Immutable List in Java
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.
Advantages of ImmutableList
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.
Class Declaration:
@GwtCompatible(serializable=true, emulated=true) public abstract class ImmutableList extends ImmutableCollection implements List, RandomAccess
Class hierarchy:
java.lang.Object ↳ java.util.AbstractCollection ↳ com.google.common.collect.ImmutableCollection ↳ com.google.common.collect.ImmutableList
Creating ImmutableList
ImmutableList can be created by various methods. These include:
From existing List using copyOf() function of Guava
// 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]
New ImmutableList using of() function from Guava
// 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]
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 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]
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 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 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 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]
