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Module 4: Creating Objects in C#


Overview 

Defining a Class

Declaring Properties

Declaring Methods

Using Constructors

Using Static Class Members

Partial Types


Lesson: Defining a Class 

What Are Classes and Objects?

What Are Value Types and Reference Types?

How to Define a Class and Create an Object

How to Organize Classes Using Namespaces

How to Define Accessibility and Scope


Multimedia: What Are Objects and Classes?


What Are Classes and Objects? 

Classes:  Are like blueprints for objects  Contain methods and data

Class Class Covered Porch kitchen Dining Room

Living Room

Objects:  Are instances of a class 

Created using the new keyword Have actions

Object Object

Bath

Office

Family Room


What Are Value Types and Reference Types? 

Value types

Reference types 

Contain a reference to the data

Stored on the heap

Must be initialized

Declared using new keyword

Cannot be null

An int is a value type

.NET garbage collection handles destruction

A class is a reference type

Directly contain data

Stored on the stack

int int ii ==

i

i; i; 42; 42;

42 42

CostObject CostObject c; c;

c

••

42 42


How to Define a Class and Create an Object 

How to define a class

public public class class Customer Customer {{ public name; public string string name; public public decimal decimal creditLimit; creditLimit; public customerID; public uint uint customerID; }} 

How to instantiate a class as an object

Customer Customer nextCustomer nextCustomer == new new Customer(); Customer(); 

How to access class variables

nextCustomer.name nextCustomer.name == "Suzan "Suzan Fine"; Fine";


How to Organize Classes Using Namespaces 

Declaring a namespace

namespace namespace CompanyName CompanyName {{ public public class class Customer Customer () () {{ }} }} 

Nested namespaces

namespace namespace CompanyName CompanyName {{ namespace namespace Sales Sales {{ public public class class Customer Customer }} }} // // Or Or namespace namespace CompanyName.Sales CompanyName.Sales 

The using statement

using using using using

System; System; CompanyName.Sales; CompanyName.Sales;

() () {{ }}

{{ ... ... }}


How to Define Accessibility and Scope ď Ž

Access modifiers are used to define the accessibility level of class members Declaration Declaration

Definition

public

Access not limited.

private

Access limited to the containing class.

internal

Access limited to this program.

protected protected internal

Access limited to the containing class and to types derived from the containing class Access limited to the containing class, derived classes, or to members of this program


Practice: Defining Classes and Creating Objects Hands-on Hands-on Practice Practice ď Žď Ž In this practice, you will define a class, In this practice, you will define a class,

instantiate instantiatean aninstance instanceof ofthe theclass, class,and and assign assignvalues valuesto tothe theclass classmembers members

10 min


Lesson: Declaring Properties ď Ž

How to Declare Properties

ď Ž

Using Properties


How to Declare Properties ď Ž

A Property has a set and a get functions

public public class class Course Course {{ private private string string courseNo; courseNo; private string courseName; private string courseName; private private double double credits; credits; public public string string CourseNo CourseNo {{ get get {{ return return courseNo; courseNo; }} set set {{ courseNo courseNo == value; value; }} }} public public string string CourseName CourseName {{ get get {{ return return courseName; courseName; }} set set {{ courseName courseName == value; value; }} }} }}


Using Properties 

How to use Properties

Course Course oCourse oCourse == new new Course(); Course(); oCourse.CourseNo oCourse.CourseNo == “MA-101”; “MA-101”; oCourse.CourseName oCourse.CourseName == “Matemathics “Matemathics I” I” oCourse.Credits oCourse.Credits == 5; 5;


Practice: Using Properties Hands-on Hands-on Practice Practice

10 min


Lesson: Declaring Methods 

How to Write a Method

How to Pass Parameters to a Method

How to Pass Parameters by Reference

How to Pass a Reference Type

How to Overload a Method

How to Use XML Code Comment Features


How to Write a Method ď Ž

A method is a command for action

class class Lion Lion {{ private private int int weight; weight; public public bool bool IsNormalWeight IsNormalWeight () () {{ if if ((weight ((weight << 100)||(weight 100)||(weight >> 250)) 250)) {{ return return false; false; }} return return true; true; }} public public void void Eat() Eat() {{ /* /* some some action action */ */ }} public public int int GetWeight() GetWeight() {return {return this.weight;} this.weight;} }} .. .. .. Lion Lion bigLion bigLion == new new Lion(); Lion(); bool bool weightNormal weightNormal == bigLion.IsNormalWeight(); bigLion.IsNormalWeight(); bigLion.Eat(); bigLion.Eat(); int int weight weight == bigLion.GetWeight(); bigLion.GetWeight();


How to Pass Parameters to a Method ď Ž

Passing by value

class class Lion Lion {{ private private int int weight; weight; public public void void SetWeight(int SetWeight(int newWeight) newWeight) {{ weight weight == newWeight; newWeight; }} }} .. .. .. Lion Lion bigLion bigLion == new new Lion(); Lion(); int int bigLionWeight bigLionWeight == 250; 250; bigLion.SetWeight( bigLion.SetWeight( bigLionWeight bigLionWeight ); );


How to Pass Parameters by Reference 

Using the ref keyword

public public void void GetAddress(ref GetAddress(ref int int number, number, ref ref string string street) street) {{ number number == this.number; this.number; street street == this.street; this.street; }} .. .. .. int int sNumber sNumber == 0; 0; string string streetName streetName == null; null; zoo.GetAddress( zoo.GetAddress( ref ref sNumber, sNumber, ref ref streetName streetName ); ); // // sNumber sNumber and and streetName streetName have have new new values values  

