声明一个Shape抽象类，在此基础上派生出Rectangle和Circle类，二者都有GetArea（）和GetPerim（）函数，GetArea用来计算对象的面积，GetPerim用来计算对象的周长。封装上述各类，-Declare an abstract class Shape, on this basis, derived classes Rectangle and Circle, the two have GetArea () and GetPerim () function, GetArea used to calculate the object' s size, GetPerim used to calculate the object perimeter. The above types of packaging,