Reply To: subtype和subclass

[hui]

非常好的文章，多谢分享。其中谈到subclass与subtype的区别时是这样说的：Subclasses allow one to reuse the code inside classes – both instance variable declarations and method definitions. Thus they are useful in supporting code reuse inside a class. Subtyping on the other hand is useful in supporting reuse externally, giving rise to a form of polymorphism。即：子类用于类的内部重用，子类型用于外部重用。这个与《冒号课堂》中提到的观点本质上是一致的：实现继承消费可重用的旧代码，接口继承生产可重用的新代码；接口继承不是为了代码重用，而是为了代码被重用。

另：该文章的PDF版可到 http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.9.7539&rep=rep1&type=pdf 下载。