Here’s a clear comparison of List.of() and Arrays.asList() in Java:

1. Mutability

• List.of() (Java 9+): Returns an immutable list. No adding, removing, or replacing elements. Any mutating operation (like add(), remove(), or set()) throws UnsupportedOperationException.
• Arrays.asList() (Java 1.2+): Returns a fixed-size list backed by the provided array. You cannot add or remove elements, but you can change elements with set().

2. Null Handling

• List.of(): Does not allow null elements. Passing a null will throw NullPointerException.
• Arrays.asList(): Allows null elements.

3. Backing

• List.of(): Creates a new, independent, immutable list. Changes to any array used to construct elements do not affect the list.
• Arrays.asList(): The returned list is backed by the provided array, so changes to the array will reflect in the list, and vice versa.

4. Use Cases

• List.of(): Best for short, immutable lists—like constants or configuration data.
• Arrays.asList(): Best for quickly wrapping an array as a list when you might want to modify elements but don’t need to change the size.

5. Example

List<String> a = List.of("A", "B");      // Immutable, no nulls
List<String> b = Arrays.asList("A", null); // Fixed-size, allows null

a.set(0, "X"); // Throws UnsupportedOperationException
b.set(0, "X"); // Works

a.add("C"); // Throws UnsupportedOperationException
b.add("C"); // Throws UnsupportedOperationException