Saturday, 25 July 2015

Difference between HashMap and ConcurrentHashMap

HashMap and ConcurrentHashMap are two different types of hashMap in java.Both implements Map interface but their internal working is different.

                                                     HashMap Vs ConcurrentHashMap


Null Value/Key

 It allow null value as well as key.
 It does not allow null values and keys.
 Thread Safe 

No.In order to make hashmap thread safe we need to use Collections.synchronized(Map) method

 It does not allow concurrent access to multiple threads
 It allows a very high level of concurrency. Multiple threads can work on different portion of ConcurrentHashMap

 It implements fail fast.
 It implements fail safe.

Study internal working of both types of hashMap .It’s very important concept asked in interviews.

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