JAVA 02 Dr. Muditha Hapudeniya MBBS, MSc, AMBCS

Out Line ● ● ● ● ● ● ●

Recap of previous lecture If then , if then else Switch While Do while For Break, continue, return

Data Types

Defining and using variable Define by the data type followed by the variable name:

int numberOfDays;

short hour;

float reactionTime; Initialized before use

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int numberOfDays; numberOfDays = 7;

Exercise â&#x2014;?

Write a java program to calculate the BMI for given weight and height.

Exercise Write a java program to calculate the following for given radius ( r ) of a circle.

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Diameter - 2r Circumference – 2πr Area – πr2 Volume – 4/3 πr3 ●

π = 3.1416

Math functions in Java ●

Lots of mathematical functions are built-in to the Java lang.

Math class in java.lang package provides these functions.

There is no need to import

Some useful functions are –

PI

abs(), ceil(), floor(), round()

max(), min()

pow()

random()

sqrt()

Example

The if-then-else Statement

The if-then-else Statement The syntax for IF-ELSE statement is if(expression) { // IF statement block : TRUE } else // optional { // ELSE statement block : FALSE }

if (value % 2 == 1) { result = "Number is Odd"; } else { result = "Number is Even"; }

Example

The switch Statement â&#x2014;?

Long list of nested IF can be replaced by switch statement Int x= 90; switch (x) { case 100: System.out.println("100"); break; case 90: System.out.println("90"); break; default: System.out.println("not found"); break; } What is the function of break ?

Example

Exercise â&#x2014;?

Modify the java program written for calculate the BMI to categorise

Category Severely underweight Underweight Normal Overweight Obese Class I Obese Class II Obese Class III

BMI range â&#x20AC;&#x201C; kg/m2 less than 16.0 from 16.1 to 18.5 from 18.6 to 25 from 26 to 30 from 31 to 35 from 36 to 40 over 41

while Statements â&#x2014;?

The while statement continually executes a block of statements while a particular condition is true while (expression) { statement(s) } int count = 1; while (count < 11) { System.out.println("Count is: " + count); count++; }

do - while Statements â&#x2014;?

Similar to while but the statements within the do block are always executed at least once do { statement(s) } while (expression);

int count = 1; do { System.out.println("Count is: " + count); count++; } while (count <= 11); Example

for Statement â&#x2014;?

for statement provides a compact way to iterate over a range of values for (initialization; termination; increment) { statement(s) } for(int i=1; i<11; i++){ System.out.println("Count is: " + i); }

while Statements â&#x2014;?

The while statement continually executes a block of statements while a particular condition is true while (expression) { statement(s) } int count = 1; while (count < 11) { System.out.println("Count is: " + count); count++; }

Branching Statements break Statement terminate a for, while, or do-while loop continue Statement skips the current iteration of a for, while , or dowhile loop return Statement exits from the current method, and control flow returns to where the method was invoked Example

Practise

Java arrays â&#x2014;?

An array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed

Declaring, Creating, Initialising, and Accessing an Array Type[] varName; int[] anArray; // declares an array of integers anArray = new int[10]; // create an array of integers anArray[0] = 100; // initialize first element anArray[1] = 200; // initialize second element anArray[2] = 300; // etc. // another way int[] anArray = {100, 200, 300, 400, 500, 600, 700, 800, 900, 1000}; // accessing a array System.out.println("Element 1 at index 0: " + anArray[0]);

Example

Multidimensional array You can also declare an array of arrays (also known as a multidimensional array) by using two or more sets of square brackets Each element, therefore, must be accessed by a corresponding number of index values. a multidimensional array is simply an array whose components are themselves arrays. String[][] names = {{"Mr. ", "Mrs. ", "Ms. "}, {"Smith", "Jones"}}; Int [][] multyArray = new int[5][5]; MultiArray[0][0]=12;

Multidimensional array int[ ][ ] aryNumbers = new int[6][5]; aryNumbers[0][0] = 10; aryNumbers[0][1] = 12; aryNumbers[0][2] = 43; aryNumbers[0][3] = 11; aryNumbers[0][4] = 22;

0

1

2

aryNumbers[1][0] = 20; aryNumbers[1][1] = 45; aryNumbers[1][2] = 56; aryNumbers[1][3] = 1; aryNumbers[1][4] = 33;

[row, column] Example

3

4

String Manipulation Useful string handling methods i = s.length()

length of the string s.

b = s.equals(t)

true if the two strings have equal values

b = s.equalsIgnoreCase(t) same as above ignoring case c = s.charAt(i)

char at position i in s.

s1 =

s.substring(i) substring from index i to the end of s.

s1 =

s.substring(i, j)

s1 =

s.toLowerCase() new String with all chars lowercase

s1 =

s.toUpperCase() new String with all chars uppercase

s1 =

s.trim() new String with whitespace deleted from front and back

s1 =

s.replace(c1, c2) new String with all c1 characters replaced by character c2.

s1 =

s.replace(cs2, cs3)

substring from index i to BEFORE index j of s.

new String with all cs2 substrings replaced by cs3.

String to Number conversion Frequently, a program ends up with numeric data in a string objectâ&#x20AC;&#x201D;a value entered by the user, for example. The Number subclasses that wrap primitive numeric types ( Byte, Integer, Double, Float, Long, and Short) each provide a class method named valueOf that converts a string to an object of that type. String s = 10; byte b = Byte.valueOf(s); Int I = Integer.valueOf(s); //The valueOf class method. Int I = Integer.parseInt(s); //The parseInt class method.

Example

Number to String conversion Sometimes you need to convert a number to a string because you need to operate on the value in its string form. There are several easy ways to convert a number to a string: int I = 10 ; String s1 = "" + i; //Concatenate "i" with an empty string; String s2 = String.valueOf(i); //The valueOf class method. toString(), that will convert its primitive type to a string int i; double d; String s3 = Integer.toString(i); //The toString class method. String s4 = Double.toString(d); //The toString class method. Example

Getting User input Method 1 You can provide values when you start the java program as command line arguments. They are stored in the main method array. public class UserInput1 { public static void main(String[] args) { String s1=args[0]; String s2=args[1]; System.out.println(s1); System.out.println(s2); }} \$> java UserInput1 1234 abcd

Example

Getting User input Method 2 For interactive user inputs you can use Scanner class in java.util package. import java.util.Scanner; // import the Scanner class public class UserInput2 { public static void main(String[] args) { Scanner scan = new Scanner(System.in); // create Scanner object String usrInput; // variable to hold the user input System.out.print("Enter the input : "); // prompt usrInput = scan.next(); // read the user input as a string System.out.println(usrInput); // print the user input }}

Example

Do more java exercises

Exercises

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Convert the BMI calculation program to useful interactive program Convert a full name in to a name with initials Get 10 numbers from the user and give mean, mode, min, max, SD

Java lecture

Msc -Bio medical informatics lecture