将笛卡尔坐标系上的点定义为一个服务类point，point类求坐标系上两点间的距离。设计测试point服务类的应用程序主类，显示输出已创建对象间的距离。(The point on the Descartes coordinate system is defined as a service class point, and the point class is used to find the distance between two points in the coordinate syste