How to get the only element from a List? How to get the only element from a Set if get(0) is not available?

If you have a list (List) and you are sure it contains exactly one element, you can access this element using index 0:

List<String> list = Arrays.asList("element");
String element = list.get(0);

For a set (Set), there is no index-based access because Set is unordered. To get the single element from a Set, you can use an iterator:

Set<String> set = new HashSet<>();
set.add("element");
String element = set.iterator().next();

It is important to ensure that the Set actually contains exactly one element, otherwise next() may throw an exception or return an incorrect element.