Java Collections singletonList() Method with Examples

by Online Tutorials Library July 22, 2022

Java Collections singletonList() Method

The singletonList() method of Java Collections class is used to get an immutable list which contains only the specified object.

Syntax

Following is the declaration of singletonList() method:

Parameter

Parameter	Description	Required/Optional
o	It is the object which will be stored in the returned List.	Required

Returns

The singletonList() method returns an immutable List which contains only the specified object.

Exceptions

Compatibility Version

Java 1.3 and above

Example 1

  import java.util.*;  public class CollectionsSingletonListExample1 {  public static void main(String[] args) {      List numList = Collections.singletonList(10);        System.out.println(“Number List elements: ” + numList);       //numList.add(20);       // throws UnsupportedOperationException       List strList = Collections.singletonList(“Hello India”);       System.out.println(“String List elements: ” + strList);      }  }  

Test it Now

Output:

Number List elements: [10]  String List elements: [Hello India]

Example 2

  import java.util.*;  public class CollectionsSingletonListExample2 {  public static void main(String[] args) {         //Create an array of string objects        String str[] = { “One”, “Two”, “Three”, “One”, “Two”, “Three”, “TutorAspire” };              //Create one list        List list = new ArrayList(Arrays.asList(str));              System.out.println(“List value before: “+list);              //Create singleton list        list = Collections.singletonList(“One”);              System.out.println(“List value after: “+list);        }  }  

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Output:

List value before: [One, Two, Three, One, Two, Three, TutorAspire ]  List value after: [One]

Example 3

  import java.util.*;  public class CollectionsSingletonListExample3 {  public static void main(String[] args) {  System.out.print(“Enter the value: “);  Scanner sc = new Scanner(System.in);  int i= sc.nextInt();              System.out.println(“Output: “+Collections.singletonList(i));              sc.close();        }  }  

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Output:

1.Enter the value: 55  Output: [55]  2.Enter the value: Java  Exception in thread "main" java.util.InputMismatchException  at java.base/java.util.Scanner.throwFor(Scanner.java:939)  at java.base/java.util.Scanner.next(Scanner.java:1594)  at java.base/java.util.Scanner.nextInt(Scanner.java:2258)  at java.base/java.util.Scanner.nextInt(Scanner.java:2212)  at myPackage.CollectionsSingletonListExample3.main(CollectionsSingletonListExample3.java:7)

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Java Collections singletonList() Method with Examples

Java Collections singletonList() Method

Syntax

Parameter

Returns

Exceptions

Compatibility Version

Example 1

Example 2

Example 3

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