1)　　定义接口PrintX，其中包括一个方法printMyWay()，这个方法没有形参，返回值为空。

2)　　编写矩形类，矩形类要求实现PrintX接口，有求面积、求周长的方法，printMyWay()方法要能显示矩形的边长、面积和周长。

3)　　编写正方形类作为矩形类的子类，正方形类继承了矩形类求面积和周长的方法，新增加求对角线长的方法，重写printMyWay()方法，要求该方法能显示正方形的边长、面积、周长和对角线长。

-1) defines the interface PrintX, including a method printMyWay (), this method is not a parameter, the return value is null. 2) preparation of a rectangle class Rectangle class required to achieve PrintX interfaces are asking area, find the circumference of the method, printMyWay () method to be able to display the rectangle side length, area and perimeter. 3) preparation of a square class as a subclass of the class rectangle, square rectangle class inherits the class for the area and perimeter of methods, new ways to increase demand diagonal, rewritten printMyWay () method, which requires that the method can display square side length, area, perimeter and diagonal.