Java ConcurrentHashMap merge() Method

The merge() method of ConcurrentHashMap class merge sets If the specified key is not already associated with a (non-null) value, associates it with the given value.

Syntax

public V merge(K key, V value, BiFunction<? super V,? super V,? extends V> remappingFunction)

Parameter

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

value - the value to use if absent

remappingFunction - the function to recompute a value if present

Returns

The new value associated with the specified key, or null if none

Throws

No Exception is thrown.

Example 1

import java.util.*; 
import java.util.concurrent.*; 
  
public class ConcurrentHashMapmergeExample1  { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String>  conmap = new ConcurrentHashMap<Integer, String>();
 
                conmap.put(1, "Java");
                conmap.put(2, "php");
                conmap.put(3, ".net");
                conmap.put(5, "python");
        
        ConcurrentHashMap<Integer, String>  conmap2 = new ConcurrentHashMap<Integer, String>();
 
                conmap2.put(1, "C");
                conmap2.put(2, "C++");
                conmap2.put(3, "Rubi");
                conmap2.put(5, "Java Script");
                
                conmap2.forEach(
                      (key, value) -> conmap.merge( key, value, (v1, v2) -> v1.equalsIgnoreCase(v2) ? v1 : v1 + "," + v2)
                               );
 
                      System.out.println(conmap);
 
    } 
}

Test it Now

Output:

{1=Java,C, 2=php,C++, 3=.net,Rubi, 5=python,Java Script}

Example 2

import java.util.*; 
import java.util.concurrent.*; 
  
public class ConcurrentHashMapmergeExample2  { 
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String>  conmap = new ConcurrentHashMap<Integer, String>();
 
                conmap.put(1, "A");
                conmap.put(2, "B");
                conmap.put(3, "C");
                conmap.put(5, "E");
        
        ConcurrentHashMap<Integer, String>  conmap2 = new ConcurrentHashMap<Integer, String>();
 
                conmap2.put(1, "F");
                conmap2.put(2, "G");
                conmap2.put(3, "H");
                conmap2.put(5, "I");
                
                conmap2.forEach(
                      (key, value) -> conmap.merge( key, value, (v1, v2) -> v1.equalsIgnoreCase(v2) ? v1 : v1 + "," + v2)
                               );
 
System.out.println(conmap);
        
    } 
}

Test it Now

Output: