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Java Collections singleton() Method with Example

Collections Class singleton() method: Here, we are going to learn about the singleton() method of Collections Class with its syntax and example.
Submitted by Preeti Jain, on February 04, 2020

Collections Class singleton() method

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

Syntax:

    public static Set singleton(Type obj);

Parameter(s):

• Type obj – represents the list(l) to be rotated.

Return value:

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

Example:

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

import java.util.*;

public class SingletonOfCollections {
    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);
        arr_l.add(50);

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

        // By using singleton() method is to
        // remove the elements 50 by using the
        // help of removeAll() method in ArrayList
        arr_l.removeAll(Collections.singleton(50));

        // Display singleton list
        System.out.println("Collections.singleton(50): " + arr_l);
    }
}

Output

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