Java Queue vs Deque vs PriorityQueue: Differences and Examples

Think about ticket line, two-door bus, emergency room. Three pictures, three behaviors. All three types hold items and hand them back one at a time. The only difference is which item comes out next:

• Queue: the one that arrived first
• Deque: the one at whichever end you choose
• PriorityQueue: the most important one

Collection
   └── Queue
         ├── Deque
         │     └── ArrayDeque, LinkedList
         └── PriorityQueue

Remember: Deque extends Queue, so a Deque can do everything a Queue does, plus more.

Remember It as Three Places

• Ticket line = Queue. First in, first out (FIFO).
• Two-door bus = Deque. Add and remove at both ends.
• Emergency room = PriorityQueue. Most urgent first, not first come.”

Queue waits, Deque doubles, PriorityQueue prioritizes.

Queue: First In, First Out

Queue<String> queue = new ArrayDeque<>();
queue.offer("Write report");
queue.offer("Fix bug");
queue.offer("Send email");

System.out.println(queue.poll()); // Write report
System.out.println(queue.poll()); // Fix bug

The first item added is the first item removed.