import java.util.List;

class Main {
    public static void main(String[] args) {
        var fixed = List.of(1, 2, 3);
        try {
            // List.of is unmodifiable
            fixed.add(4);
        } catch (UnsupportedOperationException e) {
            System.out.println("cannot modify");
        }
    }
}

List.of rejects mutation