Virtual Keyword Codelisting

Declare a method/property virtual to be able to change the implementation in a derived class
By default methods are non-virtual
Virtual cannot be used with static, abstract and override
It is an error to use virtual modifier on a static property

Code Listing: Virtual

using System;
class TestClass
{
public class Dimensions
{
public const double pi = Math.PI;
protected double x, y;
public Dimensions() {}

public Dimensions (double x, double y)
{
this.x = x;
this.y = y;
}

public virtual double Area()
{
return x*y;
}
}


public class Circle: Dimensions
{
public Circle(double r): base(r, 0) { }

public override double Area()
{
return pi * x * x;
}
}

class Sphere: Dimensions
{
public Sphere(double r): base(r, 0) {}

public override double Area()
{
return 4 * pi * x * x;
}
}



class Cylinder: Dimensions
{
public Cylinder(double r, double h): base(r, h) { }

public override double Area()
{
return 2*pi*x*x + 2*pi*x*y;
}
}


public static void Main()
{
double r = 3.0, h = 5.0;
Dimensions c = new Circle(r);
Dimensions s = new Sphere(r);
Dimensions l = new Cylinder(r, h);

// Display results:
Console.WriteLine("Area of Circle = {0:F2}", c.Area());
Console.WriteLine("Area of Sphere = {0:F2}", s.Area());
Console.WriteLine("Area of Cylinder = {0:F2}", l.Area());
}

}