Csharp/C Sharp/Class Interface/Override Virtual

Class hierarchy: override and virtual

<source lang="csharp"> /*

* C# Programmers Pocket Consultant
* Author: Gregory S. MacBeth
* Email: gmacbeth@comporium.net
* Create Date: June 27, 2003
* Last Modified Date:
*/

using System; namespace Client.Chapter_5___Building_Your_Own_Classes {

 public class MyMainClass13
 {
   static void Main(string[] args)
   {
     //The function called is based
     //upon the type called by new.
     B MyB = new C();
     MyB.Display();    //Calls C"s Display
   }
 }
 abstract class A
 {
   public abstract void Display();
 }
 class B: A
 {
   public override void Display()
   {
     Console.WriteLine("Class B"s Display Method");
   }
 }
 class C: B
 {
   public override void Display()
   {
     Console.WriteLine("Class C"s Display Method");
   }
 }
 class D: C
 {
   public override void Display()
   {
     Console.WriteLine("Class D"s Display Method");
   }
 }

}

      </source>

Demonstrate a virtual method

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Demonstrate a virtual method.

using System;

class Base {

 // Create virtual method in the base class.  
 public virtual void who() { 
   Console.WriteLine("who() in Base"); 
 } 

}

class Derived1 : Base {

 // Override who() in a derived class. 
 public override void who() { 
   Console.WriteLine("who() in Derived1"); 
 } 

}

class Derived2 : Base {

 // Override who() again in another derived class. 
 public override void who() { 
   Console.WriteLine("who() in Derived2"); 
 } 

}

public class OverrideDemo {

 public static void Main() { 
   Base baseOb = new Base(); 
   Derived1 dOb1 = new Derived1(); 
   Derived2 dOb2 = new Derived2(); 

   Base baseRef; // a base-class reference 

   baseRef = baseOb;  
   baseRef.who(); 

   baseRef = dOb1;  
   baseRef.who(); 

   baseRef = dOb2;  
   baseRef.who(); 
 } 

}

      </source>

Demonstrates the use of a virtual method to override a base class method

<source lang="csharp"> /* C# Programming Tips & Techniques by Charles Wright, Kris Jamsa Publisher: Osborne/McGraw-Hill (December 28, 2001) ISBN: 0072193794

• /

// // Virtual.cs -- Demonstrates the use of a virtual method to override // a base class method. // // Compile this program with the following command line: // C:>csc Virtual.cs namespace nsVirtual {

   using System;
   
   public class VirtualclsMain
   {
       static public void Main ()
       {
           clsBase Base = new clsBase();
           clsFirst First = new clsFirst();
           clsSecond Second = new clsSecond();
           Base.Show();
           First.Show();
           Second.Show ();
       }
   }
   class clsBase
   {
       public void Show ()
       {
           Describe ();
       }
       virtual protected void Describe ()
       {
           Console.WriteLine ("Called the base class Describe() method");
       }
   }
   class clsFirst : clsBase
   {
       override protected void Describe ()
       {
           Console.WriteLine ("Called the derived class Describe() method");
       }
   }
   class clsSecond : clsBase
   {
   }

}

      </source>

Demonstrates the use of a virtual property to override a base class property

<source lang="csharp"> /* C# Programming Tips & Techniques by Charles Wright, Kris Jamsa Publisher: Osborne/McGraw-Hill (December 28, 2001) ISBN: 0072193794

• /

// // VProp.cs -- Demonstrates the use of a virtual method to override // a base class method. // // Compile this program with the following command line: // C:>csc VProp.cs namespace nsVirtual {

   using System;
   
   public class VPropclsMain
   {
       static public void Main ()
       {
           clsBase Base = new clsBase();
           clsFirst First = new clsFirst();
           Base.SetString ("This should set the base class property");
           First.SetString ("This should set the derived class property");
           Console.WriteLine();
           Console.WriteLine (Base.GetString());
           Console.WriteLine (First.GetString());
       }
   }
   class clsBase
   {
 public void SetString (string str)
       {
           StrProp = str;
       }
       public string GetString ()
       {
           return (StrProp);
       }
       virtual protected string StrProp
       {
           get
           {
               Console.WriteLine ("Getting Base string");
               return (m_BaseString);
           }
           set
           {
               Console.WriteLine ("Setting Base string");
               m_BaseString = value;
           }
       }
       private string m_BaseString = "";
   }
   class clsFirst : clsBase
   {
       override protected string StrProp
       {
           get
           {
               Console.WriteLine ("Getting derived string");
               return (m_DerivedString);
           }
           set
           {
               Console.WriteLine ("Setting derived string");
               m_DerivedString = value;
           }
       }
       private string m_DerivedString = "";
  }

