假设我有一个接口 C 和一个实现它的类 A。
现在假设我想将 A 的实现更改为 C 中的所有函数，除了一个，使用类 B。我应该扩展 A 并覆盖 C 还是应该将 C 实现为新的独立类？
假设一些电话公司想要实现他们的基本接口 Phone 并且他们已经有一些 OldPhone 的旧实现，他们希望保留它的所有功能：拨打电话、挂断、发送 SMS - 而他们不想要改变这一切，但他们确实希望其他新功能来制造他们的新智能手机——他们应该扩展 OldPhone 还是创建一个新类？
我想知道什么时候应该扩展类，什么时候应该从一开始就实现接口——一方面我不想复制代码，但另一方面有时类型，即使它们都是 A，也是概念上不同。
If there is shared functionality in OldPhone and SmartPhone you could extract that into a (abstract)class and let both extend that and let them have the other as diffrences.
Otherwise go for interface
If you have code which you want to reuse, then extending is the better choice.
But ask yourself: is the new phone a better version of the old one or a completely new one just with similiar functions?
It rather depends on how much changes from C (old phone) to B (new phone). Using phones as an example is quite good because an old phone conceptually does the same as a new phone - it makes phone calls.
The difficultly comes when the implementation of C is tied very tightly to how the phone works. Lets say for example that the old phone insists on using a circular ring that you turn to select the number to dial rather than a key pad. In that situation, if you have complete control of the code, then you might want to try and put in a layer of abstraction between the interface and the old phone. The abstraction layer would capture just what it means to be a phone and nothing more.
Once you have the abstraction layer you can then choose whether you extend the old phone to create your new phone or create a new implementation. Either way it should be easier than you have now as the old phone will contain far less code and only those bits that are specific to it.
现在看你的要求说 B 对于大多数功能应该表现得与 A 完全一样。现在假设您选择实现即 B 实现 C。那么如果将来 A 类逻辑发生更改，那么您还必须更改 B 类。所以它不符合您的要求。
现在假设你扩展了 A。但是你与 A 紧密耦合。好像 A 改变了你的 Big 也会以同样的方式表现。
所以尽量让两个词的使用发挥最大的作用。B 实现 C 并使用A 作为委托来实现这些方法。我的回答是，对于您的情况，它不一定是每种情况下的最佳选择。
经验法则，只有在存在父子关系时才应该扩展一个类。否则去接口实现。