《HeadFirst设计模式》策略模式c实现

策略模式： 定义了算法族，分别封装起来，让它们之间可以互相替换，此模式让算法的变化独立于使用算法的客户。 The Strategy Pattern defines a family of algorithms, encapsulates each one, and makes interchangeable. Strategy lets the algorithm vary independently from clients that use it.