When the implementation of the steps may need to vary at run time. Concrete inheritance can't accommodate this; delegation can.
当这个实现的步骤需要在运行时变化。类继承不能适应这个，代理能。
When the implementation of the steps may need to vary at run time. Concrete inheritance can't accommodate this; delegation can.
当这个实现的步骤需要在运行时变化。类继承不能适应这个，代理能。
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