你已经看到了另一个类层次的实例，它很好的阐明了子类化的概念。

You've actually seen one instance of another class hierarchy that also serves as a good illustration of the idea of extension by subclassing.

youdao

你已经看到了另一个类层次的实例，它很好的阐明了子类化的概念。

You've actually seen one instance of another class hierarchy that also serves as a good illustration of the idea of extension by subclassing.

youdao