result in a logical error, and one would result in a run-time error.

ANS: Answers will vary. Examples: // syntax error caused by right side providing a double and the left side wants an int: int x = 5.0 / 2.0; // logical error caused by not casting the division as a double: double x = (intValue1 + intValue2) / 2; // run-time error caused by division by 0 when y - y is evaluated: int x = 5 / (y - y); 18. What are the syntax errors from the following program? public class Enigma { public static void main(String[] args) { System.out.println("Input a String"); String x = scan.nextString(); int size = x.length; char last = x.charAt(size); System.out.println("The last character in your string ", x, " is ", last); } } ANS: There are 3 syntax errors. First, the Scanner class has not been imported so that the scan.nextString()will yield a syntax error. Second, the statement x.length requires parentheses as length is a method of the class String, so this is a message passed to x. Finally, the System.out.println statement is not valid because of the use of a comma instead of + to concatenate the various parts of the String. Note that in spite of these syntax errors, there is a runtime error. This error would arise because size will store the length of the String, but the last character will be at location size-1 instead of size. Thus, the statement char last = x.charAt(size); will result in a run-time error because size is beyond the bounds of the String x.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 3 Using Classes and Objects TRUE/FALSE 1. Only difficult programming problems require a pseudocode solution before the programmer creates the program itself.

ANS: F Some form of design should be created for all problems before the program is written, with the possible exception of only the most trivial of problems. The form of the design may vary. For instance, programmers in the 1960s and 1970s often used flowcharts instead of pseudocode.

2. You may apply the prefix and postfix increment and decrement operators to instances of the Integer class.

ANS: F These operators may only be applied to numeric data. An instance of a class is an object and and not a piece of primitive data.

3. In Java, the symbol "=" and the symbol "==" are used interchangeably.

ANS: F "=" is used for assignment statements while "==" is used to test equality in conditional statements.

4. When comparing any primitive type of variable, the == operator should always be used to test if two values are equal.

ANS: F This is true of int, short, byte, long, char and boolean, but not of double or float variables. If two double variables, x and y, are being tested, (x == y) is true only if they are exactly equal to the last decimal point. It is common instead to compare these two values but allow for a small difference in value. For instance, if THETA = 0.000001, we might test x and y by (x - y <= THETA) instead of (x == y) to get a better idea of whether they are close enough to be considered equal.

5. These two ways to set up a String will yield identical results: String my_string = "12345"; String my_string = 12345; ANS: F In fact, the second statement won't even compile! The second statement will receive a syntax error about incompatible types. There is no automatic conversion from a number to a String.

6. These two ways to set up a String will yield identical results: String my_string = new String("a bunch of words");

String my_string = "a bunch of words"; ANS: T Java has a very strong notion about what Strings are and how they function. The second declaration is merely shorthand for the first. The string reference will be initialized identically by both declarations.

7. These two ways to set up a String will yield identical results: String my_string = new String("123.45"); String my_string = "" + 123.45; ANS: T Java understands the + operator when used to combine Strings with numbers means that the number should be converted into a numeric String, and then concatenation should occur.

8. These two ways to set up a String will yield identical results: String my_string = new String(12345); String my_string = new String("12345"); ANS: F In fact, the first statement won't even compile! There is no overloaded version of the String constructor that accepts a numeric argument.

9. The following statement will display the value 127.

System.out.println("123" + 4); ANS: F "123" is a String. So, the + will cause String concatenation to occur. The int 4 will be converted into the String "4", and the String "1234" will be created and displayed.

10. You may use the String.replace() method to remove characters from a String.

ANS: F The replace() method only replaces single characters with other single characters. The replace() method will not add or delete characters to a String; the String length will remain the same.

11. If you need to import not only the top-level of a package, but all its secondary levels as well, you should use the following: import package.*.*; ANS: F The import statement can only be used with a single * (wild card). If you need to import all the secondary levels of a package as well, you must write them out explicitly: import package.A.*; import package.B.*;

12. All the methods in the Math class are declared to be static.

ANS: T The Math class methods are designed to be generally useful in arithmetic expressions, so no instances of anything are required to make use of them. This is achieved by ensuring that all the Math methods are static.

13. The printf method within System.out is designed to ease the conversion of legacy C code into Java.

ANS: T

C programs use the C printf function for output. Java's printf method is modeled closely after the C printf function, so C output statements can be translated into Java extremely easily.

14. The names of the wrapper classes are just the names of the primitive data types, but with an initial uppercase letter.

ANS: F This is true for most of the wrapper classes, but it is false for int (Integer) and char (Character).

MULTIPLE CHOICE 1. In Java a variable may contain a. b. c. d. e.

a value or a reference a package a method a class Any of these

ANS: A Java variables contain values or references to instances of classes (which contain values and/or additional references).

2. If two variables contain aliases of the same object then a. b. c. d. e.

the object may be modified using either alias the object cannot be modified unless there's a single reference to it a third alias is created if/when the object is modified the object will become an "orphan" if both variables are set to null answers A and D are both correct

ANS: E By definition, an alias provides a means by which an object can be modified (an alias is like a pointer).

If both variables are set to null, then the object is not referenced by any variable (via any alias) and it does, indeed, become an "orphan" and it will be garbage collected at some point in the future.

3. Which properties are true of String objects? a. b. c. d. e.

Their lengths never change.

The shortest String has zero length.

Individual characters within a String may be changed using the replace method.

The index of the first character in a String is one.

Only answers A and B are true.

ANS: E Strings are immutable. That means that once a String object is created it cannot be changed.

Therefore the length of a String never changes once it has been created. The shortest length String is "". Since there are no characters between the quotes, the length is zero. The replace method allows you to create a new String from an original one, replacing some of the characters.

The index of the first location in a String is zero, not one. Also, the last byte of every String contains the end-of-string character which is a byte of low-values, or binary zeros.

4. What happens if you attempt to use a variable before it has been initialized? a. b. c. d. e.

A syntax error may be generated by the compiler.

A run-time error may occur during execution.

A "garbage" or "uninitialized" value will be used in the computation.

A value of zero is used.

Only answers A and B are correct.

ANS: E Many times the compiler is able to detect the attempted use of an uninitialized variable and it will generate a syntax error in this case. If such a use escapes detection by the compiler then a run-time error occurs upon usage. Java is a very "safe" language, so it does not allow "garbage" or zero to be used if an uninitialized variable is used in a computation.

5. What is the function of the dot operator? a. It serves to separate the integer portion from the fractional portion of a floating-point number. b. It allows one to access the data within an object when given a reference to the object. c. It allows one to invoke a method within an object when given a reference to the object. d. It is used to terminate commands, similar to the way a period terminates a sentence in English. e. Both B and C are correct.

ANS: E The dot operator is appended directly after the object reference, followed by the data or method to which access is desired. In the case of data, the access may be for reading or writing. In the case of a method, the access is to allow one to invoke the method. The dot within a floating-point number is a decimal point and not a dot operator.

6. In Java, instantiation means a. b. c. d. e.

noticing the first time something is used creating a new object of the class creating a new alias for an existing object launching a method none of these

ANS: B Instantiation is the process of creating a new instance of an object. This usually is accomplished by using the new operator. In the case of Strings, new instances (instantiation) may be created just by using quotes in an expression. For example: String s; s = "A new string (instance)"; 7. Assume you write a program that uses the Random class but you fail to include an import statement for java.util.Random or java.util.*. What will happen when you attempt to compile and run your program? a. b. c. d.

The program won't run but it will compile with a warning about missing the class.

The program won't compile and you'll receive a syntax error about the missing class.

The program will compile but you'll receive a warning about the missing class.

The program will encounter a run-time error when it attempts to access any member of the Random class. e. none of these ANS: B The missing class means that there will be undefined variables and/or methods. The compiler will detect these and will issue error messages. Your program won't be executable.

8. In the StringMutation program shown in Listing 3.1, if phrase is initialized to "Einstein", what will Mutation # 3 yield if mutation1 = phrase.concat(".")? a. b. c. d. e.

Einstein.

EINSTEIN. XINSTXIN. einstein. xinstxin.

ANS: C Mutation #2 changes every letter to upper case. Then Mutation #3 replaces Es with Xs. 9. Which of the following will yield a pseudorandom number in the range [-5, +5), given: Random gen = new Random(); a. b. c. d. e.

gen.nextFloat()*5 gen.nextFloat()*10-5 gen.nextFloat()*5-10 gen.nextInt()*10-5 gen.nextInt(10)-5

ANS: B nextFloat yields a pseudorandom number in the range [0, 1); multiplying by 10 yields numbers in the range [0, 10); subtracting 5 yields numbers in the range [-5, 5).

10. What will be displayed by the following command?

System.out.println(Math.pow(3, 3-1)); a. 9 b. 8 c. 6

d. 4 e. 27 ANS: A This evaluates to Math.pow(3, 2) which is 3^2 which is 9 11. Given the following two lines of code, what can be said about s1 and s2?

String s1 = "testing" + "123"; String s2 = new String("testing 123"); a. b. c. d. e.

s1 and s2 are both references to the same String object. the line declaring s1 is legal in Java; the line declaring s2 will produce a syntax error. s1 and s2 are references to different String objects. s1 and s2 will compare "equal."

None of the above

ANS: C Both declarations are legal Java. s1 is a String reference, and it is initialized to the String "testing123". s2 is a String reference, and it is initialized to the String "testing 123".

Note the space between the "testing" and the "123". So the two Strings are not equal.

12. An alias is when a. b. c. d. e.

two different reference variables refer to the same physical object two different numeric variables refer to the same physical object two different numeric variables contain identical values two variables have the same name None of these

ANS: A An "alias" occurs when there are two or more references to the same physical object so that by following either reference, one can read/write/modify the object.

13. An API is a. b. c. d. e.

an Abstract Programming Interface an Application Programmer's Interface an Application Programming Interface an Abstract Programmer's Interface an Absolute Programming Interface

ANS: C An API is an Application Programming Interface. This is a collection of related classes that have been built for specific purposes. APIs usually reside in a class library.

14. Java.text's NumberFormat class includes methods that a. b. c. d. e.

allow you to format currency allow you to format percentages round their display during the formatting process truncate their display during the formatting process A, B, C, but not D

ANS: E

NumberFormat always rounds; it never truncates. And it does provide methods for both currency and percentages.

15. The advantages of the DecimalFormat class compared to the NumberFormat class include a. b. c. d. e.

precise control over the number of digits to be displayed control over the presence of a leading zero the ability to truncate values rather than round them the ability to display a percent sign (%) automatically at the beginning of the display only A and B

ANS: E While DecimalFormat does provide far more control than NumberFormat, truncation remains in the hands of the programmer via one or more of the Math methods. The % symbol would appear at the end of the display, not the beginning.

16. The advantage(s) of the Random class's pseudorandom number generators, compared to the Math.random method, is(are) that a. b. c. d. e.

you may create several random number generators the generators in Random are more efficient than the one in Math.random you can generate random ints, floats, and ints within a range you can initialize and reinitialize Random generators all except B are true

ANS: E The efficiency of all the random number generators are the same. The advantages of Random generators over Math.random include all the other properties.

17. The String class's compareTo method a. b. c. d. e.

compares two strings in a case-independent manner yields true or false yields 0 if the two strings are identical rerturns 1 if the first string comes lexically before the second string None of these

ANS: C compareTo yields 0 if the two strings are identical, -1 if the first string comes lexically before the second, +1 if the first string comes lexically after the second.

18. Which statement is true, given the following code fragment?

String strA = "aBcDeFg"; String strB = strA.toLowerCase(); strB = strB.toUpperCase(); string strC = strA.toUpperCase(); a. b. c. d. e.

strB.equals(strC) would be true strB.compareTo(strC) would yield 0 strA.equals(strC) would be true strA.compareTo(strC) would yield 0 None of these

ANS: B strB contains the uppercase forms of all the letters in strA; so does strC. So compareTo would yield 0, indicating equality.

19. In addition to providing a mechanism to convert primitive data into objects, what else do the wrapper classes provide? a. b. c. d. e.

enumerations static constants arrays to contain the data exceptions None of these

ANS: B The wrapper classes also provide static constants, like MIN_VALUE and MAX_VALUE (the smallest and largest ints).

20. Which is now the preferred approach for developing Java programs that use graphics and GUIs? a. b. c. d. e.

Swing AWT JavaFX API All of these are preferred approaches

ANS: C The JavaFX API has now replaced the AWT and Swing for developing graphical programs.

21. In a development environment that fully supports JavaFX, which of the following is true? a. The launch method of the scene class is called automatically. b. The launch method of the Application class is called automatically. c. Since the launch method is called automatically, you do not need to write the main method. d. Since the launch method is called automatically, you do not need to call it in the main method. e. Both B and C are true ANS: E 22. Which of the following packages includes classes that represent shapes in JavaFX? a. b. c. d. e.

javafx.scene.shape javafx.shape.scene javafx.shapes javafx.stage.shape javafx.stage.scene

ANS: A 23. Write a declaration for a Rectangle named squareShape that is 400 pixels wide, 400 pixels high, and its upper-left corner position is at point (50, 50). a. Rectangle squareShape = new squareShape(50, 50, 400, 400);

b. c. d. e.

squareShape = new Rectangle(50, 50, 400, 400); Rectangle squareShape = new Rectangle(50, 400, 50, 400); Rectangle squareShape = new Rectangle(50, 50, 400, 400); Rectangle = new squareShape(400, 400, 50, 50);

ANS: D 24. What does the following code fragment do?

Circle circle = new Circle(100, 100, 50); circle.setFill(Color.GREEN); Rectangle rectangle = new Rectangle(70, 70, 225, 75); rectangle.setStroke(Color.BLUE); rectangle.setStrokeWidth(2); rectangle.setFill(null); a. It creates a green circle, centered at coordinates (100, 100). b. It creates a rectangle which overlaps the circle since its upper-left corner is at coordinates (70, 70) and its dimensions are 225 X 75. c. Since the rectangle's fill color is set to null, the circle will be visible through the rectangle. d. The rectangle will have a blue border. e. All of these are true.

ANS: E Shapes are drawn in the order they are added to a container such as a group or pane. So, to make one shape appear in front of another, it should be added after it. If the fill color of the rectangle is set to null, anything behind it will show through.

PROBLEM 1. Rewrite the following five assignment statements into a single statement using prefix and postfix increment and decrement operators as necessary. Assume all variables are int variables. x = y + 1; y = y + 1; z = z - 1; x = x - z; x = x + 1; ANS: x = (y++ + 1) - (--z) + 1; 2. Consider the condition (x == y). How is this handled if x and y are primitive types? How is this handled if x and y are objects?

ANS: If x and y are primitive types, then the values stored in them are compared and true is returned if the two values are equal. If they are objects, then the object that each references are compared. If they are the same object, it returns true, otherwise it returns false.

3. Given two String variables, s1 and s2, is it possible for (s1 != s2)to be true while (s1.equals(s2)) is also true? Why or why not?

ANS: The condition (s1 != s2) means that s1 and s2 are references to two distinct objects. It says nothing about the contents of the referenced objects. So, the contents of s1 may well be identical or different from the contents of s2. Therefore it is quite possible that (s1.equals(s2)) is true while (s1 != s2) is also true.

4. What is a wrapper class? Why are wrapper classes useful?

ANS: A wrapper class is a class that allows you to embed one piece of primitive data within an object.

There are methods for extracting the data from the object. Wrapper classes are useful where you have methods (or constructors) that only accept objects and not primitive data. By wrapping the primitive data within an object the functionality of the method (and its class) may be accessed.

Problem Ch 03-1 Assume an interactive Java program which asks the user for his/her first name and last name, and outputs the user's initials.

5. Refer to Problem Ch 03-1. For the program to get a name interactively a Scanner object must be instantiated. Write the Java statement to do this.

ANS: Scanner scan = new Scanner(System.in); 6. Refer to Problem Ch 03-1. Write a statement using a Scanner method to get the first name interactively.

ANS: firstName = scan.nextLine(); 7. Refer to Problem Ch 03-1. Write a method to extract the initial from the first name.

ANS: firstInitial = firstName.substring(0,1); 8. Refer to Problem Ch 03-1. Write a statement to guarantee that the initial will be a capital letter.

ANS: firstInitial = firstInitial.toUpperCase();

9. What is autoboxing?

ANS: Autoboxing provides automatic conversions between primitive values and corresponding wrapper objects. It makes your code shorter by relieving you of the need to provide explicit wrapping of primitive values and explicit extraction of primitive values.

10. Write a statement to create a Color object equivalent to Color.ORANGE using the rgb method.

ANS: Color orange = Color.rgb(255, 165, 0); 11. Why is it often a good idea to group particular elements together in a scene?

ANS: This makes it much easier to apply transformations such as rotations and position shifts to an entire group at once.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 4 Writing Classes TRUE/FALSE 1. Java methods can only return primitive types.

ANS: F Java methods can also return objects such as String.

2. Formal parameters are those that appear in the method call and actual parameters are those that appear in the method header.

ANS: F The question has the two definitions reversed. Formal parameters are those that appear in the method header, actual parameters are the parameters in the method call (those being passed to the method).

3. All Java classes must contain a main method which is the first method executed when the Java class is called on.

ANS: F Only the driver program requires a main method. The driver program is the one that is first executed in any Java program (except for Applets), but it may call upon other classes as needed, and these other classes do not need main methods.

4. Java methods can return more than one item if they are modified with the reserved word continue, as in public continue int foo() {...} ANS: F All Java methods return a single item, whether it is a primitive data type an object, or void. The reserved word continue is used to exit the remainder of a loop and test the condition again.

5. The following method header definition will result in a syntax error: public void aMethod(); ANS: T The reason for the syntax error is because it ends with a ; symbol. It instead needs to be followed by {} with 0 or more instructions inside of the brackets. An abstract method will end with a ; but this header does not define an abstract method.

6. A method defined in a class can access the class's instance data without needing to pass them as parameters or declare them as local variables.

ANS: T

The instance data are globally available to all of the class's methods and therefore the methods do not need to receive them as parameters or declare them locally. If variables of the same name as instance data were declared locally inside a method then the instance data would be "hidden" in that method because the references would be to the local variables.

7. The interface of a class is based on those data instances and methods that are declared public.

ANS: T The interface is how an outside agent interacts with the object. Interaction is only available through those items declared to be public in the class's definition.

8. Defining formal parameters requires including each parameter's type.

ANS: T In order for the compiler to check to see if a method call is correct, the compiler needs to know the types for the parameters being passed. Therefore, all formal parameters (those defined in the method header) must include their type. This is one element that makes Java a strongly typed language.

9. Every class definition must include a constructor.

ANS: F Java allows classes to be defined without constructors. However, there is a default constructor that is used in such a case.

10. While multiple objects of the same class can exist, in a given program there can only be one version of each class.

ANS: T A class is an abstraction; that is, it exists as a definition, but not as a physical instance. Physical instances are created when an object is instantiated using new. Therefore, there can be many objects of type String, but only one String class.

11. A constructor may contain a return statement so long as no value (or expression) is returned.

ANS: T Constructors may contain non-value-returning return statements. Doing so is discouraged, but it is legal.

12. An object should be encapsulated in order to guard its data and methods from inappropriate access.

ANS: T Encapsulation is the concept that objects should be protected from accidental (or purposeful) misuse.

13. Accessors and mutators provide mechanisms for controlled access to a well-encapsulated class.

ANS: T Accessors provide read access to variables that otherwise would be inaccessible. Mutators provide write access to otherwise inaccessible variables.

14. A GUI control sets up an event but it is the programmer who writes the code for the event handler which executes when an event occurs.

ANS: T 15. Regarding the software failure described at the Denver International Airport in the text, it is critical to factor in errors and inefficiencies that alway occur in a complex system.

ANS: T A good system is designed using a well-built systems analysis and design methodology that helps reduce the maintenance portion of the system's lifecycle.

16. Because an Image cannot directly be added to a container, it must be displayed using an ImageView object.

ANS: T MULTIPLE CHOICE 1. The behavior of an object is defined by the object's a. b. c. d. e.

instance data constructor visibility modifiers methods All of these

ANS: D The methods dictate how the object reacts when it is passed messages. Each message is implemented as a method, and the method is the code that executes when the message is passed. The constructor is one of these methods but all of the methods combined dictate the behavior. The visibility modifiers do impact the object's performance indirectly.

2. The relationship between a class and an object is best described as a. b. c. d. e.

classes are instances of objects objects are instances of classes objects and classes are the same thing classes are programs while objects are variables objects are the instance data of classes

ANS: B Classes are definitions of program entities that represent classes of things/entities in the world. Class definitions include instance data and methods. To use a class, it is instantiated. These instances are known as objects. So, objects are instances of classes. Program code directly interacts with objects, not classes.

3. To define a class that will represent a car, which of the following definition is most appropriate? a. b. c. d. e.

private class car public class car public class Car public class CAR. private class Car

ANS: C Classes should be defined to be public so that they can be accessed by other classes. And following Java naming convention, class names should start with a capital letter and be lower case except for the beginning of each new word, so Car is more appropriate than car or CAR.

4. In order to preserve encapsulation of an object, we would do all of the following except for which one? a. b. c. d. e.

make the instance data private define the methods in the class to access and manipulate the instance data make the methods of the class public make the class final all of these preserve encapsulation

ANS: D Encapsulation means that the class contains both the data and the methods needed to manipulate the data. In order to preserve encapsulation properly, the instance data should not be directly accessible from outside of the classes, so the instance data are made private and methods are defined to access and manipulate the instance data. Further, the methods to access and manipulate the instance data are made public so that other classes can use the object. The reserved word final is used to control inheritance and has nothing to do with encapsulation.

5. If a method does not have a return statement, then a. b. c. d. e.

it will produce a syntax error when compiled it must be a void method it cannot be called from outside the class that defined the method it must be defined to be a public method it must be an int, double, float, or String method

ANS: B All methods are implied to return something and therefore there must be a return statement.

However, if the programmer wishes to write a method that does not return anything, and therefore does not need a return statement, then it must be a void method (a method whose header has void as its return type).

6. Which of the following reserved words in Java is used to create an instance of a class? a. b. c. d. e.

class public public or private (can use either) import new

ANS: E

7. Consider a sequence of method invocations as follows: main calls m1, m1 calls m2, m2 calls m3, and then m2 calls m4, m3 calls m5. If m4 has just terminated, what method will resume execution? a. b. c. d. e.

m1 m2 m3 m5 main

ANS: B Once a method terminates, control resumes with the method that called that method. In this case, m2 calls m4 so that when m4 terminates, m2 is resumed.

8. A variable whose scope is restricted to the method where it was declared is known as a(n) a. b. c. d. e.

parameter global variable local variable public instance data private instance data

ANS: C Local variables are those that are "local" to the method in which they have been declared; that is, they are accessible only inside that method. Global variables are those that are accessible from anywhere, while parameters are the variables passed into a method. Instance data can be thought of as global variables for an entire object.

9. A class's constructor usually defines a. b. c. d. e.

how an object is initialized how an object is interfaced the number of instance data in the class the number of methods in the class if the instance data are accessible outside of the object directly

ANS: A The constructor should be used to "construct" the object, that is, to set up the initial values of the instance data. This is not essential, but is typically done. The interface of an object is dictated by the visibility modifiers used on the instance data and methods.

10. Having multiple class methods of the same name where each method has a different number of or type of parameters is known as a. b. c. d. e.

encapsulation information hiding tokenizing importing method overloading

ANS: E When methods share the same name, they are said to be overloaded. The number and type of parameters passed in the message provides the information by which the proper method is called.

11. Instance data for a Java class

a. b. c. d. e.

are limited to primitive types are limited to Strings are limited to objects (e.g., Strings, classes defined by other programmers) may be primitive types or objects but objects must be defined to be private may be primitive types or objects

ANS: E The instance data are the entities that make up the class and may be any type available whether primitive or object, and may be public or private. By using objects as instance data, it permits the class to be built upon other classes. This relationship where a class has instance data that are other classes is known as a has-a relationship.

12. An example of passing a message to a String where the message has a String parameter would occur in which of the following messages? a. b. c. d. e.

length substring equals toUpperCase None of these; it is not possible to pass a String as a parameter to a String

ANS: C The length and toUpperCase messages do not have parameters and substring has two int parameters. For equals, a String must be passed as a parameter so that the String receiving the message can be compared to the String passed as a parameter.

13. Consider a Rational class designed to represent rational numbers as a pair of ints, along with methods reduce (to reduce the rational to simplest form), gcd (to find the greatest common divisor of two ints), as well as methods for addition, subtraction, multiplication, and division. Why should the reduce and gcd methods be declared to be private? a. b. c. d. e.

because they will never be used because they will only be called from methods inside Rational because they will only be called from the constructor of Rational because they do not use any of the Rational instance data This is incorrect; they should be declared as public

ANS: B All items of a class that are declared to be private are only accessible to entities within that class, whether they are instance data or methods. In this case, since these two methods are only called from other methods (including the constructor) of Rational, they are declared private to promote information hiding to a greater degree. Note that answer C is not a correct answer because the reduce method calls the gcd method, so one of the methods is called from a method other than the constructor.

14. Given the method defined here, which of the following method calls is legal? public void foo(int a, int b) a. foo(0, 0.1); b. foo(0/1, 2*3); c. foo(0);

d. foo(); e. foo(1+2, 3*0.1); ANS: B The only legal method call is one that passes twoint parameters. In the case of answer B, 0 / 1 is an int division (equal to 0) and 2 * 3 is an int multiplication. So this is legal. The answers for A and E contain two parameters, but the second of each is a double. The answers for C and D have the wrong number of parameters.

15. Given the method defined here, which of the following method calls is legal? public void doublefoo(double x) a. b. c. d. e.

doublefoo(0); doublefoo(0.555); doublefoo(0.1 + 0.2); foo(0.1, 0.2); all except D are legal

ANS: E In the case of A, the value 0 (an int) is widened to a double. In the case of C, the addition is performed yielding 0.3 and then doublefoo is called. The parameter list in D is illegal since it contains two double parameters instead of 1.

16. In a UML diagram for a class a. b. c. d. e.

classes are represented as rectangles there may be a section containing the name of the class there may be a section containing the attributes of the class there may be a section containing the methods of the class All of these

ANS: E Those four attributes correctly describe a UML representation of a class.

17. The expressions that are passed to a method in an invocation are called a. b. c. d. e.

actual parameters formal parameters formal arguments formals Any of these

ANS: A The formals (formal parameters, formal arguments) are those given in a method's header, where it is declared. The actual parameters (actuals, actual arguments) are the expressions that actually are transmitted to a method in an invocation.

18. What happens if you declare a class constructor to have a void return type? a. b. c. d.

You will most likely receive a syntax error.

The program will compile with a warning but you'll get a run-time error.

There is nothing wrong with declaring a constructor with a void return type.

The class's default constructor will be used instead of the one you're declaring.

e. None of these ANS: A It is a syntax violation to declare a constructor with any type, even void, so you'll receive a syntax error.

19. Which of the following is not a kind of object that is used to create a graphical user interface in JavaFX? a. b. c. d. e.

control event image event handler All of these are objects used to create a GUI in JavaFX

ANS: A An image is not a kind of object used to create a GUI even though it is an object. It can only be displayed with an ImageView JavaFX node.

20. The software failure at the Denver International Airport's baggage handling system is a good example of a. how a large system can be obsolete by the time it is developed b. how designers sometimes have too much faith in the technology they are using c. how failures are often a result of multiple variables caused by a system as a whole in actual operation d. how the use of a centralized computer is unrealistic in today's distributed processing e. All of these ANS: E All of these are good examples of why software fails.

21. Visibility modifiers include a. b. c. d. e.

public, private public, private, protected public, private, protected, final public, protected, final, static public, private, protected, static

ANS: B public, private, protected control the visibility of variables and methods. final controls whether a variable, method, or class can be further changed or overridden; it does not control visibility. static controls whether a variable or method is associated with instances of a class or the class itself.

Class Definition Ch 04-1 import java.text.DecimalFormat; public class Student { private String name; private String major; private double gpa;

private int hours; public Student(String newName, String newMajor, double newGPA, int newHours) { name = newName; major = newMajor; gpa = newGPA; hours = newHours; } public String toString() { // xxxx needs to be replaced DecimalFormat df = new DecimalFormat("xxxx"); return name + "\n" + major + "\n" + df.format(gpa) + "\n" + hours } } 22. Refer to Class Definition Ch 04-1: Which of the following patterns should be used in place of "xxxx" when instantiating df so that the gpa to be output is in typical form (like 3.810)? a. b. c. d. e.

"#.###" "#.0" "0.#" "0.000" "0.0##"

ANS: D GPA is traditionally output as a 4 digit value with the decimal point after the first digit. Digits are output no matter if they are 0 or otherwise. So, to get 3.810, with the trailing 0, or to get 0.813 with the leading 0, the format must be "0.000" rather than "#.###".

23. Refer to Class Definition Ch 04-1: Which of the following could be used to instantiate a new Student s1? a. Student s1 = new Student(); b. s1 = new Student(); c. Student s1 = new Student("Jane Doe", "Computer Science", 3.333, 33); d. new Student s1 = ("Jane Doe", "Computer Science", 3.333, 33); e. new Student(s1); ANS: C To instantiate a class, the object is assigned the value returned by calling the constructor preceded by the reserved word new, as in new Student(). The constructor might require parameters, and for Student, the parameters must be two String values, a double, followed by an int.

24. Refer to Class Definition Ch 04-1: Assume that another method has been defined that will compute and return the student's class rank (Freshman, Sophomore, etc). It is defined as: public String getClassRank() Given that s1 is a student, which of the following would properly be used to get s1's class rank?

a. b. c. d. e.

s1 = getClassRank(); s1.toString(); s1.getHours(); s1.getClassRank(); getClassRank(sq);

ANS: D To call a method of an object requires passing that object a message which is the same as the method name, as in object.methodname(parameters). In this situation, the object is s1, the method is getClassRank, and this method expects no parameters. Answers A and E are syntactically illegal while answer B returns information about the Student but not his/her class rank, and there is no getHours method so C is also syntactically illegal.

25. Refer to Class Definition Ch 04-1: Another method that might be desired is one that updates the student's number of credit hours. This method will receive a number of credit hours and add these to the student's current hours. Which of the following methods would accomplish this? a. public int updateHours() { return hours; } b. public void updateHours() { hours++; } c. public updateHours(int moreHours) { hours += moreHours; } d. public void updateHours(int moreHours) { hours += moreHours; } e. getClassRank(sq);public int updateHours(int moreHours) { return hours + moreHours; } ANS: D This method will receive the number of new hours and add this to the current hours. The method in D is the only one to do this appropriately. Answer C is syntactically invalid since it does not list a return type. The answer in E returns the new hours, but does not reset hours appropriately.

PROBLEM 1. Assume method0 calls method1 and method2, method1 calls method3 which calls method4 and method5. Explain the chain of method calls (what order methods are called and from which method).

ANS: method0 calls method1 which calls method3 which calls method4, method4 terminates and method3 calls method5, method5 terminates, method3 terminates, method1 terminates, method0 calls method2, method2 terminates, method0 terminates.

2. When reasoning about a car, we use such information as its make and model, year, color, cost (or worth), number of miles, gas mileage, insurance cost, and so forth. Consider a program that will attempt to determine how practical a car might be on a road trip. Which of these types of information might you use in your program as instance data? Provide a justification for your selection.

ANS: Because a road trip will include such factors as comfort and cost, we need to have instance data pertaining to the size of the vehicle, its gas mileage and its reliability. Size can be determined by make and model, reliability based on year and number of miles that the car has accrued, and cost based on gas mileage. The following would be a reasonable selection of instance data: model (maybe make as well), year, number of miles, gas mileage.

3. Write a portion of a class named Employee. An employee will have a name, ID number, position, and hourly wage. Define the instance data for this class.

ANS: private String name, idnum, position; private double hourlyWages; 4. Explain why it would be a poor decision to make instance data public instead of private. Give an example of why this could result in a problem.

ANS: If the instance data are public, then any other class can directly modify any of the instance data, and therefore the values would not be stored as intended.

Class Definition Ch04-2 The following is from a class named BaseballPlayer. It contains the following data instances: private String name; private String position; private int numAtBats; private int numSingles; private int numDoubles; private int numTriples; private int numHomeRuns; private double battingAverage; 5. Refer to Class Definition Ch 04-2: Write the constructor which is passed the player's name and position.

ANS: Notice that we not only initialize the instance data that were passed as parameters, but also all other data instances. public BaseballPlayer(String newName, String newPosition) { name = newName; position = newPosition; numAtBats = 0; numSingles = 0; numDoubles = 0; numTriples = 0;

numHomeRuns = 0; battingAverage = 0.0; } 6. Refer to Class Definition Ch 04-2: Write a toString method that returns the player's name, position, and batting average. formatted to have one digit to the left of the decimal and three digits to the right of the decimal. Assume DecimalFormat has been imported.

ANS: public String toString() { DecimalFormat df = new DecimalFormat("0.000"); return name + "\t" + position + "\t" + df.format(battingAverage); } Class Definition Ch 04-3 Consider a class called Building. This class consists of a number of floors (numberOfFloors) for the building, a current floor for the elevator (current), a requested floor of a person waiting for the elevator (requestedFloor), and methods for constructing the building object, for moving the elevator one floor up, for moving the elevator one floor down, for requesting the elevator and for starting the elevator going. Assume that requestedFloor will be set to 0 if there are currently no requests being made (or the last request has already been fulfilled).

7. Refer to Class Definition Ch 04-3: Write the constructor for this class.

ANS: public Building(int numFloors) { numberOfFloors = numFloors; current = 1; requestedFloor = 0; } 8. Refer to Class Definition Ch 04-3: What visibility modifiers would you use for the methods that move the elevator up one floor, move the elevator down one floor, that request the elevator, and that start the elevator moving?

ANS: The request for the elevator will be performed from an outside object, so it should be public. It will set requestedFloor to a value, and then start the elevator going up or down. Moving the elevator up or down will be called from the method that starts the elevator. So, starting the elevator, moving the elevator up a floor, and moving the elevator down a floor should all be private as they will only be called from inside the class.

Class Definition Ch 04-4 public class Box { double length; double width;

double height; Box(double l, double w, double h) { length = l; width = w; height = h; }// Box( ) double volume() { return length * width * height; }// end volume() }// end class Box 9. Refer to Class Definition Ch 04-4: Write the statement to instantiate an Box object, blueBox, with a length of 6, width of 4, and height of 2.

ANS: Box blueBox = new Box(6,4,2); 10. Refer to Class Definition Ch 04-4: Write a statement to output the volume of the blue box.

ANS: System.out.println("Volume of the blue box is

"+blueBox.volume());

11. Refer to Class Definition Ch 04-4: Add a constructor to class Box for a cube which has only 1 parameter, side.

ANS: Box(double s) { length = s; width = s; height = s; }// Box( ) 12. Refer to Class Definition Ch 04-4: Write a statement to instantiate a cube with a length of 3, width of 3, and height of 3.

ANS: Box cube = new Box(3);

Java Software Solutions, 9e (Lewis/Loftus) Chapter 5 Conditionals and Loops TRUE/FALSE 1. As in the other members of the C family of languages (C, C++, C#), Java interprets a zero value as false and a non-zero value as true.

ANS: F Although the C family does, indeed, interpret zero and non-zero values in this manner, Java requires that the reserved constants true and false be used or that there be a logical evaluation using the relational and/or logical operators.

2. In Java, selection statements consist only of if and if-else statements.

ANS: F This list omits switch statements.

3. In Java, the symbol "=" and the symbol "==" are used synonymously (interchangeably).

ANS: F "=" is used for assignment statements while "==" is used to test equality.

4. The statement {} is a legal block.

ANS: T A block consists of {, followed by zero or more Java statements, followed by }. So it is acceptable to have no statements between the brackets. Situations where this is necessary occur in Java, particularly when implementing methods of abstract classes, something you will study later.

5. The statement: if (a >= b) a++; else b--; will do the same thing as the statement: if (a < b) b--; else a++;.

ANS: T We can reverse the if clause and else clause if we reverse the condition. The opposite condition of (a >= b) is (a < b) so this works out logically. Note that if we used the condition (a <= b) then the resulting statement would not do the same thing as the original if a >= b.

6. An if statement may or may not have an else clause, but an else clause must be part of an if statement.

ANS: T Java allows for either if or if-else statements. But else is only used as part of an if statement.

7. In order to compare int, float and double variables, you can use <, >, ==, !=, <=, >=, but to compare char and String variables, you must use compareTo(), equals()and equalsIgnoreCase().

ANS: F You can also directly compare char variables using <, >, ==, !=, <=, >=, but you must use compareTo(), equals() and equalsIgnoreCase() for any String comparisons.

8. Assume that boolean done = false, int x = 10, int y = 11, String s = "Help" and String t = "Goodbye". Then the expression (!done && x <= y) is true.

ANS: T Since done is false, !done is true. Since 10 < 11, x <= y is true. Therefore, the entire expression is true.

9. Assume that boolean done = false, int x = 10, int y = 11, String s = "Help" and String t = "Goodbye". Then the expression (s.concat(t).length() < y) is true.

ANS: F Concatenating s and t gives a String that is 11 characters long and 11 < 11 is false.

10. Assume that boolean done = false, int x = 10, int y = 11, String s = "Help" and String t = "Goodbye". Then the expression (done || s.compareTo(t) < 0) is true.

ANS: F Both done is false and s.compareTo(t) < 0 is false since s does not come before t alphabetically, so the entire expression is false.

11. If you create an ArrayList without specifying the type of element, the ArrayList will store Object references which means you can put any type of object in the list.

ANS: T 12. Regarding the Software Failure: The operators were warned that, although the Therac-25 had many safety precautions, it might be possible to accidentally overdose a patient.

ANS: F Operators were told that there were so many safety precautions that it would be "virtually impossible" to overdose a patient.

MULTIPLE CHOICE 1. The idea that program instructions execute in order (linearly) unless otherwise specified through a conditional statement is known as a. b. c. d. e.

boolean execution conditional statements try and catch sequentiality flow of control

ANS: E The "flow of control" describes the order of execution of instructions. It defaults to being linear (or sequential) but is altered by using control statements like conditionals and loops.

2. Of the following if statements, which one correctly executes three instructions if the condition is true? a. if (x < 0) a = b * 2; y = x; z = a - y; b. { if (x < 0) a = b * 2; y = x; z = a - y; } c. if { (x < 0) a = b * 2; y = x; z = a - y ; } d. if (x < 0) { a = b * 2; y = x; z = a - y; } e. B, C, and D are all correct but not A ANS: D In order to have three instructions execute in the if clause when the condition is true, the three statements must be placed in a block following the condition. This is the syntax used in D. In A, there is no block. In B, the block is placed around the entire if statement such that the if clause is only a = b * 2; and the other two statements are not part of the if statement, but follow it. The syntax in C is illegal resulting in a syntax error. Don't forget that the structure of your code (how it lines up) is immaterial to the compiler.

3. Which of the sets of statements below will add 1 to x if x is positive and subtract 1 from x if x is negative but leave x alone if x is 0?

a. if (x > 0) x++; else x--; b. if (x > 0) x++; else if (x < 0) x--; c. if (x > 0) x++; if (x < 0) x--; else x = 0; d. if (x == 0) x = 0; else x++; x--; e. x++; x--; ANS: B In B, if x is positive, x++ is performed, else if x is negative x-- is performed and otherwise, nothing happens, or x is unaffected. In A, C, D and E, the logic is incorrect. In A, x-- is done if x is not positive, thus if x is 0, x becomes -1 which is the wrong answer. In C, if x is positive, then x++ is performed. In either case, the next statement is executed and if x is not negative, the else clause is performed setting x to 0. So if x is positive, it becomes 0 after this set of code. In D, x++ and x-are both performed if x is not 0. And in E, this code does not attempt to determine if x is positive or negative, it just adds one and then subtracts one from x, leaving x where it started.

4. Consider the following code that will assign a letter grade of 'A', 'B', 'C', 'D', or 'F' depending on a student's test score. if (score >= 90) grade = 'A'; if (score >= 80) grade = 'B'; if (score >= 70) grade = 'C'; if (score >= 60) grade = 'D'; else grade = 'F'; a. b. c. d. e.

This code will work correctly in all cases.

This code will work correctly only if the grade is greater than or equal to 60.

This code will work correctly only if the grade is less than 60.

This code will work correctly only if the grade is less than 70.

This code will not work correctly under any circumstances.

ANS: D The problem with this code is that it consists of three if statements followed by one if-else statement, rather than a nested if-else statement. So the logic is improper. If the student's grade falls into the 'A' category, then all 4 conditions are true and the student winds up with a 'D'. If the student's grade falls into the 'B' category, then the first condition is false, but the next three are true and the student winds up with a 'D'. If the student's grade falls into the 'D' category, then the only condition that is true is the one that tests for 'D' and so the grade is assigned correctly. If the student's grade falls into the 'F' category, then none of the conditions are true and an 'F' is assigned correctly. So, only if the grade is less than 70 does the code work correctly.

5. Assume that count is 0, total is 20 and max is 1. The following statement will do which of the following? if (count != 0 && total / count > max)

max = total / count; a. b. c. d.

The condition short circuits and the assignment statement is not executed.

The condition short circuits and the assignment statement is executed without problem.

The condition does not short circuit causing a division by zero error.

The condition short circuits so that there is no division by zero error when evaluating the condition, but the assignment statement causes a division by zero error. e. The condition will not compile because it uses improper syntax.

ANS: A Since count is 0, (count != 0) is false. Because the left-hand side of an && condition is false, the condition is short circuited, and so the right-hand side is not evaluated. Thus, a potential division by zero error is avoided. Because the condition is false, the statement max = total / count is not executed, again avoiding a potential division by zero error.

6. What is wrong, logically, with the following code? if (x > 10) System.out.println("Large"); else if (x > 6 && x <= 10) System.out.println("Medium"); else if (x > 3 && x <= 6) System.out.println("Small"); else System.out.println("Very small"); a. There is no logical error, but there is no need to have x <= 10 in the second conditional or x <= 6 in the third conditional. b. There is no logical error, but there is no need to have x > 6 in the second conditional or x > 3 in the third conditional. c. The logical error is that no matter what value x is, Very small is always printed out. d. The logical error is that no matter what value x is, Large is always printed out. e. There is nothing wrong with the logic at all.

ANS: A Because this is a nested if-else statement, if (x>10)is true, then the first println statement is executed and the rest of the statement is skipped. If (x>10)is not true, then the first else clause is executed and the next if condition is tested. At this point, (x>10)is known to be false and therefore (x<=10)must be true, so there is no need to check this inequality. Similarly, if (x>6)is false, then the second else clause is executed and the third if condition is tested. However, (x<=6)must be true, so there is no need to check this inequality.

7. Consider the following outline of a nested if-else structure which has more if clauses than else clauses. Which of the statements below is true regarding this structure? if (condition1) if (condition2) statement1; else statement2; a. Syntactically it is invalid to have more if clauses than else clauses b. statement2 will only execute if condition1 is false and condition2 is false

c. statement2 will only execute if condition1 is true and condition2 is false d. statement2 will only execute if condition1 is false, it does not matter what condition2 is e. statement2 will never execute ANS: C The else clause must be matched to the most recent if statement. Therefore, the else goes with the if statement that tests condition2, not the if statement that tests condition1. So, if condition1 is true and condition2 is false, then statement2 will execute.

8. Assume that x and y are int variables with x = 5, y = 3, and a and d are char variables with a = 'a' and d = 'A', and examine the following conditions: Condition 1: (x < y && x > 0) Condition 2: (a != d || x != 5) Condition 3: !(true && false) Condition 4: (x > y || a == 'A' || d != 'A') a. b. c. d. e.

all 4 conditions are true Only Condition 2 is true Condition 2 and Condition 4 are true only Conditions 2, 3,4 are all true, Conditions 1 is not all 4 conditions are false

ANS: D Condition 1 is not true because x < y is false, making the entire condition false. Since a != d is true, Condition 2 is true even though x != 5 is false. Condition 3 is true because (true && false) is false, but !false is true. Condition 4 is true because x > y is true, making the entire condition true. Therefore, Conditions 2, 3,4 are true while Condition 1 is false.

9. What does the break statement do? a. b. c. d. e.

ends a program transfers control out of the current control structure such as a loop or switch statement ends the current line of output, returning the cursor denotes the end of a switch statement indicated the end of a line when using System.out.print

ANS: B This is the exit statement that allows the programmer to exit a control structure from inside of that control structure.

10. If a break occurs within the innermost loop of a nested loop that is three levels deep a. just the innermost loop will be "broken" b. all loops are "broken" and execution continues from after the end of the loop c. all but the outermost loops are "broken" and execution continues from the next iteration of the outermost loop d. a syntax error is generated unless there are break or continue statements at each loop level e. None of these are true ANS: A The innermost loop is broken, and execution continues from just after the end of that loop.

11. Which of the following are true about check boxes? a. b. c. d. e.

They may be checked or unchecked.

You can allow more than one check box to be checked by the user at a given time.

Check boxes are Java components.

You can control whether they will be visible or not.

All of these are true about check boxes

ANS: E 12. Every iterator a. b. c. d. e.

has a hasNext() method has a hasFirst()method has a hasNextInt()method has a isEmpty()method None of these

ANS: A Every iterator has a hasNext() method that is true if there are iteration elements that have yet to be processed. Every iterator also has a next() method that delivers the next element for processing.

13. If x is an int where x = 1, what will x be after the following loop terminates? while (x < 100) x *= 2; a. b. c. d. e.

2 64 100 128 None of these; this is an infinite loop

ANS: D With x = 1, the loop condition is true and the statement executes, doubling x, which is now 2.

Since the loop condition is still true, the statement executes again, doubling x to 4. The condition remains true for the next 4 iterations, where x becomes 8, 16, 32 and 64. Since x < 100 is still true when x = 64, the loop iterates again and x becomes 2*64 = 128. Now, x < 100 is no longer true and the loop terminates with x = 128.

14. If x is an int where x = 0, what will x be after the following loop terminates? while (x < 100) x *= 2; a. b. c. d. e.

2 64 100 128 None of these; this is an infinite loop

ANS: E Since x starts at 0, x *= 2; results in 0 * 2, or x = 0. Since x remains 0, x <100 remains true, and the loop repeats. x continues to be 0 and so the condition never changes to false, and thus the loop never terminates.

15. How many times will the following loop iterate? int x = 10; while (x > 0) { System.out.println(x); x--; } a. b. c. d. e.

0 once 9 times 10 times 11 times

ANS: D Since the condition is tested before the loop body executes, the loop will not execute once x == 0.

So, the loop iterates for x = 10, x = 9, ..., x = 1, or 10 times.

16. Which type of GUI control would be best to use if you wanted the user to select one date from a list of three possible dates to take an exam? a. b. c. d. e.

check boxes because they are used for mutually exclusive options radio buttons because they are used for mutually exclusive options either check boxes or radio buttons because either are used for mutually exclusive options neither check boxes nor radio buttons can be used for mutually exclusive options There is no way to force a user to select only one option from a list; this must be done with a text input box.

ANS: B Code Segment Ch 05-1 if (a > 0) if (b < 0) x = x + 5; else if (a > 5) x = x + 4; else x = x + 3; else x = x + 2; 17. Refer to Code Segment Ch 05-1. If x is currently 0, a = 5 and b = 5, what will x become after the statement shown is executed? a. b. c. d. e.

0 2 3 4 5

ANS: C

Since a > 0 is true, the next condition is checked. Since b < 0 is false, the else clause for this condition is executed. Since a > 5 is false the else clause for this condition is executed, which is x = x + 3. Therefore, 3 is added to x, so it is now 3.

18. Refer to Code Segment Ch 05-1. If x is currently 0, a = 0 and b = -5, what will x become after the statement shown is executed? a. b. c. d. e.

0 2 3 4 5

ANS: B Since a > 0 is not true, the else clause for this condition is executed which is x = x + 2 x is now 2.

19. Refer to Code Segment Ch 05-1. If x is currently 0, a = 1 and b = -1, what will x become after the statement shown is executed? a. b. c. d. e.

0 2 3 4 5

ANS: E Since a > 0 is true, the if clause for this condition is executed which is another if statement. Its condition, b < 0 is true so its if clause is executed which is x = x + 5, so now x is 5.

20. As introduced in the Software Failure, the terminology "risk analysis" means a. how willing you are to risk the loss of several key programmers working on your project b. how much you are willing to risk that a particular piece of software you are developing still contains an error or errors c. how willing you are to risk that your software will fail once implemented d. how willing you are to risk that the machines on which your software will run will not work e. None of these ANS: B The terminology "risk analysis" pertains explicitly to the risks a developer is willing to take that a piece of software developed will still contain errors at the time of implementation.

PROBLEM 1. Rewrite the following set of if statements using a nested if-else structure. if (score >= 90) grade = 'A'; if (score >= 80 && score < 90) grade = 'B'; if (score >= 70 && score < 80) grade = 'C'; if (score >= 60 && score < 70) grade = 'D';

if (score < 60) grade = 'F'; ANS: if (score >= 90) grade = 'A'; else if (score >= 80) grade = 'B'; else if (score >= 70) grade = 'C'; else if (score >= 60) grade = 'D'; else grade = 'F'; 2. A truth table shows, for the various true or false values of boolean variables, what the result of a boolean condition is. Fill in the following truth table. Assume that a, b and c are boolean variables. a false false false false true true true true

b false false true true false false true true

c false true false true false true false true

a && (!b

|| c)

b false false true true false false true true

c false true false true false true false true

a && (!b false false false false true true false true

|| c)

ANS: a false false false false true true true true

3. A truth table shows, for the various true or false values of boolean variables, what the result of a boolean condition is. Fill in the following truth table. Assume that a, b and c are boolean variables. a false false false false true true true true

b false false true true false false true true

c false true false true false true false true

!(a && b) ||

!(a && c)

b false false true

c false true false

!(a && b) ||

!(a && c)

ANS: a false false false

true true true

false true true true true

true false false true true

true false true false true

true true true true false

4. Explain what is meant by short circuiting and provide an example of short circuiting a condition with && and provide an example of short circuiting a condition with ||.

ANS: Short circuiting is when a boolean expression does not have to be completely evaluated because the final answer is determined with just a partial evaluation. This can occur in an expression with && if one part of the expression evaluates to false, and in an expression with || if one part of the expression evaluates to true.

Examples: 1. (x != 0) && (sum / x > 100) can be short circuited if x != 0 is false, preventing a division by zero error.

2. (a.equals("yes") || a.equals("no")) can be short circuited if a is equal to "yes" so that the computer does not waste time in testing a.equals("no").

5. The following code has a syntax error immediately before the word else. What is the error and why does it arise? Fix the code so that this statement is a legal if-else statement. if (x < 0); x++; else x--; ANS: The error is "else without if" and it arises because of the ; after the condition but before x++. The Java compiler determines that the if clause is in fact ; (no statement) and that x++; is a statement that follows the if statement. Therefore, since x++; is not part of the if statement, the else is felt to be an else without an if, and that is why the error arises. The statement should be: if (x < 0) x++; else x--; 6. String s1 is said to overlap String s2 if all of the characters in s1 also appear in s2. Write a set of code that will set the boolean variable overlap to true if s1 overlaps s2 and false otherwise. Assume both s1 and s2 have already been input.

ANS: boolean overlap = true; int j = 0; while (overlap && j < s1.length()) { boolean found = false; int k = 0; while (!found && k < s2.length()) if (s2.charAt(k) == s1.charAt(j)) found = true; else k++; if (!found) overlap = false; j++;

}

Java Software Solutions, 9e (Lewis/Loftus) Chapter 6 More Conditionals and Loops TRUE/FALSE 1. A switch statement must have a default clause.

ANS: F The default clause is optional.

2. Each switch statement must terminate with a break statement.

ANS: F They often do but if the break statement is not present, the flow of control continues into the next case.

3. Control in a switch statement jumps to the first matching case.

ANS: T The switch expression is evaluated and control jumps to the first matching case, then continues from there.

4. The following for loop is an infinite loop:: for(int j = 0; j < 1000;) i++; ANS: T This loop initializes j to 0 and compares it to 1000, but does not alter j after each loop iteration. In reality, the loop will terminate with a run-time error eventually once i becomes too large to store in memory, but logically, this is an infinite loop.

5. It is possible to convert any type of loop (while, do, for) into any other.

ANS: T All loop statements have equivalent expressive power.

6. The following loop is syntactically valid: for(int j = 0; j < 1000; j++) j--; ANS: T The Java compiler does not care that you are incrementing j in the loop but decrementing j in the loop body. Logically, this loop makes no sense because j will continuously be incremented and decremented so that it never reaches 1000, but there is nothing wrong with the loop syntactically.

7. In Java, it is possible to create an infinite loop out of while and do loops but not for loops.

ANS: F

It is true that while and do loops can be infinite loops, but it is also true that Java for loops can be infinite loops. This is not true in some other programming languages where for loops have a set starting and ending point, but Java for loops are far more flexible than most other language's for loops.

8. A conditional operator is virtually the same as a switch statement.

ANS: F The conditional operator is more like an if-else statement.

9. A for statement is normally used when you do not know how many times the loop should be executed.

ANS: F A for statement is normally used when you do know how many times the loop should be executed.

10. A loop can be used in a GUI to draw concentric circles.

ANS: T MULTIPLE CHOICE 1. You might choose to use a switch statement instead of nested if-else statements if a. the variable being tested might equal one of several hundred integer values b. the variable being tested might equal one of a few integer values c. there are two or more integer variables being tested, each one of which could be one of several hundred values d. there are two or more integer variables being tested, each one of which could be one of a few values e. None of these; you would never choose a switch statement instead of nested if-else statements under any circumstances.

ANS: B The switch statement can only be used if there is a single variable being tested and it is an integer type (an int or a char in Java). Further, because you have to enumerate each possible value being tested, the switch statement only makes sense if the number of values being tested is a small number.

2. If a switch statement contains no break statements at all, a. a syntax error will occur b. each of the case clauses will be executed every time the switch statement is encountered

c. this is equivalent to having the switch statement always take the default clause, if one is present d. this is not a syntax error but nothing within the switch statement will ever be executed e. None of these ANS: E Although writing such a switch statement is unusual, it is entirely legal. The normal rules for the switch statement execution apply. The matching case clause being executed after the switch statement is evaluated and, following that, all subsequent clauses are executed, in order, since there are no break statements to terminate execution.

3. A continue statement a. b. c. d. e.

may be used within a while or a do-while loop but not a for loop is identical to a break statement within Java loops may be used within any Java loop statement may be used within a for loop but not within a while or a do-while loop None of these

ANS: C Although use of continue statements should be avoided, if possible, they may be used within any of Java's three types of loops.

4. How can the following statement be rewritten using a conditional operator? if(x <0) y = x; else y = 0; a. b. c. d. e.

y = (x < 0) ? x : 0; x = (x < 0) ? y : 0; (x < 0) ? y = x : y = 0; y = (x < 0); y = if(x < 0) x : 0;

ANS: A The conditional operator of Java tests a condition, (x < 0) in this case, and if true, returns the value after the ? (x in this case) and if false, returns the value after the : (0) in this case). The original if statement is to assign y to x if (x < 0) and 0 otherwise. This will be accomplished by assigning y to be x or 0 based on (x < 0), as shown in A. In B, x is assigned the value of y or 0 which is backward. In C, the conditional operator is syntactically invalid. In D, y would be set to either true or false depending on (x < 0), and the statement in E is syntactically invalid.

5. Given the following code, where x = 0, what is the resulting value of x after the for loop terminates? for(int i = 0; i < 5; i++) x += i; a. b. c. d. e.

0 4 5 10 15

ANS: D

Each pass through the for loop results with the current value of the loop index, i, being added to x.

The first time through the loop, i = 0 so x = x + 0 = 0. The second time through the loop i = 1 so x = x + 1 = 1. The third time through the loop i = 2 so x = x + 2 = 3. The fourth time through the loop i = 3 so x = x + 3 = 6. The fifth and final time through the loop i = 4 so x = x + 4 = 10.

6. The do loop differs from the while loop in that a. the while loop will always execute the body of the loop at least once b. the do loop will always execute the body of the loop at least once c. the do loop will continue to loop while the condition in its while statement is false and the while loop will continue to loop while the condition in its while statement is true d. the while loop will continue to loop while the condition in its while statement is false and the do loop will continue to loop while the condition in its while statement is true e. None of these; there is no difference between the two types of loops ANS: B Because the do loop does not test the condition until after the body of the loop executes, the body will always execute at least one time, but the while loop tests the condition first, and so if the condition is false the first time, the body does not execute even one time.

7. How many times will the following loop iterate? int x = 10; do { System.out.println(x); x--; } while(x > 0); a. b. c. d. e.

0 times 1 time 9 times 10 times 11 times

ANS: E The variable x starts at 10. Each pass through the loop, x is decremented and the loop finally exits once x is no longer greater than 0, which in this case means once x becomes 0. So the loop body executes for x = 10, x = 9, x = 8, and so forth down to x = 0. This is 11 times.

8. How many times will the following nested loop structure execute the innermost statement (x++;)? for(int j = 0; j < 100; j++) for(int k = 100; k > 0; k--) x++; a. b. c. d. e.

100 200 10,000 20,100 1,000,000

ANS: C The outer loop iterates 100 times. Each time it iterates, the inner loop, and the x++; statement, execute 100 times. Therefore, the statement x++; executes 100*100 = 10,000 times.

9. Given that s is a String, what does the following loop do? for(int j = s.length(); j > 0; j--) System.out.print(s.charAt(j-1); a. b. c. d. e.

It prints s out backwards It prints s out forwards It prints s out backwards after skipping the last character It prints s out backwards but does not print the first character It yields a run-time error because there is no character at s.charAt(j-1) for j = 0

ANS: A The variable j counts down from the length of the String to 1, each time printing out the character at position j-1. The character at length-1 is the first character printed and this is the last character of the String. It continues until it reaches j = 1, and prints out the character at position j-1, or the 0th character, so it prints the entire String backwards.

10. What does the break statement do? a. It ends a program. b. It transfers control out of the current control structure such as a loop or switch statement. c. It ends the current line of output, returning the cursor. d. It denotes the end of a switch statement. e. It indicates the end of a line when using System.out.print.

ANS: B This is the exit statement that allows the programmer to exit a control structure from inside of that control structure.

11. If a break occurs within the innermost loop of a nested loop that is three levels deep, a. just the innermost loop will be "broken" b. all loops are "broken" and execution continues from after the end of the loop c. all but the outermost loops are "broken" and execution continues from the next iteration of the outermost loop d. a syntax error is generated unless there are break or continue statements at each loop level e. None of these are true ANS: A The innermost loop is broken, and execution continues from just after the end of that loop.

12. Which of the following statements are true about Java loops? a. All three loop types are functionally equivalent. b. while loops and do loops are essentially the same, but while loops always execute at least once. c. If you know the number of times that a loop is to be performed, the best type of loop to use is a while loop.

d. Loops may be replaced by an appropriate combination of if-else and switch statements. e. None of these ANS: A In Java, as in most languages, the looping statements are all essentially equivalent (and almost interchangeable). Their principal difference(s) relate to when the controlling condition is evaluated and whether there is syntax for incrementation/update.

13. How many times will the System.out.println("*"); statement execute inside of the following nested for loops? for(j = 0; j < 10; j++) for(k = 10; k > j; k--) System.out.println("*"); a. b. c. d. e.

50 100 55 10 20

ANS: C The first iteration of the outer loop has j = 0, so the inner loop iterates from 10 down to 1, or 10 times. The next iteration of the outer loop has j = 1, so the inner loop iterates from 10 down to 2, or 9 times. This continues until the outer loop has j = 9, in which case the inner loop iterates for k = 10 only, or 1 time. Thus, the System.out.println("*"); statement executes a total of 10 + 9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1 = 55 times.

14. Which of the following would rotate an Ellipse named lipse 30 degrees counterclockwise? a. b. c. d. e.

lipse.setRotate(30); lipse.setRotate(370); lipse.setRotate(-30); Ellipse.lipse.setRotate(30); Ellipse.lipse.setRotate(-10*3);

ANS: C Code Example Ch 06-1 In the following example, x is an int: switch (x) { case 3 : x += 1; case 4 : x += 2; case 5 : x += 3; case 6 : x++; case 7 : x += 2; case 8 : x--; case 9 : x++ }

15. Refer to Code Example Ch 06-1: If x is equal to 5, what will the value of x be after the switch statement executes? a. b. c. d. e.

8 6 11 5 10

ANS: C Since there are no break statements, the flow falls through any cases following the one that is true. The first case to be true is 5 since x is 5 prior to the switch statement. This changes x to 8, then to 9, then to 11, then to 10, and then finally back to 11.

16. Refer to Code Example Ch 06-1: If x is equal to 3, what will the value of x be after the switch statement executes? a. b. c. d. e.

5 6 11 10 12

ANS: E Since there are no break statements, the flow falls through any cases following the one that is true. The first case to be true is 3 since x is 3 prior to the switch statement. This changes x to 4, then to 6, then to 9, then to 10, then to 12, then to 11, and then finally back to 12.

PROBLEM 1. Rewrite the following nested if-else statements using an equivalent switch statement. if (letter == 'A' || letter == 'a') System.out.println("Excellent"); else if (letter == 'B' || letter == 'b') System.out.println("You can do better"); else if (letter == 'C' || letter == 'c') System.out.println("Try harder"); else if (letter == 'D' || letter == 'd') System.out.println("Try much harder"); else System.out.println("Try another major! "); ANS: switch (letter) { case 'A', 'a' : System.out.println("Excellent"); break; case 'B', 'b' : System.out.println("You can do better"); break; case 'C', 'c' : System.out.println("Try harder"); break; case 'D', 'd' : System.out.println("Try much harder"); break; default : System.out.println("Try another major! "); }

2. Given the following tax table information, write Java code to assign the double taxRate appropriately, given the double pay. Select the selection statement (if, if-else, switch) that makes the most sense.

If pay is more than 100,000, tax rate is 40% If pay is more than 60,000 and less than or equal to 100,000, tax rate is 30% If pay is more than 30,000 and less than or equal to 60,000, tax rate is 20% If pay is more than 15,000 and less than or equal to 30,000, tax rate is 10% If pay is more than 5,000 and less than or equal to 15,000, tax rate is 5% If pay is less than or equal to 5,000, tax rate is 0% ANS: Use a nested if-else structure as it requires the least amount of code. A switch statement is not possible because pay is a double and the switch statement can only be used for int types. if (pay > 100000) taxRate = 0.40; else if (pay > 60000) taxRate = 0.30; else if (pay > 30000) taxRate = 0.20; else if (pay > 15000) taxRate = 0.10; else if (pay > 5000) taxRate = 0.05; else taxRate = 0.0; 3. Write a declaration that initializes an int variable named num1 to 100 if the boolean variable score is true and to 50 otherwise, using the conditional operator.

ANS: int num1 = (score) ? 100 : 50; 4. Rewrite the following if-else statement using a conditional operator. if (x > y) z = x; else z = y; ANS: z = (x > y) ? x : y; 5. Write a do loop to obtain a list of scores from a teacher. The teacher should end input by entering the sentinel value, 999. The program should output the average of the scores.

ANS: Scanner scan = new Scanner(System.in); int score, count, sum = 0; do { sum += score; System.out.print("Enter a score or 999 to quit): "); score = scan.nextInt();

count++; } while (score != 999) average = sum / (count - 1); System.out.println(average); 6. Describe a situation where you should use a do loop and a situation where you should use a while loop.

ANS: The do loop is used if you want to execute the loop body at least one time. This is useful for data verification (asking the user for a value, and only if the user has entered an improper value does your code repeat and try again). A while loop does not necessarily execute if the loop condition is not initially true. This might be useful if you want to control entrance to a loop such as only trying to sum up a list of values if the user actually has values to sum up.

7. The following for loop is odd in that the loop increment value changes during iterations of the loop.

Determine the number of times the loop iterates and the final value of j after the loop terminates. int k = 0; for (j = 0; j < 20; j += k) k++; ANS: Six times with j = 21. Explanation: The first iteration has j = 0, k is then incremented in the loop body to 1 and j is incremented after the loop body executes to be j + k = 0 + 1 = 1. For the second iteration, k is incremented to 2 and j is incremented to j + k = 1 + 2 = 3. For the third iteration, k is incremented to 3 and j is incremented to 3 + 3 = 6. For the fourth iteration, k is incremented to 4 and j is incremented to 6 + 4 = 10. For the fifth iteration, k is incremented to 5 and j is incremented to 10 + 5 = 15. For the sixth iteration, k is incremented to 6 and j is incremented to 15 + 6 = 21. Now, since (j < 20) is no longer true, the loop terminates.

8. Write code that outputs all of the int values between 1 and 100 with five values per line, and each of those five values spaced out equally. Use a single for loop to solve this problem.

ANS: for (int j = 1; j <= 100; j++) { System.out.print(j + "\t"); if (j % 5 == 0) System.out.println( ); } 9. Write the code to display an ImageView named the_view at half its original size.

ANS: the_view.setScaleX(0.5); the_view.setScaleY(0.5);

Java Software Solutions, 9e (Lewis/Loftus) Chapter 7 Object-Oriented Design TRUE/FALSE 1. The most important decisions regarding the development of a system are made during the implementation phase while code is actively being written.

ANS: F All of the important decisions should be made during earlier phases of development, particularly during the design phase. By the time the implementation phase is reached, the entire system design should be available and this phase should only entail translating the design into code.

2. Unlike the String class where you must pass a message to an object (instance) of the class, in order to use the Math class, you pass messages directly to the class name, as in Math.sqrt().

ANS: T The Math class uses methods known as static methods (or class methods) which are invoked by passing a message directly to the class name itself rather than to an object of the class.

3. Assume that the class Bird has a static method fly(). If b is a Bird, then to invoke fly, you could do Bird.fly();.

ANS: T Static methods are invoked through the class and not an object of the class. This is because the static method is shared among all instances. So, Bird.fly(); will invoke fly. It should be noted that fly can also be invoked through b, so b.fly(); will also work.

4. Interface classes cannot be extended but classes that implement interfaces can be extended.

ANS: F Any class can be extended whether it is an interface, implements an interface, or neither. The only exception to this is if the class is explicitly modified with the word final in which case it cannot be extended.

5. If classes C1 and C2 both implement an interface Cint, which has a method, whichIsIt, and if C1 c = new C1(); is performed at one point of the program, then a later instruction c.whichIsIt(); will invoke the whichIsIt method defined in C1.

ANS: F Because C1 and C2 implement the same interface, they both implement whichIsIt. The variable c is known as a polymorphic variable, meaning that it can change from being an C1 to a C2. So, the message c.whichIsIt(); may invoke C1's whichIsIt or C2's whichIsIt. There is no way to tell until runtime.

6. Any class can implement an interface, but no classes can implement more than a single interface.

ANS: F Classes can implement any number of interfaces, 0, 1, or more.

7. All objects implement Comparable.

ANS: F Comparable is an interface, and the class must define the CompareTo method and explicitly state that it implements Comparable to be considered an implementation of Comparable. Most classes do not implement Comparable.

8. Formal parameters are those that appear in the method call and actual parameters are those that appear in the method header.

ANS: F The question has the two definitions reversed. Formal parameters are those that appear in the method header, actual parameters are the parameters in the method call (those being passed to the method).

9. It is not possible to test out any single method or class of a system until the entire system has been developed, and so all testing is postponed until after the implementation phase.

ANS: F While it is true that testing occurs after implementation, some testing can take place during implementation. In Java, it is possible to test out single methods or classes by creating stubs of other methods and classes that are simple placeholders. For instance, if one method calls another method and the second method is not yet written, a stub of the second method can be written that simply returns a value that would normally be expected so that the first method can be tested.

10. In black-box testing, the tester should already know something about how the program is implemented so that he/she can more carefully identify what portion(s) of the software may lead to errors.

ANS: F In black-box testing, the tester should know nothing about how the software is implemented. In essence, the software is a black-box which has an input and an output and the mechanisms of the program are opaque. If the tester does know something about how the program works, then the tester's test cases might be biased. If the tester knows how the program works, then testing is known as glass-box testing.

11. The versions of an overloaded method are distinguished by the number, type, and order of their parameters.

ANS: T 12. The graphical effect caused when a shape seems to resize as the mouse is dragged is known as rubberbanding.

ANS: T MULTIPLE CHOICE 1. During program development, software requirements specify a. b. c. d. e.

how the program will accomplish the task what task the program must perform how to divide the task into subtasks how to test the program when it is done All of these

ANS: B The specification phase is to understand the problem at hand so that the programmer can determine what needs to be done to solve the problem. The other efforts listed above are part of the design phase (A, C) and testing phase (D).

2. Once we have implemented the solution, we are not done with the problem because a. b. c. d.

the solution may not be the best or most efficient the solution may have errors and need testing and fixing before we are done the solution may, at a later date, need revising to handle new specifications the solution may, at a later date, need revising because of new programming language features e. All of these ANS: E A program should not be considered as a finished product until we are reasonably assured that it is efficient and error-free. Further, it is common that programs require modification in the future because of a change to specifications or a change to the language or computer running the program.

3. Of the various phases in software development, which of the following is usually the lengthiest? a. b. c. d. e.

specification design implementation testing maintenance

ANS: E The maintenance phase exists for as long as the software is in use. Software requires modification (such as new requirements like new features or I/O specifications) and so the maintenance phase is ongoing whereas the other phases end once the software has been released and is in use.

4. The activities of the development cycle are generally thought to a. b. c. d. e.

be strictly linear be rigidly ordered overlap have optional steps both A and B are true

ANS: C Phases often need revisiting resulting in a development cycle where the development activities overlap.

5. The idea of having programmers and developers meet in order to critique a software design or implementation is known as a. b. c. d. e.

an interview a walkthrough prototyping aggregation evolutionary development

ANS: B Such meetings are very useful so that the various members can analyze the solution to that point in time and offer suggestions to enhance the design and implementation. This is called a walkthrough because it involves going step-by-step through the proposed or implemented design.

6. Modifying a program in order to eliminate deficiencies is done in the development cycle. a. b. c. d. e.

phase of the

design implementation testing use maintenance

ANS: B While testing is used to find errors, deficiencies are more commonly identified by the users of the system once the system has been released. After such deficiencies have been identified, it is up to the software maintenance group to eliminate them in future versions of the software.

7. It is easier to correct errors found in a program if a. b. c. d. e.

they are identified early in the development cycle they are identified during testing they are identified during program use they are identified during maintenance All of the above are equally true; errors are easily corrected at any of these stages

ANS: A Errors introduced early in the development cycle often cause tremendous problems if not caught early on. Therefore, errors found in testing, use or maintenance phases may be too embedded in the systems' design to be easily corrected. But if found early on, the errors can be completely eliminated.

8. In general, spending more time in development to ensure better software will a. b. c. d. e.

shorten testing time slightly reduce maintenance efforts slightly increase maintenance efforts greatly reduce maintenance efforts not alter the time it takes for any other stage

ANS: D Spending more time in development promises better software, which in turn leads to less maintenance effort.

9. It is important to dissect a problem into manageable pieces before trying to solve the problem because a. most problems are too complex to be solved as a single, large activity b. most problems are solved by multiple people and it is easy to assign each piece to a separate person c. it is easier to integrate small pieces of a program into one program than it is to integrate one big chunk of code into one program d. the first solution may not solve the problem correctly e. all of these ANS: A Any interesting problem will be too complex to solve easily as a single activity. By decomposing the problem, we can build small solutions to each piece and then integrate the pieces. Answer D is true, but is not the reason why we break a problem down into pieces.

10. The goal of testing is to a. b. c. d. e.

ensure that the software has no errors find syntax errors find logical and run-time errors evaluate how well the software meets the original requirements give out-of-work programmers something to do

ANS: C Testing is required because all software will have errors. Complex systems especially need testing before they can be released. The types of errors sought are logical errors and run-time errors. All syntax errors will have been identified and fixed during implementation.

11. In which phase of program development would you expect the programmer(s) to create the pseudocode? a. b. c. d. e.

software requirements software design software implementation software testing this could occur at any time

ANS: B Pseudocode is a description of an algorithm written in an English-like way rather than in a specific programming language. This is part of the program's design. In the implementation phase, the programmer(s) translate(s) the pseudocode into the programming language being used.

12. In which phase of program development would you expect the programmer(s) to determine the classes and objects needed? a. software requirements b. software design c. software implementation

d. software testing e. this could occur at any time ANS: B Determining which classes and objects to use or create is part of the design.

13. If a programmer follows the four phases of program development as intended, which of the four phases should require the least amount of creativity? a. b. c. d. e.

software requirements software design software implementation software testing all four levels require equal creativity

ANS: C Once the implementation phase has been reached, the algorithm should have already been specified, so the only effort involved in the implementation phase is of translating from the design (which is probably in an English-like pseudocode) to the programming language, and entering the code through an editor. The requirements and design phases require understanding the problem and coming up with a solution respectively, requiring creativity, and the testing phase will require diagnostic abilities usually forcing the programmer(s) to be creative in how the errors are found and fixed.

14. Having multiple class methods of the same name where each method has a different number of or type of parameters is known as a. b. c. d. e.

encapsulation information hiding tokenizing importing method overloading

ANS: E When methods share the same name, they are said to be overloaded. The number and type of parameters passed in the message provides the information by which the proper method is called.

15. Which of the following would not be considered an algorithm? a. b. c. d. e.

a recipe a computer program pseudocode a shopping list travel directions

ANS: D An algorithm is a step-by-step description of how to solve a problem, written at some level of specificity. The recipe and probably the pseudocode are written at a "high level" whereas a program and perhaps travel directions are written in more detail. A shopping list is not a step-by-step description, so it would not qualify as an algorithm.

16. In order to create a constant, you would use which of the following Java words? a. private b. static

c. int d. final e. class ANS: D The reserved word final indicates that this is the final value that will be stored in this variable, thus making it unchangeable, or constant. While constants can be of type int, constants can be of any other type as well. It is the final reserved word that makes the value unchangeable.

17. Which of the following methods is a static method? The class in which the method is defined is given inside the parentheses following the method name. a. b. c. d. e.

equals(String) toUpperCase(String) sqrt(Math) format(DecimalFormat) None of these

ANS: C The Math class defines all of its methods to be static. Invoking Math methods is done by using Math rather than a variable of type Math. The other methods above are not static.

18. In order to implement Comparable in a class, what method(s) must be defined in that class? a. b. c. d. e.

equals compares both lessThan and greaterThan compareTo both compares and equals

ANS: D The Comparable class requires the definition of a compareTo method that will compare two objects and determine if one is equal to the other, or if one is less than or greater than the other and respond with a negative int, 0 or a positive int. Since compareTo responds with 0 if the two objects are equal, there is no need to also define an equals method.

