Abstract methods used when one method can implement in more than one sub class with different implementation.

抽象方法时使用一个方法可以实现在多个接头与不同的实现类。

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Any class with an abstract method is automatically abstract itself, and must be declared as such. A class may be declared abstract even if it has no abstract methods.

任一类以一个抽象方法自动地是抽象的本身，且必须被声明，一个类可以被声明是抽象的既使它没有抽象方法。

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If you have an abstract class (any class with an abstract method becomes an abstract class), you can not create an object of that class.

如果你有一个抽象类(任何类的抽象方法成为一个抽象类)，您不能创建该类的一个对象。

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