How do we create an immutable Set in Java 9?

Immutable static factory methodSet.of()Can provide a convenient way to create immutable collections in Java 9.

The set instance created using the Set.of() method has the following characteristics.

• Collections returned by factory methods are usually immutable. This means that cannot add , remove or replace elements to the collection. Calling any modifier method on a collection will throw an UnsupportedOperationException.
• If the elements in the collection are mutable, it may cause the contents of the collection to appear to change.
• You can create immutable collections using static factory methods that do not allow null elements. If you try to create a collection with null elements, NullPointerException will be thrown.
• When creating an immutable collection, duplicate elements will be rejected. Passing duplicate elements to a static factory method results in an IllegalArgumentException.
• The iteration order of collection elements is unspecified and may change. The Chinese translation of

Grammar

<strong>Set.of(E... elements)</strong>

Example

is:

Example

import java.util.Set;
public class SetOfMethodTest {
   public static void main(String args[]) {
      Set<String> names = <strong>Set.of</strong>("Adithya", "Bhavish", "Chaitanya", "Jai");
      System.out.println("Names - " + names);
      names.add("Raja");       <strong>// throws UnsupportedOperationException</strong>
   }
}

Output

<strong>Names - [Bhavish, Adithya, Jai, Chaitanya]
</strong><strong>Exception in thread "main" java.lang.UnsupportedOperationException
 at java.base/java.util.ImmutableCollections.uoe(Unknown Source)
 at java.base/java.util.ImmutableCollections$AbstractImmutableSet.add(Unknown Source)
   at SetOfMethodTest.main(SetOfMethodTest.java:8)</strong>

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