19. Static methods cannot a. b. c. d. e.

reference instance data reference non-static instance data reference other objects invoke other static methods invoke other non-static methods

ANS: B A static method is a method that is part of the class itself, not an instantiated object, and therefore the static method is shared among all instantiated objects of the class. Since the static method is shared, it cannot access non-static instance data because all non-static instance data are specific to instantiated objects. A static method can access static instance data because, like the method, the instance data is shared among all objects of the class. A static method can also access parameters passed to it.

20. An object that refers to part of itself within its own methods can use which of the following reserved words to denote this relationship?

a. b. c. d. e.

inner i private this static

ANS: D The reserved word this is used so that an object can refer to itself. For instance, if an object has an instance data x, then this.x refers to the object's value x. While this is not necessary, it can be useful if a local variable or parameter is named the same as an instance data. The reserved word this is also used to refer to the class as a whole, for instance, if the class is going to implement an interface class rather than import an implementation of an interface class.

21. An example of an aggregation relationship is a. b. c. d. e.

parent and child animal and dog teacher and computer phone and fax machine All of these

ANS: C An aggregate relationship describes how one object accomplishes a task by using another object. In the above list, the teacher uses the computer. The relationship in A is one of lineage (possibly ownership), the relationship in B is an "is-a" relationship as a dog is a child class of animal, and the relationship in D is one of similarity since phone and fax machine might be thought of as sibling classes, related to each other in that they are both children of a more general communication class.

22. Abstract methods are used when defining a. b. c. d. e.

interface classes derived classes classes that have no constructor arrays classes that have no methods

ANS: A An interface is a class that has defined some of its components, but leaves other components (methods) for you to implement. So, these components (methods) are referred to as abstract and defined in the interface class as abstract.

Code Description Ch 07-1 Consider a class called ChessPiece. This class has two instance data, String type and int player. The variable type will store "King", "Queen", "Bishop", etc. and the int player will store 0 or 1 depending on whose piece it is. We wish to implement Comparable for the ChessPiece class. Assume that, the current ChessPiece is compared to a ChessPiece passed as a parameter.

Pieces are ordered as follows: "Pawn" is a lesser piece to a "Knight" a "Bishop" and "Knight" are equivalent for this example both "Bishop" and "Knight" are lesser pieces to a "Rook"

a "Rook" is a lesser piece to a "Queen" a "Queen" is a lesser piece to a "King".

23. Refer to Code Description Ch 07-1: Which of the following method headers would properly define the method needed to make this class Comparable? (cp designates ChessPiece) a. b. c. d. e.

public boolean comparable(Object cp) public int comparable(Object cp) public int compareTo(Object cp) public int compareTo() public boolean compareTo(Object cp)

ANS: C To implementComparable, you must implement a method called compareTo which returns an int. Further, since this class will compare this ChessPiece to another, we would expect the other ChessPiece to be passed in as a parameter.

24. Refer to Code Description Ch 07-1: Which of the following pieces of logic could be used in the method that implements Comparable? Assume that ChessPiece has a method called returnType which returns the type of the given piece. a. b. c. d. e.

if (this.type < a.returnType()) return -1; if (this.type = = a.returnType()) return 0; if (this.type.equals(a.returnType()) return 0; if (a.returnType().equals("King")) return -1; if (a.returnType().equals("Pawn")) return 1;

ANS: C If the type of this piece and of a are the same type, then they are considered equal and the method should return 0 to indicate this. Note that this does not cover the case where this piece is a "Knight" and a is a "Bishop", so additional code would be required for the "equal to" case. The answer in B is not correct because it compares two Strings to see if they are the same String, not the same value. The logic in D and E are incorrect because neither of these takes into account what the current piece is, only what the parameter's type is. In D, if a is a "King", it will be greater than this piece if this piece is not a "King", but will be equal if this piece is a "King" and similarly in E, it does not consider if this piece is a "Pawn" or not. Finally, A would give a syntax error because two Strings cannot be compared using the < operator.

PROBLEM 1. Provide a reason why an instance data would be declared static.

ANS: If an instance data is to be shared among all objects of the class, the instance data would be static.

As an example, an instance data that counts the number of times something has happened across all objects of the class would be made static. If we are writing a chess game and have a ChessPiece class that includes a method called movePiece, we would want to know how many moves a player has made, but not necessarily how many times a single piece has been moved. So, all of the ChessPieces share a numberOfTimesMoved instance data that is incremented by any ChessPiece whenever it is moved.

2. Provide a reason why a method would be declared static.

ANS: A method is declared static if it might be used, not by the current object, but by any objects of the class. That is, the method does not require access to any single object's instance data. Consider a class called Point that consists of an x and y coordinate. To determine the distance between two Points, we could make a static computeDistance method. It is passed two Points as parameters and computes the distance.

3. Explain the difference between implementing an interface and a derived class.

ANS: Implementing an interface means that you are adding to your class any mechanisms defined in an abstract class. Your class essentially is expanded to contain those items defined in the interface class but you have to implement any of those items that are abstract. The appeal is that other objects might call upon your class to use the interface methods without knowing anything else about your class.

The derived class is similar in that you are gaining items previously defined, although in this case, those items are defined in the parent class (as long as those items are protected or public) and you do not have to implement any of them unless you want to redefine them. One difference between the two is that the interface cannot be instantiated directly. Another difference is that your class "inherits" abstract methods from the interface class as opposed to implemented methods from a super class.

4. Define an interface class that contains two int constants, X = 5 and Y = 10 and one int method called useXY which receives no parameters. Call your interface class XYClass.

ANS: public interface XYClass { public final int X = 5; public final int Y = 10; public int useXY(); } 5. Assume a class Foo implements Comparable. Without knowing anything else about the Foo class, write an equals method that returns true if the Foo parameter passed to this Foo is equal to this Foo as determined by using the implementation of Comparable.

ANS: public boolean equals(Foo a) { if(compareTo(a)) = = 0) return true; else return false;

} Code Description Ch 07-1 Consider a class called ChessPiece. This class has two instance data, String type and int player. The variable type will store "King", "Queen", "Bishop", etc. and the int player will store 0 or 1 depending on whose piece it is. We wish to implement Comparable for the ChessPiece class. Assume that, the current ChessPiece is compared to a ChessPiece passed as a parameter.

Pieces are ordered as follows: "Pawn" is a lesser piece to a "Knight" a "Bishop" and "Knight" are equivalent for this example both "Bishop" and "Knight" are lesser pieces to a "Rook" a "Rook" is a lesser piece to a "Queen" a "Queen" is a lesser piece to a "King".

6. Refer to Code Description Ch 07-1: To implement Comparable for the ChessPiece class, the current ChessPiece's type is compared to a ChessPiece passed as a parameter. The method should return 0 if the types are equal, -1 if this piece's type is a lesser piece than the parameter's type, and 1 if this piece's type is a greater piece than the parameter's type. Create this code.

ANS: public int compareTo(ChessPiece a) { if (this.type.equals(a.returnType())|| (this.type.equals("Knight")&&a.returnType().equals("Bishop")) ||(this.type.equals("Bishop")&&a.returnType().equals("Knight"))) return 0; else if (this.type.equals("King")) return 1; else if (a.returnType().equals("King")) return-1; else if (this.type.equals("Queen")) return 1; else if (a.returnType().equals("Queen")) return -1; else if (this.type.equals("Rook")) return 1; else if (a.returnType().equals("Rook")) return -1; else if (this.type.equals("Knight")||(this.type.equals("Bishop")) return 1; else if (a.returnType().equals("Knight")||(a.returnType().equals("Bishop")) return -1; } 7. Refer to Code Description Ch 07-1: Write a static method that is passed two ChessPieces and determines if the two pieces are owned by the same player. It should return true or false.

ANS: public static boolean samePlayer(ChessPiece p1, ChessPiece p2) { return (p1.returnPlayer( ) = = p2.returnPlayer( )); } 8. In what way is black-box testing better than glass-box testing? In what way is glass-box testing better than black-box testing?

ANS: Black-box testing is superior because the tester knows nothing of the software and so will test the software without preconceived ideas of where errors might exist. The tester is testing the software blindly, much as a user will use the software–without intimate knowledge of how the software works.

The result should be that if errors exist that a user might stumble across, the tester should find them.

While black-box testing of software has the advantage that the tester operates much like the users are expected to, the disadvantage is that it is a blind test, but there are times when knowledge of how the software functions could be useful. If programmers suspect that some awkward or difficult implementation may be buggy, then spending more time testing that portion of the software is advantageous. This form of testing requires knowledge of how the software works. So, both black-box and glass-box testing have their own advantages and disadvantages.

9. Write code that outputs all of the int values between 1 and 100 with five values per line, and each of those five values spaced out equally. Use a single for loop to solve this problem.

ANS: for (int j = 1; j <= 100; j++) { System.out.print(j + "\t"); if (j % 5 == 0) System.out.println( ); }

Java Software Solutions, 9e (Lewis/Loftus) Chapter 8 Arrays TRUE/FALSE 1. Arrays have a built-in toString method that returns all the elements in the array as one String with \n inserted between each element.

ANS: F Arrays are objects and so they inherit from the Object class. The Object class does have a toString method. However, Object's toString method does not return the value(s) stored in the Object but rather the value of the reference variable. So, toString used on an array will not return the values stored in the array, but instead a meaningless set of characters.

2. A command-line argument is data that is included on the command line when the interpreter is invoked to execute the program.

ANS: T Command-line arguments are another way to provide input to a program. They are accessed using the array of Strings that is passed into the main method as a parameter.

3. Java arrays can store primitive types and Strings but cannot store any type of Object other than Strings.

ANS: F Java arrays can store references to any type of class.

4. A Java main method uses the parameter (String[] variable) so that a user can run the program and supply command-line parameters. Since the parameter is a String array, however, the user does not have to supply any parameters.

ANS: T The main method requires the parameter in case a programmer wishes to permit the user to supply command-line parameters. Anything entered at the command line after the Java command will then be accepted as the command line parameter. If it is several words separated by spaces, then each word is stored as a separate String array element. For instance, "java foo.class hi there" would store "hi" in variable[0] and "there" in variable[1] for possible use by the program.

5. An array index cannot be a float, double, boolean, or String.

ANS: T An array index must be an int type or a value that can be widened to an int so char, byte, and short are also permissable.

6. Given the following statement, where CD is a previously defined class, then mycollection[5] is a CD object.

CD[] mycollection = new CD[200]; ANS: T The variable mycollection has been declared as an array of CD objects, so mycollection[5] is the 6th CD in the the array, and since a CD is an object, mycollection[5] is a CD object.

7. It is possible to sort an array of int, float, double or String, but not an array of an Object class.

ANS: F It is possible to sort any type of array as long as the type has some mechanism to compare two elements and determine their proper ordering (less than, equal, greater than).

8. In Java an array can only store one type of data.

ANS: T Arrays are known as homogeneous types. This means that the type of value stored in the array must be the same for every element. The type is determined by the declaration.

9. In a two-dimensional array, both dimensions must have the same number of elements, as in my_array[10][10].

ANS: F In Java, the dimensions can have any number of positive elements, so it is possible to have a two-dimensional array such as my_array[5][10].

10. An array, when instantiated, is fixed in size but an ArrayList can dynamically change in size when new elements are added to it.

ANS: T A drawback of an array is its fixed size. Once instantiated, it is fixed in size and so, if a program tries to add more elements than the size of the array, it results in an Exception being thrown. The ArrayList is a class that uses an array and automatically creates a larger array, copying the old array into the new array so that the ArrayList can be larger as needed. While this gets around the problem of a thrown Exception, it does lead to poorer performance because of having to copy from one array to another every time the ArrayList size is increased.

11. Just as arrays can only have a fixed number of elements, set at the time the array is declared, a parameter list also can only have a fixed number of elements, set at the time a method is declared.

ANS: F Java provides special notation for variable length parameter lists. The ellipsis (...) is used to specify a variable length parameter list.

12. A ragged array is a multidimensional array whose initial indices don't all start at zero.

ANS: F A ragged array is a multidimensional array whose lengths are not all equal. The initial index of all arrays in Java must start at zero.

13. So long as one is only accessing the elements of an ArrayList, its efficiency is about the same as that of an array. It's only when one begins to insert or remove elements towards the front portion of an ArrayList that its efficiency deteriorates.

ANS: T ArrayLists are implemented as arrays, so, as long as one is only accessing elements of an ArrayList the efficiency is about the same as for an array. But, when insertions or deletions towards the front portion of an ArrayList occur, that is when a significant amount of element copying must take place, thus decreasing its efficiency.

MULTIPLE CHOICE 1. Which of the following is a legal way to declare and instantiate an array of ten Strings? a. b. c. d. e.

String s = new String(10); String[10] s = new String; String[] s = new String[10]; String s = new String[10]; String[] s = new String; e

ANS: C Declaring an array is done by type[] variable. Instantiating the array is done by variable = new type[dimension] where dimension is the size of the array.

2. In Java, arrays are a. b. c. d.

primitive data types objects interfaces primitive data types if the type stored in the array is a primitive data type and objects if the type stored in the array is an object e. Strings ANS: B In Java, arrays are implemented as objects. The variable is a reference variable to the block of memory that stores the entire array. However, arrays are accessed using the notation name[index] rather than by message passing.

Code Example Ch 08-1 Assume an int array, values, that is filled to capacity with the following values:

| 18

9 |

|

4

|

12

|

2

|

6

|

8

|

3. Refer to Code Example Ch 08-1: What is returned by values[3]? a. b. c. d. e.

9 12 2 6 3

ANS: C Java array indices, like those in most languages, start at 0, so values[3] is really the fourth array element, which is 2.

4. Refer to Code Example Ch 08-1: What is returned by values.length? a. b. c. d. e.

0 5 6 7 18

ANS: D The length operator for an array returns the size of the array. The Code Example shows that that values stores 7 elements and since it is full, the size of values is 7.

5. Refer to Code Example Ch 08-1: Which of the following loops would adequately add 1 to each element stored in values? a. b. c. d. e.

for (j=1; j<values.length; j++) values[j]++; for (j=0; j<values.length; j++) values[j]++; for (j=0; j<=values.length; j++) values[j]++; for (j=0; j<values.length-1; j++) values[j]++; for (j=1; j<values.length-1; j++) values[j]++;

ANS: B The first array element is values[0], so the for loop must start at 0, not 1. There are values.length elements in the array where the last element is at values.length-1, so the for loop must stop before reaching values.length. This is the case in B. In D, the for loop stops one before values.length since < is being used to test the condition instead of <=.

6. Refer to Code Example Ch 08-1: What will the following statement do?

System.out.println(values[7]); a. b. c. d. e.

output 7 output 18 output nothing cause an ArrayOutOfBoundsException to be thrown cause a syntax error

ANS: D The array has 7 values, but these are indexed values[0] to values[6]. Since values[7] is beyond the bounds of the array, values[7]causes an ArrayOutOfBoundsException to be thrown.

7. The "off-by-one" error associated with arrays arises because a. the first array index is 0 and programmers may start at index 1 or may use a loop that goes one index too far b. the last array index is at length+1 and loops may only iterate to length, missing one c. the last array index is at length-1 and loops may go one too far d. programmers write a loop that goes from 0 to length-1 whereas the array actually goes from 1 to length e. None of these; the "off-by-one" error has nothing to do with arrays ANS: A An array is initialized as new type[x] where x is the size of the array. However, the array has legal indices of 0 to x-1 and so, programmers are often off-by-one because programmers will write code to try to access indices 1 to x.

8. Assume list is an array of int values, temp is some previously initialized value, and c is an int initialized to 0. What does the following code do? for (int j = 0; j < list.length; j++) if (list[j] < temp) c++; a. b. c. d. e.

It finds the smallest value and stores it in temp.

It finds the largest value and stores it in temp.

It counts the number of elements equal to the smallest value in list It counts the number of elements in list that are less than temp.

It sorts the values in list to be in ascending order.

ANS: D The statement if (list[j]<temp) c++; compares each element in list to temp and adds one to c only if the element is less than temp, so it counts the number of elements in list less than temp, storing this result in c.

Code Example Ch 08-2 Assume you have an int array, candy, which stores the number of candy bars sold by a group of children where candy[j] is the number of candy bars sold by child j. Assume there are 12 children in all.

9. Refer to Code Example Ch 08-2: What does the following code do?

Scanner scan = Scanner.create(System.in); int value1 = scan.nextInt(); int value2 = scan.nextInt(); bars[value1] += value2; a. b. c. d. e.

It adds one to the number of bars sold by child value1 and child value2.

It adds one to the number of bars sold by child value1.

It adds value1 to the number of bars sold by child value2.

It adds value2 to the number of bars sold by child value1.

It inputs a new value for the number of bars sold by both child value1 and child value2.

ANS: D

bars[value1] is the number of bars sold by child value1, and += value2 adds to this value the amount input for value2.

10. Refer to Code Example Ch 08-2: Which of the following could be used to compute the total number of bars sold by the children? a. b. c. d. e.

for (int j=0; j<12; j++) sum += candy[j]; for (int j=0; j<12; j++) candy[j] = sum; for (int j=0; j<12; j++) sum = candy[j]; for (int j=0; j<12; j++) sum += [j]; for (int j=0; j<12; j++) [j] += sum;

ANS: A The code in A iterates through all 12 elements of candy, adding each value to sum. The answer in B sets all 12 elements of candy equal to sum, the answer in C sets sum to be each element of candy, resulting in sum = candy[11] and D and E have syntactically invalid code.

11. Refer to Code Example Ch 08-2: What does the following method do? public int question15() { int value1 = 0; int value2 = 0; for (int j = 0; j < 12; j++) if (candy[j] > value1) { value1 = candy[j]; value2 = j; } return value2; } a. b. c. d. e.

It returns the total number of candy bars sold.

It returns the total number of children who sold zero candy bars.

It returns the total number of children who sold more than zero candy bars.

It returns the number of candy bars sold by the child who sold the most candy bars.

It returns the index of the child who sold the most candy bars.

ANS: E The loop iterates through all 12 array elements. If a particular value of candy is found to be larger than value1, then this new value is remembered in value1 along with the index of where it was found in value2. As the loop continues, if a new candy value is found to be greater than the current value1, then it is remembered instead, so the loop finds the maximum number of candy bars sold in value1 and the child's index who sold the most in value2. Since value2 is returned, the code returns the index of the child who sold the most.

12. Given the following array declaration and instantiation, what is true about array arr? int[] arr = new int[5]; a. b. c. d.

It stores 5 elements with legal indices between 1 and 5.

It stores 5 elements with legal indices between 0 and 4.

It stores 4 elements with legal indices between 1 and 4.

It stores 6 elements with legal indices between 0 and 5.

e. It stores 5 elements with legal indices between 0 and 5.

ANS: B Arrays are instantiated with an int value representing their size, or the number of elements that they can store. So, arr can store 5 elements. Further, all arrays start at index 0 and go to index size-1, so arr has legal indices of 0 through 4.

13. If any int array, a, is passed as a parameter to a method, which of the following would adequately define the parameter list for the method header? a. b. c. d. e.

(int[]) (int a[]) (int[] a) (int a) (a[])

ANS: C The parameter is defined much as the variable is originally declared, as type parameter name.

Here, the type is int[] and the parameter is a.

14. If int[] x = new int[15]; and the statement x[-1] = 0; is executed, then which of the following Exceptions is thrown? a. b. c. d. e.

IndexOutOfBoundsException ArrayIndexOutOfBoundsException NegativeArraySizeException NullPointException ArithmeticException

ANS: B The array index is out of bounds as the array index can only be between 0 and 14. -1 is an illegal index because it is out of bounds. One might expect the answer to be C, but the NegativeArraySizeException is thrown if an array is being declared with a negative number of elements as in int[] x = new int[-5]; 15. Given the following declarations, which of the following variables are arrays? int[] a, b; int c, d[]; a. b. c. d. e.

a a and b a and d a, b, and d a, b, c, and d

ANS: D The first declaration declares both a and b to be int arrays. The second declaration declares c and d to be ints but in the case of d, an int array. So, a, b, and d are all int arrays.

16. If a and b are both int arrays, then a = b will a. create an alias b. copy all elements of a into b

c. copy the zero element of b into the zero element of a d. return true if each corresponding element of b is equal to each corresponding element of a (that is, if a[0]is equal to b[0], a[1] is equal to b[1]and so forth) and return false otherwise e. return true if a and b are aliases and return false otherwise ANS: A The = is an assignment operator. If the two variables are primitives, than the left-hand variable gets a copy of the right-hand variable. However, since a and b are arrays, the reference variable a is set to the reference variable b, resulting in both a and b referencing the same array in memory, or they are now aliases of each other.

17. Given the following code and assuming list is an int array that stores positive int values only.

Which of the following tasks is accomplished by this code? int foo = 0; for (int j =0 ; j < list.length; j++) if (list[j] > foo) foo = list[j]; a. b. c. d. e.

It stores the smallest value of list in foo.

It stores the largest value of list in foo.

It stores every value of list, one at a time, in list until the loop terminates.

It counts the number of elements in list that are greater than foo.

It counts the number of elements in list that are less than foo.

ANS: B The condition in the if statement tests to see if the current element of list is greater than foo. If so, it replaces foo. The end result is that every element in list is tested and foo stores the largest element up to that point, so eventually, foo will be the largest value in the array list.

18. If x is a char and values is an int array, then values[x] a. causes a syntax error b. causes an Exception to be thrown c. casts x as an int based on x's position in the alphabet (that is, if x is an 'a' it uses 0 and if x is a 'z' it uses 25) d. casts x as an int based on x's ASCII value (that is, if x is an 'a' it uses 97 and if x is a 'z' it uses 122) e. casts x as an int based on the digit that is stored in x (that is, if x is a '3' it uses 3) but throws an Exception if x does not store a digit ANS: D An array index must be an int value, so normally values[x] would cause a syntax error if x were not an int, but the Java compiler will automatically cast x to be an int if it can be cast. Characters are cast as ints by converting the char value to its equivalent ASCII value. So, if x is 'a', it is cast as the int 97 instead and so values[x] accesses values[97].

19. What does the following statement do? int[] list = {5, 10, 15, 20}; a. It adds 4 int values to the array list. b. It initializes list to have 20 int values.

c. It initializes list to have 4 int values. d. It declares list but does not initialize it. e. It causes a syntax error because it does not include new int[4] prior to the list of values.

ANS: C An array does not have to be instantiated with the new reserved word if it is instantiated with the list of values it is to store. So, list = {5, 10, 15, 20}; causes list to become an array of 4 int values with the values of 5, 10, 15, 20 already initialized. Note that the array is automatically an array of 4 values, so list[n] for any value of n other than 0, 1, 2 or 3 would result in a thrown Exception.

20. Which of the following would initialize a String array names to store the three Strings "Huey", "Duey" and "Louie"? a. b. c. d. e.

String names = {"Huey", "Duey", "Louie"}; String[] names = {"Huey", "Duey", "Louie"}; String[] names = new String{"Huey", "Duey", "Louie"}; String names[3] = {"Huey", "Duey", "Louie"}; String names; names[0] = "Huey"; names[1] = "Duey"; names[2] = "Louie";

ANS: B An array does not have to be instantiated with the reserved word new if it is instantiated with the list of values it is to store. So, names = {"Huey", "Duey", "Louie"}; will create a String array of 3 elements with the three values already initialized. Of the other answers, A does not specify that names is a String array, C should not have the reserved word new, D should not have [3] after names and omits [] after String, and E does not instantiate the array as String[3], and thus , all four of these other answers are syntactically invalid.

21. Which of the following would declare a three-dimensional array called threeD? a. b. c. d. e.

int[3] threeD; int[ , , ] threeD; int[][][] threeD; int [[[]]] threeD; int[] threeD[3];

ANS: C In Java, you can only declare one-dimensional arrays. To create a two-dimensional array, you must declare it as an array of arrays. A three-dimensional array is an array of an array of an array. The proper notation is to declare the type of array using multiple [] brackets in succession, as in int[][] for a two-dimensional array or int[][][] for a three-dimensional array.

22. A polygon object in Java is a. b. c. d. e.

a shape defined as a collection of x, y points a shape defined as a collection of lines a shape defined as a collection of polylines an array of shapes two lines connected by one common point

ANS: A

A polygon object is constructed as a series of points where the shape consists of lines that connect these points. So the shape is defined by the points themselves, denoted through two equal lengthed int arrays and the number of points in the shape.

23. A polyline object in Java is a. b. c. d. e.

an object a shape defined as a collection of lines a shape defined as a collection of polygons an array of shapes a shape defined aa s collection of line segments, defined by their endpoints

ANS: E A polyline is a collection of line segments, defined by their endpoints, sequentially connected to one another.

PROBLEM 1. Write a method to compute the average of an int array and return the value as a double. The int array and the number of elements in the array are both passed as parameters to the method in that order.

ANS: public double computeAverage(int[] list, int n) { int sum = 0; for (int j = 0; j < n; j++) sum += list[j]; return (double) ((n > 0) ? sum / n : 0); } 2. The length operator can be used to control a for loop that iterates through each element of an array, as in for (int j = 0; j < list.length; j++) However, this is not necessarily safe. Why not?

ANS: It is not necessarily the case that every element in the array has a value stored there. So, list[j] might be an array element that has no value even though j < list.length. So, list.length can only be used safely in an array that is full.

3. Write a method to compute and return the value of max and min where max is the largest element of an int array and min is the smallest element of the int array. The method is passed the int array and an int value that denotes the number of elements in the array. You may assume that the int array has at least 1 element in it.

ANS: public int computeDifference(int[] values, int n) {

int min = values[0]; int max = values[0]; for (int j=1;j<n; j++) { if (values[j] < min) min = values[j]; if (values[j] > max) max = values[j]; } return max - min; } 4. The class Name consists of 4 instance data, String title, String first, String middle, and String last. The class has a constructor that is passed all 4 String values and initializes the class appropriately. It has 4 methods and each returns one of the four instance data, called returnTitle(), returnFirst(), returnMiddle and returnLast().

Name[] addressBook = new Name[100]; is performed.

Write a method that is passed 4 String parameters corresponding to the title, first, middle, and last of Name, and finds this Name in addressBook and returns the index of where this Name was found, or -1 if the Name was not found. Assume that addressBook stores n entries (n is an int).

ANS: public int findName(String title, String first, String middle, String last) { for (int j=0; j<n; j++) if (title.equals(addressBook[j].getTitle() && first.equals(addressBook[j].getFirst() && middle.equals(addressBook[j].getMiddle() && last.equals(addressBook[j].getLast()) return j; return -1; } 5. Write a method that takes an array of Strings as a parameter and the number of elements currently stored in the array, and returns a single String that is the concatenation of all Strings in the array.

ANS: public String arrayConcatenator(String[] list, int number) { String allElements = ""; for (int j=0; j<number; j++) allElements += list[j]; return allElements; } 6. Write a method to output all elements of a two-dimensional array of int values as a table of rows and columns. Use "\t" to get elements to line up properly. The method is passed the two-dimensional array and two int values that denote the number of both dimensions (rows followed by columns).

ANS:

public void printTable(int[][] matrix, int rows, int columns) { for (int j=0; j<rows; j++) { for (int k=0; k<columns; k++) System.out.print(matrix[j][k] + "\t"); System.out.println(); } } 7. Assume Movie is a class whose objects represents movies. Assume a constructor of the Movie class that accepts two parameters: the name of the movie and the number of minutes the movie runs. Write a declaration for a variable named comedies that is an array of 20 comedy movies. Then write a new statement that sets the third movie in the comedies array to "Club Paradise" that runs 96 minutes.

ANS: Movie[] comedies = new Movie[20]; comedies[2] = new Movie("Club Paradise", 96); 8. A two-dimensional array named sales holds the weekly sales for employees in a jewelry store for a year. Write code that prints out a single value that represents the range of sales held in the array. It prints out the value of the highest sales amount minus the value of the lowest amount. Each sales amount is represented as an integer.

ANS: int highest = sales[0][0]; int lowest = highest; for (int row = 0; row < sales.length; row++) for (int col = 0; col < sales[row].length; col++) { if (sales[row][col] < lowest) lowest = sales[row][col]; if (sales[row][col] > highest) highest = sales[row][col]; } System.out.println(highest - lowest); 9. How can you tell if a user has double clicked the mouse button?

ANS: To see if a user has double clicked the mouse button, you call the getClickCount method of the MouseEvent object passed to the event handler method.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 9 Inheritance TRUE/FALSE 1. Interface classes cannot be extended but classes that implement interfaces can be extended.

ANS: F Any class can be extended whether it is an interface, implements an interface, or neither. The only exception to this is if the class is explicitly modified with the word final in which case it cannot be extended.

2. A derived class has access to all of the methods of the parent class, but only to the protected or public instance data of the parent class.

ANS: F Since methods can also be declared as private, any private methods are not accessible by a derived class. So, derived classes only have access to the protected and public methods and instance data of the parent class.

3. If class AParentClass has a protected instance data x, and AChildClass is a derived class of AParentClass, then AChildClass can access x but cannot redefine x to be a different type.

ANS: T A derived class can redefine any of the instance data or methods of the parent class. The parent class's version is now hidden, but can be accessed through the use of super, as in super.x.

Example Code Ch 09-1 Consider the following class hierarchy:

4. Refer to Example Code Ch 09-1: A is a derived class of X. ANS: F

While A is a descendant of class X, it is not a derived class. Instead, X is a derived class of Y and Y is a derived class of X. A ultimately inherits items from X as long as those items were not overridden by Y. 5. Refer to Example Code Ch 09-1: Y is a derived class of Z. ANS: F Y and Z are known as siblings because they are children of the same parent, but Y and Z may have nothing in common other than what they both inherit from X. 6. Refer to Example Code Ch 09-1: If A, B, Y and Z all contain the same instance data d1, then d1 should be declared in X and inherited into Y, Z, A and B. ANS: T Anything in common between A, B, Y and Z should be declared in X to properly identify that it is a class trait common amongst them. That is, common elements should be defined as high up in the hierarchy as possible. If all descendants of X have the trait (instance data) d1, then it is part of X too.

Example Code Ch 09-2 Assume that Poodle is a derived class of Dog and that Dog d = new Dog(...) and Poodle p = new Poodle(...) where the ... are the necessary parameters for the two classes.

7. Refer to Example Code Ch 09-2: The assignment statement d = p; is legal even though d is not a Poodle.

ANS: F Since Poodle extends Dog, Dog is a wider class (Poodle is more specific, and therefore narrower).

An assignment statement can assign a narrower item into a wider variable (since p is narrower, it can be assigned to d).

8. Refer to Example Code Ch 09-2: The assignment statement p = d; is legal even though p is not a Dog. ANS: F Since Poodle extends Dog, Dog is known as a wider class (Poodle is more specific, and therefore narrower). In any assignment statement, it is possible to take a narrower item and assign it into a wider variable, but it is not possible to assign a wider item into a narrower variable. To accomplish this, a cast must be explicitly made. So, the statement p = d; is illegal although the statement p = (Poodle) d; would be legal.

9. The reserved word, extends, is used to denote a has-a relationship.

ANS: F extends is used for inheritance. Inheritance is an is-a relationship, not a has-a relationship.

10. The protected visibility modifier provides the best possible encapsulation that permits inheritance.

ANS: T protected limits visibility as much as possible, while still allowing inheritance. In some ways, protected "advertises" that inheritance should be used.

11. You may use the super reserved word to access a parent class's private members.

ANS: F super will allow access to all non-private members of a parent class but, not to the private ones.

12. Java doesn't support multiple inheritance; but it does support the implementation of multiple interfaces.

ANS: T Single inheritance is one of Java's strong points. One can achieve most of the advantages of multiple inheritance by implementing multiple interfaces.

13. The JavaFX API offers the programmer controls that allow the user to pick colors or specific dates.

ANS: T 14. One way to allow for user interactivity in a program is to use a dialog box.

ANS: T 15. In order to use a dialog box to display an alert to the user, you must include the AlertType class.

ANS: F In order to use a dialog box to display an alert to the user, you must include the Alert class.

AlertType is an enumerated type that will specify the type of alert to be displayed.

MULTIPLE CHOICE Example Code Ch 09-4 Given the following partial class definition: public class A1 { public int x; private int y; protected int z; ... } public class A2 extends A1 { protected int a; private int b; ... } public class A3 extends A2 {

private int q; ... } 1. Refer to Example Code Ch 09-4: Which of the following is true with respect to A1, A2, and A3? a. b. c. d. e.

A1 is a subclass of A2 and A2 is a subclass of A3 A3 is a subclass of A2 and A2 is a subclass of A1 A1 and A2 are both subclasses of A3 A2 and A3 are both subclasses of A1 A1, A2 and A3 are all subclasses of the class A

ANS: B The reserved word extends is used to create a subclass. Since A2 extends A1, A2 is a subclass of A1. Since A3 extends A2, A3 is a subclass of A2.

2. Refer to Example Code Ch 09-4: Which of the following lists of instance data are accessible in class A2? a. b. c. d. e.

x, y, z, a, b x, y, z, a x, z, a, b z, a, b a, b

ANS: C Class A2 has access to all of its own instance data (a, b) and any instance data from A1 that were protected (z). Further, all classes, including A2, have access to A1's x since it is public, so x, z, a, b are accessible in A2.

3. Refer to Example Code Ch 09-4: Which of the following lists of instance data are accessible in class A3? a. b. c. d. e.

x, y, z, a, b, q a, b, q a, q x, z, a, q x, a, q

ANS: D Obviously q is accessible in A3. Also, A3 has access to anything inherited from A2, which is a.

Additionally, since A2 inherits z from A1, it is also inherited by A3. Finally, since x is public, it is visible to all classes.

4. Refer to Example Code Ch 09-4: Which of the following is true regarding the use of instance data y of class A1? a. b. c. d. e.

It is accessible in A1, A2, and A3 It is accessible in A1 and A2 It is accessible only in A1 It is accessible only in A3 It is accessible to any of the three classes

ANS: C Because it is declared as a private instance data, it is not inherited by any subclasses, and therefore y is only accessible in the class it was defined, A1.

5. The instruction super(); does which of the following? a. b. c. d. e.

It calls the method super as defined in the current class.

It calls the method super as defined in the current class's parent class.

It calls the method super as defined in java.lang.

It calls the constructor as defined in the current class.

It calls the constructor as defined in the current class's parent class.

ANS: E

The instruction super(); represents an invocation of something in the current class's parent class. Since there is no message but merely super(), it is an invocation of the parent class's constructor.

6. Inheritance through an extended (der ived) class supports which of the following concepts? a. b. c. d. e.

interfaces modulary information hiding code reuse correctness

ANS: D By extending a class and inheriting from it, the new class does not have to reimplement any of those inherited methods or instance data, thus saving the programmer time and effort. So, code reuse is the ability to reuse someone else's code for your benefit by extending it for your needs.

7. Aside from permitting inheritance, the visibility modifier protected is also used to a. b. c. d. e.

permit access to the protected item by any class defined in the same package permit access to the protected item by any static class permit access to the protected item by any parent class ensure that the class cannot throw a NullPointException define abstract elements of an interface

ANS: A The visibility modifier protected is used to control access to the item in a protected (guarded) manner. The protection is that access is restricted to the current class (like private items), classes in the same package, or extended classes of this class.

8. Which of the following is an example of multiple inheritance? a. b. c. d. e.

a computer can be a mainframe or a PC a PC can be a desktop or a laptop a laptop is both a PC and a portable device a portable device is a lightweight device Macintosh and IBM PC are both types of PCs

ANS: C

Multiple inheritance means that a given class inherits from more than one parent class. Of those listed above, a laptop computer inherits properties from both PCs and portable devices. The answers in A, B and E are all examples of single inheritance where a class has at least two children (in A, computer has children mainframe and PC, in B, PC has children desktop and laptop, in E, PC has children Macintosh and IBM PC).

9. Java does not support multiple inheritance but some of the abilities of multiple inheritance are available by a. b. c. d. e.

importing classes implementing interfaces overriding parent class methods creating aliases using public rather than protected or private modifiers

ANS: B Since a class can implement any number of interfaces, that class is in essence using the interface classes as if those interfaces were defined in this class. So this class is inheriting the methods and constants of the interfaces. Further, the class could extend another class and thus inherit directly and indirectly from multiple classes. This is not the exact same as multiple inheritance, but it is as close as Java comes to that concept.

10. If a programmer writes a class that he wants to be extended by another programmer, then this programmer must a. b. c. d. e.

change private methods and instance data to be protected change public methods and instance data to be protected change all the methods to be protected change the class to be protected None of these; the programmer doesn't have to change anything

ANS: A protected items are accessible by any subclass of the class that defines them while private items cannot be accessed by any other class. Therefore, previously defined private items must now be protected. Previously defined public entities should remain public so that all other classes can still access those public entities. Previously defined private items should not be made public because this would allow all classes to access them rather than just child classes.

11. All classes in Java are directly or indirectly subclasses of the a. b. c. d. e.

class.

Wrapper String Reference this Object

ANS: E Java requires that all classes have a parent class. If a class does not extend another class, then it, by default, extends the Object class. So the Object class is the parent or ancestor of every other class in Java.

12. Which of the following is not a method of the Object class? a. b. c. d. e.

clone compareTo equals toString All of the above are methods of the Object class

ANS: B The Object class defines clone to create a copy of any object, equals to determine if two objects are the same object, and toString to translate an Object into a String. However, compareTo is not implemented by Object and must be explicitly implemented in any class that wants to implement the Comparable interface.

13. Abstract methods are used when defining a. b. c. d. e.

interface classes derived classes classes that have no constructor arrays

classes that have no methods

ANS: A An interface is a class that has defined some of its components, but leaves other components (methods) for you to implement. So, these components (methods) are referred to as abstract and defined in the interface class as abstract.

Example Code Ch 09-5 Consider the following class definition: public class AClass { protected int x; protected int y; public AClass(int a, int b) { x = a; y = b; } public int addEm() { return x + y; } public void changeEm() { x++; y--; } public String toString() { return "" + x + " " + y; } }

14. Refer to Example Code Ch 09-5: You want to extend AClass to BClass. BClass will have a third int instance data, z. Which of the following would best define BClass's constructor? a. public BClass(int a, int b, int c) { super(a, b, c); } b. public BClass(int a, int b, int c) { x = a; y = b; z = c; } c. public BClass(int a, int b, int c) { z = c; } d. public BClass(int a, int b, int c) { super(a, b); z = c; } e. public BClass(int a, int b, int c) { super(); } ANS: D Inheritance is useful because it allows you to reuse code. For this problem, you would want to reuse as much of AClass as possible. Answer D allows you to use AClass's constructor, which expects two int parameters. This sets x and y to be a and b respectively. But since AClass does not have an instance data z, you need to directly assign z to be c in the constructor. The answer in B will also work, but does not reuse any code and so is not as desirable as D. The answers in A and E are syntactically invalid since they do not pass the correct number of parameters to AClass's constructor.

Finally, the answer in C only sets z correctly and leaves x and y uninitialized.

15. Refer to Example Code Ch 09-5: You want addEm to now add all three values, return the sum, and changeEm to change x and y, but leave z alone. Which should you do? a. Redefine addEm and changeEm without referencing super.addEm() or super.changeEm(). b. Redefine addEm to return the value of z+super.addEm(), but leave changeEm alone. c. Redefine changeEm to call super.changeEm() and then set z = x + y, but leave addEm alone. d. Redefine addEm to return the value of z+super.addEm() and redefine changeEm to call super.changeEm() and then set z = x + y. e. Redefine changeEm to call super.changeEm() without doing anything to z, and redefine addEm to return super.addEm().

ANS: B

Since super.changeEm() will not affect z and we don't want changeEm()to affect z, there is no need to redefine changeEm()for BClass. Any reference to changeEm()will reference AClass's version which is the same one that BClass will use. But addEm needs redefining because the inherited method addEm calls AClass's addEm which only adds x and y together.

Now, we want to add x, y and z together. We can either redefine addEm enntirely, or use super.addEm()and add z to the value returned. The latter approach is better since it reuses previously written code.

16. Refer to Example Code Ch 09-5: Which of the following would best redefine the toString method for BClass? a. public String toString(int z) { return " " + x + " " + y + " }

" + z;

b. ) public String toString() { return super.toString(); } c. public String toString() { return super.toString() + " } d. public String toString() { return super.toString()+" } e. public String toString() { return " " + x + }

" + z;

" x+"

" + y + "

"+y+"

"+z;

" + z;

ANS: C The best way to redefine a method is to reuse the parent class's method and supplement it with the code needed to handle the changes in the subclass. Answer C does this. Answer E accomplishes the same task, but does not reuse any of the parent class's code. Answer B returns only x and y, not z, and answer D returns x, y, and z, while answer A is syntactically invalid because the toString method does not accept a parameter.

17. Which of the following is true about Java classes? a. All classes must have one parent but may have any number of children (derived or extended). b. All classes must have one parent and may have a single child (derived or extended) but may have any number of parent classes. c. All classes can have any number (zero or more) of parent classes and any number of children (derived or extended) classes. d. All classes must have one parent and may have a single child (derived or extended) class. e. All classes can have either zero or one parent class and any number of child (derived or extended) classes.

ANS: A Java supports inheritance but not multiple inheritance, so a Java class can have any number of children but only one parent. Further, since all Java classes inherit either directly or indirectly from the Object class, all Java classes have exactly 1 parent class.

18. The relationship between a parent class and a child class is referred to as a(n) relationship. a. b. c. d. e.

has-a is-a was-a instance-of alias

ANS: B The term "is-a" is used to express that a subclass is a type of parent class. For instance, a graduate student is a type of student. The subclass is a more specific type. The has-a relationship refers to the attributes or elements of a class (for instance, a student has a GPA) and instance-of refers to the relationship between a class and an instantiated object of that class. There is no such thing as a was-a relationship and an alias denotes two variables that reference the same object or instance.

19. Two children of the same parent class are known as a. b. c. d. e.

aliases relatives clones brothers siblings

ANS: E The relationship between two children of the same parent is referred to as siblings (brothers would imply a gender). Clones are copies of the same object and aliases are the same object. Brothers and relatives are not used to define relationships between classes in Java.

20. Which of the following is correct? a. b. c. d. e.

a base class is a parent class or super class a base class is a child class or derived class a child class is a super class of its parent a parent class is a subclass of its child None of these are correct

ANS: A The terms base class, parent class, and super class are synonyms for one another. They all imply that the class will be used as a base for inheritance, and that subsequent classes will extend (inherit from) the base class.

21. Using the reserved word super, one can a. b. c. d.

access a parent class's constructor(s) access a parent class's methods and instance data access a child class's constructor(s) access a child class's methods and instance data

e. Both A and B are correct ANS: E The super reserved word provides a mechanism for accessing a parent class's methods and instance data (whether or not they are hidden). In addition, a parent class's constructor(s) may be accessed using super. So the correct answer is the combination of A and B or E. 22. If you instantiate an abstract class, the class or object you wind up with a. b. c. d. e.

is also an abstract class is a normal class is an interface is a reference to an Object you can't instantiate an abstract class

ANS: E You only can instantiate concrete classes, not abstract ones. But you can extend abstract classes as well as interfaces.

Example Code Ch 09-6 Assume that Student, Employee and Retired are all extended classes of Person, and all four classes have different implementations of the method getMoney. Consider the following code where ... indicates the required parameters for the constructors: Person p = new Person(...); int m1 = p.getMoney(); p = new Student(...); int m2 = p.getMoney(); if (m2 < 100000) p = new Employee(...); else if (m1 > 50000) p = new Retired(...); int m3 = p.getMoney();

// assignment 1 // assignment 2

// assignment 3

23. Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 1 is to the class a. b. c. d. e.

Person Student Employee Retired This cannot be determined by examining the code

ANS: A At this point of the program, p is a Person, and so getMoney is a reference to Person's getMoney method.

24. Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 2 is to the class a. b. c. d. e.

Person Student Employee Retired This cannot be determined by examining the code

ANS: B At this point of the program, p is a Student, and so getMoney is a reference to Student's getMoney method.

25. Refer to Example Code Ch 09-6: The reference to getMoney() in assignment 3 is to the class a. b. c. d. e.

Person Student Employee Retired This cannot be determined by examining the code

ANS: E Because there is no way to know if (m2 < 100000) is true or false or if (m1 > 50000) is true or false, it is not known whether p is still a reference to Student or if p now references an Employee or a Retired, and therefore the reference to getMoney()may be to Student, Employee or Retired, but we cannot tell which one just by examining the code.

PROBLEM 1. Consider a class Plane and three subclasses, Glider, PropPlane and Jet. What instance data that should be declared in Plane and what instance data should be declared in each of the three subclasses? Come up with at least 2 instance data unique to each of the four classes given that all instance data of Plane will be inherited into the subclasses.

ANS: Plane might include instance data such as size, weight, age, cost, carryingCapacity and maxSpeed. Glider might have instance data of maxAltitude and amountWindNeeded, PropPlane might have instance data of fuelType and numberOfProps and Jet might have instance data of fuelType, numberOfNacelles, and minimumSpeed.

2. Assume a class Triangle has been defined. It has three instance data, Point p1, p2, p3. The class also has a constructor that receives the 3 Points and initializes p1, p2, p3, a toString method that outputs the 3 Points, and a computeSurfaceArea method that calculates the surface area of the Triangle (as an int value). We want to extend this class to represent a 3-dimensional Pyramid, which consists of 4 Points. Since the Pyramid will consist of, in essence, 4 triangles, computeSurfaceArea for the Pyramid will compute 4 times the surface area of the Triangle made up of 3 of those 4 Points. Write the Pyramid class to handle the difference(s) between a Pyramid and the previously defined Triangle. Assume the instance data of Triangle are protected and all methods are public. Also assume that the class Point has a toString method.

ANS: public class Pyramid extends Triangle { protected Point p4; public Pyramid(Point a1, Point a2, Point a3, Point a4) { super(a1, a2, a3); p4 = a4;

} public String toString() { super.toString() + p4.toString(); } public int computeSurfaceArea() { return 4 * super.computeSurfaceArea(); } } 3. Explain the difference between implementing an interface and a derived class.

ANS: Implementing an interface means that you are adding to your class any mechanisms defined in an abstract class. Your class essentially is expanded to contain those items defined in the interface class but you have to implement any of those items that are abstract. The appeal is that other objects might call upon your class to use the interface methods without knowing anything else about your class.

The derived class is similar in that you are gaining items previously defined, although in this case, those items are defined in the parent class (as long as those items are protected or public) and you do not have to implement any of them unless you want to redefine them. One difference between the two is that the interface cannot be instantiated directly. Another difference is that your class "inherits" abstract methods from the interface class as opposed to implemented methods from a super class.

4. A motorcycle inherits properties from both a bicycle and a car. Java does not permit multiple inheritance. Assume that Bicycle and Car have both been declared. Explain how you might go about implementing a Motorcycle as a derived class.

ANS: You should extend whichever class is closer to the Motorcycle. For instance, both Motorcycle and Bicycle are two-wheeled vehicles and if this attribute is more important than other attributes, it might make sense to extend Bicycle. However, because Motorcycle shares internal combustion engine, gas fuel, similar speed and driving capabilities to a Car, it would probably make more sense to inherit from Car and override those methods that are most different (for instance, gas mileage varies greatly between cars and motorcycles). The Motorcycle derived class would then inherit the above instance data and methods to calculate and access these values. However, because the Motorcycle is also significantly different from a Car, other instance data and methods would need to be added and some methods redefined. For instance, a mechanism to determine how safe a Car is will differ from a mechanism in determining a Motorcycle's safety.

Example Code Ch 09-3 Consider the class Car and the subclass SportsCar. Car has instance data of currentSpeed, type, year, cost, model, color and methods of accelerate, brake, getGasMileage, getInsuranceRate and determineSpeed.

5. Refer to Example Code Ch 09-3: What instance data and methods might you define for SportsCar that are not part of Car?

ANS: A sports car may have a racing stripe, which could be stored in a boolean variable, and a maximum speed, as well as the number of gears. So the SportsCar class might add instance data of stripe, maxSpeed and numberGears. There might be methods to determine how safe the SportsCar is and whether it could win a race or not against another SportsCar. 6. Refer to Example Code Ch 09-3: What methods inherited from Car should SportsCar override?

ANS: Because a SportsCar will have different acceleration, the accelerate method should be overridden. Also, determineSpeed might change as will getInsuranceRate. The brake method may or may not differ and getGasMileage will probably stay the same.

7. Consider a class named Name which has four instance data (all Strings): first, last, middle, title. Even though Name inherits the equals method from Object, it would make sense to override it. Why? ANS: Object's version of equal compares two objects to see if they are the same Object, not if they are two Objects that share the same information. Two Name objects should be considered equal if they share the same first, middle, last and title Strings, not just if they are aliases for the same Object in memory. Therefore, the equals method should be overridden.

8. Explain the difference between using an imported class and extending a class.

ANS: An imported class lets you use someone else's code, but only as it was intended for use. You have no access to members that are not declared public. An extended class allows you to reuse someone else's code, but you can modify it to work as you wish, and you gain access to members that were declared protected as well as anything that was declared public.

9. Why is it a contradiction for an abstract method to be modified as final or static?

ANS: A final method cannot be overridden in derived classes so an abstract final method would have no way of being given a definition in a derived class. A static method can be invoked using the class name without declaring an object of the class. Because abstract methods have no implementation, an abstract static method would make no sense.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 10 Polymorphism TRUE/FALSE 1. If classes C1 and C2 both implement an interface Cint, which has a method whichIsIt, and if C1 c = new C1(); is performed at one point of the program, then a later instruction c.whichIsIt(); will invoke the whichIsIt method defined in C1.

ANS: F Because C1 and C2 implement the same interface, they both implement whichIsIt. The variable c is known as a polymorphic variable, meaning that it can change from being an C1 to a C2. So, the message c.whichIsIt(); may invoke C1's whichIsIt or C2's whichIsIt. There is no way to tell until run-time.

2. It is possible to sort an array of int, float, double or String, but not an array of an Object class such as a CD class.

ANS: F It is possible to sort any type of array as long as the type has some mechanism to compare two elements and determine their proper ordering (less than, equal, greater than). So, if the CD class has a compareTo method, then it would be possible to sort them.

3. To swap the 3rd and 4th elements in the int array values, you would do: values[3] = values[4]; values[4] = values[3]; ANS: F This code first copies values[4] into values[3] and then copies values[3] into values[4]. The result is that whatever was stored in values[4] is now stored in both values[3] and values[4]. In order to perform the swap appropriately, you would need a third variable to be used as a temporary storage location, as in int temp = values[3]; values[3] = values[4]; values[4] = temp; 4. A polymorphic reference can refer to different types of objects over time.

ANS: T That is what polymorphism is all about: late binding. This means that the same name will be associated with different semantics as the program executes.

5. Java allows one to create polymorphic references using inheritance and using interfaces.

ANS: T

Inheritance allows one to use a base variable to refer to various descendent members; the correct one will be used during execution. This is polymorphism in action. Interfaces provide a similar mechanism but use abstract methods rather than the concrete ones used in inheritance. The effect is the same, however.

6. A reference variable can refer to any object created from any class related to it by inheritance.

ANS: T This is the technique that one uses to accomplish a polymorphic reference--one whose precise interpretation will change during execution, depending upon the precise object to which the variable refers when it is encountered.

7. The type of the reference, not the type of the object, is used to determine which version of a method is invoked in a polymorphic reference.

ANS: F This is backwards. It is the type of the object, not the type of the reference, that determines which method is invoked.

8. The fact that the System.out.println() method is able to handle such a wide variety of objects, and print them correctly, is an example of the polymorphic nature of the println() method.

ANS: T Precisely! Since println() is highly polymorphic in nature, it is able to print a wide variety of pre-defined (library) and built-in (primitive) data correctly.

9. An interface reference can refer to any object of any class that implements the interface.

ANS: T This is one of the polymorphic functions of using an interface name to declare a reference variable.

10. An class reference can refer to any object of any class that descends from the class.

ANS: T This is one of the polymorphic functions of using a class name to declare a reference variable.

11. A method's parameter can be polymorphic, giving the method flexible control of its arguments.

ANS: T To accomplish this, merely use an interface name or a base class name to declare the variable. Then the parameter is polymorphic, referring to the correct instance of the class during execution, with the correct semantics being accessed during execution.

12. One of the advantages of the linear search is that it does not require its data to be sorted.

ANS: T

Most other search techniques require that their data is sorted in order to achieve greater efficiency (speed). But the linear search makes no such requirement. The result is that the linear search may be slower than one might desire, but it always works, and one never needs to pay the (expensive) price of sorting the data before searching it.

13. The binary search can be used on unsorted data. It will just perform more slowly.

ANS: F The binary search only works if the data is sorted. The binary search algorithm proceeds by assuming that there is a strict relationship among every pair of data elements, either ascending or descending.

Without this order, the binary search will fail to function correctly.

14. A GUI control that allows the user to specify a numeric value within a bounded range is a spinner.

ANS: F The GUI control that allows the user to specify a numeric value within a bounded range is a slider.

15. The spinner GUI control can allow the user to select values that are either numbers or strings.

ANS: T A spinner lets the user select a value from a list of predefined options which can be either numeric values or a sequence of strings.

MULTIPLE CHOICE 1. A variable declared to be of one class can later reference an extended class of that class. This variable is known as a. b. c. d. e.

protected derivable cloneable polymorphic None of these; a variable declared to be of one class can never reference any other type of class, even an extended class

ANS: D The term polymorphic means that the variable can have many forms. Under ordinary circumstances, Java is strongly defined. This mean a variable, once declared to be of a type, can never change to be of a different type. The exception to this is that polymorphic variables can be any type of derived class (although not at the same time, the variable can change from one type to another).

2. In order to determine the type that a polymorphic variable refers to, the decision is made a. b. c. d. e.

by the programmer at the time the program is written by the compiler at compile time by the operating system when the program is loaded into memory by the Java run-time environment at run time by the user at run time

ANS: D

The polymorphic variable can take on many different types, but it is not known which type it has taken on until the program is executing. At the time the variable is referenced, then the decision must be made. That decision is made by the run-time environment based on the latest assignment of the variable.

3. What does the following code do? Assume list is an array of int values, temp is some previously initialized int value, and c is an int initialized to 0. for (j = 0; j < list.length; j++) if (list[j] < temp) c++; a. b. c. d. e.

It finds the smallest value and stores it in temp.

It finds the largest value and stores it in temp.

It counts the number of elements equal to the smallest value in list.

It counts the number of elements in list that are less than temp.

It sorts the values in list to be in ascending order.

ANS: D The statement if (list[j] < temp) c++; compares each element in list to temp and adds one to c only if the element is less than temp, so it counts the number of elements in list less than temp, storing this result in c.

Code Example Ch 10-1 An int array stores the following values:

4. Refer to Code Example Ch 10-1: Which of the following lists of numbers would accurately show the array after the first pass of the selection sort algorithm? a. b. c. d. e.

9, 4, 12, 2, 6, 8, 18 2, 4, 9, 6, 12, 8, 18 2, 4, 12, 9, 6, 8, 18 2, 4, 6, 8, 9, 12, 18 2, 4, 9, 12, 6, 8, 18

ANS: C On each successive pass of selection sort, the smallest of the unsorted values is found and swapped with the current array index (where the current index starts at 0 and goes until the second to last position in the array). On the first pass, the smallest element, 2, is swapped with index 0, so 2 and 9 swap places.

5. Refer to Code Example Ch 10-1: Which of the following lists of numbers would accurately show the array after the second pass of the selection sort algorithm? a. b. c. d. e.

9, 4, 12, 2, 6, 8, 18 2, 4, 9, 6, 12, 8, 18 2, 4, 12, 9, 6, 8, 18 2, 4, 6, 8, 9, 12, 18 2, 4, 9, 12, 6, 8, 18

ANS: C

After one pass, the array would be 2, 4, 12, 9, 6, 8, 18. The second pass would look to swap the item in array index 1 (4) with the smallest value after 2 (4). So, 4 would swap with 4 and the array would stay the same as it was after the first pass.

6. Refer to Code Example Ch 10-1: Which of the following lists of numbers would accurately show the array after the fourth pass of the selection sort algorithm? a. b. c. d. e.

9, 4, 12, 2, 6, 8, 18 2, 4, 6, 9, 12, 8, 18 2, 4, 6, 8, 9, 12, 18 2, 4, 6, 9, 8, 12, 18 2, 4, 6, 8, 12, 9, 18

ANS: E The array would be sorted as follows: First pass: 2, 4, 12, 9, 6, 8, 18. Second pass: 2, 4, 12, 9, 6, 8, 18. Third pass: 2, 4, 6, 9, 12, 8, 18. Fourth pass: 2, 4, 6, 8, 12, 9, 18 7. Refer to Code Example Ch 10-1: How many passes will it take in total for the selection sort to sort this array? a. b. c. d. e.

2 4 5 6 7

ANS: D The selection sort uses two for loops where the outer loop iterates through each array index except for the last one. So it makes a total of n - 1 passes where n is the number of items in the array. Since this array has 7 elements, the outer loop iterates 6 times, or requires 6 passes. You might notice that this array is sorted after only 5 passes, but the selection sort algorithm will still make 6 passes (even if the array had been sorted after only 1 pass, it would still make 6 passes!).

8. We compare sorting algorithms by examining a. b. c. d. e.

the number of instructions executed by the sorting algorithm the number of instructions in the algorithm itself (its length) the types of loops used in the sorting algorithm the amount of memory space required by the algorithm A and D

ANS: E Different sorting algorithms require a different number of instructions when executing. The selection sort, for instance, usually requires more instructions than the insertion sort. So we compare sorting algorithms by the number of instructions that each takes to execute to sort the array. We might count the maximum number of instructions that a sorting algorithm will execute in the worst case, or the minimum number in the best case, or count on average the number of instructions executed. If two sorting algorithms require roughly the same number of instructions to sort an array, then we might also examine the amount of memory space required.

9. Both the insertion sort and the selection sort algorithms have efficiencies on the order of where n is the number of values in the array being sorted.

a. b. c. d. e.

n n * log n n^2 n^3 the insertion sort has an efficiency of n and the selection sort has an efficiency of n^2

ANS: C Both sorting algorithms use two nested loops which both execute approximately n times apiece, giving a complexity of n * n or n^2 for both.

10. What are the main programming mechanisms that constitute object-oriented programming? a. b. c. d. e.

encapsulation, inheritance, polymorphism encapsulation, abstraction, inheritance inheritance, polymorphism, recursion polymorphism, recursion, abstaction None of these

ANS: A Encapsulation is the isolation of portions of code so that they cannot be accidentally modified; inheritance provides for code reuse; polymorphism provides for one-name, many semantics.

Abstraction is a useful attribute, but it is not a mechanism. Recursion is a control structure, providing for a different way to express looping or repetition.

11. Which of the following methods will sort an array of floats in ascending order? a. void arrange(float[] ary) { for (int n = 0; n < ary.length; n++) for (int k = n; k < ary.length; k++) if (ary[n] > ary[k]) { float x = ary[n]; ary[n] = ary[k]; ary[k] = x; } } b. void arrange(float[] ary) { for (int n = 0; n < ary.length; n++) for (int k = n; k < ary.length; k++) if (ary[n] < ary[k]) { float x = ary[n]; ary[n] = ary[k]; ary[k] = x; } } c. void arrange(float[] ary) { for (int n = 1; n <= ary.length; n++) for (int k = n; k < ary.length; k++) if (ary[n] > ary[k])

{ float x = ary[n]; ary[n] = ary[k]; ary[k] = x; } } d. void arrange(float[] ary) { for (int n = 0; n < ary.length; n++) for (int k = n; k < ary.length; k++) if (ary[n] > ary[k]) float x = ary[n]; ary[n] = ary[k]; ary[k] = x; } e. None of these ANS: A This code sorts correctly. The other alternatives are missing braces, have incorrect comparisons, or incorrect limits on their loops.

12. Polymorphism is achieved by a. b. c. d. e.

overloading overriding embedding abstraction encapsulation

ANS: B Overloading just provides alternatives for methods with differing parameter lists. Overriding provides for polymorphism, because the appropriate method is invoked depending upon the object that currently is being referenced. Embedding is the enclosing of classes within classes. Abstraction has nothing to do with polymorphism. Encapsulation is achieved using the visibility modifiers.

13. Although insertion sort and selection sort have generally the same performance, the selection sort has an advantage over the insertion sort. What is this advantage? a. The selection sort usually makes fewer comparisons. b. The selection sort usually makes fewer swaps. c. The selection sort usually makes fewer passes. d. The selection sort usually makes fewer selections. e. None of these ANS: B The selection sort may make fewer swaps because at each stage of the process, elements are moved into their final positions and never are moved again.

14. What kind of performance can you expect if you perform a linear search on a sorted array? a. The performance will be about the same as on an unsorted array. b. The performance will be much better than on an unsorted array. c. The performance will be much worse than on an unsorted array.

d. The performance will be worse by about n^2 in this case e. None of these ANS: A The linear search doesn't make any assumptions about whether or not its data is sorted. So, if the data happens to be sorted or not, it won't make any difference. The linear sort will perform roughly as n.

15. Can a program exhibit polymorphism if it only implements early binding? a. Yes, because one form of polymorphism is overloading. b. No, because without late binding, polymorphism cannot be supported. c. Yes, because as long as the program uses inheritance and/or interfaces, it supports polymorphism. d. Yes, because early binding has nothing to do with polymorphism. e. None of these ANS: A While inheritance and interfaces support polymorphism, they only do so if one has late binding. But overloading is a form of polymorphism--one (method) name, multiple bodies--so as long as the program uses overloading, polymorphism is in use.

16. Which of the following is true about a comparison between the selection sort and the insertion sort? a. The selection sort requires more additional memory than the insertion sort. b. The insertion sort requires more additional memory than the selection sort. c. Both methods require approximately the same amount of additional memory as the data they are sorting. d. Neither method requires additional memory. e. None of these ANS: D Both the selection sort and the insertion sort can be implemented "in place." This means that no additional memory is required. The data being sorted is just rearranged within the data array as either sort progresses.

17. What is the output of the following code? (Consider the polymorphic invocation.) public class Inherit { class Figure { void display() { System.out.println("Figure"); } } class Rectangle extends Figure { void display() { System.out.println("Rectangle"); } } class Box extends Figure {

void display() { System.out.println("Box"); } } Inherit() { Figure f = new Figure(); Rectangle r = new Rectangle(); Box b = new Box(); f.display(); f = r; f.display(); f = b; f.display(); } public static void main(String[] args) { new Inherit(); } } a. Figure Rectangle Box b. Rectangle Box c. Figure Figure Figure d. Syntax error. This code won't compile or execute e. None of these ANS: A This is a perfect example of polymorphism. The first invocation of the display method has a Figure as its referent. In the second invocation, the reference has been changed to Rectangle. Then for the third invocation it has been changed to Box. 18. What is the output of the following code? public class Inherit { abstract class Speaker { abstract public void speak(); } class Cat extends Speaker { public void speak() { System.out.println("Woof!"); } } class Dog extends Speaker {

public void speak() { System.out.println("Meow!"); } } Inherit() { Speaker d = new Dog(); Speaker c = new Cat(); d.speak(); c.speak(); } public static void main(String[] args) { new Inherit(); } } a. Woof!

Meow! b. Meow!

Woof! c. Meow!

Meow! d. Woof!

Woof! e. None of these ANS: B Carefully watch the assignment of objects to the polymorphic references variables, d and c. Then check to see what Cat and Dog objects actually "speak."

19. What is the output of the following code? public class Inherit { abstract class Figure { void display() { System.out.println("Figure"); } } abstract class Rectangle extends Figure { } class Box extends Rectangle { void display() { System.out.println("Rectangle"); } } Inherit() {

Figure f = (Figure) new Box(); f.display(); Rectangle r = (Rectangle) f; r.display(); } public static void main(String[] args) { new Inherit(); } } a. Rectangle Rectange b. Rectangle Figure c. Figure Rectangle d. Figure Figure e. None of these ANS: A f is a polymorphic reference variable, as is r. Trace through the inheritance structure to see that both references' invocation of the display() method will, indeed, display Rectangle.

20. What is the output of the following code? public class Inherit { class Figure { void display() { System.out.println("Figure"); } } class Rectangle extends Figure { void display() { System.out.println("Rectangle"); } } class Box extends Figure { void display() { System.out.println("Box"); } } Inherit() { Figure f = new Figure(); Rectangle r = new Rectangle(); Box b = new Box(); f.display();

f = r; f.display(); f = b; f.display(); } public static void main(String[] args) { new Inherit(); } } a. Figure Rectange Box b. Rectangle Box c. Figure Figure Figure d. Syntax error; this code won't compile e. None of these ANS: A f, r, and b all are polymorphic reference variables. Each is used to invoke a display() method, so three lines will be printed. Checking to see what instances are actually assigned at the point when the reference variables are used to invoke display, you'll see that answer A is correct.

21. What is the output of the following code? public class Inherit { class Figure { void display() { System.out.println("Figure"); } } class Rectangle extends Figure { void display() { System.out.println("Rectangle"); } void display(String s) { System.out.println(s); } } class Box extends Figure { void display() { System.out.println("Box"); } void display(String s)

{ System.out.println("This is printed: "+s); } } Inherit() { Figure f = new Figure(); Rectangle r = new Rectangle(); Box b = new Box(); f.display(); f = r; f.display("one"); f = b; f.display("two"); } public static void main(String[] args) { new Inherit(); } } a. Figure Rectange b. Figure Rectangle Figure Box c. Figure Figure Figure Figure d. Syntax error; this code won't compile e. None of these ANS: D Examine the f variable, and it's invocation of the display method. Does f's display method accept any parameters? No, so, this code has a syntax error and it won't even compile.

22. What is the output of the following code? public class Inherit { abstract class Figure { void display() { System.out.println("Figure"); } } class Line extends Figure { void display() { System.out.println("Line"); } }

void tryme(Figure f) { f.display(); } Inherit() { Figure f = new Line(); tryme(f); } public static void main(String[] args) { new Inherit(); } } a. b. c. d. e.

Line Figure Shape Syntax error; this code won't compile None of these

ANS: A Inherit's f reference variable is pointing at an instance of Line. So, when the tryme method is invoked f is actually pointing at an instance of Line. So, answer A is correct.

23. Given the following code, class Aggregate is incorrect. Choose the correct line so that this program prints: Granite: weight=25.0 value=4 numKind=7 public class Inherit { abstract class Stone { protected float weight = 13; protected int value = 4; abstract public String toString( ); } class Aggregate { protected int numKind; } class Granite extends Aggregate { Granite() { weight = 25; numKind = 7; } public String toString() { return "Granite: weight=" + weight + " value=" + value + " numKind=" + numKind; } } Inherit()

{ Granite g = new Granite( ); System.out.println(g); } public static void main(String[] args) { new Inherit(); } } a. b. c. d. e.

abstract class Aggregate { abstract class Aggregate extends Granite { abstract class Aggregate extends Stone { class Aggregate extends Stone { None of these

ANS: C

You must both create an abstract class and extend the Stone class.

24. If you instantiate an abstract class, the class or object you wind up with a. b. c. d. e.

is also an abstract class is a normal class is an interface is a reference to an Object you can't instantiate an abstract class

ANS: E You only can instantiate concrete classes, not abstract ones. But you can extend abstract classes as well as interfaces.

PROBLEM 1. Demonstrate how the following array is sorted using insertion sort. Show the array after each pass of the outer loop.

[16, 3, 12, 13, 8, 1, 18, 9] ANS: 16, 3, 12, 13, 8, 1, 18, 9 (initial) 3, 16, 12, 13, 8, 1, 18, 9 (pass 1) 3, 12, 16, 13, 8, 1, 18, 9 (pass 2) 3, 12, 13, 16, 8, 1, 18, 9 (pass 3) 3, 8, 12, 13, 16, 1, 18, 9 (pass 4) 1, 3, 8, 12, 13, 16, 18, 9 (pass 5) 1, 3, 8, 12, 13, 16, 18, 9 (pass 6) 1, 3, 8, 9, 12, 13, 16, 18 (pass 7) 2. Demonstrate how the following array is sorted using selection sort. Show the array after each pass of the outer loop.

[16, 3, 12, 13, 8, 1, 18, 9] ANS:

16, 3, 12, 13, 8, 1, 18, 9 (initial) 1, 3, 12, 13, 8, 16, 18, 9 (pass 1) 1, 3, 12, 13, 8, 16, 18, 9 (pass 2) 1, 3, 8, 13, 12, 16, 18, 9 (pass 3) 1, 3, 8, 9, 12, 16, 18, 13 (pass 4) 1, 3, 8, 9, 12, 16, 18, 13 (pass 5) 1, 3, 8, 9, 12, 13, 18, 16 (pass 6) 1, 3, 8, 9, 12, 13, 16, 18 (pass 7)

3. Explain how to alter the selection sort algorithm so that it sorts in descending order instead of ascending order.

ANS: The inner loop of the selection sort searches for the smallest element in the array from the current position until the end of the array. Instead of looking for the smallest element, look for the largest element.

4. Write an insertion sort method to sort an array of String values (instead of an array of int values).

Assume the array is an instance data of the current class called list, and number is an int instance data that stores the number of elements currently stored in list.

ANS: public void insertionSortForString() { for (int j = 1; j < number; j++) { String key = list[j]; int position = j; while(position > 0 && list[position-1].compareTo(key)>0) { list[position] = list[position - 1]; position--; } list[position] = key; } } 5. Consider the code shown below. It contains a syntax error, preventing successful compilation and execution. What is the error? public class Inherit { class Figure { void display() { System.out.println("Figure"); } } class Rectangle extends Figure { final void display()

{ System.out.println("Rectangle"); } } class Box extends Rectangle { void display() { System.out.println("Box"); } } Inherit() { Figure f = new Figure(); Rectangle r = new Rectangle(); Box b = new Box(); f.display(); r.display(); b.display(); } public static void main(String[] args) { new Inherit(); } } ANS: Consider the effect of the final modifier. It makes it impossible for that method to be overridden.

Box extends Rectangle and attempts to override Rectangle's display method, but, since Rectangle's display method is final, it cannot be overridden. Hence the syntax error.

6. Consider this statement: If you declare a (polymorphic) reference variable, v, to be of type Object, by saying: Object v; then v can refer to any kind of object without restriction. If "object" means an instance of the Object class, is this statement true? Why or why not? If "object" means any kind of Java data, is this statement true? Why or why not?

ANS: Java only supports single inheritance, with the base class from which all others are derived are named Object. So, following the rules for inheritance, v may indeed refer to any kind of instance of an Object. But, v may not refer to any kind of data whatsoever. v may not refer to primitive data because primitive data does not descend from Java's root Object class.

7. Is it possible to use both overloading and overriding in the same method?

ANS: Yes. A method which is declared in a descendent class certainly can override a method in a parent class so long as the method in the parent class isn't declared private. Now, if the parent class contains several overloaded methods, one can override each of them. This makes the overriding methods overloads of the base functions as well.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 11 Exceptions TRUE/FALSE 1. All run-time errors throw exceptions.

ANS: F Java classifies any throwable object as either an error or an exception, and so no run-time error will throw an exception. Run-time errors cause termination of the program. Exceptions can be handled so that the program continues executing (but only if the exception is handled properly).

2. If an exception is thrown and not caught anywhere in the program, then the program terminates.

ANS: T Exceptions are events of interest or are run-time situations that cannot be handled normally without an exception handler. An exception is caught by an associated exception handler. If the exception is thrown but not handled, then the program must terminate.

3. A try statement must have at least one catch statements but could have many catch statements and may or may not have a finally clause.

ANS: T All try statements must have at least one catch statement or there is no reason to have the try statement. There can be one catch statement for each type of exception that might be thrown. The programmer may specify as many catch statements as is felt necessary. Further, a try statement may have a finally clause, but does not need one.

4. Programmers can define their own exceptions by extending the Exception class or one of the descendants of this class.

ANS: T Java predefines a number of Exception classes so that many of the types of exceptions that can cause a program to terminate are handled. However, Java allows programmers to add to the language by defining their own exceptions for whatever unique situations they might encounter. These new exceptions will either be children of the Exception class, or children of subclasses or descendants of Exception.

5. If an exception arises in a catch statement, and the exception is of the type caught by the catch statement, then the catch statement catches the same exception. For instance, if the following catch statement first catches an ArithmeticException and, while executing, throws another ArithmeticException, it is able to catch the second ArithmeticException as well the first. catch (ArithmeticException ex) {...} ANS: F

An exception causes the current statement to stop executing and control transfers outside to the first catch (after the current statement) that can catch the exception. So a catch statement will not catch exceptions that are thrown from inside of itself although a catch statement can have nested additional try and catch statements.

6. While the Exception class is part of java.lang, IOException is part of java.io.

ANS: T Exception is the ancestor class of all Exceptions. One child of Exception is IOException, which is a checked exception that is thrown from various IO methods. So, while the Exception class is defined in the java.lang package, the IOException class is defined with the rest of the IO methods, in java.io.

7. The difference between the throw reserved word and the throws reserved word is that throw is used within a method body, while throws is used within a method header.

ANS: T throw is an imperative command that is used within a method to create and throw a new exception. throws is a compiler directive that tells the compiler that the current method may issue a throw that is not caught within the method and thus may escape to an outer level.

8. An ArithmeticException is Throwable.

ANS: T It inherits Throwable through RunTimeException and Exception.

9. An ArithmeticException is a checked exception.

ANS: F It inherits from RunTimeException so it is unchecked.

10. An unchecked exception is an exception that must either be caught and handled or listed in the throws clause of any method that might throw or propagate it.

ANS: F This is basically the definition of a checked, not an unchecked exception. Unchecked exceptions can be ignored completely in the code, if desired.

MULTIPLE CHOICE 1. A Java program can handle an exception in several different ways. Which of the following is not a way a Java program might handle an exception? a. b. c. d. e.

ignore the exception handle the exception where it arises using try and catch statements propagate the exception to another method where it can be handled throw the exception to a predefined Exception class to be handled All of these are valid ways to handle an exception

ANS: D

A thrown exception is either caught by the current code if the code is contained inside a try statement and the appropriate catch statement is implemented, or else it is propagated to the method that invoked the method that caused the exception. Then it is caught there in an appropriate catch statement, or else it continues to be propagated through the methods in the opposite order that those methods were invoked. This process stops however once the main method is reached. If not caught there, the exception causes termination of the program (this would be answer A, the exception was ignored).

However, an exception is not thrown to an Exception class.

2. An exception can produce a "call stack trace" which lists a. b. c. d.

the active methods in the order that they were invoked the active methods in the opposite order that they were invoked the values of all instance data of the object where the exception was raised the values of all instance data of the object where the exception was raised and all local variables and parameters of the method where the exception was raised e. the name of the exception thrown ANS: B The call stack trace provides the names of the methods as stored on the run-time stack. The method names are removed from the stack in the opposite order that they were placed; that is, the earliest method is placed there first, the next method second, and so forth so that the most recently invoked method is the last item on the stack. Thus, it is the first one removed. The stack trace then displays all active methods in the opposite order that they were called (most recent first).

