Collections singletonMap() method in Java with Examples

Last Updated : 11 May, 2021

The singletonMap() method of java.util.Collections class is used to return an immutable map, mapping only the specified key to the specified value. The returned map is serializable.

Syntax: 

public static  Map singletonMap(K key, V value)


Parameters: This method takes the following parameters as a argument: 

  • key - the sole key to be stored in the returned map.
  • value - the value to which the returned map maps key.

Return Value: This method returns an immutable map containing only the specified key-value mapping.

Below are the examples to illustrate the singletonMap() method

Example 1:  

Java 
// Java program to demonstrate
// singletonMap() method
// for <String, String> Value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // create singleton map
            // using singletonMap() method
            Map<String, String>
                map = Collections
                          .singletonMap("key", "Value");

            // printing the singletonMap
            System.out.println("Singleton map is: "
                               + map);
        }

        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output: 
Singleton map is: {key=Value}

 

Example 2:

Java 
// Java program to demonstrate
// singletonMap() method
// for <Integer, Boolean> Value

import java.util.*;

public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {

        try {

            // create singleton map
            // using singletonMap() method
            Map<Integer, Boolean>
                map = Collections
                          .singletonMap(100, true);

            // printing the singletonMap
            System.out.println("Singleton map is: "
                               + map);
        }

        catch (IllegalArgumentException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

Output: 
Singleton map is: {100=true}

 
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