My experiment shows that the following code: Queue q = new ArrayBlockingQueue(2); System.out.println(q.add(1)); System.out.println(q.add(2)); System.out.println(q.add(3)); will print true twice and then will fall down: java.lang.IllegalStateException: Queue full at java.util.AbstractQueue.add(AbstractQueue.java:98) at java.util.concurrent.ArrayBlockingQueue.add(ArrayBlockingQueue.java:312) ...