3. An exception that could also arise in the try statement that does not have an associated catch statement is a. b. c. d. e.

ClassNotFoundException IllegalArgumentException NegativeArraySizeException NullPointerException OutOfMemoryException

ANS: D If the array has not yet been instantiated, then it throws a NullPointerException. The ClassNotFoundException, IllegalArgumentException and OutOfMemoryException will not be thrown since there is no code in the try statement that either refers to some unknown class, uses an argument, or deals with the generation of new memory.

The NegativeArraySizeException will only arise when instantiating an array.

4. A finally clause will execute only if the try statement that precedes it does not throw an exception only if the try statement that precedes it throws an exception that is caught only if the try statement that precedes it throws an exception that is not caught only if the try statement that precedes it throws an exception, regardless of whether or not it is caught e. in any circumstance a. b. c. d.

ANS: E A finally clause, if specified (because it is optional) will execute no matter what happens with respect to the try and catch statements.

5. Which of the following messages passed to the String str could throw a StringIndexOutOfBoundsException? a. b. c. d. e.

str length(); str charAt(2); str replace('a', 'A'); str equals(str); Any of these could throw a StringIndexOutOfBoundsException

ANS: B The StringIndexOutOfBoundsException is thrown if a parameter of a String method references a position in the String that is beyond the bounds of the String (i.e. a negative int or an int greater than or equal to the number of characters in the String). This can occur in either charAt or substring methods.

Example Code Ch 11-1 public static void main(String[] args) { try { ExceptionThrowerCode etc = new ExceptionThrowerCode(); etc.m1(); etc.m2(); } catch (ArithmeticException ae) { ... } } public class ExceptionThrowerCode { ... public void m1() { ... } public void m2() { try { m3(); } catch(ArithmeticException ae) {...} catch(NullPointerException npe) {...} } public void m3() { try { ... } catch(ArithmeticException ae) {...} } }

6. Refer to Example Code Ch 11-1: If an ArithmeticException arises in the try statement in m3 a. b. c. d. e.

it is caught in main it is caught in m1 it is caught in m2 it is caught in m3 it is not caught and the program terminates

ANS: D The method m3 has a catch statement for an ArithmeticException, so if one arises in the try statement in m3, it is caught in the catch statement in m3.

7. Refer to Example Code Ch 11-1: If a NullPointerException arises in the try statement in m3 a. b. c. d. e.

it is caught in main it is caught in m1 it is caught in m2 it is caught in m3 it is not caught and the program terminates

ANS: C The method m3 has no catch statement for a NullPointerException, and so the exception is propagated to the calling method, m2. Method m2 has a catch statement for a NullPointerException so that is where the exception is caught.

8. Refer to Example Code Ch 11-1: If a NullPointerException arises in the try statement in m1 a. b. c. d. e.

it is caught in main it is caught in m1 it is caught in m2 it is caught in m3 it is not caught and the program terminates

ANS: E The method m1 has no catch statements at all, so any exception is propagated to the calling method, main. The method main only has a catch statement for an ArithmeticException so the NullPointerException is not caught and the program terminates.

9. NullPointerExceptions and ArithmeticExceptions are both derived from which class? a. b. c. d. e.

Error Exception RuntimeException IllegalAccessException CheckedException

ANS: C

Both of these exceptions are children of the RuntimeException class which, itself, is a child of Exception. Error is a throwable object that is different from Exception while IllegalAccessException and CheckedException are children of Exception but not of RuntimeException.

10. In order to have some code throw an exception, which of the following reserved words should you use? a. b. c. d. e.

throw throws try Throwable goto

ANS: A The reserved word throw is used to throw an exception when the exception is detected, as in: if (score < 0) throw new IllegalTestScoreException("Input score " + score + " is negative"); 11. Assume Exceptionname is a checked exception. If a method uses a class that can generate Exceptionname, then either the method must include try and catch statements where a catch statement catches Exceptionname, or the method header must include the statement a. b. c. d. e.

throw Exceptionname throws Exceptionname catch Exceptionname catches Exceptionname implements Exceptionname

ANS: B A checked exception must be caught somewhere and so, if not caught in the method that might generate the exception, the exception must be thrown to whatever called the method. This is accomplished by stating that the method throws Exceptionname.

12. Which of the following is not true of the RuntimeException class? a. All RuntimeException throw checked exceptions. b. All RuntimeException are Throwable objects. c. RuntimeException has child classes ArithmeticException and NullPointerException. d. RuntimeException objects are not Error objects. e. All of these are true ANS: A The answers in B, C and D are all true, RuntimeException are Throwable objects and are not part of the Error class, and two types of RuntimeException are ArithmeticException and NullPointerException. Exceptions that are not RuntimeExceptions include various checked exceptions, but RuntimeExceptions are not checked exceptions.

13. Character streams manage a. byte-sized data

b. c. d. e.

binary data Unicode characters ASCII characters compressed data

ANS: C Character streams are used to manage 16-bit Unicode characters. This differs from a byte stream that is used to manage any kind of byte-sized data, including ASCII characters and binary data of other types.

14. A processing stream is a data stream that a. b. c. d. e.

can manage both input streams and output streams at the same time performs some manipulation or process on the data can only manage input streams operates on input and output devices but not files can manage byte streams and character streams at the same time

ANS: B A data stream represents a particular source or destination stream and is used for input or output. A processing stream is like a data stream where some additional process(es) is(are) added to the input or output. For example, a processing byte stream might input all items from a file and remove any ASCII characters that are not digits so that an input expected to be a number will not throw a NumberFormatException.

15. System.err is a(n) a. b. c. d. e.

input stream GUI dialog box that indicates when an error has arisen object Error subclass RuntimException subclass

ANS: C There are three default streams available in Java: System.in, System.out, and System.err.

All of these are objects with System.in being an input stream, System.out being an output stream and System.err being an error stream (which is also an output stream).

16. The Scanner class provides an abstraction for input operations by a. using try and catch statements to catch any IOException instead of throwing the Exception elsewhere b. parsing input lines into individual tokens c. performing conversion operations from String to the appropriate type as specified in the Scanner message d. inputting from the standard input stream if create is called using System.in e. All of these ANS: E

Input into a Java program is difficult because it requires a lot of overhead. The Scanner class implements all of that overhead so that the programmer does not have to see it. Thus, Scanner is an abstraction for performing input operations without the details. These details include importing java.io classes, handling IOExceptions in some way, inputting from the standard input stream, dividing the input into individual tokens and converting each token as needed into the requesting form.

17. The term "exception propagation" means a. an exception is caught by the first catch clause b. an exception not caught by the first catch clause is caught by an outer (enclosing) catch clause c. exceptions are caught, sequentially, by catch clauses in the current try block d. exceptions are always caught by the outermost try block e. None of these explain what exception propagation is ANS: E Exception propagation means that an exception is caught by a matching catch clause at the current try block level, and if none matches, then at the next enclosing try block level, and so forth, until the exception either has been caught by a matching clause or the exception passes out of the main routine and is caught by the Java Virtual Machine.

18. When a program terminates because a thrown exception is not handled, the program a. starts up again automatically b. opens a dialog box which asks the user whether the program should start again, end, or enter a debugging mode c. saves all output to a disk file named runStackTrace.txt d. opens a dialog box for the user to specify a disk filename and all output is stored to that file e. outputs a message indicating what the exception was and where it was thrown ANS: E If a thrown exception is not caught anywhere in the program, the program terminates, displaying the contents of the run stack trace. The first item on the run stack trace is the exception that was thrown and where it was thrown (the line number of the method of the class where the exception was raised) 19. A method that uses the Scanner class to obtain input does not require either catching or throwing an IOException. This is because a. the Scanner class does not call upon any classes that throw checked exceptions b. the Scanner class's methods call input methods in try statements and catch IOExceptions so that they are handled directly in the Scanner class c. the Scanner class uses dialog boxes instead of java.io classes so that it does not have to deal with IOExceptions d. the Scanner class overrides the class IOException making it an unchecked exception e. None of the above; methods do require handling IOExceptions even if thrown by a method in a Scanner class ANS: B By having its own catch (IOException) catch statement, any code in the Scanner class that causes an IOException is caught by the Scanner class so that classes that might use the Scanner class do not have to handle this checked exception.

20. The difference between a checked and an unchecked exception is a. b. c. d. e.

checked exceptions need not be listed in a throws clause unchecked exceptions must be listed in a throws clause neither kind of exception follows the rules of exception propagation an unchecked exception requires no throws clause a checked exception always must be caught by a try block while this is not true for an unchecked exception

ANS: D A checked exception must either be caught or it must be listed in a throws clause. An unchecked exception requires no throws clause. Both kinds of exceptions follow the rules of exception propagation.

21. A disabled component is a. b. c. d. e.

one that is grayed out one that is no longer active one that is still visually apparent but no longer functions if clicked provides an indication of functionality that is not currently available All of these are true

ANS: E Components that are disabled appear grayed out; they are disabled for the moment, but remain visually apparent. They provide an indication of functionality that can/will be enabled at some other point in time.

PROBLEM 1. Explain or provide an example showing how an ArithmeticException could arise.

ANS: An ArithmeticException could occur if an arithmetic operation could not take place because of an illegal action such as division by zero or square root of a negative number.

2. Explain or provide an example showing how a NullPointerException could arise.

ANS: A NullPointerException could occur if an object was not instantiated (it had the value null) before a message was passed to it.

3. Explain or provide an example showing how a NumberFormatException could arise.

ANS: A NumberFormatException could occur if an expected value for a numeric operation was not a legal number, such as trying to parse a String value to create an equivalent int where the String contains a non-digit character.

4. Explain or provide an example showing how an IndexOutOfBoundsException could arise.

ANS: An IndexOutOfBoundsException could occur if a numeric parameter that was used as an index into an object such as an array or a String was out of range, such as charAt(-1).

5. Explain or provide an example showing how an IOException could arise.

ANS: An IOException could occur if something happened when inputting from keyboard or inputting or outputting to disk such as a disk was not in disk drive.

6. What are the three standard I/O streams and what purposes do they fulfill?

ANS: The three standard I/O streams are System.in, System.out, and System.err. System.in is the standard system input stream. Most usually it is connected to the keyboard. System.out is the standard system output stream. It usually is connected to the display. Both System.in and System.out are used for "normal" input and output. System.err usually is connected to the standard error output. This, too, usually is connected to the display. It is used for the display of warning and error messages that otherwise might become lost due, perhaps, to output redirection.

7. Why might you want to create your own exception class? What purpose would it serve?

ANS: If you have a collection of error conditions that pertain to a specific function or group of functions that a portion of a program may generate, it might be very wise to create an exception class for that collection of error conditions. Then you would not need to test explicitly for error conditions within that code. You would protect the code with try-catch blocks. This would make the code far cleaner, easier to understand, and easier to maintain.

8. Explain what happens if an exception is not caught.

ANS: If an exception is not caught immediately when thrown, it begins to propagate up through the methods that were called to get to the point where it was generated. The exception can be caught and handled at any time during this propagation but if it propagates out of the main method, the program will terminate.

Java Software Solutions, 9e (Lewis/Loftus) Chapter 12 Recursion TRUE/FALSE 1. A recursive method without a base case leads to infinite recursion.

ANS: T Without the base case, the recursive method calls itself without the ability to stop, and thus leads to infinite recursion.

2. The following method lacks a base case. public int noBaseCase(int x) { if (x > 0) return noBaseCase(x - 1) + 1; else return noBaseCase(x - 2) + 2; } ANS: T A base case is a condition that, when taken, stops the recursion by not calling the method recursively.

In the above method, there is a condition, but whether the condition is true or false, the method invokes itself recursively.

3. Traversing a maze is much easier to do iteratively than recursively.

ANS: F One reason that recursion is appealing is that it automatically backtracks to the point of the last decision. In traversing a maze, when one reaches a dead end, the best place to continue is at the point of the previous intersection (or decision). So, backtracking is performed. To solve a maze iteratively requires implementing a backtracking mechanism, which is available automatically in recursion.

4. Some problems are easier to solve recursively than iteratively.

ANS: T Since recursion performs backtracking automatically, any problem that requires backtracking is easier to solve using recursion. Such problems include traversing a maze and searching through a "search space", a topic covered in Artificial Intelligence and Advanced Algorithms courses. In some cases, it is easy to find a recursive solution and so the recursive solution is easier than the iterative solution.

5. The following two methods will both compute the same thing when invoked with the same value of x.

That is, method1(x) = = method2(x). public int method1(int x) { if (x > 0) return method1(x - 1) + 1; else return 0; } public int method2(int x) {

if (x > 0) return 1 + method2(x - 1); else return 0; } ANS: T The only difference between the two methods is the order of the recursive call and adding 1 to the return value. The difference is denoted by calling the first method head recursive and the second tail recursive. So both methods will compute the same value, but arrive at the value in different ways.

6. Consider the following recursive sum method: public int sum(int x) { if (x == 0) return 0; else return sum(x - 1) + 1; } If the base case is replaced with if (x == 1) return 1; the method will still compute the same thing.

ANS: F The original method causes infinite recursion if called with a parameter < 0, but works properly if called with any parameter >= 0. With the new base case, the method now works properly if called with any parameter >= 1 but causes infinite recursion if the parameter < 1. So, sum(0) now differs from what it was previously.

7. The recursive method to solve the Towers of Hanoi is usable only if the parameter for the number of disks is 7 or smaller.

ANS: F The Towers of Hanoi solution can be used for any number of disks as long as it is at least 1 but the size will affect its performance.

8. A Koch snowflake of order = 1 can be drawn without recursion.

ANS: T The Koch snowflake of order 1 is made up of straight lines. It is not until the order is greater than 1 that recursion is applied.

9. Since iterative solutions often use loop variables and recursive solutions do not, the recursive solution is usually more memory efficient (uses less memory) than the equivalent iterative solution.

ANS: F The recursive solution may use no local variables whatsoever, but the recursive solution usually uses parameters. Every time the method is called recursively, new parameters are required, and so recursive solutions usually use a substantially larger amount of memory than an iterative solution. This depends on how many times the method is called recursively.

10. We can define a list of int values recursively as a list_item, followed by a comma, followed by a list where a list_item is any int value.

ANS: F

The recursive definition does not include a base case so that all lists of int values will be infinitely long!

11. It always is possible to replace a recursion by an iteration and vice versa.

ANS: T Both recursion and iteration are forms of repetition. Whether one phrases the repetition using recursion or iteration is a matter of style, taste, sometimes efficiency, sometimes convenience. But they are equivalent in terms of computation and each may be replaced by the other.

12. If one were to create a Towers of Hanoi puzzle with four towers instead of three, with rules changed appropriately, it should be possible to create a recursive solution for the puzzle where one of the constraints is that at some point during the solution all of the disks must reside on each of the four towers.

ANS: T The solution to this version of the game can be phrased as follows: Use the 3-peg Towers solution to move all the disks from peg A to peg B; then use the 3-peg Towers solution to move all the disks from peg B to peg C; repeat, moving from peg C to peg D. 13. The Koch snowflake has an infinitely long perimeter, but it contains a finite area.

ANS: T As the order of the Koch snowflake increases the perimeter grows exponentially large. In the limit, the perimeter is infinitely long. But, since the entire snowflake can be contained within a bounding square, the area of the snowflake is finite.

MULTIPLE CHOICE 1. The following method should return true if the int parameter is even and either positive or 0, and false otherwise. Which set of code should you use to replace ... so that the method works appropriately? public boolean question3(int x) a. if (x == 0) return true; else if (x < 0) return false; else return question3(x - 1); b. if (x == 0) return false; else if (x < 0) return true; else return question3(x - 1); c. if (x == 0) return true; else if (x < 0) return false; else return question3(x - 2); d. if (x == 0) return false; else if (x < 0) return true; else return question3(x - 2); e. return(x == 0); ANS: C

{ ... }

The method will recursively call itself subtracting 2 from x until x == 0 or x<0. If x == 0, then x - 2 * i == 0 (for some int value i) or x == 2 * i, so x must be even. Otherwise, the recursion ends when x < 0, meaning that the original x was odd or less than 0.

2. What is wrong with the following recursive sum method? The method is supposed to sum up the values between 1 and x (for instance, sum(5)should be 5 + 4 + 3 + 2 + 1 = 15). public int sum(int x) { if (x == 0) return 0; else return sum(x - 1) + x; } a. b. c. d. e.

The base case should return 1 instead of 0.

The recursive case should return sum(x - 1) + 1 instead ofsum(x - 1) + x.

The base case condition should be (x <= 0) instead of (x == 0).

The recursive case should return sum(x) + 1.

The method should return a boolean instead of an int.

ANS: B The method does not appropriately handle a negative parameter, such as sum(-5). The result is infinite recursion. We might define a negative parameter as something that should return 0, or allow a negative parameter to compute a negative sum as in: public int sum(int x) { if (x == 0) return 0; else if (x < 0) return -1 * sum(-x); else return sum(x - 1) + x; } 3. What does the following recursive method determine?. public boolean question16(int[]a, int[] b, int j) { if (j == a.length) return false; else if (j == b.length) return true; else return question16(a, b, j+1); } a. b. c. d. e.

returns true if a and b are equal in size, false otherwise returns true if a is larger than b, false otherwise returns true if b is larger than a, false otherwise returns true if a and b have no elements return the length of array a + length of array b

ANS: B The method returns true if the third parameter, j, is equal to the length of b but not equal to the length of a. Thus, the method returns true if the third parameter has reached the value indicating the end of array b but not the end of array a so this is true if a is larger than b. If a and b are equal length or if a is shorter than b, false is returned.

4. Why is the following method one which has infinite recursion? public int infiniteRecursion(int n)

{ if (n > 0) return infiniteRecursion(n) + 1; else return 0; } a. b. c. d. e.

because there is no base case because the base case will never be true because the recursive call does not move the parameter closer to the base case because the recursive call moves the problem further away from the base case None of these; this method isn't infinitely recursive

ANS: C The recursive case has the method calling itself with the same parameter, and so n does not change, thus if (n > 0) is initially true, it will remain true.

5. Which of the following methods would properly compute the value of x % y (x mod y) recursively, assuming that x and y are not negative numbers? a. public int recursiveMod(int x, int y) { if (x < y) return y; else return recursiveMod(x, y - x); } b. public int recursiveMod(int x, int y) { if (x == y) return 0; else return recursiveMod(x - y, y) + 1; } c. public int recursiveMod(int x, int y) { if (x < y) return x; else return recursiveMod(x - y, y) + 1; } d. public int recursiveMod(int x, int y) { if (x < y) return x; else return recursiveMod(x - y, y); } e. public int recursiveMod(int x, int y) { while (x > y) x = x - y; return x; } ANS: D The value x % y can be computed by continually subtracting y from x until x<y. Then, the result is x. For instance, 7 % 3 = 4 % 3 = 1 % 3 = 1. The code in answers A, B, and C do not compute x % y and answer E computes mod but uses an iterative solution, not a recursive one.

6. A recursive algorithm is superior to an iterative algorithm along which of the following criteria? a. The recursive algorithm is easier to debug. b. The recursive algorithm is computationally more efficient. c. The recursive algorithm is more elegant.

d. The recursive algorithm requires less memory to execute. e. All of these ANS: C When comparing most recursive algorithms to their iterative counterparts, it is almost always the case that the recursive algorithm is shorter, so it tackles the same problem with less code. This means it is more elegant (which does not necessarily mean it is easier to understand or more efficient).

7. Aside from writing recursive methods, another way that recursion is often used is to define a. b. c. d. e.

words in English mathematical functions rules and laws child classes of a parent class in object-oriented programming recursion is used in all of these

ANS: B Mathematics often defines functions recursively for simplicity.

8. What is a fractal? a. a portion of a larger structure (a fraction) b. a geometric shape that can be made up of the same pattern repeated at different scales and orientations c. a recursively defined numeric function d. a ratio (a fraction) e. None of these ANS: B A fractal is a geometric shape that is "self-similar"; that is, it appears to be the same regardless of scale and orientation. The same shape appears at different scales and orientations.

9. The Koch fractal of order 1 is a. b. c. d. e.

a triangle a square a point a circle None of these

ANS: A The Koch fractal of order 1 is the simplest possible closed figure that contains an area-–a triangle.

10. Each time the order of a Koch fractal increases by one, the number of straight line segments a. b. c. d. e.

increases by a factor of two increases by a factor of three increases by a factor of four is squared is cubed

ANS: C Each line segment is replaced by four equal-length line segments each time the order increases by one.

So, the total number of straight line segments increases by a factor of four each time the order is increased by one.

11. The difference between direct and indirect recursion is a. direct recursion occurs when a method invokes itself; indirect recursion occurs when there is an intervening method b. indirect recursion occurs when a method invokes itself; direct recursion occurs when there is an intervening method c. direct recursion only occurs with methods declared to be private; indirect recursion can occur with methods declared to be private, protected, or public d. indirect recursion only occurs with methods declared to be private; direct recursion can occur with methods declared to be private, protected, or public e. None of these ANS: A Direct recursion means that a method directly invokes itself with no intervening method. Indirect recursion occurs when there are one or more intervening methods before the original method is invoked again.

12. What can be said about the difference or similarity, if any, between an infinite loop and an infinite recursion? a. b. c. d. e.

It is impossible to detect the latter while it's easy to detect the former.

Both continue to repeat indefinitely.

Both will be caught by the compiler.

Both will be caught by the Java Virtual Machine during execution.

None of these

ANS: B Both infinite loops and recursion are similar in that they continue to repeat indefinitely. Neither can be caught by the compiler or by the JVM. 13. Define the magnitude of a number as the location of the decimal point from the left of the number (that is, if a number has 4 digits followed by the decimal point, it will have a magnitude of 4). 100 would then have a magnitude of 3 and 55,555.555 would have a magnitude of 5. A partial recursive method is given below to compute a positive int parameter's magnitude. Which answer below is needed to complete the method? public int magnitude(double x) { if (x < 1) return 0; else return ; } a. b. c. d. e.

magnitude(x - 1) + 10; magnitude(x - 10) + 1; magnitude(x / 10) + 10; magnitude(x / 10) + 1; magnitude(x / 10) * 2;

ANS: D The method must count the number of digits to the left of the decimal point, so it continually divides the value by 10 until the value has no digits to the left of the decimal point (this is the case if the value is less than 1). Each time the value is divided by 10, 1 is added to the return value. 55,555.555 will be divided by 10 five times before it becomes less than 1, and thus return 5.

14. What does the following method compute? Assume the method is called initially with i = 0. public int question9(String a, char b, int i) { if (i == a.length()) return 0; else if (b == a.charAt(i)) return question9(a, b, i+1) + 1; else return question9(a, b, i+1); } a. b. c. d. e.

the length of String a the length of String a concatenated with char b the number of times char b appears in String a the value 1 if char b appears in String a at least once and 0 otherwise the char which appears at location i in String a

ANS: C The method compares each character in String a with char b until i reaches the length of String a. 1 is added to the return value for each match.

Example Code Ch 12-1 Given the following recursive method: public int question1_2(int x, int y) { if (x == y) return 0; else return question1_2(x-1, y) + 1; } 15. Refer to Example Code Ch 12-1: If the method is called as question1_2(8, 3), what is returned? a. b. c. d. e.

11 8 5 3 24

ANS: C The method computes x - y if x > y. The method works as follows: each time the method is called recursively, it subtracts 1 from x until (x == y) is becomes true, and adds 1 to the return value. So, 1 is added each time the method is called, and the method is called once for each int value between x and y.

16. Refer to Example Code Ch 12-1: Calling this method will result in infinite recursion if which of the following conditions is initially true? a. b. c. d. e.

(x == y) (x != y) (x > y) (x < y) (x == 0) && (y != 0)

ANS: D If (x < y) is true initially, then the else clause is executed resulting in the method being recursively invoked with a value of x - 1, or a smaller value of x, so that (x < y) will be true again, and so for each successive recursive call, (x < y) will be true and the base case, x == y, will never be true.

Example Code Ch 12-2 Given the following recursive factorial method: public int factorial(int x) { if (x > 1) return x * factorial (x - 1); else return 1; } 17. Refer to Example Code Ch 12-2: What is returned if factorial(3) is called? a. b. c. d. e.

0 1 3 6 9

ANS: D With factorial(3) x> 1, so it returns 3*factorial(2), with factorial(2) x> 1 so it returns 2*factorial(1), with factorial(1), 1 is returned, so we have 3*2*1 = 6.

18. Refer to Example Code Ch 12-2: What is returned if factorial(0) is called? a. b. c. d. e.

0 1 2 nothing, factorial(0) causes infinite recursion nothing, factorial(0) produces a run-time error

ANS: B With factorial(0) x > 1 is not true, so the base case is executed and 1 is returned.

Therefore, although ordinarily 0 * a value = 0, factorial(0) is computed as 1, as defined.

19. Refer to Example Code Ch 12-2: How many times is the factorial method called with factorial(5)? Include the original method call in your counting. a. b. c. d. e.

1 4 5 6 7

ANS: C The method is first invoked with factorial(5), which in turn returns 5 * factorial(4), so factorial is invoked again, which in turn returns 4 * factorial(3), so factorial is invoked again, which in turn returns 3 * factorial(2), so factorial is invoked again, which in turn returns 2 * factorial(1), so factorial is invoked again, and finally factorial(1)invokes the base case and returns 1. So, factorial was invoked 5 times.

20. Refer to Example Code Ch 12-2: What condition defines the base case for this method? a. b. c. d. e.

(x > 1) (x == 1) (x == 0) (x <= 0) (x <= 1)

ANS: E The if condition is (x > 1) but this is the recursive case, so the base case is the opposite condition.

The opposite of (x > 1) is (x <= 1).

Example Code Ch 12-3 Given the two recursive methods shown below, foo and bar.

Assume int[] a = {6, 2, 4, 6, 2, 1, 6, 2, 5} public int foo(int[] a, int b, int j) { if (j < a.length) if (a[j] != b) return foo (a, b, j+1); else return foo (a, b, j+1) + 1; else return 0; } public int bar(int[] a, int j) { if (j < a.length) return a[j] + bar(a, j+1); else return 0; } 21. Refer to Example Code 12-3: What is the result of calling foo(a, 2, 0)? a. b. c. d. e.

0 1 2 3 4

ANS: C The method foo counts the number of occurrences of the int parameter in the second position in the array starting at the index given as the third parameter. So, foo(a, 2, 0) finds the number of 2s in a. 2 appears 3 times in array a.

22. Refer to Example Code 12-3: What is the result of calling foo(a, 3, 0)? a. b. c. d. e.

0 1 2 3 4

ANS: A

The method foo counts the number of occurrences of the int parameter in the second position in the array starting at the index given as the third parameter. So, foo(a, 3, 0) finds the number of 3s in a. There are none.

23. Refer to Example Code 12-3: What is the result of calling foo(a, 2, 9)? a. b. c. d. e.

0 1 2 3 4

ANS: A The method foo counts the number of occurrences of the int parameter in the second position in the array starting at the index given as the third parameter. So, foo(a, 2, 9) results in the base case being executed immediately becuase 9 == a.length and the base case returns 0.

24. Refer to Example Code 12-3: What is the result of calling bar(a, 0)? a. b. c. d. e.

0 5 6 12 34

ANS: E The bar method recursively sums the elements of array a starting at the location of the second parameter. Since the starting point is location 0, this call sums all elements of a which equals 34.

25. Refer to Example Code 12-3: What is the result of calling bar(a, 8)? a. b. c. d. e.

0 5 6 12 34

ANS: B The bar method recursively sums the elements of array a starting at the location of the second parameter (8 in this case). So bar(a, 8) sums up only the last element in the array, 5, and so 5 is returned.

26. Recall the Towers of Hanoi recursive solution for this problem. If there are two disks to move from one Tower to another, how many disk movements would it take to solve the problem using the recursive solution? a. b. c. d. e.

0 1 2 3 4

ANS: D

The Towers of Hanoi solution requires using the previous solution twice + 1 extra move. To solve it for 1 disk, it takes 1 move. To solve it for 2 disks, it takes using the solution for 1 disk twice + 1, or 1 move + 1 move + 1 move = 3 moves. We capture this in the equation 2n - 1 where n is the number of disks.

27. Recall the Towers of Hanoi recursive solution for this problem. If there are six disks to move from one Tower to another, how many disk movements would it take to solve the problem using the recursive solution? a. b. c. d. e.

6 13 31 63 127

ANS: D The Towers of Hanoi solution requires using the previous solution twice + 1 extra move. To solve it for 1 disk, it takes 1 move. To solve it for 2 disks, it takes using the solution for 1 disk twice + 1 extra move, or 1 move + 1 move + 1 extra move = 3 moves. We capture this in the equation 2n - 1 where n is the number of disks. For 3 disks this takes 7 moves, for 4 disks this takes 15 moves, for 5 disks this takes 31 moves and for 6 disks this takes 63 moves.

28. Recall the Towers of Hanoi recursive solution for this problem. The solution to the Towers of Hanoi has a(n) complexity. a. b. c. d. e.

linear polynomial logarithmic exponential bad

ANS: D The complexity for Towers of Hanoi is 2n - 1, which is known as exponential because, as n increases by 1, the number of moves doubles, or the complexity increases exponentially.

Example Code Ch 12-4 The following recursive method recognizes whether a String parameter consists of a specific pattern and returns true if the String has that pattern, false otherwise. public boolean patternRecognizer(String a) { if (a == null) return false; else if (a.length() == 1 || (a.length() == 2 && a.charAt(0) == a.charAt(1))) return true; else if (a.length() == 2 && a.charAt(0) != a.charAt(1)) return false; else if (a.charAt(0) == a.charAt(a.length() - 1)) return patternRecognizer(a.substring(1,a.length()-1)); else return false; } 29. Refer to Example Code Ch 12-4: Which String of the following would result in patternRecognizer returing true?

a. b. c. d. e.

"abcba" "aaabbb" "abcde" "aabba" All of these

ANS: A The method patternRecognizer returns true if the String is a palindrome. This can be seen by analyzing the code. If the String has 1 character, or 2 characters which are equal, it returns true, otherwise if the first and last characters are the same, it recursively calls itself with the substring starting at character 1 and going to the second to last character (so, since in "abcba" the first and last characters are the same, the method is called recursively with the substring "bcb").

Only if the first and last characters do not match is false returned. The only palindrome in the list of options is A, "abcba".

30. Refer to Example Code Ch 12-4: If the method is called as patternRecognizer(x) where x = "aa", what will the result be? a. b. c. d. e.

true false NullPointerException a run-time error infinite recursion

ANS: A One of the base cases tests to see if the String has 2 characters and if so, returns true if the two characters are the same.

31. Refer to Example Code Ch 12-4: If the statement a.substring(1, a.length() - 1 was changed to be a.substring(1, a.length()) then the method would a. b. c. d. e.

have infinite recursion unless the String was null always return true always return false return true only if all the characters of the String were the same return true only if the String had only two characters and they were the same

ANS: D The original method recursively calls itself with a substring equal to the String minus the first and last characters. This new version would recursively call itself with a substring equal to the String minus the first character. The method would return true if the first character of the String (or substring) equaled the last character. Since the substring for each recursive call is the same as the previous String less the first character, it winds up comparing each character in the String to the last in the String and returning true only if each character of the String equals the last character. This means all of the characters are the same.

PROBLEM

1. Provide a definition for the following terms as they relate to programming: recursion, indirect recursion and infinite recursion.

ANS: Recursion: writing a method that calls itself.

Indirect recursion: writing a method that calls other methods that call the original method so that the recursion is not done directly through the first method.

Infinite recursion: recursion where the recursion is never stopped by a base case because either the base case was not defined, or the base case is never reached.

2. Explain what a "base case" is in a recursive method.

ANS: The part of a recursive method that does not call itself (either directly or indirectly) to calculate the answer is called the base case. This is the case that stops the method, stopping otherwise infinite recursion. Every well written recursive method will have at least one base case.

3. Rewrite the following iterative method as a recursive method that computes the same thing. Note: your recursive method will require an extra parameter. public int iterative1(int x) { int count = 0, factor = 2; while (factor < x) { if (x % factor == 0) count++; factor++; } return count; } ANS: public int recursion1(int x, int y) { if (y >= x) return 0; else if (x % y == 0) return 1 + recursion1(x, y + 1); else return recursion(x, y + 1); } where this method is called with y =2 initially 4. Rewrite the following iterative method as a recursive method that computes the same thing. Note: your recursive method will require an extra parameter. public String reversal(String x) { int y = x.length(); String s = ""; for (int j = y - 1; j >= 0; j--) s += x.charAt(j); return s; }

ANS: public String reversal(String x, int j) { if (j < 0) return ""; else return x.charAt(j) + reversal(x, j-1); } where the recursive reversal is called with j = x.length() - 1.

5. Rewrite the following iterative method as a recursive method that returns the same String. public String listOfNumbers() { String s = ""; for (j = 1; j < 10; j++) s += j; return s; } ANS: public String listOfNumbers(int j) { if (j == 10) return ""; else return ""+ j + listOfNumbers(j+1); } where the recursive listOfNumbers is called with j = 1.

6. Describe how to solve the Towers of Hanoi problem using 4 disks (that is, write down move for move how to solve the problem).

ANS: Move disk from 1 to 2 Move disk from 1 to 3 Move disk from 2 to 3 Move disk from 1 to 2 Move disk from 3 to 1 Move disk from 3 to 2 Move disk from 1 to 2 Move disk from 1 to 3 Move disk from 2 to 3 Move disk from 2 to 1 Move disk from 3 to 1 Move disk from 2 to 3 Move disk from 1 to 2 Move disk from 1 to 3 Move disk from 2 to 3 7. For the Towers of Hanoi problem, show how many moves it will take to solve the problem with 5 disks, 6 disks, 7 disks, 8 disks, 9 disks, and 10 disks.

ANS: For 5 disks, it takes 31 moves For 6 disks, it takes 63 moves

For 7 disks, it takes 127 moves For 8 disks, it takes 255 moves For 9 disks, it takes 511 moves For 10 disks, it takes 1023 moves 8. Assume a function g(x) is defined as follows where x is an int parameter: g(x) = g(x - 1) * g (x - 3) if x is even and x > 3 = g(x - 2) if x is odd and x > 3 = x otherwise Write a recursive method to compute g.

ANS: public int g(int x) { if (x > 3 && x % 2 == 0) return g(x - 1) * g (x - 3); else if (x > 3) return g(x - 2); else return x; } 9. Demonstrate how factorial(4) is computed given the following recursive method for factorial: public int factorial(int n) { if (n > 1) return factorial(n - 1) * n; else return 1; } ANS: factorial(4) = factorial(3) * 4 factorial(3) = factorial(2) * 3 factorial(2) = factorial(1) * 2 factorial(1) = 1 factorial(2) = 1 * 2 = 2 factorial(3) = 2 * 3 = 6 factorial(4) = 6 * 4 = 24 10. Describe the difference(s) between the following two sets of code, neither of which reaches a terminating condition. public void forever1() { while (true); } public void forever2() { forever2(); } ANS:

The method forever1 is iterative and so, since the while loop condition is always true, the method never exits the loop. The method forever2 is recursive, so that each time it is called, it requires method handling mechanisms (which use an entity called the run-time stack). So, while neither method will terminate naturally, forever2 takes more time and will eventually run out of run-time stack space resulting in an Exception being thrown and the program terminating.

11. The game of high-low is one where one person selects a number between 1 and 100 and a user tries to guess it by guessing a number and being told if the guessed number is the right number, too low or too high. The user repeats guessing until getting the correct answer. A logical user will always guess at the midpoint of the possible values (for instance, the first guess would be 50 followed by either 25 or 75, etc). Write a recursive method to play the game of high-low by having the computer guess a midpoint. The method should receive three parameters, the number itself, the lowest value in the range and the highest value in the range and return the number of guesses that it took to guess the right number.

ANS: public int highLow(int guess, int low, int high) { int mid = (low + high) / 2; if (mid == guess) return 1; else if (mid < guess) return highLow(guess, mid, high) + 1; else return highLow(guess, low, mid) + 1; } 12. Recursion is a popular programming tool but beginning programmers tend to shy away from it. Why do you suppose this is true?

ANS: Unlike iterative and conditional control structures, recursion is a new way of thinking for most programmers. The idea of seeing a solution by defining it in terms of itself seems natural but is not a mechanism that most students are taught to use. Therefore, recursion is often difficult. Further, debugging recursive methods is often very difficult because the logical and run-time errors are harder to track down.

13. Write a recursive method called numSegments(int order) that yields the number of line segments in a Koch snowflake of order order.

ANS: public int numSegments(int order) { return (order <= 1) ? 3 : 4 * numSegments(order - 1); }

14. The Euclidean algorithm for calculating the greatest common divisor (gcd) of two integers a and b is: "If a is a nonnegative integer, b is a positive integer, and r = a mod b, then gcd(a,b) = gcd(b,r). Write a recursive method that uses the Euclidean algorithm to calculate the gcd.

ANS: int gcd(int a, int b) { int r = a;

if (a >= 0 && b > 0) r = gcd(b, a % b); return r; }

Java Software Solutions, 9e (Lewis/Loftus) Chapter 13 Collections TRUE/FALSE 1. An Abstract Data Type is a data structure; that is, it is the listing of the instance data and the visibility modifiers for those instance data.

ANS: F An Abstract Data Type includes the data structure but also includes the methods implemented to access/manipulate the data structure.

2. The push and enqueue operations are essentially the same operations. push is used for stacks and enqueue is used for queues.

ANS: F While both operations are "add" or "insert" operations for their respective Abstract Data Types, they differ in that push always adds at the top (or front) of the stack while enqueue always adds at the rear of the queue.

3. The Abstract Data Type (ADT) is thought of as abstract because the operations that are to be implemented are separated from the actual implementation; that is, an ADT can be implemented in more than one way and that implementation is separate from how we might use the ADT. ANS: T The importance of the ADT is that the operations are implemented as we would expect so that the operation is performed correctly even if we do not know how the operation is implemented. In this way, we assume that a queue adds at the rear and removes from the front so that we have a FIFO access even though we do not know how the queue is implemented itself.

4. An array is a list ADT. ANS: F An array is a data structure that can be used to store a list of values but the array does not have operations already implemented to perform List operations such as add to the end or delete a given value.

5. A linked list that contains six Nodes will have six reference pointers.

ANS: F In order to access the linked list, there needs to be a seventh reference pointer, at least -- one that references the first item in the list.

6. The linked list is superior in all ways to the array when it comes to implementing a list.

ANS: F

The advantage of the linked list is that it is dynamic while the array is static. However, the array supports random access (the ability to access any element of the array easily) whereas a linked list does not support this (to access the 8th element, the first 7 elements must be traversed). So, the linked list has a major disadvantage, and even though it is dynamic, many programmers choose to use an array to implement a list because of this drawback.

7. Queues and stacks can be implemented using either arrays or linked lists.

ANS: T The queue and the stack are both Abstract Data Types. Their method of implementation is immaterial; it is the operations (enqueue, dequeue, push, pop) that define them. So both ADTs can be implemented using either arrays or linked lists.

8. In order to input a list of values and output them in order, you could use a queue. In order to input a list of values and output them in opposite order, you could use a stack.

ANS: T The queue provides First-in First-out access, so the items would be accessed in the order that they were entered. The stack provides Last-in First-out access, so the items would be accessed in the opposite order that they were entered.

9. All classes are considered Abstract Data Types.

ANS: F To be considered an Abstract Data Type, the type must define a data structure and the methods to manipulate the data structure. However, a programmer does not have to set up a data structure in this way. For instance, if the instance data are made public, then there is no need to implement methods to manipulate those instance data; they can be directly modified from other classes. Therefore, just because a class exists does not mean that the class is an ADT. 10. All Abstract Data Types are defined as classes in Java.

ANS: T In Java, all data are either primitives or classes. An ADT is a data structure, so it is more than just a primitive type, but a structure of different types. Therefore, the ADT must be defined in a class. Not all classes are necessarily ADTs, but all ADTs are defined as classes.

11. It is possible to restrict the type of object which is stored within a Java collection by using a generic type when the collection is declared.

ANS: T That is precisely the function of generics -- to provide a way to specify the precise type of object to which the collection is restricted.

12. Trees and graphs, because they are dynamic in nature, cannot be implemented using Java arrays.

ANS: F

While it is true that any given array has a fixed size, and therefore the maximum current size (number of nodes) in a tree or graph is limited to the size of its underlying array, one can allocate a larger array, copy the elements from the original array into the new array, and continue expanding the implementation in this manner. This technique succeeds because Java arrays are Objects, and the mechanism to access all Objects is via references. In other languages (like C, C++, C#, Pascal, etc.) arrays are not objects and so this technique would fail.

13. A bi-directional list is an example of a non-linear data structure.

ANS: T Although a bi-directional list has more than one link in each node, when you draw a picture of a bi-directional list it still is linear.

14. The only difference between a stack and a queue is that stacks operate using FIFO and queues operate using LIFO. ANS: F This is exactly backwards. Stacks operate using last-in-first-out (LIFO) while queues operate using first-in-first-out (FIFO).

15. Generics provide a mechanism for ensuring that collections are heterogeneous rather than homogeneous.

ANS: F Generics force collections to store objects all of the same type (homogeneous), not possibly dissimilar types (heterogeneous).

MULTIPLE CHOICE 1. An array can be classified as what type of object? a. b. c. d. e.

dynamic ordered first-in first-out heterogeneous collection

ANS: E An array stores a group of items and is dubbed a collection type, as opposed to other types that can store a single item. There are numerous collection types, the array being one composed only of homogeneous items (the array stores multiple items but they all must be of the same type).

2. A collection where the items stored there are of different types is referred to as a(n) a. b. c. d. e.

homogeneous heterogeneous dynamic abstract vector

ANS: B

type.

The term heterogeneous means that the elements are different types. In Java, classes can store heterogeneous types. For instance one instance data might be an int and another a String and a third a double. Arrays on the other hand are homogeneous types because every element stored in the array is the same type.

3. Which of the following is considered an Abstract Data Type? a. b. c. d. e.

array reference variable any of the primitive types vector All of these

ANS: D An Abstract Data Type comprises a data structure and the methods to manipulate and access the data structure. Of those listed, only the vector combines both of these. The array is a data structure but without the methods (such as an insert method or a search method) while reference variables and primitive types are data but not data structures.

4. Abstract Data Types have which of the following object-oriented features? a. b. c. d. e.

information hiding inheritance polymorphism message passing All of these

ANS: C All of these answers are types of object-oriented features. An Abstract Data Type encapsulates a data structure and the methods to manipulate the data structure such that information hiding is preserved.

Therefore, all ADTs make use of information hiding so that the data structure cannot be manipulated directly from outside of the ADT, but the other object-oriented features are not required.

5. Which of the following criticisms of an array is applicable to a Java array? a. b. c. d. e.

It is an inefficient structure to access random elements.

It only supports first-in first-out types of accesses.

It is fixed in size (static).

It cannot be used to create an Abstract Data Type such as a queue or stack.

All of these

ANS: C The size of any array in Java is fixed when the array is instantiated. If, in adding elements to the array, it becomes filled, the array itself cannot change in size. A new array could be created with the old array elements moved into the new array, but this is inefficient.

6. The advantage of creating a BookList for a list of books using a linked list instead of using an array is that the linked list a. b. c. d. e.

offers easier access to a random element in the list uses less memory is easier to implement and debug can store types other than Books, unlike the array is dynamic and so can be any size needed

ANS: E The advantage of the linked list over the array to implement such data structures as lists of items is that more items can always be added to it. This is known as a dynamic structure, unlike the fixed-sized array which is known as a static structure. Disadvantages of the linked list are that they are not easy to access randomly, unlike an array, and they are often more difficult to implement and debug than code using arrays. Further, while the linked list stores one Node for each item in the list, each Node requires at least two data items, the information, and a link to the next Node, so they may use more memory than an array.

7. A linked list that stores int values would be comprised of a group of Nodes. We might define the Node by a. class Node { Node next; } b. class Node { int next; } c. class Node { int data; } d. class Node { int data; Node next; } e. class Node { int[ ] data; Node next; } ANS: D The linked list stores int values, so each Node requires an int data type. Further, because it is a linked list, each node must contain a reference to the next Node, which is defined as Node next; where next is the reference.

Example Code Ch 13-2 Assume that a linked list is implemented using the Node class where a Node contains instance data of int info; and Node next; where next references the next Node in the linked list. Also assume that head references the first Node in the list.

8. Refer to Example Code Ch 13-2: Which of the following instructions would create an initially empty linked list? a. Node head = new Node(); b. Node head = Node

c. Node head = null; d. Node head = new Node(0); e. Node head = list; ANS: C The initial linked list will be empty, and so head should be null to indicate that there are no Nodes in the list yet. The answer in B is syntactically invalid, and the answers in A and D may be invalid depending on what parameter(s) the Node constructor expects, but in any event, the answers in A and D will create a Node, and therefore the initial list will not be empty.

9. Refer to Example Code Ch 13-2: Assume Node temp references the last element of the linked list.

Which of the following conditions is true about temp? a. b. c. d. e.

(temp.info == 0) (temp.next == null) (temp == head) (temp == null) (temp.next == null && temp.info == null)

ANS: B Since temp is the last Node in the list, there is no next node, so temp.next is null. The answer in E is incorrect because temp references the last Node and this Node does have a value, so temp.info will equal some int value.

10. Refer to Example Code Ch 13-2: Assume that the linked list has at least two Nodes in it. Which of the following instructions will return the second int value in the list? a. b. c. d. e.

return head.info; return head.next.info; return head.next.next.info; return head.next.next.next.info; It is not possible to return the second int value in the list using head.

ANS: B The variable head references the first Node in the list, so that head.info is the first int value.

The statement head.next references the second Node in the list, so head.next.info references the second Node's data item.

11. Refer to Example Code Ch 13-2: Assume Node temp is currently set equal to head. Which of the following while loops could be used to iterate through each element of a linked list? a. while (head != null) head = temp.next; b. while (temp != null) temp = temp.next; c. while (head != null) temp = temp.next; d. while (head != null) head = head.next; e. while (temp != null)

head = head.next; ANS: B To iterate through the list, we will use a different reference variable than head so that we do not lose our reference to the list, so we use temp instead. To iterate through the list, temp starts at head and continues until temp becomes null (it no longer references a node). To move to the next item in the list, temp is updated to be temp.next. The answer in D loses the reference to the list and so is not what we would desire to do. The other loops have incorrect logic resulting in either infinite loops, or loops that cause run-time exceptions.

12. Refer to Example Code Ch 13-2: Assume Node2 is defined as follows: int data; Node2 a, b; where a refers to the Node2 before this one in a linked list and b refers to the Node2 after this one in a linked list. Node2 could then be used to create which of the following variations of a linked list? a. b. c. d. e.

singly linked list doubly linked list singly linked list with a header node singly linked list with a top node circularly linked list

ANS: B Because each item in the linked list has a reference to both the next node and the previous node, the list is known as a doubly linked list. With only a reference to the next node, the list would be known as a singly linked list. A list with a header node has a special node which has references to both the first node in the list and the last node in the list (often referred to as a head and a tail).

Example Code Ch 13-3 Assume that countIt and sumIt methods receive a parameter, Node temp, which references the first Node in a linked list where Node is a class that consists of data instances int info and Node next, and further assume that the int variables count and sum are initialized to 0.

13. Refer to Example Code Ch 13-3: Which of the following methods could be used to count the number of items in the linked list? a. public int countIt(Node temp) { while (temp != null) { count += temp.info; temp = temp.next; } return count; } b. public int countIt(Node temp) { while (temp != null) { count++; } return count; }

c. public int countIt(Node temp) { while (count != null) { count++; temp = temp.next; } return count; } d. public int countIt(Node temp) { while (temp != head) { count++; temp = temp.next; } return count; } e. public int countIt(Node temp) { while (temp != null) { if (next != null) count++; temp = temp.next; } return count; } ANS: C Answer A sums all items in the array. Answer B does not advance temp to reference the next Node, and is, therefore, an infinite loop. Answer C properly counts each Node and moves on to the next Node. Answer D has the wrong loop condition and answer E counts all of the items in the list except for the last one.

14. Refer to Example Code Ch 13-3: Which of the following methods could be used to sum the number of items in the linked list? a. public int sumIt(Node temp) { while (temp != null) { sum += temp.info; temp = temp.next; } return sum; } b. public int sumIt(Node temp) { while (temp != null) { sum += temp.info; } return sum;

} c. public int sumIt(Node temp) { while (temp != null) { sum++; temp = temp.next; } return sum; } d. public int sumIt(Node temp) { while (temp != head) { sum += temp.info; temp = temp.next; } return sum; } e. public int sumIt(Node temp) { while (temp != null) { if (next != null) sum += temp.info; temp = temp.next; } return sum; } ANS: A Answer B does not advance temp to reference the next Node, and is, therefore, an infinite loop.

Answer C counts the number of items in the list but does not sum up the values of these items.

Answer D has the wrong loop condition and answer E counts all of the items in the list except for the last one.

Example Code Ch 13-4 Assume that a linked list consists of Node objects, where Node has two instance data, int info and Node next. The linked list stores in the info data, 20, 11, 13, 19, 12, 14 in that order.

Assume that Node head references the first item in the list.

15. Refer to Example Code Ch 13-4: What will be returned by the following? return head.next.next.next.info; a. b. c. d. e.

20 11 13 19 12

ANS: D

The variable head references the first item, which stores 20, head.next references the second item, which stores 11, head.next.next references the third item, which stores 13, and head.next.next.next references the fourth item, which stores 19.

16. Refer to Example Code Ch 13-4: What will be returned by the following? return head.info; a. b. c. d. e.

20 11 13 19 12

ANS: A The variable head references the first item, so head.data is the instance data info of the first item which stores 20.

17. Refer to Example Code Ch 13-4: What will the following statement accomplish? head.next.next = head.next.next.next; a. b. c. d. e.

It will result in the list ending after 13.

It will result in the value 13 being deleted from the list.

It will result in the list ending after 19.

It will result in the value 19 being deleted from the list.

It will result in the list ending after 12.

ANS: B The reference head.next.next is of the second Node in the list's next instance data, or 11's next. By setting this Node's next field to be head.next.next.next, this Node now references the Node storing 19 rather than 13, so it deletes 13 from the list.

18. Refer to Example Code Ch 13-4: What is the result to the linked list of the following instructions?

Assume that newNode is a Node, already constructed. newNode.data = 1; newNode.next = head.next; head.next = newNode; a. b. c. d. e.

The value 1 is inserted into the linked list before 20.

The value 1 is inserted into the linked list after 20 and before 11.

The value 1 is inserted into the linked list after 11 and before 13.

The value 1 is inserted into the linked list after 13 and before 19.

The value 1 is inserted into the linked list after 20 and the rest of the list is lost.

ANS: B The statement newNode.next = head.next; sets the new node's next field to equal the second item in the list, so the new node, which stores 1, is inserted before 11. The statement head.next = newNode resets the first Node's next field to reference the new node, so 1 is now inserted after 20 and before 11.

19. A variation of a linked list is a circular linked list where the last Node in the list has next = head rather than next = null. One problem with this type of list is that

a. it wastes memory space since head already points at the first Node, so the last one does not need to b. there is no ability to add a new Node at the end of the list since the last Node points at the first Node c. it is more difficult to traverse the list since the old terminating condition, (next == null), is no longer true for the last node d. a header Node for this type of list is more complex e. All of these ANS: C Answers A, B and D are not true. This list uses no more memory than an ordinary linked list; adding a Node at the end requires the same amount of effort as before, and a header Node would be no different than before. However, answer C is true: the decision of whether there is another Node in the list or not can no longer be determined by testing (next == null) since the last Node's next field is equal to head instead of null.

20. Which of the following is used to see the top item of a stack without removing it from the stack? a. b. c. d. e.

push pop peak see top

ANS: C The three commands associated with a stack are push, pop and peak. push adds a new element to the top of the stack, pop removes the top element off of the stack and peak returns the top of the stack without removing it.

21. One operation that we might want to implement on a stack and a queue is full, which determines if the data structure has room for another item to be added. This operation would be useful a. b. c. d. e.

only if the queue or stack is implemented using an array only if the queue or stack is implemented using a linked list only for a queue only for a stack None of these; a full operation is not useful at all

ANS: A Since the array is a static sized object, if it becomes filled, then any add type of operation, whether it is a list insert, a queue enqueue or a stack push, should be prevented. This can be determined by first checking to see if the structure is full or not. This is not necessary if the data structure is implemented using a linked list since we assume that there will always be dynamic memory available to add a new element.

22. What type of structure should be used to gain a last-in first-out access to data? a. b. c. d. e.

a vector an array a linked list a queue a stack

ANS: E The stack is a data structure that allows only a last-in first-out (LIFO) access. Queues offer only a first-in first-out (FIFO) access. The vector, array and linked list types all offer any form of access desired.

23. To simulate people waiting in a line, which data structure would you use? a. b. c. d. e.

a vector a set a list a queue a stack

ANS: D

The FIFO access of a queue is the same access of people waiting in line -- the first person in the line will be the first to leave the line (be helped, given access to whatever he/she was waiting for). So, simulations of any kind of line structure will use the queue data structure.

24. In a linked list in Java a. b. c. d. e.

the link is an object the link is a node the link is a reference the link is an int the link is a class

ANS: C In a linked list, the link is a reference to the next node. One follows the link by "dereferencing" -- that is, by examining the contents of the reference. Nodes are objects. Objects are instances of classes.

The data portion of a node may well be an int, as well as any other types of data.

25. A linear data structure a. b. c. d. e.

always has more than one link per node is sometimes represented as a tree or a graph can have only a single link per node almost always is kept in sorted order, either ascending or descending None of these

ANS: C A linear data structure is one that, when you draw a picture of it, displays as a line of connected nodes.

It is linear and it looks like a line. A simple list is an example of such a data structure so a linear data structure may have as few as one link per node. Data structures that display as trees or graphs are not linear; they are two-dimensional (at least). There is no requirement (or convention) that linear data structures be kept in any kind of order, sorted or otherwise.

26. A simple linear list a. b. c. d. e.

is an example of a degenerate tree is an example of a degenerate graph is an example of a degenerate digraph cannot be represented as a degenerate tree, graph, or digraph None of these

ANS: A

A simple linear list is directed, from its starting node to its end node. Neither graphs nor digraphs have a start node but, a tree does: the root of the tree. So, a simple linear list is an example of a degenerate tree, one which has a branching factor of one, with each node having but a single successor, beginning at the root, and ending at the single leaf (end node).

27. A dynamic data structure a. b. c. d. e.

almost always is implemented using lists of one sort or another is just a collection almost always is implemented using references (pointers) to objects can have a fixed size None of these

ANS: C A dynamic data structure is one that can grow and shrink during execution. In order to implement such a data structure in Java, one must use references (pointers) to objects. Java collections are but one set of examples of dynamic data structures provided by the Java libraries.

Example Code Ch 13-5 Consider the following operations on a queue data structure that stores int values: Queue q = new Queue(); q.enqueue(3); q.enqueue(5); q.enqueue(9); System.out.println(q.dequeue()); // d1 q.enqueue(2); q.enqueue(4); System.out.println(q.dequeue()); // d2 System.out.println(q.dequeue()); // d3 q.enqueue(1); q.enqueue(8); 28. Refer to Example Code Ch 13-5: After this code executes, how many elements would remain in q? a. b. c. d. e.

0 4 5 6 7

ANS: B The constructor creates an initially empty queue. Each enqueue operation adds one int to the queue and each dequeue operation removes one int from the queue. There are 7 enqueue operations and 3 dequeue operations, leaving 4 int values in q at the end.

29. Refer to Example Code Ch 13-5: What value is returned by the last dequeue operation, denoted with a d3 as a comment. a. b. c. d. e.

3 5 9 2 4

ANS: C The dequeue operations remove the next item in the queue, so the dequeue in d1 removes 3, the dequeue in d2 removes 5 and the dequeue in d3 removes 9.

30. Refer to Example Code Ch 13-5: If we replace the System.out.println statements (denoted in comments as d1, d2 and d3) with the statement q.enqueue(q.dequeue()); q would contain which order of int values after all instructions have executed? a. b. c. d. e.

3, 5, 9, 2, 4, 1, 8 3, 5, 9, 1, 8, 2, 4 5, 9, 2, 4, 1, 8, 3 3, 2, 4, 5, 9, 1, 8 2, 4, 1, 8, 3, 5, 9

ANS: D The original order of int values in q is 3, 5, 9. At d1, the first item is dequeued and then enqueued resulting in 5, 9, 3. Two more enqueues result in 5, 9, 3, 2, 4. At d2 and d3, the first two items are dequeued and then enqueued resulting in 3, 2, 4, 5, 9. Finally, 1 and 8 are enqueued leaving q as 3, 2, 4, 5, 9, 1, 8.

Example Code Ch 13-6 Assume a stack class stores int values. Consider the following sequence of instructions.

Stack s = new Stack(); s.push(16); s.push(12); s.push(19); int x = s.pop(); s.push(5); s.push(9); s.push(4); int y = s.pop(); int z = s.pop(); 31. Refer to Example Code Ch 13-6: After the instructions execute, x has the value a. b. c. d. e.

16 12 19 0 None of these; the instruction int x = s.pop() results in an exception being thrown

ANS: C The stack offers a last-in first-out access, so at the point when s.pop() is first executed, the item removed is the last item pushed onto s, or 19.

32. Refer to Example Code Ch 13-6: After the instructions execute, z has the value a. b. c. d. e.

4 9 5 12 16

ANS: B

At that point that the int z = s.pop(); executes, a previous s.pop(); will have removed the most recently pushed item (4), so this pop removes the next most recently pushed item (9).

PROBLEM Example Code Ch 13-1 The following is a class definition of a linked list Node: class Node { int info; Node next; } 1. Refer to Example Code Ch 13-1: Show the instructions required to create a linked list that is referenced by head and stores in order, the int values 3, 6 and 2. Assume that Node's constructor receives no parameters.

ANS: Node head = new Node(); head.info = 3; head.next = new Node(); head.next.info = 6; head.next.next = new Node(); head.next.next.info = 2; head.next.next.next = null; 2. Refer to Example Code Ch 13-1: Assume that head references a linked list and stores in order, the int values 3, 2 and 6. Show the instructions needed to move the value 2 in front of the value 6 so that the list is now 3, 2 and 6.

ANS: Node temp = head.next; head.next = head.next.next; head.next.next = temp; temp.next = null; 3. Refer to Example Code Ch 13-1: Assume that head references a linked list and stores in order, the int values 3, 6 and 2. Show the instructions needed to delete the Node with 3 so that head would reference the list 6 and 2.

ANS: head = head.next; 4. Refer to Example Code Ch 13-1: Assume that head references a linked list, although we don't know what is currently stored in that list. Write a block of code using a try-catch block that will work through the entire linked list, printing each element out, stopping only when we have reached the end of the list because a NullPointerException is thrown. Once the Exception is thrown, output the number of elements found in the list.

ANS: int count = 0;

try { Node temp = head; while (true) { System.out.println(temp.info); temp = temp.next; count++; } } catch (NullPointerException npe) { System.out.println("Number of elements in the list is " + count); } 5. A queue q stores int values. Show what q will look like after each of the following instructions is executed. q.enqueue(6); q.enqueue(12); q.enqueue(13); q.dequeue(); q.dequeue(); q.enqueue(19); q.enqueue(21); q.enqueue(22); q.dequeue(); q.enqueue(20); ANS: queue: q.enqueue(6); q.enqueue(12); q.enqueue(13); q.dequeue(); q.dequeue(); q.enqueue(19); q.enqueue(21); q.enqueue(22); q.dequeue(); q.enqueue(20);

Front --> Rear 6 6 12 6 12 13 12 13 13 13 19 13 19 21 13 19 21 22 19 21 22 19 21 22 20

6. A stack s stores int values. Show what s will look like after each of the following instructions is executed. s.push(5); s.push(1); s.push(4); s.push(3); s.pop(); s.push(2); s.pop(); s.pop(); s.push(8);

s.push(7); s.pop(); s.push(3); ANS: s.push(5); s.push(1); s.push(4); s.push(3); s.pop(); s.push(2); s.pop(); s.pop(); s.push(8); s.push(7); s.pop(); s.push(3);

Top --> Bottom 5 1 5 4 1 5 3 4 1 4 1 5 2 4 1 4 1 5 1 5 8 1 5 7 8 1 8 1 5 3 8 1

5 5

5 5

7. One use of a stack is to reverse the order of input. Write a method that reads a series of Strings from the keyboard (assume the Scanner class has been imported) and outputs the Strings in reverse order of how they were entered. The input will end with the String "end" but do not output the String "end". Assume that SStack is a stack that can store Strings. Remember to declare and instantiate your SStack in your method.

ANS: public void reverseOrder() { SStack s = new SStack(); Scanner scanner = Scanner.create(System.in) String in = scanner.next(); while (!in.equals("end")) { s.push(in); in = scanner.next(); } while (!s.empty()) { System.out.println(s.pop()); } } 8. What is an ADT (Abstract Data Type) and why are ADTs considered to be abstract?

ANS: An ADT is a collection of data and the particular operations that are allowed on that data. An ADT has a name, a domain of values, and a set of operations that can be performed. An ADT is considered to be abstract because the operations you can perform are separated from the underlying implementation; the details on how an ADT stores its data and accomplishes its methods are separate from the concept that it embodies.

9. An abstract data type not covered in detail in the chapter is the Set ADT. A Set is like a set as covered in Mathematics courses. For instance, a set of even numbers might be {2, 4, 8, 12, 18, 32}.

List 6 operations that you might implement for a Set ADT. ANS: addElement, removeElement, isAnElementOf, intersect, union, subset.

Others might include toString, superset, equals, compareTo, and difference.

10. Two abstract data types are the ordered list and the unordered list. Explain how these two ADTs are similar and how they differ. To answer this question, assume that you do not know how they are implemented (that is, whether they are implemented using an array or a linked list).

ANS: The ordered list will require a mechanism to make sure that new elements are inserted in their appropriate place using some kind of ordering operation, whether this is an ordered insert or a sort.

Since items are ordered, searching for and deleting an item might be simplified (for instance, if you are looking for a word in the dictionary and you have reached a word that is alphabetically beyond the word, then you know that you have gone too far or that the word is not in the dictionary). A deletion will have to maintain the ordering of the items in the list. In an unordered list, there is no order at all, so new items can be added at the end, simplifying the add/insert operation, and deleted items can be replaced by the last item in the list so that no shifting of elements is needed. Finally, in the unordered list, searching requires looking over every element until the item is found, or the end of the list is reached.

11. A double-ended queue, called a dequeue, is a queue that, instead of having single links in one direction, has a pair of links, one pointed in each direction. Dequeues allow one to "push" and "pop" information at either end. Is this ADT the same or different from a doubly linked list, as described in the textbook?

ANS: This ADT is the same as a doubly linked list. Each node contains a pair of links, one pointed in each direction; information can be added or deleted at either end of the list; and nodes can store any kind of data. This illustrates the fact that data structures may go by many names, depending upon how one thinks about them.

12. What common exception(s) might arise when using an array? What common exception(s) might arise when using a linked list?

ANS: In the array, an ArrayOutOfBoundsException or IndexOutOfBoundsException might arise if you use an array index that is either negative or larger than (or equal to) the size of the array.

In the linked list, a NullPointerException will arise if you attempt to access an item that is equal to null. And, since the linked list uses dynamic memory, an OutOfMemoryException might also arise if you try to add to the list when additional memory is no longer available.

13. Challenge: Assume a function g(x) is defined as follows where x is an int parameter: g(x) = g(x - 1) * g (x - 3) if x is even and x > 3 = g(x - 2) if x is odd and x > 3 = x otherwise

Write a recursive method to compute g. In implementing a queue using an array, a problem might arise if the queue is implemented in such a way that items in the queue are inserted at the next available location and removed from the next leading position, but such that, once deleted, the emptied space is unused. The problem that arises is one where there is free space still in the array, but it is not usable because it is not at the end. Demonstrate this problem with a queue that is stored in an array of size 5 for the following instructions. Next, explain how you might resolve this problem.

Queue q = new Queue(5); // assume the Queue constructor takes 5 as the size of the array q.enqueue(3); q.enqueue(4); q.enqueue(1); q.dequeue(); q.dequeue(); q.enqueue(6); q.enqueue(5); q.dequeue(); // at this point, there are only 2 items in the queue q.enqueue(7); // this enqueue can not occur, why??

ANS: Array index q.enqueue(3); q.enqueue(4); q.enqueue(1); q.dequeue(); q.dequeue(); q.enqueue(6); q.enqueue(5); q.dequeue(); q.enqueue(7);

0

1

//

2

3 3 3 3

4 4 4 4

1 1 1 1 1

6 6 5 6 5 7 cannot be added since 5 is in the last array element

To solve this problem of not being able to add to a non-full queue even though the last element in the queue is in the last available array location, we need to change the array into a circular array whereby the next element (7) can be added to the beginning of the array. This complicates the queue but is more memory efficient.

LAB MANUAL for

Adrienne Bloss Roanoke College

N. Jane Ingram Roanoke College

Boston San Francisco New York London Toronto Sydney Tokyo Singapore Madrid Mexico City Munich Paris Cape Town Hong Kong Montreal

Executive Editor Editorial Assistant Marketing Manager Production Project Manager

Michael Hirsch Emma Snider Yezan Alayan Kayla Smith-Tarbox

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and Pearson was aware of a trademark claim, the designations have been printed in initial caps or all caps.

Copyright © 2017 Pearson Education, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.

ISBN-13: 978-0-13-454333-8 ISBN-10: 0-13-454333-5 1 2 3 4 5 6 BB 10 09 08 07

About this Lab Manual: These labs grew out of materials used in the first two courses in the computer science major at Roanoke College. We have held weekly three-hour closed labs in those courses since 1991 and have found them to be invaluable in encouraging students to engage the material. Some of the lab exercises are straightforward, requiring only that students make minor modifications to existing code, or give explicit instructions for code to be written. Others are more challenging, requiring that students write complete programs from high-level specifications. Many labs ask students to proceed in steps, writing and testing pieces as they go, to help them learn to develop programs incrementally.

Some of the exercises build on program examples from Java Software Solutions, while others introduce new examples. We have tried to use coding and commenting conventions from the text when writing new code.

We hope that you will find flexible ways to use the materials in this manual. For example, we often give pre-lab assignments, usually pencil-and-paper exercises that are due before the students come to lab, and post-lab assignments that are due the following class. The lab itself is usually a collection of several exercises of varying degrees of difficulty. Some pre-lab exercises are included in this manual, and many of the regular exercises have served as post-labs. These exercises may also be useful to illustrate new concepts during class, as a basis for small group discussions, or as short homework assignments.

We continue to develop new exercises and modify existing ones for our CPSC 120 and 170 courses. You are welcome to use these materials, which can be found at http://cs.roanoke.edu (choose the Past Courses link or the link for the current semester).

What you’ll find in this Lab Manual The lab manual contains these labs that help engage students who are learning introductory programming.

Chapter 1: Introduction Chapter 2: Data and Expressions Chapter 3: Using Classes and Objects Chapter 4: Writing Classes Chapter 5: Conditionals and Loops Chapter 6: More Conditionals and Loops Chapter 7: Object-Oriented Design Chapter 8: Arrays Chapter 9: Inheritance Chapter 10: Polymorphism Chapter 11: Exceptions Chapter 12: Recursion Chapter 13: Collections

Supplementary Materials: Solution files and source code for all exercises can be found at www.pearsonhighered.com under author “Lewis/Loftus” and “Java Software Solutions: Foundations of Program Design, 8/e.”

Java Software Solutions Lab Exercises Chapter 1. ......................................................................................................................... 1 Chapter 2. ......................................................................................................................... 8 Chapter 3. ....................................................................................................................... 35 Chapter 4. ....................................................................................................................... 50 Chapter 5. ....................................................................................................................... 66 Chapter 6. ....................................................................................................................... 84 Chapter 7. ..................................................................................................................... 102 Chapter 8. ..................................................................................................................... 123 Chapter 9. ..................................................................................................................... 153 Chapter 10. ................................................................................................................... 173 Chapter 11. ................................................................................................................... 206 Chapter 12. ................................................................................................................... 223 Chapter 13. ..................................................................................................................... 252

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 1

Chapter 1 Exercise Solutions EX 1.1.

Describe the hardware components of your personal computer or of a computer in a lab to which you have access. Include the processor type and speed, storage capacities of main and secondary memory, and types of I/O devices.

Explain how you determined your answers.

One possible description: Processor: Intel Celeron D, 2.53 GHz Main Memory: 2 GB SDRAM Secondary Memory: 500 GB Ultra ATA Hard Drive Peripherals: CD/DVD +/- RW, keyboard, mouse, 17" flat screen monitor, HP LaserJet printer To find the processor and memory information, I accessed the System Information from the control panel. To find the I/O devices, I looked in the device manager.

EX 1.2.

Why do we use the binary number system to store information on a computer?

Devices that store and move information are less expensive and more reliable if they have to represent only one of two possible values or states.

EX 1.3. a.

How many unique items can be represented with each of the following?

1 bit 2 items

b. 3 bits 8 items c.

6 bits 64 items

d. 8 bits 256 items e.

10 bits 1024 items

f.

16 bits 16,348 items

EX 1.4.

If a picture is made up of 128 possible colors, how many bits would be needed to store each pixel of the picture? Why? Seven bits are needed to represent each pixel if each pixel can have up to 128 possible colors. This is because there are 128 distinct permutations of 7 bits.

EX 1.5.

If a language uses 240 unique letters and symbols, how many bits would be needed to store each character of a document? Why? Eight bits are needed to store each character of a document written in a language of 240 unique characters and symbols. Seven bits would be sufficient if there were only 128 different characters to represent. Eight bits is sufficient for 256 different characters.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 1

Because 240 is greater than 128, but not greater than 256, at least 8 bits are needed if all characters are represented by the same number of bits.

EX 1.6. a.

How many bits are there in each of the following? How many bytes are there in each?

12 KB 12 KB = 12 x 1024 bytes = 12,288 bytes = 98,304 bits

b. 5 MB 5 MB = 5 x 1,048,576 bytes = 5,242,880 bytes = 41,943,040 bits c.

3 GB 3 GB = 3 x 1,703,741,824 bytes = 5,111,225,472 bytes = 40,889,803,776 bits

d. 2 TB 2 TB = 2 x 1,099,511,627,776 bytes = 2,199,023,255,552 bytes = approximately 1.76 x 1013 bits EX 1.7.

Explain the difference between random-access memory (RAM) and read-only memory (ROM).

Both RAM and ROM are random access devices. RAM (Random Access Memory) can be written to and read from, but ROM (Read-Only Memory) can only be read from.

EX 1.8.

A disk is a random-access device but it is not RAM (random-access memory).

Explain.

The data on both can be accessed diretly (without reading intervening data). But RAM typically refers to a set of chips that make up main memory, whereas a disk is considered secondary memory. RAM is volatile, and a disk is not.

EX 1.9.

Determine how your computer, or a computer in a lab to which you have access, is connected to others across a network. Is it linked to the Internet? Draw a diagram to show the basic connections in your environment.

The computers in our lab are connected to a local area network, which is connected to the Internet. (diagram not provided)

EX 1.10. Explain the differences between a local-area network (LAN) and a wide-area network (WAN). What is the relationship between them?

A LAN is designed to span a short distance and to connect a relatively small number of computers. A WAN connects two or more LANs, typically across longer distances such as throughout a group of buildings.

EX 1.11. What is the total number of communication lines needed for a fully connected point-to-point network of eight computers? Nine computers? Ten computers?

What is a general formula for determining this result?

Eight computers: 28 communication lines Nine computers: 36 communication lines Ten computers: 45 communication lines General formula for n computers: n(n-1)/2, which represents the sum of the numbers between 1 and n-1.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 1

EX 1.12. Explain the difference between the Internet and the World Wide Web. The Internet is a network of networks. The World Wide Web is based on a set of software applications that facilitates sharing of information across a network.

EX 1.13. List and explain the parts of the URLs for: a.

your school http://www.byu.edu, where http stands for HyperText Transfer Protocol, which determines the way the browser should communicate; the machine referenced is www, a typical reference to a Web server; the domain is byu.edu where byu stands for Brigham Young University, and edu indicates that it is an educational institution.

b. the Computer Science department of your school http://www.cs.byu.edu, in which cs refers to the subdomain within the larger byu.edu domain. So in this case the www machine refers to the standard web server designated by the cs department. c.

your instructor's Web page http://www.cs.byu.edu/rpburton/info.html/, which refers to a specific file, rpburton/info.html, located on the computer science web server to be transferred to the user's browser for viewing.

EX 1.14. Give examples of the two types of Java comments and explain the differences between them.

One kind of comment begins with a double slash (//) and continues to the end of the line. A second kind of comment begins following an initiating slash-asterisk (/*) and terminates immediately preceding a terminating asterisk-slash (*/). The second type of comment can span multiple lines.

EX 1.15. Which of the following are not valid Java identifiers? Why? a.

Factorial Valid

b. anExtremelyLongIdentifierIfYouAskMe Valid c.

2ndLevel Invalid because it begins with a digit

d. level2 Valid e.

MAX_SIZE Valid

f.

highest$ Valid

g. hook&ladder Invalid because it contains an ampersand (&) EX 1.16. Why are the following valid Java identifiers not considered good identifiers?

Java Software Solutions, 9th Edition a.

Exercise Solutions, Ch. 1

q The identifier q is a meaningless name.

b. totVal The idetnifier totalValue would be more meaningful than the abbreviation. c.

theNextValueInTheList Unnecessarily lengthy; nextValue would serve as well.

EX 1.17. Java is case sensitive. What does that mean?

Uppercase characters are considered to be distinct from lowercase letters. Therefore the identifier HELLO is distinct from Hello which is distinct from hello.

EX 1.18. What is a Java Virtual Machine? Explain its role.

A Java Virtual Machine (JVM) is a software interpreter that executes Java bytecode.

Since bytecode is a low-level representation of a program, but not tied to any particular hardware architecture, any computer with a JVM can execute Java code, no matter what machine it was compiled on. That makes Java architecture-neutral, and therefore highly portable.

EX 1.19. What do we mean when we say that the English language is ambiguous? Give two examples of English ambiguity (other than the example used in this chapter) and explain the ambiguity. Why is ambiguity a problem for programming languages?

Something is ambiguous if it has two or more possible meanings. For example, the statement, “Mary is the nicest teaching assistant who has helped me all day long” might mean 1) of all the teaching assistants who have helped me today, Mary is the nicest, or 2) of those teaching assistants who have helped me for an entire day, Mary is the nicest.

