C#多态机制

using System;

public class DrawingObject
{
    public virtual void Draw()
    {
        Console.WriteLine("I'm just a generic drawing object.");
    }
}

using System;

public class Line : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Line.");
    }
}

public class Circle : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Circle.");
    }
}

public class Square : DrawingObject
{
    public override void Draw()
    {
        Console.WriteLine("I'm a Square.");
    }
}

using System;

public class DrawDemo
{
    public static int Main( )
    {
        DrawingObject[] dObj = new DrawingObject[4];

        dObj[0] = new Line();
        dObj[1] = new Circle();
        dObj[2] = new Square();
        dObj[3] = new DrawingObject();

        foreach (DrawingObject drawObj in dObj)
        {
            drawObj.Draw();
        }

        return 0;
    }
}

Output:

I'm a Line.
I'm a Circle.
I'm a Square.
I'm just a generic drawing object.

与C++相比，C#是一门明确的语言。子类重载了父类的函数要用new，重载了虚函数要用override，还能直接用base指代父类。