Create Immutable Set in Java

Immutable Set is a Set which immutable.

An ImmutableSet does not allow the null element either.

If we try to create an ImmutableSet with a null element, NullPointerException will be thrown. If any attempt made to add the null element in the set, UnsupportedOperationException will be thrown.

You cannot add or delete objects to it, but you can modify the objects stored it.

The advantage of any immutable collection (Set, Map, List) is thread-safety. We need not want to add thread safety code.

We will see the example of how to create the immutable set in Java

Using Collections.unmodifiableSet


package com.javacodestuffs.core.interfaces.set;

import java.util.Collections;
import java.util.HashSet;
import java.util.Set;

public class ImmutableSetExample {
    
   public static void main(String args[]) {
      Set set = new HashSet();
     
      // HashSet
      set.add(1234);
      set.add(5555);
      set.add(6543);
      set.add(7890);
      System.out.println(set);
      
      //Conver set object to immutable
      Set immutableSet = Collections.unmodifiableSet(set);
      immutableSet.add(4523);
   }
}

output:
[1234, 7890, 5555, 6543]
Exception in thread "main" java.lang.UnsupportedOperationException
	at java.util.Collections$UnmodifiableCollection.add(Collections.java:1055)
	at com.javacodestuffs.core.interfaces.set.ImmutableSetExample.main(ImmutableSetExample.java:21)

Using the copyOf() method in Guava We use an existing Set to create an ImmutableSet

We have maven dependency



    com.google.common
    google-collect
    1.0-rc1


package com.javacodestuffs.core.interfaces.set;

import java.util.*; 
import com.google.common.collect.ImmutableSet; 
import java.io.*; 

class ImmutableSetExample1 
{ 
	public static void main(String args[]) 
	{ 
		// creating empty set 
		Set set = new HashSet(); 
		set.add("Summer"); 
		set.add("Rainy"); 
		set.add("Winter"); 
		
		// An immutable copy of set 
		Set immutableSet  = ImmutableSet.copyOf(set); 
			
		System.out.println(immutableSet); 
	} 
} 

output:
[Summer, Rainy,Winter]

Using Java 9 Factory Of() method

In Java, if we use of with Set, Map, or List, an Immutable Set is created.



package com.javacodestuffs.core.interfaces.set; 
import java.util.*; 
 

public class ImmutableSetJava9 
{ 
	public static void main(String args[]) 
	{		 
		// non-empty immutable set 
		Set immutableSet = Set.of("Hello", "World"); 
			
		System.out.println(immutableSet);			 
	} 
} 

output:
[World, Hello]

If we try to change an ImmutableSet? It throws UnsupportedOperationException



package com.javacodestuffs.core.interfaces.set;

import java.util.*; 
public class ImmutableSetJava9 
{ 
	public static void main(String args[]) 
	{		 
		// non-empty immutable set 
		Set immutableSet = Set.of("Hello", "World"); 
			
	 
		System.out.println(immutableSet);
		
		immutableSet.add(null); 
        immutableSet.add("Welcome"); 
	} 
} 
output:
[Hello, World]

Exception in thread "main" java.lang.UnsupportedOperationException
	at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:71)
	at java.base/java.util.ImmutableCollections$AbstractImmutableSet.add(ImmutableCollections.java:281)
	at ImmutableSetJava9.main(ImmutableSetJava9.java:14)

Post/Questions related to Create Immutable Set in Java

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In this article, we have seen how to Create an Immutable Set in Java with examples. All source code in the article can be found in the GitHub repository.

Javacodestuffs

Create Immutable Set in Java