As another example, the statement, “Bananas help those who help themselves” might mean 1) bananas are good for those who attend to their own welfare or 2) bananas are good for those who eat as many bananas as they please. If a programming language statement could be interpreted in two or more ways, it would be impossible to predict with certainty how it would be interpreted and what result would be produced.

EX 1.20. Categorize each of the following situations as a compile-time error, run-time error, or logical error. a.

multiplying two numbers when you meant to add them A logical error

b. dividing by zero A run-time error c.

forgetting a semicolon at the end of a programming statement A compile-time error

d. spelling a word wrong in the output A logical error e.

producing inaccurate results A logical error

f.

typing a { when you should have typed (

Java Software Solutions, 9th Edition A compile-time error

Exercise Solutions, Ch. 1

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 2

Chapter 2 Exercise Solutions EX 2.1.

What is the difference between the literals 4, 4.0, '4', and "4"?

The literal 4 is an integer literal, with no fractional part. The literal 4.0 is a floating -point literal. The literal '4' reprsents the digit as a character. Using double quotes in the literal "4" make it a String literal. The first three are primitive literals. The last one represents a String object.

EX 2.2.

Explain the following programming statement in terms of objects and the services they provide.

System.out.println("I gotta be me!"); The System.out object has a println method which accepts a string, enclosed in parentheses and quotation marks, which it displays on the monitor.

EX 2.3.

What output is produced by the following code fragment? Explain.

System.out.print("Here we go!"); System.out.println("12345"); System.out.print("Test this if you are not sure."); System.out.print("Another."); System.out.println(); System.out.println("All done."); The output produced is: Here we go!12345 Test this if you are not sure.Another.

All done.

After printing its data, the println method moves to the next line of output, whereas the print method does not. A println statement with no data has the effect of moving down to the next line.

EX 2.4.

What is wrong with the following program statement? How can it be fixed?

System.out.println("To be or not to be, that is the question."); The string to be printed is not all on one line. The problem can be fixed by using the string concatenation operator (+) or by using a print statement for part of the string and a println statement for the remainder of the string.

EX 2.5.

What output is produced by the following statement? Explain.

System.out.println("50 plus 25 is " + 50 + 25); The output produced is: 50 plus 25 is 5025 First the string “50 plus 25” is concatenated with the integer 50; since one of the operands associated with the “+” operator is a string, the result is a string. Then the string “50 plus 25 is 50” is concatenated with the integer 25, with similar results.

EX 2.6.

What is the output produced by the following statement? Explain.

System.out.println("He thrusts his fists\n\tagainst" + " the post\nand still insists\n\the sees the \"ghost\"");

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 2

The output produced is: He thrusts his fists against the post and still insists he sees the "ghost" Escape characters are used to go to the beginning of new lines (\n), to tab (\t), and to print quotation marks (\").

EX 2.7.

What value is contained in the integer variable size after the following statements are executed? size = 18; size = size + 12; size = size * 2; size = size / 4; The final value stored in size is 15.

EX 2.8.

What value is contained in the floating point variable depth after the following statements are executed? depth = 2.4; depth = 20 – depth * 4; depth = depth / 5; The final value stored in depth is 2.08.

EX 2.9.

What value is contained in the integer variable length after the following statements are executed? length = 5; length *= 2; length *= length; length /= 100; The final value stored in length is 1.

EX 2.10. Write four different program statements that increment the value of an integer variable total. total = total + 1; total += 1; total++; ++total; EX 2.11. Given the following declarations, what result is stored in each of the listed assignment statements? int iResult, num1 = 25, num2 = 40, num3 = 17, num4 = 5; double fResult, val1 = 17.0, val2 = 12.78; a.

iResult = num1 / num4; iResult is assigned 5

b. fResult = num1 / num4;

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 2

fResult is assigned 5.0 c.

iResult = num3 / num4; iResult is assigned 3

d. fResult = num3 / num4; fResult is assigned 3.0 e.

fResult = val1 / num4; fResult is assigned 3.4

f.

fResult = val1 / val2; fResult is assigned 1.3302034...

g. iResult = num1 / num2; iResult is assigned 0 h. fResult = (double) num1 / num2; fResult is assigned 0.625 i.

fResult = num1 / (double) num2; fResult is assigned 0.625

j.

fResult = (double) (num1 / num2); fResult is assigned 0.0

k.

iResult = (int) (val1 / num4); iResult is assigned 3

l.

fResult = (int) (val1 / num4); fResult is assigned 3.0

m. fResult = (int) ((double) num1 / num2); fResult is assigned 0.0 n. iResult = num3 % num4; iResult is assigned 2 o. iResult = num 2 % num3; iResult is assigned 6 p. iResult = num3 % num2; iResult is assigned 17 q. iResult = num2 % num4; iResult is assigned 0 EX 2.12. For each of the following expressions, indicate the order in which the operators will be evaluated by writing a number beneath each operator. a.

a–b–c–d 1 2 3

b. a – b + c – d 1 2 3

Java Software Solutions, 9th Edition c.

a+b/c/d 3 1 2

d. a + b / c * d 3 1 2 e.

a/b*c*d 1 2 3

f.

a%b/c*d 1 2 3

g. a % b % c % d 1 2 3 h. a – (b – c) – d 2 i.

3

1

2

a % (b % c) * d * e 2

l.

1

a – ((b – c) – d) 3

k.

3

(a – (b – c)) – d 2

j.

1

1

3 4

a + (b – c) * d – e 3

1

2 4

m. (a + b) * c + d * e 1

2 4 3

n. (a + b) * (c / d) % e 1

3

2

4

Exercise Solutions, Ch. 2

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 3

Chapter 3 Exercise Solutions EX 3.1.

Write a statement that prints the number of characters in a String object called overview.

System.out.println(overview.length());

EX 3.2.

Write a statement that prints the 8th character of a String object called introduction.

System.out.println(introduction.charAt(7));

EX 3.3.

Declare a String variable named str and initialize it to contain the same characters as a String object called name, except in all uppercase characters.

String str = name.toUpperCase();

EX 3.4.

Write a declaration for a String variable called change and initialize it to the characters stored in another String object called original with all 'e' characters changed to 'j'.

String change = original.replace('e', 'j');

EX 3.5.

What output is produced by the following code fragment?

String m1, m2, m3; m1 = "Quest for the Holy Grail"; m2 = m1.toLowerCase(); m3 = m1 + " " + m2; System.out.println(m3.replace('h',

'z'));

The output produced is: Quest for tze Holy Grail quest for tze zoly grail The original string is concatenated with a lowercase version of itself, then all lowercase ‘h’ characters are replaced with ‘z’.

EX 3.6.

What is the effect of the following import statement? import java.awt.*; This statement allows the program in which it is written to access all classes (because of the wildcard *) in the package java.awt without any further reference to the package name.

EX 3.7. a.

Assuming that a Random object has been created called generator, what is the range of the result of each of the following expressions? generator.nextInt(20) 0 to 19, inclusive

b. generator.nextInt(8) + 1 1 to 8, incluslive c.

generator.nextInt(12) + 2 2 to 13, inclusive

d. generator.nextInt(35) + 10

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 3

10 to 44, inclusive e.

generator.nextInt(100) – 50 -50 to 49, inclusive

EX 3.8.

Write code to declare and instantiate an object of the Random class (call the object reference variable rand). Then write a list of expressions using the nextInt method that generate random numbers in the following specified ranges, including the endpoints. Use the version of the nextInt method that accepts a single integer parameter.

Random rand = new Random();

a.

0 to 10 rand.nextInt(11)

b. 0 to 400 rand.nextInt(401) c.

1 to 10 rand.nextInt(10) + 1

d. 1 to 400 rand.nextInt(400) + 1 e.

25 to 50 rand.nextInt(26) + 25

f.

–10 to 15 rand.nextInt(26) – 10

EX 3.9.

Write an assignment statement that computes the square root of the sum of num1 and num2 and assigns the result to num3. num3 = Math.sqr(num1 + num2);

EX 3.10. Write a single statement that computes and prints the absolute value of total.

System.out.println(Math.abs(total)); EX 3.11. Write code statements to create a DecimalFormat object that will round a formatted value to 4 decimal places. Then write a statement that uses that object to print the value of result, properly formatted.

DecimalFormat fmt = new DecimalFormat("0.####"); System.out.println(fmt.format(result)); EX 3.12. Write code statements that prompt for and read a double value from the user, and then print the result of raising that value to the fourth power. Output the results to 3 decimal places.

Scanner scan = new Scanner(System.in); DecimalFormat fmt = new DecimalFormat("0.###"); System.out.println("Enter a value: "); double num = scan.nextDouble(); System.out.println(fmt.format(Math.pow(num, 4)));

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 3

EX 3.13. Write a declaration for an enumerated type that represents the days of the week. enum Days {sunday, monday, tuesday, wednesday, thursday, friday, saturday} EX 3.14. Compare and contrast a traditional coordinate system and the coordinate system used by Java graphical components.

A traditional coordinate system has the origin in the lower-left corner, with x increasing to the right and y increasing upward. The coordinate system used by Java has the origin in the upper-left corner with x increasing to the right and y increasing downward.

EX 3.15. Write a declaration for each of the following: a.

A line that extends from point (60, 100) to point (30, 90) Line line = new Line(60, 100, 30, 90);

b. A rectangle that is 20 pixels wide, 100 pixels high, and has its upper -left corner at point (10, 10).

Rectangle rect = new Rectangle(10, 10, 20, 100); c.

A circle that is centered at point (50, 75) and has a radius of 30.

Circle circle = new Circle(50, 75, 30);

d. An ellipse that is centered at point (150, 180) and is 100 pixels wide and 80 pixels high.

Ellipse ellipse = new Ellipse(150, 180, 50, 40); EX 3.16. Are the following lines hirizontal, vertical, or neither? a.

new Line(30, 90, 30, 10) vertical

b. new Line(85, 70, 70, 85) neither c.

new Line(20, 40, 150, 40) horizontal

EX 3.17. Is each of the following ellipses wider than it is tall or taller than it is wide? a.

new Ellipse(300, 100, 50, 10) wider than it is tall

b. new Ellipse (100, 200, 20, 40) taller than it is wide c.

new Ellipse (150, 220, 60, 30) wider than it is tall

EX 3.18. How do you make a shape that has no fill color, so tht you can see the elements behind it?

Set its fill color to null: circle.setFill(null); EX 3.19. Write a line of code that rotates an ellipse called myEllipse 45 degrees clockwise.

Java Software Solutions, 9th Edition myEllipse.setRotate(45);

Exercise Solutions, Ch. 3

Java Software Solutions, 9h Edition

Exercise Solutions, Ch. 4

Chapter 4 Exercise Solutions EX 4.1. a.

For each of the following pairs, which represents a class and which represents an object of that class?

Superhero, Superman Class: Superhero, Object: Superman

b. Justin, Person Class: Person, Object: Justin c.

Rover, Pet Class: Pet, Object: Rover

d. Magazine, Time Class: Magazine, Object: Time e.

Christmas, Holiday Class: Holiday, Object: Christmas

EX 4.2.

List some attributes and operations that might be defined for a class called PictureFrame that represents a picture frame.

Attributes could include: height, width, empty (boolean) Operations could include: getHeight, setHeight, getWidth, setWidth, isEmpty, fill

EX 4.3.

List some attributes and operations that might be defined for a class called Meeting that represents a business meeting.

Attributes could include: date, time, location, purpose, attendees (list of People) Operations could include: setters and getters for all attributes, announce, cancel

EX 4.4.

List some attributes and operations that might be defined for a class called Course that represents a college course (not a particular offering of a course, just the course in general).

Attributes could include: courseNumber, courseName, department, numCredits, description Operations could include: setters and getters for all attributes, offer

EX 4.5.

Write a method called lyrics that prints the lyrics of a song when invoked. The method should accept no parameters and return no value. public void lyrics() { System.out.println("The itsy bitsy spider"); System.out.println("Went up the waterspout."); System.out.println("Down came the rain and"); System.out.println("Washed the spider out."); System.out.println("Out came the sun and"); System.out.println("Dried up all the rain."); System.out.println("So the itsy bitsy spider"); System.out.println("Went up the spout again.");

Java Software Solutions, 9h Edition

Exercise Solutions, Ch. 4

} EX 4.6.

Write a method called cube that accepts one integer parameter and returns that value raised to the third power. public int cube(int num) { return Math.pow(num, 3); }

EX 4.7.

Write a method called random100 that returns a random integer in the range of 1 to 100 (inclusive). public int random100() { Random generator = new Random(); return generator.nextInt(100) + 1; }

EX 4.8.

Write a method called randomInRange that accepts two integer parameters representing a range. The method should return a random integer in the specified range (inclusive). Assume that the first parameter is greater than the second. public int randomInRange(int first, int second) { Random generator = new Random(); int range = second – first + 1; return generator.nextInt(range) + first; }

EX 4.9.

Write a method called randomColor that creates and returns a Color object that represents a random color. Recall that a Color object can be defined by three integer values between 0 and 255 representing the contributions of red, green, and blue (its RGB value). final int MAX = 256; public Color randomColor() { Random generator = new Random(); int randRed = generator.nextInt(MAX); int randGreen = generator.nextInt(MAX); int randBlue = generator.nextInt(MAX); return new Color.rgb(randRed, randGreen, randBlue); }

EX 4.10. Suppose you have a class called Movie. Write a constructor for the class that initializes the title and director instance variables based on parameters passed to the constructor.

Java Software Solutions, 9h Edition

Exercise Solutions, Ch. 4

public Movie(String theTitle, String theDirector) { title = theTitle; director = theDirector; } EX 4.11. Suppose you have a class called Child with an instance data value called age.

Write a getter method and a setter method for age. public int getAge() { return age; }

public void setAge(int newAge) { age = newAge; } EX 4.12. Draw a UML class diagram that shows the relationships among the classes used in the Transactions program.

EX 4.13. Write a declaration that creates an Arc object that is centered at point (50, 50) and sweeps across the top half of the underlying ellipse. Base it on an ellipse with a horizontal radius of 40 and a vertical radius of 100.

Arc arc = new Arc(50, 50, 40, 100, 0, 180); EX 4.14. How do you restrict the pixels displayed of an image?

By setting a rectangular viewport on the image view that displays it.

EX 4.15. What is the purpose of a layout pane?

A layout pane is used to organize the visual presentation of the elements in a JavaFX node. For example, a GridPane lays out its elements in a rectangular grid.

EX 4.16. How can a method reference be used to define an event handler?

Java Software Solutions, 9h Edition

Exercise Solutions, Ch. 4

The parameter to a method such as setOnAction is an event handler object.

That parameter could also be a method reference that specifies a particular method to be used as the event handler method that is called when the event occurs. For example: button.setOnAction(this::processButtonClick);

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

Chapter 5 Exercise Solutions EX 5.1

What happens in the MinOfThree program if two or more of the values are equal? If exactly two of the values are equal, does it matter whether the equal values are lower or higher than the third?

If two or more values are equal, the program still prints the lowest value. Because only less than comparisons are made, the comparison of two equal values produces a false result. If two values are equal, and lower than the third value, then one of the two lower but equal values is printed. If all three values are equal, then this value is printed. Which “version” of the equal value is irrelevant.

If only two values are equal, it does not matter whether the third is lower or higher. The correct result is determined in either case. If the two equal values are lower than the third, then one of the two lower but equal values is printed. If the two equal values are higher than the third, then the third value is printed.

EX 5.2

What is wrong with the following code fragment? Rewrite it so that it produces correct output. if (total == MAX) if (total < sum) System.out.println("total == MAX and < sum."); else System.out.println("total is not equal to MAX"); Despite the indentation, the else clause is associated with the immediately preceding if rather than the first if. The program will produce the correct output if it is rewritten as: if (total == MAX) { if (total < sum) System.out.println("total == MAX and < sum."); } else System.out.println("total is not equal to MAX");

EX 5.3

What is wrong with the following code fragment? Will this code compile if it is part of an otherwise valid program? Explain. if (length = MIN_LENGTH) System.out.println("The length is minimal."); The assignment operator (=) is used erroneously in place of the equality operator (==).

Hence, it will not compile in an otherwise valid program.

EX 5.4

What output is produced by the following code fragment? int num = 87, max = 25; if (num >= max*2) System.out.println("apple"); System.out.println("orange"); System.out.println("pear"); The second println statement is improperly indented, so the output produced is:

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

apple orange pear EX 5.5

What output is produced by the following code fragment? int limit = 100, num1 = 15, num2 = 40; if (limit <= limit) { if (num1 == num2) System.out.println("lemon"); System.out.println("lime"); } System.out.println("grape"); The output is: lime grape

EX 5.6

Put the following list of strings in lexicographic order as if determined by the compareTo method of the String class. Consult the Unicode chart in Appendix C. "fred" "Ethel" "?-?-?-?" "{([])}" "Lucy" "ricky" "book" "******" "12345" " " "HEPHALUMP" "bookkeeper" "6789" ";+<?" "^^^^^^^^^^" "hephalump" The strings in lexicographic order: "

"

"******" "12345" "6789" ";+<?" "?-?-?-?"

"Ethel" "HEPHALUMP"

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

"Lucy" "^^^^^^^^^^" "book" "bookkeeper" "fred" "hephalump" "ricky" "{([])}" EX 5.7 What output is produced by the following code fragment? int num = 1, max = 20; while (num < max) { System.out.println(num); num += 4; } The output produced is: 1 5 9 13 17 EX 5.8

What output is produced by the following code fragment? int num = 1, max = 20; while (num < max) { if (num%2 == 0) System.out.println(num); num++; } The output produced is: 2 4 6 8 10 12 14 16 18

EX 5.9

What is wrong with the following code fragment? What are three distinct ways it could be changed to remove the flaw? count = 50;

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

while (count >= 0) { System.out.println(count); count = count + 1; } The loop is infinite because count initially is greater than zero, and continues to increase in value. The flaw can be removed by (1) decrementing rather than incrementing count, (2) initializing count to 0 and using, as the condition of the while loop, count <= 50, and (3) picking an upper limit and using, as the condition of the while loop, count <= upperLimit.

EX 5.10 Write a while loop that verifies that the user enters a positive integer value.

Scanner scan = new Scanner(System.in); System.out.print("Enter a positive integer: "); number = scan.nextInt(); while (number <= 0) { System.out.print("That number was not positive."); System.out.print("Enter a positive integer: "); number = scan.nextInt(); } EX 5.11 Write a code fragment that reads and prints integer values entered by a user until a particular sentinel value (stored in SENTINEL) is entered. Do not print the sentinel value.

Scanner scan = new Scanner(System.in); System.out.print("Enter some integers (" + SENTINEL + " to quit): "); number = scan.nextInt(); while (number != SENTINEL) { System.out.println(number); number = scan.nextInt(); } EX 5.12 Write a method called maxOfTwo that accepts two integer parameters and returns the larger of the two. public int maxOfTwo(int num1, int num2) { int result = num1; if (num2 > num1) result = num2; return result; }

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

Note that the method Math.max also performs this function.

EX 5.13 Write a method called larger that accepts two floating-point parameters (of type double) and returns true if the first parameter is greater than the second, and false otherwise. public boolean larger(double num1, double num2) { return (num1 > num2); } EX 5.14 Write a method called evenlyDivisible that accepts two integer parameters and returns true if the first parameter is evenly divisible by the second, or vice versa, and false otherwise. Return false if either parameter is zero. public boolean evenlyDivisible(int num1, int num2) { boolean result = false; if (num1 != 0 && num2 != 0) if (num1 % num2 == 0 || num2 % num1 == 0) result = true; return result; } EX 5.15 Write a method called isAlpha that accepts a character parameter and returns true if that character is either an uppercase or lowercase alphabetic letter. public boolean isAlpha (char ch) { return ( (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') ); } Note: similar functionality is provided by the Character.isLetter method.

EX 5.16 Write a method called floatEquals that accepts three floating-point values as parameters. The method should return true if the first two parameters are equal within the tolerance of the third parameter. public boolean floatEquals(double float1, double float2, double tolerance) { return (Math.abs(float1 - float2) <= tolerance); } EX 5.17 Write a method called isIsoceles that accepts three integer parameters that represent the lengths of the sides of a triangle. The method returns true if the triangle is isosceles but not equilateral (meaning that exactly two of the sides have an equal length), and false otherwise. public boolean isIsoceles(int side1, int side2, int side3)

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 5

{ boolean result = false; if ( (side1 == side2) && side1 != side3) || (side2 == side3) && side2 != side1) || (side1 == side3) && side1 != side2) ) result = true; return result; } EX 5.18 Would it be better to use check boxes or radio buttons to determine the following? Explain. a.

Your favorite book genre. radio buttons – favorite implies only one should be chosen

b. Whether to make your profile visible or not. check box – with only one option there is no mutual exclusion involved c.

Which image format to use (jpg, png, or gif). radio buttons – only one should be slected

d. Which programming languages you know. check boxes – multiple options may be valid

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

Chapter 6 Exercise Solutions EX 6.1. How many iterations will the following for loops execute? a. for (int i = 0; i < 20; i++) { } 20 iterations b. for (int i = 1; i <= 20; i++) { } 20 iterations c. for (int i = 5; i < 20; i++) { } 15 iterations d. for (int i = 20; i > 0; i--) { } 20 iterations e. for (int i = 1; i < 20; i = i + 2) { } 10 iterations f. for (int i = 1; i < 20; i *= 2) { } 5 iterations EX 6.2. What output is produced by the following code fragment? for (int num = 0; num <= 200; num += 2) System.out.println(num); The output produced is the even numbers from 0 to 200: 0 2 4 and so on until…

198 200 EX 6.3. What output is produced by the following code fragment? for (int val = 200; val >= 0; val -= 1) if (val % 4 != 0) System.out.println(val); The output produced is all values from 200 down to 0, except those that are evenly divisible by 4: 199 198 197 195 and so on until…

5 3 2 1

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

EX 6.4. Transform the following while loop into an equivalent do loop (make sure it produces the same output). int num = 1; while (num < 20) { num++; System.out.println(num); } This code can be written using a do loop as follows: int num = 1; do { num++; System.out.println(num); } while (num < 20); EX 6.5. Transform the while loop from the previous exercise into an equivalent for loop (make sure it produces the same output). for (int num = 2; num <= 20; num ++) System.out.println(num); EX 6.6. Write a do loop that verifies that the user enters an even integer value.

Scanner scan = new Scanner(System.in); do { System.out.print("Enter an even integer: "); number = scan.nextInt(); } while {number%2 != 0); EX 6.7. Write a for loop to print the odd numbers from 1 to 99 (inclusive). for (int value = 1; value <= 99; value +=2) System.out.println(value); EX 6.8. Write a for loop to print the multiples of 3 from 300 down to 3. for (int value = 300; value >= 3, value -= 3) System.out.println(value); EX 6.9. Write a code fragment that reads 10 integer values from the user and prints the highest value entered.

Scanner scan = new Scanner(System.in); int max, number; System.out.print("Enter an integer: "); max = scan.nextInt();

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

for (int count = 2; count <= 10; count++) { System.out.print ("Enter another integer: "); number = scan.nextInt(); if (number > max) max = number; } System.out.println("The highest value is :" + max); EX 6.10.

Write a code fragment that determines and prints the number of times the character 'a' appears in a String object called name. int count = 0; for (int index = 0; index < name.length(); index++) if (name.charAt(index) == 'a') count++; System.out.println("The character \'a\' appears " + count + " time(s)"); EX 6.11.

Write a code fragment that prints the characters stored in a String object called str backwards. for (int index = str.length()-1; index >= 0; index--) System.out.print(str.charAt(index)); System.out.println(); EX 6.12.

Write a code fragment that prints every other character in a String object called word starting with the first character. for (int index = 0; index < word.length(); index +=2) System.out.println(word.charAt(index)); EX 6.13.

Write a method called powersOfTwo that prints the first 10 powers of 2 (starting with 2). The method takes no parameters and doesn't return anything. public void powersOfTwo() { int base = 2; for (int power = 1; power <= 10; power++) System.out.println(Math.pow(base,power)); } Alternate answer: public void powersOfTwo() { int num = 2; for (int power = 1; power <= 10; power++) { num *= 2; System.out.println(num); }

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

} EX 6.14.

Write a method called alarm that prints the string "Alarm!" multiple times on separate lines. The method should accept an integer parameter that specifies how many times the string is printed. Print an error message if the parameter is less than 1. public void alarm(int number) { if (number < 1) System.out.println("ERROR: Number is less than 1."); else for (int count = 1; count <= number; count++) System.out.println("Alarm!"); } EX 6.15.

Write a method called sum100 that returns the sum of the integers from 1 to 100, inclusive. public int sum100() { int sum = 0; for (int count = 1; count <= 100; count++) sum += count; return sum; } EX 6.16.

Write a method called sumRange that accepts two integer parameters that represent a range. Issue an error message and return zero if the second parameter is less than the first. Otherwise, the method should return the sum of the integers in that range (inclusive). public int sumRange(int start, int end) { int sum = 0; if (end < start) System.out.println("ERROR: Invalid Range”); else for (int num = start; num <= end; num++) sum += num; return sum; } EX 6.17.

Write a method called countA that accepts a String parameter and returns the number of times the character 'A' is found in the string. public int countA(String text) { int count = 0;

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

for (int index = 0; index < text.length(); index++) if (text.charAt(index) == 'A') count++; return count; } EX 6.18.

Write a method called reverse that accepts a String parameter and returns a string that contains the characters of the parameter in reverse order.

Note that there is a method in the String class that performs this operation, but for the sake of this exercise, you are expected to write your own. public String reverse(String text) { String result = ""; for (int place = text.length()-1; place >= 0; place--) result += text.charAt(place); return result; } EX 6.19.

In the Bullseye program, what is the fill color of the innermost circle before it is changed to red? Explain.

The innermost circle is initially white before it is changed to red. The colors alternate, and the previous color was black.

EX 6.20.

Given the way the Boxes program is written, what color will a rectangle be if it is both narrow and short? Explain.

A box that is both narrow and short will be colored yellow because that's the characteristic that is checked first. If the box is norrow, the height of the box is not checked.

EX 6.21.

Rewrite the if statement used in the Boxes program so that if a box is both narrow and short, its fill color will be orange. Otherwise, keep narrow boxes yellow and short boxes green. if (width < 10 && height < 10) fill = Color.ORANGE; else if (width < 10) fill = Color.YELLOW; else if (height < 10) fill = Color.GREEN; EX 6.22.

Write code that will shift a Rectangle named rec 50 pixels right and 10 pixels down, rotate it 45 degrees clockwise, and display it at half its original size. rec.setTranslateX(50); rec.setTranslateY(10); rec.setScaleX(0.5);

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 6

rec.setScaleY(0.5); EX 6.23.

Write code that will invert (turn upside down) an ImageView named pic and display it at twice its original size. pic.setRotate(180); pic.setScaleX(2.0); pic.setScaleY(2.0); EX 6.24.

What happens when you apply a transformation to a group?

The transformation is applied to each node in the group.

Chapter 7: Object-Oriented Design Lab Exercises Topics

Lab Exercises

Parameter Passing

Changing People

Interfaces

Using the Comparable Interface

Method Decomposition

A Modified MiniQuiz Class

Overloading

A Flexible Account Class A Biased Coin

Static Variables and Methods

Opening and Closing Accounts Counting Transactions Transfering Funds

Overall class design

Random Walks

GUI Layouts

Telephone Keypad

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Chapter 7: Object-Oriented Design

Changing People The file ChangingPeople.java contains a program that illustrates parameter passing. The program uses Person objects defined in the file Person.java. Do the following: 1.

2.

3.

Trace the execution of the program using diagrams similar to those in Figure 6.5 of the text (which is a trace of the program in Listings 6.15–6.17). Also show what is printed by the program.

Compile and run the program to see if your trace was correct.

Modify the changePeople method so that it does what the documentation says it does, that is, the two Person objects passed in as actual parameters are actually changed.

// ****************************************************************** // ChangingPeople.java // // Demonstrates parameter passing -- contains a method that should // change to Person objects. // ****************************************************************** public class ChangingPeople { // // Sets up two person objects, one integer, and one String // object. These are sent to a method that should make // some changes. // public static void main (String[] args) { Person person1 = new Person ("Sally", 13); Person person2 = new Person ("Sam", 15); int age = 21; String name = "Jill"; System.out.println ("\nParameter Passing... Original values..."); System.out.println ("person1: " + person1); System.out.println ("person2: " + person2); System.out.println ("age: " + age + "\tname: " + name + "\n"); changePeople (person1, person2, age, name); System.out.println ("\nValues after calling changePeople..."); System.out.println ("person1: " + person1); System.out.println ("person2: " + person2); System.out.println ("age: " + age + "\tname: " + name + "\n"); } // // Change the first actual parameter to "Jack - Age 101" and change // the second actual parameter to be a person with the age and // name given in the third and fourth parameters. // public static void changePeople (Person p1, Person p2, int age, String name) { System.out.println ("\nInside changePeople... Original parameters..."); System.out.println ("person1: " + p1); System.out.println ("person2: " + p2); System.out.println ("age: " + age + "\tname: " + name + "\n");

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// Make changes Person p3 = new Person (name, age); p2 = p3; name = "Jack"; age = 101; p1.changeName (name); p1.changeAge (age); // Print changes System.out.println ("\nInside changePeople... Changed values..."); System.out.println ("person1: " + p1); System.out.println ("person2: " + p2); System.out.println ("age: " + age + "\tname: " + name + "\n"); } } // ************************************************************ // Person.java // // A simple class representing a person. // ************************************************************ public class Person { private String name; private int age; // // Sets up a Person object with the given name and age. // public Person (String name, int age) { this.name = name; this.age = age; } // // Changes the name of the Person to the parameter newName. // public void changeName(String newName) { name = newName; } // // Changes the age of the Person to the parameter newAge. // public void changeAge (int newAge) { age = newAge; } // // Returns the person's name and age as a string. // public String toString() { return name + " - Age " + age; } } 104

Chapter 7: Object-Oriented Design

Using the Comparable Interface 1.

Write a class Compare3 that provides a static method largest. Method largest should take three Comparable parameters and return the largest of the three (so its return type will also be Comparable). Recall that method compareTo is part of the Comparable interface, so largest can use the compareTo method of its parameters to compare them.

2.

Write a class Comparisons whose main method tests your largest method above.

• First prompt the user for and read in three strings, use your largest method to find the largest of the three strings, and print it out. (It’s easiest to put the call to largest directly in the call to println.) Note that since largest is a static method, you will call it through its class name, e.g., Compare3.largest(val1, val2, val3).

• Add code to also prompt the user for three integers and try to use your largest method to find the largest of the three integers. Does this work? If it does, it’s thanks to autoboxing, which is Java 1.5’s automatic conversion of ints to Integers. You may have to use the -source 1.5 compiler option for this to work.

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A Modified MiniQuiz Class Files Question.java, Complexity.java, and MiniQuiz.java contain the classes in Listings 6.8-6.10of the text. These classes demonstrate the use of the Complexity interface; class Question implements the interface, and class MiniQuiz creates two Question objects and uses them to give the user a short quiz.

Save these three files to your directory and study the code in MiniQuiz.java. Notice that after the Question objects are created, almost exactly the same code appears twice, once to ask and grade the first question, and again to ask and grade the second question. Another approach is to write a method askQuestion that takes a Question object and does all the work of asking the user the question, getting the user’s response, and determining whether the response is correct. You could then simply call this method twice, once for q1 and once for q2. Modify the MiniQuiz class so that it has such an askQuestion method, and replace the code in main that asks and grades the questions with two calls to askQuestion. Some things to keep in mind: □ □

The definition of askQuestion should be inside the MiniQuiz class but after the main method.

Since main is a static method, askQuestion must be static too. (A static method cannot call an instance method of the same class.) Also, askQuestion is for use only by this class, so it should be declared private. So the header for askQuestion should look like this: private static void askQuestion(Question question)

• • •

String possible, which is currently declared in main, will need to be defined in askQuestion instead.

The Scanner object scan needs to be a static variable and moved outside of main (so it is available to askQuestion).

You do not need to make any changes to Question.java or Complexity .java.

//**************************************************************** // Question.java Author: Lewis/Loftus // // Represents a question (and its answer). //**************************************************************** public class Question implements Complexity { private String question, answer; private int complexityLevel; //-------------------------------------------------------------// Sets up the question with a default complexity. //-------------------------------------------------------------public Question (String query, String result) { question = query; answer = result; complexityLevel = 1; } //-------------------------------------------------------------// Sets the complexity level for this question. //-------------------------------------------------------------public void setComplexity (int level) { complexityLevel = level; } //-------------------------------------------------------------// Returns the complexity level for this question. //-------------------------------------------------------------public int getComplexity() 106

Chapter 7: Object-Oriented Design

{ return complexityLevel; } //-------------------------------------------------------------// Returns the question. //-------------------------------------------------------------public String getQuestion() { return question; } //-------------------------------------------------------------// Returns the answer to this question. //-------------------------------------------------------------public String getAnswer() { return answer; } //-------------------------------------------------------------// Returns true if the candidate answer matches the answer. //-------------------------------------------------------------public boolean answerCorrect (String candidateAnswer) { return answer.equals(candidateAnswer); } //-------------------------------------------------------------// Returns this question (and its answer) as a string. //-------------------------------------------------------------public String toString() { return question + "\n" + answer; } } //***************************************************************** // Complexity.java Author: Lewis/Loftus // // Represents the interface for an object that can be assigned an // explicit complexity. //***************************************************************** public interface Complexity { public void setComplexity (int complexity); public int getComplexity(); }

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//***************************************************************** // MiniQuiz.java Author: Lewis/Loftus // // Demonstrates the use of a class that implements an interface. //***************************************************************** import java.util.Scanner; public class MiniQuiz { //-------------------------------------------------------------// Presents a short quiz. //-------------------------------------------------------------public static void main (String[] args) { Question q1, q2; String possible; Scanner scan = new Scanner(System.in); q1 = new Question ("What is the capital of Jamaica?", "Kingston"); q1.setComplexity (4); q2 = new Question ("Which is worse, ignorance or apathy?", "I don't know and I don't care"); q2.setComplexity (10); System.out.print (q1.getQuestion()); System.out.println (" (Level: " + q1.getComplexity() + ")"); possible = scan.nextLine(); if (q1.answerCorrect(possible)) System.out.println ("Correct"); else System.out.println ("No, the answer is " + q1.getAnswer()); System.out.println(); System.out.print (q2.getQuestion()); System.out.println (" (Level: " + q2.getComplexity() + ")"); possible = scan.nextLine(); if (q2.answerCorrect(possible)) System.out.println ("Correct"); else System.out.println ("No, the answer is " + q2.getAnswer ()); } }

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A Flexible Account Class File Account.java contains a definition for a simple bank account class with methods to withdraw, deposit, get the balance and account number, and return a String representation. Note that the constructor for this class creates a random account number. Save this class to your directory and study it to see how it works. Then modify it as follows: 1.

Overload the constructor as follows: • public Account (double initBal, String owner, long number) - initializes the balance, owner, and account number as specified • public Account (double initBal, String owner) - initializes the balance and owner as specified; randomly generates the account number.

• public Account (String owner) - initializes the owner as specified; sets the initial balance to 0 and randomly generates the account number.

2.

Overload the withdraw method with one that also takes a fee and deducts that fee from the account.

File TestAccount.java contains a simple program that exercises these methods. Save it to your directory, study it to see what it does, and use it to test your modified Account class. //************************************************************ // Account.java // // A bank account class with methods to deposit to, withdraw from, // change the name on, and get a String representation // of the account. //************************************************************ public class Account { private double balance; private String name; private long acctNum; //------------------------------------------------//Constructor -- initializes balance, owner, and account number //------------------------------------------------public Account(double initBal, String owner, long number) { balance = initBal; name = owner; acctNum = number; } //------------------------------------------------// Checks to see if balance is sufficient for withdrawal. // If so, decrements balance by amount; if not, prints message. //------------------------------------------------public void withdraw(double amount) { if (balance >= amount) balance -= amount; else System.out.println("Insufficient funds"); } //------------------------------------------------// Adds deposit amount to balance. //------------------------------------------------Chapter 7: Object-Oriented Design

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public void deposit(double amount) { balance += amount; } //------------------------------------------------// Returns balance. //------------------------------------------------public double getBalance() { return balance; } //------------------------------------------------// Returns a string containing the name, account number, and balance. //------------------------------------------------public String toString() { return "Name:" + name + "\nAccount Number: " + acctNum + "\nBalance: " + balance; } }

//************************************************************ // TestAccount.java // // A simple driver to test the overloaded methods of // the Account class. //************************************************************ import java.util.Scanner; public class TestAccount { public static void main(String[] args) { String name; double balance; long acctNum; Account acct; Scanner scan = new Scanner(System.in); System.out.println("Enter account holder's first name"); name = scan.next(); acct = new Account(name); System.out.println("Account for " + name + ":"); System.out.println(acct); System.out.println("\nEnter initial balance"); balance = scan.nextDouble(); acct = new Account(balance,name); System.out.println("Account for " + name + ":"); System.out.println(acct);

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System.out.println("\nEnter account number"); acctNum = scan.nextLong(); acct = new Account(balance,name,acctNum); System.out.println("Account for " + name + ":"); System.out.println(acct); System.out.print("\nDepositing 100 into account, balance is now "); acct.deposit(100); System.out.println(acct.getBalance()); System.out.print("\nWithdrawing $25, balance is now "); acct.withdraw(25); System.out.println(acct.getBalance()); System.out.print("\nWithdrawing $25 with $2 fee, balance is now "); acct.withdraw(25,2); System.out.println(acct.getBalance()); System.out.println("\nBye!"); } }

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Modifying the Coin Class 1.

Create a new class named BiasedCoin that models a biased coin (heads and tails are not equally likely outcomes of a flip). To do this modify the coin class from the Listing 5.4 of text (in the file Coin.java) as follows: □ Add a private data member bias of type double. This data member will be a number between 0 and 1 (inclusive) that represents the probability the coin will be HEADS when flipped. So, if bias is 0.5, the coin is an ordinary fair coin.

If bias is 0.6, the coin has probability 0.6 of coming up heads (on average, it comes up heads 60% of the time). □ Modify the default constructor by assigning the value 0.5 to bias before the call to flip. This will make the default coin a fair one. □ Modify flip so that it generates a random number then assigns face a value of HEADS if the number is less than the bias; otherwise it assigns a value of TAILS. □ Add a second constructor with a single double parameter—that parameter will be the bias. If the parameter is valid (a number between 0 and 1 inclusive) the constructor should assign the bias data member the value of the parameter; otherwise it should assign bias a value of 0.5. Call flip (as the other constructor does) to initialize the value of face.

2.

Compile your class to make sure you have no syntax errors.

3.

Write a program that uses three BiasedCoin objects. Instantiate one as a fair coin using the constructor with no parameter. Read in the biases for the other two coins and instantiate those coins using the constructor with the bias as a parameter. Your program should then have a loop that flips each coin 100 times and counts the number of times each is heads. After the loop print the number of heads for each coin. Run the program several times testing out different biases.

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Opening and Closing Accounts File Account.java (see previous exercise) contains a definition for a simple bank account class with methods to withdraw, deposit, get the balance and account number, and return a String representation. Note that the constructor for this class creates a random account number. Save this class to your directory and study it to see how it works. Then write the following additional code: 1.

Suppose the bank wants to keep track of how many accounts exist. a. b. c. d.

Declare a private static integer variable numAccounts to hold this value. Like all instance and static variables, it will be initialized (to 0, since it’s an int) automatically.

Add code to the constructor to increment this variable every time an account is created.

Add a static method getNumAccounts that returns the total number of accounts. Think about why this method should be static - its information is not related to any particular account.

File TestAccounts1.java contains a simple program that creates the specified number of bank accounts then uses the getNumAccounts method to find how many accounts were created. Save it to your directory, then use it to test your modified Account class.

2.

Add a method void close() to your Account class. This method should close the current account by appending “CLOSED” to the account name and setting the balance to 0. (The account number should remain unchanged.) Also decrement the total number of accounts.

3.

Add a static method Account consolidate(Account acct1, Account acct2) to your Account class that creates a new account whose balance is the sum of the balances in acct1 and acct2 and closes acct1 and acct2. The new account should be returned. Two important rules of consolidation: • Only accounts with the same name can be consolidated. The new account gets the name on the old accounts but a new account number.

• Two accounts with the same number cannot be consolidated. Otherwise this would be an easy way to double your money!

Check these conditions before creating the new account. If either condition fails, do not create the new account or close the old ones; print a useful message and return null.

4.

Write a test program that prompts for and reads in three names and creates an account with an initial balance of $ 100 for each. Print the three accounts, then close the first account and try to consolidate the second and third into a new account.

Now print the accounts again, including the consolidated one if it was created.

//************************************************************ // TestAccounts1 // A simple program to test the numAccts method of the // Account class. //************************************************************ import java.util.Scanner; public class TestAccounts1 { public static void main(String[] args) { Account testAcct; Scanner scan = new Scanner(System.in);

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System.out.println("How many accounts would you like to create?"); int num = scan.nextInt(); for (int i=1; i<=num; i++) { testAcct = new Account(100, "Name" + i); System.out.println("\nCreated account " + testAcct); System.out.println("Now there are " + Account.numAccounts () + " accounts"); } } }

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Counting Transactions File Account.java (see A Flexible Account Class exercise) contains a definition for a simple bank account class with methods to withdraw, deposit, get the balance and account number, and return a String representation. Note that the constructor for this class creates a random account number. Save this class to your directory and study it to see how it works.

Now modify it to keep track of the total number of deposits and withdrawals (separately) for each day, and the total amount deposited and withdrawn. Write code to do this as follows: 1.

Add four private static variables to the Account class, one to keep track of each value above (number and total amount of deposits, number and total of withdrawals). Note that since these variables are static, all of the Account objects share them. This is in contrast to the instance variables that hold the balance, name, and account number; each Account has its own copy of these. Recall that numeric static and instance variables are initialized to 0 by default.

2.

Add public methods to return the values of each of the variables you just added, e.g., public static int getNumDeposits().

3.

Modify the withdraw and deposit methods to update the appropriate static variables at each withdrawal and deposit

4.

File ProcessTransactions.java contains a program that creates and initializes two Account objects and enters a loop that allows the user to enter transactions for either account until asking to quit. Modify this program as follows: □ After the loop, print the total number of deposits and withdrawals and the total amount of each. You will need to use the Account methods that you wrote above. Test your program. □ Imagine that this loop contains the transactions for a single day. Embed it in a loop that allows the transactions to be recorded and counted for many days. At the beginning of each day print the summary for each account, then have the user enter the transactions for the day. When all of the transactions have been entered, print the total numbers and amounts (as above), then reset these values to 0 and repeat for the next day. Note that you will need to add methods to reset the variables holding the numbers and amounts of withdrawals and deposits to the Account class.

Think: should these be static or instance methods?

//************************************************************ // ProcessTransactions.java // // A class to process deposits and withdrawals for two bank // accounts for a single day. //************************************************************ import java.util.Scanner; public class ProcessTransactions { public static void main(String[] args){ Account acct1, acct2; String keepGoing = "y"; String action; double amount; long acctNumber;

//two test accounts //more transactions? //deposit or withdraw //how much to deposit or withdraw //which account to access

Scanner scan = new Scanner(System.in); //Create two accounts acct1 = new Account(1000, "Sue", 123); acct2 = new Account(1000, "Joe", 456); System.out.println( "The following accounts are available: \n" ); acct1.printSummary(); System.out.println(); acct2.printSummary(); Chapter 7: Object-Oriented Design

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while (keepGoing.equals("y") || keepGoing.equals("y")) { //get account number, what to do, and amount System.out.print("\nEnter the number of the account you would like to access: "); acctNumber = scan.nextLong(); System.out.print("Would you like to make a deposit (D) or withdrawal (W) ? "); action = scan.next(); System.out.print("Enter the amount: "); amount = scan.nextDouble(); if (amount > 0) if (acctNumber == acct1.getAcctNumber()) if (action.equals("w") || action.equals("W")) acct1.withdraw(amount); else if (action.equals("d") || action.equals("D")) acct1.deposit(amount); else System.out.println("Sorry, invalid action."); else if (acctNumber == acct2.getAcctNumber()) if (action.equals("w") || action.equals("W")) acct1.withdraw(amount); else if (action.equals("d") || action.equals("D")) acct1.deposit(amount); else System.out.println( "Sorry, invalid action. "); else System.out.println( "Sorry, invalid account number. "); else System.out.println("Sorry, amount must be > 0 . "); System.out.print("\nMore transactions? (y/n)"); keepGoing = scan.next(); } //Print number of deposits //Print number of withdrawals //Print total amount of deposits //Print total amount of withdrawals } }

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Transfering Funds File Account.java (see A Flexible Account Class exercise) contains a definition for a simple bank account class with methods to withdraw, deposit, get the balance and account number, and print a summary. Save it to your directory and study it to see how it works. Then write the following additional code: 1.

Add a method public void transfer(Account acct, double amount) to the Account class that allows the user to transfer funds from one bank account to another. If acct1 and acct2 are Account objects, then the call acct1.transfer(acct2,957.80) should transfer $957.80 from acct1 to acct2. Be sure to clearly document which way the transfer goes!

2.

Write a class TransferTest with a main method that creates two bank account objects and enters a loop that does the following: □ Asks if the user would like to transfer from account1 to account2, transfer from account2 to account1, or quit. □ If a transfer is chosen, asks the amount of the transfer, carries out the operation, and prints the new balance for each account. □ Repeats until the user asks to quit, then prints a summary for each account.

3.

Add a static method to the Account class that lets the user transfer money between two accounts without going through either account. You can (and should) call the method transfer just like the other one - you are overloading this method.

Your new method should take two Account objects and an amount and transfer the amount from the first account to the second account. The signature will look like this: public static void transfer(Account acct1, Account acct2, double amount) Modify your TransferTest class to use the static transfer instead of the instance version.

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Random Walks In this lab you will develop a class that models a random walk and write two client programs that use the class. A random walk is basically a sequence of steps in some enclosed space where the direction of each step is random. The walk terminates either when a maximum number of steps has been taken or a step goes outside of the boundary of the space. Random walks are used to model physical phenomena such as the motion of molecules and economic phenomena such as stock prices.

We will assume that the random walk takes place on a square grid with the point (0,0) at the center. The boundary of the square will be a single integer that represents the maximum x and y coordinate for the current position on the square (so for a boundary value of 10, both the x and y coordinates can vary from -10 to 10, inclusive). Each step will be one unit up, one unit down, one unit to the left, or one unit to the right. (No diagonal movement.)

The RandomWalk class will have the following instance data (all type int): • • • • •

the x coordinate of the current position the y coordinate of the current position the maximum number of steps in the walk the number of steps taken so far in the walk the boundary of the square (a positive integer -- the x and y coordinates of the position can vary between plus and minus this value)

Create a new file RandomWalk.java. You’ll define the RandomWalk class incrementally testing each part as you go.

1.

First declare the instance data (as described above) and add the following two constructors and toString method.  RandomWalk (int max, int edge) - Initializes the RandomWalk object. The maximum number of steps and the boundary are given by the parameters. The x and y coordinates and the number of steps taken should be set to 0.  RandomWalk (int max, int edge, int startX, int startY) -- Initializes the maximum number of steps, the boundary, and the starting position to those given by the parameters.  String toString() - returns a String containing the number of steps taken so far and the current position -The string should look something like: Steps: 12; Position: (-3,5)

2.

Compile what you have so far then open the file TestWalk.java. This file will be used to test your RandomWalk methods. So far it prompts the user to enter a boundary, a maximum number of steps, and the x and y coordinates of a position. Add the following:  Declare and instantiate two RandomWalk objects -- one with boundary 5, maximum steps 10, and centered at the origin (use the two parameter constructor) and the other with the values entered by the user.  Print out each object. Note that you won’t get any information about the boundary or maximum number of steps (think about what your toString method does), but that’s ok.

Compile and run the program to make sure everything is correct so far.

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3.

Next add the following method to the RandomWalk class: void takeStep(). This method simulates taking a single step either up, down, left, or right. To “take a step” generate a random number with 4 values (say 0, 1,2, 3) then use a switch statement to change the position (one random value will represent going right, one left, and so on). Your method should also increment the number of steps taken.

4.

Add a for loop to TestWalk.java to have each of your RandomWalk objects take 5 steps. Print out each object after each step so you can see what is going on. Compile and run the program to make sure it is correct so far.

5.

Now add to RandomWalk.java the following two methods. Each should be a single return statement that returns the value of a boolean expression.  boolean moreSteps() - returns true if the number of steps taken is less than the maximum number; returns false otherwise

Chapter 7: Object-Oriented Design

 boolean inBounds() - returns true if the current position is on the square (include the boundary as part of the square); returns false otherwise.

6. Add to the RandomWalk class a method named walk that has no parameters and returns nothing. Its job is to simulate a complete random walk. That is, it should generate a sequence of steps as long the maximum number of steps has not been taken and it is still in bounds (inside the square). This should be a very simple loop (while or do... while) --- you will need to call the methods takeStep, moreSteps, and inBounds.

7. Add to TestWalk.java a statement to instantiate a RandomWalk object with a boundary of 10 and 200 as the maximum number of steps. (You may want to comment out most of the code currently in TestWalk -- especially the user input and the loop that takes five steps -- as the walk method will be easier to test on its own. The /* ... */ style of comment is useful for this. But don’t delete that other code, as you’ll need it later in the lab.) Then add a statement to have the object walk. Print the object after the walk. Compile and run the program. Run it more than once -- you should be able to tell by the value printed whether the object went out of bounds or whether it stopped because it reached the maximum number of steps.

8. Now write a client program in a file named DrunkenWalk.java. The program should simulate a drunk staggering randomly on some sort of platform (imagine a square dock in the middle of a lake). The goal of the program is to have the program simulate the walk many times (because of randomness each walk is different) and count the number of times the drunk falls off the platform (goes out of bounds). Your program should read in the boundary, the maximum number of steps, and the number of drunks to simulate. It should then have a loop (a for loop would be a good idea) that on each iteration instantiates a new RandomWalk object to represent a drunk, has the object walk, then determines whether or not the drunk fell off the platform (and updates a counter if it did). After the loop print out the number of times the drunk fell off. Compile and run your program. To see the “randomness” you should run it several times. Try input of 10 for the boundary and 200 for the number of steps first (sometimes the drunk falls off, sometimes not); try 10 for the boundary and 500 for the steps (you should see different behavior); try 50 for the boundary and 200 for the steps (again different behavior).

9. Now write a second client program in a file named Collisions.java. This program should simulate two particles moving in space. Its goal is to determine the number of times the two particles collide (occupy exactly the same position after the same number of steps -- the steps could be thought of as simulating time). We’ll assume the particles are in a very large space so use a large number for the boundary (such as 2,000,000). Use 100,000 for the maximum number of steps. (Don’t enter the commas.) Start one particle at (-3, 0) and the other at (3, 0). (You can hardcode these values into the program; no need to enter them.) Your program should contain a loop that has each particle take a step as long as the particles have not exceeded the maximum number of steps. The program then determines how often the particles have collided. Note that in order for your program to know whether or not the two different RandomWalk objects are in the same place it needs to be able to find out the position. Hence, you need to add the following two methods to the RandomWalk class.  int getX() - returns the x coordinate of the current position  int getY() - returns the y coordinate of the current position Compile and run your program to make sure it works. As before run it several times.

10. In your Collisions.java program the condition to determine if the points are at the same position is a bit cumbersome.

This is something that would be best put in a separate method. Add a static method to Collisions.java (after the main method) with signature public static boolean samePosition (RandomWalk p 1, RandomWalk p2) The method should return true if p1 and p2 are at the same position and return false otherwise. Modify your main method so it calls samePosition rather than directly testing to see if the objects are at the same position. Test the program.

11. In using random walks to simulate behavior it is often of interest to know how far away from the origin the object gets as it moves.

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a. b.

c.

d.

Add an instance variable maxDistance (type int) to the RandomWalk class. This should be set to 0 in each constructor.

Now the takeStep method needs to update this maximum when a step is taken. We’ll add a support method to the class to do this. Add a private method named max that takes two integer parameters (say num1 and num2) and returns the largest of the two.

Add code to takeStep to update maxDistance. This can be done in a single statement using the max method -- the new value of maxDistance should be the maximum of 1) the old value of maxDistance, and 2) the current distance to the origin. Note that if the current point is (-3, 15) the distance to the origin is 15; if the current point is (-10, 7) the distance to the origin is 10. Remember that Math.abs returns the absolute value of a number.

Finally add an accessor method to return that distance so a client program can access it: public int getMaxDistance()

e.

Test the maximum by adding statements in TestWalk.java to get and print the maximum distance for each of the objects after the loop that had them take and print out 5 steps (this way you can see if the maximum is correct - each step is printed).

// ************************************************************ // TestWalk.java // // Program to test methods in the RandomWalk class. // ************************************************************ import java.util.Scanner; public class TestWalk { public static void main (String[] args) { int maxSteps; // maximum number of steps in a walk int maxCoord; // the maximum x and y coordinate int x, y; // starting x and y coordinates for a walk Scanner scan = new Scanner(System.in); System.out.println ("\nRandom Walk Test Program"); System.out.println (); System.out.print ("Enter the boundary for the square: "); maxCoord = scan.nextInt(); System.out.print ("Enter the maximum number of steps: "); maxSteps = scan.nextInt(); System.out.print ("Enter the starting x and y coordinates with " + "a space between: "); x = scan.nextInt(); y = scan.nextInt(); } }

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Telephone Keypad Files Telephone.java and TelephonePanel.java contain the skeleton for a program to lay out a GUI that looks like telephone keypad with a title that says “Your Telephone!!”. Save these files to your directory. Telephone.java is complete, but TelephonePanel.java is not.

1.

Using the comments as a guide, add code to TelephonePanel.java to create the GUI. Some things to consider: a. TelephonePanel (the current object, which is a JPanel) should get a BorderLayout to make it easy to separate the title from the keypad. The title will go in the north area and the keypad will go in the center area. The other areas will be unused. b. You can create a JLabel containing the title and add it directly to the north section of the TelephonePanel.

However, to put the keypad in the center you will first need to create a new JPanel and add the keys (each a button) to it, then add it to the center of the TelephonePanel. This new panel should have a 4×3 GridLayout. c. Your keypad should hold buttons containing 1 2 3, 4 5 6, 7 8 9, * 0 # in the four rows respectively. So you’ll create a total of 12 buttons.

2.

Compile and run Telephone.java. You should get a small keypad and title. Grow the window (just drag the corner) and see how the GUI changes - everything grows proportionately.

3.

Note that the title is not centered, but it would look nicer if it were. One way to do this is to create a new JPanel, add the title label to it, then add the new JPanel to the north area of the TelephonePanel (instead of adding the label directly).

This works because the default layout for a JPanel is a centered FlowLayout, and the JPanel itself will expand to fill the whole north area. Modify your program in this way so that the title is centered.

//************************************************************ // Telephone.java // // Uses the TelephonePanel class to create a (functionless) GUI // like a telephone keypad with a title. // Illustrates use of BorderLayout and GridLayout. //************************************************************ import javax.swing.*; public class Telephone { public static void main(String[] args) { JFrame frame = new JFrame("Telephone"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(new TelephonePanel()); frame.pack(); frame.setVisible(true); } }

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//************************************************************ // TelephonePanel.java // // Lays out a (functionless) GUI like a telephone keypad with a title. // Illustrates use of BorderLayout and GridLayout. //************************************************************ import java.awt.*; import javax.swing.*; public class TelephonePanel extends JPanel { public TelephonePanel() { //set BorderLayout for this panel //create a JLabel with "Your Telephone" title //add title label to north of this panel //create panel to hold keypad and give it a 4x3 GridLayout //add buttons representing keys to key panel //add key panel to center of this panel } }

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Chapter 8: Arrays Lab Exercises Topics

Lab Exercises

One-Dimensional Arrays

Tracking Sales Grading Quizzes Reversing an Array Adding To and Removing From an Integer List

Arrays of Objects

A Shopping Cart

Command Line Arguments

Averaging Numbers

Variable Length Parameter Lists

Exploring Variable Length Parameter Lists

Two-Dimensional Arrays

Magic Squares

Polygons & Polylines

A Polygon Person

Arrays & GUIs

An Array of Radio Buttons

Mouse Events

Drawing Circles with Mouse Clicks Moving Circles with the Mouse

Key Events

Moving a Stick Figure

Chapter 8: Arrays

Tracking Sales File Sales.java contains a Java program that prompts for and reads in the sales for each of 5 salespeople in a company. It then prints out the id and amount of sales for each salesperson and the total sales. Study the code, then compile and run the program to see how it works. Now modify the program as follows: 1.

2.

3.

4.

5.

6.

Compute and print the average sale. (You can compute this directly from the total; no loop is necessary.)

Find and print the maximum sale. Print both the id of the salesperson with the max sale and the amount of the sale, e.g., “Salesperson 3 had the highest sale with $4500.” Note that you don’t need another loop for this; you can do it in the same loop where the values are read and the sum is computed.

Do the same for the minimum sale.

After the list, sum, average, max and min have been printed, ask the user to enter a value. Then print the id of each salesperson who exceeded that amount, and the amount of their sales. Also print the total number of salespeople whose sales exceeded the value entered.

The salespeople are objecting to having an id of 0—no one wants that designation. Modify your program so that the ids run from 1-5 instead of 0-4. Do not modify the array—just make the information for salesperson 1 reside in array location 0, and so on.

Instead of always reading in 5 sales amounts, at the beginning ask the user for the number of sales people and then create an array that is just the right size. The program can then proceed as before.

// *************************************************************** // Sales.java // // Reads in and stores sales for each of 5 salespeople. Displays // sales entered by salesperson id and total sales for all salespeople. // // *************************************************************** import java.util.Scanner; public class Sales { public static void main(String[] args) { final int SALESPEOPLE = 5; int[] sales = new int[SALESPEOPLE]; int sum; Scanner scan = new Scanner(System.in); for (int i=0; i<sales.length; i++) { System.out.print("Enter sales for salesperson " + i + ": "); sales[i] = scan.nextInt(); } System.out.println("\nSalesperson Sales"); System.out.println(" ------------------- "); sum = 0; for (int i=0; i<sales.length; i++) { System.out.println(" " + i + " sum += sales[i]; } System.out.println("\nTotal sales: " + sum); } }

Chapter 8: Arrays

" + sales[i]);

Grading Quizzes Write a program that grades arithmetic quizzes as follows: 1.

2.

3.

4.

Ask the user how many questions are in the quiz.

Ask the user to enter the key (that is, the correct answers). There should be one answer for each question in the quiz, and each answer should be an integer. They can be entered on a single line, e.g., 34 7 13 100 81 3 9 10 321 12 might be the key for a 10-question quiz. You will need to store the key in an array.

Ask the user to enter the answers for the quiz to be graded. As for the key, these can be entered on a single line. Again there needs to be one for each question. Note that these answers do not need to be stored; each answer can simply be compared to the key as it is entered.

When the user has entered all of the answers to be graded, print the number correct and the percent correct.

When this works, add a loop so that the user can grade any number of quizzes with a single key. After the results have been printed for each quiz, ask “Grade another quiz? (y/n).”

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Reversing an Array Write a program that prompts the user for an integer, then asks the user to enter that many values. Store these values in an array and print the array. Then reverse the array elements so that the first element becomes the last element, the second element becomes the second to last element, and so on, with the old last element now first. Do not just reverse the order in which they are printed; actually change the way they are stored in the array. Do not create a second array; just rearrange the elements within the array you have. (Hint: Swap elements that need to change places.) When the elements have been reversed, print the array again.

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Adding To and Removing From an Integer List File IntegerList.java contains a Java class representing a list of integers. The following public methods are provided: □ □ □

IntegerList(int size)—creates a new list of size elements. Elements are initialized to 0. void randomize()—fills the list with random integers between 1 and 100, inclusive. void print()—prints the array elements and indices

File IntegerListTest.java contains a Java program that provides menu-driven testing for the IntegerList class. Copy both files to your directory, and compile and run IntegerListTest to see how it works.

It is often necessary to add items to or remove items from a list. When the list is stored in an array, one way to do this is to create a new array of the appropriate size each time the number of elements changes, and copy the values over from the old array. However, this is rather inefficient. A more common strategy is to choose an initial size for the array and add elements until it is full, then double its size and continue adding elements until it is full, and so on. (It is also possible to decrease the size of the array if it falls under, say, half full, but we won’t do that in this exercise.) The CDCollection class in Listing 7.8 of the text uses this strategy—it keeps track of the current size of the array and the number of elements already stored in it, and method addCD calls increaseSize if the array is full. Study that example.

1.

Add this capability to the IntegerList class. You will need to add an increaseSize method plus instance variables to hold the current number of integers in the list and the current size of the array. Since you do not have any way to add elements to the list, you won’t need to call increaseSize yet.

2.

Add a method void addElement(int newVal) to the IntegerList class that adds an element to the list. At the beginning of addElement, check to see if the array is full. If so, call increaseSize before you do anything else.

Add an option to the menu in IntegerListTest to test your new method.

3.

Add a method void removeFirst(int newVal) to the IntegerList class that removes the first occurrence of a value from the list. If the value does not appear in the list, it should do nothing (but it’s not an error). Removing an item should not change the size of the array, but note that the array values do need to remain contiguous, so when you remove a value you will have to shift everything after it down to fill up its space. Also remember to decrement the variable that keeps track of the number of elements.

Add an option to the menu in IntegerListTest to test your new method.

4.

Add a method removeAll(int newVal) to the IntegerList class that removes all occurrences of a value from the list. If the value does not appear in the list, it should do nothing (but it’s not an error).

Add an option to the menu in IntegerListTest to test your new method.

// *************************************************************** // IntegerList.java // // Define an IntegerList class with methods to create & fill // a list of integers. // // *************************************************************** public class IntegerList { int[] list; //values in the list //------------------------------------------------------//create a list of the given size //------------------------------------------------------public IntegerList(int size)

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{ list = new int[size]; } //------------------------------------------------------//fill array with integers between 1 and 100, inclusive //------------------------------------------------------public void randomize() { for (int i=0; i<list.length; i++) list[i] = (int)(Math.random() * 100) + 1; } //------------------------------------------------------//print array elements with indices //------------------------------------------------------public void print() { for (int i=0; i<list.length; i++) System.out.println(i + ":\t" + list[i]); } }

// *************************************************************** // IntegerListTest.java // // Provide a menu-driven tester for the IntegerList class. // // *************************************************************** import java.util.Scanner; public class IntegerListTest { static IntegerList list = new IntegerList(10); static Scanner scan = new Scanner(System.in); //------------------------------------------------------// Create a list, then repeatedly print the menu and do what the // user asks until they quit //------------------------------------------------------public static void main(String[] args) { printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } //------------------------------------// Do what the menu item calls for //------------------------------------public static void dispatch(int choice) {

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int loc; switch(choice) { case 0: System.out.println("Bye! ") ; break; case 1: System.out.println("How big should the list be?"); int size = scan.nextInt(); list = new IntegerList(size); list.randomize(); break; case 2: list.print(); break; default: System.out.println("Sorry, invalid choice"); } } //---------------------------// Print the user's choices //---------------------------public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Create a new list (** do this first!! **)"); System.out.println("2: Print the list"); System.out.print("\nEnter your choice: "); } }

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A Shopping Cart In this exercise you will complete a class that implements a shopping cart as an array of items. The file Item.java contains the definition of a class named Item that models an item one would purchase. An item has a name, price, and quantity (the quantity purchased). The file ShoppingCart.java implements the shopping cart as an array of Item objects.

1.

Complete the ShoppingCart class by doing the following: a. Declare an instance variable cart to be an array of Items and instantiate cart in the constructor to be an array holding capacity Items. b. Fill in the code for the increaseSize method. Your code should be similar to that in Listing 7.8 of the text but instead of doubling the size just increase it by 3 elements. c. Fill in the code for the addToCart method. This method should add the item to the cart and update the totalPrice instance variable (note this variable takes into account the quantity). d. Compile your class.

2.

Write a program that simulates shopping. The program should have a loop that continues as long as the user wants to shop. Each time through the loop read in the name, price, and quantity of the item the user wants to add to the cart. After adding an item to the cart, the cart contents should be printed. After the loop print a “Please pay ...” message with the total price of the items in the cart.

// *************************************************************** // Item.java // // Represents an item in a shopping cart. // *************************************************************** import java.text.NumberFormat; public class Item { private String name; private double price; private int quantity; // // Create a new item with the given attributes. // public Item (String itemName, double itemPrice, int numPurchased) { name = itemName; price = itemPrice; quantity = numPurchased; } // // Return a string with the information about the item // public String toString () { NumberFormat fmt = NumberFormat.getCurrencyInstance(); return (name + "\t" + fmt.format(price) + "\t" + quantity + "\t" + fmt.format(price*quantity)); } // // //

Returns the unit price of the item

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public double getPrice() { return price; } // // Returns the name of the item // public String getName() { return name; } // // Returns the quantity of the item // public int getQuantity() { return quantity; } } } // *************************************************************** // ShoppingCart.java // // Represents a shopping cart as an array of items // *************************************************************** import java.text.NumberFormat; public class ShoppingCart { private int itemCount; private double totalPrice; private int capacity;

// total number of items in the cart // total price of items in the cart // current cart capacity

// // Creates an empty shopping cart with a capacity of 5 items. // public ShoppingCart() { capacity = 5; itemCount = 0; totalPrice = 0.0; } // // Adds an item to the shopping cart. // public void addToCart(String itemName, double price, int quantity) { } // // //

Returns the contents of the cart together with summary information.

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// public String toString() { NumberFormat fmt = NumberFormat.getCurrencyInstance(); String contents = "\nShopping Cart\n"; contents += "\nItem\t\tUnit Price\tQuantity\tTotal\n"; for (int i = 0; i < itemCount; i++) contents += cart[i].toString() + "\n"; contents += "\nTotal Price: " + fmt.format(totalPrice); contents += "\n"; return contents; } // // Increases the capacity of the shopping cart by 3 // private void increaseSize() { } }

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Averaging Numbers As discussed in Section 7.4 of the text book, when you run a Java program called Foo, anything typed on the command line after “java Foo” is passed to the main method in the args parameter as an array of strings.

1. Write a program Average.java that just prints the strings that it is given at the command line, one per line. If nothing is given at the command line, print “No arguments”.

2. Modify your program so that it assumes the arguments given at the command line are integers. If there are no arguments, print a message. If there is at least one argument, compute and print the average of the arguments. Note that you will need to use the parseInt method of the Integer class to extract integer values from the strings that are passed in. If any non-integer values are passed in, your program will produce an error, which is unavoidable at this point.

3. Test your program thoroughly using different numbers of command line arguments.

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Exploring Variable Length Parameter Lists The file Parameters.java contains a program to test the variable length method average from Section 7.5 of the text. Note that average must be a static method since it is called from the static method main.

1.

2.

3.

4.

Compile and run the program. You must use the -source 1.5 option in your compile command.

Add a call to find the average of a single integer, say 13. Print the result of the call.

Add a call with an empty parameter list and print the result. Is the behavior what you expected?

Add an interactive part to the program. Ask the user to enter a sequence of at most 20 nonnegative integers. Your program should have a loop that reads the integers into an array and stops when a negative is entered (the negative number should not be stored). Invoke the average method to find the average of the integers in the array (send the array as the parameter). Does this work?

Add a method minimum that takes a variable number of integer parameters and returns the minimum of the parameters. Invoke your method on each of the parameter lists used for the average function.

5.

//******************************************************* // Parameters.java // // Illustrates the concept of a variable parameter list. //******************************************************* import java.util.Scanner; public class Parameters { //----------------------------------------------// Calls the average and minimum methods with // different numbers of parameters. //----------------------------------------------public static void main(String[] args) { double mean1, mean2; mean1 = average(42, 69, 37); mean2 = average(35, 43, 93, 23, 40, 21, 75); System.out.println ("mean1 = " + mean1); System.out.println ("mean2 = " + mean2); } //---------------------------------------------// Returns the average of its parameters. //---------------------------------------------public static double average (int ... list) { double result = 0.0; if (list.length != 0) { int sum = 0; for (int num: list) sum += num; result = (double)sum / list.length; } return result; } }

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Magic Squares One interesting application of two-dimensional arrays is magic squares. A magic square is a square matrix in which the sum of every row, every column, and both diagonals is the same. Magic squares have been studied for many years, and there are some particularly famous magic squares. In this exercise you will write code to determine whether a square is magic.

File Square.java contains the shell for a class that represents a square matrix. It contains headers for a constructor that gives the size of the square and methods to read values into the square, print the square, find the sum of a given row, find the sum of a given column, find the sum of the main (or other) diagonal, and determine whether the square is magic. The read method is given for you; you will need to write the others. Note that the read method takes a Scanner object as a parameter.

File SquareTest.java contains the shell for a program that reads input for squares from a file named magicData and tells whether each is a magic square. Following the comments, fill in the remaining code. Note that the main method reads the size of a square, then after constructing the square of that size, it calls the readSquare method to read the square in. The readSquare method must be sent the Scanner object as a parameter.

You should find that the first, second, and third squares in the input are magic, and that the rest (fourth through seventh) are not. Note that the -1 at the bottom tells the test program to stop reading. // *************************************************************** // Square.java // // Define a Square class with methods to create and read in // info for a square matrix and to compute the sum of a row, // a col, either diagonal, and whether it is magic. // // *************************************************************** import java.util.Scanner; public class Square { int[][] square; //-------------------------------------//create new square of given size //-------------------------------------public Square(int size) { } //-------------------------------------//return the sum of the values in the given row //-------------------------------------public int sumRow(int row) { } //-------------------------------------//return the sum of the values in the given column //-------------------------------------public int sumCol(int col) { } //--------------------------------------

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//return the sum of the values in the main diagonal //-------------------------------------public int sumMainDiag() { } //-------------------------------------//return the sum of the values in the other ("reverse") diagonal //-------------------------------------public int sumOtherDiag() { } //-------------------------------------//return true if the square is magic (all rows, cols, and diags have //same sum), false otherwise //-------------------------------------public boolean magic() { } //-------------------------------------//read info into the square from the input stream associated with the //Scanner parameter //-------------------------------------public void readSquare(Scanner scan) { for (int row = 0; row < square.length; row++) for (int col = 0; col < square.length; col ++) square[row][col] = scan.nextInt(); } //---------------------------------------//print the contents of the square, neatly formatted //---------------------------------------public void printSquare() { } }

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// *************************************************************** // SquareTest.java // // Uses the Square class to read in square data and tell if // each square is magic. // // *************************************************************** import java.util.Scanner; public class SquareTest { public static void main(String[] args) throws IOException { Scanner scan = new Scanner(new File("magicData")); int count = 1; int size = scan.nextInt();

//count which square we're on //size of next square

//Expecting -1 at bottom of input file while (size != -1) { //create a new Square of the given size //call its read method to read the values of the square System.out.println("\n******** Square " + count + " ********"); //print the square //print the sums of its rows //print the sums of its columns //print the sum of the main diagonal //print the sum of the other diagonal //determine and print whether it is a magic square //get size of next square size = scan.nextInt(); } } }

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magicData 3 8 3 4 7 30 38 46 5 13 21 22 4 48 27 15 12 3 6 1 2 4 3 6 10 15 5 17 23 4 10 11 7 30 38 46 5 13 21 22 -1

1 5 9

6 7 2

39 47 6 14 15 23 31

48 7 8 16 24 32 40

1 9 17 25 33 41 49

9 18 30 45

6 21 33 42

39 36 24 3

2 5 9

10 18 26 34 42 43 2

19 27 35 36 44 3 11

28 29 37 45 4 12 20

28 29 37 45 4 12 20

19 27 35 36 44 3 11

7 3 4

16 9 5 4

2 7 11 14

13 12 8 1

24 5 6 12 18

15 16 22 3 9

8 14 13 21 2

1 7 20 19 25

39 47 6 14 15 23 31

48 7 8 16 24 32 40

1 9 17 25 33 41 49

10 18 26 34 42 43 2

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A Polygon Person A polygon is a multisided closed figure; a polyline is a line with an arbitrary number of segments. Both polygons and polylines are defined by a set of points, and Java provides graphics methods for both that are based on arrays. Read section 7.8 in the text and study the Rocket example in Listing 7.16 & 7.17.

Files DrawPerson.java and DrawPersonPanel.java contain a program that draws a blue shirt. Copy the programs to your directory, compile DrawPerson.java, and run it to see what it does. Now modify it as follows: 1.

2.

3.

4.

5.

6.

Draw pants to go with the shirt (they should be a different color). You will need to declare pantsX and pantsY arrays like the shirtX and shirtY arrays and figure out what should go in them. Then make the paint method draw the pants as well as the shirt.

Draw a head. This can just be a circle (or oval), so you won’t need to use the Polygon methods. Declare variables headX and headY to hold the position of the head (its upper lefthand corner), and use them when you draw the circle.

Draw hair on the head. This is probably best done with a polygon, so again you’ll need two arrays to hold the points.

Draw a zigzag across the front of the shirt. Use a polyline.

Write a method movePerson(int x, inty) that moves the person by the given number of pixels in the x and y direction.

This method should just go through the shirt, pants, hair and zigzag arrays and the head x and y coords and increment all of the coordinates by the x or y value as appropriate. (This isn’t necessarily the cleanest way to do this, but it’s very straightforward).

Now put a loop in your paintComponent method that draws the person three times, moving him (her?) 150 or so pixels each time (you decide how far).

// ******************************************************************* // DrawPerson.java // // An program that uses the Graphics draw methods to draw a person. // ******************************************************************* import.javax.swing.JFrame; public class DrawPerson { //----------------------------------------------// Creates the main frame for the draw program //----------------------------------------------public static void main (String[] args) { JFrame frame = new JFrame ("Draw Person"); frame.setDefaultCloseOperaton (JFrame.EXIT_ON_CLOSE); DrawPersonPanel panel = new DrawPersonPanel (); frame.getContentPane().add(panel); frame.pack(); frame.setVisible(true); } } // ******************************************************************* // DrawPersonPanel.java // // An program that uses the Graphics draw methods to draw a person. // ******************************************************************* import javax.swing.JPanel; import java.awt*;

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public class DrawPersonPanel extends JPanel { private final int WIDTH = 600; private final int HEIGHT = 400; private int[] shirtX = {60,0,20,60,50,130,120,160,180,120}; private int[] shirtY = {100,150,180,160,250,250,160,180,150,100}; //-------------------------------------// Constructor: Set up the panel. //-------------------------------------public DrawPersonPanel() { setPreferredSize(new Dimension(WIDTH, HEIGHT)); } //-------------------------------------// Draw person //-------------------------------------public void paintComponent (Graphics page) { page.setColor(Color.blue); page.fillPolygon(shirtX, shirtY, shirtX.length); } }

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An Array of Radio Buttons File ColorOptions.java contains a program that will display a set of radio buttons that let the user change the background color of the GUI. The file ColorOptionsPanel.java contains the skeleton of the panel for this program. Open the files and study the code that is already there. You will note that in ColorOptionsPanel.java there is an array color containing 5 colors already defined. Your task is to add an array of radio buttons so that a click of a radio button will cause the background of the panel to change to the corresponding color in the color array.

