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Immutable List in Java - GeeksforGeeks

Last Updated : 11 Jul, 2025

• ImmutableList, as suggested by the name, is a type of List which is immutable. It means that the content of the List are fixed or constant after declaration, that is, they are read-only.
• If any attempt made to add, delete and update elements in the List, UnsupportedOperationException is thrown.
• An ImmutableList does not allow null element either.
• If any attempt made to create an ImmutableList with null element, NullPointerException is thrown. If any attempt is made to add null element in List, UnsupportedOperationException is thrown.

• They are thread safe.
• They are memory efficient.
• Since they are immutable, hence they can be passed over to third party libraries without any problem.

that it is an immutable collection, not collection of immutable objects, so the objects inside it can be modified.

@GwtCompatible(serializable=true,
               emulated=true)
public abstract class ImmutableList
extends ImmutableCollection
implements List, RandomAccess

java.lang.Object
  ↳ java.util.AbstractCollection
      ↳ com.google.common.collect.ImmutableCollection
          ↳ com.google.common.collect.ImmutableList 

ImmutableList can be created by various methods. These include:

1. From existing List using copyOf() function of Guava Java

   // Below is the Java program to create ImmutableList
   
   import com.google.common.collect.ImmutableList;
   import java.util.*;
   
   class GFG {
   
       // Function to create ImmutableList from List
       public static <T> void iList(List<T> list)
       {
           // Create ImmutableMap from Map using copyOf()
           ImmutableList<T> immutableList =
                             ImmutableList.copyOf(list);
   
           // Print the ImmutableMap
           System.out.println(immutableList);
       }
   
       public static void main(String[] args)
       {
           List<String> list = new ArrayList<>(
               Arrays.asList("Geeks", "For", "Geeks"));
   
           iList(list);
       }
   }
   

   Output:

   [Geeks, For, Geeks]
   

2. New ImmutableList using of() function from Guava Java

   // Below is the Java program to create ImmutableList
   
   import com.google.common.collect.ImmutableList;
   import java.util.*;
   
   class GFG {
   
       // Function to create ImmutableList
       public static void iList()
       {
           // Create ImmutableList using of()
           ImmutableList<String> immutableList = 
                  ImmutableList.of("Geeks", "For", "Geeks");
   
           // Print the ImmutableMap
           System.out.println(immutableList);
       }
   
       public static void main(String[] args)
       {
           iList();
       }
   }
   

   Output:

   [Geeks, For, Geeks]
   

3. Using Java 9 Factory Of() method In Java, use of() with Set, Map or List to create an Immutable List. Please Note: The programs below are of Java 9. Hence you would need a Java 9 compiler to run them. Java

   // Java code illustrating of() method to
   // create a ImmutableSet
   import java.util.*;
   import com.google.common.collect.ImmutableList;
   
   class GfG {
       public static void main(String args[])
       {
           // non-empty immutable set
           List<String> list = List.of("Geeks", "For", "Geeks");
   
           // Let's print the list
           System.out.println(list);
       }
   }
   

   Output:

   [Geeks, For, Geeks]
   

4. Using Builder() from ImmutableList In Guava, ImmnutableList class provides a function Builder(). Through this function, a new ImmutableList can be created, or an ImmutableList can be created from an existing List or both.
   • Creating a new ImmutableList Java

     // Java code illustrating of() method to
     // create a ImmutableList
     import java.util.*;
     import com.google.common.collect.ImmutableList;
     
     class GfG {
         public static void main(String args[])
         {
             // non-empty immutable set
             ImmutableList<String> iList = ImmutableList.<String>builder()
                                               .add("Geeks", "For", "Geeks")
                                               .build();
     
             // Let's print the List
             System.out.println(iList);
         }
     }
     

     Output:

     [Geeks, For, Geeks]
     

   • Creating an ImmutableList from existing List Java

     // Java code illustrating of() method to
     // create a ImmutableList
     import java.util.*;
     import com.google.common.collect.ImmutableList;
     
     class GfG {
         public static void main(String args[])
         {
             // non-empty immutable set
             List<String> list = List.of("Geeks", "For", "Geeks");
             ImmutableList<String> iList = ImmutableList.<String>builder()
                                               .addAll(list)
                                               .build();
     
             // Let's print the List
             System.out.println(iList);
         }
     }
     

     Output:

     [Geeks, For, Geeks]
     

   • Creating a new ImmutableList including the existing List Java

     // Java code illustrating of() method to
     // create a ImmutableList
     import java.util.*;
     import com.google.common.collect.ImmutableList;
     
     class GfG {
         public static void main(String args[])
         {
             // non-empty immutable set
             List<String> list = List.of("Geeks", "For", "Geeks");
             ImmutableList<String> iList = ImmutableList.<String>builder()
                                               .addAll(list)
                                               .add("Computer", "Portal", )
                                               .build();
     
             // Let's print the set
             System.out.println(iList);
         }
     }
     

     Output:

     [Geeks, For, Geeks, Computer, Portal]
     

As mentioned earlier, the below program will throw

.

// Java code to show that UnsupportedOperationException
// will be thrown when ImmutableList is modified.
import java.util.*;

class GfG {
    public static void main(String args[])
    {
        // empty immutable map
        List<String> list = List.of();

        // Lets try adding element in  List
        List.add("Geeks");
    }
}

Output :

Exception in thread "main" java.lang.UnsupportedOperationException
    at com.google.common.collect.ImmutableCollection.add(ImmutableCollection.java:218)
    at ImmutableListDemo.main(Main.java:16)

Collections.unmodifiableList creates a wrapper around the same existing List such that the wrapper cannot be used to modify it. However we can still change original List.

// Java program to demonstrate that a List created using
// Collections.unmodifiableList() can be modified indirectly.
import java.io.*;
import java.util.*;

class GFG {
    public static void main(String[] args)
    {
        List<String> list = new ArrayList<>();
        list.add("Geeks");

        // Create ImmutableList from List using copyOf()
        List<String> iList = Collections.unmodifiableList(list);

        // We change List and the changes reflect in iList.
        list.add("For");
        list.add("Geeks");

        System.out.println(iList);
    }
}

[Geeks, For, Geeks]

If we create an ImmutableList from an existing List and change the existing List, the ImmutableList does not change because a copy is created.

// Below is a Java program for
// Creating an immutable List using copyOf()
// and modifying original List.
import java.io.*;
import java.util.*;
import com.google.common.collect.ImmutableList;

class GFG {
    public static void main(String[] args)
    {
        List<String> list = new ArrayList<>();
        list.add("Geeks");

        // Create ImmutableList from List using copyOf()
        ImmutableList<String> iList = ImmutableList.copyOf(list);

        // We change List and the changes wont reflect in iList.
        list.add("For");
        list.add("Geeks");

        System.out.println(iList);
    }
}

Output :

[Geeks]

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