定义一个抽象类Shape,它包含两个属性X和Y和一个抽象方法Area()。不同的形状如Rentangle(矩形），circle(圆）派生自Shape类，并为每个图形计算面积。每个派生类都有各自的Area()重写实现。创建相应的实例并求出其面积。

我写了抽象类Shape，和Rentangle(矩形），圆一样的写法就不多写了！！！
 abstract class Shape
    {
        public Shape()
        {
        }
        public Shape(double x,double y)
        {
            this.x = x;
            this.y = y;
        }
        private double x;
        public double X
        {
            get { return x; }
            set { x = value; }
        }
        private double y;
        public double Y
        {
            get { return y; }
            set { y = value; }
        }
        public abstract double Area();
    }
    class Rentangle:Shape
    {
        public Rentangle(double x, double y)
        {
            base.X = x;
            base.Y = y;
        }

        public override double Area()
        {
            return X * Y;
        }
    }

对不起 少些了一行代码
Rentangle 构造函数下面应该写上 :base(x,y)

谢谢了。