现在我可以为pop方法编写行为，即确保当栈在逻辑上为空时，抛出一个异常。

Now I can code the behavior for the pop method, which ensures that if the stack is logically empty, an exception will be thrown.

youdao

在这种情况下，如果push没有被调用(或者从逻辑上讲，栈为空)的情况下确保pop抛出一个异常，则意味着栈有一个状态。

In this case, ensuring that pop throws an exception if push hasn't been called (or logically, if the stack is empty) means that the stack has a state.

youdao