Why ArrayBlockingQueue hasn't been blocked when the queue is full

Question

I have a simple test for ArrayBlockingQueue as below:

public class TestQueue {

    static class Producer implements Runnable {
        private ArrayBlockingQueue<Integer> queue;
        private int index;

        public Producer(ArrayBlockingQueue<Integer> queue, int index) {
            this.queue = queue;
            this.index = index;
        }

        @Override
        public void run() {
            try {
                queue.put(index);

                System.out.println("producer: " + index);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    static class Consumer implements Runnable {
        private ArrayBlockingQueue<Integer> queue;

        public Consumer(ArrayBlockingQueue<Integer> queue) {
            this.queue = queue;
        }

        @Override
        public void run() {
            try {
                while(true) {
                    System.out.println("consumer: " + queue.take());
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        ArrayBlockingQueue<Integer> queue = new ArrayBlockingQueue<>(3);

        for (int i = 0; i < 10; i++) {
            Producer producer = new Producer(queue, i);

            new Thread(producer).start();
        }

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

        Consumer consumer = new Consumer(queue);

        new Thread(consumer).start();
    }
}

The result is:

producer: 2
producer: 0
producer: 1
consumer: 0
producer: 4
producer: 6
consumer: 2
etc...

my problem is, I have defined the size of ArrayBlockingQueue as 3, while the producer has put 2, 0 and 1, totally 3 items into the queue, and the queue is full now, then the consumer has consumed 0, the size of the queue should be 2 now, and then, the producer put 4 into the queue, the queue should be full now, why the producer can still put 6 into the queue, it's supposed to be blocked

Answer 1

The take/put action and the print are not atomic.

producer: 6 is printed before consumer: 2, does not mean the producer put 6 before the consumer consume 2.

For example:

1. consumer execute queue.take(), and take 2
2. producer execute queue.put(6)
3. producer print producer: 6
4. consumer pint consumer: 2