组合模式 c#

using System;
using System.Collections;
using System.Collections.Generic;
using System.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        public abstract class Shape
        {
            private string name;

            public Shape(string name)
            {
                this.name = name;
            }

            public abstract double Area();

            public abstract void Display();
        }

        public class Circle : Shape
        {
            private double radius;

            public Circle(string name, double radius) : base(name)
            {
                this.radius = radius;
            }

            public override double Area()
            {
                return Math.Round(Math.PI*radius*radius);
            }

            public override void Display()
            {
                Console.WriteLine("面积 : " + Area());
            }
        }

        public class Line : Shape
        {
            public Line(string name) : base(name)
            {
            }

            public override double Area()
            {
                Console.WriteLine("can not calculat area");
                return 0;
            }

            public override void Display()
            {
                Console.WriteLine("can not display area");
            }
        }

        static void Main(string[] args)
        {
            Circle circle = new Circle("circle", 5f);
            circle.Display();

            Line line = new Line("line");
            line.Display();
        }
    }
}