已知二维空间点Point2D类的定义如下，在此基础上派生出三维空间点Point3D类。根据数学，增加成员变量z，定义三个参数的构造方法和无参数的构造方法(对应原点的对象)，重写toString()和getDistance()方法，重写equals()方法。TestPoint类的main()方法定义3个以上点做测试，结果格式如下所示。(The definition of Point2D class of two dimensional space points is as follows. On this basis, the Point3D class of 3D space point is derived. According to mathematics, we increase the membership variable Z, define the construction method of three parameters and the construction method without parameter (the object corresponding to the origin), rewrite the toString () and getDistance () methods, and rewrite the equals () method. The TestPoint (main) method of class defines more than 3 points for testing, and the result format is as follows.)