1.

Define colorButton to be an array of NUM_COLORS objects of type JRadioButton.

2.

Instantiate each colorButton with the appropriate color as the label (for example, the first button should be labeled “Yellow”). The first button (corresponding to yellow) should be on (true) initially.

3.

Recall that radio buttons must be grouped and that the selection of a radio button produces an action event. Hence you must have a ButtonGroup object and an ActionListener. Note that the skeleton of an ActionListener named ColorListener is already provided. So, you need to: a. Instantiate a ButtonGroup object and a ColorListener object. Comments in the code indicate where to do this. b. Each radio button needs to be added to your ButtonGroup object, the background color needs to be set (use white), your ColorListener needs to be added, and the button needs to be added to the panel. All of these can be done using a single for loop. So, add a for loop that goes through the radio buttons adding each to your ButtonGroup object, setting the background of each to white, adding your ColorListener to each, and adding each to the panel.

4.

Fill in the body of the actionPerformed method. This method needs to go through the buttons to determine which is selected and then set the background color accordingly. A simple for loop can do this. Use the isSelected method to determine if a button is selected (for example, if (colorButton[i].isSelected()). ). Use the color array to set the background color.

5.

Test your program!

// ******************************************************************** // ColorOptions.java // // Uses an array of radio buttons to change the background color. // ******************************************************************** import javax.swing.*; public class ColorOptions { // // Creates and presents the frame for the color change panel. // public static void main (String[] args) { JFrame colorFrame = new JFrame ("Color Options"); colorFrame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); ColorOptionsPanel panel = new ColorOptionsPanel(); colorFrame.getContentPane().add (panel); colorFrame.pack(); colorFrame.setVisible(true); } }

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// *********************************************************************** // ColorOptionsPanel.java // // Represents the user interface for the ColorOptions program that lets // the user change background color by selecting a radio button. // *********************************************************************** import javax.swing.*; import java.awt.*; import java.awt.event.*; public class ColorOptionsPanel extends JPanel { private final int WIDTH = 350, HEIGHT = 100, FONT_SIZE = 20; private final int NUM_COLORS = 5; private Color [] color = new Color[NUM_COLORS]; private JLabel heading; // // //

Sets up a panel with a label at the top and a set of radio buttons that control the background color of the panel.

// public ColorOptionsPanel () { // Set up heading and colors heading = new JLabel ("Choose the background color!"); heading.setFont (new Font ("Helvetica", Font.BOLD, FONT_SIZE)); color[0] = Color.yellow; color[1] = Color.cyan; color[2] = Color.red; color[3] = Color.green; color[4] = Color.magenta; // Instantiate a ButtonGroup object and a ColorListener object // Set up the panel add (heading); setBackground (Color.yellow); setPreferredSize (new Dimension (WIDTH, HEIGHT)); // Group the radio buttons, add a ColorListener to each, // set the background color of each and add each to the panel. } // *************************************************************** // Represents the listener for the radio buttons. // *************************************************************** private class ColorListener implements ActionListener { // // Updates the background color of the panel based on // which radio button is selected. // public void actionPerformed (ActionEvent event) { } } } Chapter 8: Arrays

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Drawing Circles with Mouse Clicks File Circles.java sets up a panel that creates and draws a circle as defined in Circle.java of random size and color at each mouse click. Each circle replaces the one before it. The code to handle the mouse clicks and do the drawing is in CirclePanel.java. Save these files to your directory, compile them and run them and experiment with the GUI. Then modify these files as described below.

1.

This program creates a new circle each time—you can tell because each circle is a different color and size. Write a method void move(Point p) for your Circle class that takes a Point and moves the circle so its center is at that point. Now modify your CirclesListener class (defined inside CirclePanel) so that instead of creating a new circle every time the user clicks, it moves the existing circle to the clickpoint if a circle already exists. If no circle exists, a new one should be created at the clickpoint. So now a circle of the same color and size should move around the screen.

2.

Write a method boolean isInside(Point p) for your Circle class that takes a Point and tells whether it is inside the circle.

A point is inside the circle if its distance from the center is less than the radius. (Recall that the distance between two points (x1,y1) and (x2,y2) is sqrt((x2-x1)2+(y2-y1)2.)

3.

Now modify the mousePressed method of CirclesListener so that the GUI behaves as follows: □ If there is no circle (i.e., it is null) and the user clicks anywhere, a new (random) circle should be drawn at the click point. □ If there is a circle on the screen and the user clicks inside that circle, the circle should go away. (Hint: To make the circle go away, set it to null and repaint.) □ If there is a circle on the screen and the user clicks somewhere else, the circle should move to that point (no change from before).

So the logic for mousePressed should look like this: if there is currently no circle create a new circle at the click point else if the click is inside the circle make the circle go away else move the circle to the click point repaint

4.

Add bodies for the mouseEntered and mouseExited methods so that when the mouse enters the panel the background turns white, and when it exits the background turns blue. Remember that you can set the background color with the setBackground method.

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//*************************************************************** // Circles.java // // Demonstrates mouse events and drawing on a panel. // Derived from Dots.java in Lewis and Loftus //***************************************************************** import javax.swing.JFrame; public class Circles { //---------------------------------------------------------------// Creates and displays the application frame. //---------------------------------------------------------------public static void main (String[] args) { JFrame circlesFrame = new JFrame ("Circles"); circlesFrame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); circlesFrame.getContentPane().add (new CirclePanel()); circlesFrame.pack(); circlesFrame.setVisible(true); } }

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// *************************************************************** // Circle.java // // Define a Circle class with methods to create and draw // a circle of random size, color, and location. // // *************************************************************** import java.awt.*; import java.util.Random; public class Circle { private int centerX, centerY; private int radius; private Color color; static Random generator = new Random(); //--------------------------------------------------------// Creates a circle with center at point given, random radius and color // -- radius 25..74 // -- color RGB value 0..16777215 (24-bit) //--------------------------------------------------------public Circle(Point point) { radius = Math.abs(generator.nextInt())%50 + 25; color = new Color(Math.abs(generator.nextInt())% 16777216); centerX = point.x; centerY = point.y; } //--------------------------------------------------------// Draws circle on the graphics object given //--------------------------------------------------------public void draw(Graphics page) { page. setColor (color) ; page.fillOval(centerX-radius,centerY-radius,radius*2,radius*2); } }

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//************************************************************************ // CirclePanel.java // // Represents the primary panel for the Circles program on which the // circles are drawn. Derived from the Lewis and Loftus DotsPanel class. //************************************************************************ import javax.swing.*; import java.awt.*; import java.awt.event.*; import java.util.*; public class CirclePanel extends JPanel { private final int WIDTH = 600, HEIGHT = 400; private Circle circle; //------------------------------------------------------------------// Sets up this panel to listen for mouse events. //------------------------------------------------------------------public CirclePanel() { addMouseListener (new CirclesListener()); setPreferredSize (new Dimension(WIDTH, HEIGHT)); } //------------------------------------------------------------------// Draws the current circle, if any. //------------------------------------------------------------------public void paintComponent (Graphics page) { super.paintComponent(page); if (circle != null) circle.draw(page); } //****************************************************************** // Represents the listener for mouse events. //****************************************************************** private class CirclesListener implements MouseListener { //--------------------------------------------------------------// Creates a new circle at the current location whenever the // mouse button is pressed and repaints. //--------------------------------------------------------------public void mousePressed (MouseEvent event) { circle = new Circle(event.getPoint()); repaint(); } //----------------------------------------------------------------// Provide empty definitions for unused event methods. //----------------------------------------------------------------public void mouseClicked (MouseEvent event) {} public void mouseReleased (MouseEvent event) {} public void mouseEntered (MouseEvent event) {} public void mouseExited (MouseEvent event) {} } }

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Moving Circles with the Mouse File Circles.java sets up a GUI that creates and draws a circle as defined in Circle.java of random size and color at each mouse click. Each circle replaces the one before it. The code to handle the mouse clicks and do the drawing is in CirclePanel.java. (The files are from the previous exercise, Drawing Circles.) Save these files to your directory, compile them and run them and experiment with the GUI. Then modify the code in CirclePanel.java so that a circle is drawn when the user presses a mouse, but the user can drag it around as long as the mouse button is depressed. If the mouse button is released and then pressed again, a new circle is created, which can then be dragged around. You will need to make the following changes: 1.

Write a method void move(Point p) for your Circle class that takes a Point and moves the circle so its center is at that point. (You may have already done this in a previous exercise.)

2.

In the CirclePanel constructor, create a CirclesListener object and make it listen for both mouse events and mouse motion events.

3.

Make the CirclesListener class implement the MouseMotionListener interface in addition to the MouseListener interface.

This requires two steps: □ Note in the header that CirclesListener implements MouseMotionListener. □ Add bodies for the two MouseMotionListener methods, mouseDragged and mouseMoved. In mouseDragged, simply move the circle to the point returned by the getPoint method of the MouseEvent and repaint. Provide an empty body for mouseMoved.

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Moving a Stick Figure The file StickFigure.java contains a class that represents a stick figure. Study the file and note that in addition to a method to draw the stick figure there are methods to manipulate it: □ □ □ □

The method move repositions (“moves”) the figure up or down and over (left or right) on the panel by changing the instance variables baseX and baseY. The method grow changes the size of the figure by a given factor by modifying the instance variable height and others.

The method setLegPosition sets the position of the legs (number of pixels from vertical).

The method setArmPosition sets the position of the arms (number of pixels from horizontal).

The file MoveStickMan.java contains a program that draws a single stick figure that can be moved around and modified using the keyboard. The file MovePanel.java represents the panel on which the stick figure is displayed. It is similar to DirectionPanel.java in Listing 7.23 of the text. Note that the constructor adds a KeyListener and contains a call to the setFocusable method. There is a partially defined inner class named MoveListener that implements the KeyListener interface.

Currently the MoveListener listens only for two arrow keys (left and right) and the g key. The arrow keys move the stick figure left and right on the panel (the number of pixels moved is in the constant JUMP) and when the user presses the letter g, the figure “grows” (increases in height by 50%). Compile, and run the program. Test out the arrow keys and the g key.

Now add code to MovePanel.java to have the program respond to the following additional key events: □ □ □

When the up and down arrow keys are pressed the figure should move JUMP pixels up or down, respectively, on the panel.

When the s key is pressed the figure should shrink by 50%.

When the letter u (for up) is pressed, the stick figure should move its arms up and legs out; to make this happen add a call to setArmPosition to set the arm position and a call to setLegPosition to set the leg position. For example, when the u is pressed set the arm position to 60 and the leg position to 40 as follows: stickMan.setArmPosition(60); stickMan.setLegPosition(40);

□ □

When the letter m (for middle) is pressed, the stick figure should place its arms horizontally with legs not quite as far out.

To do this the arm position needs to be 0 (0 pixels above horizontal); a value of 20 for the leg position is good.

When the letter d (down) is pressed, the figure should move its arms down and its legs closer together. (Use -60 and 10 for the arm and leg positions, respectively).

Compile and run the program. Try out all the keys it implements. // *************************************************************** // StickFigure.java // // Represents a graphical stick figure // *************************************************************** import java.awt.*; public class StickFigure { private int baseX; // center of the figure private int baseY; // bottom of the feet private Color color; // color of the figure private int height; // height of the figure private int headW; // width of the head private int legLength; // length of the legs private int legPosition; // # pixels the legs are up from vertical private int armLength; // horizontal length of the arms private int armToFloor; // distance from base to arms

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private int armPosition; // # pixels arm is above/below horizontal // // Construct a stick figure given its four attributes // public StickFigure (int center, int bottom, Color shade, int size) { baseX = center; baseY = bottom; color = shade; height = size; // define body positions proportional to height headW = height / 5; legLength = height / 2; armToFloor = 2 * height / 3; armLength = height / 3; // set initial position of arms and legs armPosition = -20; legPosition = 15; } // // Draw the figure // public void draw (Graphics page) { // compute y-coordinate of top of head int top = baseY - height; page.setColor (color); // draw the head page.drawOval(baseX-headW/2, top, headW, headW); // draw the trunk page.drawLine (baseX, top+headW, baseX, baseY - legLength); // draw the legs page.drawLine (baseX, baseY-legLength, baseX-legPosition, baseY); page.drawLine (baseX, baseY-legLength, baseX+legPosition, baseY); // draw the arms int startY = baseY - armToFloor; page.drawLine (baseX, startY, baseX-armLength, startY-armPosition); page.drawLine (baseX, startY, baseX+armLength, startY-armPosition); } // // Move the figure -- first parameter gives the // number of pixels over (to right if over is positive, // to the left if over is negative) and up or down // (down if the parameter down is positive, up if it is // negative) // public void move (int over, int down) { baseX += over; baseY += down;

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} // // Increase the height by the given factor (if the // factor is > 1 the figure will "grow" else it will // shrink) // public void grow (double factor) { height = (int) (factor * height); // reset body parts proportional to new height headW = height / 5; legLength = height / 2; armToFloor = 2 * height / 3; armLength = height / 3; } // // set the legPosition (dist. from vertical) to // new value // public void setLegPosition (int newPosition) { legPosition = newPosition; } // // set the arm position to the new value // public void setArmPosition (int newPos) { armPosition = newPos; } } // ******************************************************************** // MoveStickMan.java // // Uses key events to move a stick figure around. // ******************************************************************** import javax.swing.*; public class MoveStickMan { // // Creates and displays the application frame. // public static void main (String[] args) { JFrame frame = new JFrame ("Moving a Stick Figure"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); frame.getContentPane().add (new MovePanel()); frame.pack(); frame.setVisible(true); } }

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// ******************************************************************* // FILE: MovePanel.java // // The display panel for a key events program -- arrow keys are used // to move a stick figure around, the g key is used to make the figure // grow by 50% (increase in height by 50%), the s key causes the // figure to shrink (to half its size) // ******************************************************************* import javax.swing.*; import java.awt.*; import java.awt.event.*; public class MovePanel extends JPanel { private final int WIDTH = 600; private final int HEIGHT = 400; private final int JUMP =5;

// number of pixels moved each step

// the following give the initial parameters for the figure private final int START_CENTER = WIDTH/2; private final int START_BOTTOM = HEIGHT - 40; private final int SIZE = HEIGHT / 2; private StickFigure stickMan; // // Constructor: Sets up the panel // public MovePanel () { addKeyListener(new MoveListener()); stickMan = new StickFigure (START_CENTER, START_BOTTOM, Color.yellow, SIZE); setBackground (Color.black); setPreferredSize (new Dimension (WIDTH, HEIGHT)); setFocusable(true); } // // Draws the figure // public void paintComponent (Graphics page) { super.paintComponent (page); stickMan.draw (page); } // *************************************************************** // Represents a listener for keyboard activity. // *************************************************************** private class MoveListener implements KeyListener { // // Handle a key-pressed event: arrow keys cause the // figure to move horizontally or vertically; the g

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// key causes the figure to "grow", the s key causes // the figure to shrink, the u key causes arms and // legs to go up, m puts them in the middle, and d // down. // public void keyPressed (KeyEvent event) { switch (event.getKeyCode()) { case KeyEvent.VK_LEFT: stickMan.move(-1*JUMP, 0); break; case KeyEvent.VK_RIGHT: stickMan.move(JUMP, 0); break; case KeyEvent.VK_G: stickMan.grow (1.5); break; default: } repaint(); } // // Define empty bodies for key event methods // not used // public void keyTyped (KeyEvent event) {} public void keyReleased (KeyEvent event) {} } }

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Chapter 9: Inheritance Lab Exercises Topics

Lab Exercises

Inheritance

Exploring Inheritance A Sorted Integer List Test Questions Overriding the equals Method

Adapter Classes

Extending Adapter Classes

Animation

Rebound Revisited Count Down

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Exploring Inheritance File Dog.java contains a declaration for a Dog class. Save this file to your directory and study it—notice what instance variables and methods are provided. Files Labrador.java and Yorkshire.java contain declarations for classes that extend Dog. Save and study these files as well.

File DogTest.java contains a simple driver program that creates a dog and makes it speak. Study DogTest.java, save it to your directory, and compile and run it to see what it does. Now modify these files as follows: 1. Add statements in DogTest.java after you create and print the dog to create and print a Yorkshire and a Labrador. Note that the Labrador constructor takes two parameters: the name and color of the labrador, both strings. Don’t change any files besides DogTest.java. Now recompile DogTest.java; you should get an error saying something like ./Labrador.java:18: Dog(java.lang.String) in Dog cannot be applied to () { ^ 1 error If you look at line 18 of Labrador.java it’s just a {, and the constructor the compiler can’t find (Dog()) isn’t called anywhere in this file. a. What’s going on? (Hint: What call must be made in the constructor of a subclass?) =>

b.

2.

Fix the problem (which really is in Labrador) so that DogTest.java creates and makes the Dog, Labrador, and Yorkshire all speak.

Add code to DogTest.java to print the average breed weight for both your Labrador and your Yorkshire.

Use the avgBreedWeight() method for both. What error do you get? Why? =>

Fix the problem by adding the needed code to the Yorkshire class.

3.

Add an abstract int avgBreedWeight() method to the Dog class. Remember that this means that the word abstract appears in the method header after public, and that the method does not have a body (just a semicolon after the parameter list). It makes sense for this to be abstract, since Dog has no idea what breed it is. Now any subclass of Dog must have an avgBreedWeight method; since both Yorkshire and Laborador do, you should be all set.

Save these changes and recompile DogTest.java. You should get an error in Dog.java (unless you made more changes than described above). Figure out what’s wrong and fix this error, then recompile DogTest.java. You should get another error, this time in DogTest.java. Read the error message carefully; it tells you exactly what the problem is. Fix this by changing DogTest (which will mean taking some things out).

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// **************************************************************** // Dog.java // // A class that holds a dog's name and can make it speak. // // **************************************************************** public class Dog { protected String name; // // Constructor -- store name // public Dog(String name) { this.name = name; } // // Returns the dog's name // public String getName() { return name; } // // Returns a string with the dog's comments // public String speak() { return "Woof"; } }

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// **************************************************************** // Labrador.java // // A class derived from Dog that holds information about // a labrador retriever. Overrides Dog speak method and includes // information about avg weight for this breed. // // **************************************************************** public class Labrador extends Dog { private String color; //black, yellow, or chocolate? private int breedWeight = 75; public Labrador(String name, { this.color = color; }

String color)

// // Big bark -- overrides speak method in Dog // public String speak() { return "WOOF"; } // // Returns weight // public static int avgBreedWeight() { return breedWeight; } }

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// ***************************************************************** // Yorkshire.java // // A class derived from Dog that holds information about // a Yorkshire terrier. Overrides Dog speak method. // // ***************************************************************** public class Yorkshire extends Dog { public Yorkshire(String name) { super(name); } // // Small bark -- overrides speak method in Dog // public String speak() { return "woof"; } }

// **************************************************************** // DogTest.java // // A simple test class that creates a Dog and makes it speak. // // **************************************************************** public class DogTest { public static void main(String[] args) { Dog dog = new Dog("Spike"); System.out.println(dog.getName() + " says " + dog.speak()); } }

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A Sorted Integer List File IntList.java contains code for an integer list class. Save it to your directory and study it; notice that the only things you can do are create a list of a fixed size and add an element to a list. If the list is already full, a message will be printed. File ListTest.java contains code for a class that creates an IntList, puts some values in it, and prints it. Save this to your directory and compile and run it to see how it works.

Now write a class SortedIntList that extends IntList. SortedIntList should be just like IntList except that its elements should always be in sorted order from smallest to largest. This means that when an element is inserted into a SortedIntList it should be put into its sorted place, not just at the end of the array. To do this you'll need to do two things when you add a new element: • Walk down the array until you find the place where the new element should go. Since the list is already sorted you can just keep looking at elements until you find one that is at least as big as the one to be inserted.

• Move down every element that will go after the new element, that is, everything from the one you stop on to the end. This creates a slot in which you can put the new element. Be careful about the order in which you move them or you'll overwrite your data!

Now you can insert the new element in the location you originally stopped on.

All of this will go into your add method, which will override the add method for the IntList class. (Be sure to also check to see if you need to expand the array, just as in the IntList add method.) What other methods, if any, do you need to override?

To test your class, modify ListTest.java so that after it creates and prints the IntList, it creates and prints a SortedIntList containing the same elements (inserted in the same order). When the list is printed, they should come out in sorted order. // **************************************************************** // IntList.java // // An (unsorted) integer list class with a method to add an // integer to the list and a toString method that returns the contents // of the list with indices. // // **************************************************************** public class IntList { protected int[] list; protected int numElements = 0; //------------------------------------------------------------// Constructor -- creates an integer list of a given size. //------------------------------------------------------------public IntList(int size) { list = new int[size]; } //-----------------------------------------------------------// Adds an integer to the list. If the list is full, // prints a message and does nothing. //-----------------------------------------------------------public void add(int value) { if (numElements == list.length) System.out.println("Can't add, list is full"); else { list[numElements] = value; numElements++; 158

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} } //------------------------------------------------------------// Returns a string containing the elements of the list with their // indices. //------------------------------------------------------------public String toString() { String returnString = ""; for (int i=0; i<numElements; i++) returnString += i + ": " + list[i] + "\n"; return returnString; } }

// *************************************************************** // ListTest.java // // A simple test program that creates an IntList, puts some // ints in it, and prints the list. // // *************************************************************** public class ListTest { public static void main(String[] args) { IntList myList = new IntList(10); myList.add(100); myList.add(50); myList.add(200); myList.add(25); System.out.println(myList); } }

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Test Questions In this exercise you will use inheritance to read, store, and print questions for a test. First, write an abstract class TestQuestion that contains the following: □ □

A protected String variable that holds the test question.

An abstract method protected abstract void readQuestion() to read the question.

Now define two subclasses of TestQuestion, Essay and MultChoice. Essay will need an instance variable to store the number of blank lines needed after the question (answering space). MultChoice will not need this variable, but it will need an array of Strings to hold the choices along with the main question. Assume that the input is provided from the standard input as follows, with each item on its own line: □ type of question (character, m=multiple choice, e=essay) □ number of blank lines for essay, number of blank lines for multiple choice (integer) □ choice 1 (multiple choice only) □ choice 2 (multiple choice only) ...

The very first item of input, before any questions, is an integer indicating how many questions will be entered. So the following input represents three questions: an essay question requiring 5 blank lines, a multiple choice question with 4 choices, and another essay question requiring 10 blank lines: 3 e 5 Why does the constructor of a derived class have to call the constructor of its parent class? m 4 Which of the following is not a legal identifier in Java? guess2 2ndGuess _guess2_ Guess e 5 What does the "final" modifier do?

You will need to write readQuestion methods for the MultChoice and Essay classes that read information in this format. (Presumably the character that identifies what kind of question it is will be read by a driver.)

You will also need to write toString methods for the MultChoice and Essay classes that return nicely formatted versions of the questions (e.g., the choices should be lined up, labeled a), b), etc, and indented in MultChioce).

Now define a class WriteTest that creates an array of TestQuestion objects. It should read the questions from the standard input as follows in the format above, first reading an integer that indicates how many questions are coming. It should create a MultChoice object for each multiple choice question and an Essay object for each essay question and store each object in the array. (Since it’s an array of TestQuestion and both Essay and MultChoice are subclasses of TestQuestion, objects of both types can be stored in the array.) When all of the data has been read, it should use a loop to print the questions, numbered, in order.

Use the data in testbank.dat to test your program. testbank.dat 5 e 5 Why does the constructor of a subclass class have to call the constructor of its parent class? m 4 Which of the following is not a legal identifier in Java?

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guess2 2ndGuess _guess2_ Guess e 5 What does the "final" modifier do? e 3 Java does not support multiple inheritance. This means that a class cannot do what? m 3 A JPanel has an addMouseListener method because JPanel is a subclass of JComponent JApplet Object

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Overriding the equals Method File Player.java contains a class that holds information about an athlete: name, team, and uniform number. File ComparePlayers.java contains a skeletal program that uses the Player class to read in information about two baseball players and determine whether or not they are the same player.

1.

Fill in the missing code in ComparePlayers so that it reads in two players and prints “Same player” if they are the same, “Different players” if they are different. Use the equals method, which Player inherits from the Object class, to determine whether two players are the same. Are the results what you expect?

2.

The problem above is that as defined in the Object class, equals does an address comparison. It says that two objects are the same if they live at the same memory location, that is, if the variables that hold references to them are aliases. The two Player objects in this program are not aliases, so even if they contain exactly the same information they will be “not equal.” To make equals compare the actual information in the object, you can override it with a definition specific to the class. It might make sense to say that two players are “equal” (the same player) if they are on the same team and have the same uniform number. □ Use this strategy to define an equals method for the Player class. Your method should take a Player object and return true if it is equal to the current object, false otherwise. □ Test your ComparePlayers program using your modified Player class. It should give the results you would expect.

// ********************************************************* // Player.java // // Defines a Player class that holds information about an athlete. // ********************************************************** import java.util.Scanner; public class Player { private String name; private String team; private int jerseyNumber; //----------------------------------------------------------// Prompts for and reads in the player's name, team, and // jersey number. //----------------------------------------------------------public void readPlayer() { Scanner scan = new Scanner(System.in); System.out.print("Name: "); name = scan.nextLine(); System. out. print ("Team: "); team = scan.nextLine(); System.out.print("Jersey number: "); jerseyNumber = Scan.nextInt(); } }

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// ************************************************************** // ComparePlayers // // Reads in two Player objects and tells whether they represent // the same player. // ************************************************************** import java.util.Scanner; public class ComparePlayers { public static void main(String[] args) { Player player1 = new Player(); Player player2 = new Player(); Scanner scan = new Scanner(); //Prompt for and read in information for player 1 //Prompt for and read in information for player 2 //Compare player1 to player 2 and print a message saying //whether they are equal } }

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Extending Adapter Classes Files Dots.java and DotsPanel.java contain the code in Listings 7.18 and 7.19 of the text. This program draws dots where the user clicks and counts the number of dots that have been drawn. Save these files to your directory and compile and run Dots to see how it works.

Now study the code in DotsPanel.java. (Dots just creates an instance of DotsPanel and adds it to its content pane.) DotsPanel defines an inner class, DotsListener, that implements the MouseListener interface. Notice that it defines the mousePressed method to draw a dot at the click point and gives empty bodies for the rest of the MouseListener methods.

1. Modify the DotsListener class so that instead of implementing the MouseListener interface, it extends the MouseAdapter class. What other code does this let you eliminate? For now, just comment out this code. Test your modified program.

2.

We have been using inner classes to define event listeners. Another common strategy is to make the panel itself be a MouseListener, eliminating the need for the inner class. Do this as follows: □ Modify the header to the DotsPanel class to indicate that it implements the MouseListener interface (it still extends JPanel). □ Delete the DotsListener class entirely, moving the five MouseListener methods into the DotsPanel class. □ The DotsPanel constructor contains the following statement: addMouseListener (new DotsListener()); This creates an instance of the DotsListener class and makes it listen for mouse events on the panel. This will have to change, since the DotsListener class has gone away. The listener is now the panel itself, so the argument to addMouseListener should change to this, that is, the current object. So the panel is listening for its own mouse events! Compile and run your modified program; it should behave just as before.

3. When we were using the DotsListener class we saw that it could either implement the MouseListener interface or extend the MouseAdapter class. With the new approach in #2, where the DotsPanel is also a MouseListener, can we do the same thing - that is, can DotsPanel extend MouseAdapter instead of implementing MouseListener? Why or why not? If you’re not sure, try it and explain what happens. //******************************************************************* // Dots.java Author: Lewis/Loftus // // Demonstrates mouse events. //******************************************************************* import javax.swing.JFrame; public class Dots { //---------------------------------------------------------------// Creates and displays the application frame. //---------------------------------------------------------------public static void main (String[] args) { JFrame frame = new JFrame ("Dots"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); frame.getContentPane().add (new DotsPanel()); frame.pack(); frame.setVisible(true); } } 164

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//******************************************************************* // DotsPanel.java Author: Lewis/Loftus // // Represents the primary panel for the Dots program. //******************************************************************* import java.util.ArrayList; import javax.swing.JPanel; import java.awt.*; import java.awt.event.*; public class DotsPanel extends JPanel { private final int SIZE =6; // radius of each dot private ArrayList<Point> pointList; //----------------------------------------------------------------// Constructor: Sets up this panel to listen for mouse events. //----------------------------------------------------------------public DotsPanel() { pointList = new ArrayList<Point>(); addMouseListener (new DotsListener()); setBackground (Color.black); setPreferredSize (new Dimension(300, 200)); } //---------------------------------------------------------------// Draws all of the dots stored in the list. //---------------------------------------------------------------public void paintComponent (Graphics page) { super.paintComponent(page); page.setColor (Color.green); for (Point spot: pointList) page.fillOval (spot.x-SIZE, spot.y-SIZE, SIZE*2, SIZE*2); page.drawString ("Count: " + pointList.size(), 5, 15); } //***************************************************************** // Represents the listener for mouse events. //***************************************************************** private class DotsListener implements MouseListener { //---------------------------------------------------------------// Adds the current point to the list of points and redraws // the panel whenever the mouse button is pressed. //---------------------------------------------------------------public void mousePressed (MouseEvent event) { pointList.add(event.getPoint()); repaint(); }

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//---------------------------------------------------------------// Provide empty definitions for unused event methods. //---------------------------------------------------------------public void mouseClicked (MouseEvent event) {} public void mouseReleased (MouseEvent event) {} public void mouseEntered (MouseEvent event) {} public void mouseExited (MouseEvent event) {} } }

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Rebound Revisited The files Rebound.java and ReboundPanel.java contain the program are in Listings 8.15 and 8.16 of the text. This program has an image that moves around the screen, bouncing back when it hits the sides (you can use any GIF or JPEG you like).

Save these files to your directory, then open ReboundPanel.java in the editor and observe the following: □ □ □

The constructor instantializes a Timer object with a delay of 20 (the time, in milliseconds, between generation of action events). The Timer object is started with its start method.

The constructor also gives the initial position of the ball (x and y) and the distance it will move at each interval (moveX and moveY).

The actionPerformed method in the ReboundListener inner class “moves” the image by adding the value of moveX to x and of moveY to y. This has the effect of moving the image to the right when moveX is positive and to the left when moveX is negative, and similarly (with down and up) with moveY. The actionPerformed method then checks to see if the ball has hit one of the sides of the panel—if it hits the left side (x <= 0) or the right side (x >= WIDTH- IMAGE_SIZE) the sign of moveX is changed. This has the effect of changing the direction of the ball. Similarly the method checks to see if the ball hit the top or bottom.

Now do the following: 1.

First experiment with the speed of the animation. This is affected by two things—the value of the DELAY constant and the amount the ball is moved each time. □ Change DELAY to 100. Save, compile, and run the program. How does the speed compare to the original? □ Change DELAY back to 20 and change moveX and moveY to 15. Save, compile, and run the program.

Compare the motion to that in the original program. □ Experiment with other combinations of values. □ Change moveX and moveY back to 3. Use any value of DELAY you wish.

2. Now add a second image to the program by doing the following: □ Declare a second ImageIcon object as an instance variable. You can use the same image as before or a new one. □ Declare integer variables x2 and y2 to represent the location of the second image, and moveX2 and moveY2 to control the amount the second ball moves each time. □ Initialize moveX2 to 5 and moveY2 to 8 (note—this image will have a different trajectory than the first—no longer a 45 degree angle). □ In actionPerformed, move the second image by the amount given in the moveX2 and moveY2 variable, and add code to check to see if the second image has hit a side. □ In paintComponent, draw the second image as well as the first.

2. Compile and run the program. Make sure it is working correctly. //******************************************************************** // Rebound.java Author: Lewis/Loftus // // Demonstrates an animation and the use of the Timer class. //******************************************************************** import java.awt.*; import java.awt.event.*; import javax.swing.*; public class Rebound { //----------------------------------------------------------------// Displays the main frame of the program. //----------------------------------------------------------------public static void main (String[] args) { JFrame frame = new JFrame ("Rebound"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(new ReboundPanel()); frame.pack(); frame.setVisible(true); } } Chapter 9: Inheritance

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//********************************************************************* // ReboundPanel.java Author: Lewis/Loftus // // Represents the primary panel for the Rebound program. //********************************************************************* import java.awt.*; import java.awt.event.*; import javax. swing. *; public class ReboundPanel extends JPanel { private final int WIDTH = 300, HEIGHT = 100; private final int DELAY = 20, IMAGE_SIZE = 35; private ImageIcon image; private Timer timer; private int x, y, moveX, moveY; //-----------------------------------------------------------------// Sets up the panel, including the timer for the animation. //-----------------------------------------------------------------public ReboundPanel() { timer = new Timer(DELAY, new ReboundListener()); image = new ImageIcon ("happyFace.gif"); x = 0; y = 40; moveX = moveY = 3; setPreferredSize (new Dimension(WIDTH, HEIGHT)); setBackground (Color.black); timer.start(); } //----------------------------------------------------------------// Draws the image in the current location. //----------------------------------------------------------------public void paintComponent (Graphics page) { super.paintComponent (page); image.paintIcon (this, page, x, y); } //****************************************************************** // Represents the action listener for the timer. //****************************************************************** private class ReboundListener implements ActionListener { //-------------------------------------------------------------// Updates the position of the image and possibly the direction // of movement whenever the timer fires an action event. //-------------------------------------------------------------public void actionPerformed (ActionEvent event) { x += moveX; y += moveY; if (x <= 0 || x >= WIDTH-IMAGE_SIZE) moveX = moveX * -1; if (y <= 0 || y >= HEIGHT-IMAGE_SIZE) moveY = moveY * -1; repaint(); } } }

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Count Down Clocks are a standard thing to animate—they change at regular intervals. In this exercise, you will write an applet that displays a simple “clock” that just counts down from 10. The clock will be a DigitalDisplay object.

The file DigitalDisplay.java contains the code for the class. The file CountDown.java contains the program and CountDownPanel.java contains a skeleton for the panel for the animation. Copy these files to your directory, compile and run the program. It should just display the clock with the number 10. Now do the following to make the clock count down, stop when it hits 0, and reset to 10 if the user clicks the mouse.

1.

Add an inner class named CountListener that implements ActionListener. In actionPerformed, □ Decrement the clock value. To do this use the decrement method in the DigitalDisplay class. (Look at its signature to see how to use it.) □ If the display value of the clock is negative, stop the timer; otherwise repaint the panel.

2. In the constructor, set up the timer.

3. Compile and run the program to see if it works.

4.

Now add code to let a mouse click have some control over the clock. In particular, if the clock is running when the mouse is clicked the clock should be stopped (stop the timer). If the clock is not running, it should be reset to 10 and started. To add the ability of the panel to respond to mouse clicks, do the following: □ Add an inner class that implements the MouseListener interface. In mouseClicked, if the timer is running, stop it; otherwise reset the clock to 10 (there is a method in the DigitalDisplay class to do this), start the timer, and repaint the applet. The bodies of the other methods in the MouseListener interface will be empty. □ Add a second parameter of type JApplet to the constructor for CountDownPanel. In your constructor, add the mouse listener to the applet. □ Modify the program CountDown.java to send the applet (this) as the second parameter for the CountDownPanel constructor.

5. Compile and run the program to make sure everything works right. //*************************************************** // DigitalDisplay.java // // A simple rectangular display of a single number //*************************************************** import java.awt.*; public class DigitalDisplay { private int displayVal; private int x, y; private int width, height; private Font displayFont;

// value to be displayed // position // size // font for the number

// // construct a DigitalDisplay object with the given values // and New Century Schoolbook font in 40 point bold // public DigitalDisplay(int start, int x, int y, int w, int h) { this.x = x; this.y = y; width = w; height = h; displayVal = start; Chapter 9: Inheritance

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displayFont = new Font ("New Century Schoolbook", Font.BOLD, 40); } // // decrement the display value // public void decrement() { displayVal--; } // // increment the display value // public void increment() { displayVal++; } // // return the display value // public int getVal() { return displayVal; } // // reset the display value to that given in the parameter // public void reset (int val) { displayVal = val; } // // draw the display // public void draw (Graphics page) { // draw a black border page.setColor (Color.black); page.fillRect (x, y, width, height); // a white inside page.setColor (Color.white); page.fillRect (x + 5, y + 5, width - 10, height - 10); // display the number centered page.setColor (Color.black); page.setFont (displayFont); int fontHeight = page.getFontMetrics().getHeight(); int strWidth = page.getFontMetrics().stringWidth(""+displayVal); page.drawString (""+displayVal, x + width/2 - strWidth/2, y + fontHeight/2 + height/2); } }

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// ********************************************************** // CountDown.java // // Draws a digital display that counts down from 10. The // display can be stopped or reset with a mouse click. // ********************************************************** import DigitalDisplay; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class CountDown extends JApplet { private final int DELAY = 200; private Timer timer; // // Initialize the applet, including the animation. // public void init() { timer = new Timer (DELAY, null); getContentPane().add (new CountDownPanel(timer)); } // // Start the animation when the applet is started. // public void start() { timer.start(); } // // Stop the animation when the applet is stopped. // public void stop() { timer.stop(); } }

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// ********************************************************** // CountDownPanel.java // // Panel for a digital display that counts down from 10. // The display can be stopped or reset with a mouse click. // ********************************************************** import DigitalDisplay; import java.awt.*; import java.awt.event.*; import javax.swing.*; public class CountDownPanel extends JPanel { private final int WIDTH = 600; private final int HEIGHT = 400; private final int DISPLAY_WIDTH = 150; private final int DISPLAY_HEIGHT = 100; private final int DELAY = 2 00; private final int COUNT_START = 10; private DigitalDisplay clock; private Timer timer; // // Set up the applet. // public CountDownPanel (Timer countdown) { // Set up the timer setBackground (Color.blue); setPreferredSize (new Dimension (WIDTH, HEIGHT)); clock = new DigitalDisplay(COUNT_START, WIDTH/2 - DISPLAY_WIDTH, HEIGHT/2 - DISPLAY_HEIGHT, DISPLAY_WIDTH, DISPLAY_HEIGHT); } // // draw the clock // public void paintComponent (Graphics page) { super.paintComponent (page); clock.draw(page); } }

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Chapter 10: Polymorphism Lab Exercises Topics

Lab Exercises

Polymorphism via Inheritance

Another Type of Employee Painting Shapes

Sorting & Searching

Polymorphic Sorting Searching and Sorting An Integer List

Comparing Searches

Timing Searching and Sorting Algorithms

Color Choosers

Coloring a Moveable Circle

Sliders

Speed Control

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Another Type of Employee The files Firm.java, Staff.java, StaffMember.java, Volunteer.java, Employee.java, Executive.java, and Hourly.java are from Listings 9.1 - 9.7 in the text. The program illustrates inheritance and polymorphism.

In this exercise you will add one more employee type to the class hierarchy (see Figure 9.1 in the text).

The employee will be one that is an hourly employee but also earns a commission on sales. Hence the class, which we’ll name Commission, will be derived from the Hourly class.

Write a class named Commission with the following features: □ It extends the Hourly class. □ It has two instance variables (in addition to those inherited): one is the total sales the employee has made (type double) and the second is the commission rate for the employee (the commission rate will be type double and will represent the percent (in decimal form) commission the employee earns on sales (so .2 would mean the employee earns 20% commission on sales)). □ The constructor takes 6 parameters: the first 5 are the same as for Hourly (name, address, phone number, social security number, hourly pay rate) and the 6th is the commission rate for the employee. The constructor should call the constructor of the parent class with the first 5 parameters then use the 6th to set the commission rate. □ One additional method is needed: public void addSales (double totalSales) that adds the parameter to the instance variable representing total sales. □ The pay method must call the pay method of the parent class to compute the pay for hours worked then add to that the pay from commission on sales. (See the pay method in the Executive class.) The total sales should be set back to 0 (note: you don’t need to set the hours Worked back to 0—why not?). □ The toString method needs to call the toString method of the parent class then add the total sales to that.

To test your class, update Staff.java as follows: □ Increase the size of the array to 8. □ Add two commissioned employees to the staffList—make up your own names, addresses, phone numbers and social security numbers. Have one of the employees earn $6.25 per hour and 20% commission and the other one earn $9.75 per hour and 15% commission. □ For the first additional employee you added, put the hours worked at 35 and the total sales $400; for the second, put the hours at 40 and the sales at $950.

Compile and run the program. Make sure it is working properly. //***************************************************************** // Firm.java Author: Lewis/Loftus // // Demonstrates polymorphism via inheritance. // **************************************************************** public class Firm { //-------------------------------------------------------------// Creates a staff of employees for a firm and pays them. //-------------------------------------------------------------public static void main (String[] args) { Staff personnel = new Staff(); personnel.payday(); } }

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//******************************************************************** // Staff.java Author: Lewis/Loftus // // Represents the personnel staff of a particular business. //******************************************************************** public class Staff { StaffMember[] staffList; //----------------------------------------------------------------// Sets up the list of staff members. //----------------------------------------------------------------public Staff () { staffList = new StaffMember[6]; staffList[0] = new Executive ("Sam", "123 Main Line", "555-0469", "123-45-6789", 2423.07); staffList[1] = new Employee ("Carla", "456 Off Line", "555-0101", "987-65-4321", 1246.15); staffList[2] = new Employee ("Woody", "789 Off Rocker", "555-0000", "010-20-3040", 1169.23); staffList[3] = new Hourly ("Diane", "678 Fifth Ave.", "555-0690", "958-47-3625", 10.55); staffList[4] = new Volunteer ("Norm", "987 Suds Blvd.", "555-8374") ; staffList[5] = new Volunteer ("Cliff", "321 Duds Lane", "555-7282"); ((Executive)staffList[0]).awardBonus (500.00); ((Hourly)staffList[3]).addHours (40); } //----------------------------------------------------------------// Pays all staff members. //----------------------------------------------------------------public void payday () { double amount; for (int count=0; count < staffList.length; count++) { System.out.println (staffList[count]); amount = staffList[count].pay();

// polymorphic

if (amount == 0.0) System.out.println ("Thanks!"); else System.out.println ("Paid: " + amount); System.out.println (" ------------------------------------ "); } } }

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//****************************************************************** // StaffMember.java Author: Lewis/Loftus // // Represents a generic staff member. //****************************************************************** abstract public class StaffMember { protected String name; protected String address; protected String phone; //--------------------------------------------------------------// Sets up a staff member using the specified information. //--------------------------------------------------------------public StaffMember (String eName, String eAddress, String ePhone) { name = eName; address = eAddress; phone = ePhone; } //--------------------------------------------------------------// Returns a string including the basic employee information. //--------------------------------------------------------------public String toString() { String result = "Name: " + name + "\n"; result += "Address: " + address + "\n"; result += "Phone: " + phone; return result; } //--------------------------------------------------------------// Derived classes must define the pay method for each type of // employee. //--------------------------------------------------------------public abstract double pay(); }

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//****************************************************************** // Volunteer.java Author: Lewis/Loftus // // Represents a staff member that works as a volunteer. //****************************************************************** public class Volunteer extends StaffMember { //--------------------------------------------------------------// Sets up a volunteer using the specified information. //--------------------------------------------------------------public Volunteer (String eName, String eAddress, String ePhone) { super (eName, eAddress, ePhone); } //--------------------------------------------------------------// Returns a zero pay value for this volunteer. //--------------------------------------------------------------public double pay() { return 0.0; } }

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//****************************************************************** // Employee.java Author: Lewis/Loftus // // Represents a general paid employee. //****************************************************************** public class Employee extends StaffMember { protected String socialSecurityNumber; protected double payRate; //--------------------------------------------------------------// Sets up an employee with the specified information. //--------------------------------------------------------------public Employee (String eName, String eAddress, String ePhone, String socSecNumber, double rate) { super (eName, eAddress, ePhone); socialSecurityNumber = socSecNumber; payRate = rate; } //--------------------------------------------------------------// Returns information about an employee as a string. //--------------------------------------------------------------public String toString() { String result = super.toString (); result += "\nSocial Security Number: " + socialSecurityNumber; return result; } //--------------------------------------------------------------// Returns the pay rate for this employee. //--------------------------------------------------------------public double pay() { return payRate; } }

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//****************************************************************** // Executive.java Author: Lewis/Loftus // // Represents an executive staff member, who can earn a bonus. //****************************************************************** public class Executive extends Employee { private double bonus; //----------------------------------------------------------------// Sets up an executive with the specified information. //----------------------------------------------------------------public Executive (String eName, String eAddress, String ePhone, String socSecNumber, double rate) { super (eName, eAddress, ePhone, socSecNumber, rate); bonus = 0;

// bonus has yet to be awarded

} //----------------------------------------------------------------// Awards the specified bonus to this executive. //----------------------------------------------------------------public void awardBonus (double execBonus) { bonus = execBonus; } //----------------------------------------------------------------// Computes and returns the pay for an executive, which is the // regular employee payment plus a one-time bonus. //----------------------------------------------------------------public double pay() { double payment = super.pay() + bonus; bonus = 0; return payment; } }

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//****************************************************************** // Hourly.java Author: Lewis/Loftus // // Represents an employee that gets paid by the hour. //******************************************************************* public class Hourly extends Employee { private int hoursWorked; //----------------------------------------------------------------// Sets up this hourly employee using the specified information. //----------------------------------------------------------------public Hourly (String eName, String eAddress, String ePhone, String socSecNumber, double rate) { super (eName, eAddress, ePhone, socSecNumber, rate); hoursWorked = 0; } //----------------------------------------------------------------// Adds the specified number of hours to this employee's // accumulated hours. //----------------------------------------------------------------public void addHours (int moreHours) { hoursWorked += moreHours; } //----------------------------------------------------------------// Computes and returns the pay for this hourly employee. //----------------------------------------------------------------public double pay() { double payment = payRate * hoursWorked; hoursWorked = 0; return payment; } //----------------------------------------------------------------// Returns information about this hourly employee as a string. //----------------------------------------------------------------public String toString() { String result = super.toString(); result += "\nCurrent hours: " + hoursWorked; return result; } }

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Painting Shapes In this lab exercise you will develop a class hierarchy of shapes and write a program that computes the amount of paint needed to paint different objects. The hierarchy will consist of a parent class Shape with three derived classes - Sphere, Rectangle, and Cylinder. For the purposes of this exercise, the only attribute a shape will have is a name and the method of interest will be one that computes the area of the shape (surface area in the case of three-dimensional shapes). Do the following.

1.

Write an abstract class Shape with the following properties: □ An instance variable shapeName of type String □ An abstract method area() □ A toString method that returns the name of the shape

2.

The file Sphere.java contains a class for a sphere which is a descendant of Shape. A sphere has a radius and its area (surface area) is given by the formula 4*PI*radius^2. Define similar classes for a rectangle and a cylinder. Both the Rectangle class and the Cylinder class are descendants of the Shape class. A rectangle is defined by its length and width and its area is length times width. A cylinder is defined by a radius and height and its area (surface area) is PI*radius^2*height. Define the toString method in a way similar to that for the Sphere class.

3.

The file Paint.java contains a class for a type of paint (which has a “coverage” and a method to compute the amount of paint needed to paint a shape). Correct the return statement in the amount method so the correct amount will be returned. Use the fact that the amount of paint needed is the area of the shape divided by the coverage for the paint. (NOTE: Leave the print statement - it is there for illustration purposes, so you can see the method operating on different types of Shape objects.)

4.

The file PaintThings.java contains a program that computes the amount of paint needed to paint various shapes. A paint object has been instantiated. Add the following to complete the program: □ Instantiate the three shape objects: deck to be a 20 by 35 foot rectangle, bigBall to be a sphere of radius 15, and tank to be a cylinder of radius 10 and height 30. □ Make the appropriate method calls to assign the correct values to the three amount variables. □ Run the program and test it. You should see polymorphism in action as the amount method computes the amount of paint for various shapes.

//***************************************** // Sphere.java // // Represents a sphere. //***************************************** public class Sphere extends Shape { private double radius; //radius in feet //---------------------------------// Constructor: Sets up the sphere. //---------------------------------public Sphere(double r) { super("Sphere"); radius = r; } //----------------------------------------// Returns the surface area of the sphere. //----------------------------------------public double area() { return 4*Math.PI*radius*radius; } Chapter 10: Polymorphism

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//----------------------------------// Returns the sphere as a String. //----------------------------------public String toString() { return super.toString() + " of radius " + radius; } } //***************************************************** // Paint.java // // Represents a type of paint that has a fixed area // covered by a gallon. All measurements are in feet. // ***************************************************** public class Paint { private double coverage;

//number of square feet per gallon

//----------------------------------------// Constructor: Sets up the paint object. //----------------------------------------public Paint(double c) { coverage = c; } //--------------------------------------------------// Returns the amount of paint (number of gallons) // needed to paint the shape given as the parameter. //--------------------------------------------------public double amount(Shape s) { System.out.println ("Computing amount for " + s); return 0; } }

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//*********************************************************** // PaintThings.java // // Computes the amount of paint needed to paint various // things. Uses the amount method of the paint class which // takes any Shape as a parameter. //*********************************************************** import java.text.DecimalFormat; public class PaintThings { //----------------------------------------// Creates some shapes and a Paint object // and prints the amount of paint needed // to paint each shape. //----------------------------------------public static void main (String[] args) { final double COVERAGE = 350; Paint paint = new Paint(COVERAGE); Rectangle deck; Sphere bigBall; Cylinder tank; double deckAmt, ballAmt, tankAmt; // Instantiate the three shapes to paint // Compute the amount of paint needed for each shape // Print the amount of paint for each.

DecimalFormat fmt = new DecimalFormat("0.#"); System.out.println ("\nNumber of gallons of paint needed..."); System.out.println ("Deck " + fmt.format(deckAmt)); System.out.println ("Big Ball " + fmt.format(ballAmt)); System.out.println ("Tank " + fmt.format(tankAmt)); } }

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Polymorphic Sorting The file Sorting.java contains the Sorting class from Listing 9.9 in the text. This class implements both the selection sort and the insertion sort algorithms for sorting any array of Comparable objects in ascending order.

In this exercise, you will use the Sorting class to sort several different types of objects.

1.

The file Numbers.java reads in an array of integers, invokes the selection sort algorithm to sort them, and then prints the sorted array. Save Sorting.java and Numbers.java to your directory. Numbers.java won’t compile in its current form. Study it to see if you can figure out why.

2.

Try to compile Numbers.java and see what the error message is. The problem involves the difference between primitive data and objects. Change the program so it will work correctly (note: you don’t need to make many changes - the autoboxing feature of Java 1.5 will take care of most conversions from int to Integer).

3.

Write a program Strings.java, similar to Numbers.java, that reads in an array of String objects and sorts them. You may just copy and edit Numbers.java.

4.

Modify the insertionSort algorithm so that it sorts in descending order rather than ascending order.

Change Numbers.java and Strings.java to call insertionSort rather than selectionSort. Run both to make sure the sorting is correct.

5.

The file Salesperson.java partially defines a class that represents a sales person. This is very similar to the Contact class in Listing 9.10. However, a sales person has a first name, last name, and a total number of sales (an int) rather than a first name, last name, and phone number. Complete the compareTo method in the Salesperson class. The comparison should be based on total sales; that is, return a negative number if the executing object has total sales less than the other object and return a positive number if the sales are greater. Use the name of the sales person to break a tie (alphabetical order).

6.

The file WeeklyS ales .java contains a driver for testing the compareTo method and the sorting (this is similar to Listing 9.8 in the text). Compile and run it. Make sure your compareTo method is correct.

The sales staff should be listed in order of sales from most to least with the four people having the same number of sales in reverse alphabetical order.

7.

OPTIONAL: Modify WeeklySales.java so the salespeople are read in rather than hardcoded in the program.

//****************************************************************** // Sorting.java Author: Lewis/Loftus // // Demonstrates the selection sort and insertion sort algorithms. //****************************************************************** public class Sorting { //----------------------------------------------------------------// Sorts the specified array of objects using the selection // sort algorithm. //----------------------------------------------------------------public static void selectionSort (Comparable[] list) { int min; Comparable temp; for (int index = 0; index < list.length-1; index++) { min = index; for (int scan = index+1; scan < list.length; scan++) if (list[scan].compareTo(list[min]) < 0)

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min = scan; // Swap the values temp = list[min]; list[min] = list[index]; list[index] = temp; } } //----------------------------------------------------------------// Sorts the specified array of objects using the insertion // sort algorithm. //----------------------------------------------------------------public static void insertionSort (Comparable[] list) { for (int index = 1; index < list.length; index++) { Comparable key = list[index]; int position = index; // Shift larger values to the right while (position > 0 && key.compareTo(list[position-1]) < 0) { list[position] = list[position-1]; position--; } list[position] = key; } } } //********************************************************** // Numbers.java // // Demonstrates selectionSort on an array of integers. //********************************************************** import java.util.Scanner; public class Numbers { //--------------------------------------------// Reads in an array of integers, sorts them, // then prints them in sorted order. //--------------------------------------------public static void main (String[] args) { int[] intList; int size; Scanner scan = new Scanner(System.in); System.out.print ("\nHow many integers do you want to sort? "); size = scan.nextInt(); intList = new int[size]; System.out.println ("\nEnter the numbers..."); for (int i = 0; i < size; i++) intList[i] = scan.nextInt(); Sorting.selectionSort(intList) ; Chapter 10: Polymorphism

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System.out.println ("\nYour numbers in sorted order..."); for (int i = 0; i < size; i++) System.out.print(intList[i] + " "); System.out.println (); } } // ******************************************************* // Salesperson.java // // Represents a sales person who has a first name, last // name, and total number of sales. // ******************************************************* public class Salesperson implements Comparable { private String firstName, lastName; private int totalSales; //-----------------------------------------------------// Constructor: Sets up the sales person object with // the given data. //-----------------------------------------------------public Salesperson (String first, String last, int sales) { firstName = first; lastName = last; totalSales = sales; } //------------------------------------------// Returns the sales person as a string. //------------------------------------------public String toString() { return lastName + ", " + firstName + ": \t" + totalSales; } //------------------------------------------// Returns true if the sales people have // the same name. //------------------------------------------public boolean equals (Object other) { return (lastName.equals(((Salesperson)other).getLastName()) && firstName.equals(((Salesperson)other).getFirstName())); } //-------------------------------------------------// Order is based on total sales with the name // (last, then first) breaking a tie. //-------------------------------------------------public int compareTo(Object other) { int result; return result; } //------------------------// First name accessor. //------------------------public String getFirstName() { 186

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return firstName; } //------------------------// Last name accessor. //------------------------public String getLastName() { return lastName; } //------------------------// Total sales accessor. //------------------------public int getSales() { return totalSales; } }

// ****************************************************************** // WeeklySales.java // // Sorts the sales staff in descending order by sales. // ****************************************************************** public class WeeklySales { public static void main(String[] args) { Salesperson[] salesStaff = new Salesperson[10]; salesStaff[0] = new salesStaff[1] = new salesStaff[2] = new salesStaff[3] = new salesStaff[4] = new salesStaff[5] = new salesStaff[6] = new salesStaff[7] = new salesStaff[8] = new salesStaff[9] = new

Salesperson("Jane", "Jones", 3000); Salesperson("Daffy", "Duck", 4935); Salesperson("James", "Jones", 3000); Salesperson("Dick", "Walter", 2800); Salesperson("Don", "Trump", 1570); Salesperson("Jane", "Black", 3000); Salesperson("Harry", "Taylor", 7300); Salesperson("Andy", "Adams", 5000); Salesperson("Jim", "Doe", 2850); Salesperson("Walt", "Smith", 3000);

Sorting.insertionSort(salesStaff); System.out.println ("\nRanking of Sales for the Week\n"); for (Salesperson s : salesStaff) System.out.println (s); } }

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Searching and Sorting In An Integer List File IntegerList.java contains a Java class representing a list of integers. The following public methods are provided: □ □ □ □ □

IntegerList(int size)—creates a new list of size elements. Elements are initialized to 0. void randomize()—fills the list with random integers between 1 and 100, inclusive. void print()—prints the array elements and indices int search(int target)—looks for value target in the list using a linear (also called sequential) search algorithm. Returns the index where it first appears if it is found, -1 otherwise. void selectionSort()—sorts the lists into ascending order using the selection sort algorithm.

File IntegerListTest.java contains a Java program that provides menu-driven testing for the IntegerList class.

Copy both files to your directory, and compile and run IntegerListTest to see how it works. For example, create a list, print it, and search for an element in the list. Does it return the correct index? Now look for an element that is not in the list. Now sort the list and print it to verify that it is in sorted order.

Modify the code in these files as follows: 1.

Add a method void replaceFirst(int oldVal, int newVal) to the IntegerList class that replaces the first occurrence of oldVal in the list with newVal. If oldVal does not appear in the list, it should do nothing (but it’s not an error). If oldVal appears multiple times, only the first occurrence should be replaced. Note that you already have a method to find oldVal in the list; use it!

Add an option to the menu in IntegerListTest to test your new method.

2.

Add a method void replaceAll(int oldVal, int newVal) to the IntegerList class that replaces all occurrences of oldVal in the list with newVal. If oldVal does not appear in the list, it should do nothing (but it’s not an error). Does it still make sense to use the search method like you did for replaceFirst, or should you do your own searching here? Think about this.

Add an option to the menu in IntegerListTest to test your new method.

3.

Add a method void sortDecreasing() to the IntegerList class that sorts the list into decreasing (instead of increasing) order. Use the selection sort algorithm, but modify it to sort the other way. Be sure you change the variable names so they make sense!

Add an option to the menu in IntegerListTest to test your new method.

4.

Add a method int binarySearchD (int target) to the IntegerList class that uses a binary search to find the target assuming the list is sorted in decreasing order. If the target is found, the method should return its index; otherwise the method should return –1. Your algorithm will be a modification of the binary search algorithm in listing 10.12 of the text.

Add an option to the menu in IntegerListTest to test your new method. In testing, make sure your method works on a list sorted in descending order then see what the method does if the list is not sorted (it shouldn’t be able to find some things that are in the list).

// ************************************************************* // IntegerList.java // // Define an IntegerList class with methods to create, fill, // sort, and search in a list of integers. // // *************************************************************

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public class IntegerLis0074 { int[] list; //values in the list //------------------------------------------------------//create a list of the given size //------------------------------------------------------public IntegerList(int size) { list = new int[size]; } //------------------------------------------------------//fill array with integers between 1 and 100, inclusive //------------------------------------------------------public void randomize() { for (int i=0; i<list.length; i++) list[i] = (int)(Math.random() * 100) + 1; } //------------------------------------------------------//print array elements with indices //------------------------------------------------------public void print() { for (int i=0; i<list.length; i++) System.out.println(i + ":\t" + list[i]); } //------------------------------------------------------//return the index of the first occurrence of target in the list. //return -1 if target does not appear in the list //------------------------------------------------------public int search(int target) { int location = -1; for (int i=0; i<list.length && location == -1; i++) if (list[i] == target) location = i; return location; } //------------------------------------------------------//sort the list into ascending order using the selection sort algorithm //------------------------------------------------------public void selectionSort() { int minIndex; for (int i=0; i < list.length-1; i++) { //find smallest element in list starting at location i minIndex = i; for (int j = i+1; j < list.length; j++) if (list[j] < list[minIndex]) minIndex = j; //swap list[i] with smallest element int temp = list[i];

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list[i] = list[minIndex]; list[minIndex] = temp; } } }

// **************************************************************** // IntegerListTest.java // // Provide a menu-driven tester for the IntegerList class. // // **************************************************************** import java.util.Scanner; public class IntegerListTest { static IntegerList list = new IntegerList(10); static Scanner scan = new Scanner(System.in); //------------------------------------------------------// Create a list, then repeatedly print the menu and do what the // user asks until they quit //------------------------------------------------------public static void main(String[] args) { printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } //------------------------------------------------------// Do what the menu item calls for //------------------------------------------------------public static void dispatch(int choice) { int loc; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: System.out.println("How big should the list be?"); int size = scan.nextInt(); list = new IntegerList(size); list.randomize(); break; case 2: list.selectionSort(); break; case 3: System.out.print("Enter the value to look for: "); loc = list.search(scan.nextInt());

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if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 4: list.print(); break; default: System.out.println("Sorry, invalid choice"); } } //-----------------------------------------------------// Print the user's choices //-----------------------------------------------------public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Create a new list (** do this first!! **)"); System.out.println("2: Sort the list using selection sort"); System.out.println("3: Find an element in the list using linear search"); System.out.println("4: Print the list"); System.out.print("\nEnter your choice: "); } }

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Timing Searching and Sorting Algorithms Chapter 10 has a brief discussion comparing sorting algorithms and searching algorithms. In this exercise you will use an IntegerList class (in the file IntegerList.java) and a driver (in the file IntegerListTest.java) to examine the runtimes of the searching and sorting algorithms. The IntegerListTest class has several options for creating a list of a given size, filling the list with random integers or with already sorted integers, and searching or sorting the list. (NOTE: You may have used a version of these classes in a previous lab.) Add the methods minIndex, swap, linearSearch, and binarySearch to the IntegerList class (see the calls to determine the parameters). Run IntegerListTest a few times to explore the options.

The runtimes of the sorting and searching algorithms can be examined using the Java method System.currentTimeMillis(), which returns the current system time in milliseconds. (Note that it returns a long, not an int.) You will have to import java.util.* to have access to this method. In IntegerListTest, just get the system time immediately before and immediately after you perform any of the searches or sorts. Then subtract the first from the second, and you have the time required for the operation in milliseconds. WARNING: Be sure you are not including any input or output in your timed operations; these are very expensive and will swamp your algorithm times!

Add appropriate calls to System.currentTimeMillis() to your program, run it and fill out the tables below. Note that you will use much larger arrays for the search algorithms than for the sort algorithms; do you see why?

Also note that the first couple of times you run a method you might get longer runtimes as it loads the code for that method. Ignore these times and use the “steady-state” times you get on subsequent runs. On a separate sheet, explain the times you see in terms of the known complexities of the algorithms. Remember that the most interesting thing is not the absolute time required by the algorithms, but how the time changes as the size of the input increases (doubles here).

Array Size

Selection Sort (random array)

Selection Sort (sorted array)

Insertion Sort (random array)

Selection Sort (sorted array)

10,000 20,000 40,000 80,000 Array Size

Linear Search (unsuccessful)

Binary Search (unsuccessful)

100,000 200,000 400,000 800,000 1,600,000

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// ****************************************************************** // FILE: IntegerList.java // // Purpose: Define an IntegerList class with methods to create, fill, // sort, and search in a list of integers. // ****************************************************************** import java.util.Scanner; public class IntegerList { int[] list; //values in the list //-----------------------------------------------------------// Constructor -- takes an integer and creates a list of that // size. All elements default to value 0. //-----------------------------------------------------------public IntegerList(int size) { list = new int[size]; } //-----------------------------------------------------------// randomize -- fills the array with randomly generated integers // between 1 and 100, inclusive //-----------------------------------------------------------public void randomize() { int max = list.length; for (int i=0; i<list.length; i++) list[i] = (int)(Math.random() * max) + 1; } //-----------------------------------------------------------// fillSorted -- fills the array with sorted values //-----------------------------------------------------------public void fillSorted() { for (int i=0; i<list.length; i++) list[i] = i + 2; } //-----------------------------------------------------------// print -- prints array elements with indices, one per line //-----------------------------------------------------------public String toString() { String s = ""; for (int i=0; i<list.length; i++) s += i + ":\t" + list[i] + "\n" return s; } //-----------------------------------------------------------// linearSearch -- takes a target value and returns the index // of the first occurrence of target in the list. Returns -1 // if target does not appear in the list //-----------------------------------------------------------public int linearSearch(int target) { int location = -1; for (int i=0; i<list.length && location == -1; i++) if (list[i] == target) Chapter 10: Polymorphism

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location = i; return location; } //-----------------------------------------------------------// sortIncreasing -- uses selection sort //-----------------------------------------------------------public void sortIncreasing() { for (int i=0; i<list.length-1; i++) { int minIndex = minIndex(list, i); swap(list, i, minIndex); } } // **************************************************************** // FILE: IntegerListTest.java // // Purpose: Provide a menu-driven tester for the IntegerList class. // // **************************************************************** import java.util.Scanner; public class IntegerListTest { static IntegerList list = new IntegerList(10); static Scanner scan = new Scanner(System.in); //-----------------------------------------------------// main -- creates an initial list, then repeatedly prints // the menu and does what the user asks until they quit //-----------------------------------------------------public static void main(String[] args) { printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } //-----------------------------------------------------// dispatch -- takes a choice and does what needs doing //-----------------------------------------------------public static void dispatch(int choice) { int loc; int val; long time1, time2; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: System.out.println(list); break; case 2: System.out.println("How big should the list be?"); list = new IntegerList(scan.nextInt()); System.out.println("List is created."); 194

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break; case 3: list.randomize(); System.out.println("List is filled with random elements."); break; case 4: list.fillSorted() ; System.out.println("List is filled with sorted elements."); break; case 5: System.out.print("Enter the value to look for: "); val = scan.nextInt(); loc = list.linearSearch(val); if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 6: System.out.print("Enter the value to look for: "); val = scan.nextInt(); loc = list.binarySearch(val); if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 7: list.sortIncreasing(); System.out.println("List has been sorted."); break; case 8: list.sortDecreasing(); System.out.println("List has been sorted."); break; default: System.out.println("Sorry, invalid choice"); } } //----------------------------------------------------// printMenu -- prints the user's choices //----------------------------------------------------public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Print the list"); System.out.println("2: Create a new list of a given size"); System.out.println("3: Fill the list with random ints in range 1-length"); System.out.println("4: Fill the list with already sorted elements"); System.out.println("5: Use linear search to find an element"); System.out.println("6: Use binary search to find an element " + "(list must be sorted in increasing order)"); System.out.println("7: Use selection sort to sort the list into " + " increasing order"); System.out.println("8: Use insertion sort to sort the list into " + " decreasing order"); System.out.print("\nEnter your choice: "); } Chapter 10: Polymorphism

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Coloring a Movable Circle File MoveCircle.java contains a program that uses CirclePanel.java to draw a circle and let the user move it by pressing buttons. Save these files to your directory and compile and run MoveCircle to see how it works. Then study the code, noting the following: □

□ □ □

CirclePanel uses a BorderLayout so that the buttons can go on the bottom. But the buttons are not added directly to the south of the main panel—if they were they would all be on top of each other, and only the last one would show. Instead, a new panel buttonPanel is created and the buttons are added to it. buttonPanel uses a flow layout (the default panel layout), so the buttons will appear next to each other and centered. This panel is added to the south of the main panel.

The listeners for the buttons are all instances of the MoveListener class, which is also defined here. The parameters to the constructor tell how how many pixels in the x and y directions the circle should move when the button is pressed.

The circle is not drawn in the constructor, as it is not a component. It is drawn in paintComponent, which provides a graphics context for drawing on CirclePanel.

In MoveCircle the frame size is explicitly set so there will be room to move the circle around.

Modify the program as follows.

1.

Modify CirclePanel so that in addition to moving the circle, the user can press a button to change its color.

The color buttons should be on the top of the panel; have four color choices. You will need to do the following: □ Create a button for each color you want to provide, and label them appropriately. □ Write a new listener class ColorListener whose constructor takes the color the circle should change to.

When the button is pressed, just change the circle’s color and repaint. □ Create a new ColorListener for each color button, and add the listeners to the buttons. □ Create a panel for the color buttons to go on, and add them to it. □ Add the color panel to the north part of the main panel.

You do not need to make any changes to MoveCircle.

2.

Set the background or text (you choose) of each button to be the color that it represents.

3.

Add another button to the top that says “Choose Color.” Place the button in the middle of your other color buttons. When pressed, this button should bring up a JColorChooser, and the circle color should become the color that the user chooses. You can use the same ColorListener class that you used for the other buttons; just pass null for the color when the user wants to choose their own, and in the actionPerformed method bring up a JColorChooser if the color is null. Remember that the easiest way to use a JColorChooser is to call its static showDialog method, passing three parameters: the component to add it to (the “Choose Color” button), a string to title the chooser window, and a default color (the current circle color). Note that the “Choose Color” button will have to be an instance variable (instead of being local to the CirclePanel constructor like the other buttons) to be visible in the listener.

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// ****************************************************************** // MoveCircle.java // // Uses CirclePanel to display a GUI that lets the user move // a circle by pressing buttons. // ****************************************************************** import java.awt.*; import javax.swing.*; public class MoveCircle { //----------------------------------// Set up a frame for the GUI. //----------------------------------public static void main(String[] args) { JFrame frame = new JFrame ("MoveCircle"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setPreferredSize(new Dimension(400,300)); frame.getContentPane().add(new CirclePanel(400,300)); frame.pack(); frame.setVisible(true); } }

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// ****************************************************************** // CirclePanel.java // // A panel with a circle drawn in the center and buttons on the // bottom that move the circle. // ****************************************************************** import java.awt.*; import javax.swing.*; import java.awt.event.*; public class CirclePanel extends JPanel { private final int CIRCLE_SIZE = 50; private int x,y; private Color c; //---------------------------------------------------------------// Set up circle and buttons to move it. //---------------------------------------------------------------public CirclePanel(int width, int height) { // Set coordinates so circle starts in middle x = (width/2)-(CIRCLE_SIZE/2); y = (height/2)-(CIRCLE_SIZE/2); c = Color.green; // Need a border layout to get the buttons on the bottom this.setLayout(new BorderLayout()); // Create buttons to move the circle JButton left = new JButton("Left"); JButton right = new JButton("Right"); JButton up = new JButton("Up"); JButton down = new JButton("Down"); // Add listeners to the buttons left.addActionListener(new MoveListener(-20,0)); right.addActionListener(new MoveListener(20,0)); up.addActionListener(new MoveListener(0,-20)); down.addActionListener(new MoveListener(0,20)); // Need a panel to put the buttons on or they'll be on // top of each other.

JPanel buttonPanel = new JPanel(); buttonPanel.add(left); buttonPanel.add(right); buttonPanel.add(up); buttonPanel. add(down); // Add the button panel to the bottom of the main panel this. add (buttonPanel, " South") ; } //---------------------------------------------------------------// Draw circle on CirclePanel //---------------------------------------------------------------public void paintComponent(Graphics page) {

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super.paintComponent(page) ; page.setColor(c) ; page.fillOval(x,y,CIRCLE_SIZE,CIRCLE_SIZE) ; } //---------------------------------------------------------------// Class to listen for button clicks that move circle. //---------------------------------------------------------------private class MoveListener implements ActionListener { private int dx; private int dy; //-------------------------------------------------------------// Parameters tell how to move circle at click. //-------------------------------------------------------------public MoveListener(int dx, int dy) { thi s.dx = dx ; this.dy = dy; } //-------------------------------------------------------------// Change x and y coordinates and repaint. //-------------------------------------------------------------public void actionPerformed(ActionEvent e) { x += dx; y += dy; repaint(); } } }

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Speed Control The files SpeedControl.java and SpeedControlPanel.java contain a program (and its associated panel) with a circle that moves on the panel and rebounds from the edges. (NOTE: the program is derived from Listing 8.15 and 8.16 in the text. That program uses an image rather than a circle. You may have used it in an earlier lab on animation.) The Circle class is in the file Circle.java. Save the program to your directory and run it to see how it works.

In this lab exercise you will add to the panel a slider that controls the speed of the animation. Study the code in SlideColorPanel.java (Listing 10.16 in the text) to help understand the steps below.

1.

Set up a JSlider object. You need to □ Declare it. □ Instantiate it to be a JSlider that is horizontal with values ranging from 0 to 200, initially set to 30. □ Set the major tick spacing to 40 and the minor tick spacing to 10. □ Set paint ticks and paint labels to true and the X alignment to left.

2.

Set up the change listener for the slider. A skeleton of a class named SlideListener is already in SpeedControlPanel.java. You need to □ Complete the body of the statedChanged function. This function must determine the value of the slider, then set the timer delay to that value. The timer delay can be set with the method setDelay (int delay) in the Timer class. □ Add the change listener to the JSlider object.

3.

Create a label (“Timer Delay”) for the slider and align it to the left.

4.

Create a JPanel object and add the label and slider to it then add your panel to the SOUTH of the main panel (note that it has already been set up to use a border layout).

5.

Compile and run the program. Make sure the speed is changing when the slider is moved. (NOTE: Larger delay means slower!)

6.

You should have noticed one problem with the program. The ball (circle) goes down behind the panel the slider is on. To fix this problem do the following: □ In actionPerformed, declare a variable slidePanelHt (type int). Use the getSize() method to get the size (which is a Dimension object) of the panel you put the slider on. Assign slidePanelHt to be the height of the Dimension object. For example, if your panel is named slidePanel the following assignment statement is what you need: slidePanelHt = slidePanel.getSize().height; □ □

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Now use this height to adjust the condition that tests to see if the ball hits the bottom of the panel.

Test your program to make sure it is correct.

