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

import java.util.concurrent.*; 
  
public class ConcurrentHashMapputIfAbsentExample1  { 
  
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<String, Integer> mapcon 
            = new ConcurrentHashMap<>(); 
        mapcon.put("alfabets", 26); 
        mapcon.put("digits", 9); 
        mapcon.put("vowels", 5);        
        System.out.println("ConcurrentHashMap values : " + mapcon.toString());  
        mapcon.putIfAbsent("consonent",  21); 
        System.out.println("new ConcurrentHashMap after  putIfAbsent : "+ mapcon); 
    } 
}

Test it Now

Output:

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

Example 2

import java.util.concurrent.*; 
  
import java.util.*; 
  
public class ConcurrentHashMapputIfAbsentExample2 { 
  
    public static void main(String[] args) 
    { 
          // crete a HashMap and add some values 
        HashMap<String, Integer> mapcon 
            = new HashMap<>(); 
        mapcon.put("k1", 100); 
        mapcon.put("k2", 200); 
        mapcon.put("k3", 300); 
        mapcon.put("k4", 400); 
        System.out.println("HashMap values :\n " + mapcon.toString());  
        mapcon.putIfAbsent("k5", 300); 
        mapcon.putIfAbsent("k6",  10); 
        System.out.println("New HashMap after putIfAbsent :\n "+ mapcon); 
    } 
}

Test it Now

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}

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