Collections synchronizedMap() method in Java with Examples - GeeksforGeeks

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

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