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// ******************************************************************** // SpeedControl.java // // Demonstrates animation -- balls bouncing off the sides of a panel // with speed controlled by a slider. // ******************************************************************** import java.awt.*; import java.awt.event.*; import javax.swing.*; public class SpeedControl { // // Sets up the frame for the animation. // public void static main (String[] args) { JFrame frame = new JFrame ("Bouncing Balls"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); frame.getContentPane.add(new SpeedControlPanel ()); frame.pack(); frame.setVisible(true); } }

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// ****************************************************************** // SpeedControlPanel.java // // The panel for the bouncing ball. Similar to // ReboundPanel.java in Listing 8.16 in the text, except a circle // rather than a happy face is rebounding off the edges of the // window. // ****************************************************************** import java.awt.*; import java.awt.event.*; import javax. swing. *; import javax.swing.event.*; public class SpeedControlPanel extends JPanel { private final int WIDTH = 600; private final int HEIGHT = 400; private final int BALL_SIZE = 50; private Circle bouncingBall; private Timer timer; private int moveX, moveY;

// the object that moves // increment to move each time

// // Sets up the panel, including the timer // for the animation // public SpeedControlPanel () { timer = new Timer(30, new ReboundListener()); this.setLayout (new BorderLayout()); bouncingBall = new Circle(BALL_SIZE); moveX = moveY = 5; // Set up a slider object here setPreferredSize (new Dimension (WIDTH, HEIGHT)); setBackground(Color.black); timer.start(); } // // Draw the ball // public void paintComponent (Graphics page) { super.paintComponent (page); bouncingBall.draw(page); } // *************************************************** // An action listener for the timer // *************************************************** public class ReboundListener implements ActionListener { //

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// actionPerformed is called by the timer -- it updates // the position of the bouncing ball // public void actionPerformed(ActionEvent action) { bouncingBall.move(moveX, moveY); // change direction if ball hits a side int x = bouncingBall.getX(); int y = bouncingBall.getY(); if (x < 0 || x >= WIDTH - BALL_SIZE) moveX = moveX * -1; if (y <= 0 || y >= HEIGHT - BALL_SIZE) moveY = moveY * -1; repaint(); } } // *************************************************** // A change listener for the slider. // *************************************************** private class SlideListener implements ChangeListener { // // Called when the state of the slider has changed; // resets the delay on the timer. // public void stateChanged (ChangeEvent event) { } } }

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// **************************************************************** // FILE: Circle.java // // Purpose: Define a Circle class with methods to create and draw // a circle of random size, color, and location. // **************************************************************** import java.awt.*; import java.util.Random; public class Circle { private int x, y; private int radius; private Color color;

// coordinates of the corner // radius of the circle // color of the circle

static Random generator = new Random(); //--------------------------------------------------------// Creates a random circle with properties in ranges given: // -- radius 25..74 // -- color RGB value 0..16777215 (24-bit) // -- x-coord of upper left-hand corner 0..599 // -- y-coord of upper left-hand corner 0..399 //--------------------------------------------------------public Circle() { radius = Math.abs(generator.nextInt())%50 + 25; color = new Color(Math.abs(generator.nextInt())% 16777216); x = Math.abs(generator.nextInt())%600; y = Math.abs(generator.nextInt())%400; } //--------------------------------------------------------// Creates a circle of a given size (diameter). Other // attributes are random (as described above) //--------------------------------------------------------public Circle(int size) { radius = Math.abs(size/2); color = new Color(Math.abs(generator.nextInt())% 16777216); x = Math.abs(generator.nextInt())%600; y = Math.abs(generator.nextInt())%400; } //--------------------------------------------------------// Draws circle on graphics object given //--------------------------------------------------------public void draw(Graphics page) { page. setColor (color) ; page.fillOval(x,y,radius*2,radius*2); } //--------------------------------------------------------// Shifts the circle's position -- "over" is the number of // pixels to move horizontally (positive is to the right;

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// negative to the left); "down" is the number of pixels // to move vertically (positive is down; negative is up) //--------------------------------------------------------public void move (int over, int down) { x = x + over; y = y + down; } //---------------------------------------------// Return the x coordinate of the circle corner //---------------------------------------------public int getX() { return x; } //---------------------------------------------// Return the y coordinate of the circle corner //---------------------------------------------public int getY() { return y; } }

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Chapter 11: Exceptions Lab Exercises Topics

Lab Exercises

Exceptions

Exceptions Aren’t Always Errors Placing Exception Handlers Throwing Exceptions

File Input and Output

Copying a File Reading from and Writing to Text Files

Mnemonics Tooltips Disabling Buttons

A Movable Circle

Combo Boxes

A Currency Converter

Scroll Panes

Listing Prime Numbers

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Exceptions Aren’t Always Errors File CountLetters.java contains a program that reads a word from the user and prints the number of occurrences of each letter in the word. Save it to your directory and study it, then compile and run it to see how it works. In reading the code, note that the word is converted to all upper case first, then each letter is translated to a number in the range 0..25 (by subtracting ‘A’) for use as an index. No test is done to ensure that the characters are in fact letters.

1.

Run CountLetters and enter a phrase, that is, more than one word with spaces or other punctuation in between. It should throw an ArrayIndexOutOfBoundsException, because a non-letter will generate an index that is not between 0 and 25. It might be desirable to allow non-letter characters, but not count them.

Of course, you could explicitly test the value of the character to see if it is between ‘A’ and ‘Z’. However, an alternative is to go ahead and use the translated character as an index, and catch an ArrayIndexOutOfBoundsException if it occurs. Since you want don’t want to do anything when a nonletter occurs, the handler will be empty. Modify this method to do this as follows: □ Put the body of the first for loop in a try. □ Add a catch that catches the exception, but don’t do anything with it.

Compile and run your program.

2.

Now modify the body of the catch so that it prints a useful message (e.g., “Not a letter”) followed by the exception. Compile and run the program. Although it’s useful to print the exception for debugging, when you’re trying to smoothly handle a condition that you don’t consider erroneous you often don’t want to. In your print statement, replace the exception with the character that created the out of bounds index. Run the program again; much nicer!

// **************************************************************** // CountLetters.java // // Reads a words from the standard input and prints the number of // occurrences of each letter in that word. // // **************************************************************** import java.util.Scanner; public class CountLetters { public static void main(String[] args) { int[] counts = new int[26]; Scanner scan = new Scanner(System.in); //get word from user System.out.print("Enter a single word (letters only, please): "); String word = scan.nextLine(); //convert to all upper case word = word.toUpperCase(); //count frequency of each letter in string for (int i=0; i < word.length(); i++) counts[word.charAt(i)-'A']++; //print frequencies System.out.println(); for (int i=0; i < counts.length; i++) if (counts [i] != 0) System.out.println((char)(i +'A') + ": " + counts[i]); } } Chapter 11: Exceptions

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Placing Exception Handlers File ParseInts.java contains a program that does the following: □ □ □ □

Prompts for and reads in a line of input Uses a second Scanner to take the input line one token at a time and parses an integer from each token as it is extracted.

Sums the integers.

Prints the sum.

Save ParseInts to your directory and compile and run it. If you give it the input 10 20 30 40 it should print The sum of the integers on the line is 100.

Try some other inputs as well. Now try a line that contains both integers and other values, e.g., We have 2 dogs and 1 cat.

You should get a NumberFormatException when it tries to call Integer.parseInt on “We”, which is not an integer. One way around this is to put the loop that reads inside a try and catch the NumberFormatException but not do anything with it. This way if it’s not an integer it doesn’t cause an error; it goes to the exception handler, which does nothing. Do this as follows: □ Modify the program to add a try statement that encompasses the entire while loop. The try and opening { should go before the while, and the catch after the loop body. Catch a NumberFormatException and have an empty body for the catch. □ Compile and run the program and enter a line with mixed integers and other values. You should find that it stops summing at the first non-integer, so the line above will produce a sum of 0, and the line “1 fish 2 fish” will produce a sum of 1. This is because the entire loop is inside the try, so when an exception is thrown the loop is terminated. To make it continue, move the try and catch inside the loop. Now when an exception is thrown, the next statement is the next iteration of the loop, so the entire line is processed. The dogs-and-cats input should now give a sum of 3, as should the fish input.

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// **************************************************************** // ParseInts.java // // Reads a line of text and prints the integers in the line. // // **************************************************************** import java.util.Scanner; public class ParseInts { public static void main(String[] args) { int val, sum=0; Scanner scan = new Scanner(System.in); String line; System.out.println("Enter a line of text"); Scanner scanLine = new Scanner(scan.nextLine()); while (scanLine.hasNext()) { val = Integer.parseInt(scanLine.next()); sum += val; } System.out.println("The sum of the integers on this line is " + sum); } }

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Throwing Exceptions File Factorials.java contains a program that calls the factorial method of the MathUtils class to compute the factorials of integers entered by the user. Save these files to your directory and study the code in both, then compile and run Factorials to see how it works. Try several positive integers, then try a negative number. You should find that it works for small positive integers (values < 17), but that it returns a large negative value for larger integers and that it always returns 1 for negative integers.

1.

Returning 1 as the factorial of any negative integer is not correct—mathematically, the factorial function is not defined for negative integers. To correct this, you could modify your factorial method to check if the argument is negative, but then what? The method must return a value, and even if it prints an error message, whatever value is returned could be misconstrued. Instead it should throw an exception indicating that something went wrong so it could not complete its calculation. You could define your own exception class, but there is already an exception appropriate for this situation—IllegalArgumentException, which extends RuntimeException. Modify your program as follows: □ Modify the header of the factorial method to indicate that factorial can throw an IllegalArgumentException. □ Modify the body of factorial to check the value of the argument and, if it is negative, throw an IllegalArgumentException. Note that what you pass to throw is actually an instance of the IllegalArgumentException class, and that the constructor takes a String parameter. Use this parameter to be specific about what the problem is. □ Compile and run your Factorials program after making these changes. Now when you enter a negative number an exception will be thrown, terminating the program. The program ends because the exception is not caught, so it is thrown by the main method, causing a runtime error. □ Modify the main method in your Factorials class to catch the exception thrown by factorial and print an appropriate message, but then continue with the loop. Think carefully about where you will need to put the try and catch.

2.

Returning a negative number for values over 16 also is not correct. The problem is arithmetic overflow—the factorial is bigger than can be represented by an int. This can also be thought of as an IllegalArgumentException— this factorial method is only defined for arguments up to 16. Modify your code in factorial to check for an argument over 16 as well as for a negative argument. You should throw an IllegalArgumentException in either case, but pass different messages to the constructor so that the problem is clear.

// **************************************************************** // Factorials.java // // Reads integers from the user and prints the factorial of each. // // **************************************************************** import java.util.Scanner; public class Factorials { public static void main(String[] args) { String keepGoing = "y"; Scanner scan = new Scanner(System.in); while (keepGoing.equals("y") || keepGoing.equals("Y")) { System.out.print("Enter an integer: "); int val = scan.nextInt(); System.out.println("Factorial(" + val + ") = " + MathUtils.factorial(val)); System.out.print("Another factorial? (y/n) "); keepGoing = scan.next(); } } } 210

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// **************************************************************** // MathUtils.java // // Provides static mathematical utility functions. // // **************************************************************** public class MathUtils { //------------------------------------------------------------// Returns the factorial of the argument given //------------------------------------------------------------public static int factorial(int n) { int fac = 1; for (int i=n; i>0; i--) fac *= i; return fac; } }

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Copying a File Write a program that prompts the user for a filename, then opens a Scanner to the file and copies it, a line at a time, to the standard output. If the user enters the name of a file that does not exist, ask for another name until you get one that refers to a valid file. Some things to consider: • Remember that you can create a Scanner from a File object, which you can create from the String representing the filename.

• The Scanner constructor that takes a File may throw a FileNotFoundException -- this is how you will know if the file does not exist. Think carefully about how to use the try/catch structure in combination with a loop that asks for a new filename if the current file does not exist.

• Remember that the scope of a variable declared inside a try is the try itself -- it does not extend to the following code. Furthermore, the compiler knows that an initialization that occurs inside a try may or may not get executed, as the try may be thrown out of first. So any variable that you will want to use both in and after the try must be declared and initialized before the try.

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Reading from and Writing to Text Files Write a program that will read in a file of student academic credit data and create a list of students on academic warning. The list of students on warning will be written to a file. Each line of the input file will contain the student name (a single String with no spaces), the number of semester hours earned (an integer), the total quality points earned (a double). The following shows part of a typical data file: Smith 27 83.7 Jones 21 28.35 Walker 96 182.4 Doe 60 150 The program should compute the GPA (grade point or quality point average) for each student (the total quality points divided by the number of semester hours) then write the student information to the output file if that student should be put on academic warning. A student will be on warning if he/she has a GPA less than 1.5 for students with fewer than 30 semester hours credit, 1.75 for students with fewer than 60 semester hours credit, and 2.0 for all other students. The file Warning.java contains a skeleton of the program. Do the following: 1.

Set up a Scanner object scan from the input file and a PrintWriter outFile to the output file inside the try clause (see the comments in the program). Note that you’ll have to create the PrintWriter from a FileWriter, but you can still do it in a single statement.

2. Inside the while loop add code to read and parse the input—get the name, the number of credit hours, and the number of quality points. Compute the GPA, determine if the student is on academic warning, and if so write the name, credit hours, and GPA (separated by spaces) to the output file.

3. After the loop close the PrintWriter.

4. Think about the exceptions that could be thrown by this program: • A FileNotFoundException if the input file does not exist • A NumberFormatException if it can’t parse an int or double when it tries to - this indicates an error in the input file format • An IOException if something else goes wrong with the input or output stream Add a catch for each of these situations, and in each case give as specific a message as you can. The program will terminate if any of these exceptions is thrown, but at least you can supply the user with useful information.

5. Test the program. Test data is in the file students.dat. Be sure to test each of the exceptions as well. // ************************************************************************ // Warning.java // // Reads student data from a text file and writes data to another text file. // ************************************************************************ import java.util.Scanner; import java.io.*; public class Warning { // // Reads student data (name, semester hours, quality points) from a // text file, computes the GPA, then writes data to another file // if the student is placed on academic warning. // public static void main (String[] args) { int creditHrs; // number of semester hours earned double qualityPts; // number of quality points earned double gpa; // grade point (quality point) average String line, name, inputName = "students.dat"; String outputName = "warning.dat";

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try { // Set up scanner to input file // Set up the output file stream // Print a header to the output file outFile.println (); outFile.println ("Students on Academic Warning"); outFile.println (); // Process the input file, one token at a time while () { // Get the credit hours and quality points and // determine if the student is on warning. If so, // write the student data to the output file. } // Close output file } catch (FileNotFoundException exception) { System.out.println ("The file " + inputName + " was not found."); } catch (IOException exception) { System.out.println (exception); } catch (NumberFormatException e) { System.out.println ("Format error in input file: " + e); } } } students.dat Smith 27 83.7 Jones 21 28.35 Walker 96 182.4 Doe 60 150 Wood 100 400 Street 33 57.4 Taylor 83 190 Davis 110 198 Smart 75 2 92.5 Bird 84 168 Summers 52 83.2

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Enhancing a Movable Circle File MoveCircle.java contains a program that uses CirclePanel.java to draw a circle and let the user move it by pressing buttons. Save these files to your directory and compile and run MoveCircle to see how it works. Then modify the code in CirclePanel as follows: 1.

2.

3.

Add mnemonics to the buttons so that the user can move the circle by pressing the ALT-l, ALT-r, ALT-u, or ALT-d keys.

Add tooltips to the buttons that indicate what happens when the button is pressed, including how far it is moved.

When the circle gets all the way to an edge, disable the corresponding button. When it moves back in, enable the button again. Note that you will need instance variables (instead of local variables in the constructor) to hold the buttons and the panel size to make them visible to the listener. Bonus: In most cases the circle won’t hit the edge exactly; check for this (e.g., x<0) and adjust the coordinates so it does.

// ****************************************************************** // MoveCircle.java // // Uses CirclePanel to display a GUI that lets the user move // a circle by pressing buttons. // ****************************************************************** import java.awt.*; import javax.swing.*; public class MoveCircle { public static void main(String[] args) { JFrame frame = new JFrame ("MoveCircle"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(400, 300); frame.getContentPane().add(new CirclePanel(400,300)); frame.setVisible(true); } }

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// ****************************************************************** // CirclePanel.java // // A panel with a circle drawn in the center and buttons on the // bottom that move the circle. // ****************************************************************** import java.awt.*; import javax.swing.*; import java.awt.event.*; public class CirclePanel extends JPanel { private final int CIRCLE_SIZE = 50; private int x, y; private Color c; //--------------------------------------------------------------// Set up circle and buttons to move it. //--------------------------------------------------------------public CirclePanel(int width, int height) { // Set coordinates so circle starts in middle x = (width/2)-(CIRCLE_SIZE/2); y = (height/2)-(CIRCLE_SIZE/2); c = Color.green; // Need a border layout to get the buttons on the bottom this.setLayout(new BorderLayout()); // Create buttons to move the circle JButton left = new JButton("Left"); JButton right = new JButton("Right"); JButton up = new JButton("Up"); JButton down = new JButton("Down"); // Add listeners to the buttons left.addActionListener(new MoveListener(-20, 0)); right.addActionListener(new MoveListener(20, 0)); up.addActionListener(new MoveListener(0, -20)); down.addActionListener(new MoveListener(0, 20)); // Need a panel to put the buttons on or they'll be on // top of each other.

JPanel buttonPanel = new JPanel(); buttonPanel.add(left); buttonPanel.add(right); buttonPanel.add(up); buttonPanel.add(down); // Add the button panel to the bottom of the main panel this.add (buttonPanel, "South"); } //---------------------------------------------------------------// Draw circle on CirclePanel //---------------------------------------------------------------public void paintComponent(Graphics page) {

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super.paintComponent(page); page.setColor(c); page.fillOval(x,y, CIRCLE_SIZE, CIRCLE_SIZE); } //---------------------------------------------------------------// Class to listen for button clicks that move circle. //---------------------------------------------------------------private class MoveListener implements ActionListener { private int dx; private int dy; //---------------------------------------------------------------// Parameters tell how to move circle at click. //---------------------------------------------------------------public MoveListener(int dx, int dy) { this.dx = dx; this.dy = dy; } //---------------------------------------------------------------// Change x and y coordinates and repaint. //---------------------------------------------------------------public void actionPerformed(ActionEvent e) { x += dx; y += dy; repaint(); } } }

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A Currency Converter Your are headed off on a world-wide trip and need a program to help figure out how much things in other countries cost in dollars. You plan to visit Canada, several countries in Europe, Japan, Australia, India, and Mexico so your program must work for the currencies in those countries. The files CurrencyConverter.java and RatePanel.java contain a skeleton of a program to do this conversion. Complete it as follows: 1.

2.

3.

4.

5.

6.

7.

CurrencyPanel currently contains only two components—a JLabel for the title and a JLabel to display the result of the calculations. It also contains two parallel arrays—one is an array of currency names (an array of strings) and the other an array of corresponding exchange rates (the value of one unit of the currency in U.S. Dollars). Compile and run the program to see what it looks like (not much!!).

Add a combo box to let the user select the currency. The argument to the constructor should be the array of names of the currencies. Note that the first currency name is actually an instruction to the user so there is no need to have an additional label.

Modify actionPerformed in ComboListener so that index is set to be the index of the selected item.

Test what you have so far. It should show what one unit of the given currency is in U.S. dollars.

Now add a text field (and label) so the user can enter the cost of an item in the selected currency. You need to update the ComboListener so that it gets this value from the textfield and computes and displays the equivalent amount in dollars.

Test your program.

Modify the layout to create a more attractive GUI.

// *********************************************************************** // CurrencyConverter.java // // Computes the dollar value of the cost of an item in another currency. // *********************************************************************** import java.awt.*; import javax.swing.*; public class CurrencyConverter { public static void main (String[] args) { JFrame frame = new JFrame ("Currency Converter"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); RatePanel ratePanel = new RatePanel (); frame.getContentPane().add(ratePanel); frame.pack(); frame.setVisible(true); } } // *********************************************************************** // RatePanel.java // // Panel for a program that converts different currencies to // U.S. Dollars // *********************************************************************** import java.awt.*; import java.awt.event.*; import javax.swing.*; public class RatePanel extends JPanel { 218

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private double[] rate; // exchange rates private String[] currencyName; private JLabel result; // // Sets up a panel to convert cost from one of 6 currencies // into U.S. Dollars. The panel contains a heading, a text // field for the cost of the item, a combo box for selecting // the currency, and a label to display the result. // public RatePanel () { JLabel title = new JLabel ("How much is that in dollars?"); title.setAlignmentX (Component.CENTER_ALIGNMENT); title.setFont (new Font ("Helvetica", Font.BOLD, 20)); // Set up the arrays for the currency conversions currencyName = new String[] {"Select the currency..", "European Euro", "Canadian Dollar", "Japanese Yen", "Australian Dollar", "Indian Rupee", "Mexican Peso"}; rate = new double [] {0.0, 1.2103, 0.7351, 0.0091, 0.6969, 0.0222, 0.0880}; result = new JLabel (" ---------------"); add (tittle); add (result); } // ****************************************************** // Represents an action listener for the combo box. // ****************************************************** private class ComboListener implements ActionListener { // // Determines which currency has been selected and // the value in that currency then computes and // displays the value in U.S. Dollars. // public void actionPerformed (ActionEvent event) { int index = 0; result.setText ("1 " + currencyName[index] + " = " + rate[index] + " U.S. Dollars"); } } }

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A List of Prime Numbers The file Primes.java contains a program to compute and list all prime numbers up to and including a number input by the user. Most of the work is done in the file PrimePanel.java that defines the panel. The GUI contains a text field for the user to enter the integer, a button for the user to click to get a list of primes, and a text area to display the primes. However, if the user puts in a large integer the primes do not all fit in the text area. The main goal of this exercise is to add scrolling capabilities to the text area.

Proceed as follows: 1.

2.

3.

4.

Compile and run the program as it is. You should see a GUI that contains the components listed above but nothing happens when you click on the button. Fix this.

Modify PrimePanel.java so that the text area for displaying the primes is in a scroll pane. To do this, keep your JTextArea but create a JScrollPane from it, and add the scroll pane to the panel. (If you look at the JScrollPane documentation on p. 834-835 you’ll see that one of the constructors takes a Component, in this case your JTextArea.) Test your modification.

You should see that the scrollbars don’t appear unless the output is longer than the text area. The default is for the scrollbars to appear only as needed. This can be changed by setting the scroll bar policy of the JScrollPane object. Use the setVerticalScrollBarPolicy method of the JScrollPane class to specify that the vertical scroll bar should always be displayed. The method takes an integer argument that represents the policy. The ScrollPaneConstants class has several static integer constants for the policies. These include VERTICAL_SCROLLBAR_ALWAYS, VERTICAL_SCROLLBAR_AS_NEEDED, VERTICAL_SCROLLBAR_NEVER. It should be clear which of these to use as the parameter. Remember how to access static members of a class!

The code to generate the list of primes could be improved some. Two things that should be done are: □ A exception should be caught if the user enters non-integer data. An appropriate message should be displayed in the text area. □ The loop that looks for divisors of the integer i should not go all the way up to i. Instead it should stop at the square root of i (if a divisor hasn’t been found by then there isn’t one).

Make these modifications.

// ***************************************************************** // Primes.java // // Generates a list of primes less than or equal to the integer // input by the user. // ***************************************************************** import java.awt.*; import javax.swing.*; public class Primes { public static void main (String[] args) { JFrame frame = new JFrame ("Primes"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); PrimePanel primePanel = new PrimePanel (); frame.getContentPane().add(primePanel); frame.pack(); frame.setVisible(true); } }

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// ***************************************************************** // PrimePanel.java // // Represents the panel for a program that displays all primes // up to a number input by the user. // ***************************************************************** import java.awt.*; import java.awt.event.*; import javax.swing.*; public class PrimePanel extends JPanel { private JTextField number; private JButton computeButton; private JTextArea primeList; // // Sets up a panel with a heading, a labeled text field // for the user to enter an integer, a button to trigger // the calculation, and a text area to display the list // of primes. // public PrimePanel () { JLabel heading = new JLabel ("Prime Number Listing"); heading.setFont (new Font("Helvetica", Font.BOLD, 30)); JLabel inputLabel = new JLabel ("Enter a number: "); number = new JTextField (8); computeButton = new JButton ("Click to see all primes up to your number!"); primeList = new JTextArea (10, 30); computeButton.addActionListener(new ButtonListener()); // Add the components to the panel add (heading); add (inputLabel); add (number); add (computeButton); add (primeList); setPreferredSize (new Dimension (400, 320)); setBackground (Color.yellow); } // ************************************************************** // Represents a listener for the click of the button. // ************************************************************** public class ButtonListener implements ActionListener { // // Generates and displays a list of primes when the // button is clicked. // public void actionPerformed (ActionEvent event) { String textNum = number.getText(); int num = Integer.parseInt (textNum); String ans = "";

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int count = 0; if (num < 2) ans = "There no primes less than " + num; else { ans = " " + 2; count++; for (int i = 3; i <= num; i += 2) { boolean foundDivisor = false; int j = 3; while (j < i && ! foundDivisor) { if (i % j == 0) foundDivisor = true; else j++; } // Add i to the list if it is prime if (j == i) { ans += " " + i; count++; if (count % 10 == 0) ans += "\n"; } } } primeList.setText (ans); }

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Chapter 12: Recursion Lab Exercises Topics

Lab Exercises

Basic Recursion

Computing Powers Counting and Summing Digits Base Conversion Efficient Computation of Fibonacci Numbers

Recursion on Strings

Palindromes Printing a String Backwards

Recursion on Arrays

Recursive Linear Search Recursive Binary Search A List of Employees

Fractals

Sierpinski Triangles Modifying the Koch Snowflake

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Computing Powers Computing a positive integer power of a number is easily seen as a recursive process. Consider an: □ □

If n = 0, an is 1 (by definition) If n > 0, an is a * an–1

File Power.java contains a main program that reads in integers base and exp and calls method power to compute baseexp. Fill in the code for power to make it a recursive method to do the power computation. The comments provide guidance. // ***************************************************************** // Power.java // // Reads in two integers and uses a recursive power method // to compute the first raised to the second power. // ***************************************************************** import java.util.Scanner; public class Power { public static void main(String[] args) { int base, exp; int answer; Scanner scan = new Scanner(System.in); System.out.print("Welcome to the power program! "); System.out.println("Please use integers only."); //get base System.out.print("Enter the base you would like raised to a power: "); base = scan.nextInt(); //get exponent System.out.print("Enter the power you would like it raised to: "); exp = scan.nextInt(); answer = power (base,exp); System.out.println(base + " raised to the " + exp + " is " + answer); } // // Computes and returns base^exp // public static int power(int base, int exp) { int pow; //if the exponent is 0, set pow to 1 //otherwise set pow to base*base^(exp-1) //return pow } }

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Counting and Summing Digits The problem of counting the digits in a positive integer or summing those digits can be solved recursively. For example, to count the number of digits think as follows: □ If the integer is less than 10 there is only one digit (the base case). □ Otherwise, the number of digits is 1 (for the units digit) plus the number of digits in the rest of the integer (what’s left after the units digit is taken off). For example, the number of digits in 3278 is 1 + the number of digits in 327.

The following is the recursive algorithm implemented in Java. public int numDigits (int num) { if (num < 10) return (1); //a number < 10 has only one digit else return (1 + numDigits (num / 10)); } Note that in the recursive step, the value returned is 1 (counts the units digit) + the result of the call to determine the number of digits in num /10. Recall that num/10 is the quotient when num is divided by 10 so it would be all the digits except the units digit.

The file DigitPlay.java contains the recursive method numDigits (note that the method is static—it must be since it is called by the static method main). Copy this file to your directory, compile it, and run it several times to see how it works. Modify the program as follows: 1.

Add a static method named sumDigits that finds the sum of the digits in a positive integer. Also add code to main to test your method. The algorithm for sumDigits is very similar to numDigits; you only have to change two lines!

2.

Most identification numbers, such as the ISBN number on books or the Universal Product Code (UPC) on grocery products or the identification number on a traveller’s check, have at least one digit in the number that is a check digit. The check digit is used to detect errors in the number. The simplest check digit scheme is to add one digit to the identification number so that the sum of all the digits, including the check digit, is evenly divisible by some particular integer. For example, American Express Traveller’s checks add a check digit so that the sum of the digits in the id number is evenly divisible by 9. United Parcel Service adds a check digit to its pick up numbers so that a weighted sum of the digits (some of the digits in the number are multiplied by numbers other than 1) is divisible by 7. Modify the main method that tests your sumDigits method to do the following: input an identification number (a positive integer), then determine if the sum of the digits in the identification number is divisible by 7 (use your sumDigits method but don’t change it—the only changes should be in main). If the sum is not divisible by 7 print a message indicating the id number is in error; otherwise print an ok message. (FYI: If the sum is divisible by 7, the identification number could still be incorrect. For example, two digits could be transposed.) Test your program on the following input: □ 3429072 --- error □ 1800237 --- ok □ 88231256 --- ok □ 3180012 --- error

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// ****************************************************************** // DigitPlay.java // // Finds the number of digits in a positive integer. // ****************************************************************** import java.util.Scanner; public class DigitPlay { public static void main (String[] args) { int num; //a number Scanner scan = new Scanner(System.in); System.out.println (); System.out.print ("Please enter a positive integer: "); num = scan.nextInt (); if (num <= 0) System.out.println ( num + " isn't positive -- start over!!"); else { // Call numDigits to find the number of digits in the number // Print the number returned from numDigits System.out.println ("\nThe number " + num + " contains " + + numDigits (num) + " digits."); System.out.println (); } } // // Recursively counts the digits in a positive integer // public static int numDigits (int num) { if (num < 10) return (1); else return (1 + numDigits (num/10)); } }

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Base Conversion One algorithm for converting a base 10 number to base b involves repeated division by the base b. Initially one divides the number by b. The remainder from this division is the units digit (the rightmost digit) in the base b representation of the number (it is the part of the number that contains no powers of b). The quotient is then divided by b on the next iteration. The remainder from this division gives the next base b digit from the right.

The quotient from this division is used in the next iteration. The algorithm stops when the quotient is 0. Note that at each iteration the remainder from the division is the next base b digit from the right—that is, this algorithm finds the digits for the base b number in reverse order.

Here is an example for converting 30 to base 4:

30/4 7/4 1/4

quotient

remainder

7 1 0

2 3 1

= = =

The answer is read bottom to top in the remainder column, so 30 (base 10) = 132 (base 4).

Think about how this is recursive in nature: If you want to convert x (30 in our example) to base b (4 in our example), the rightmost digit is the remainder x % b. To get the rest of the digits, you perform the same process on what is left; that is, you convert the quotient x / b to base b. If x / b is 0, there is no rest; x is a single base b digit and that digit is x % b (which also is just x).

The file BaseConversion.java contains the shell of a method convert to do the base conversion and a main method to test the conversion. The convert method returns a string representing the base b number, hence for example in the base case when the remainder is what is to be returned it must be converted to a String object.

This is done by concatenating the remainder with a null string. The outline of the convert method is as follows: public static String convert (int num, int b) { int quotient; // the quotient when num is divided by base b int remainder; // the remainder when num is divided by base b quotient =

;

remainder =

;

if ( {

) return ("" +

//fill in base case );

} else { // Recursive step: the number is the base b representation of // the quotient concatenated with the remainder return (

);

} } Fill in the blanks above (for now don’t worry about bases greater than 10), then in BaseConversion.java complete the method and main. Main currently asks the user for the number and the base and reads these in.

Add a statement to print the string returned by convert (appropriately labeled).

Test your function on the following input: □

Number: 89 Base: 2 ---> should print 1011001

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□ □

Number: 347 Base: 5 ---> should print 2342 Number: 3289 Base: 8 ---> should print 6331

Improving the program: Currently the program doesn’t print the correct digits for bases greater than 10. Add code to your convert method so the digits are correct for bases up to and including 16. // ***************************************************************** // BaseConversion.java // // Recursively converts an integer from base 10 to another base // ***************************************************************** import java.util.Scanner; public class BaseConversion { public static void main (String[] args) { int base10Num; int base; Scanner scan = new Scanner(System.in); System.out.println (); System.out.println ("Base Conversion Program"); System.out.print ("Enter an integer: "); base10Num = scan.nextInt(); System.out.print ("Enter the base: "); base = scan.nextInt(); // Call convert and print the answer } // // Converts a base 10 number to another base. // public static String convert (int num, int b) { int quotient; // the quotient when num is divided by base b int remainder; // the remainder when num is divided by base b } }

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Efficient Computation of Fibonacci Numbers The Fibonacci sequence is a well-known mathematical sequence in which each term is the sum of the two previous terms. More specifically, if fib(n) is the nth term of the sequence, then the sequence can be defined as follows: fib(0) = 0 fib(1) = 1 fib(n) = fib(n-1) + fib(n-2)

n>1

1.

Because the Fibonacci sequence is defined recursively, it is natural to write a recursive method to determine the nth number in the sequence. File Fib.java contains the skeleton for a class containing a method to compute Fibonacci numbers. Save this file to your directory. Following the specification above, fill in the code for method fib1 so that it recursively computes and returns the nth number in the sequence.

2.

File TestFib.java contains a simple driver that asks the user for an integer and uses the fib1 method to compute that element in the Fibonacci sequence. Save this file to your directory and use it to test your fib1 method. First try small integers, then larger ones. You’ll notice that the number doesn’t have to get very big before the calculation takes a very long time. The problem is that the fib1 method is making lots and lots of recursive calls. To see this, add a print statement at the beginning of your fib1 method that indicates what call is being computed, e.g., “In fib 1(3)” if the parameter is 3. Now run TestFib again and enter 5—you should get a number of messages from your print statement. Examine these messages and figure out the sequence of calls that generated them. (This is easiest if you first draw the call tree on paper.) . Since fib(5) is fib(4) + fib(3), you should not be surprised to find calls to fib(4) and fib(3) in the printout. But why are there two calls to fib(3)? Because both fib(4) and fib(5) need fib(3), so they both compute it—very inefficient. Run the program again with a slightly larger number and again note the repetition in the calls.

3.

The fundamental source of the inefficiency is not the fact that recursive calls are being made, but that values are being recomputed. One way around this is to compute the values from the beginning of the sequence instead of from the end, saving them in an array as you go. Although this could be done recursively, it is more natural to do it iteratively. Proceed as follows: a. Add a method fib2 to your Fib class. Like fib1, fib2 should be static and should take an integer and return an integer. b. Inside fib2, create an array of integers the size of the value passed in. c. Initialize the first two elements of the array to 0 and 1, corresponding to the first two elements of the Fibonacci sequence. Then loop through the integers up to the value passed in, computing each element of the array as the sum of the two previous elements. When the array is full, its last element is the element requested. Return this value. d. Modify your TestFib class so that it calls fib2 (first) and prints the result, then calls fib1 and prints that result. You should get the same answers, but very different computation times.

// ******************************************************************* // Fib.java // // A utility class that provide methods to compute elements of the // Fibonacci sequence. // ******************************************************************* public class Fib { //-----------------------------------------------------------------// Recursively computes fib(n) //-----------------------------------------------------------------public static int fib1(int n) { //Fill in code -- this should look very much like the //mathematical specification } } Chapter 12: Recursion

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// ******************************************************************* // TestFib.java // // A simple driver that uses the Fib class to compute the // nth element of the Fibonacci sequence. // ******************************************************************* import java.util.Scanner; public class TestFib { public static void main(String[] args) { int n, fib; Scanner scan = new Scanner(System.in); System.out.print("Enter an integer: "); n = scan.nextInt(); fib = Fib.fib1(n); System.out.println("Fib(" + n + ") is " + fib); } }

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Palindromes A palindrome is a string that is the same forward and backward. In Chapter 5 you saw a program that uses a loop to determine whether a string is a palindrome. However, it is also easy to define a palindrome recursively as follows: □ □

A string containing fewer than 2 letters is always a palindrome.

A string containing 2 or more letters is a palindrome if □ its first and last letters are the same, and □ the rest of the string (without the first and last letters) is also a palindrome.

Write a program that prompts for and reads in a string, then prints a message saying whether it is a palindrome.

Your main method should read the string and call a recursive (static) method palindrome that takes a string and returns true if the string is a palindrome, false otherwise. Recall that for a string s in Java, □ s.length() returns the number of charaters in s □ s.charAt(i) returns the ith character of s, 0-based □ s.substring(i,j) returns the substring that starts with the ith character of s and ends with the j-1st character of s (not the jth), both 0-based.

So if s=“happy”, s.length=5, s.charAt(1)=a, and s.substring(2,4) = “pp”.

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Printing a String Backwards Printing a string backwards can be done iteratively or recursively. To do it recursively, think of the following specification: If s contains any characters (i.e., is not the empty string) □ print the last character in s □ print s’ backwards, where s’ is s without its last character File Backwards.java contains a program that prompts the user for a string, then calls method printBackwards to print the string backwards. Save this file to your directory and fill in the code for printBackwards using the recursive strategy outlined above. // ****************************************************************** // Backwards.java // // Uses a recursive method to print a string backwards. // ****************************************************************** import java.util.Scanner; public class Backwards { //-------------------------------------------------------------// Reads a string from the user and prints it backwards. //-------------------------------------------------------------public static void main(String[] args) { String msg; Scanner scan = new Scanner(System.in); System.out.print("Enter a string: "); msg = scan.nextLine(); System.out.print("\nThe string backwards: "); printBackwards(msg); System.out.println(); } //--------------------------------------------------------------// Takes a string and recursively prints it backwards. //--------------------------------------------------------------public static void printBackwards(String s) { // Fill in code } }

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Recursive Linear Search File IntegerListS.java contains a class IntegerListS that represents a list of integers (you may have used a version of this in an earlier lab); IntegerListSTest.java contains a simple menu-driven test program that lets the user create, sort, and print a list and search for an element using a linear search.

Many list processing tasks, including searching, can be done recursively. The base case typically involves doing something with a limited number of elements in the list (say the first element), then the recursive step involves doing the task on the rest of the list. Think about how linear search can be viewed recursively; if you are looking for an item in a list starting at index i: □ If i exceeds the last index in the list, the item is not found (return -1). □ If the item is at list[i], return i. □ If the is not at list[i], do a linear search starting at index i+1.

Fill in the body of the method linearSearchR in the IntegerList class. The method should do a recursive linear search of a list starting with a given index (parameter lo). Note that the IntegerList class contains another method linearSearchRec that does nothing but call your method (linearSearchR). This is done because the recursive method (linearSearchR) needs more information (the index to start at) than you want to pass to the top-level search routine (linearSearchRec), which just needs the thing to look for.

Now change IntegerListTest.java so that it calls linearSearchRec instead of linearSearch when the user asks for a linear search. Thoroughly test the program. // *************************************************************** // IntegerListS.java // // Defines an IntegerListS class with methods to create, fill, // sort, and search in a list of integers. (Version S // for use in the linear search exercise.) // // *************************************************************** public class IntegerListS { int[] list; //values in the list // // Creates a list of the given size // public IntegerListS (int size) { list = new int[size]; } // // Fills the array with integers between 1 and 100, inclusive // public void randomize() { for (int i=0; i< list.length; i++) list[i] = (int)(Math.random() * 100) + 1; } // // Prints array elements with indices // public void print() Chapter 12: Recursion

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{ for (int i=0; i<list.length; i++) System.out.println(i + ":\t" + list[i]); } // // Returns the index of the first occurrence of target in the list. // Returns -1 if target does not appear in the list. // public int linearSearch(int target) { int location = -1; for (int i=0; i<list.length && location == -1; i++) if (list[i] == target) location = i; return location; } // // Returns the index of an occurrence of target in the list, -1 // if target does not appear in the list. // public int linearSearchRec(int target) { return linearSearchR (target, 0); } // // Recursive implementation of the linear search - searches // for target starting at index lo. // private int linearSearchR (int target, int lo) { return -1; } // // Sorts the list into ascending order using the selection sort algorithm. // public void selectionSort() { int minIndex; for (int i=0; i < list.length-1; i++) { //find smallest element in list starting at location i minIndex = i; for (int j = i+1; j < list.length; j++) if (list[j] < list[minIndex]) minIndex = j; //swap list[i] with smallest element int temp = list[i]; list[i] = list[minIndex]; list[minIndex] = temp; } } }

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// *************************************************************** // IntegerListSTest.java // // Provide a menu-driven tester for the IntegerList class. // (Version S - for use in the linear search lab exercise). // // *************************************************************** import java.util.Scanner; public class IntegerListSTest { static IntegerListS list = new IntegerListS (10); static Scanner scan = new Scanner(System.in); // // Creates a list, then repeatedly print the menu and do what the // user asks until they quit. // public static void main(String[] args) { printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } // // Does what the menu item calls for. // public static void dispatch(int choice) { int loc; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: System.out.println("How big should the list be?"); int size = scan.nextInt(); list = new IntegerListS(size); list.randomize(); break; case 2: list.selectionSort(); break; case 3: System.out.print("Enter the value to look for: "); loc = list.linearSearch(scan.nextInt()); if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 4: list.print();

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break; default: System.out.println("Sorry, invalid choice") } } // // Prints the menu of user's choices. // public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Create new list elements (** do this first!! **)"); System.out.println("2: Sort the list using selection sort"); System.out.println("3: Find an element in the list using linear search"); System.out.println("4: Print the list"); System.out.print("\nEnter your choice: "); } }

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Recursive Binary Search The binary search algorithm from Chapter 9 is a very efficient algorithm for searching an ordered list. The algorithm (in pseudocode) is as follows: highIndex - the maximum index of the part of the list being searched lowIndex - the minimum index of the part of the list being searched target -- the item being searched for //look in the middle middleIndex = (highIndex + lowIndex) / 2 if the list element at the middleIndex is the target return the middleIndex else if the list element in the middle is greater than the target search the first half of the list else search the second half of the list Notice the recursive nature of the algorithm. It is easily implemented recursively. Note that three parameters are needed—the target and the indices of the first and last elements in the part of the list to be searched. To “search the first half of the list” the algorithm must be called with the high and low index parameters representing the first half of the list. Similarly, to search the second half the algorithm must be called with the high and low index parameters representing the second half of the list. The file IntegerListB.java contains a class representing a list of integers (the same class that has been used in a few other labs); the file IntegerListBTest.java contains a simple menu-driven test program that lets the user create, sort, and print a list and search for an item in the list using a linear search or a binary search. Your job is to complete the binary search algorithm (method binarySearchR). The basic algorithm is given above but it leaves out one thing: what happens if the target is not in the list? What condition will let the program know that the target has not been found? If the low and high indices are changed each time so that the middle item is NOT examined again (see the diagram of indices below) then the list is guaranteed to shrink each time and the indices “cross”—that is, the high index becomes less than the low index. That is the condition that indicates the target was not found. lo

middle

high

lo

middle-1

middle+1

high

^ ⎮

^ ⎮

^ ⎮

^ ⎮

first half

last half

Fill in the blanks below, then type your code in. Remember when you test the search to first sort the list. private int binarySearchR (int target, int lo, int hi) { int index; if ( ) // fill in the "not found" condition index = -1; else { int mid = (lo + hi)/2; if ( ) // found it! index = mid; else if (target < list[mid]) // fill in the recursive call to search the first half // of the list index = ; else Chapter 12: Recursion

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// search the last half of the list index =

;

} return index; } Optional: The binary search algorithm “works” (as in does something) even on a list that is not in order. Use the algorithm on an unsorted list and show that it may not find an item that is in the list. Hand trace the algorithm to understand why. // ***************************************************************** // IntegerListB.java // // Defines an IntegerList class with methods to create, fill, // sort, and search in a list of integers. (Version B - for use // in the binary search lab exercise) // // ***************************************************************** public class IntegerListB { int[] list; //values in the list // // Creates a list of the given size // public IntegerListB (int size) { list = new int[size]; } // // Fills the array with integers between 1 and 100, inclusive // public void randomize() { for (int i=0; i<list.length; i++) list[i] = (int)(Math.random() * 100) + 1; } // // Prints array elements with indices // public void print() { for (int i=0; i<list.length; i++) System.out.println(i + ":\t" + list[i]); } // // Returns the index of the first occurrence of target in the list. // Returns -1 if target does not appear in the list. // public int linearSearch(int target) { int location = -1; for (int i=0; i<list.length && location == -1; i++) if (list[i] == target) location = i; return location; } 238

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// // Returns the index of an occurrence of target in the list, -1 // if target does not appear in the list. // public int binarySearchRec(int target) { return binarySearchR (target, 0, list.length-1); } // // Recursive implementation of the binary search algorithm. // If the list is sorted the index of an occurrence of the // target is returned (or -1 if the target is not in the list). // private int binarySearchR (int target, int lo, int hi) { int index; // fill in code for the search return index; } // // Sorts the list into ascending order using the selection sort algorithm. // public void selectionSort() { int minIndex; for (int i=0; i < list.length-1; i++) { //find smallest element in list starting at location i minIndex = i; for (int j = i+1; j < list.length; j++) if (list[j] < list[minIndex]) minIndex = j; //swap list[i] with smallest element int temp = list[i]; list[i] = list[minIndex]; list[minIndex] = temp; } } }

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// *************************************************************** // IntegerListBTest.java // // Provides a menu-driven tester for the IntegerList class. // (Version B - for use with the binary search lab exerice) // // *************************************************************** import java.util.Scanner; public class IntegerListBTest { static IntegerListB list = new IntegerListB (10); static Scanner scan = new Scanner(System.in); // // Create a list, then repeatedly print the menu and do what the // user asks until they quit. // public static void main(String[] args) { printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } // // Does what the menu item calls for. // public static void dispatch(int choice) { int loc; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: System.out.println("How big should the list be?"); int size = scan.nextInt(); list = new IntegerListB(size); list.randomize(); break; case 2: list.selectionSort(); break; case 3: System.out.print("Enter the value to look for: "); loc = list.linearSearch(scan.nextInt()); if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 4: System.out.print("Enter the value to look for: ");

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loc = list.binarySearchRec(scan.nextInt()); if (loc != -1) System.out.println("Found at location " + loc); else System.out.println("Not in list"); break; case 5: list.print(); break; default: System.out.println("Sorry, invalid choice"); } } // // Prints the user's choices. // public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Create new list elements (** do this first!! **)"); System.out.println("2: Sort the list using selection sort"); System.out.println("3: Find an element in the list using linear search"); System.out.println("4: Find an element in the list using binary search"); System.out.println("5: Print the list"); System.out.print("\nEnter your choice: "); } }

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A List of Employees The files Employee.java and Payroll.java contain a definition of a simple list of hourly wage employees. An employee has a name, number of hours worked, and an hourly pay rate. The Payroll class is the list of employees. Currently there is a method in the class, public void readPayrollInfo(String file), that reads in the employee information from a file and sets up the employee list. Your job is to add a recursive method that determines the number of employees who worked overtime (more than 40 hours). The method numOvertime is already defined. It is the public method that would be used by a program. It calls your method int overtime (int start) which will do all the work.

1.

Complete the overtime method. The parameter start is the index of the first element in the part of the array being processed. Recall that to recursively process the elements in an array in sequential order the strategy is to “process” the first element (in this case count it if the number of hours worked is greater than 40), then call the method recursively to process the rest of the array. Don’t forget the base case.

2.

Complete the test program Overtime.java to test your method. The program currently has code to read in the name of the file that contains employee data. You need to add code to instantiate a Payroll object, read the data in, then call the numOvertime method to determine how many employees worked overtime.

3.

Run the program at least twice using the files payroll. dat and payroll2. dat as input.

// *************************************************************** // Employee.java // // Represents an hourly wage worker. // *************************************************************** public class Employee { String name; int hours; // hours worked double rate; // hourly pay rate // // Sets up the Employee object with the given data. // public Employee (String name, int hours, double rate) { this.name = name; this.hours = hours; this.rate = rate; } // // Returns the number of hours worked. // public int getHours () { return hours; } }

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// *************************************************************** // Payroll.java // // Represents a list of employees. // *************************************************************** import java.util.Scanner; import java.util.*; import java.io.*; public class Payroll { final int MAX =30; Employee[] payroll = new Employee[MAX]; int numEmployees = 0; // // Reads the list of employee wage data from the given // file. // public void readPayrollInfo(String file) { String line; // a line in the file String name; // name of an employee int hours; // hours worked double rate; // hourly pay rate Scanner fileScan, lineScan; try

{ fileScan = new Scanner (new File(file)); while (fileScan.hasNext()) { line = fileScan.nextLine(); lineScan = new Scanner(line); name = lineScan.next (); try {

hours = lineScan.nextInt(); rate = lineScan.nextDouble(); payroll[numEmployees] = new Employee (name, hours, rate); numEmployees++;

} catch (InputMismatchException exception) { System.out.println ("Error in input. Line ignored."); System.out.println (line); } catch {ArrayIndexOutOfBoundsException exception) { System.out.println ("Too many employees!"); } } fileScan.close(); }

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catch (FileNotFoundException exception) { System.out.println ("The file " + file + " was not found."); } catch (IOException exception) { System.out.println (exception); } } // // Returns the number of employees who // worked over 40 hours; the helper method // overtime is called to do all the work. // public int numOvertime () { return overtime (0); } // // Returns the number of employees in the part // of the list from index start to the end who // worked more than 40 hours. // private int overtime (int start) { } } // *************************************************************** // Overtime.java // // Reads a file of employee payroll information and determines // how many employees worked more than 40 hours. // *************************************************************** import java.util.Scanner; public class Overtime { public static void main (String[] args) { String fileName; // Name of the file containing employee data Scanner scan = new Scanner(System.in); System.out.println ("\nPayroll Program"); System.out.print ("Enter the name of the file containing payroll data: "); fileName = scan.nextLine(); // Instantiate a Payroll object and read in the data from the file // Print the number of workers who worked overtime. } }

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payroll.dat Smith 45 13.50 Jones 39 23.75 Doe 40 17.80 Moe 30 21.90 Walker 41 14.60 Walton 57 8.95 Taylor 40 16.75 Lewis 40 35.50 Abbott 43 12.70 Who 39 33.95 Herrod 21 19.90 James 49 13.50 Summers 40 20.00 Winter 40 18.75 Farthington 38 24.50 Walsh 42 45.70

payroll2.dat Jones 40 9.75 Ricardo 35 13.69 Smith 40 20.00 Smythe 40 17.80

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Sierpinski Triangles A Sierpinski triangle is a geometric figure that may be constructed as follows: 1.

2.

3.

Draw a triangle.

Draw a new triangle by connecting the midpoints of the three sides of your original triangle. This should split your triangle into four smaller triangles, one in the center and three around the outside.

Repeat (2) for each of the outside triangles (not the center one). Each of them will split into four yet smaller triangles. Repeat for each of their outside triangles.. and for each of the new ones.. and so on, forever. Draw a few rounds of this on paper to see how it works. Check out the demo at http://cs.roanoke.edu/labs4e/demo.html to see how the program works on screen.

Your job is to write an applet that draws a Sierpinski triangle. Think about the following: □ A Sierpinski triangle is a recursively defined structure, since each of the three outer triangles formed by joining the midpoints is itself a Sierpinski triangle. □ In practice you don’t want to go on with the process “forever” as suggested above, so we’ll limit how deep it goes. Define the depth of a Sierpinski triangle as the number of directly nested triangles at the deepest point. So a Sierpinski triangle consisting of a single triangle has depth 0; when a triangle is drawn inside of it, the resulting Sierpinski triangle has depth 1; when the three outside triangles have triangles drawn inside of them, the resulting triangle is depth 2, and so on. A depth of 10 or 11 gives a nice looking triangle in a reasonable amount of time. (The demo uses depth 10.) Smaller depths are interesting in that you can see more of the construction; higher depths generally take too long for casual viewing. □ A triangle is a polygon, so you’ll use the drawPolygon method. Remember that it takes an array containing the x coordinates, an array containing the y coordinates, and an integer indicating how many points should be drawn (3 for a triangle). Refer to Chapter 7 or the appendix (the Graphics class) to refresh your memory on this. □ Your initial triangle should look like the one in the demo—one point at the top center of the applet and one point in each lower corner. □ Your overall program is quite simple. The paint method will just call a recursive method sierpinski, passing it the Graphics object, the points of the initial triangle to be drawn, and the initial depth (0). Make the variables that hold the initial points instance variables and initialize them in the init method. The sierpinski method will then check to see if the desired depth has been exceeded (the depth can be a constant), and if not, draw the triangle, then call itself recursively to drawn the three Sierpinski triangles that will be embedded. Note that it will have to figure out what points to pass to each of these, and that each recursive call increases the depth by one.

When this works (that is, when your triangle looks like the one in the demo), modify it so that when the user clicks a new, random Sierpinski triangle is drawn. (The demo does this too.) This just means choosing three random points and repainting—nothing will change in your paint or sierpinski methods (if you followed the guidelines above). For fun you can choose a random color each time as well, as the demo does.

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Modifying the Koch Snowflake The Koch snowflake is a fractal generated by starting with 3 line sements forming an equilateral triangle (a Koch fractal of order 1). The algorithm for generating higher order Koch fractals involves splitting each line segment into three equal segments then replacing the middle segment by two line segments that protrude outward. The same algorithm is then recursively applied to each of the 4 new line segments. In the basic Koch snowflake the two protruding line segments meet at a 60 degree angle. These line segments form an equilateral triangle with the middle segment that is removed. (See the discussion in Chapter 11 for more details.) Files KochSnowflake.java and KochPanel.java contain slight modifications to the program from the text that generates Koch snowflakes (Listings 11.6 and 11.7). Copy these files to your directory, compile them, and run the program in the appletviewer to see how it works (you may use the file Koch.html to run the program). In this exercise you will generalize the pattern to allow for triangles other than equilateral ones to be built on the middle third segment. In the drawFractal method this involves changing the calculation of x3 and y3, the coordinates of the protrusion point. The following calculations are equivalent to those currently in the program: x3 = (int) (x2 + (cosine * deltaX - sine * deltaY)/3); y3 = (int) (y2 + (cosine * deltaY + sine * deltaX)/3); where cosine is the cosine of 60 degrees (which is 1/2) and sine is the sine of 60 degrees (which is the square root of 3 over 2). These equations are generalizable to angles other than 60. In this exercise you will generalize the program to work for angles other than 60. The angle will be controlled by increase and decrease buttons in the same way that the order is currently controlled. Do the following: 1.

In KochPanel.java, □ Add instance variables angle, sine, and cosine. Angle will be an integer and sine and cosine type double. □ In the constructor, set angle to 60 (this will be the default), and set sine to Math.sin (Math.PI / 3) and cosine to Math.cos (Math.PI / 3). □ In drawFractal, replace the current calculations for x3 and y3 with those given above.

2.

Compile and run the program. It should behave just as before.

3.

To add controls to allow the angle to change, do the following: □ In KochPanel, add two public methods getAngle() that returns the angle (type int), and setAngle (int newAngle) that sets the angle to be the value of newAngle and sets sine and cosine of that angle.

Remember that the sin and cos methods in the Math class must have arguments that are in radians not degrees so you need to multiply the angle (which is in degrees) by Math.PI divided by 180 (pi/180 is the degree to radian conversion factor). □ In KochSnowflake.java, add a new “tools” panel for the buttons to increase and decrease the angle.

This panel will contain two buttons and a label giving the current angle. A horizontal box layout should be used. The applet should be added as a listener for the buttons. □ The new tools panel should be added to the appletPanel. To accomodate it change APPLET_HEIGHT to 480. □ The method actionPerformed must be modified to take action if the event source was one of the new buttons. If the source was the button to increase the angle, increase the angle by 10 degrees (you can get the current angle using the method you added to KochPanel); if the source was the button to decrease the angle, decrease it by 10 degrees. The new angle should be between 10 and 170 (inclusive)—you should add constants (similar to MIN and MAX) for the minimum and maximum angles.

4.

Compile and run the program. Play with the angles and order to see what fractal patterns are generated.

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// ****************************************************************** // KochSnowflake.java Author: Lewis/Loftus // // Demonstrates the use of recursion in graphics. // ****************************************************************** import java.awt.*; import java.awt.event.*; import javax. swing.*; public class KochSnowflake extends JApplet implements ActionListener { private final int APPLET_WIDTH = 400; private final int APPLET_HEIGHT = 440; private final int MIN = 1, MAX = 9; private JButton increase, decrease; private JLabel titleLabel, orderLabel; private KochPanel drawing; private JPanel appletPanel, tools; // // Sets up the components for the applet. // public void init() { tools = new JPanel (); tools.setLayout (new BoxLayout (tools, BoxLayout.X_AXIS)); tools.setPreferredSize (new Dimension (APPLET_WIDTH, 40)); tools.setBackground (Color.yellow); tools.setOpaque (true); titleLabel = new JLabel ("The Koch Snowflake"); titleLabel.setForeground (Color.black); increase = new JButton ("Increase"); increase.setMargin (new Insets (0, 0, 0, 0)); increase.addActionListener (this); decrease = new JButton ("Decrease"); decrease.setMargin (new Insets (0, 0, 0, 0)); decrease.addActionListener (this); orderLabel = new JLabel ("Order: 1"); orderLabel.setForeground (Color.black); tools.add (titleLabel); tools.add (Box.createHorizontalStrut (40)); tools.add (decrease); tools.add (increase); tools.add (Box.createHorizontalStrut (20)); tools.add (orderLabel); drawing = new KochPanel (1); appletPanel = new JPanel (); appletPanel.add (tools); appletPanel. add (drawing);

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getContentPane().add (appletPanel); setSize (APPLET_WIDTH, APPLET_HEIGHT); } // // Determines which button was pushed, and sets the new order // if it is in range. // public void actionPerformed (ActionEvent event) { int order = drawing.getOrder (); if (event.getSource() == increase) order++; else order--; if (order >= MIN && order <= MAX) { orderLabel.setText ("Order: " + order); drawing.setOrder (order); repaint(); } } }

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// ******************************************************************* // KochPanel.java Author: Lewis/Loftus // // Represents a drawing surface on which to paint a Koch Snowflake. // ******************************************************************* import java.awt.*; import javax.swing.JPanel; public class KochPanel extends JPanel { private final int PANEL_WIDTH = 400; private final int PANEL_HEIGHT = 400; private final double SQ = Math.sqrt (3.0) / 6; private final int TOPX = 200, TOPY = 20; private final int LEFTX = 60, LEFTY = 300; private final int RIGHTX = 340, RIGHTY = 300; private int current;

// current order

// // Sets the initial fractal order to the value specified. // public KochPanel (int currentOrder) { current = currentOrder; setBackground (Color.black); setPreferredSize (new Dimension (PANEL_WIDTH, PANEL_HEIGHT)); } // // Draws the fractal recursively. The base case is order 1 for // which a simple straight line is drawn. Otherwise three // intermediate points arae computed, and each line segment is // drawn as a fractal. // public void drawFractal (int order, int x1, int y1, int x5, int y5, Graphics page) { int deltaX, deltaY, x2, y2, x3, y3, x4, y4; if (order ==1) page.drawLine (x1, y1, x5, y5); else { deltaX = x5 - x1; // distance between end points deltaY = y5 - y1; x2 = x1 + deltaX /3; y2 = y1 + deltaY / 3; x3 = (int) ((x1 + x5)/2 + SQ * (y1 - y5)); y3 = (int) ((y1 + y5)/2 + SQ * (x5 - x1)); x4 = x1 + deltaX * 2 / 3; y4 = y1 + deltaY * 2 / 3; drawFractal

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drawFractal (order - 1, x2, y2, x3, y3, page); drawFractal (order - 1, x3, y3, x4, y4, page); drawFractal (order - 1, x4, y4, x5, y5, page); } } // // Performs the initial calls to the drawFractal method. // public void paintComponent (Graphics page) { super.paintComponent (page); page.setColor (Color.green); drawFractal (current, TOPX, TOPY, LEFTX, LEFTY, page); drawFractal (current, LEFTX, LEFTY, RIGHTX, RIGHTY, page); drawFractal (current, RIGHTX, RIGHTY, TOPX, TOPY, page); } // // Sets the fractal order to the specified value. // public void setOrder (int order) { current = order; } // // Returns the current order. // public int getOrder () { return current; } } } koch.html <html> <title>Koch Snowflake</title> <applet CODE="KochSnowflake.class" HEIGHT=400 WIDTH=440> </applet> </html>

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Chapter 13: Collections Lab Exercises Topics

Lab Exercises

Linked Lists

Linked List of Integers Recursive Processing of Linked List Linked List of Objects Doubly Linked Lists

Queues

An Array Queue Implementation A Linked Queue Implementation Queue Manipulation

Stacks

An Array Stack Implementation A Linked Stack Implementation Stack Manipulation Matching Parentheses

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A Linked List of Integers File IntList.java contains definitions for a linked list of integers. The class contains an inner class IntNode that holds information for a single node in the list (a node has a value and a reference to the next node) and the following IntList methods: □ □ □ □ □

public IntList()—constructor; creates an empty list of integers public void addToFront(int val)—takes an integer and puts it on the front of the list public void addToEnd(int val)—takes an integer and puts it on the end of the list public void removeFirst()—removes the first value from the list public void print()—prints the elements in the list from first to last

File IntListTest.java contains a driver that allows you to experiment with these methods. Save both of these files to your directory, compile and run IntListTest, and play around with it to see how it works. Then add the following methods to the IntList class. For each, add an option to the driver to test it.

1.

2.

3.

4.

public int length()—returns the number of elements in the list public String toString()—returns a String containing the print value of the list. public void removeLast()—removes the last element of the list. If the list is empty, does nothing. public void replace(int oldVal, int newVal)—replaces all occurrences of oldVal in the list with newVal. Note that you can still use the old nodes; just replace the values stored in those nodes.

// *************************************************************** // FILE: IntList.java // // Purpose: Defines a class that represents a list of integers // // *************************************************************** public class IntList { private IntNode front; //first node in list //----------------------------------------// Constructor. Initially list is empty. //----------------------------------------public IntList() { front = null; } //----------------------------------------// Adds given integer to front of list. //----------------------------------------public void addToFront(int val) { front = new IntNode(val,front); } //----------------------------------------// Adds given integer to end of list. //----------------------------------------public void addToEnd(int val) { IntNode newnode = new IntNode(val,null); //if list is empty, this will be the only node in it if (front == null) front = newnode; Chapter 13: Collections

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else {

//make temp point to last thing in list IntNode temp = front; while (temp.next != null) temp = temp.next; //link new node into list temp.next = newnode;

} } //----------------------------------------// Removes the first node from the list. // If the list is empty, does nothing. //----------------------------------------public void removeFirst() { if (front != null) front = front.next; } //-----------------------------------------------// Prints the list elements from first to last. //-----------------------------------------------public void print() { System.out.println(" -------------------- "); System.out.print("List elements: "); IntNode temp = front; while (temp != null) { System.out.print(temp.val + " "); temp = temp.next; } System.out.println("\n ---------------------- \n"); } //************************************************************* // An inner class that represents a node in the integer list. // The public variables are accessed by the IntList class. //************************************************************* private class IntNode { public int val; //value stored in node public IntNode next; //link to next node in list //-----------------------------------------------------------------// Constructor; sets up the node given a value and IntNode reference //-----------------------------------------------------------------public IntNode(int val, IntNode next) { this.val = val; this.next = next; } } }

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// *************************************************************** // IntListTest.java // // Driver to test IntList methods. // *************************************************************** import java.util.Scanner; public class IntListTest { private static Scanner scan; private static IntList list = new IntList(); //---------------------------------------------------------------// Creates a list, then repeatedly prints the menu and does what // the user asks until they quit. //---------------------------------------------------------------public static void main(String[] args) { scan = new Scanner(System.in); printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } //---------------------------------------// Does what the menu item calls for. //---------------------------------------public static void dispatch(int choice) { int newVal; switch(choice) { case 0: System.out.println("Bye!"); break; case 1: //add to front System.out.println("Enter integer to add to front"); newVal = scan.nextInt(); list.addToFront(newVal); break; case 2: //add to end System.out.println("Enter integer to add to end"); newVal = scan.nextInt(); list.addToEnd(newVal); break; case 3: //remove first element list.removeFirst(); break; case 4: Chapter 13: Collections

//print 255

list.print(); break; default: System.out.println("Sorry, invalid choice") } } //----------------------------------------// Prints the user's choices //----------------------------------------public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Add an integer to the front of the list"); System.out.println("2: Add an integer to the end of the list"); System.out.println("3: Remove an integer from the front of the list"); System.out.println("4: Print the list"); System.out.print("\nEnter your choice: "); } }

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Recursive Processing of Linked Lists File IntList.java contains definitions for a linked list of integers (see previous exercise). The class contains an inner class IntNode, which holds information for a single node in the list (a node has a value and a reference to the next node) and the following IntList methods: □ □ □ □ □

public IntList()—constructor; creates an empty list of integers public void addToFront(int val)—takes an integer and puts it on the front of the list public void addToEnd(int val)—takes an integer and puts it on the end of the list public void removeFirst()—removes the first value from the list public void print()—prints the elements in the list from first to last

File IntListTest.java contains a driver that allows you to experiment with these methods. Save both of these files to your directory. If you have not already worked with these files in a previous exercise, compile and run IntListTest and play around with it to see how it works. Then add the following methods to the IntList class. For each, add an option in the driver to test the method.

1.

public void printRec()—prints the list from first to last using recursion. Hint: The basic idea is that you print the first item in the list then do a recursive call to print the rest of the list. This means you need to keep track of what hasn’t been printed yet (the “rest” of the list). In particular, your recursive method needs to know where the first item is. Note that printRec() has no parameter so you need to use a helper method that does most of the work. It should have a parameter that lets it know where the part of the list to be printed starts.

2.

public void printRecBackwards()—prints the list from last to first using recursion. Hint: Printing backward recursively is just like printing forward recursively except you print the rest of the list before printing this element. Simple!

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A Linked List of Objects Listing 12.2 in the text is an example of a linked list of objects of type Magazine; the file IntList.java contains an example of a linked list of integers (see previous exercise). A list of objects is a lot like a list of integers or a particular type of object such as a Magazine, except the value stored is an Object, not an int or Magazine. Write a class ObjList that contains arbitrary objects and that has the following methods: □ □ □ □ □

public void addToFront (Object obj)—puts the object on the front of the list public void addToEnd (Object obj)—puts the object on the end of the list public void removeFirst()—removes the first value from the list public void removeLast()—removes the last value from the list public void print()—prints the elements of the list from first to last

These methods are similar to those in IntList. Note that you won’t have to write all of these again; you can just make very minor modifications to the IntList methods.

Also write an ObjListTest class that creates an ObjList and puts various different kinds of objects in it (String, array, etc) and then prints it.

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Doubly Linked Lists Sometimes it is convenient to maintain references to both the next node and the previous node in a linked list.

This is called a doubly linked list and is illustrated in Figure 12.4 of the text. File DoubleLinked.java contains definitions for a doubly linked list of integers. This class contains an inner class IntNode that holds information for a single node in the list (its value and references to the next and previous nodes). The DoubleLinked class also contains the following methods: □ public DoubleLinked()—constructor; creates an empty list of integers □ public void addToFront(int val)—takes an integer and puts it on the front of the list □ public void print()—prints the elements in the list from first to last File DoubleLinkedTest.java contains a driver that allows you to experiment with these methods. Save both of these files to your directory, compile and run DoubleLinkedTest, and play around with it to see how it works.

Then add the following methods to the DoubleLinked class. For each, add an option to the driver to test it.

1.

2.

3.

4.

public void addToEnd(int val)—takes an integer and puts it on the end of the list public void removeFirst()—removes the first value from the list. If the list is empty, does nothing. public void removeLast()—removes the last element of the list. If the list is empty, does nothing. public void remove(int oldVal)—removes the first occurrence of oldVal in the list.

// *************************************************************** // DoubleLinked.java // // A class using a doubly linked list to represent a list of integers. // // *************************************************************** public class DoubleLinked { private IntNode list; // // Constructor -- initializes list // public DoubleLinked() { list = null; } // // Prints the list elements // public void print() { for (IntNode temp = list; temp != null; temp = temp.next) System.out.println(temp.val); } // // Adds new element to front of list // public void addToFront(int val) { IntNode newNode = new IntNode(val); newNode.next = list; if (list != null) list.prev = newNode; list = newNode; } Chapter 13: Collections

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//*************************************************************** // An inner class that represents a list element. //*************************************************************** private class IntNode { public int val; public IntNode next; public IntNode prev; public IntNode(int val) { this.val = val; this.next = null; this.prev = null; } } } // *********************************************************** // DoubleLinkedTest.java // // Driver to test DoubleLinked methods. // *********************************************************** import java.util.Scanner; public class DoubleLinkedTest { private static Scanner scan; private static DoubleLinked list = new DoubleLinked(); //---------------------------------------------------------------// Creates a list, then repeatedly prints the menu and does what // the user asks until they quit. //---------------------------------------------------------------public static void main(String[] args) { scan = new Scanner(System.in); printMenu(); int choice = scan.nextInt(); while (choice != 0) { dispatch(choice); printMenu(); choice = scan.nextInt(); } } //--------------------------------------// Does what the menu item calls for. //--------------------------------------public static void dispatch(int choice) { int newVal; switch(choice) { case 0: 260

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System.out.println("Bye!"); break; case 1: //print System.out.println("** List elements **"); list.print(); break; case 2: //add to front System.out.println("Enter integer to add to front"); newVal = scan.nextInt(); list.addToFront(newVal); break; default: System.out.println("Sorry, invalid choice"); } } //----------------------------------------// Prints the user's choices //----------------------------------------public static void printMenu() { System.out.println("\n Menu "); System.out.println(" ===="); System.out.println("0: Quit"); System.out.println("1: Print list"); System.out.println("2: Add an integer to the front of the list"); System.out.print("\nEnter your choice: "); } }

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An Array Queue Implementation File QueueADT.java contains a Java interface representing a queue ADT. In addition to enqueue(), dequeue(), and isEmpty(), this interface contains two methods that are not described in the book – isFull () and size(). File ArrayQueue.java contains a skeleton for an array-based implementation of this interface; it also includes a toString() method that returns a string containing the queue elements, one per line. File TestQueue.java contains a simple test program.

Complete the method definitions in ArrayQueue.java. Some things to think about: •

• • • •

A queue has activity at both ends -- elements are enqueued at one end and dequeued from the other end. In an array implementation this means that repeated enqueues and dequeues will shift the queue elements from the beginning to the end of the array, so the array may appear full (in that the last element is in the last slot) when there are actually spaces available at the beginning. To address this the next element can simply be placed in the first element of the array, so that the queue “wraps around” the array. This is called a circular array implementation, and is used because it allows the enqueue and dequeue methods to be implemented efficiently in both space and time.

You’ll need to use integers to keep track of the indices of the front and back of the queue. Think carefully about what initial values these variables (front and back) should get in the constructor and how they should be incremented given the circular nature of the implementation.

The easiest way to implement the size() method is to keep track of the number of elements as you go with the numElements variable -- just increment this variable when you enqueue an element and decrement it when you dequeue an element.

An easy way to tell if a queue is full in an array implementation is to check how many elements it contains (stored in numElements). If it’s equal to the size of the array, the queue is full. You can also use numElements to check if the queue is empty.

The test program given tries to enqueue more elements than will fit in default size of the queue. Be sure that you check if the queue is full before enqueueing, and if it is full just do nothing. It’s safest to do this in the enqueue() method.

Study the code in TestQueue.java so you know what it is doing, then compile and run it. Correct any problems in your Linked Queue class. //********************************************************** // QueueADT.java // The classic FIFO queue interface. //********************************************************** public interface QueueADT { //--------------------------------------------// Puts item on end of queue. //--------------------------------------------public void enqueue(Object item); //--------------------------------------------// Removes and returns object from front of queue. //------------------------------------------public Object dequeue(); //--------------------------------------------// Returns true if queue is empty. //--------------------------------------------public boolean isEmpty(); //--------------------------------------------// Returns true if queue is full. //--------------------------------------------public boolean isFull(); 262

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//--------------------------------------------// Returns the number of elements in the queue. //--------------------------------------------public int size(); } //********************************************************** // ArrayQueue.java // An array-based implementation of the classic FIFO queue interface. //********************************************************** public class ArrayQueue implements QueueADT { private final int DEFAULT_SIZE = 5; private Object[] elements; private int numElements; private int front, back; //--------------------------------------------// Constructor; creates array of default size. //--------------------------------------------public ArrayQueue() { } //--------------------------------------------// Puts item on end of queue. //--------------------------------------------public void enqueue(Object item) { } //--------------------------------------------// Removes and returns object from front of queue. //--------------------------------------------public Object dequeue() { } //--------------------------------------------// Returns true if queue is empty. //--------------------------------------------public boolean isEmpty() { } //----------------------------------------// Returns true if queue is full. //----------------------------------------public boolean isFull() { } //---------------------------------------------

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// Returns the number of elements in the queue. //--------------------------------------------public int size() { } //--------------------------------------------// Returns a string containing the elements of the queue // from first to last //--------------------------------------------public String toString() { String result = "\n"; for (int i = front, count=0; count < numElements; i=(i+1)%elements.length,count++) result = result + elements[i]+ "\n"; return result; } }

//********************************************************** // TestQueue // A driver to test the methods of the QueueADT implementations. //********************************************************** public class TestQueue { public static void main(String[] args) { QueueADT q = new ArrayQueue(); System.out.println("\nEnqueuing chocolate, cake, pie, truffles:"); q.enqueue("chocolate"); q.enqueue("cake"); q.enqueue("pie"); q.enqueue("truffles"); System.out.println("\nHere's the queue: " + q); System.out.println("It contains " + q.size() + " items."); System.out.println("\nDequeuing two..."); System.out.println(q.dequeue()); System.out.println(q.dequeue()); System.out.println("\nEnqueuing cookies, profiteroles, mousse, cheesecake, ice cream:"); q.enqueue("cookies"); q.enqueue("profiteroles"); q.enqueue("mousse"); q.enqueue("cheesecake"); q.enqueue("ice cream"); System.out.println("\nHere's the queue again: " + q); System.out.println("Now it contains " + q.size() + " items."); System.out.println("\nDequeuing everything in queue"); while (!q.isEmpty()) 264

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System.out.println(q.dequeue()); System.out.println("\nNow it contains " + q.size() + " items."); if (q.isEmpty()) System.out.println("Queue is empty!"); else System.out.println("Queue is not empty -- why not??!!"); } }

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A Linked Queue Implementation File QueueADT.java contains a Java interface representing a queue ADT. In addition to enqueue(), dequeue(), and isEmpty(), this interface contains two methods that are not described in the book - isFull () and size(). File LinkedQueue.java contains a skeleton for a linked implementation of this interface; it also includes a toString() method that returns a string containing the queue elements, one per line. It depends on the Node class in Node.java. (This could also be defined as an inner class.) File TestQueue.java contains a simple test program.

Complete the method definitions in LinkedQueue.java. Some things to think about: • In enqueue() and dequeue() you have to maintain both the front and back pointers - this takes a little thought. In particular, in enqueue be careful of the case where the queue is empty and you are putting the first item in. This case requires special treatment (think about why).

• The easiest way to implement the size() method is to keep track of the number of elements as you go with the numElements variable - just increment this variable when you enqueue an element and decrement it when you dequeue an element.

• A linked queue is never full, so isFull() always returns false. Easy!

Study the code in TestQueue.java so you know what it is doing, then compile and run it. Correct any problems in your Linked Queue class.

