containskey
containskey-
Unfortunately , as written , it is possible for another thread to insert a value with the same key between the time the containsKey () method returns and the time the put () method is called .
不幸的是，在containsKey（）方法返回到put（）方法被调用这段时间内，可能会有另一个线程也插入一个带有相同键的值。
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When a Map is accessed from multiple threads , it 's common to use either containsKey () or get () to find out whether a given key is present before storing the key / value pair .
当一个Map被从多个线程访问时，通常使用containsKey（）或者get（）来查看给定键是否在存储键/值对之前出现。