Difference between HashMap and ConcurrentHashMap.

In multiple threaded environment HashMap is usually faster than ConcurrentHashMap .

ConcurrentHashMap does not allow NULL values as well as key can not be null in ConcurrentHashMap .While In HashMap there can only be one null key .

ConcurrentHashMap is thread-safe while HashMap is not thread-safe .

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Set and its implementations

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Java / Map and its implementations

Difference between HashMap and ConcurrentHashMap.

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