java.util · java.base · since Java 1.6

Deque

declaration

public interface Deque<E> extends Queue<E>, SequencedCollection<E>

Double-ended queue: efficient add/remove at both ends. Serves as both the modern Stack (push/pop) and a plain Queue.

Deque is the modern replacement for the legacy Stack class — push/pop/peek give the same LIFO discipline without Stack's synchronization overhead or its ill-advised extension of Vector.

Key methods

`void addFirst(E) / addLast(E)`	Throwing insert at either end — IllegalStateException if capacity-restricted and full.
`boolean offerFirst(E) / offerLast(E)`	Capacity-safe insert at either end — returns false instead of throwing.
`E removeFirst() / removeLast()`	Throwing removal from either end — NoSuchElementException if empty.
`E pollFirst() / pollLast()`	Null-returning removal from either end.
`E getFirst() / getLast()`	Throwing inspection of either end — NoSuchElementException if empty.
`E peekFirst() / peekLast()`	Null-returning inspection of either end.
`void push(E) / E pop()`	Stack aliases: push = addFirst, pop = removeFirst (throws if empty).
`Iterator<E> descendingIterator()`	Iterate tail-to-head.