Java ConcurrentHashMap replace() Method

The replace() method of ConcurrentHashMap class replaces the entry for a key only if it is currently mapped to some value.

Syntax

public V replace(K key, V value)

public boolean replace(K key, V oldValue, V newValue)

Parameter

key - key with which the specified value is associated

oldValue - value expected to be associated with the specified key

newValue - value to be associated with the specified key

Returns

true if the value was replaced

Throw

NullPointerException.

Example 1

import java.util.concurrent.*; 
  
import java.util.*; 
  
public class  ConcurrentHashMapreplaceExample1 { 
  
    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());  
        //replace the value of key k1 to 1000
        mapcon.replace("k1" , 1000);
        System.out.println("New HashMap after remove :\n "+ mapcon); 
    } 
} 

Test it Now

Output:

HashMap values :
 {k1=100, k2=200, k3=300, k4=400}
New HashMap after remove :
 {k1=1000, k2=200, k3=300, k4=400}

Example 2

import java.util.concurrent.*; 
  
 import java.util.*; 
  
public class  ConcurrentHashMapreplaceExample2 { 
  
    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());  
        //replace the value of key k2 to 2000
        mapcon.replace("k2" , 200 , 2000);
        System.out.println("New HashMap after remove :\n "+ mapcon); 
    } 
} 

Test it Now

Output:

HashMap values :
 {k1=100, k2=200, k3=300, k4=400}
New HashMap after remove :
 {k1=100, k2=2000, k3=300, k4=400}

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