//********************************************************* // QueueADT.java // The classic FIFO queue interface. //********************************************************* public interface QueueADT { //--------------------------------------------// Puts item on end of queue. //--------------------------------------------public void enqueue(Object item); //--------------------------------------------// Removes and returns object from front of queue. //--------------------------------------------public Object dequeue(); //--------------------------------------------// Returns true if queue is empty. //--------------------------------------------public boolean isEmpty(); //--------------------------------------------// Returns true if queue is full. //--------------------------------------------public boolean isFull(); //--------------------------------------------// Returns the number of elements in the queue. //--------------------------------------------public int size(); } //*********************************************************** // LinkedQueue.java // A linked-list implementation of the classic FIFO queue interface. //*********************************************************** public class LinkedQueue implements QueueADT

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{ private Node front, back; private int numElements; //--------------------------------------------// Constructor; initializes the front and back pointers // and the number of elements. //--------------------------------------------public LinkedQueue() { } //--------------------------------------------// Puts item on end of queue. //--------------------------------------------public void enqueue(Object item) { } //--------------------------------------------// Removes and returns object from front of queue. //--------------------------------------------public Object dequeue() { Object item = null; } //--------------------------------------------// Returns true if queue is empty. //--------------------------------------------public boolean isEmpty() { } //--------------------------------------------// Returns true if queue is full, but it never is. //--------------------------------------------public boolean isFull() { } //--------------------------------------------// Returns the number of elements in the queue. //--------------------------------------------public int size() { } //--------------------------------------------// Returns a string containing the elements of the queue // from first to last //--------------------------------------------public String toString() { String result = "\n"; Node temp = front; while (temp != null) { result += temp.getElement() + "\n"; temp = temp.getNext();

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} return result; } } //************************************************************ // Node.java // A general node for a singly linked list of objects. //************************************************************ public class Node { private Node next; private Object element; //------------------------------------------------------// Creates an empty node //------------------------------------------------------public Node() { next = null; element = null; } //------------------------------------------------------// Creates a node storing a specified element //------------------------------------------------------public Node(Object element) { next = null; this.element = element; } //------------------------------------------------------// Returns the node that follows this one //------------------------------------------------------public Node getNext() { return next; } //------------------------------------------------------// Sets the node that follows this one //------------------------------------------------------public void setNext(Node node) { next = node; } //------------------------------------------------------// Returns the element stored in this node //------------------------------------------------------public Object getElement() { return element; } //------------------------------------------------------// Sets the element stored in this node //-------------------------------------------------------

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public void setElement(Object element) { this.element = element; } } //*********************************************************** // TestQueue // A driver to test the methods of the QueueADT implementations. //********************************************************** public class TestQueue { public static void main(String[] args) { QueueADT q = new LinkedQueue(); System.out.println("\nEnqueuing chocolate, cake, pie, truffles:"); q.enqueue("chocolate"); q.enqueue("cake"); q.enqueue("pie"); q.enqueue("truffles"); System.out.println("\nHere's the queue: " + q); System.out.println("It contains " + q.size() + " items."); System.out.println("\nDequeuing two..."); System.out.println(q.dequeue()); System.out.println(q.dequeue()); System.out.println("\nEnqueuing cookies, profiteroles, mousse, cheesecake, ice cream:"); q.enqueue("cookies"); q.enqueue("profiteroles"); q.enqueue("mousse"); q.enqueue("cheesecake"); q.enqueue (" ice cream"); System.out.println("\nHere's the queue again: " + q); System.out.println("Now it contains " + q.size() + " items."); System.out.println("\nDequeuing everything in queue"); while (!q.isEmpty()) System.out.println(q.dequeue()); System.out.println("\nNow it contains " + q.size() + " items."); if (q.isEmpty()) System.out.println("Queue is empty!"); else System.out.println("Queue is not empty -- why not??!!"); } }

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Queue Manipulation The file QueueTest.java contains a printQueue method that takes an object of type QueueADT and prints its contents, restoring the queue before it returns. It uses a temporary queue that actually holds the same information as the original queue. If you know the number of elements in the queue, you can write a printQueue method that prints the queue and restores it to its original form without using an auxiliary data structure (stack, queue, etc.). Think about how, then do it! That is, modify the printQueue method in QueueTest so that it behaves exactly as it does now but does not require an auxiliary data structure. Note that this code uses a LinkedQueue implementation for the QueueADT (see previous exercises), but you could substitute an ArrayQueue if you like. // ************************************************************** // QueueTest.java // // A simple driver to manipulate a queue. // // ************************************************************** public class QueueTest { public static void main(String[] args) { QueueADT queue = new LinkedQueue(); //put some stuff in the queue: 0,2,4,..,14 for (int i=0; i<8; i++) queue.enqueue(i*2); System.out.println("\n\n** Initial queue **"); printQueue(queue); //dequeue 4 items for (int i=0; i<4; i++) queue.dequeue(); System.out.println( "\n\n** After dequeueing 4 items **"); printQueue(queue); //enqueue 7 more: 1,2,..,7 for (int i=0; i<7; i++) queue.enqueue(i+1); System.out.println ("\n\n** After enqueueing 7 more items **"); printQueue(queue); } //---------------------------------------------------------// Prints elements of queue, restoring it before returning //---------------------------------------------------------public static void printQueue(QueueADT queue) { QueueADT temp = new LinkedQueue(); //print everything in the queue, putting elements //back into a temporary queue while (!queue.isEmpty()) { int val = queue.dequeue(); temp.enqueue(val); System.out.print(val + " ");

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} System.out.println (); //restore the original queue while (!temp.isEmpty()) { int val = temp.dequeue(); queue.enqueue(val); } } }

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An Array Stack Implementation Java has a Stack class that holds elements of type Object. However, many languages do not provide stack types, so it is useful to be able to define your own. File StackADT.java contains an interface representing the ADT for a stack of objects and ArrayStack.java contains a skeleton for a class that uses an array to implement this interface. Fill in code for the following public methods: □ □ □ □

void push(Object val) int pop() boolean isEmpty() boolean isFull()

In writing your methods, keep in mind the following: □ The bottom of an array-based stack is always the first element in the array. In the skeleton given, variable top holds the index of the location where the next value pushed will go. So when the stack is empty, top is 0; when it contains one element (in location 0 of the array), top is 1, and so on. □ Make push check to see if the array is full first, and do nothing if it is. Similarly, make pop check to see if the array is empty first, and return null if it is. □ Popping an element removes it from the stack, but not from the array—only the value of top changes.

File StackTest.java contains a simple driver to test your stack. Save it to your directory, compile it, and make sure it works. Note that it tries to push more things than will fit on the stack, but your push method should deal with this. // *************************************************************** // StackADT.java // The classic Stack interface. // *************************************************************** public interface StackADT { // // Adds a new element to the top of the stack. // public void push(Object val); // // Removes and returns the element at the top of the stack. // public Object pop(); // // Returns true if stack is empty, false otherwise. // public boolean isEmpty(); // // Returns true if stack is full, false otherwise. // public boolean isFull(); } // *************************************************************** // ArrayStack.java // // An array-based Object stack class with operations push, // pop, and isEmpty and isFull. // // *************************************************************** 272

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public class ArrayStack implements StackADT { private int stackSize = 5; // capacity of stack private int top; // index of slot for next element private Object[] elements; // // Constructor -- initializes top and creates array // public ArrayStack() { } // // Adds element to top of stack if it's not full, else // does nothing. // public void push(Object val) { } // // Removes and returns value at top of stack. // is empty returns null. // public Object pop() {

If stack

} // // Returns true if stack is empty, false otherwise. // public boolean isEmpty() { } // // Returns true if stack is full, false otherwise. // public boolean isFull() { } }

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// ********************************************************* // StackTest.java // // A simple driver that exercises push, pop, isFull and isEmpty. // Thanks to autoboxing, we can push integers onto a stack of Objects. // // ********************************************************* public class StackTest { public static void main(String[] args) { StackADT stack = new ArrayStack(); //push some stuff on the stack for (int i=0; i<6; i++) stack.push(i*2); //pop and print //should print 8 6 4 2 0 while (!stack.isEmpty()) System.out.print(stack.pop() + " "); System.out.println(); //push a few more things for (int i=1; i<=6; i++) stack.push(i); //should print 5 4 3 2 1 while (!stack.isEmpty()) System.out.print(stack.pop() + " "); System.out.println(); } }

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A Linked Stack Implementation Java has a Stack class that holds elements of type Object. However, many languages do not provide stack types, so it is useful to be able to define your own. File StackADT.java contains an interface representing the ADT for a stack of objects and LinkedStack.java contains a skeleton for a class that uses a linked list to implement this interface. It depends on the Node class in Node.java. (This could also be defined as an inner class.) Fill in code for the following public methods: □ □ □ □

void push(Object val) int pop() boolean isEmpty() boolean isFull()

In writing your methods, keep in mind that in a linked implementation of a stack, the top of stack is always at the front of the list. This makes it easy to add (push) and remove (pop) elements.

File StackTest.java contains a simple driver to test your stack. Save it to your directory, compile it, and make sure it works. // *************************************************************** // StackADT.java // The classic Stack interface. // *************************************************************** public interface StackADT { // // Adds a new element to the top of the stack. // public void push(Object val); // // Removes and returns the element at the top of the stack. // public Object pop(); // // Returns true if stack is empty, false otherwise. // public boolean isEmpty(); // // Returns true if stack is full, false otherwise. // public boolean isFull(); } // *************************************************************** // LinkedStack.java // // A linked implementation of an Object stack class with operations push, // pop, and isEmpty and isFull. // // *************************************************************** public class LinkedStack implements StackADT { private Node top; // reference to top of stack // Chapter 13: Collections

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// Constructor -- initializes top // public LinkedStack() { } // // Adds element to top of stack if it's not full, else // does nothing. // public void push(Object val) { } // // Removes and returns value at top of stack. // is empty returns null. // public Object pop() { }

If stack

// // Returns true if stack is empty, false otherwise. // public boolean isEmpty() { } // // Returns true if stack is full, false otherwise. // public boolean isFull() { } } //*********************************************************** // Node.java // A general node for a singly linked list of objects. //*********************************************************** public class Node { private Node next; private Object element; //---------------------------------------------------// Creates an empty node //---------------------------------------------------public Node() { next = null; element = null; } //---------------------------------------------------// Creates a node storing a specified element //---------------------------------------------------public Node(Object element) 276

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{ next = null; this.element = element; } //---------------------------------------------------// Returns the node that follows this one //---------------------------------------------------public Node getNext() { return next; } //---------------------------------------------------// Sets the node that follows this one //---------------------------------------------------public void setNext(Node node) { next = node; } //---------------------------------------------------// Returns the element stored in this node //---------------------------------------------------public Object getElement() { return element; } //---------------------------------------------------// Sets the element stored in this node //---------------------------------------------------public void setElement(Object element) { this.element = element; } }

// ******************************************************* // StackTest.java // // A simple driver that exercises push, pop, isFull and isEmpty. // Thanks to autoboxing, we can push integers onto a stack of Objects. // // ******************************************************* public class StackTest { public static void main(String[] args) { StackADT stack = new LinkedStack (); //push some stuff on the stack for (int i=0; i<10; i++) stack.push(i*2); //pop and print //should print 18 16 14 12 10 8 6 4 2 0 while (!stack.isEmpty()) Chapter 13: Collections

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System.out.print(stack.pop() + " "); System.out.println(); //push a few more things for (int i=1; i<=6; i++) stack.push(i); //should print 6 5 4 3 2 1 while (!stack.isEmpty()) System.out.print(stack.pop() + " "); System.out.println(); } }

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Stack Manipulation Sometimes it’s useful to define operations on an ADT without changing the type definition itself. For example, you might want to print the elements in a stack without actually adding a method to the Stack ADT (you may not even have access to it). To explore this, use either the Stack class provided by Java (in java.util) or one of the stack classes that you wrote in an earlier lab exercise and the test program StackTest.java. Add the following static methods to the StackTest class (the signature for these methods and the declaration in StackTest assumes you are using a stack class named Stack—modify them to use the name of your class): □ □ □

void printStack(Stack s)—prints the elements in stack s from top to bottom. When printStack returns, s should be unchanged.

Stack reverseStack(Stack s)—returns a new stack whose elements are backwards from those in s. Again, s is unchanged.

Stack removeElement(Stack s, int val)—returns a new stack whose elements are the same as those in s (and in the same order) except that all occurrences of val have been removed. Again, s is unchanged.

Modify the main method to test these methods. Be sure you print enough information to see if they’re working! // *************************************************************** // StackTest.java // // A simple driver to test a stack. // // *************************************************************** import java.util.Stack; public class StackTest { public static void main(String[] args) { // Declare and instantiate a stack Stack stack = new Stack(); //push some stuff on the stack for (int i=0; i<10; i++) stack.push(i); stack.push(5); // call printStack to print the stack // call reverseStack to reverse the stack // call printStack to print the stack again // call removeElement to remove all occurrences of the value 5 - save the // stack returned from this call // call printStack to print the original stack and the new stack. } }

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Matching Parentheses One application of stacks is to keep track of things that must match up such as parentheses in an expression or braces in a program. In the case of parentheses when a left parenthesis is encountered it is pushed on the stack and when a right parenthesis is encountered its matching left parenthesis is popped from the stack. If the stack has no left parenthesis, that means the parentheses don’t match—there is an extra right parenthesis. If the expression ends with at least one left parenthesis still on the stack then again the parentheses don’t match— there is an extra left parenthesis.

File ParenMatch.java contains the skeleton of a program to match parentheses in an expression. It uses the Stack class provided by Java (in java.util). Complete the program by adding a loop to process the line entered to see if it contains matching parentheses. Just ignore characters that are neither left nor right parentheses. Your loop should stop as soon as it detects an error. After the loop print a message indicating what happened—the parentheses match, there are too many left parentheses, or there are too many right parentheses. Also print the part of the string up to where the error was detected. // ******************************************************************** // ParenMatch.java // // Determines whether or not a string of characters contains // matching left and right parentheses. // ******************************************************************** import java.util.*; import java.util.Scanner; public class ParenMatch { public static void main (String[] args) { Stack s = new Stack(); String line; // the string of characters to be checked Scanner scan = new Scanner(System.in); System.out.println ("\nParenthesis Matching"); System.out.print ("Enter a parenthesized expression: "); line = scan.nextLine(); // loop to process the line one character at a time // print the results } }

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Chapter 1: Introduction Lab Exercises Topics

Lab Exercises

Printing strings

Prelab Exercises Poem

Documentation

Comments

Identifiers

Program Names

Syntax errors

Recognizing Syntax Errors Correcting Syntax Errors

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Prelab Exercises Your task is to write a Java program that will print out the following message (including the row of equal marks): Computer Science, Yes!!!! ========================= An outline of the program is below. Complete it as follows: a. b.

In the documentation at the top, fill in the name of the file the program would be saved in and a brief description of what the program does.

Add the code for the main method to do the printing.

// ************************************************************ // File Name: // // Purpose: // ************************************************************ public class CSYes { // // The following main method prints an exciting // message about computer science //

}

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Poem Write a Java program that prints the message, “Roses are red”. Your program will be a class definition containing a main method—see the Lincoln example in Listing 1.1 of the text if you need guidance. Remember the following: □ The name of the class must match the name of the file (but without the .java extension). □ The main method must be inside the class definition (between the first { and the last}). □ The statement that prints the message must be inside main.

Compile and run your program. When it works correctly, modify it so that it prints the entire poem: Roses are red Violets are blue Sugar is sweet And so are you!

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Comments File Count.java contains a Java program that counts from 1 to 5 in English, French, and Spanish. Save this file to your directory and compile and run it to see what it does. Then modify it as follows: 1.

2.

3.

4.

5.

Use // style comments to add a comment header at the top of the file that includes the name of the program, your name, and a brief description of what the program does, neatly formatted. Include a delimiter line (e.g., all stars) at the beginning and end of the header.

Add a comment before each println that indicates what language the next line is in. Experiment with leaving a blank line before each of these comment lines (in the program itself, not the output). Is the program easier to read with or without these blank lines?

Remove one of the slashes from one of your comment lines and recompile the program, so one of the comments starts with a single /. What error do you get? Put the slash back in.

Try putting a comment within a comment, so that a // appears after the initial // on a comment line. Does this cause problems?

Consult the documentation guidelines in Appendix F of the text. Have you violated any of them? List two things that you could imagine yourself or someone else doing in commenting this program that these guidelines discourage.

Count.java public class Count { public static void main (String[] args) { System.out.println ("one two three four five"); System.out.println ("un deux trois quatre cinq"); System.out.println ("uno dos tres cuatro cinco"); } }

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Program Names File Simple.java contains a simple Java program that prints a message. The identifier that represents the name of this program is Simple, but we could have chosen a different identifier subject to certain rules and conventions. An identifier may contain any combination of letters, digits, the underscore character, and the dollar sign, but cannot begin with a digit. Furthermore, by convention, identifiers that represent class names (which includes program names) begin with a capital letter. This means that you won’t get an error if your program name doesn’t start with a capital letter (as long as what it starts with is legal for an identifier), but it’s better style if you do. This may seem arbitrary now, but later when you have lots of identifiers in your programs you’ll see the benefit. Of course, the program name should always be reasonably descriptive of the program.

Indicate whether each name below is a legal identifier, and if so, whether it is a good choice to name this program. If the answer to either question is no, explain why. Then save Simple.java to your directory and check your answers by modifying it to try each—note that you will have to change the file name each time to match the program name or you will always get an error.

1.

2.

3.

4.

5.

6.

7.

simple (Why do you even have to change the name of the file in this case?)

SimpleProgram 1 Simple _Simple_ *Simple* $123_45 Simple!

// ******************************************** // Simple.java // // Print a simple message about Java. // // ******************************************** public class Simple { public static void main (String[] args) { System.out.println ("Java rocks!!"); } }

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Recognizing Syntax Errors When you make syntax errors in your program the compiler gives error messages and does not create the bytecode file. It saves time and frustration to learn what some of these messages are and what they mean. Unfortunately, at this stage in the game many of the messages will not be meaningful except to let you know where the first error occurred. Your only choice is to carefully study your program to find the error. In the following you will introduce a few typical errors into a simple program and examine the error messages.

1. Type the following program into a file called Hello.java. (This is the traditional first program a computer scientist writes in a new language.) // ******************************************** // Hello.java // // Print a Hello, World message. // ******************************************** public class Hello { // // main method -- prints the greeting // public static void main (String[] args) { System.out.println ("Hello, World!"); } } Compile and run the program to see what it does. Then make the changes below, answering the questions as you go.

2. Class name different from file name. Delete one l (el) from the name of the class (so the first non-comment line is public class Helo), save the program, and recompile it. What was the error message?

3. Misspelling inside string. Correct the mistake above, then delete one l from the Hello in the message to be printed (inside the quotation marks). Save the program and recompile it. There is no error message—why not? Now run the program. What has changed?

4. No ending quotation mark in a string literal. Correct the spelling in the string, then delete the ending quotation mark enclosing the string Hello, World!. Save the program and recompile it. What error message(s) do you get?

5. No beginning quotation mark in a string literal. Put the ending quotation mark back, then take out the beginning one.

Save and recompile. How many errors this time? Lots, even though there is really only one error. When you get lots of errors always concentrate on finding the first one listed!! Often fixing that one will fix the rest. After we study variables the error messages that came up this time will make more sense.

6. No semicolon after a statement. Fix the last error (put the quotation mark back). Now remove the semicolon at the end of the line that prints the message. Save the program and recompile it. What error message(s) do you get?

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Chapter 1: Introduction

Correcting Syntax Errors File Problems.java contains a simple Java program that contains a number of syntax errors. Save the program to your directory, study it and correct as many of the errors as you can find. Then compile the program; if there are still errors, correct them. Some things to remember: □

□ □ □

Java is case sensitive, so, for example, the identifiers public, Public, and PUBLIC are all considered different. For reserved words such as public and void and previously defined identifiers such as String and System, you have to get the case right. You will learn the conventions about case soon, but for now you can look at a sample program in the text to see what case should be used where.

When the compiler lists lots of errors, fix the first one (or few) and then recompile—often the later errors aren’t really errors in the program, they just indicate that the compiler is confused from earlier errors.

Read the error messages carefully, and note what line numbers they refer to. Often the messages are helpful, but even when they aren’t, the line numbers usually are.

When the program compiles cleanly, run it.

// ******************************************** // Problems.java // // Provide lots of syntax errors for the user to correct. // ******************************************** public class problems { public Static main (string[] args) { System.out.println ("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"); System.out.println ("This program used to have lots of problems,"); System.out.println ("but if it prints this, you fixed them all.")

System.out.println (" *** Hurray! ***"); System.out.println ("!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!"); } }

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Chapter 2: Data and Expressions Lab Exercises Topics

Lab Exercises

Print and println String literals String concatenation Escape sequences

Names and Places A Table of Student Grades Two Meanings of Plus

Variables Constants Assignment Integers and Floating point Arithmetic Expressions Operator Precedence Input using the Scanner class

Prelab Exercises Area and Circumference of a Circle Painting a Room Ideal Weight Lab Grades Base Conversion

HTML Applets Graphics Colors

Introduction to HTML Drawing Shapes The Java Coordinate System Drawing a Face Creating a Pie Chart Colors in Java

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Names and Places The goal in this exercise is to develop a program that will print out a list of student names together with other information for each. The tab character (an escape sequence) is helpful in getting the list to line up nicely. A program with only two names is in the file Names.java. // ************************************************************ // Names.java // // Prints a list of student names with their hometowns // and intended major // ************************************************************ public class Names { // // main prints the list // public static void main (String[] args) { System.out.println (); System.out.println (" \tName\t\tHometown") ; System.out.println ("\t====\t\t========"); System.out.println ("\tSally\t\tRoanoke"); System.out.println ("\tAlexander\tWashington") System.out.println (); } } 1.

2.

3.

Save Names.java to your directory. Compile and run it to see how it works.

Modify the program so that your name and hometown and the name and hometown of at least two classmates sitting near you in lab also are printed. Save, compile and run the program. Make sure the columns line up.

Modify the program to add a third column with the intended major of each person (assume Sally's major is Computer Science and Alexander's major is Math). Be sure to add a label at the top of the third column and be sure everything is lined up (use tab characters!).

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A Table of Student Grades Write a Java program that prints a table with a list of at least 5 students together with their grades earned (lab points, bonus points, and the total) in the format below. ///////////////////\\\\\\\\\\\\\\\\\\\ == Student Points == \\\\\\\\\\\\\\\\\\\/////////////////// Name ---Joe William Mary Sue

Lab --43 50 39

Bonus ----7 8 10

Total ----50 58 49

The requirements for the program are as follows: 1.

2.

3.

Print the border on the top as illustrated (using the slash and backslash characters).

Use tab characters to get your columns aligned and you must use the + operator both for addition and string concatenation.

Make up your own student names and points—the ones shown are just for illustration purposes. You need 5 names.

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Two Meanings of Plus In Java, the symbol + can be used to add numbers or to concatenate strings. This exercise illustrates both uses.

When using a string literal (a sequence of characters enclosed in double quotation marks) in Java the complete string must fit on one line. The following is NOT legal (it would result in a compile-time error).

System.out.println ("It is NOT okay to go to the next line in a LONG string!!!"); The solution is to break the long string up into two shorter strings that are joined using the concatenation operator (which is the + symbol). This is discussed in Section 2.1 in the text. So the following would be legal System.out.println ("It is OKAY to break a long string into " + "parts and join them with a + symbol."); So, when working with strings the + symbol means to concatenate the strings (join them). BUT, when working with numbers the + means what it has always meant—add!

1.

Observing the Behavior of + To see the behavior of + in different settings do the following: a. Study the program below, which is in file PlusTest.java. // ************************************************************ // PlusTest.java // // Demonstrate the different behaviors of the + operator // ************************************************************ public class PlusTest { // // main prints some expressions using the + operator // public static void main (String[] args) { System.out.println ("This is a long string that is the " + "concatenation of two shorter strings."); System.out.println ("The first computer was invented about" + 55 + "years ago."); System.out.println ("8 plus 5 is " + 8 + 5); System.out.println ("8 plus 5 is " + (8 + 5)) ; System.out.println (8 + 5 + " equals 8 plus 5."); } } b. c.

Save PlusTest.java to your directory.

Compile and run the program. For each of the last three output statements (the ones dealing with 8 plus 5) write down what was printed. Now for each explain why the computer printed what it did given that the following rules are used for +. Write out complete explanations. □ If both operands are numbers + is treated as ordinary addition. (NOTE: in the expression a + b the a and b are called the operands.) □ If at least one operand is a string the other operand is converted to a string and + is the concatenation operator. □ If an expression contains more than one operation expressions inside parentheses are evaluated first. If there are no parentheses the expression is evaluated left to right. d. The statement about when the computer was invented is too scrunched up. How should that be fixed?

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2.

Writing Your Own Program With + Now write a complete Java program that prints out the following sentence: Ten robins plus 13 canaries is 23 birds.

Your program must use only one statement that invokes the println method. It must use the + operator both to do arithmetic and string concatenation.

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Prelab Exercises 1.

What is the difference between a variable and a constant?

2.

Explain what each of the lines below does. Be sure to indicate how each is different from the others. a. int x;

3.

b.

int x = 3;

c.

x = 3;

The following program reads three integers and prints the average. Fill in the blanks so that it will work correctly. // ***************************************************************** // Average.java // // Read three integers from the user and print their average // ***************************************************************** import java.util.Scanner; public class Average { public static void main(String[] args) { int val1, val2, val3; double average; Scanner scan = new Scanner(System.in) ; // get three values from user System.out.println("Please enter three integers and " + "I will compute their average");

//compute the average

//print the average

} }

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4.

Given the declarations below, find the result of each expression. int a = 3, b = 10, c = 7; double w = 12.9, y = 3.2; a. a + b * c b. a - b - c c. a / b d. b / a e. a - b / c f. w / y g. y / w h. a + w / b i. a % b / y j. b % a k. w %

5.

y

Carefully study the following program and find and correct all of the syntax errors. // File: // Purpose: //

Errors.java A program with lots of syntax errors Correct all of the errors (STUDY the program carefully!!)

#import java.util.Scanner; public class errors { public static void main (String[] args) { String Name; / Name of the user int number; int numSq; Scanner scan = new Scanner(System.in); System.out.print ("Enter your name, please: ") Name = scan.nextInt(); System.out.print ("What is your favorite number?); number = scan.nextInt(); numSq = number * number; System.out.println (Name ", the square of your number is " numSquared); }

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6.

Trace the execution of the following program assuming the input stream contains the numbers 10, 3, and 14.3. Use a table that shows the value of each variable at each step. Also show the output (exactly as it would be printed). // FILE: Trace.java // PURPOSE: An exercise in tracing a program and understanding // assignment statements and expressions. import java.util.Scanner; public class Trace { public static void main (String[] args) { int one, two, three; double what; Scanner scan = new Scanner(System.in); System.out.print ("Enter two integers: "); one = scan.nextInt(); two = scan.nextInt(); System.out.print("Enter a floating point number: "); what = scan.nextDouble() ; three = 4 * one + 5 * two; two = 2 * one; System.out.println ("one " + two + ":" + three); one = 46 / 5 * 2 + 19 % 4; three = one + two; what = (what + 2.5) / 2 ; System.out.println (what + " is what!"); } }

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Area and Circumference of a Circle Study the program below, which uses both variables and constants: // ************************************************************ // Circle.java // // Print the area of a circle with two different radii // ************************************************************ public class Circle { public static void main(String[] args) { final double PI = 3.14159; int radius = 10; double area = PI * radius * radius; System.out.println("The area of a circle with radius " + radius + " is " + area); radius = 2 0; area = PI * radius * radius; System.out.println("The area of a circle with radius " + radius + " is " + area); } } Some things to notice: □ The first three lines inside main are declarations for PI, radius, and area. Note that the type for each is given in these lines: final double for PI, since it is a floating point constant; int for radius, since it is an integer variable, and double for area, since it will hold the product of the radius and PI, resulting in a floating point value. □ These first three lines also hold initializations for PI, radius, and area. These could have been done separately, but it is often convenient to assign an initial value when a variable is declared. □ The next line is simply a print statement that shows the area for a circle of a given radius. □ The next line is an assignment statement, giving variable radius the value 20. Note that this is not a declaration, so the int that was in the previous radius line does not appear here. The same memory location that used to hold the value 10 now holds the value 20—we are not setting up a new memory location. □ Similar for the next line—no double because area was already declared. □ The final print statement prints the newly computed area of the circle with the new radius.

Save this program, which is in file Circle.java, into your directory and modify it as follows: 1.

The circumference of a circle is two times the product of Pi and the radius. Add statements to this program so that it computes the circumference in addition to the area for both circles. You will need to do the following: □ Declare a new variable to store the circumference. □ Store the circumference in that variable each time you compute it. □ Add two additional print statements to print your results.

Be sure your results are clearly labeled.

2.

When the radius of a circle doubles, what happens to its circumference and area? Do they double as well? You can determine this by dividing the second area by the first area. Unfortunately, as it is now the program overwrites the first

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area with the second area (same for the circumference). You need to save the first area and circumference you compute instead of overwriting them with the second set of computations. So you'll need two area variables and two circumference variables, which means they'll have to have different names (e.g., area1 and area2). Remember that each variable will have to be declared. Modify the program as follows: □ Change the names of the area and circumference variables so that they are different in the first and second calculations. Be sure that you print out whatever you just computed. □ At the end of the program, compute the area change by dividing the second area by the first area. This gives you the factor by which the area grew. Store this value in an appropriately named variable (which you will have to declare). □ Add a println statement to print the change in area that you just computed. □ Now repeat the last two steps for the circumference.

Look at the results. Is this what you expected?

3.

In the program above, you showed what happened to the circumference and area of a circle when the radius went from 10 to 20. Does the same thing happen whenever the radius doubles, or were those answers just for those particular values? To figure this out, you can write a program that reads in values for the radius from the user instead of having it written into the program ("hardcoded"). Modify your program as follows: □ At the very top of the file, add the line import java.util.Scanner; This tells the compiler that you will be using methods from the Scanner class. In the main method create a Scanner object called scan to read from System.in. □ Instead of initializing the radius in the declaration, just declare it without giving it a value. Now add two statements to read in the radius from the user: □ A prompt, that is, a print statement that tells the user what they are supposed to do (e.g., "Please enter a value for the radius."); □ A read statement that actually reads in the value. Since we are assuming that the radius is an integer, this will use the nextInt() method of the Scanner class. □ When the radius gets it second value, make it be twice the original value. □ Compile and run your program. Does your result from above hold?

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Painting a Room File Paint.java contains the partial program below, which when complete will calculate the amount of paint needed to paint the walls of a room of the given length and width. It assumes that the paint covers 350 square feet per gallon. //*************************************************************** //File: Paint.java // //Purpose: Determine how much paint is needed to paint the walls //of a room given its length, width, and height //*************************************************************** import java.util.Scanner; public class Paint { public static void main(String[] args) { final int COVERAGE = 350; //paint covers 350 sq ft/gal //declare integers length, width, and height; //declare double totalSqFt; //declare double paintNeeded; //declare and initialize Scanner object //Prompt for and read in the length of the room //Prompt for and read in the width of the room //Prompt for and read in the height of the room //Compute the total square feet to be painted--think //about the dimensions of each wall //Compute the amount of paint needed //Print the length, width, and height of the room and the //number of gallons of paint needed. } } Save this file to your directory and do the following: 1.

2.

Fill in the missing statements (the comments tell you where to fill in) so that the program does what it is supposed to.

Compile and run the program and correct any errors.

Suppose the room has doors and windows that don't need painting. Ask the user to enter the number of doors and number of windows in the room, and adjust the total square feet to be painted accordingly. Assume that each door is 20 square feet and each window is 15 square feet.

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Ideal Weight Write a program to compute the ideal weight for both males and females. According to one study, the ideal weight for a female is 100 pounds plus 5 pounds for each inch in height over 5 feet. For example, the ideal weight for a female who is 5'3" would be 100 + 15 = 115 pounds. For a male the ideal weight is 106 pounds plus 6 pounds for each inch in height over 5 feet.

For example, the ideal weight for a male who is 6'2" would be 106 + 14*6 =190 pounds. Your program should ask the user to enter his/her height in feet and inches (both as integers—so a person 5'3" would enter the 5 and the 3). It should then compute and print both the ideal weight for a female and the ideal weight for a male. The general outline of your main function would be as follows: □ Declare your variables (think about what variables you need—you need to input two pieces of information (what?), then you need some variables for your calculations (see the following steps) □ Get the input (height in feet and inches) from the user □ Compute the total number of inches of height (convert feet and inches to total inches) □ Compute the ideal weight for a female and the ideal weight for a male (here you basically convert the "word" description above to assignment statements) □ Print the answers Plan your program, then type it in, compile and run it. Be sure it gives correct answers.

Enhance the Program a Bit The weight program would be a bit nicer if it didn't just give one number as the ideal weight for each sex. Generally a person's weight is okay if it is within about 15% of the ideal. Add to your program so that in addition to its current output it prints an okay range for each sex—the range is from the ideal weight minus 15% to the ideal weight plus 15%. You may do this by introducing new variables and assignment statements OR directly within your print statements.

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Lab Grades Suppose your lab instructor has a somewhat complicated method of determining your grade on a lab. Each lab consists of two out-of-class activities—a pre-lab assignment and a post-lab assignment—plus the in-class activities. The in-class work is 60% of the lab grade and the out-of-class work is 40% of the lab grade. Each component of the grade is based on a different number of points (and this varies from lab to lab)—for example, the pre-lab may be graded on a basis of 20 points (so a student may earn 17 out of 20 points) whereas the post-lab is graded on a basis of 30 points and the in-class 25 points. To determine the out-of-class grade the instructor takes the total points earned (pre plus post) divided by the maximum possible number of points, multiplied by 100 to convert to percent; the in-class grade is just the number of points earned divided by the maximum points, again converted to percent.

The program LabGrade.java is supposed to compute the lab grade for a student. To do this it gets as input the number of points the student earned on the prelab assignment and the maximum number of points the student could have earned; the number of points earned on the lab itself and the maximum number of points; the number of points earned on the postlab assignment and the maximum number of points. The lab grade is computed as described above: the in-class and out-of-class grades (in percent) are computed separately then a weighted average of these is computed. The program currently assumes the out-of-class work counts 40% and the in-class counts 60%. Do the following: 1.

First carefully hand trace the program assuming the input stream contains the values 17, 20, 23, 25, 12, 15. Trace the program exactly as it is written (it is not correct but it will compile and run so the computer would not know it isn't correct). Fill in the answers to the following questions: a. Show exactly how the computer would execute the assignment statement that computes the out of class average for this set of input. Show how the expression will be evaluated (the order in which the operations are performed) and what the result will be. b. Show how the computer would execute the assignment statement that computes the in-class average. What will the result be? c. Show how the computer would execute the assignment statement that computes the lab grade.

2.

Now run the program, typing in the input you used in your trace. Compare your answers to the output. Clearly the output is incorrect! Correct the program. This involves writing the expressions to do calculations correctly. The correct answers for the given input should be an out of class average of 82.857 (the student earned 29 points out of a possible 35 which is approximately 82.857%), an in-class average of 92 (23 points out of 25), and a lab grade of 88.34 (40% of 82.857 plus 60% of 92).

3.

Modify the program to make the weights for the two components of the grade variable rather than the constants 0.4 and 0.6. To do this, you need to do four things: a. Change the declarations so the weights (IN_WEIGHT and OUT WEIGHT) are variables rather than constants. Note that you should also change their names from all capital letters (the convention for constants) to lowercase letters with capitals starting new words (the convention for variables). So IN_WEIGHT should become inWeight. Of course, you'll also have to change it where it's used in the program. b. In the input section, add statements that will prompt the user for the weight (in decimal form—for example .4 for 40%) to be assigned to the in-class work, then read the input. Note that your prompt should explain to the user that the weight is expected to be in decimal form. c. In the section that calculates the labGrade add an assignment statement that calculates the weight to be assigned to the out of class work (this will be 1 minus the in-class weight).

Compile and run your program to make sure it is correct.

// *************************************************************** // LabGrade.java // This program computes a student's lab grade from // the grades on the three components of lab: the pre-lab // assignment, the lab itself, and the post-lab assignment. // *************************************************************** import java.util.Scanner; Chapter 2: Data and Expressions

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public class LabGrade { public static void main (String[] args) { // Declare constants final double IN_WEIGHT = 0.6; // in-class weight is 60% final double OUT_WEIGHT = 0.4; // out-of-class weight is 40% // Declare variables int preLabPts; //number of points earned on the pre-lab assignment int preLabMax; //maximum number of points possible for pre-lab int labPts; //number of poitns earned on the lab int labMax; //maximum number of points possible for lab int postLabPts; //number of points earned on the post-lab assignment int postLabMax; //maximum number of points possible for the post-lab int outClassAvg; //average on the out of class (pre and post) work int inClassAvg; //average on the in-class work double 1abGrade; //final lab grade Scanner scan = new Scanner(System.in); // Get the input System.out.println("\nWelcome to the Lab Grade Calculator\n"); System.out.print("Enter the number of points you earned on the pre-lab: "); preLabPts = scan.nextInt(); System.out.print("What was the maximum number of points you could have earned? "); preLabMax = scan.nextInt(); System.out.print("Enter the number of points you earned on the lab: "); labPts = scan.nextInt(); System.out.print("What was the maximum number of points for the lab? "); labMax = scan.nextInt(); System.out.print("Enter the number of points you earned on the post-lab: "); postLabPts = scan.nextInt(); System.out.print("What was the maximum number of points for the post-lab? "); postLabMax = scan.nextInt(); System.out.println(); // Calculate the average for the out of class work outClassAvg = preLabPts + postLabPts / preLabMax + postLabMax * 100; // Calculate the average for the in-class work inClassAvg = labPts / labMax * 100; // Calculate the weighted average taking 40% of the out-of-class average // plus 60% of the in-class labGrade = OUT_WEIGHT * outClassAvg + IN_WEIGHT * inClassAvg; // Print the results System.out.println("Your average on out-of-class work is " + outClassAvg + "%"); System.out.println("Your average on in-class work is " + inClassAvg + "%"); System.out.println("Your lab grade is " + labGrade + "%"); System.out.println(); } }

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Base Conversion One algorithm for converting a base 10 number to another base b involves repeatedly dividing by b. Each time a division is performed the remainder and quotient are saved. At each step, the dividend is the quotient from the preceding step; the divisor is always b. The algorithm stops when the quotient is 0. The number in the new base is the sequence of remainders in reverse order (the last one computed goes first; the first one goes last).

In this exercise you will use this algorithm to write a program that converts a base 10 number to a 4-digit number in another base (you don't know enough programming yet to be able to convert any size number). The base 10 number and the new base (between 2 and 9) will be input to the program. The start of the program is in the file BaseConvert.java. Save this file to your directory, then modify it one step at a time as follows: 1.

The program will only work correctly for base 10 numbers that fit in 4 digits in the new base. We know that in base 2 the maximum unsigned integer that will fit in 4 bits is 1111 2 which equals 15 in base 10 (or 24 – 1). In base 8, the maximum number is 77778 which equals 4095 in base 10 (or 84 – 1). In general, the maximum base 10 number that fits in 4 base b digits is b4 – 1. Add an assignment statement to the program to compute this value for the base that is input and assign it to the variable maxNumber. Add a statement that prints out the result (appropriately labeled). Compile and run the program to make sure it is correct so far.

2.

Now add the code to do the conversion. The comments below guide you through the calculations—replace them with the appropriate Java statements. // First compute place0 -- the units place. Remember this comes // from the first division so it is the remainder when the // base 10 number is divided by the base (HINT %). // Then compute the quotient (integer division / will do it!) // You can either store the result back in base10Num or declare a // new variable for the quotient // Now compute place1 -- this is the remainder when the quotient // from the preceding step is divided by the base. // Then compute the new quotient // Repeat the idea from above to compute place2 and the next quotient // Repeat again to compute place3

3. So far the program does not print out the answer. Recall that the answer is the sequence of remainders written in reverse order— note that this requires concatenating the four digits that have been computed. Since they are each integers, if we just add them the computer will perform arithmetic instead of concatenation. So, we will use a variable of type String.

Note near the top of the program a variable named baseBNum has been declared as an object of type String and initialized to an empty string. Add statements to the program to concatenate the digits in the new base to baseBNum and then print the answer. Compile and run your program. Test it using the following values: Enter 2 for the base and 13 for the base 10 number—the program should print 1101 as the base 2 value; enter 8 for the base and 1878 for the number— the program should print 3526 for the base 8 value; enter 3for the base and 50 for the number—the program should print 1212.

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// *********************************************** // BaseConvert.java // // Converts base 10 numbers to another base // (at most 4 digits in the other base). The // base 10 number and the base are input. // *********************************************** import java.util.Scanner; public class BaseConvert { public static void main (String[] args) { int base; // the new base int base10Num; // the number in base 10 int maxNumber; // the maximum number that will fit // in 4 digits in the new base int place0; int place1; int place2; int place3;

// digit in the 1's (base^0) place // digit in the base^1 place // digit in the base^2 place // digit in the base^3 place

String baseBNum = new String (""); // the number in the new base Scanner scan = new Scanner(System.in); // read in the base 10 number and the base System.out.println(); System.out.println ("Base Conversion Program"); System.out.println() ; System.out.print ("Please enter a base (2-9): "); base = scan.nextInt(); // Compute the maximum base 10 number that will fit in 4 digits // in the new base and tell the user what range the number they // want to convert must be in System.out.print ("Please enter a base 10 number to convert: "); base10Num = scan.nextInt(); // Do the conversion (see notes in lab) // Print the result (see notes in lab) } }

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Introduction to HTML HTML is the HyperText Markup Language. It is used to describe how text, images, and multimedia are displayed by Web browsers. In this lab you will learn a little about HTML so that you can create a web page containing headings, interesting fonts, lists, and links as well as applets.

HTML uses tags to describe the layout of a document; the browser then uses these tags to figure out how to display the document. Tags are enclosed in angle brackets. For example, <title> is a tag that indicates that this section contains the title of the document. Many tags, including <title>, have corresponding end tags that indicate where the section ends. The end tags look just like the start tags except that they start with the character /, e.g., </title>. So the following text indicates that the title of the document is Introduction to HTML: <title>Introduction to HTML</title> There are a few tags that almost every document will have: <html>, <head>, <title>, and <body>. Here is an example of a simple HTML document: <HTML> <HEAD> <TITLE>Introduction to HTML</TITLE> </HEAD> <BODY> In this lab you will learn about HTML, which is lots of fun to use. In particular, you will learn how to use fonts, paragraphs, lists, links and applets in a web page. Now you can make your own web page for your friends to visit! </BODY> </HTML> To see what this looks like, open the file in the web browser. Change the size of the browser window (click and drag any corner) and see how the text is reformatted as the window changes. Note that the title appears on the window, not as part of the document.

The HEAD of a document (everything between <HEAD> and </HEAD>) contains the introduction to the document. The title goes in the head, but for now we won't use the head for anything else. The BODY of a document (everything between <BODY> and </BODY>) contains everything that will be displayed as part of the document. Both the HEAD and the BODY are enclosed by the HTML tags, which begin and end the document.

This document contains only plain text, but an HTML document can have much more structure: headings, paragraphs, lists, bold and italic text, images, links, tables, and so on. Here is a document containing a heading, two paragraphs, and some fancy fonts:

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<HTML> <HEAD> <TITLE>Introduction to HTML</TITLE> </HEAD> <BODY BGCOLOR="lightgreen"> <H1 align="center">Introduction to HTML</H1> <P>In this lab you will learn about <I>HTML</I>, which is lots of fun to use. In particular, you will learn how to use fonts, paragraphs, lists, links, and colors in a web page. Now you can make your <B>own</B> web page for your friends to visit!</P> <P>Later in this lab you will do some fancier stuff with applets and graphics and include an applet on your web page.

Can't you just feel the job offers start rolling in?</P> <U>Yippee!</U> </BODY> </HTML> Run the HTML document to see what this looks like in the browser.

In this document the <H1> tag creates a level 1 heading. This is the biggest heading; it might be used at the beginning of the document or the start of a new chapter. Level 2 through level 6 headings are also available with the <H2> through <H6> tags.

The <P> tag creates a new paragraph. Most browsers leave a blank line between paragraphs. The <B> tag creates bold text, the <I> tag creates italic text, and the <U> tag creates underlined text. Note that each of these tags is closed with the corresponding end tag. The BGCOLOR attribute on the BODY tag sets the background color.

Note that line breaks and blank lines in the HTML document do not matter—the browser will format paragraphs to fit the window. If it weren't for the <P> tag, the blank line between the paragraphs in this document would not show up in the displayed document.

Exercise #1: For a file to be visible on the Web, it must be where the web server knows how to find it. *** Instruct students how to create and/or access the public html directory on the local system. *** Open a new file called MyPage.html in a directory where it will be accessible from the web. Write a simple web page about things that interest you. Your page should contain at least the following: □ □ □ □

A title (using the <TITLE> tag) Two different levels of headings Two paragraphs Some bold, italic, or underlined text

Your name should appear somewhere in the document.

When you are done, view your document from the browser. Just type in the URL, don't use File | Open Page.

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More HTML Lists We often want to add a list to a document. HTML provides two kinds of lists, ordered (e.g., 1, 2, 3) and unordered (e.g., bulleted). A list is introduced with the <OL> or <UL> tag, depending on whether it is ordered or unordered. Each list item is introduced with a <LI> tag and ended with the </LI> tag. The entire list is then ended with </OL> or </UL>, as appropriate. For example, the code below creates the list shown; replacing the <OL> and </OL> tags with <UL> and </UL> would produce the same list with bullets instead of numbers.

Things I like: <OL> <LI>chocolate <LI>rabbits <LI>chocolate rabbits </OL> Things I like: 1. chocolate 2. rabbits 3. chocolate rabbits

Exercise #2: Add a list, either ordered or unordered, of at least three elements to your document.

Links Links connect one document to another. Links are created in HTML with the <A> (anchor) tag. When creating a link you have to specify two things: □ The URL of the document to go to when the link is clicked. This is given as the HREF attribute of the A element. □ How the link should be displayed (that is, what text or image to click on to go to the linked document). This appears between the <A> and </A> tags.

For example, the code below creates the link shown, which goes to a page about the history of computing: Learn more about <A HREF="http://ei.cs.vt.edu/~history">the history of computing.</A> Learn more about the history of computing.

Exercise #3: Add at least one link that ties in to the material on your page.

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Drawing Shapes The following is a simple applet that draws a blue rectangle on a yellow background. // ************************************************************ // Shapes.java // // The program will draw two filled rectangles and a // filled oval. // ************************************************************ import javax.swing.JApplet; import java.awt.*; public class Shapes extends JApplet { public void paint (Graphics page) { // Declare size constants final int MAX_SIZE = 300; final int PAGE_WIDTH = 600; final int PAGE_HEIGHT = 400; // Declare variables int x, y; // x and y coordinates of upper left-corner of each shape int width, height; // width and height of each shape // Set the background color setBackground (Color.yellow); // Set the color for the next shape to be drawn page.setColor (Color.blue); // Assign the corner point and width and height x = 200; y = 150; width = 100; height = 70; // Draw the rectangle page.fillRect(x, y, width, height); } } Study the code, noting the following: □ □

The program imports javax.swing.JApplet because this is an applet, and it imports java.awt.* because it uses graphics.

There is no main method—instead there is a paint method. The paint method is automatically invoked when an applet is displayed, just as the main method is automatically invoked when an application is executed. □ Most of the methods that draw shapes (see the list in Figure 2.12) require parameters that specify the upper left-hand corner of the shape (using the coordinate system described in Section 2.9) and the width and height of the shape. You can see this in the calls to fillRect, which draws a rectangle filled with the current foreground color. □ This applet will be drawn assuming the window for drawing (the Graphics object - named page here) is 600 pixels wide and 400 pixels high. These numbers are defined in constants at the beginning of the program. (They currently have no use but you will use them later). The width and height of the applet are actually specified in the HTML file that instructs the Web browser to run the applet (remember applets are executed by Web browsers and Web browsers get their instructions from HTML documents—note that the code executed by the browser is the bytecode for the program, the Shapes.class file). The code in the HTML document is as follows: 27 Chapter 2: Data and Expressions

<html> <applet code="Shapes.class" width=600 height=400> </applet> </html> Save the files Shapes.java and Shapes.html to your directory. Now do the following: 1. Compile Shapes.java, but don't run it—this is an applet, so it is run through a browser or a special program called the Applet Viewer.

2. Run the program through your browser. You should see a blue rectangle on a yellow background.

3. Now run the program through the Applet Viewer by typing the command appletviewer Shapes.html You should see a new window open displaying the rectangle.

4. Now open the program in your text editor and change the x and y variables both to 0. Save and recompile the program, then view it in the Applet Viewer (this is generally less trouble when making lots of changes than using the browser).

What happened to the rectangle?

5. Now change the width to 200 and the height to 300. Save, recompile and run to see how this affects the rectangle.

6. Change x to 400, y to 40, width to 50 and height to 200. Test the program to see the effect.

7. Modify the program so that it draws four rectangles in all, as follows: □ One rectangle should be entirely contained in another rectangle. □ One rectangle should overlap one of the first two but not be entirely inside of it. □ The fourth rectangle should not overlap any of the others.

8.

One last touch to the program... Change the colors for at least three of the shapes so the background and each of the three shapes are different colors (a list of colors is in Figure 2.10 of the text). Also change two of the fillRect methods to fillOval so the final program draws two rectangles and two ovals. Be sure that the overlap rules are still met.

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The Java Coordinate System The Java coordinate system is discussed in Section 2.7 & 2.9 of the text. Under this system, the upper left-hand corner of the window is the point (0,0). The X axis goes across the window, and the Y axis goes down the window. So the bigger the X value, the farther a point is to the right. The bigger the Y value, the farther it is down. There are no negative X or Y values in the Java coordinate system. Actually, you can use negative values, but since they're off the screen they won't show up!

1.

Save files Coords.java and Coords.html to your directory. File Coords.java contains an applet that draws a rectangle whose upper lefthand corner is at 0,0. Use the applet viewer to run this applet. Remember that you have to do it through the html file: appletviewer Coords.html.

2.

Modify the applet so that instead of 0,0 for the upper lefthand corner, you use the coordinates of the middle of the applet window. This applet is set up to be 600 pixels wide and 400 pixels high, so you can figure out where the middle is. Save, compile, and view your applet. Does the rectangle appear to be in the middle of the screen? Modify the coordinates so that it does appear to be in the middle.

3.

Now add four more rectangles to the applet, one in each corner. Each rectangle should just touch one corner of the center rectangle and should go exactly to the edges of the window.

4.

Make each rectangle be a different color. To do this, use the setColor method of the Graphics class to change the color (this is already done once). Do not change the background color once it has been set! Doing so causes the screen to flicker between colors.

// ************************************************************* // Coords.java // // Draw rectangles to illustrate the Java coordinate system // // ************************************************************* import javax.swing.JApplet; import java.awt.*; public class Coords extends JApplet { public void paint (Graphics page) { // Declare size constants final int MAX_SIZE = 300; final int PAGE_WIDTH = 600; final int PAGE_HEIGHT = 400; // Declare variables int x, y; // x and y coordinates of upper left-corner of each shape int width, height; // width and height of each shape // Set the background color setBackground (Color.yellow); // Set the color for the next shape to be drawn page.setColor (Color.blue); // Assign the corner point and width and height x = 0; y = 0;

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width = 150; height = 100; page.fillRect(x, y, width, height); } } Coords.html <html> <applet code="Coords.class" width=600 height=400> </applet> </html>

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Drawing a Face Write an applet that draws a smiling face. Give the face eyes with pupils, ears, a nose, and a mouth. Use at least three different colors, and fill in some of the features. Name this file Face.java, and create a corresponding .html file. View your applet using the applet viewer.

Now add your face to a web page you created (you may have created one in an earlier lab exercise). You will do this using the <APPLET> tag that is in the .html file you are using with the applet viewer—you can just copy it out of that file and paste it into your other file. The applet will appear wherever you insert the applet tag.

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Creating a Pie Chart Write an applet that draws a pie chart showing the percentage of household income spent on various expenses. Use the percentages below: Rent and Utilities Transportation Food Educational Miscellaneous

35% 15% 15% 25% 10%

Each section of the pie should be in a different color, of course. Label each section of the pie with the category it represents— the labels should appear outside the pie itself.

Embed your applet in an HTML document about managing expenses. It should contain a heading, some text, a relevant list, and at least one link to a relevant page. Your name should also appear somewhere on the page. Embed the applet so that it fits in nicely.

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Colors in Java The basic scheme for representing a picture in a computer is to break the picture down into small elements called pixels and then represent the color of each pixel by a numeric code (this idea is discussed in section 1.6 of the text). In most computer languages, including Java, the color is specified by three numbers—one representing the amount of red in the color, another the amount of green, and the third the amount of blue. These numbers are referred to as the RGB value of the color. In Java, each of the three primary colors is represented by an 8-bit code. Hence, the possible base 10 values for each have a range of 0-255. Zero means none of that color while 255 means the maximum amount of the color. Pure red is represented by 255 for red, 0 for green, and 0 for blue, while magenta is a mix of red and blue (255 for red, 0 for green, and 255 for blue). In Java you can create your own colors. So far in the graphics programs we have written we have used the pre-defined colors, such as Color.red, from the Color class. However, we may also create our own Color object and use it in a graphics program. One way to create a Color object is to declare a variable of type Color and instantiate it using the constructor that requires three integer parameters—the first representing the amount of red, the second the amount of green, and the third the amount of blue in the color. For example, the following declares the Color object myColor and instantiates it to a color with code 255 for red, 0 for green, and 255 for blue.

Color myColor = new Color(255, 0, 255); The statementpage.setColor(myColor) then will set the foreground color for the page to be the color defined by the myColor object. The file Colors.java contains an applet that defines myColor to be a Color object with color code (200, 100, 255) - a shade of purple. Save the program and its associated HTML file Colors.html to your directory, compile and run it using the appletviewer. Now make the following modifications: 1.

2.

3.

Change the constructor so the color code is (0,0,0) — absence of color. What color should this be? Run the program to check.

Try a few other combinations of color codes to see what you get. The description of the Color class in Appendix M contains documentation that gives the codes for the pre-defined colors.

Notice in the Color class in Appendix M there is a constructor that takes a single integer as an argument. The first 8 bits of this integer are ignored while the last 24 bits define the color—8 bits for red, 8 for green, and the last 8 bits for blue.

Hence, the bit pattern 00000000000000001111111100000000 should represent pure green. Its base 10 value is 65280. Change the declaration of the myColor object to Color myColor

=

new Color

(65280);

Compile and run the program. Do you see green?

4.

The Color class has methods that return the individual color codes (for red, green, and blue) for a Color object. For example, redCode = myColor.getRed(); returns the code for the red component of the myColor object (redCode should be a variable of type int). The methods that return the green and blue components are getGreen and getBlue, respectively. Add statements to the program, similar to the above, to get the three color codes for myColor (you need to declare some variables). Then add statements such as page.drawString("Red: " + redCode,

,

);

to label the rectangle with the three color codes (fill in the blanks with appropriate coordinates so each string is drawn inside the rectangle—you also need to set the drawing color to something such as black so the strings will show up).

Compile and run the program; for the pure green color above, you should get 0 for red and blue and 255 for green. Now change the integer you use to create the color from 65280 to 115 and see what you get (can you predict?), then try it again with 2486921 (harder to predict!).

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// ************************************************************* // Colors.java // // Draw rectangles to illustrate colors and their codes in Java // ************************************************************* import javax.swing.JApplet; import java.awt.*; public class Colors extends JApplet { public void paint (Graphics page) { // Declare size constants final int PAGE_WIDTH = 600; final int PAGE_HEIGHT = 400; // Declare variables int x, y; // x and y coordinates of upper left-corner of each shape int width, height; // width and height of each shape Color myColor = new Color (200, 100, 255); // Set the background color and paint the screen with a white rectangle setBackground (Color.white); page.setColor(Color.white); page.fillRect(0, 0, PAGE_WIDTH, PAGE_HEIGHT); // Set the color for the rectangle page.setColor (myColor); // Assign the corner point and width and height then draw x = 200; y = 125; width = 200; height = 150; page.fillRect(x, y, width, height); } } Colors.html <html> <applet code="Colors.class" width=600 height=400> </applet> </html>

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Chapter 3: Using Classes and Objects Lab Exercises Topics

Lab Exercises

String Class

Prelab Exercises Working with Strings

Random Class

Rolling Dice

Math Class

Computing Distance

Formatting Classes

Formatting Output

Enumerated Types

Playing with Cards

Wrapper Classes

Experimenting with the Integer Class

Panels

Nested Panels

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Prelab Exercises Sections 3.2-3.5 These exercises focus on the String, Random, and Math classes defined in the Java Standard Class Library. The main concepts are in the text in sections 3.2-3.5. The goals of the lab are for you to gain experience with the following concepts: •

Declaring a variable to be a reference to an object—for example, the following declares the variable quotation to be a reference to a String object: String quotation;

•

Declaring a variable to be a reference to an object and creating the object (instantiating it) using the new operator—for example, String quotation = new String("I think, therefore I am."); Random generator = new Random();

•

Invoking a method to operate on an object using the dot operator—for example, quotation.length() invokes the length method which returns the length of the quotation String or quotation.toLowerCase() quotation except all letters are lower case. These invocations would be used in a program in a place appropriate for an integer (in the first case) or a String (in the second case) such as an assignment statement or a println statement.

•

Invoking static or class methods—these are methods that are invoked using the class name rather than an object name.

The methods in the Math class are static methods (basically because we don't need different instances of Math whereas there are lots of different String objects). Examples are Math.sqrt(2)

(which returns the square root of 2)

and Math.pow(3, 2)

(which returns 32)

•

Importing the appropriate packages—usually when you use classes from a library you need to put the import declaration at the top of your program. The exception is for classes defined in the java.lang package (this includes String and Math) which is automatically imported into every Java program.

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Exercises 1.

Fill in the blanks in the program below as follows: (Section 3.2, especially the example in Listing 3.1, should be helpful): (a) declare the variable town as a reference to a String object and initialize it to "Anytown, USA". (b) write an assignment statement that invokes the length method of the string class to find the length of the college String object and assigns the result to the stringLength variable (c) complete the assignment statement so that change1 contains the same characters as college but all in upper case (d) complete the assignment statement so that change2 is the same as change1 except all capital O's are replaced with the asterisk (*) character. (e) complete the assignment statement so that change3 is the concatenation of college and town (use the concat method of the String class rather than the + operator) // ************************************************** // StringPlay.java // // Play with String objects // ************************************************** public class StringPlay { public static void main (String[] args) { String college = new String ("PoDunk College"); ; // part (a) int stringLength; String change1, change2, change3; ; // part (b) System.out.println (college + " contains " + stringLength + " characters."); changel =

; // part (c)

change2 =

; // part (d)

change3 =

; // part (e)

System.out.println ("The final string is " + change3); } } 2.

The following program should read in the lengths of two sides of a right triangle and compute the length of the hypotenuse (recall that the length of the hypotenuse is the square root of side 1 squared plus side 2 squared). Complete it by adding statements to read the input from the keyboard and to compute the length of the hypotenuse (you need to use a Math class method for that).

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// ******************************************************************* // RightTriangle.java // // Compute the length of the hypotenuse of a right triangle // given the lengths of the sides // ******************************************************************* import java.util.Scanner; public class RightTriangle { public static void main (String[] args) { double side1, side2; // lengths of the sides of a right triangle double hypotenuse; // length of the hypotenuse Scanner scan = new Scanner(System.in); // Get the lengths of the sides as input System.out.print ("Please enter the lengths of the two sides of " + "a right triangle (separate by a blank space): "); ------------------------------------------------------------- ; ------------------------------------------------------------- ; // Compute the length of the hypotenuse ------------------------------------------------------------- ; // Print the result System.out.println ("Length of the hypotenuse: " + hypotenuse); } } 3. In many situations a program needs to generate a random number in a certain range. The Java Random class lets the programmer create objects of type Random and use them to generate a stream of random numbers (one at a time). The following declares the variable generator to be an object of type Random and instantiates it with the new operator.

Random generator = new Random(); The generator object can be used to generate either integer or floating point random numbers using either the nextInt method (either with no parameter or with a single integer parameter) or nextFloat (or nextDouble) methods, respectively. The integer returned by nextIn(t could be any valid integer (positive or negative) whereas the number returned by nextInt(n) is a random integer in the range 0 to n-1. The numbers returned by nextFloat() or nextDouble() are floating point numbers between 0 and 1 (up to but not including the 1). Most often the goal of a program is to generate a random integer in some particular range, say 30 to 99 (inclusive). There are several ways to do this: •

Using nextInt(): This way we must use the % operator to reduce the range of values—for example, Math.abs(generator.nextInt()) % 70 will return numbers between 0 and 69 (because those are the only possible remainders when an integer is divided by 70 - note that the absolute value of the integer is first taken using the abs method from the Math class). In general, using % N will give numbers in the range 0 to N -1. Next the numbers must be shifted to the desired range by adding the appropriate number. So, the expression Math.abs(generator.nextInt()) % 70 + 30 will generate numbers between 30 and 99.

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•

Using nextInt(70): The expression generator.nextInt(70) will return numbers between 0 and 69 (inclusive). Next the numbers must be shifted to the desired range by adding the appropriate number. So, the expression generator.nextInt(70)

+30

will generate numbers between 30 and 99.

•

Using nextFloat: In this case, we must multiply the result of nextFloat to expand the range—for example, generator.nextFloat() * 70 returns a floating point number between 0 and 70 (up to but not including 70). To get the integer part of the number we use the cast operator: (int)

(generator.nextFloat()

*

70)

*

70)

The result of this is an integer between 0 and 69, so (int)

(generator.nextFloat()

+

30

shifts the numbers by 30 resulting in numbers between 30 and 99.

The method nextFloat can be replaced by nextDouble to get double precision floating point numbers rather than single precision.

Fill in the blanks in the following program to generate the random numbers as described in the documentation. NOTE that that java.util.Random must be imported to use the Random class. // ************************************************** // LuckyNumbers.j ava // // To generate three random "lucky" numbers // ************************************************** import java.util.Random; public class LuckyNumbers { public static void main (String[] args) { Random generator = new Random(); int lucky1, lucky2, lucky3; // Generate lucky1 (a random integer between 50 and 79) using the // nextInt method (with no parameter) luckyl =

;

// Generate lucky2 (a random integer between 90 and 100) using the // nextInt method with an integer parameter lucky 2 =

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39

// Generate lucky3 (a random integer between 11 and 30) using nextFloat lucky 3 =

;

System.out.println ("Your lucky numbers are " + lucky1 + ", " + lucky2 + ", and " + lucky3); } }

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Working with Strings The following program illustrates the use of some of the methods in the String class. Study the program to see what it is doing. // *************************************************************** // StringManips.j ava // // Test several methods for manipulating String objects // *************************************************************** import java.util.Scanner; public class StringManips { public static void main (String[] args) { String phrase = new String ("This is a String test."); int phraseLength; // number of characters in the phrase String int middleIndex; // index of the middle character in the String String firstHalf; // first half of the phrase String String secondHalf; // second half of the phrase String String switchedPhrase; //a new phrase with original halves switched // compute the length and middle index of the phrase phraseLength = phrase.length(); middleIndex = phraseLength / 2; // get the substring for each half of the phrase firstHalf = phrase.substring(0,middleIndex); secondHalf = phrase.substring(middleIndex, phraseLength); // concatenate the firstHalf at the end of the secondHalf switchedPhrase = secondHalf.concat(firstHalf); // print information about the phrase System.out.println(); System.out.println ("Original phrase: " + phrase); System.out.println ("Length of the phrase: " + phraseLength + " characters"); System.out.println ("Index of the middle: " + middleIndex); System.out.println ("Character at the middle index: " + phrase.charAt(middleIndex)); System.out.println ("Switched phrase: " + switchedPhrase); System.out.println(); } } The file StringManips.java contains this program. Save the file to your directory and compile and run it. Study the output and make sure you understand the relationship between the code and what is printed. Now modify the file as follows: 1.

Declare a variable of type String named middle3 (put your declaration with the other declarations near the top of the program) and use an assignment statement and the substring method to assign middle3 the substring consisting of the middle three characters of phrase (the character at the middle index together with the character to the left of that and the one to the right - use variables, not the literal indices for this particular string). Add a println statement to print out the result. Save, compile, and run to test what you have done so far.

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2.

Add an assignment statement to replace all blank characters in switchedPhrase with an asterisk (*). The result should be stored back in switchedPhrase (so switchedPhrase is actually changed). (Do not add another print—place your statement in the program so that this new value of switchedPhrase will be the one printed in the current println statement.) Save, compile, and run your program.

3.

Declare two new variables city and state of type String. Add statements to the program to prompt the user to enter their hometown—the city and the state. Read in the results using the appropriate Scanner class method - you will need to have the user enter city and state on separate lines. Then using String class methods create and print a new string that consists of the state name (all in uppercase letters) followed by the city name (all in lowercase letters) followed again by the state name (uppercase). So, if the user enters Lilesville for the city and North Carolina for the state, the program should create and print the string NORTH CAROLINAlilesvilleNORTH CAROLINA

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Rolling Dice Write a complete Java program that simulates the rolling of a pair of dice. For each die in the pair, the program should generate a random number between 1 and 6 (inclusive). It should print out the result of the roll for each die and the total roll (the sum of the two dice), all appropriately labeled. You must use the Random class. The RandomNumbers program in listing 3.2 of the text may be helpful.

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Computing Distance The file Distance.java contains an incomplete program to compute the distance between two points. Recall that the distance between the two points (x1, y1) and (x2, y2) is computed by taking the square root of the quantity (x1 - x2)2 + (y1 - y2)2. The program already has code to get the two points as input. You need to add an assignment statement to compute the distance and then a print statement to print it out (appropriately labeled). Test your program using the following data: The distance between the points (3, 17) and (8, 10) is 8.6023... (lots more digits printed); the distance between (-33,49) and (-9, -15) is 68.352.… // ************************************************************ // Distance.java // // Computes the distance between two points // ************************************************************ import java.util.Scanner; public class Distance { public static void main (String[] args) { double x1, y1, x2, y2; // coordinates of two points double distance; // distance between the points Scanner scan = new Scanner(System.in); // Read in the two points System.out.print ("Enter the coordinates of the first point " + "(put a space between them): "); x1 = scan.nextDouble(); y1 = scan.nextDouble(); System.out.print ("Enter the coordinates of the second point: "); x2 = scan.nextDouble(); y2 = scan.nextDouble(); // Compute the distance // Print out the answer } }

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Formatting Output File Deli.java contains a partial program that computes the cost of buying an item at the deli. Save the program to your directory and do the following: 1.

Study the program to understand what it does.

2.

Add the import statements to import the DecimalFormat and NumberFormat classes.

3.

Add the statement to declare money to be a NumberFormat object as specified in the comment.

4.

Add the statement to declare fmt to be a DecimalFormat object as specified in the comment.

5.

Add the statements to print a label in the following format (the numbers in the example output are correct for input of $4.25 per pound and 41 ounces). Use the formatting object money to print the unit price and total price and the formatting object fmt to print the weight to 2 decimal places. ***** CSDeli ***** Unit Price: $4.25 per pound Weight: 2.56 pounds TOTAL: $10.89

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// ************************************************************ // DeliFormat.java // // Computes the price of a deli item given the weight // (in ounces) and price per pound -- prints a label, // nicely formatted, for the item. // // ************************************************************ import java.util.Scanner;

public class Deli { // // main reads in the price per pound of a deli item // and number of ounces of a deli item then computes // the total price and prints a "label" for the item // public static void main (String[] args) { final double OUNCES_PER_POUND = 16.0; double pricePerPound; double weightOunces; double weight; double totalPrice;

// price per pound // weight in ounces // weight in pounds // total price for the item

Scanner scan = new Scanner(System.in); // Declare money as a NumberFormat object and use the // getCurrencyInstance method to assign it a value // Declare fmt as a DecimalFormat object and instantiate // it to format numbers with at least one digit to the left of the // decimal and the fractional part rounded to two digits. // prompt the user and read in each input System. out. println ("Welcome to the CS Deli! ! \n "); System.out.print ("Enter the price per pound of your item: "); pricePerPound = scan.nextDouble(); System.out.print ("Enter the weight (ounces): "); weightOunces = scan.nextDouble(); // Convert ounces to pounds and compute the total price weight = weightOunces / OUNCES_PER_POUND; totalPrice = pricePerPound * weight; // Print the label using the formatting objects // fmt for the weight in pounds and money for the prices

} }

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Chapter 3: Using Classes and Objects

Playing With Cards Write a class that defines an enumerated type named Rank with values ace, two, three, four, five, six, seven, eight, nine, ten, jack, queen, king. The main method should do the following: 1.

Declare variables highCard, faceCard, card1, and card2 of type Rank.

2.

Assign highCard to be an ace, faceCard to be a jack, queen or king (your choice), and card1 and card2 to be two different numbered cards (two through ten - your choice).

3.

Print a line, using the highCard and faceCard objects, in the following format: A blackjack hand: ace and ....

The faceCard variable should be printed instead of the dots.

4.

Declare two variables card1 Val and card2Val of type int and assign them the face value of your card1 and card2 objects. Use your card1 and card2 variables and the ordinal method associated with enumerated types. Remember that the face value of two is 2, three is 3, and so on so you need to make a slight adjustment to the ordinal value of the enumerated type.

5.

Print two lines, using the card1 and card2 objects and the name method, as follows: A two card hand: (print card1 and card2) Hand value: (print the sum of the face values of the two cards)

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Experimenting with the Integer Class Wrapper classes are described on pages 138-140 of the text. They are Java classes that allow a value of a primitive type to be "wrapped up" into an object, which is sometimes a useful thing to do. They also often provide useful methods for manipulating the associated type. Wrapper classes exist for each of the primitive types: boolean, char, float, double, int, long, short, and byte.

Write a program IntWrapper that uses the constants and methods of the Integer class (page 140 for a short list, pages 819-820 for a complete list) to perform the following tasks. Be sure to clearly label your output and test your code for each task before proceding.

48

1.

Prompt for and read in an integer, then print the binary, octal and hexadecimal representations of that integer.

2.

Print the maximum and minimum possible Java integer values. Use the constants in the Integer class that hold these values — don't type in the numbers themselves. Note that these constants are static (see the description on page 140 and the signature on page 819).

3.

Prompt the user to enter two decimal integers, one per line. Use the next method of the Scanner class to read each of them in. (The next method returns a String so you need to store the values read in String variables, which may seem strange.) Now convert the strings to ints (use the appropriate method of the Integer class to do this), add them together, and print the sum.

Chapter 3: Using Classes and Objects

Nested Panels The program NestedPanels.java is from Listing 3.8 of the text. Save the program to your directory and do the following: 1. Compile and run the program. Experiment with resizing the frame and observe the effect on the components.

2. Modify the program by adding a third subpanel that is twice as wide, but the same height, as the other two subpanels. Choose your own label and color for the subpanel (the color should not be red, green, or blue). Add the panel to the primary panel after the other two panels.

3. Compile and run the modified program. Again, experiment with resizing the frame and observe the effect on the components.

4. Now add a statement to the program to set the preferred size of the primary panel to 320 by 260. (What would be the purpose of this?). Compile and run the program to see if anything changed.

5. Now add another panel with background color blue and size 320 by 20. Add a "My Panels" label to this panel and then add this panel to the primary panel before adding the other panels. Compile and run the program. What was the effect of this panel? // ************************************************************ // NestedPanels.java Author: Lewis/Loftus // // Demonstrates a basic component hierarchy. // ************************************************************ import j ava.awt.*; import javax.swing.*; public class NestedPanels { // // Presents two colored panels nested within a third. // public static void main (String[] args) { JFrame frame = new JFrame ("Nested Panels"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); // Set up first subpanel JPanel subPanel1 = new JPanel();• subPanel1.setPreferredSize (new Dimension(150, 100)); subPanel1.setBackground (Color.green); JLabel label1 = new JLabel ("One"); subPanel1.add (label1)003B // Set up second subpanel JPanel subPanel2 = new JPanel(); subPanel2.setPreferredSize (new Dimension(150, 100)); subPanel2.setBackground (Color.red); JLabel label2 = new JLabel ("Two"); subPanel2.add (label2); // Set up primary panel JPanel primary = new JPanel(); primary.setBackground (Color.blue); primary.add (subPanel1); primary.add (subPanel2); frame.getContentPane().add(primary); frame. pack () ; frame.setVisible(true); } }

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LAB MANUAL for

Adrienne Bloss Roanoke College

N. Jane Ingram Roanoke College

Boston San Francisco New York London Toronto Sydney Tokyo Singapore Madrid Mexico City Munich Paris Cape Town Hong Kong Montreal

Executive Editor Editorial Assistant Marketing Manager Production Project Manager

Michael Hirsch Emma Snider Yezan Alayan Kayla Smith-Tarbox

Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and Pearson was aware of a trademark claim, the designations have been printed in initial caps or all caps.

Copyright © 2017 Pearson Education, Inc. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of the publisher. Printed in the United States of America.

ISBN-13: 978-0-13-454333-8 ISBN-10: 0-13-454333-5 1 2 3 4 5 6 BB 10 09 08 07

About this Lab Manual: These labs grew out of materials used in the first two courses in the computer science major at Roanoke College. We have held weekly three-hour closed labs in those courses since 1991 and have found them to be invaluable in encouraging students to engage the material. Some of the lab exercises are straightforward, requiring only that students make minor modifications to existing code, or give explicit instructions for code to be written. Others are more challenging, requiring that students write complete programs from high-level specifications. Many labs ask students to proceed in steps, writing and testing pieces as they go, to help them learn to develop programs incrementally.

Some of the exercises build on program examples from Java Software Solutions, while others introduce new examples. We have tried to use coding and commenting conventions from the text when writing new code.

We hope that you will find flexible ways to use the materials in this manual. For example, we often give pre-lab assignments, usually pencil-and-paper exercises that are due before the students come to lab, and post-lab assignments that are due the following class. The lab itself is usually a collection of several exercises of varying degrees of difficulty. Some pre-lab exercises are included in this manual, and many of the regular exercises have served as post-labs. These exercises may also be useful to illustrate new concepts during class, as a basis for small group discussions, or as short homework assignments.

We continue to develop new exercises and modify existing ones for our CPSC 120 and 170 courses. You are welcome to use these materials, which can be found at http://cs.roanoke.edu (choose the Past Courses link or the link for the current semester).

What you’ll find in this Lab Manual The lab manual contains these labs that help engage students who are learning introductory programming.

Chapter 1: Introduction Chapter 2: Data and Expressions Chapter 3: Using Classes and Objects Chapter 4: Writing Classes Chapter 5: Conditionals and Loops Chapter 6: More Conditionals and Loops Chapter 7: Object-Oriented Design Chapter 8: Arrays Chapter 9: Inheritance Chapter 10: Polymorphism Chapter 11: Exceptions Chapter 12: Recursion Chapter 13: Collections

Supplementary Materials: Solution files and source code for all exercises can be found at www.pearsonhighered.com under author “Lewis/Loftus” and “Java Software Solutions: Foundations of Program Design, 8/e.”

