中介者模式: 用一个中介对象来封装一系列的对象交互。中介者使各对象不需要显式地相互引用，从而使其耦合松散，而且可以独立地改变它们之间的交互。-Intermediary model: using an intermediary object to encapsulate the set of objects interact. Intermediaries to make objects do not need to explicitly refer to each other, making it loose coupling, and can be changed independently of the interaction between them.