输出也可能比仅指定模拟管脚编号更为具体，但是本机编号灵活性更好，因为它不会将任何一个管脚束缚到某一项作业上。

The output can be more specific than just specifying the analog pin number, but the generic number allows flexibility because it does not tie down any one pin to any one job.

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创建一个模拟对象类作为具体类中的一个子类。

Create a mock object class as a subclass of the concrete class.

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模拟具体类和接口的能力。

Ability to mock concrete classes and interfaces.

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