Queue: Dequeue

Task: Remove the value at the front

Queue<Integer> q = new ArrayDeque<>(); q.offer(v);   // enqueue: join at the rearq.peek();     // read the front, leave it thereq.poll();     // dequeue: take from the frontq.size();     // how many are waiting

What you are watching

Dequeueing removes the value at the front and returns it. 12 had been waiting longest, so 12 leaves first, and everything behind it moves forward one place - 27 becomes the front and 5 moves up behind it. Nothing overtakes and nothing is skipped: the only value that can leave is the one that has been waiting longest.