Java 9 introduced new factory methods for lists, List.of:
List<String> strings = List.of("first", "second");
What's the difference between the previous and the new option? That is, what's the difference between this:
Arrays.asList(1, 2, 3);
and this:
List.of(1, 2, 3);
Arrays.asList returns a mutable list while the list returned by List.of is structurally immutable:
List<Integer> list = Arrays.asList(1, 2, null);
list.set(1, 10); // OK
List<Integer> list = List.of(1, 2, 3);
list.set(1, 10); // Fails with UnsupportedOperationException
Arrays.asList allows null elements while List.of doesn't:
List<Integer> list = Arrays.asList(1, 2, null); // OK
List<Integer> list = List.of(1, 2, null); // Fails with NullPointerException
contains behaves differently with nulls:
List<Integer> list = Arrays.asList(1, 2, 3);
list.contains(null); // Returns false
List<Integer> list = List.of(1, 2, 3);
list.contains(null); // Fails with NullPointerException
Arrays.asList returns a view of the passed array, so the changes to the array will be reflected in the list too. For List.of this is not true:
Integer[] array = {1,2,3};
List<Integer> list = Arrays.asList(array);
array[1] = 10;
System.out.println(list); // Prints [1, 10, 3]
Integer[] array = {1,2,3};
List<Integer> list = List.of(array);
array[1] = 10;
System.out.println(list); // Prints [1, 2, 3]