Java / Java 21 Collection Framework features Interview questions
What is the SequencedCollection interface?
SequencedCollection<E> is a new interface in java.util that sits directly under Collection<E> in the hierarchy and represents any collection whose elements have a well-defined encounter order, from first to last.
It adds seven methods: addFirst(E), addLast(E), getFirst(), getLast(), removeFirst(), removeLast(), and reversed(). Most of these were promoted up from Deque, which already had first/last semantics.
SequencedCollection<String> names = new ArrayList<>(List.of("Ann", "Ben", "Cid")); names.addFirst("Aya"); System.out.println(names.getLast()); // Cid
If a concrete class doesn't logically support one of these operations (for example, adding to an immutable list), calling it throws UnsupportedOperationException instead of silently failing.
SequencedCollection sits in the hierarchy directly under:
Most of the methods on SequencedCollection were originally defined on:
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