Collections synchronizedMap() method in Java with Examples

Last Updated : 06 May, 2020

The synchronizedMap() method of java.util.Collections class is used to return a synchronized (thread-safe) map backed by the specified map. In order to guarantee serial access, it is critical that all access to the backing map is accomplished through the returned map.

Syntax:

public static <K, V> Map<K, V> synchronizedMap(Map<K, V> m)

Parameters: This method takes the map as a parameter to be “wrapped” in a synchronized map.

Return Value: This method returns a synchronized view of the specified map.

Below are the examples to illustrate the synchronizedMap() method.

Example 1:

   // Java program to demonstrate 
// synchronizedMap() method 
// for <String, String> Value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // creating object of Map<String, String> 
            Map<String, String> 
                map = new HashMap<String, String>(); 
  
            // populate the map 
            map.put("Value1", "20"); 
            map.put("Value2", "30"); 
            map.put("Value3", "40"); 
  
            // printing the Collection 
            System.out.println("Map : " + map); 
  
            // create a synchronized map 
            Map<String, String> 
                synmap = Collections.synchronizedMap(map); 
  
            // printing the Collection 
            System.out.println("Synchronized map is : "
                               + synmap); 
        } 
  
        catch (IllegalArgumentException e) { 
            System.out.println("Exception thrown : " + e); 
        } 
    } 
} 
 
  

Output:

  Map : {Value3=40, Value1=20, Value2=30}  Synchronized map is : {Value3=40, Value1=20, Value2=30}

Example 2:

   // Java program to demonstrate 
// synchronizedMap() method 
// for <String, Boolean> Value 
  
import java.util.*; 
  
public class GFG1 { 
    public static void main(String[] argv) 
        throws Exception 
    { 
  
        try { 
  
            // creating object of Map<String, Boolean> 
            Map<String, Boolean> 
                map = new HashMap<String, Boolean>(); 
  
            // populate the map 
            map.put("Bramha", true); 
            map.put("Vishnu", true); 
            map.put("Mahesh", true); 
  
            // printing the Collection 
            System.out.println("Map : " + map); 
  
            // create a synchronized map 
            Map<String, Boolean> 
                synmap = Collections.synchronizedMap(map); 
  
            // printing the Collection 
            System.out.println("Synchronized map is : "
                               + synmap); 
        } 
        catch (IllegalArgumentException e) { 
  
            System.out.println("Exception thrown : " + e); 
        } 
    } 
} 
 
  

Output:

  Map : {Bramha=true, Vishnu=true, Mahesh=true}  Synchronized map is : {Bramha=true, Vishnu=true, Mahesh=true}

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