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。
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。
This is usually not a problem in practice — it is not common practice to use a mutable object like a List as a key in a HashMap.
实践过程中这通常不是问题——我们并不经常使用象List这样的可修改对象做为hashmap中的关键字。
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