perl对象经典例题：创建两个类Bean.pm和Coffee.pm，其中Coffee.pm继承Bean.pm的一些功能。此例演示如何从基类（或称超类）继承实例变量，其方法为调用基类的构造函数并把自己的实例变量加到新对象中。-The Perl object classic example: create two classes Bean.pm and Coffee.pm, some of the features of Coffee.pm inheritance in Bean.pm. This example demonstrates how to　a base class (or super class) inherited instance variables, and the instance variables to the new object in the method for their own constructor calls the base class.