C# Lesson 7

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 • Instanceclass members belong to a specific occurrence of a class • Static memberscan 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 Implemented using 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 CIS 330