如果某项操作被宣布为抽象的那么继承的类必须提供了一个具体的实施方案。

If an operation is declared as abstract then the inheriting class must provide a concrete implementation.

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在继承中，派生类接受基类的成员变量和方法。这表示继承的顺序必须在对象构造的时候被遵守。

In inheritance, the derived class receives the base class member variables and methods. This means that an order of inheritance must be followed during the construction of an object.

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第三方的类必须被重写，只能从抽象类继承。

A third party class must be rewritten to extend only from the abstract class.

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