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Java Collections singletonList() Method with Example

Collections Class singletonList() method: Here, we are going to learn about the singletonList() method of Collections Class with its syntax and example.
Submitted by Preeti Jain, on February 07, 2020

Collections Class singletonList() method

• singletonList() method is available in java.util package.
• singletonList() method is used to return an immutable list [i.e. immutable List is a list that contains the given object (obj) only.]
• singletonList() method is a static method, so it is accessible with classname and if we try to access the method with the class object then we will not get an error.
• singletonList() method does not throw an exception at the time of returning an immutable List.

Syntax:

    public static List singletonList(Type obj);

Parameter(s):

• Type obj – represents the object to be saved in the returned List.

Return value:

The return type of this method is List, it returns an immutable list that contains only the given object (obj).

Example:

//Java program is to demonstrate the example of
// singletonList(Type obj) method of Collections

import java.util.*;

public class SingletonListOfCollections {
    public static void main(String args[]) {
        // Instatiates a array list object
        List < Integer > arr_l = new ArrayList < Integer > ();

        // By using add() method is to add
        //objects in an array list 
        arr_l.add(10);
        arr_l.add(20);
        arr_l.add(30);
        arr_l.add(40);
        arr_l.add(50);
        arr_l.add(50);

        // Display ArrayList
        System.out.println("Array List: " + arr_l);

        // By using singletonList() method is to
        // list the given elements only
        arr_l = Collections.singletonList(100);

        // Display SingletonList
        System.out.println("Collections.singletonList(100): " + arr_l);
    }
}

Output

Array List: [10, 20, 30, 40, 50, 50]
Collections.singletonList(100): [100]