在C#上以环形式构造一个形状

using System;

public class Shape
{
    public virtual void Draw()
    {
        Console.WriteLine("Drawing a shape...");
    }
}

public class Circle : Shape
{
    private double radius;

    public Circle(double radius)
    {
        this.radius = radius;
    }

    public override void Draw()
    {
        Console.WriteLine("Drawing a circle with radius {0}...", radius);
    }
}

public class Ring : Shape
{
    private double innerRadius;
    private double outerRadius;

    public Ring(double innerRadius, double outerRadius)
    {
        this.innerRadius = innerRadius;
        this.outerRadius = outerRadius;
    }

    public override void Draw()
    {
        Console.WriteLine("Drawing a ring with inner radius {0} and outer radius {1}...", innerRadius, outerRadius);
    }
}

public class Program
{
    public static void Main(string[] args)
    {
        Shape shape1 = new Circle(5);
        shape1.Draw();

        Shape shape2 = new Ring(3, 7);
        shape2.Draw();
    }
}