Java ConcurrentHashMap compute() Method

The compute() method of ConcurrentHashMap class is used to compute the mapping for the specified key and its current value.

Syntax

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

Parameter

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

remappingFunction - the function to compute a value.

Returns

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

Throws

NullPointerException

IllegalStateException

RuntimeException

Example 1

//import statement  
import java.util.concurrent.ConcurrentHashMap; 
import java.util.*; 
import java.util.function.BiFunction;
  
public class ConcurrentHashMapcomputeExample1 { 
  
    public static void main(String[] args) 
    { 
        Map<String, String> chm = new ConcurrentHashMap<String, String>(); 
  //put is used to add value to map
        chm.put("1", "1"); 
        chm.put("2", "10"); 
        chm.put("3", "100"); 
        chm.put("4", "2"); 
        chm.put("5", "20"); 
        chm.put("6", "200"); 
  
        System.out.println("Values in map with detail: \n"
                           + chm.toString()); 
          chm.compute("6", (key , val) 
                                 -> val + 100); 
        System.out.println("Map after using  compute(): "
                    
                + chm); 
    }
}

Test it Now

Output:

Values in map with detail: 
{1=1, 2=10, 3=100, 4=2, 5=20, 6=200}
Map after using  compute(): {1=1, 2=10, 3=100, 4=2, 5=20, 6=200100}

Example 2

import java.util.concurrent.*; 
  
public class ConcurrentHashMapcomputeExample2 { 
  
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<Integer, String> 
            conmap = new ConcurrentHashMap<>(); 
        conmap.put(1, "Java"); 
        conmap.put(2, "php"); 
        conmap.put(3, ".net"); 
        System.out.println("ConcurrentHashMap value detail: "
                           + conmap.toString()); 
        conmap.compute(2, (key, val) 
                           -> val.concat(" (Angular)")); 
        conmap.compute(3, (key, val) 
                           -> val.concat(" (java Script)")); 
        
        System.out.println("New ConcurrentHashMap after compute: "
                           + conmap); 
    } 
}

Test it Now

Output:

ConcurrentHashMap value detail: {1=Java, 2=php, 3=.net}
New ConcurrentHashMap after compute: {1=Java, 2=php (Angular), 3=.net (java Script)}

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