More often than not, they involve mutable object state.

而它们时常也会涉及易变的对象状态。

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Clearly, this approach is a pain but the solution is easy: Never use a mutable object type as a key in a HashMap.

很显然，这种方法很糟糕，但是解决方法也很简单：永远不要将可变对象类型用作hashmap中的键。

youdao

This makes a difference when the default is a mutable object such as a list, dictionary, or instances of most classes.

当默认值是一个可变对象，诸如链表、字典或大部分类实例时，会产生一些差异。

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