Definite assignment Using the out parameter keyword  Allows you to initialize a variable in a method


How to Pass a Reference Type ď Ž

When you pass a reference type to a method, the method can alter the actual object

class class Zoo Zoo {{ public public void void AddLion( AddLion( newLion.location newLion.location .. .. .. }} }}

Lion Lion newLion newLion )) {{ == "Exhibit "Exhibit 3"; 3";

.. .. .. Zoo Zoo myZoo myZoo == new new Zoo(); Zoo(); Lion Lion babyLion babyLion == new new Lion(); Lion(); myZoo.AddLion( myZoo.AddLion( babyLion babyLion ); ); // // babyLion.location babyLion.location is is "Exhibit "Exhibit 3" 3"


How to Overload a Method ď Ž

Overloading enables you to create multiple methods within a class that have the same name but different signatures class class Zoo Zoo {{ public public void void {{ ... ... }} public public void void

}}

... ... }}

AddLion(Lion AddLion(Lion newLion) newLion) AddLion(Lion AddLion(Lion newLion, newLion, int int exhibitNumber) exhibitNumber) {{


How to Use XML Code Comment Features ď Ž

Three forward slashes (///) inserts XML comments

ď Ž

Hovering over a section of code produces a pop-up menu for accessing class member information


Practice: Writing and Calling a Method

Hands-on Hands-on Practice Practice

ď Žď Ž In this practice, you will add a method to In this practice, you will add a method to

an ananimal animalclass class

10 min


Lesson: Using Constructors 

How to Initialize an Object

How to Overload a Constructor


How to Initialize an Object 

Instance constructors are special methods that implement the actions required to initialize an object 

Have the same name as the name of the class

Default constructor takes no parameters

public public class class Lion Lion {{ public public Lion() Lion() {{ Console.WriteLine("Constructing Console.WriteLine("Constructing Lion"); Lion"); }} }} 

Readonly 

Used to assign a value to a variable in the constructor


How to Overload a Constructor ď Ž

Create multiple constructors that have the same name but different signatures ď Ź

Specify an initializer with this

public public class class Lion Lion {{ private name; private string string name; private age; private int int age;

}}

public public Lion() Lion() :: this( this( "unknown", "unknown", 00 )) {{ Console.WriteLine("Default: Console.WriteLine("Default: {0}", {0}", name); name); }} public public Lion( Lion( string string theName, theName, int int theAge theAge )) {{ name name == theName; theName; age age == theAge; theAge; Console.WriteLine("Specified: Console.WriteLine("Specified: {0}", {0}", name); name); }}


Practice: Using Constructors

Hands-on Hands-on Practice Practice ď Žď Ž In this practice, you will modify the In this practice, you will modify the

solution solutionto tothe thelast lastpractice, practice,so sothat thatitit uses usesconstructors constructorsto toinitialize initializeanimal animal objects objectsproperly properly

10 min


Lesson: Using Static Class Members ď Ž

How to Use Static Class Members

ď Ž

How to Initialize a Class


How to Use Static Class Members 

Static Members 

Belong to the class

Initialize before an instance of the class is created

Shared by all instances of the class

class class Lion Lion {{ public public static static string string family family == "felidae"; "felidae"; }} ... ... // // AA Lion Lion object object is is not not created created in in this this code code Console.WriteLine( Console.WriteLine( "Family: "Family: {0}", {0}", Lion.family Lion.family ); );


How to Initialize a Class 

Static Constructors 

Will only ever be executed once

Run before the first object of that type is created

Have no parameters

Do not take an access modifier

May co-exist with a class constructor

Used to initialize a class


Practice: Using Static Class Members

Hands-on Hands-on Practice Practice

ď Žď Ž In this practice, you will modify a class to In this practice, you will modify a class to

use usestatic staticclass classmembers members

10 min


Lesson: Partial Types 

How to Declare Partial Types

Using Partial Types


How to Declare Partial Types ď Ž

Partial classes allow you to split a class definition across multiple source files. The benefit of this approach is that it hides details of the class definition so that derived classes can focus on more significant portions.

public public partial partial class class Course Course {{ private private string string courseNo; courseNo; private private string string courseName; courseName;

}}

public public string string CourseNo CourseNo {{ ... ... }}

partial partial class class Course Course {{ public public void void Display() Display() {{ Console.WriteLine("Course Console.WriteLine("Course Information:"); Information:"); Console.WriteLine("\tCourse Console.WriteLine("\tCourse No.: No.: "+this.CourseNo); "+this.CourseNo); Console.WriteLine("\tCourse Console.WriteLine("\tCourse Name: Name: "+this.CourseName); "+this.CourseName); }} }}


How to Use Partial Types

Course Course oCourse oCourse == new new Course(); Course(); oCourse.CourseNo oCourse.CourseNo == “MA-101”; “MA-101”; oCourse.CourseName oCourse.CourseName == “Matemathics “Matemathics I” I” oCourse.Credits oCourse.Credits == 5; 5; oCouse.Display(); oCouse.Display();


Review 

Defining a Class

Declaring Methods

Using Constructors

Using Static Class Members

Creando Objetos en C#  

Manual C sharp

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