委托帮助子类去实现它的责任，你想委托某一个帮助子类来局部化信息。

Classes delegate responsibility to one of several helper subclasses, and you want to localize the knowledge of which helper subclass is the delegate.

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这帮助减少可能性的bug数：所有的子类被要求去做，满足了一个清晰的职责。

This helps to reduce the likelihood of bugs: all subclasses are required to do, is fulfill a clear contract.

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