Collections: SequencedCollection reversed() without copying

Java 21 added SequencedCollection, so List, Deque and LinkedHashSet share addFirst, getFirst and a reversed() view.

Code

SequencedCollection<String> steps = new ArrayList<>(List.of("build", "test", "deploy"));

System.out.println("first = " + steps.getFirst() + ", last = " + steps.getLast());
System.out.println("reversed view = " + steps.reversed());

steps.addFirst("checkout");
steps.addLast("verify");
System.out.println("after addFirst/addLast = " + steps);

Output

first = build, last = deploy
reversed view = [deploy, test, build]
after addFirst/addLast = [checkout, build, test, deploy, verify]

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Published 2026-07-30