CIS 330 1

C# Lesson 7

Introduction to Classes

CIS 330 2

Objectives

• Implement Constructors.

• Know the difference between instance and static members.

• Understand Destructors.

• Familiarization with Class Members.

CIS 330 3

Classes • Classes are declared by using the

keyword class followed by the class name and a set of class members surrounded by curly braces

• Every class has a constructor that initializes class members when the class is created

• Constructors do not have return values and always have the same name as the class

CIS 330 4

Classes (cont)class OutputClass

{    string myString;

    // Constructor    public OutputClass(string inputString)     {        myString = inputString;    }

    // Instance Method    public void printString()     {        Console.WriteLine("{0}", myString);    }

    // Destructor    ~OutputClass()     {        // Some resource cleanup routines    }}

CIS 330 5

Classes (cont)• In C#, there are two types of class members

– Instance class members belong to a specific occurrence of a class

– Static members can be accessed simply by using the syntax <classname>.<static class member>. There is only ever one copy of a static class member.  Use static constructor to initialize static fields in a class

• Destructors look just like constructors, except they start with a tilde, "~". They are normally called by the C# garbage collector.

CIS 330 6

Class Member Types• Constructors • Destructors • Fields • Methods • Properties • Indexers • Delegates • Events • Nested Classes

CIS 330 7

C# Lesson 8

Class Inheritance

CIS 330 8

Objectives

• Implement Base Classes.

• Implement Derived Classes.

• Initialize Base Classes from Derived Classes.

• Learn How to Call Base Class Members.

• Learn How to Hide Base Class Members.

CIS 330 9

Inheritance Example public class ParentClass

{    public ParentClass()    {        Console.WriteLine("Parent Constructor.");    }

    public void print()    {        Console.WriteLine("I'm a Parent Class.");    }}

public class ChildClass : ParentClass{    public ChildClass()    {        Console.WriteLine("Child Constructor.");    }

    public static void Main()    {        ChildClass child = new ChildClass();

        child.print();    }}

CIS 330 10

Inheritance• Can create a child class ChildClass, using

existing code from ParentClass • This is accomplished through the ChildClass

declaration– public class ChildClass : ParentClass

• C# supports single class inheritance only. However, it does allow multiple interface inheritance

• ChildClass has exactly the same capabilities as ParentClass

CIS 330 11

Inheritance (cont)• Can access base class members

– prefixing the method name with "base.“– through an explicit cast ((Parent)child).print();  

• The new modifier on a Child class enables this method to hide the Parent class method, thus explicitly preventing polymorphism

CIS 330 12

C# Lesson 9

Polymorphism

CIS 330 13

Objectives

• Learn What Polymorphism Is.

• Implement a Virtual Method.

• Override a Virtual Method.

• Use Polymorphism in a Program.

CIS 330 14

Polymorphism Example public class DrawingObject

{    public virtual void Draw()    {        Console.WriteLine("I'm just a generic drawing object.");    }}

public class Line : DrawingObject{    public override void Draw()    {        Console.WriteLine("I'm a Line.");    }}

public class Circle : DrawingObject{    public override void Draw()    {        Console.WriteLine("I'm a Circle.");    }}

CIS 330 15

Polymorphism Implementedusing System;

public class DrawDemo{    public static int Main( )    {        DrawingObject[] dObj = new DrawingObject[4];

        dObj[0] = new Line();        dObj[1] = new Circle();        dObj[2] = new Square();        dObj[3] = new DrawingObject();

        foreach (DrawingObject drawObj in dObj)        {            drawObj.Draw();        }

        return 0;    }}

CIS 330 16

Summary

• Polymorphism. It allows you to implement derived class methods through a base class pointer during run-time

• Implemented a derived class method that overrides a virtual method