Virtual methods and polymorphism

using System; //from  j  a  v  a 2s .c o  m
 
class Shape {  
  double pri_width;  // private 
  double pri_height; // private 
  string pri_name;   // private 
  
  public Shape() {  
    width = height = 0.0;  
    name = "null";  
  }  
  
  public Shape(double w, double h, string n) {  
    width = w;  
    height = h;  
    name = n;  
  }  
  
  public Shape(double x, string n) {  
    width = height = x;  
    name = n;  
  }  
  
  public Shape(Shape 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;  
  }   
}  
  
class Triangle : Shape {  
  string style; // private 
    
  public Triangle() {  
    style = "null";  
  }  
  
  public Triangle(string s, double w, double h) : 
    base(w, h, "triangle") {  
      style = s;   
  }  
  
  public Triangle(double x) : base(x, "triangle") {  
    style = "isosceles";   
  }  
  
  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);  
  }  
}  
  
class Rectangle : Shape {   
  public Rectangle(double w, double h) : base(w, h, "rectangle"){ }  
  
  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;   
  }   
}  
  
class DynShapes {  
  public static void Main() {  
    Shape[] shapes = new Shape[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 Shape(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();    
    }  
  }  
}