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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7.2.1 泛化和特化
我们来设计Dog类模型继承体系图。先创建一个名为Dog的类，我们找出了各种各样品种的狗的共同之处。该概念有时被称为泛化到特化，这是使用继承时的又一个重要的考虑因素。即在继承树中越往下，事情变得越特殊。最通用的事情位于树的顶端。在Dog继承树中，Dog类是树的顶端，并且是最通用的分类。其他品种的类（GoldenRetriever类，LhasaApso类和Basenji类）更具体。继承的思想就是通过分解共性从通用走向具体。
图7.4 Dog类继承体系图
在Dog继承模型中，我们刚开始通过找出共同的行为来建模。比如尽管金毛猎犬和拉萨阿普索犬拥有不同的行为，但这些品种的狗都有一些共同的行为，比如它们都会吠叫。然后我们意识到不是所有的狗都会吠叫，有些会用假嗓音叫。因此，我们不得不把吠叫行为放置到单独的BarkingDog类中，而将用假嗓音叫的行为放置到YodelingDog类中。然而，我们意识到吠叫的狗和不会吠叫的狗仍然共享一些通用的行为，比如它们都会喘气。因此我们保留Dog类，让BarkingDog和YodelingDog类继承自它。现在Basenji可以继承自YodelingDog，而LhasaApso和GoldenRetrierer可以继承自BarkingDog。
我们也可以决定不为BarkingDog和YodelingDog创建两个截然不同的类。我们可以为每个独立品种的类实现各自的吠叫和假嗓音叫，因为每种狗的叫声是不同的。这只是众多设计决策的其中一个示例。大概最好的方案是将吠叫和喘气作为接口实现。第8章会讨论这一点。 ...
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