August 2021
Intermediate to advanced
450 pages
4h 46m
Chinese
Content preview from 面向对象的思考过程（原书第5版）
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9.3.1 聚合
最直观的组合方式就是聚合。聚合意味着复杂的对象由其他对象构成。电视机是进行娱乐活动的干净整洁的平台。当收看高清电视时，你只看到了单个设备。大多数时候你不会思考高清电视机事实上是由一些晶体管、一个屏幕、一个控制器等器件组成。当然你可以看到用于控制高清电视机的开关，你也确实看得到屏幕。不过这不是通常人们认识高清电视机的方式。当进入一个电器商场时，销售人员不会说“请看这个晶体管、屏幕和开关等的聚合体”，他会说“请看这台高清电视机”。
同样，当你买汽车时，不会选择组成汽车的各个独立的组件。你并不会决定买什么样的火花塞以及什么样的门把手，你会直接买一辆车。当然你可以选择一些配件，但整个汽车对象已经提供了绝大多数的组件。汽车对象又由很多复杂的和简单的对象构成（请看图9.4）。
图9.4 车的聚合体系图
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