How can you reverse the elements of a list?

There is a factory method in the Collections factory class simply called reverse that does exactly that.

java
List<String> names = new ArrayList<>(List.of("Ana", "Bob", "Cid"));
Collections.reverse(names);
// names = ["Cid", "Bob", "Ana"]

Note that there are several traps in this method.

This method takes a List and not a Collection, because a Collection is not ordered, so it does not make sense to try to reverse it.

This method modifies your list, so your list needs to be modifiable, and it also needs to have a ListIterator that supports the set operation. That's the case for an ArrayList, a LinkedList, and even the list you get when you call Arrays.asList(...) — but this is still something you need to keep in mind if your application uses other implementations.

java
List<Integer> fixedSize = Arrays.asList(1, 2, 3);
Collections.reverse(fixedSize); // OK: fixedSize = [3, 2, 1]

List<Integer> immutable = List.of(1, 2, 3);
Collections.reverse(immutable); // throws UnsupportedOperationException

You also have a reversed() method, added as part of the SequencedCollection interface extended by List. This reversed() method returns a view on your original list, without modifying it — so it also works on non-modifiable lists.

java
List<Integer> immutable = List.of(1, 2, 3);
List<Integer> view = immutable.reversed();
// view = [3, 2, 1], immutable is untouched

Note that this view is modifiable if the original list is itself modifiable, and in that case, modifying the view modifies the original list.

java
List<Integer> original = new ArrayList<>(List.of(1, 2, 3));
List<Integer> view = original.reversed();
view.set(0, 99);
// original = [1, 2, 99]

Using Collections.reverse may be costly, as it needs to process your whole list to reverse it. Creating a view with reversed() is a lightweight process, because what you get is a wrapper that operates lazily on your list.