May 19th, 2013 at 12:33 AM

Polymorphism C#

Polymorphism is often referred to as the third pillar of object-oriented programming, after encapsulation and inheritance. Virtual methods enable you to work with groups of related objects in a uniform way. For example, suppose you have a drawing application that enables a user to create various kinds of shapes on a drawing surface. You don't know at compile time which specific types of shapes the user will create. However, the application has to keep track of all the various types of shapes that are created, and it has to update them in response to user mouse actions. You can use polymorphism to solve this problem in two basic steps: Create a class hierarchy in which each specific shape class derives from a common base class. Use a virtual method to invoke the appropriate method on any derived class through a single call to the base class method. First, create a base class called Shape, and derived classes such as Rectangle, Circle, and Triangle. Give the Shape class a virtual method called Draw, and override it in each derived class to draw the particular shape that the class represents. Create a List<Shape> object and add a Circle, Triangle, and Rectangle to it. Example 2

public class Shape
{
    // A few example members
    public int X { get; private set; }
    public int Y { get; private set; }
    public int Height { get; set; }
    public int Width { get; set; }

    // Virtual method
    public virtual void Draw()
    {
        Console.WriteLine("Performing base class drawing tasks");
    }
}

public class Circle : Shape
{
    public override void Draw()
    {
        // Code to draw a circle...
        Console.WriteLine("Drawing a circle");
        base.Draw();
    }
}
public class Rectangle : Shape
{
    public override void Draw()
    {
        // Code to draw a rectangle...
        Console.WriteLine("Drawing a rectangle");
        base.Draw();
    }
}
public class Triangle : Shape
{
    public override void Draw()
    {
        // Code to draw a triangle...
        Console.WriteLine("Drawing a triangle");
        base.Draw();
    }
}

[code] // Polymorphism at work #1: a Rectangle, Triangle and Circle // can all be used wherever a Shape is expected. No cast is // required because an implicit conversion exists from a derived // class to its base class. var shapes = new List<Shape> { new Rectangle(), new Triangle(), new Circle() }; // Polymorphism at work #2: the virtual method Draw is // invoked on each of the derived classes, not the base class. foreach (var shape in shapes) { shape.Draw(); } /* Output: Drawing a rectangle Performing base class drawing tasks Drawing a triangle Performing base class drawing tasks Drawing a circle Performing base class drawing tasks */ [code]