java.util.Collections.singleton() Method

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Description

The singleton(T) method is used to return an immutable set containing only the specified object.

Declaration

Following is the declaration for java.util.Collections.singleton() method.

public static <T> Set<T> singleton(T o)

Parameters

o − This is the sole object to be stored in the returned set.

Return Value

The method call returns an immutable set containing only the specified object.

Exception

NA

Example

The following example shows the usage of java.util.Collections.singleton()

package com.tutorialspoint;

import java.util.*;

public class CollectionsDemo {
   public static void main(String args[]) {
      
      // create an array of string objs
      String init[] = { "One", "Two", "Three", "One", "Two", "Three" };

      // create two lists
      List list1 = new ArrayList(Arrays.asList(init));
      List list2 = new ArrayList(Arrays.asList(init));

      // remove from list1
      list1.remove("One");
      System.out.println("List1 value: "+list1);

      // remove from list2 using singleton
      list2.removeAll(Collections.singleton("One"));		   
      System.out.println("The SingletonList is :"+list2);
   }
}

Let us compile and run the above program, this will produce the following result.

List1 value: [Two, Three, One, Two, Three]
The SingletonList is :[Two, Three, Two, Three]