Queue interface là gì và khi nào nên dùng?

Queue<E> là collection FIFO (First-In-First-Out) — "xếp hàng".

API có 2 phiên bản:

Dùng offer/poll/peek để tránh exception khi rỗng.

// ArrayDeque — KHUYẾN NGHỊ cho FIFO bình thường
Queue<String> q = new ArrayDeque<>();
q.offer("a"); q.offer("b");
q.poll();                          // "a"

// PriorityQueue — KHÔNG FIFO! Sắp theo Comparable/Comparator
PriorityQueue<Integer> pq = new PriorityQueue<>();
pq.offer(3); pq.offer(1);
pq.poll();                         // 1 — min-heap

Deque<E> extends Queue — thao tác cả 2 đầu. ArrayDeque thay thế Stack legacy.

Concurrent queue: ConcurrentLinkedQueue (lock-free), LinkedBlockingQueue (producer-consumer), DelayQueue (delay).

Dùng cho: producer-consumer, BFS, task scheduling, message buffer, rate limiting.

Default: ArrayDeque (single-thread); LinkedBlockingQueue (multi-thread); PriorityQueue (cần priority).

Queue<E> is a FIFO (First-In-First-Out) collection — "queueing up".

The API has two flavours:

Use offer/poll/peek to avoid exceptions on empty.

// ArrayDeque — RECOMMENDED for plain FIFO
Queue<String> q = new ArrayDeque<>();
q.offer("a"); q.offer("b");
q.poll();                          // "a"

// PriorityQueue — NOT FIFO! Orders by Comparable/Comparator
PriorityQueue<Integer> pq = new PriorityQueue<>();
pq.offer(3); pq.offer(1);
pq.poll();                         // 1 — min-heap

Deque<E> extends Queue — both-end operations. ArrayDeque replaces the legacy Stack.

Concurrent queues: ConcurrentLinkedQueue (lock-free), LinkedBlockingQueue (producer-consumer), DelayQueue (delayed).

Use for: producer-consumer, BFS, task scheduling, message buffering, rate limiting.

Defaults: ArrayDeque (single-thread); LinkedBlockingQueue (multi-thread); PriorityQueue (priority).