耦合和聚合（或者内聚）我敢保证这两个词，你会经常听到。同时我也敢说，你问一下你所有的同事，不会有几个人可以清楚地定义这两个词。以下定义来自《UML和模式应用 面向对象分析和设计导论》中译版，姚淑珍译。英文版《Applying UML and Patterns An introduction to Object-Oriented Analysis and Design》By Craig Larman

Firstly and most importantly, Designs that exhibit low coupling and high cohesion are preferred. What is coupling? coupling就是两个class之间的相关程度，所以越低越好。 Figure 1b provides an alternate design involving t