Use virtual methods and polymorphism : Override Virtual : Class Interface C# Source Code

    

/*
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();    
    }  
  }  
}