Collections synchronizedMap() method in Java with Examples

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}