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// New Shape derived class named Triangle.

public class Triangle : Shape, IPointy

{

public Triangle() { }

public Triangle(string name) : base(name) { }

public override void Draw()

{ Console.WriteLine("Drawing {0} the Triangle", PetName); }

// IPointy Implementation.

public byte Points

{

get { return 3; }

}

}

Now, update your existing Hexagon type to also support the IPointy interface type:

// Hexagon now implements IPointy.

public class Hexagon : Shape, IPointy

{

public Hexagon(){ }

public Hexagon(string name) : base(name){ }

public override void Draw()

{ Console.WriteLine("Drawing {0}  the Hexagon", PetName); }

// IPointy Implementation.

public byte Points

{

get { return 6; }

}

}

To sum up the story so far, the Visual Studio 2008 class diagram shown in Figure 9-2 illustrates

IPointy-compatible classes using the popular “lollipop” notation. Notice again that Circle and

ThreeDCircle do not implement IPointy, as this behavior makes no sense for these particular types.

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Figure 9-2.

The shapes hierarchy (now with interfaces)