We can't instantiate instances of abstract classes, even when all their field and method members are concrete.

我们不能实例化一个抽象类，即使它们的字段和方法都是具体的。

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Client classes can be coded to require only the abstract type, leaving the strategies and outcomes of implementation to the concrete class instances passed to them at run time.

客户机类可被编码为只需要抽象类型，而把实现策略和结果留给在运行时传递给它们的具体类实例。

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Another helpful addition to PHP V5 is the abstract class, which makes it easy to have one base class to implement the core of an interface from which you then create concrete classes.

PHP V 5中另一个有帮助的新功能是抽象类，使用抽象类可以轻松地用一个基类实现接口的核心部分，然后用该接口创建实体类。

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