java定义一个点类(point),包含x,y坐标数据成员,显示函数(show)和计算面积(getarea)的函数成员。

Class Point{public int x;public int y;public Point(){}public void show(){}public int getarea(){}}Class Circle extends Point{public int r;public Circle(){}public int getarea(){return r*r;}}Class Line{public Point a=null;public Point b=null;public Line(int