These classes delegate responsibility for base class behavior to an instance of the base class.
这些类将基础类行为的责任委托给基础类的一个实例。
Provides a base class for specifying dynamic behavior at run time.
提供用于指定运行时的动态行为的基类。
For example, you may extend a class to change the behavior of the base-class methods.
例如，您可能会扩充一个类别以变更基底类别方法的行为。
Overrides should call the base implementation to preserve this behavior.
重写应调用基实现来保留此行为。
Overrides should call the base implementation to preserve this behavior.
重写应调用基实现来保留此行为。
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