C#中的类（Class）

using System;

namespace testClassApp
{
    /// <summary>
    /// Class1 的摘要说明。
    /// </summary>
    class Class1
    {
        /// <summary>
        /// 应用程序的主入口点。
        /// </summary>
        [STAThread]
        static void Main(string[] args)
        {
            //
            // TODO: 在此处添加代码以启动应用程序
            //

            double len = 2.5;
            double wid = 3.0;
            double rad = 4.1;
            Rectangle aRect = new Rectangle();
            aRect.length = len;
            aRect.width = wid;
            Circle aCirc = new Circle (rad);
            Console.WriteLine ("Area of Rect is:{0}",aRect.Area ());
                Console.WriteLine ("Area of Rect is:{0}",aRect.Area (2));
            Console.WriteLine ("Area of Circ is:{0}",aCirc.Area ());
        }
    }

    abstract class Shape                //抽象基类，不可实例化
    {
        public const double pi=3.14;    //常量
        protected double x, y;            //私有，可继承变量

        public Shape()                    //默认构造函数
        {
            x=y=0;
        }
        public Shape(double x,double y)    //带参数构造函数
        {
            this.x = x;
            this.y = y;
        }
        public abstract double Area();    //抽象方法，需重载
    }

    class Rectangle: Shape
    {
        public Rectangle():base(){}
        public Rectangle(double x, double y): base(x,y){}//使用基类构造函数
        public  double Area()    //函数重载
        {
            return (x*y);
        }
        public  double Area(double x)    //函数重载
        {
            return (x*x);
        }
        public double length    //属性：矩形长度
        {
            get
            {
                return x;
            }
            set
            {
                if (value>0){x = value;}
            }
        }
        public double width        //属性：矩形宽度
        {
            get
            {
                return y;
            }
            set
            {
                if (value>0){y = value;}
            }
        }

    }

    class Ellipse: Shape
    {
        public Ellipse(double x, double y):base(x,y){}//使用基类Shape的构造函数
        public override double Area()    //函数重载
        {
            return pi*x*y;
        }
    }
    class Circle: Ellipse
    {
        public Circle(double r):base(r,0){}    //使用基类Ellipse的构造函数
        public override double Area()    //函数重载
        {
            return pi*x*x;
        }
    }

    
}