Java ConcurrentHashMap putIfAbsent() Method

The putIfAbsent() method of ConcurrentHashMap class maps the specified keys and values if the specified key is not already mapped with any value.

Syntax

Parameter

key – key with which the specified value is to be associated

value – value to be associated with the specified key

Returns

The previous value associated with key, or null if there was no mapping for key

Throw

NullPointerException.

Example 1

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Output:

ConcurrentHashMap values : {vowels=5, digits=9, alfabets=26}  new ConcurrentHashMap after  putIfAbsent : {vowels=5, consonent=21, digits=9, alfabets=26}  

Example 2

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Output:

HashMap values :   {k1=100, k2=200, k3=300, k4=400}  New HashMap after putIfAbsent :   {k1=100, k2=200, k3=300, k4=400, k5=300, k6=10}