Java Utility Library

Java Collections - singleton() Method

The java.util.Collections.singleton() method returns an immutable set containing only the specified object. The returned set is serializable.

Syntax

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

Here, T is the type of element in the set.

Parameters

`o`	Specify the sole object to be stored in the returned set.

Return Value

Returns an immutable set containing only the specified object.

Exception

NA.

Example:

In the example below, the java.util.Collections.singleton() method returns an immutable set containing only the specified elements.

import java.util.*;

public class MyClass {
  public static void main(String[] args) {
    String[] lst = {"10", "20", "30", "40", "10", "10", "20"};

    //creating two lists
    List<String> MyList1 = 
        new ArrayList<String>(Arrays.asList(lst)); 
    List<String> MyList2 = 
        new ArrayList<String>(Arrays.asList(lst)); 

    //remove occurrences of "10" from MyList1
    //using remove() method
    MyList1.remove("10");
    System.out.println("MyList1 contains: " + MyList1); 

    //remove occurrences of "10" from MyList2
    //using singleton() method
    MyList2.removeAll(Collections.singleton("10"));
    System.out.println("MyList2 contains: " + MyList2); 
  }
}

The output of the above code will be:

MyList1 contains: [20, 30, 40, 10, 10, 20]
MyList2 contains: [20, 30, 40, 20]

❮ Java.util - Collections