You should also remember that static classes that preserve state between method calls should be made thread safe by default.
您还应该记得，在方法调用之间保留状态的静态类在默认情况下应该是线程安全的。
Some classes retain state information from one method invocation to the next, and it is difficult to make such classes thread-safe in any practical way.
有些类保留从一个方法调用到下一个方法调用的状态信息，要在实践中使这样的类成为线程安全的是困难的。
One advantage of immutable classes is that they are thread-safe.
(不可变类的一个优点就是它们是线程安全的)。
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