When to Use List.of vs Arrays.asList in Java: Immutable vs Mutable Lists Explained

Introduction

Java provides convenient ways to create lists, such as

List.of

and

Arrays.asList

. Although both can create collection objects easily, they have significant differences. This article explains the differences between

List.of()

and

Arrays.asList()

, their use cases, and when to choose each.

List.of()

List.of()

is a factory method introduced in Java 9 for creating an immutable list containing the specified elements. Key points:

Immutability: the list cannot be modified after creation.

Fixed size: adding or removing elements is not supported.

Null values: null elements are not allowed; attempting to add null throws

NullPointerException

.

Example:

<code>List&lt;String&gt; immutable_list = List.of("apple", "banana", "orange");</code>

Arrays.asList()

Arrays.asList()

has been available since early Java versions. It creates a fixed‑size list backed by the specified array. Its characteristics:

Mutability: the list allows element updates but not addition or removal.

Array‑backed: changes to the list affect the underlying array and vice versa.

Fixed size: attempts to add or remove elements throw

UnsupportedOperationException

.

Null values: unlike

List.of()

, null elements are permitted.

Example:

<code>List&lt;String&gt; mutable_list = Arrays.asList("red", "green", "blue");</code>

Application Scenarios

List.of()

Use when you need a fixed‑size, immutable collection. It guarantees collection integrity and prevents accidental modifications.

<code>import java.util.List;

public class ListOfExample {
    public static void main(String[] args) {
        String[] colorsArray = { "Red", "Green", "Blue" };
        List&lt;String&gt; colors = List.of(colorsArray);
        colorsArray[0] = "Yellow";
        System.out.println(colors.get(0).equals(colorsArray[0])); // false
        System.out.println(colors.get(1).equals(colorsArray[1])); // true
        System.out.println(colors.get(2).equals(colorsArray[2])); // true
    }
}
</code>

Arrays.asList()

Use when you need a fixed‑size, array‑backed collection that can be modified, with changes reflected in the original array.

<code>import java.util.Arrays;
import java.util.List;

public class ArraysAsListExample {
    public static void main(String[] args) {
        String[] colorsArray = { "Red", "Green", "Blue" };
        List&lt;String&gt; colors = Arrays.asList(colorsArray);
        colors.set(0, "Yellow");
        System.out.println(colors.get(0).equals(colorsArray[0])); // true
        System.out.println(colors.get(1).equals(colorsArray[1])); // true
        System.out.println(colors.get(2).equals(colorsArray[2])); // true
    }
}
</code>

Conclusion

Understanding the differences between

List.of()

and

Arrays.asList()

is crucial for Java developers.

List.of()

creates an immutable, fixed‑size list, while

Arrays.asList()

produces a mutable list backed by an array. By considering their characteristics and appropriate scenarios, you can select the right method for your specific programming needs.