Step1:

为实验3中定义的矩形类派生一个子类：正方形类。正方形类的操作同样是求周长和面积。则这个子类除了从父类继承来的方法之外，还需要定义哪些方法？列出正方形类的所有域与方法。编程验证所编写的正方形类。

Step2:

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

Step3:

改写矩形类使之实现Printable接口，用printItMyWay()方法将矩形的相关信息（长，宽，周长，面积）打印在屏幕上。

Step4:

改写正方形类，重载printItMyWay()方法，将正方形的边长、周长、面积打印在屏幕上。

Step5: 最后将矩形和正方形组织成一个包MyFigures。

-Step1: for the experiment three rectangle defined class derived a subclass: Square classes. Square type of operation is also seeking perimeter and area. Then in addition to this subclass inherited from the parent class methods, but also need to define what methods? Square class lists all domains and methods. Written verification squares programming class. Step2: defines the interface Printable, including a method printItMyWay (), this method does not shape parameter, the return value is null. Step3: rewrite Rectangle class that met Printable interface with printItMyWay () method of the rectangle information (length, width, perimeter, area) printed on the screen. Step4: rewrite the square class, overloading printItMyWay () method, the square side length, perimeter, area printed on the screen. Step5: Finally, rectangles and squares organized into a package MyFigures.