Immutable ArrayList in Java with Example

In this tutorial, we will learn how to make immutable ArrayList with an example.

We will see two examples to make immutable ArrayList:

• First, we will see how to create an immutable ArrayList using Collections.unmodifiableList() method with an example
• Second, we will see how to create the Immutable ArrayList with Java 9 List.of() factory method example.

Create Immutable ArrayList with Collections.unmodifiableList() Exmaple

In the following, we create an immutable ArrayList using Collections.unmodifiableList() method with an example

public class ImmutableListExample {

    public static void main(String[] args) {

        // Creating an ArrayList of String using
        List < String > fruits = new ArrayList < > ();
        // Adding new elements to the ArrayList
        fruits.add("Banana");
        fruits.add("Apple");
        fruits.add("mango");
        fruits.add("orange");

        fruits = Collections.unmodifiableList(fruits);

        // Creating Immutable List
        //fruits.add("Strawberry"); // Exception in thread "main"
        // java.lang.UnsupportedOperationException<String> fruits = List.of("Banana", "Apple", "Mango", "Orange");
        fruits.forEach(e - > System.out.println(e));
    }
}

Output:

Banana
Apple
mango
orange

Create the Immutable ArrayList Example - Java 9 List.of() Method

Let's use List.of() static factory methods to create immutable ArrayList.

package net.javaguides.corejava.java9;

import java.util.List;

/**
 * Java 9 Immutable List Example
 * @author Ramesh Fadatare
 *
 */
public class ImmutableListExample {

    public static void main(String[] args) {

        // Creating Immutable List
        List < String > fruits = List.of("Banana", "Apple", "Mango", "Orange");
        fruits.forEach(e - > System.out.println(e));

        // You can't add Elements Immutable List
        // fruits.add("Strawberry"); // Exception in thread "main" java.lang.UnsupportedOperationException

        // in single list
        List < String > list = List.of("A", "B", "C", "D");
        list.forEach(e - > System.out.println(e));
    }
}

Output:

Banana
Apple
mango
orange
A
B
C
D

Conclusion

In this tutorial, we have seen how to make immutable ArrayList using Collections.unmodifiableList() method and Java 9 List.of() factory method with an example.

Collections Examples

• Java LinkedHashMap Example
  
• Java HashSet Example
  
• Java LinkedList Example
  
• Java ArrayList Example
  
• How To Remove Duplicate Elements From ArrayList In Java?
  
• Different Ways to Iterate over List, Set, and Map in Java
• Java Comparator Interface Example
• Java Comparable Interface Example
• Java IdentityHashMap Example
• Java WeakHashMap Example
• Java EnumMap Example
• Java CopyOnWriteArraySet Example
• Java EnumSet Class Example
• Guide to Java 8 forEach Method
• Different Ways to Iterate over a List in Java [Snippet]
• Different Ways to Iterate over a Set in Java [Snippet]
• Different Ways to Iterate over a Map in Java [Snippet]
• Iterate over TreeSet in Java Example
• Iterate over LinkedHashSet in Java Example
• Remove First and Last Elements of LinkedList in Java
• Iterate over LinkedList using an Iterator in Java
• Search an Element in an ArrayList in Java
• Iterate over ArrayList using Iterator in Java
• Remove Element from HashSet in Java
• Iterating over a HashSet using Iterator

References

• Java 9 List.of() Method - Create Immutable List Example

• https://www.javaguides.net/p/java-9-tutorial.html