}

      </source>

illustrates polymorphism

<source lang="csharp"> /* Mastering Visual C# .NET by Jason Price, Mike Gunderloy Publisher: Sybex; ISBN: 0782129110

• /

/*

 Example7_2.cs illustrates polymorphism

• /

using System;

// declare the MotorVehicle class class MotorVehicle {

 // declare the fields
 public string make;
 public string model;
 // define a constructor
 public MotorVehicle(string make, string model)
 {
   this.make = make;
   this.model = model;
 }
 // define the Accelerate() method (may be overridden in a
 // derived class)
 public virtual void Accelerate()
 {
   Console.WriteLine(model + " accelerating");
 }

}

// declare the Car class (derived from MotorVehicle) class Car : MotorVehicle {

 // define a constructor
 public Car(string make, string model) :
 base(make, model)
 {
   // do nothing
 }
 // override the base class Accelerate() method
 public override void Accelerate()
 {
   Console.WriteLine("Pushing gas pedal of " + model);
   base.Accelerate();  // calls the Accelerate() method in the base class
 }

}

// declare the Motorcycle class (derived from MotorVehicle) class Motorcycle : MotorVehicle {

 // define a constructor
 public Motorcycle(string make, string model) :
 base(make, model)
 {
   // do nothing
 }
 // override the base class Accelerate() method
 public override void Accelerate()
 {
   Console.WriteLine("Twisting throttle of " + model);
   base.Accelerate();  // calls the Accelerate() method in the base class
 }

}

public class Example7_2 {

 public static void Main()
 {
   // create a Car object and call the object"s Accelerate() method
   Car myCar = new Car("Toyota", "MR2");
   myCar.Accelerate();
   // create a Motorcycle object and call the object"s Accelerate() method
   Motorcycle myMotorcycle = new Motorcycle("Harley-Davidson", "V-Rod");
   myMotorcycle.Accelerate();
 }

}

      </source>

Method override 3

<source lang="csharp"> /* Learning C# by Jesse Liberty Publisher: O"Reilly ISBN: 0596003765

• /

using System;
class Dog
{
    private int weight;
    // constructor
    public Dog(int weight)
    {
        this.weight = weight;
    }
    // override Object.ToString
    public override string ToString()
    {
        return weight.ToString();
    }
}

public class TesterOverride
{
    static void Main()
    {
        int i = 5;
        Console.WriteLine("The value of i is: {0}", i.ToString());
        Dog milo = new Dog(62);
        Console.WriteLine("My dog Milo weighs {0} pounds", milo.ToString());
    }
}
          
      </source>

Polymorphism

<source lang="csharp">

using System; public class MotorVehicle {

   public string make;
   public string model;
   public MotorVehicle(string make, string model) {
       this.make = make;
       this.model = model;
   }
   public virtual void Accelerate() {
       Console.WriteLine(model + " accelerating");
   }

} public class Product : MotorVehicle {

   public Product(string make, string model) :
       base(make, model) {
   }
   public override void Accelerate() {
       Console.WriteLine("Pushing gas pedal of " + model);
       base.Accelerate();
   }

} public class Motorcycle : MotorVehicle {

   public Motorcycle(string make, string model) :
       base(make, model) {
       // do nothing
   }
   public override void Accelerate() {
       Console.WriteLine("Twisting throttle of " + model);
       base.Accelerate();
   }

}

class MainClass {

   public static void Main() {
       Product myProduct = new Product("Toyota", "MR2");
       myProduct.Accelerate();
       Motorcycle myMotorcycle =
         new Motorcycle("Harley-Davidson", "V-Rod");
       myMotorcycle.Accelerate();
   }

}

</source>

Test Polymorphism Virtual Functions

<source lang="csharp"> /* A Programmer"s Introduction to C# (Second Edition) by Eric Gunnerson Publisher: Apress L.P. ISBN: 1-893115-62-3

