java.util · java.base · since Java 1.5

Queue

declaration

public interface Queue<E> extends Collection<E>

A holding collection with head-first removal. Two method families: throwing (add/remove/element) and value-returning (offer/poll/peek) — pick per how exceptional emptiness is.

Two parallel method families cover the same three operations: offer/poll/peek return a special value (false/null) on failure; add/remove/element throw instead — pick the family that matches how exceptional emptiness or fullness is for the call site.

Key methods

`boolean offer(E)`	Insert — for capacity-restricted queues, returns false on failure instead of throwing.
`E poll() / E peek()`	Remove-and-return / inspect the head — return null if the queue is empty.
`boolean add(E)`	Insert — throws IllegalStateException if the queue is capacity-restricted and full.
`E remove() / E element()`	Remove-and-return / inspect the head — throw NoSuchElementException if the queue is empty.