The singletonList() method of java.util.Collections class is used to return an immutable list containing only the specified object. The returned list is serializable. This list will always contain only one element thus the name singleton list. When we try to add/remove an element on the returned singleton list, it would give UnsupportedOperationException.
Syntax:
public static List singletonList(T o)
Parameters:
This method takes the object o as a parameter to be stored in the returned list.
Return Value:
This method returns an immutable list containing only the specified object.
Below are the examples to illustrate the singletonList() method
Example 1:
Java
// Java program to demonstrate// singletonList() method// for <String> Valueimport java.util.*;public class GFG1 { public static void main(String[] argv) throws Exception { try { // create singleton list // using method singletonList() method List<String> list = Collections.singletonList("E"); // print the list System.out.println("singletonList : " + list); } catch (IllegalArgumentException e) { System.out.println("Exception thrown : " + e); } }} |
Output
singletonList : [E]
Example 2:
Java
// Java program to demonstrate// singletonList() method// for <Integer> Valueimport java.util.*;public class GFG1 { public static void main(String[] argv) throws Exception { try { // create singleton list // using method singletonList() method List<Integer> list = Collections.singletonList(20); // print the list System.out.println("singletonList : " + list); } catch (IllegalArgumentException e) { System.out.println("Exception thrown : " + e); } }} |
Output
singletonList : [20]