• /

// 01 - Object-Oriented Basics\Polymorphism and Virtual Functions // copyright 2000 Eric Gunnerson using System; public PolymorphismVirtualFunctions {

   public static void CallPlay(MusicServer ms)
   {
       ms.Play();
   }
   public static void Main()
   {
       MusicServer ms = new WinAmpServer();
       CallPlay(ms);
       ms = new MediaServer();
       CallPlay(ms);
   }

} public abstract class MusicServer {

   public abstract void Play();

} public class WinAmpServer: MusicServer {

   public override void Play() 
   {
       Console.WriteLine("WinAmpServer.Play()");
   }

} public class MediaServer: MusicServer {

   public override void Play() 
   {
       Console.WriteLine("MediaServer.Play()");
   }

}

      </source>

Use virtual methods and polymorphism

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

// Use virtual methods and polymorphism.

using System;

class TwoDShape {

 double pri_width;  // private 
 double pri_height; // private 
 string pri_name;   // private 
 
 // A default constructor.  
 public TwoDShape() {  
   width = height = 0.0;  
   name = "null";  
 }  
 
 // Parameterized constructor.  
 public TwoDShape(double w, double h, string n) {  
   width = w;  
   height = h;  
   name = n;  
 }  
 
 // Construct object with equal width and height.  
 public TwoDShape(double x, string n) {  
   width = height = x;  
   name = n;  
 }  
 
 // Construct an object from an object.  
 public TwoDShape(TwoDShape ob) {  
   width = ob.width;  
   height = ob.height;  
   name = ob.name;  
 }  
 
 // Properties for width, height, and name 
 public double width { 
   get { return pri_width; } 
   set { pri_width = value; } 
 } 

 public double height { 
   get { return pri_height; } 
   set { pri_height = value; } 
 } 

 public string name { 
   get { return pri_name; } 
   set { pri_name = value; } 
 } 
 
 public void showDim() {  
   Console.WriteLine("Width and height are " +  
                      width + " and " + height);  
 }  
 
 public virtual double area() {   
   Console.WriteLine("area() must be overridden");  
   return 0.0;  
 }   

}

// A derived class of TwoDShape for triangles. class Triangle : TwoDShape {

 string style; // private 
   
 // A default constructor.  
 public Triangle() {  
   style = "null";  
 }  
 
 // Constructor for Triangle.  
 public Triangle(string s, double w, double h) : 
   base(w, h, "triangle") {  
     style = s;   
 }  
 
 // Construct an isosceles triangle.  
 public Triangle(double x) : base(x, "triangle") {  
   style = "isosceles";   
 }  
 
 // Construct an object from an object.  
 public Triangle(Triangle ob) : base(ob) {  
   style = ob.style;  
 }  
 
 // Override area() for Triangle. 
 public override double area() {  
   return width * height / 2;  
 }  
 
 // Display a triangle"s style. 
 public void showStyle() {  
   Console.WriteLine("Triangle is " + style);  
 }  

}

// A derived class of TwoDShape for rectangles. class Rectangle : TwoDShape {

 // Constructor for Rectangle.  
 public Rectangle(double w, double h) :  
   base(w, h, "rectangle"){ }  
 
 // Construct a square.  
 public Rectangle(double x) :  
   base(x, "rectangle") { }  
 
 // Construct an object from an object.  
 public Rectangle(Rectangle ob) : base(ob) { }  
 
 // Return true if the rectangle is square. 
 public bool isSquare() {   
   if(width == height) return true;   
   return false;   
 }   
    
 // Override area() for Rectangle. 
 public override double area() {   
   return width * height;   
 }   

}

public class DynShapes {

 public static void Main() {  
   TwoDShape[] shapes = new TwoDShape[5];  
 
   shapes[0] = new Triangle("right", 8.0, 12.0);  
   shapes[1] = new Rectangle(10);  
   shapes[2] = new Rectangle(10, 4);  
   shapes[3] = new Triangle(7.0);  
   shapes[4] = new TwoDShape(10, 20, "generic"); 
 
   for(int i=0; i < shapes.Length; i++) {  
     Console.WriteLine("object is " + shapes[i].name);  
     Console.WriteLine("Area is " + shapes[i].area());  
 
