Java ConcurrentHashMap computeIfPresent() Method

The computeIfPresent() method of ConcurrentHashMap class computes a new mapping given the key and its current mapped value If the value for the specified key is present.

Syntax

public V computeIfPresent(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.*;   
import java.util.*;   
public class ConcurrentHashMapcomputeIfPresentExample1 {   
    public static void main(String[] args) 
    { 
        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.computeIfPresent("k4", (key , val)  -> val + 100); 
       
        mapcon.computeIfPresent("k5", (key , val)  -> val + 100); 
      
        System.out.println("New HashMap after computeIfPresent :\n "+ mapcon); 
    } 
} 

Test it Now

Output:

HashMap values :
 {k1=100, k2=200, k3=300, k4=400}
New HashMap after computeIfPresent :
 {k1=100, k2=200, k3=300, k4=500}

Example 2

import java.util.concurrent.*; 
  
public class ConcurrentHashMapcomputeIfPresentExample2 { 
  
    public static void main(String[] args) 
    { 
        ConcurrentHashMap<String, Integer> mapcon = new ConcurrentHashMap<>(); 
        mapcon.put("A", 26); 
        mapcon.put("B", 98); 
        mapcon.put("C", 55);        
        System.out.println("ConcurrentHashMap values :\n "+ mapcon.toString());  
         mapcon.computeIfPresent("C", (key , val)  -> val + 100); 
        System.out.println("new ConcurrentHashMap after  computeIfPresent :\n " + mapcon); 
    } 
} 

Test it Now

Output:

ConcurrentHashMap values :
 {A=26, B=98, C=55}
new ConcurrentHashMap after  computeIfPresent :
 {A=26, B=98, C=155}

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