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C# / CSharp Tutorial » Class » virtual 
7.23.12.Use virtual methods and polymorphism.
using System; 
 
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 == heightreturn 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[0new Triangle("right"8.012.0);  
    shapes[1new Rectangle(10);  
    shapes[2new Rectangle(104);  
    shapes[3new Triangle(7.0);  
    shapes[4new Shape(1020"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();    
    }  
  }  
}
object is triangle
Area is 48

object is rectangle
Area is 100

object is rectangle
Area is 40

object is triangle
Area is 24.5

object is generic
area() must be overridden
Area is 0
7.23.virtual
7.23.1.Virtual Methods and Overriding
7.23.2.Override virtual functions
7.23.3.new virtual method
7.23.4.Override virtual method
7.23.5.Define virtual function in base and its subclass
7.23.6.Class inheritance with virtual method
7.23.7.Illustrates versioning: virtual/new
7.23.8.Illustrates polymorphism
7.23.9.Demonstrate a virtual method.
7.23.10.When a virtual method is not overridden, the base class method is used
7.23.11.Virtual method in a multilevel hierarchy
7.23.12.Use virtual methods and polymorphism.
7.23.13.Virtual Accessor
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