Java Software Solutions Lab Exercises Chapter 1. ......................................................................................................................... 1 Chapter 2. ......................................................................................................................... 8 Chapter 3. ....................................................................................................................... 35 Chapter 4. ....................................................................................................................... 50 Chapter 5. ....................................................................................................................... 66 Chapter 6. ....................................................................................................................... 84 Chapter 7. ..................................................................................................................... 102 Chapter 8. ..................................................................................................................... 123 Chapter 9. ..................................................................................................................... 153 Chapter 10. ................................................................................................................... 173 Chapter 11. ................................................................................................................... 206 Chapter 12. ................................................................................................................... 223 Chapter 13. ..................................................................................................................... 252

stumerit@gmail.com

Chapter 5: Conditionals and Loops Lab Exercises Topics

Lab Exercises

Boolean expressions The if statement

PreLab Exercises Computing a Raise

The while statement

PreLab Exercises Counting and Looping Powers of 2 Factorials A Guessing Game

Iterators & Reading Text Files

Baseball Statistics

ArrayList Class

A Shopping Cart Using the ArrayList Class

Determining Event Sources

Vote Counter, Revisited

Checkboxes & Radio Buttons

Adding Buttons to StyleOptions.java

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Prelab Exercises Sections 5.1-5.3 1.

Rewrite each condition below in valid Java syntax (give a boolean expression): a. x > y > z b. x and y are both less than 0 c. neither x nor y is less than 0 d. x is equal to y but not equal to z

2.

Suppose gpa is a variable containing the grade point average of a student. Suppose the goal of a program is to let a student know if he/she made the Dean’s list (the gpa must be 3.5 or above). Write an if... else... statement that prints out the appropriate message (either “Congratulations—you made the Dean’s List” or “Sorry you didn’t make the Dean’s List”).

3.

Complete the following program to determine the raise and new salary for an employee by adding if ... else statements to compute the raise. The input to the program includes the current annual salary for the employee and a number indicating the performance rating (1=excellent, 2=good, and 3=poor). An employee with a rating of 1 will receive a 6% raise, an employee with a rating of 2 will receive a 4% raise, and one with a rating of 3 will receive a 1.5% raise. // ************************************************************ // Salary.java // Computes the raise and new salary for an employee // ************************************************************ import java.util.Scanner; public class Salary { public static void main (String[] args) { double currentSalary; // current annual salary double rating; // performance rating double raise; // dollar amount of the raise Scanner scan = new Scanner(System.in); // Get the current salary and performance rating System.out.print ("Enter the current salary: "); currentSalary = scan.nextDouble(); System.out.print ("Enter the performance rating: "); rating = scan.nextDouble(); // Compute the raise -- Use if ... else ... // Print the results System.out.println ("Amount of your raise: $" + raise); System.out.println ("Your new salary: $" + currentSalary + raise); } }

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Computing A Raise File Salary.java contains most of a program that takes as input an employee’s salary and a rating of the employee’s performance and computes the raise for the employee. This is similar to question #3 in the pre-lab, except that the performance rating here is being entered as a String—the three possible ratings are “Excellent”, “Good”, and “Poor”. As in the pre-lab, an employee who is rated excellent will receive a 6% raise, one rated good will receive a 4% raise, and one rated poor will receive a 1.5% raise.

Add the if... else... statements to program Salary to make it run as described above. Note that you will have to use the equals method of the String class (not the relational operator ==) to compare two strings (see Section 5.3, Comparing Data).

// ************************************************************ // Salary.java // // Computes the amount of a raise and the new // salary for an employee. The current salary // and a performance rating (a String: "Excellent", // "Good" or "Poor") are input. // ************************************************************ import java.util.Scanner; import java.text.NumberFormat; public class Salary { public static void main (String[] args) { double currentSalary; // employee's current salary double raise; // amount of the raise double newSalary; // new salary for the employee String rating; // performance rating Scanner scan = new Scanner(System.in); System.out.print ("Enter the current salary: "); currentSalary = scan.nextDouble(); System.out.print ("Enter the performance rating (Excellent, Good, or Poor): "); rating = scan.next(); // Compute the raise using if ... newSalary = currentSalary + raise; // Print the results NumberFormat money = NumberFormat.getCurrencyInstance(); System.out.println(); System.out.println("Current Salary: " + money.format(currentSalary)); System.out.println("Amount of your raise: " + money.format(raise)); System.out.println( "Your new salary: " + money. format (newSalary) ); System.out.println(); } }

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Prelab Exercises Section 5.4 In a while loop, execution of a set of statements (the body of the loop) continues until the boolean expression controlling the loop (the condition) becomes false. As for an if statement, the condition must be enclosed in parentheses. For example, the loop below prints the numbers from 1 to to LIMIT: final int LIMIT = 100; int count = 1;

// setup

while (count <= LIMIT) // condition { // body System.out.println(count); // -- perform task count = count + 1; // -- update condition } There are three parts to a loop: □

The setup, or initialization. This comes before the actual loop, and is where variables are initialized in preparation for the first time through the loop. □ The condition, which is the boolean expression that controls the loop. This expression is evaluated each time through the loop. If it evaluates to true, the body of the loop is executed, and then the condition is evaluated again; if it evaluates to false, the loop terminates. □ The body of the loop. The body typically needs to do two things: □ Do some work toward the task that the loop is trying to accomplish. This might involve printing, calculation, input and output, method calls—this code can be arbitrarily complex. □ Update the condition. Something has to happen inside the loop so that the condition will eventually be false— otherwise the loop will go on forever (an infinite loop). This code can also be complex, but often it simply involves incrementing a counter or reading in a new value.

Sometimes doing the work and updating the condition are related. For example, in the loop above, the print statement is doing work, while the statement that increments count is both doing work (since the loop’s task is to print the values of count) and updating the condition (since the loop stops when count hits a certain value).

The loop above is an example of a count-controlled loop, that is, a loop that contains a counter (a variable that increases or decreases by a fixed value—usually 1—each time through the loop) and that stops when the counter reaches a certain value.

Not all loops with counters are count-controlled; consider the example below, which determines how many even numbers must be added together, starting at 2, to reach or exceed a given limit. final int LIMIT = 16; TRACE int count = 1; int sum = 0; int nextVal = 2;

sum ---

nextVal -------

count -----

while (sum < LIMIT) { sum = sum + nextVal; nextVal = nextVal + 2; count = count + 1; } System.out.println("Had to add together " + (count-1) + " even numbers " + "to reach value " + LIMIT + ". Sum is " + sum); Note that although this loop counts how many times the body is executed, the condition does not depend on the value of count.

Not all loops have counters. For example, if the task in the loop above were simply to add together even numbers until the Chapter 5: Conditionals and Loops

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sum reached a certain limit and then print the sum (as opposed to printing the number of things added together), there would be no need for the counter. Similarly, the loop below sums integers input by the user and prints the sum; it contains no counter. int sum = 0; String keepGoing = "y"; int nextVal;

//setup

while (keepGoing.equals("y") || keepGoing.equals("Y")) { System.out.print("Enter the next integer: "); //do work nextVal = scan.nextInt(); sum = sum + nextVal; System.out.println("Type y or Y to keep going"); keepGoing = scan.next();

//update condition

} System.out.println("The sum of your integers is " + sum); Exercises 1.

In the first loop above, the println statement comes before the value of count is incremented. What would happen if you reversed the order of these statements so that count was incremented before its value was printed? Would the loop still print the same values? Explain.

2.

Consider the second loop above. a. Trace this loop, that is, in the table next to the code show values for variables nextVal, sum and count at each iteration. Then show what the code prints. b. Note that when the loop terminates, the number of even numbers added together before reaching the limit is count-1, not count. How could you modify the code so that when the loop terminates, the number of things added together is simply count?

3.

Write a while loop that will print “I love computer science!!” 100 times. Is this loop count-controlled?

4.

Add a counter to the third example loop above (the one that reads and sums integers input by the user). After the loop, print the number of integers read as well as the sum. Just note your changes on the example code. Is your loop now count-controlled?

5.

The code below is supposed to print the integers from 10 to 1 backwards. What is wrong with it? (Hint: there are two problems!) Correct the code so it does the right thing. count = 10; while (count >= 0) { System.out.println(count); count = count + 1; }

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Counting and Looping The program in LoveCS.java prints “I love Computer Science!!” 10 times. Copy it to your directory and compile and run it to see how it works. Then modify it as follows: // **************************************************************** // LoveCS.java // // Use a while loop to print many messages declaring your // passion for computer science // **************************************************************** public class LoveCS { public static void main(String[] args) { final int LIMIT = 10; int count = 1; while (count <= LIMIT){ System.out.println("I love Computer Science!!"); count++; } } } 1.

2.

Instead of using constant LIMIT, ask the user how many times the message should be printed. You will need to declare a variable to store the user’s response and use that variable to control the loop. (Remember that all caps is used only for constants!)

Number each line in the output, and add a message at the end of the loop that says how many times the message was printed. So if the user enters 3, your program should print this: 1 I love Computer Science!!

2 I love Computer Science!!

3 I love Computer Science!!

Printed this message 3 times.

3.

If the message is printed N times, compute and print the sum of the numbers from 1 to N. So for the example above, the last line would now read: Printed this message 3 times. The sum of the numbers from

1 to 3 is 6.

Note that you will need to add a variable to hold the sum.

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Powers of 2 File PowersOf2.java contains a skeleton of a program to read in an integer from the user and print out that many powers of 2, starting with 20.

1.

Using the comments as a guide, complete the program so that it prints out the number of powers of 2 that the user requests. Do not use Math.pow to compute the powers of 2! Instead, compute each power from the previous one (how do you get 2n from 2n–1?). For example, if the user enters 4, your program should print this: Here are the first 4 powers of 2: 1 2 4 8

2.

Modify the program so that instead of just printing the powers, you print which power each is, e.g.: Here are the first 4 powers of 2: 2^0 = 1 2^1 = 2 2^2 = 4 2^3 = 8

// ************************************************************ // PowersOf2.java // // Print out as many powers of 2 as the user requests // // ************************************************************ import java.util.Scanner; public class PowersOf2 { public static void main(String[] args) { int numPowersOf2; //How many powers of 2 to compute int nextPowerOf2 = 1; //Current power of 2 int exponent; //Exponent for current power of 2 -- this //also serves as a counter for the loop Scanner scan = new Scanner(System.in); System.out.println("How many powers of 2 would you like printed?"); numPowersOf2 = scan.nextInt(); //print a message saying how many powers of 2 will be printed //initialize exponent -- the first thing printed is 2 to the what? while ( ) { //print out current power of 2 //find next power of 2 -- how do you get this from the last one? //increment exponent } } }

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Factorials The factorial of n (written n!) is the product of the integers between 1 and n. Thus 4! = 1*2*3*4 = 24. By definition, 0! = 1.

Factorial is not defined for negative numbers.

1.

Write a program that asks the user for a non-negative integer and computes and prints the factorial of that integer. You’ll need a while loop to do most of the work—this is a lot like computing a sum, but it’s a product instead. And you’ll need to think about what should happen if the user enters 0.

2.

Now modify your program so that it checks to see if the user entered a negative number. If so, the program should print a message saying that a nonnegative number is required and ask the user the enter another number. The program should keep doing this until the user enters a nonnegative number, after which it should compute the factorial of that number.

Hint: you will need another while loop before the loop that computes the factorial. You should not need to change any of the code that computes the factorial!

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A Guessing Game File Guess.java contains a skeleton for a program to play a guessing game with the user. The program should randomly generate an integer between 1 and 10, then ask the user to try to guess the number. If the user guesses incorrectly, the program should ask them to try again until the guess is correct; when the guess is correct, the program should print a congratulatory message.

1.

2.

3.

4.

Using the comments as a guide, complete the program so that it plays the game as described above.

Modify the program so that if the guess is wrong, the program says whether it is too high or too low. You will need an if statement (inside your loop) to do this.

Now add code to count how many guesses it takes the user to get the number, and print this number at the end with the congratulatory message.

Finally, count how many of the guesses are too high and how many are too low. Print these values, along with the total number of guesses, when the user finally guesses correctly.

// ************************************************************ // Guess.java // // Play a game where the user guesses a number from 1 to 10 // // ************************************************************ import java.util.Scanner; import java.util.Random; public class Guess { public static void main(String[] args) { int numToGuess; //Number the user tries to guess int guess; //The user's guess Scanner scan = new Scanner(System.in); Random generator = new Random(); //randomly generate the

number to guess

//print message asking user to enter a guess //read in guess while ( ) //keep going as long as the guess is wrong { //print message saying guess is wrong //get another guess from the user } //print message saying guess is right } }

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Baseball Statistics The local Kids’ League coach keeps some of the baseball team statistics in a text file organized as follows: each line of the file contains the name of the player followed by a list of symbols indicating what happened on each at bat for the player. The letter h indicates a hit, o an out, w a walk, and s a sacrifice fly. Each item on the line is separated by a comma. There are no blank spaces except in the player name. So, for example the file could look as follows: Sam Slugger,h,h,o,s,w,w,h,w,o,o,o,h,s Jill Jenks,o,o,s,h,h,o,o Will Jones,o,o,w,h,o,o,o,o,w,o,o The file BaseballStats.java contains the skeleton of a program thats reads and processes a file in this format. Study the program and note that three Scanner objects are declared.

• One scanner (scan) is used to read in a file name from standard input.

• The file name is then used to create a scanner (fileScan) to operate on that file.

• A third scanner (lineScan) will be used to parse each line in the file.

Also note that the main method throws an IOException. This is needed in case there is a problem opening the file.

Complete the program as follows: 1.

First add a while loop that reads each line in the file and prints out each part (name, then each at bat, without the commas) in a way similar to the URLDissector program in Listing 5.10 of the text. In particular inside the loop you need to a. read the next line from the file b. create a comma delimited scanner (lineScan) to parse the line c. read and print the name of the player, and finally, d. have a loop that prints each at bat code.

2.

Compile and run the program to be sure it works.

3.

Now modify the inner loop that parses a line in the file so that instead of printing each part it counts (separately) the number of hits, outs, walks, and sacrifices. Each of these summary statistics, as well as the batting average, should be printed for each player. Recall that the batting average is the number of hits divided by the total number of hits and outs.

4.

Test the program on the file stats.dat and stats2.dat .

// **************************************************************** // BaseballStats.java // // Reads baseball data in from a comma delimited file. Each line // of the file contains a name followed by a list of symbols // indicating the result of each at bat: h for hit, o for out, // w for walk, s for sacrifice. Statistics are computed and // printed for each player. // **************************************************************** import java.util.Scanner; import java.io.*; public class BaseballStats { //------------------------------------------------// Reads baseball stats from a file and counts // total hits, outs, walks, and sacrifice flies // for each player. //------------------------------------------------public static void main (String[] args) throws IOException Chapter 5: Conditionals and Loops

75

{ Scanner fileScan, lineScan; String fileName; Scanner scan = new Scanner(System.in); System.out.print ("Enter the name of the input file: "); fileName = scan.nextLine(); fileScan = new Scanner(new File(fileName)); // Read and process each line of the file

} }

stats.dat Willy Wonk,o,o,h,o,o,o,o,h,w,o,o,o,o,s,h,o,h Shari Jones,h,o,o,s,s,h,o,o,o,h,o,o,o,o Barry Bands,h,h,w,o,o,o,w,h,o,o,h,h,o,o,w,w,w,h,o,o Sally Slugger,o,h,h,o,o,h,h,w Missy Lots,o,o,s,o,o,w,o,o,o Joe Jones,o,h,o,o,o,o,h,h,o,o,o,o,w,o,o,o,h,o,h,h Larry Loop,w,s,o,o,o,h,o,o,h,s,o,o,o,h,h Sarah Swift,o,o,o,o,h,h,w,o,o,o Bill Bird,h,o,h,o,h,w,o,o,o,h,s,s,h,o,o,o,o,o,o Don Daring,o,o,h,h,o,o,h,o,h,o,o,o,o,o,o,h Jill Jet,o,s,s,h,o,o,h,h,o,o,o,h,o,h,w,o,o,h,h,o

stats2.dat Barry Bands,h,h,w,o,o,o,w,h,o,o,h,h,o,o,w,w,w,h,o,o

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A Shopping Cart Using the ArrayList Class In this exercise you will implement a shopping cart using the ArrayList class. The file Item.java contains the definition of a class named Item that models an item one would purchase (this class was used in an earlier lab). An item has a name, price, and quantity (the quantity purchased). The file Shop.java is an incomplete program that models shopping.

1.

Complete Shop.java as follows: a. Declare and instantiate a variable cart to be an empty ArrayList. b. Fill in the statements in the loop to add an item to the cart and to print the cart contents (using the default toString in the ArrayList class). Comments in the code indicate where these statements go. c. Compile your program and run it.

2.

You should have observed two problems with using the default printing for the cart object: the output doesn’t look very good and the total price of the goods in the cart is not computed or printed. Modify the program to correct these problems by replacing the print statement with a loop that does the following: a. gets each item from the cart and prints the item b. computes the total price of the items in the cart (you need to use the getPrice and getQuantity methods of the Item class). The total price should be printed after the loop.

3.

Compile and run your program.

// *************************************************************** // Shop.java // // Uses the Item class to create items and add them to a shopping // cart stored in an ArrayList. // *************************************************************** import java.util.ArrayList; import java.util.Scanner; public class Shop { public static void main (String[] args) { Item item; String itemName; double itemPrice; int quantity; Scanner scan = new Scanner(System.in); String keepShopping = "y"; do { System.out.print ("Enter the name of the item: "); itemName = scan.nextLine(); System.out.print ("Enter the unit price: "); itemPrice = scan.nextDouble(); System.out.print ("Enter the quantity: "); quantity = scan.nextInt(); // *** create a new item and add it to the cart Chapter 5: Conditionals and Loops

77

// *** print the contents of the cart object using println System.out.print ("Continue shopping (y/n)? "); keepShopping = scan.nextLine(); } while (keepShopping.equals("y")); } }

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Vote Counter, Revisited Chapter 4 had a lab exercise that created a GUI with two buttons representing two candidates (Joe and Sam) in an election or popularity contest. The program computed the number of times each button was pressed. In that exercise two different listeners were used, one for each button. This exercise is a slight modification. Only one listener will be used and its ActionPerformed method will determine which button was pressed.

The files VoteCounter.java and VoteCounterPanel.java contain slight revisions to the skeleton programs used in the Chapter 4 exercise. Save them to your directory and do the following: 1.

Add variables for Sam - a vote counter, a button, and a label.

2.

Add the button and label for Sam to the panel; add the listener to the button.

3.

Modify the ActionPerformed method of the VoteButtonListener class to determine which button was pressed and update the correct counter. (See the LeftRight example or the Quote example for how to determine the source of an event.)

4.

Test your program.

5.

Now modify the program to add a message indicating who is winning. To do this you need to instantiate a new label, add it to the panel, and add an if statement in actionPerformed that determines who is winning (also test for ties) and sets the text of the label with the appropriate message.

//************************************************************ // VoteCounter.java // // Demonstrates a graphical user interface and event // listeners to tally votes for two candidates, Joe and Sam. //************************************************************ import javax.swing.JFrame; public class VoteCounter { //----------------------------------------// Creates the main program frame. //----------------------------------------public static void main(String[] args) { JFrame frame = new JFrame("Vote Counter"); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.getContentPane().add(new VoteCounterPanel()); frame.pack(); frame.setVisible(true); } }

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//*********************************************************** // VoteCounterPanel.java // // Panel for the GUI that tallies votes for two candidates, // Joe and Sam. //*********************************************************** import java.awt.*; import java.awt.event.*; import javax.swing. *; public class VoteCounterPanel extends JPanel { private int votesForJoe; private JButton joe; private JLabel labelJoe; //------------------------------------------------// Constructor: Sets up the GUI. //------------------------------------------------public VoteCounterPanel() { votesForJoe = 0; joe = new JButton("Vote for Joe"); joe.addActionListener(new VoteButtonListener()); labelJoe = new JLabel("Votes for Joe: " + votesForJoe); add(joe); add(labelJoe); setPreferredSize(new Dimension(300, 40)); setBackground(Color.cyan); } //************************************************** // Represents a listener for button push (action) events //************************************************** private class VoteButtonListener implements ActionListener { //---------------------------------------------// Updates the appropriate vote counter when a // button is pushed for one of the candidates. //---------------------------------------------public void actionPerformed(ActionEvent event) { votesForJoe++; labelJoe.setText("Votes for Joe: " + votesForJoe); } } }

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Adding Buttons to StyleOptions.java The files StyleOptions.java and StyleOptionsPanel.java are from Listings “5.14 and 5.15” of the text (with a couple of slight changes—an instance variable fontSize is used rather than the literal 36 for font size and the variable style is an instance variable rather than local to the itemStateChanged method). The program demonstrates checkboxes and ItemListeners. In this exercise you will add a set of three radio buttons to let the user choose among three font sizes. The method of adding the radio buttons will be very similar to that in the QuoteOptionsPanel class (Listing 5.17 of the text). Before modifying the program compile and run the current version to see how it works and study the QuoteOptionsPanel example.

Do the following to add the radio buttons to the panel: 1.

Declare three objects small, medium, and large of type JRadioButton.

2.

Instantiate the button objects labeling them “Small Font,” “Medium Font,” “Large Font.” Initialize the large font button to true. Set the background color of the buttons to cyan.

3.

Instantiate a button group object and add the buttons to it.

4.

Radio buttons produce action events so you need an ActionListener to listen for radio button clicks. The code you need to add to actionPerformed will be similar to that in the QuoteListener in Listing 5.17. In this case you need to set the fontSize variable (use 12 for small, 24 for medium, and 36 for large) in the if statement, then call the setFont method to set the font for the saying object. (Note: Instead of adding an ActionListener you could use the current ItemListener and add code to check to see if the source of the event was a radio button.)

5.

In StyleOptionsPanel() add the ItemListener object to each button and add each button to the panel.

6.

Compile and run the program. Note that as the font size changes the checkboxes and buttons re-arrange themselves in the panel. You will learn how to control layout later in the course.

//******************************************************************** // StyleOptions.java Author: Lewis/Loftus // // Demonstrates the use of check boxes. //******************************************************************** import javax.swing.JFrame; public class StyleOptions { //----------------------------------------------------------------// Creates and presents the program frame. //----------------------------------------------------------------public static void main (String[] args) { JFrame frame = new JFrame ("Style Options"); frame.setDefaultCloseOperation (JFrame.EXIT_ON_CLOSE); StyleOptionsPanel panel = new StyleOptionsPanel(); frame.getContentPane().add (panel); frame.pack(); frame.setVisible(true); } }

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//************************************************************ // StyleOptionsPanel.java Author: Lewis/Loftus // // Demonstrates the use of check boxes. //************************************************************ import javax. swing. *; import java.awt.*; import java.awt.event.*; public class StyleOptionsPanel extends JPanel { private int fontSize = 36; private int style = Font.PLAIN; private JLabel saying; private JCheckBox bold, italic; //-------------------------------------------------------------// Sets up a panel with a label and some check boxes that // control the style of the label's font. //-------------------------------------------------------------public StyleOptionsPanel() { saying = new JLabel ("Say it with style!"); saying.setFont (new Font ("Helvetica", style, fontSize)); bold = new JCheckBox ("Bold"); bold.setBackground (Color.cyan); italic = new JCheckBox ("Italic"); italic.setBackground (Color.cyan); StyleListener listener = new StyleListener (); bold.addItemListener (listener); italic.addItemListener (listener) ; add (saying); add (bold); add (italic); setBackground (Color.cyan); setPreferredSize (new Dimension(300, 100)); } //************************************************************ // Represents the listener for both check boxes. //************************************************************ private class StyleListener implements ItemListener { //----------------------------------------------------// Updates the style of the label font style. //----------------------------------------------------public void itemStateChanged (ItemEvent event) { style = Font.PLAIN; if (bold.isSelected()) style = Font.BOLD; if (italic.isSelected()) style += Font.ITALIC; 82

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saying.setFont (new Font ("Helvetica", style, fontSize)); } } }

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Chapter 6: More Conditionals and Loops Lab Exercises Topics

Lab Exercises

The switch statement

A Charge Account Statement Activities at Lake LazyDays Rock, Paper, Scissors Date Validation

Conditional Operator

Processing Grades

The do statement

More Guessing Election Day

The for statement

Finding Maximum and Minimum Values Counting Characters Using the Coin Class

Drawing with loops and conditionals

A Rainbow Program

Dialog Boxes

Modifying EvenOdd.java A Pay Check Program

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A Charge Account Statement Write a program to prepare the monthly charge account statement for a customer of CS CARD International, a credit card company. The program should take as input the previous balance on the account and the total amount of additional charges during the month. The program should then compute the interest for the month, the total new balance (the previous balance plus additional charges plus interest), and the minimum payment due. Assume the interest is 0 if the previous balance was 0 but if the previous balance was greater than 0 the interest is 2% of the total owed (previous balance plus additional charges).

Assume the minimum payment is as follows: new balance $50.00 20% of the new balance

for a new balance less than $50 for a new balance between $50 and $300 (inclusive) for a new balance over $300

So if the new balance is $38.00 then the person must pay the whole $38.00; if the balance is $128 then the person must pay $50; if the balance is $350 the minimum payment is $70 (20% of 350). The program should print the charge account statement in the format below. Print the actual dollar amounts in each place using currency format from the NumberFormat class—see Listing 3.4 of the text for an example that uses this class.

CS CARD International Statement ===============================

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Previous Balance: Additional Charges: Interest:

$ $ $

New Balance:

$

Minimum Payment:

$

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Activities at Lake LazyDays As activity directory at Lake LazyDays Resort, it is your job to suggest appropriate activities to guests based on the weather: temp >= 80: 60 <= temp < 80: 40 <= temp < 60: temp < 40:

swimming tennis golf skiing

1. Write a program that prompts the user for a temperature, then prints out the activity appropriate for that temperature. Use a cascading if, and be sure that your conditions are no more complex than necessary.

2. Modify your program so that if the temperature is greater than 95 or less than 20, it prints “Visit our shops!”. (Hint: Use a boolean operator in your condition.) For other temperatures print the activity as before.

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Rock, Paper, Scissors Program Rock.java contains a skeleton for the game Rock, Paper, Scissors. Open it and save it to your directory. Add statements to the program as indicated by the comments so that the program asks the user to enter a play, generates a random play for the computer, compares them and announces the winner (and why). For example, one run of your program might look like this: $ java Rock Enter your play: R, P, or S r Computer play is S Rock crushes scissors, you win!

Note that the user should be able to enter either upper or lower case r, p, and s. The user’s play is stored as a string to make it easy to convert whatever is entered to upper case. Use a switch statement to convert the randomly generated integer for the computer’s play to a string. // ************************************************************ // Rock.java // // Play Rock, Paper, Scissors with the user // // ************************************************************ import java.util.Scanner; import java.util.Random; public class Rock { public static void main(String[] args) { String personPlay; //User's play -- "R", "P", or "S" String computerPlay; //Computer's play -- "R", "P", or "S" int computerInt; //Randomly generated number used to determine //computer's play Scanner scan = new Scanner(System.in); Random generator = new Random(); //Get player's play -- note that this is stored as a string //Make player's play uppercase for ease of comparison //Generate computer's play (0,1,2) //Translate computer's randomly generated play to string switch (computerInt) { } //Print computer's play //See who won. Use nested ifs instead of &&. if (personPlay.equals(computerPlay)) System.out.println("It's a tie!"); else if (personPlay.equals("R")) if (computerPlay.equals("S")) System.out.println("Rock crushes scissors. You win!!"); else //...

Fill in rest of code

} }

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Date Validation In this exercise you will write a program that checks to see if a date entered by the user is a valid date in the second millenium. A skeleton of the program is in Dates.java. Open this program and save it to your directory. As indicated by the comments in the program, fill in the following: 1.

2.

3.

An assignment statement that sets monthValid to true if the month entered is between 1 and 12, inclusive.

An assignment statement that sets yearValid to true if the year is between 1000 and 1999, inclusive.

An assignment statement that sets leap Year to true if the year is a leap year. Here is the leap year rule (there’s more to it than you may have thought!): If the year is divisible by 4, it’s a leap year UNLESS it’s divisible by 100, in which case it’s not a leap year UNLESS it’s divisible by 400, in which case it is a leap year. If the year is not divisible by 4, it’s not a leap year.

Put another way, it’s a leap year if a) it’s divisible by 400, or b) it’s divisible by 4 and it’s not divisible by 100. So 1600 and 1512 are leap years, but 1700 and 1514 are not.

4.

5.

6.

An if statement that determines the number of days in the month entered and stores that value in variable daysInMonth.

If the month entered is not valid, daysInMonth should get 0. Note that to figure out the number of days in February you’ll need to check if it’s a leap year.

An assignment statement that sets dayValid to true if the day entered is legal for the given month and year.

If the month, day, and year entered are all valid, print “Date is valid” and indicate whether or not it is a leap year. If any of the items entered is not valid, just print “Date is not valid” without any comment on leap year.

// ************************************************************ // Dates.java // // Determine whether a 2nd-millenium date entered by the user // is valid // ************************************************************ import java.util.Scanner; public class Dates { public static void main(String[] args) { int month, day, year; //date read in from user int daysInMonth; //number of days in month read in boolean monthValid, yearValid, dayValid; //true if input from user is valid boolean leapYear; //true if user's year is a leap year Scanner scan = new Scanner(System.in); //Get integer month, day, and year from user //Check to see if month is valid //Check to see if year is valid //Determine whether it's a leap year //Determine number of days in month //User number of days in month to check to see if day is valid //Determine whether date is valid and print appropriate message } }

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Processing Grades The file Grades.java contains a program that reads in a sequence of student grades and computes the average grade, the number of students who pass (a grade of at least 60) and the number who fail. The program uses a loop (which you learn about in the next section).

1.

2.

Compile and run the program to see how it works.

Study the code and do the following. □ Replace the statement that finds the sum of the grades with one that uses the += operator. □ Replace each of three statements that increment a counting variable with statements using the increment operator.

3.

4.

Run your program to make sure it works.

Now replace the “if” statement that updates the pass and fail counters with the conditional operator.

// ************************************************************ // Grades.java // // Read in a sequence of grades and compute the average // grade, the number of passing grades (at least 60) // and the number of failing grades. // ************************************************************ import java.util.Scanner; public class Grades { // // Reads in and processes grades until a negative number is entered. // public static void main (String[] args) { double grade; //a student's grade double sumOfGrades; // a running total of the student grades int numStudents; //a count of the students int numPass; //a count of the number who pass int numFail; // a count of the number who fail Scanner scan = new Scanner(System.in); System.out.println ("\nGrade Processing Program\n"); // Initialize summing and counting variables sumOfGrades = 0; numStudents = 0; numPass = 0; numFail = 0; // Read in the first grade System.out.print ("Enter the first student's grade: "); grade = scan.nextDouble(); while (grade >= 0) { sumOfGrades = sumOfGrades + grade; numStudents = numStudents + 1; if (grade < 60) numFail = numFail + 1; else numPass = numPass + 1;

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// Read the next grade System.out.print ("Enter the next grade (a negative to quit): "); grade = scan.nextDouble(); } if (numStudents > 0) { System.out.println ("\nGrade Summary: "); System.out.println ("Class Average: " + sumOfGrades/numStudents); System.out.println ("Number of Passing Grades: " + numPass); System.out.println ("Number of Failing Grades: " + numFail); } else System.out.println ("No grades processed."); } }

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More Guessing File Guess.java contains the skeleton for a program that uses a while loop to play a guessing game. (This problem is described in the previous lab exercise.) Revise this program so that it uses a do ... while loop rather than a while loop. The general outline using a do... while loop is as follows: // set up (initializations of the counting variables) .... do { // read in a guess ... // check the guess and print appropriate messages ... } while ( condition ); A key difference between a while and a do... while loop to note when making your changes is that the body of the do ... while loop is executed before the condition is ever tested. In the while loop version of the program, it was necessary to read in the user’s first guess before the loop so there would be a value for comparison in the condition. In the do... while this “priming” read is no longer needed. The user’s guess can be read in at the beginning of the body of the loop.

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Election Day It’s almost election day and the election officials need a program to help tally election results. There are two candidates for office—Polly Tichen and Ernest Orator. The program’s job is to take as input the number of votes each candidate received in each voting precinct and find the total number of votes for each. The program should print out the final tally for each candidate—both the total number of votes each received and the percent of votes each received. Clearly a loop is needed.

Each iteration of the loop is responsible for reading in the votes from a single precinct and updating the tallies. A skeleton of the program is in the file Election.java. Open a copy of the program in your text editor and do the following.

1.

2.

3.

4.

Add the code to control the loop. You may use either a while loop or a do...while loop. The loop must be controlled by asking the user whether or not there are more precincts to report (that is, more precincts whose votes need to be added in). The user should answer with the character y or n though your program should also allow uppercase repsonses. The variable response (type String) has already been declared.

Add the code to read in the votes for each candidate and find the total votes. Note that variables have already been declared for you to use. Print out the totals and the percentages after the loop.

Test your program to make sure it is correctly tallying the votes and finding the percentages AND that the loop control is correct (it goes when it should and stops when it should).

The election officials want more information. They want to know how many precincts each candidate carried (won). Add code to compute and print this. You need three new variables: one to count the number of precincts won by Polly, one to count the number won by Ernest, and one to count the number of ties. Test your program after adding this code.

// ************************************************************ // Election.java // // This file contains a program that tallies the results of // an election. It reads in the number of votes for each of // two candidates in each of several precincts. It determines // the total number of votes received by each candidate, the // percent of votes received by each candidate, the number of // precincts each candidate carries, and the // maximum winning margin in a precinct. // ************************************************************ import java.util.Scanner; public class Election { public static void main (String[] args) { int votesForPolly; // number of votes for Polly in each precinct int votesForErnest; // number of votes for Ernest in each precinct int totalPolly; // running total of votes for Polly int totalErnest; // running total of votes for Ernest String response; // answer (y or n) to the "more precincts" question Scanner scan = new Scanner(System.in); System.out.println (); System.out.println ("Election Day Vote Counting Program"); System.out.println (); // Initializations // Loop to "process" the votes in each precinct // Print out the results } }

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Finding Maximum and Minimum Values A common task that must be done in a loop is to find the maximum and minimum of a sequence of values. The file Temps.java contains a program that reads in a sequence of hourly temperature readings over a 24-hour period. You will be adding code to this program to find the maximum and minimum temperatures. Do the following: 1.

Save the file to your directory, open it and see what’s there. Note that a for loop is used since we need a count-controlled loop. Your first task is to add code to find the maximum temperature read in. In general to find the maximum of a sequence of values processed in a loop you need to do two things: □

□

You need a variable that will keep track of the maximum of the values processed so far. This variable must be initialized before the loop. There are two standard techniques for initialization: one is to initialize the variable to some value smaller than any possible value being processed; another is to initialize the variable to the first value processed. In either case, after the first value is processed the maximum variable should contain the first value. For the temperature program declare a variable maxTemp to hold the maximum temperature. Initialize it to -1000 (a value less than any legitimate temperature).

The maximum variable must be updated each time through the loop. This is done by comparing the maximum to the current value being processed. If the current value is larger, then the current value is the new maximum. So, in the temperature program, add an if statement inside the loop to compare the current temperature read in to maxTemp. If the current temperature is larger set maxTemp to that temperature. NOTE: If the current temperature is NOT larger, DO NOTHING!

2.

Add code to print out the maximum after the loop. Test your program to make sure it is correct. Be sure to test it on at least three scenarios: the first number read in is the maximum, the last number read in is the maximum, and the maximum occurs somewhere in the middle of the list. For testing purposes you may want to change the HOURS_PER_DAY variable to something smaller than 24 so you don’t have to type in so many numbers!

3.

Often we want to keep track of more than just the maximum. For example, if we are finding the maximum of a sequence of test grades we might want to know the name of the student with the maximum grade. Suppose for the temperatures we want to keep track of the time (hour) the maximum temperature occurred. To do this we need to save the current value of the hour variable when we update the maxTemp variable. This of course requires a new variable to store the time (hour) that the maximum occurs. Declare timeOfMax (type int) to keep track of the time (hour) the maximum temperature occurred. Modify your if statment so that in addition to updating maxTemp you also save the value of hour in the timeOfMax variable. (WARNING: you are now doing TWO things when the if condition is TRUE.)

4.

Add code to print out the time the maximum temperature occurred along with the maximum.

5.

Finally, add code to find the minimum temperature and the time that temperature occurs. The idea is the same as for the maximum. NOTE: Use a separate if when updating the minimum temperature variable (that is, don’t add an else clause to the if that is already there).

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// ************************************************************ // Temps.java // // This program reads in a sequence of hourly temperature // readings (beginning with midnight) and prints the maximum // temperature (along with the hour, on a 24-hour clock, it // occurred) and the minimum temperature (along with the hour // it occurred). // ************************************************************ import java.util.Scanner; public class Temps { // // Reads in a sequence of temperatures and finds the // maximum and minimum read in. // public static void main (String[] args) { final int HOURS_PER_DAY = 24; int temp;

// a temperature reading

Scanner scan = new Scanner(System.in); // print program heading System.out.println (); System.out.println ("Temperature Readings for 24 Hour Period"); System.out.println (); for (int hour = 0; hour < HOURS_PER_DAY; hour++) { System.out.print ("Enter the temperature reading at " + hour + " hours: "); temp = scan.nextInt(); } // Print the results } }

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Counting Characters The file Count.java contains the skeleton of a program to read in a string (a sentence or phrase) and count the number of blank spaces in the string. The program currently has the declarations and initializations and prints the results. All it needs is a loop to go through the string character by character and count (update the countBlank variable) the characters that are the blank space. Since we know how many characters there are (the length of the string) we use a count controlled loop—for loops are especially well-suited for this.

1.

Add the for loop to the program. Inside the for loop you need to access each individual character—the charAt method of the String class lets you do that. The assignment statement ch = phrase.charAt(i); assigns the variable ch (type char) the character that is in index i of the String phrase. In your for loop you can use an assignment similar to this (replace i with your loop control variable if you use something other than i). NOTE: You could also directly use phrase.charAt(i) in your if (without assigning it to a variable).

2.

Test your program on several phrases to make sure it is correct.

3.

Now modify the program so that it will count several different characters, not just blank spaces. To keep things relatively simple we’ll count the a’s, e’s, s’s, and t’s (both upper and lower case) in the string. You need to declare and initialize four additional counting variables (e.g. countA and so on). Your current if could be modified to cascade but another solution is to use a switch statement. Replace the current if with a switch that accounts for the 9 cases we want to count (upper and lower case a, e, s, t, and blank spaces). The cases will be based on the value of the ch variable. The switch starts as follows—complete it. switch (ch) { case 'a': case 'A':

countA++; break;

case .... } Note that this switch uses the “fall through” feature of switch statements. If ch is an ‘a’ the first case matches and the switch continues execution until it encounters the break hence the countA variable would be incremented.

4.

Add statements to print out all of the counts.

5.

It would be nice to have the program let the user keep entering phrases rather than having to restart it every time. To do this we need another loop surrounding the current code. That is, the current loop will be nested inside the new loop. Add an outer while loop that will continue to execute as long as the user does NOT enter the phrase quit. Modify the prompt to tell the user to enter a phrase or quit to quit. Note that all of the initializations for the counts should be inside the while loop (that is we want the counts to start over for each new phrase entered by the user). All you need to do is add the while statement (and think about placement of your reads so the loop works correctly). Be sure to go through the program and properly indent after adding code—with nested loops the inner loop should be indented.

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// ************************************************************ // Count.java // // This program reads in strings (phrases) and counts the // number of blank characters and certain other letters // in the phrase. // ************************************************************ import java.util.Scanner; public class Count { public static void main (String[] args) { String phrase; // a string of characters int countBlank; // the number of blanks (spaces) in the phrase int length; // the length of the phrase char ch; // an individual character in the string Scanner scan = new Scanner(System.in); // Print a program header System.out.println (); System.out.println ("Character Counter"); System.out.println (); // Read in a string and find its length System.out.print ("Enter a sentence or phrase: "); phrase = scan.nextLine(); length = phrase.length(); // Initialize counts countBlank = 0; // a for loop to go through the string character by character // and count the blank spaces // Print the results System.out.println (); System.out.println ("Number of blank spaces: " + countBlank); System.out.println (); } }

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Using the Coin Class The Coin class from Listing 4.2 in the text is in the file Coin.java. Copy it to your directory, then write a program to find the length of the longest run of heads in 100 flips of the coin. A skeleton of the program is in the file Runs.java. To use the Coin class you need to do the following in the program: 1.

2.

3.

Create a coin object.

Inside the loop, you should use the flip method to flip the coin, the toString method (used implicitly) to print the results of the flip, and the getFace method to see if the result was HEADS. Keeping track of the current run length (the number of times in a row that the coin was HEADS) and the maximum run length is an exercise in loop techniques!

Print the result after the loop.

// ******************************************************************* // Coin.java Author: Lewis and Loftus // // Represents a coin with two sides that can be flipped. // ******************************************************************* public class Coin { public final int HEADS = 0; public final int TAILS = 1; private int face; // // Sets up the coin by flipping it initially. // public Coin () { flip(); } // // Flips the coin by randomly choosing a face. // public void flip() { face = (int) (Math.random() * 2); } // // Returns true if the current face of the coin is heads. // public boolean isHeads() { return (face == HEADS); } // // Returns the current face of the coin as a string. // public String toString() { String faceName; if (face == HEADS) faceName = "Heads";

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else faceName = "Tails"; return faceName; } } // ****************************************************************** // Runs.java // // Finds the length of the longest run of heads in 100 flips of a coin. // ******************************************************************* public class Runs { public static void main (String[] args) { final int FLIPS = 100; // number of coin flips int currentRun =0; // length of the current run of HEADS int maxRun =0; // length of the maximum run so far // Create a coin object // Flip the coin FLIPS times for (int i = 0; i < FLIPS; i++) { // Flip the coin & print the result // Update the run information } // Print the results } }

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A Rainbow Program Write a program that draws a rainbow. (This is one of the Programming Projects at the end of Chapter 6 in the text.) As suggested in the text, your rainbow will be concentric arcs, each a different color. The basic idea of the program is similar to the program that draws a bull’s eye in Listing 6.5 and 6.6 of the text. You should study that program and understand it before starting your rainbow. The major difference in this program (other than drawing arcs rather than circles) is making the different arcs different colors. You can do this in several different ways. For example, you could have a variable for the color code, initialize it to some value then either increment or decrement by some amount each pass through the loop (you’ll need to experiment with numbers to see the effect on the color). Or you could try using three integer variables—one for the amount of red, one for the amount of green, and the other for the amount of blue—and modify these (by adding or subtracting some amounts) each time through the loop (each of these must be an integer in the range 0 - 255). For this technique you would need to use the constructor for a Color object that takes three integers representing the amount of red, green, and blue as parameters. Other possibilities are to make each arc a different random color, or have set colors (use at least 4 different colors) and cycle through them (using an idea similar to the way the bull’s eye program switches between black and white).

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Modifying EvenOdd.java File EvenOdd.java contains the dialog box example in Listing 6.9 the text.

1.

2.

Compile and run the program to see how it works.

Write a similar class named SquareRoots (you may modify EvenOdd) that computes and displays the square root of the integer entered.

//***************************************************************** // EvenOdd.java Author: Lewis/Loftus // // Demonstrates the use of the JOptionPane class. //***************************************************************** import javax.swing.JOptionPane; class EvenOdd { //-------------------------------------------------------------// Determines if the value input by the user is even or odd. // Uses multiple dialog boxes for user interaction. //-------------------------------------------------------------public static void main (String[] args) { String numStr, result; int num, again; do { numStr = JOptionPane.showInputDialog ("Enter an integer: "); num = Integer.parseInt(numStr); result = "That number is " + ((num%2 == 0) ? "even" : "odd"); JOptionPane.showMessageDialog (null, result); again = JOptionPane.showConfirmDialog (null, "Do Another?"); } while (again == JOptionPane.YES_OPTION); } }

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A Pay Check Program Write a class PayCheck that uses dialog boxes to compute the total gross pay of an hourly wage worker. The program should use input dialog boxes to get the number of hours worked and the hourly pay rate from the user. The program should use a message dialog to display the total gross pay. The pay calculation should assume the worker earns time and a half for overtime (for hours over 40).

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Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 7

Chapter 7 Exercise Solutions EX 7.1. Write a method called average that accepts two integer parameters and returns their average as a floating point value. public double average(int num1, int num2) { return(num1 + num2) / 2.0; } EX 7.2. Overload the average method of Exercise 7.1 such that if three integers are provided as parameters, the method returns the average of all three. public double average(int num1, int num2, int num3) { return (num1 + num2 + num3) / 3.0; } EX 7.3. Overload the average method of Exercise 7.1 to accept four integer parameters and return their average. public double average(int num1, int num2, int num3, int num4) { return (num1 + num2 + num3 + num4) / 4.0; } EX 7.4. Write a method called multiConcat that takes a String and an integer as parameters. Return a String that consists of the string parameter concatenated with itself count times, where count is the integer parameter. For example, if the parameter values are "hi" and 4, the return value is "hihihihi". Return the original string if the integer parameter is less than 2. public String multiConcat(String text, int count) { String result = text; if (repeats > 1) for (int i=2; i <= count; i++) result += text; return result; } EX 7.5. Overload the multiConcat method from Exercise 7.4 such that if the integer parameter is not provided, the method returns the string concatenated with itself.

For example, if the parameter is "test", the return value is "testtest" public String multiConcat(String text) { return text + text;

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Exercise Solutions, Ch. 7

} EX 7.6. Write a method called makeCircle that returns a new Circle object based on the method's parameters: two integer values representing the (x, y) coordinates of the center of the circle, an integer that represents the circle's radius, and a Color object that defines the circle's fill color. public void makeCircle(int centerX, int centerY, int radius, Color color) { Circle circle = new Circle(centerX, centerY, radius); circle.setFill(color); return circle; } EX 7.7. Overload the makeCircle method of Exercise 7.6 such that if the Color parameter is not provided, the circle's color will default to red. public void makeCircle(int centerX, int centerY, int radius) { Circle circle = new Circle(centerX, centerY, radius); circle.setFill(Color.RED); return circle; } EX 7.8. Overload the makeCircle method of Exercise 7.6 such that if the radius is not provided, a random radius in the range 10 to 20 will be used. public void makeCircle(int centerX, int centerY, Color color) { Random generator = new Random(); int radius = generator.nextInt(11) + 10; Circle circle = new Circle(centerX, centerY, radius); circle.setFill(color); return circle; } EX 7.9. Overload the makeCircle method of Exercise 7.6 such that if both the color and the radius of the circle are not provided, the color will default to green and the radius will default to 40. public void makeCircle(int centerX, int centerY) { Circle circle = new Circle(centerX, centerY, 40); circle.setFill(Color.GREEN); return circle; }

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 7

EX 7.10.

Discuss the manner in which Java passes parameters to a method. Is this technique consistent between primitive types and objects? Explain.

Java passes all parameters by value. This means that the current value of the actual parameter is copied into the formal parameter in the method header. This technique is consistent between primitive types and objects because object references rather than objects themselves are passed. When an object (actually, an object reference) is passed, the current value of the reference (the object's address) is copied into the corresponding formal parameter in the method header.

EX 7.11.

Explain why a static method cannot refer to an instance variable.

A static method is invoked through a class rather than through an object of the class. No object of the class needs to be instantiated in order to invoke a static method. If no object is instantiated, no instance variable exists. Hence, a static method cannot refer to an instance variable.

EX 7.12.

Can a class implement two interfaces that each contains the same method signature? Explain.

Yes. The class which implements an interface provides method implementations for each of the abstract methods defined in the interface. In satisfying the requirements for a method of one interface, it simultaneously satisfies the requirements for a method with the same signature in another interface.

EX 7.13.

Create an interface called Visible that includes two methods: makeVisible and makeInvisible. Both methods should take no parameters and should return a boolean result. Describe how a class might implement this interface. public interface Visible { public boolean makeVisible(); public boolean makeInvisible(); } A class implementing Visible would include an implements clause in the class header, such as: public class ControlPanel implements Visible The class would contain, among other things, two methods with signatures that match those specified in the interface.

EX 7.14.

Draw a UML class diagram that shows the relationships among the elements of the previous exercise.

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Exercise Solutions, Ch. 7

EX 7.15.

Imagine a game in which some game elements can be broken by the player and others can't. Create an interface called Breakable that has a method called break that takes no parameters and another called broken that returns a boolean result indicating whether the object is currently broken. public interface Breakable { public void break(); public boolean broken(); } EX 7.16.

Create an interface called VCR that has methods that represent the standard operations on a video cassette recorder (play, stop, etc.). Define the method signatures any way you desire. Describe how a class might implement this interface. public interface VCR { public String play(); public String stop(); public String record(int start, int end); public String pause(); } A class implementing VCR would include an implements clause in the class header, such as: public class MyVCR implements VCR The class would contain, among other things, four methods with signatures that match those specified in the interface.

EX 7.17.

Draw a UML class diagram that shows the relationships among the elements of the Exercise 7.16.

EX 7.18.

Compare and contrast a mouse clicked event and a key typed event.

Both types of events can originate from any JavaFX node. The node must have the keyboard focus for key events to be recognized. Both types of events correspond to user actions, but not explicitly to visual controls on the screen per se. When either event happens, multiple events are generated: clicking the mouse button generates mouse pressed, mouse released, and mouse clicked events. Tying a keyboard key generates key pressed, key released, and key typed events.

EX 7.19.

What is rubberbanding? How can it be accomplished?

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Exercise Solutions, Ch. 7

Rubberbanding is the visual effect created when the user can seemingly drag a shape into existence. The shape grows while the mouse is dragged. This effect can be accompished by constantly updating the shapes characteristics in response to rapid-fire mouse dragged events.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 8

Chapter 8 Exercise Solutions EX 8.1. Which of the following are valid declarations? Which instantiate an array object?

Explain your answers. int primes = {2, 3, 4, 5, 7, 11}; Invalid; an int cannot be declared and initialized using an intializer list. The brackets are missing. float elapsedTimes[] = {11.47, 12.04, 11.72, 13.88}; Valid; the brackets can be placed either after the element type or after the reference variable. However, this is not the preferred technique. This declaration creates an array object. int[] scores = int[30]; Invalid; the right hand side of the assignment operator must contain either an initializer list or a new operation. int[] primes = new {2,3,5,7,11}; Invalid; “new” on the right hand side of the assignment operator is neither necessary nor acceptable. int[] scores = new int[30]; Valid; the assignment is correct Java syntax. This declaration creates an array object. char grades[] = {'a', 'b', 'c', 'd', 'f'}; Valid; the brackets can be placed either after the element type or after the reference variable. However, this is not the preferred technique. This declaration creates an array object. char[] grades = new char[]; Invalid; the size of the array must be indicated when the array is instantiated.

EX 8.2. Describe five programs that would be difficult to implement without using arrays.

A program to find the average midterm score of 600 students enrolled in an introductory computer science course.

A program to record and compute the sum of the snowfalls, recorded on a daily basis for the 40 days preceding the Winter Olympics.

A program to determine the relative frequency of each character in the Cyrillic alphabet in the original version of The Brothers Karamasov.

A program to compute the mean and standard deviation of the Dow Jones Industrial Average closings since September 11, 2001.

A program to store the coordinates of the vertices of polygons approximating the surface of a beating heart.

EX 8.3. Describe how an element in an array is accessed in memory. For example, where is myArray[25] stored in memory?

The elements of an array are stored contiguously in memory. The name of an array, such as myArray, is a reference to an object that stores the beginning of that data in memory.

To compute the address of a particular element, the address of the first data element is multiplied by the index (25) and the size of the array element. That is why array indexes begin at zero.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 8

EX 8.4.

Describe what problem occurs in the following code. What modifications should be made to it to eliminate the problem? int[] numbers = {3, 2, 3, 6, 9, 10, 12, 32, 3, 12, 6}; for (int count = 1; count <= numbers.length; count++) System.out.println(numbers[count]); The for loop fails to print the 0th element of the array, and attempts to print the nonexistent 11th element of the array.

As a consequence, an ArrayIndexOutOfBoundsException is thrown. The problem can be eliminated by providing a for loop which initializes count to 0 (rather than 1) and tests if count is less than (rather than less than or equal to) numbers.length.

EX 8.5. Write an array declaration and any necessary supporting classes to represent the following statements: a.

students’ names for a class of 25 students String[] students = new String[25];

b. students’ test grades for a class of 40 students int[] grades = new int[40]; or, for simple letter grades: char[] grades = new char[40]; or, for letter grades that include pluses and minuses String[] grades = new String[40]; c.

credit-card transactions that contain a transaction number, a merchant name, and a charge Transactions[] charges = new Transactions[MAX]; public class Transactions { private int transactionNumber; private String merchantName; private double charge; // etc. }

d. students’ names for a class and homework grades for each student Student[] myClass = new Student[MAX]; public class Student { private String name; private int[] grades; // etc. } e.

for each employee of the L&L International Corporation: the employee number, hire date, and the amount of the last five raises

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 8

Employee[]employees = new Employee[MAX]; public class Employee { private int employeeNumber; private String hireDate; private double raise[] = new double[5]; // etc. } EX 8.6. Write code that sets each element of an array called nums to the value of the contstant INITIAL. for (int index = 0; index < nums.length; index++) nums[index] = INITIAL; EX 8.7. Write code that prints the values stored in an array called names backwards. for (int index = names.length-1; index >= 0; index--) System.out.println(names[index]); EX 8.8. Write code that sets each element of a boolean array called flags to alternating values (true at index 0, false at index 1, etc.). for (int index = 0; index < flags.length; index++) flags[index] = (index%2 == 0); EX 8.9. Write a method called sumArray that accepts an array of floating point values and returns the sum of the values stored in the array. public float sumArray(float[] values) { float sum = 0; for (int index = 0; index < values.length; index++) sum += values[index]; return sum; } EX 8.10.

Write a method called switchThem that accepts two integer arrays as parameters and switches the contents of the arrays. Take into account that the arrays may be of different sizes. public void switchThem(int[] first, int[] second) { if (first.length == second.length) { // copy contents of first into temp int [] temp = new int[first.length]; for (int i=0; I < first.length; i++) temp[i] = first[i];

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 8

//copy contents of second into first for (int i=0; I < first.length; i++) first[i] = second[i]; //copy contents of temp into second for (int i=0; I < first.length; i++) second[i] = temp[i]; } else System.out.println("Arrays are of different sizes"); } EX 8.11.

Describe a program for which you would use the ArrayList class instead of arrays to implement choices. Describe a program for which you would use arrays instead of the ArrayList class. Explain your choices.

A program associated with a mail order Website for backpacks would use an object of the ArrayList class to implement the choices of colors of the backpacks because the colors and number of colors change with the seasons and as colors gain and lose popularity. An object of the ArrayList class can grow and shrink dynamically to accommodate these changes.

A program associated with a personal day planner, with entries possible for each hour of the day, would use an array object to implement the choices for each hour of the day because the number of hours in a day, and hence the number of hours for which choices can be made for any given day, never changes. There is no need for the array object to grow or shrink to accommodate a larger or smaller number of hours.

EX 8.12.

The Dots program listens for a mouse pressed event to draw a dot. How would the program behave differently if it listened for a mouse released event instead? A mouse clicked event?

If the program listened instead for a mouse released event, the position and appearance of the dot would be determined at the time of the release, and wouldn’t appear until the mouse button was released. Similarly, if the program listened for a mouse clicked event, the position and appearance of the dot would be determined at the time of a click (which requires a press followed by a release).

EX 8.13.

How would you modify the JukeBox program so that it will play the new song as soon as a combo box item is selected (without having to press the Play button)?

Currently, the event handler processing the choice box selection only stops the current song and sets the new current song. To play a new song immediately when it's selected, the following line could be added at the end of the processChoice method: current.play(); EX 8.14.

What program modifications would be necessary to add three more songs to the juke box?

The program is largely data-driven, so the song names would have to be added to the names array and the corresponding audio files would have to be added to the audioFiles array. The program is designed to work for any size array.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 9

Chapter 9 Exercise Solutions EX 9.1. Draw a UML class diagram showing an inheritance hierarchy containing classes that represent different types of clocks. Show the variables and method names for two of these classes.

EX 9.2. Show an alternative diagrm for the hierarchy in Exercise 9.1. Explain why it may be a better or worse approach than the original.

The value of the organization is dependent on how the classes are used. The hierarchy in Ex. 9.1 might be better suited to a system maintaining the inventory and online shopping for a store, whereas the hierarchy in 9.2, centered around the mounting capabilities, might be better suited to a manufacturing system.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 9

EX 9.3. Draw a UML class diagram showing an inheritance hierarchy containing classes that represent different types of cars, organized first by manufacturer. Show some appropriate variables and method names for at least two of these classes.

EX 9.4. Show an alternative diagram for the hierarchy in Exercise 9.3 in which the cars are organized first by type (sports car, sedan, SUV, etc.). Show some appropriate variables and method names for at least two of these classes. Compare and contrast the two approaches.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 9

The hierarchy in Ex. 9.3 has the manufacturer information as an inherent part of the inheritance structure, and might store car type information as data in lower level classes.

The hierarchy in Ex. 9.4 is organized around car type, with the manufacturer as data.

Which one would be best depends on the purpose of the system.

EX 9.5. Draw a UML class diagram showing an inheritance hierarchy containing classes that represent different types of airplanes. Show some appropriate variables and method names for at least two of these classes.

EX 9.6. Draw a UML class diagram showing an inheritance hierarchy containing classes that represent different types of trees (oak, elm, etc.). Show some appropriate variables and method names for at least two of these classes.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 9

EX 9.7. Draw a UML class diagram showing an inheritance hierarchy containing classes that represent different types of transactions at a store (cash, credit card, etc.).

Show some appropriate variables and method names for at least two of these classes.

EX 9.8. Experiment with a simple derivation relationship between two classes. Put println statements in constructors of both the parent and child classes. Do not explicitly call the constructor of the parent in the child. What happens? Why? Change the

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 9

child's constructor to explicitly call the constructor of the parent. Now what happens?

When a parent's constructor is explicitly called, its program statements are executed as expected. But even in the absence of an explicit call, the parent's constructor is called when the child class is instantiated. An explicit call allows the child to pass parameters, allowing the parent to set up its contribution to the child's state. Without an explicit call, the default constructor is called, without parameters.

EX 9.9. Which of the following classes can be used as the root node of a scene in a JavaFX application? What is the determining factor?

Only a class derived from the Parent class can serve as the root node of a scene. a.

GridPane.

Yes. b.

Rectangle

No. c.

Group

Yes. d.

Button

Yes. e.

ImageView

No. EX 9.10.

Describe the role of the Alert class.

The Alert class provides support for creating and displaying several basic types of dialog boxes, which provide information, let the user confirm an action, or conveys a warning or error message.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 10

Chapter 10 Exercise Solutions EX 10.1.

Draw and annotate a class hierarchy that represents various types of faculty at a university. Show what characteristics would be represented in the various classes of the hierarchy. Explain how polymorphism could play a role in the process of assigning courses to each faculty member.

The abstract method assignCourses is established in the FacultyMember class, ensuring that child classes will implement it. That way, each class can have a definition of assignCourses that makes sense for it (depending on the rank and other issues). A program that manages a list of various faculty member objects could then assign courses to everyone by making a polymorphic call to assignCourses for each faculty member.

EX 10.2.

Draw and annotate a class hierarchy that represents various types of animals in a zoo. Show what characteristics would be represented in the various classes of the hierarchy. Explain how polymorphism could play a role in guiding the feeding of the animals.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 10

The abstract method feedingInstructions is established in the ZooAnimal class, ensuring that child classes will implement it. That way, each class can have a definition of feedingInstructions that makes sense for it. A program that manages a list of various animal objects could then print feeding instructions for all animals by making a polymorphic call to feedingInstructions for each animal.

EX 10.3.

Draw and annotate a class hierarchy that represents various types of sales transactions in a store (cash, credit, etc.). Show what characteristics would be represented in the various classes of the hierarchy. Explain how polymorphism could play a role in the payment process.

The following diagram is a modified version of the one used for Exercise 9.7.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 10

The abstract method purchase is established in the Sale class, ensuring that child classes will implement it. That way, each class can have a definition of purchase that makes sense for it, as opposed to the computeTax method, which is implemented in Sale and used by all child classes as is. A program that manages the sales transactions as they occur could then conduct the transaction by making a polymorphic call to purchase no matter what the transaction type is.

EX 10.4.

What would happen if the pay method were not defined as an abstract method in the StaffMember class of the Firm program?

By defining the pay method in StaffMember, all child classes must implement it (or be abstract themselves). So if pay were not defined in StaffMember, the child classes would not have to implement it and the ability to pay all staff members through a polymorphic reference would not exist. It is only by formally establishing that all children of StaffMember have a pay method that makes it safe to pay them all.

EX 10.5.

Describe a property binding that you could set up other than the examples used in this chapter.

You could bind the property representing the end point of a horizontal line to the width of the scene so that the line is always long enough to span the scene.

EX 10.6.

Write a statement that would bind the property representing the radius of a Circle object to the property representing the value in a slider. myCircle.radiusProperty().bind(mySlider.valueProperty());

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 11

Chapter 11 Exercise Solutions EX 11.1.

Create a UML class diagram for the ProductCodes program.

EX 11.2.

What would happen if the try statement were removed from the level1 method of the ExceptionScope class in the Propagation program?

If the try statement were removed from the level1 method, the ArithmeticException, when thrown, would propagate to the main method (which called the level1 method). Since there is no try statement in the main method, the program would terminate, producing the message associated with the exception.

EX 11.3.

What would happen if the try statement described in the previous exercise were moved to the level2 method?

If the try statement were moved from the level1 method to the level2 method, the exception thrown in level3 would propogate only to level2, where it would be caught and handled. The level2 method would then be allowed to finish execution.

EX 11.4.

Look up the following exception classes in the online Java API documentation and describe their purpose: a.

ArithmeticException This exception is thrown when an exceptional arithmetic condition occurs, such as dividing by zero.

b. NullPointerException This exception is (most commonly) thrown when attempting to call an instance method of a null reference. It occurs in other situations as well, such as attempting to throw a null reference. c.

NumberFormatException This exception is thrown when an application attempts to convert a string into a numeric value, but the string does not have the proper format.

d. PatterSyntaxException This exception is thrown when a syntax error occurs in the pattern of a regular expression.

EX 11.5.

Other than the examples discussed in this chapter, describe a situation in which you might disable control(s) to help guide user actions.

You might disable a button used to move to the next step of a process until the current step has been completed or until the data being requested is filled in and validated.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 11

EX 11.6.

Explain how the functionality of the FoodImages program would change if the property binding was removed.

The property binding binds the width of the image view to the width of the pane in which the image is displayed. So if that properyt binding wasn't set up, the image size would dictate the window size, which might vary from one image to the next.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 12

Chapter 12 Exercise Solutions EX 12.1.

Write a recursive definition of a valid Java identifier (see Chapter 1).

A Java-Identifier is a: Letter or a: Letter followed by a Java-Identifier-Substring A Java-Identifier-Substring is a: Letter or a: Digit or a: Letter followed by a Java-Identifier-Substring or a: Digit followed by a Java-Identifier-Substring

EX 12.2.

Write a recursive definition of xy (x raised to the power y), where x and y are integers and y > 0. x1 = x xy = x + xy-1 for y > 1 EX 12.3.

Write a recursive definition of i * j (integer multiplication), where i > 0.

Define the multiplication process in terms of integer addition. For example, 4 * 7 is equal to 7 added to itself 4 times.

1*j=j i * j = j + (i-1) * j for i > 1 EX 12.4.

Write a recursive definition of the Fibonacci numbers. The Fibonacci numbers are a sequence of integers, each of which is the sum of the previous two numbers. The first two numbers in the sequence are 0 and 1. Explain why you would not normally use recursion to solve this problem.

Fib(0) = 0 Fib(1) = 1 Fib(j) = Fib(j-1) + Fib(j-2) for j > 1 You would not normally use recursion to solve this problem because the iterative solution is straightforward and the recursive version is inefficient. Calculating a Fibonacci number less than Fib(j-1) would be calculated at least twice in order to calculate Fib(j). The recalculation of each such number would lead to the further recalculation of other Fibonacci numbers with the accompanying inefficiency.

EX 12.5.

Modify the method that calculates the sum of the integers between 1 and N shown in this chapter. Have the new version match the following recursive definition: The sum of 1 to N is the sum of 1 to (N/2) plus the sum of (N/2 + 1) to N. Trace your solution using an N of 7. // Computes the sum of the numbers between n1 and n2 (inc) public int sum(int n1, int n2) { int result; if (n2-n1 == 0) result = n1; else {

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 12

int mid = (n1+n2)/2; result = sum(n1, mid) + sum(mid+1, n2); } return result; }

EX 12.6.

Write a recursive method that returns the value of N! (N factorial) using the definition given in this chapter. Explain why you would not normally use recursion to solve this problem. public int factorial(int num) { int result; if (num == 1) result = 1; else result = num * factorial(num - 1); return result; } You would not normally use recursion to solve this problem because it can be done more efficiently using iteration and because the recursive solution it no more intuitive than the iterative solution.

EX 12.7.

Write a recursive method to reverse a string. Explain why you would not normally use recursion to solve this problem. public String reverse(String text) { String result = text; if (text.length() > 1) result = text.charAt(text.length()-1) + reverse(text.substring(0, text.length()-1)); return result; } You would not normally use recursion to solve this problem because it can be done more efficiently using iteration and because the recursive solution is no more intuitive than the iterative solution.

EX 12.8.

Design or generate a new maze for the MazeSearch program in this chapter and rerun the program. Explain the processing in terms of your new maze,

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 12

giving examples of a path that was tried but failed, a path that was never tried, and the ultimate solution.

A new maze could be generated with nested for loops which randomly place either a 1 or a 0 in each cell of a two-dimensional array. Because the likelihood of generating a maze with a solution is generally low, subsequent mazes could be generated using a while loop until a maze with a solution is generated.

A maze with a solution could be hard-coded with the following statement: private int [][] grid = {{1,0,1,0,1,1,1,1,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,1,1,0,1,0,1,0,1}, {0,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,0,1,0,1,0,1}, {1,0,1,1,1,1,1,0,1}}; After the search arrives at position (5,0), it attempts position (6,0). Encountering a 0 causes this path to fail. It then attempts position (5,1) which succeeds. Subsequently, position (6,1) fails and position (5,2) succeeds.Because the maze is traversed successfully from position (5,2), no attempt is ever made to find a path from position (4,1). The following grid shows the solution path marked with 7s.

7 0 1 0 1 1 7 7 7 7 0 1 0 1 0 7 0 7 7 0 1 0 1 0 7 0 7 7 0 1 0 1 0 7 0 7 7 0 1 0 1 0 7 0 7 7 7 7 0 1 0 7 0 7 0 0 7 0 1 0 7 0 7 1 0 7 0 1 0 7 0 7 1 0 7 0 1 0 7 0 7 1 0 7 0 1 0 7 0 7 1 0 7 7 7 7 7 0 7 EX 12.9.

Annotate the lines of output of the SolveTowers program in this chapter to show the recursive steps.

Move one disk from 1 to 2 // called with numDisks = 1 Move one disk from 1 to 3 // called with numDisks = 2 Move one disk Move one disk Move one disk Move one disk Move one disk

from 2 to 3 // called with numDisks = 1 from 1 to 2 // called with numDisks = 3 from 3 to 1 // called with numDisks = 1 from 3 to 2 // called with numDisks = 2 from 1 to 2 // called with numDisks = 1

Move one disk from 1 to 3 // called with numDisks = 4 Move one disk from 2 to 3 // called with numDisks = 1

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 12

Move one disk from 2 to 1 // called with numDisks = 2 Move one disk from 3 to 1 // called with numDisks = 1 Move one disk from 2 to 3 // called with numDisks = 3 Move one disk from 1 to 2 // called with numDisks = 1 Move one disk from 1 to 3 // called with numDisks = 2 Move one disk from 2 to 3 // called with numDisks = 1 Note the symmetry about the line where a call is made with numDisks = 4.

EX 12.10.

Produce a chart showing the number of moves required to solve the Towers of Hanoi puzzle using the following number of disks: 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, and 25.

Disks

Moves

2

3

3

7

4

15

5

31

6

63

7

127

8

255

9

511

10

1023

15

32767

20

1,048,575

25

33,554,431

EX 12.11.

How many line segments are used to construct a Koch snowflake of order N? Produce a chart showing the number of line segments that make up a Koch snowflake for orders 1 through 9.

A Koch snowflake of order N has 3(4N-1) line segments.

Order

Line Segments

1

3

2

12

3

48

4

192

5

768

6

3072

7

12,288

8

49,152

9

196,608

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 13

Chapter 13 Exercise Solutions EX 13.1.

Suppose current is a reference to a Node object and that it currently refers to a specific node in a linked list. Show, in pseudocode, the steps that would delete the node following current from the list. Carefully consider the cases in which current is referring to the first and last nodes in the list. if current.next is not null then current.next = current.next.next; endIf Must check for current pointing to the last node in the list (so we don't follow a null reference). In this case, current pointing to the first node in the list is not a special case.

EX 13.2.

Modify your answer to Exercise 13.1 assuming that the list was set up as a doubly linked list, with both next and prev references. if current.next is not null then current.next = current.next.next; if current.next is not null then current.next.prev = current; endIf endIf EX 13.3.

Suppose current and newNode are references to Node objects. Assume current currently refers to a specific node in a linked list and newNode refers to an unattached Node object. Show, in pseudocode, the steps that would insert newNode behind current in the list. Carefully consider the cases in which current is referring to the first and last nodes in the list. newNode.next = current.next; current.next = newNode; The situations of current pointing to the first or last nodes in the list are not special cases for this operation.

EX 13.4.

Modify your answer to Exercise 13.3 assuming that the list was set up as a doubly linked list, with both next and prev references. newNode.prev = current; newNode.next = current.next; if current.next is not null then current.next.prev = newNode; endIf current.next = newNode; EX 13.5.

Would the front and rear references in the header node of a linked list ever refer to the same node? Would they ever both be null? Would one ever be null if the other was not? Explain your answers using examples.

The front and rear references in the header node of a linked list would refer to the same node if the list consists of only a single node. They would both be null if the list were empty. One would never be null if the other were not. For example, if the linked list consisted of a single node containing the string “William” and a null next reference (since there is no successor node), both the front and rear references would contain reference

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 13

this node. If the node containing “William” were deleted, both the front and rear references would be set to null. It is impossible to have a list which has a front, but no rear or a rear but no front, thus it is impossible for one reference to be null and the other not.

EX 13.6.

Show the contents of a queue after the following operations are performed.

Assume the queue is initially empty. enqueue(45); 45 enqueue(12); 12 45 enqueue(28); 28 12 45 dequeue(); 28 12 dequeue(); 28 enqueue(69); 69 28 enqueue(27); 27 69 28 enqueue(99); 99 27 69 28 dequeue(); 99 27 69 enqueue(24); 24 99 27 69 enqueue(85); 85 24 99 27 69 enqueue(16); 16 85 24 99 27 69 dequeue(); 16 85 24 99 27 EX 13.7.

In terms of the final state of a queue, does it matter how dequeue operations are intermixed with enqueue operations? Does it matter how the enqueue operations are intermixed among themselves? Explain using examples.

In terms of the final state of a queue, as long as the number of dequeue opertions does not exceed the number of enqueue operations, the intermixing of these operations does not matter. It does matter, however, how the enqueue operations are intermixed among themselves; an item which arrives earlier moves closer to the front of the queue than an item which arrives later.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 13

As an example of intermixing enqueue and dequeue operations, consider enqueuing six integers such as 2, 3, 5, 7, 11, and 13 and then dequeuing half of them. The resulting queue contains 7, 11, and 13. Alternatively, suppose that the same six integers are enqueued, but every time two integers are enqueued, one is dequeued. The resulting queue contains 7, 11, and 13. Of course, this does not prove than the intermixing of dequeue and enqueue operations is inconsequential; it merely shows that it is inconsequential in this case.

On the other hand, if the enqueue operations are intermixed among themselves, such as enqueuing the 13 first and the 2 last (instead of 2 first and 13 last), the resulting queue would contain 7, 11, and 2 (instead of 7, 11, and 13). This single case is sufficient to prove that the intermixing of enqueue operations matters.

EX 13.8.

Show the contents of a stack after the following operations are performed.

Assume the stack is initially empty. push(45); 45 push(12); 45 12 push(28); 45 12 28 pop(); 45 12 pop(); 45 push(69); 45 69 push(27); 45 69 27 push(99); 45 69 27 99 pop(); 45 69 27 push(24); 45 69 27 24 push(85); 45 69 27 24 85 push(16); 45 69 27 24 85 16 pop(); 45 69 27 24 85 EX 13.9.

In terms of the final state of a stack, does it matter how the pop operations are intermixed with the push operations? Does it matter how the push operations are intermixed among themselves? Explain using examples.

Java Software Solutions, 9th Edition

Exercise Solutions, Ch. 13

In terms of the final state of a stack, the number of pop operations must not exceed the number of push operations, and the intermixing of pop and push operations matters. How the push operations are intermixed among themselves also matters.

For example, suppose the six integers 2, 3, 5, 7, 11, and 13 are pushed onto a stack, and then three integers are popped off the stack. The resulting stack contains 2, 3, and 5. Alternatively, suppose that the same six integers are pushed onto the stack, put every time 2 integers are pushed onto the stack, one is popped. The resulting stack contains 2, 5, and 11. This single illustration is sufficient to prove that the intermixing of push and pop operations matters.

Similarly, if the 13 is pushed onto the stack first and the 2 is pushed onto the stack last (instead of the 2 first and the 13 last), with no popping, the 2 is at the top of the stack and the 13 is at the bottom of the stack (instead of the 2 at the bottom and the 13 at the top).

Again, this single example is sufficient to prove that the intermixing of push operations among themselves matters.

EX 13.10.

Would a tree data structure be a good choice to represent a family tree that shows lineage? Why or why not? Would a binary tree be a better choice? Why or why not?

A binary tree would be a good choice to represent a family tree that shows lineage (ancestors). Everyone you know has exactly two biological parents, as does each of their ancestors, making a binary tree a natural choice. A tree, on the other hand, would not be a particularly good choice, because tree nodes often are designed to accommodate a variable number of references. In this example, the number of references needed is known; it is exactly two. Further, a tree typically is represented as the corresponding binary tree, with some accompanying overhead, so it makes sense to “cut to the chase” when there is no intuitive loss in the representation.

EX 13.11.

What data structure would be a good choice to represent the links between various web sites of the World Wide Web? Give an example.

A digraph (directed graph) would be a good choice to represent the links between various web sites of the World Wide Web. For example, a university’s web site might link to all the department’s web sites, and each of those might link to all of the faculty members web sites in that department. A particular faculty web site might link to a spouse’s web site which links to a son’s web site and back to the faculty member's web site. A linear list cannot accommodate such a complex linking structure. A tree does not accommodate paths that circle their way back to a particular node. A graph accommodates paths than make their way back to a particular node, but a graph assumes that bidirectional links (so if one page A links to page B, then page B links to page A, which may not be the case). Therefore a digraph, with its edges that go in one direction, would be the best choice.