     Console.WriteLine();    
   }  
 }  

}

      </source>

Virtual and overload

<source lang="csharp"> /*

* C# Programmers Pocket Consultant
* Author: Gregory S. MacBeth
* Email: gmacbeth@comporium.net
* Create Date: June 27, 2003
* Last Modified Date:
*/

using System; namespace Client.Chapter_5___Building_Your_Own_Classes {

 public class MyMainClass12 {
   static void Main(string[] args)
   {
     //The function called is based
     //upon the type called by new.
     B MyB = new C();
     D MyD = new D();
     MyB.Display();    //Calls C Display
     MyD.Display();    //Calls D Display
   }
 }
 public interface A
 {
   void Display();
 }
 class B: A
 {
   public virtual void Display()
   {
     Console.WriteLine("Class B"s Display Method");
   }
 }
 class C: B
 {
   public override void Display()
   {
     Console.WriteLine("Class C"s Display Method");
   }
 }
 class D: C
 {
   public override void Display()
   {
     Console.WriteLine("Class D"s Display Method");
   }
 }

}

      </source>

Virtual keyword can be used to start a new inheritance ladder

<source lang="csharp"> using System; public class Class1 {

   public static void Main(string[] strings) {
       BankAccount ba = new BankAccount();
       Test1(ba);
       SavingsAccount sa = new SavingsAccount();
       Test1(sa);
       Test2(sa);
       SpecialSaleAccount ssa = new SpecialSaleAccount();
       Test1(ssa);
       Test2(ssa);
       Test3(ssa);
       SaleSpecialCustomer ssc = new SaleSpecialCustomer();
       Test1(ssc);
       Test2(ssc);
       Test3(ssc);
       Test4(ssc);
   }
   public static void Test1(BankAccount account) {
       Console.Write("to Test(BankAccount)");
       account.Withdrawal(100);
   }
   public static void Test2(SavingsAccount account) {
       Console.Write("to Test(SavingsAccount)");
       account.Withdrawal(100);
   }
   public static void Test3(SpecialSaleAccount account) {
       Console.Write("to Test(SpecialSaleAccount)");
       account.Withdrawal(100);
   }
   public static void Test4(SaleSpecialCustomer account) {
       Console.Write("to Test(SaleSpecialCustomer)");
       account.Withdrawal(100);
   }

} public class BankAccount {

   virtual public void Withdrawal(double dWithdrawal) {
       Console.WriteLine(" invokes BankAccount.Withdrawal()");
   }

} public class SavingsAccount : BankAccount {

   override public void Withdrawal(double dWithdrawal) {
       Console.WriteLine(" invokes SavingsAccount.Withdrawal()");
   }

} public class SpecialSaleAccount : SavingsAccount {

   new virtual public void Withdrawal(double dWithdrawal) {
       Console.WriteLine(" invokes SpecialSaleAccount.Withdrawal()");
   }

} public class SaleSpecialCustomer : SpecialSaleAccount {

   override public void Withdrawal(double dWithdrawal) {
       Console.WriteLine
         (" invokes SaleSpecialCustomer.Withdrawal()");
   }

}

</source>

When a virtual method is not overridden, the base class method is used

<source lang="csharp"> /* C#: The Complete Reference by Herbert Schildt Publisher: Osborne/McGraw-Hill (March 8, 2002) ISBN: 0072134852

• /

/* When a virtual method is not overridden,

  the base class method is used. */ 

using System;

class Base {

 // Create virtual method in the base class.  
 public virtual void who() { 
   Console.WriteLine("who() in Base"); 
 } 

}

class Derived1 : Base {

 // Override who() in a derived class. 
 public override void who() { 
   Console.WriteLine("who() in Derived1"); 
 } 

}

class Derived2 : Base {

 // This class does not override who(). 

}

public class NoOverrideDemo {

 public static void Main() { 
   Base baseOb = new Base(); 
   Derived1 dOb1 = new Derived1(); 
   Derived2 dOb2 = new Derived2(); 

   Base baseRef; // a base-class reference 

   baseRef = baseOb;  
   baseRef.who(); 

   baseRef = dOb1;  
   baseRef.who(); 

   baseRef = dOb2;  
   baseRef.who(); // calls Base"s who() 
 } 

}

      </source>