Queues represent ordered work. ArrayDeque is a strong general-purpose implementation for stack and queue operations. PriorityQueue orders elements according to priority.

Deque<String> stack = new ArrayDeque<>();
stack.push("first");
stack.push("second");
System.out.println(stack.pop());

Queue<String> queue = new ArrayDeque<>();
queue.offer("job-1");
queue.offer("job-2");
System.out.println(queue.poll());

PriorityQueue<Integer> priorities = new PriorityQueue<>();
priorities.offer(50);
priorities.offer(10);
System.out.println(priorities.poll());

A priority queue's internal array is not globally sorted; it maintains a heap property sufficient to retrieve the highest- or lowest-priority element efficiently.