What is the difference between the add and offer methods in a Queue in Java?

java

queue-implementation

java-8

thread-safety

byNikita Barsukov·Jan 11, 2025

At the heart of it, Queue.add() throws an IllegalStateException when it can't insert due to capacity limits. On the flipside, Queue.offer() simply returns a false, maintaining its composure under pressure.

Queue<Integer> queue = new LinkedList<>();
queue.add(1); // Throws IllegalStateException, "I object!" if full
boolean inserted = queue.offer(2); // Casually returns false, "It's not you, it's me!" if full

Blinking cursor? Use `add()`. When capacity becomes an issue: `offer()`

The add() method is great for situations where you expect space to be aplenty, like in a LinkedList or PriorityQueue, which have no capacity restrictions. Remember, the add() method is like that friend who always manages to squeeze into a packed subway car. No hold barred!

Flash to the offer() method, gracefully returning a false, avoiding exceptions. The nuts and bolts of a heavy-traffic system demand this politeness from offer(). Too many threads pushing hard? Use offer() for fluent control without the exceptions' drama.

Taming Errors: `add()` throws a tantrum, `offer()` bows out gracefully

Error handling is crucial in dealing with the results. For method add(), you better be ready to catch an IllegalStateException. offer() on the other hand, returns a booleans that you can use to craft your next move.

Consult the blueprints: underlying implementations

Underneath the surface, Java's Queue interface leaves room for different behaviours in its implementations. For instance, PriorityQueue has no capacity limits, while others including LinkedBlockingQueue and ArrayBlockingQueue may react differently.

For thread-safe queues or Deque implementations as in ConcurrentLinkedQueue and LinkedBlockingQueue, the add and offer behaviors may not behave as you'd expect in concurrent conditions.