public ReferenceQueue() 
{

}

Constructs a new reference-object queue.

 boolean enqueue(Reference r) 
{
          /* Called only by Reference class */
        synchronized (r) {
            if (r.queue == ENQUEUED) return false;
            synchronized (lock) {
                r.queue = ENQUEUED;
                r.next = (head == null) ? r : head;
                head = r;
                queueLength++;
                if (r instanceof FinalReference) {
                    sun.misc.VM.addFinalRefCount(1);
                }
                lock.notifyAll();
                return true;
            }
        }
}

 public Reference poll() 
{
        synchronized (lock) {
            return reallyPoll();
        }
}

Polls this queue to see if a reference object is available. If one is available without further delay then it is removed from the queue and returned. Otherwise this method immediately returns null.

 public Reference remove() throws InterruptedException 
{
        return remove(0);
}

Removes the next reference object in this queue, blocking until one becomes available.

 public Reference remove(long timeout) throws IllegalArgumentException, InterruptedException 
{
        if (timeout <  0) {
            throw new IllegalArgumentException("Negative timeout value");
        }
        synchronized (lock) {
            Reference< ? extends T > r = reallyPoll();
            if (r != null) return r;
            for (;;) {
                lock.wait(timeout);
                r = reallyPoll();
                if (r != null) return r;
                if (timeout != 0) return null;
            }
        }
}

Removes the next reference object in this queue, blocking until either one becomes available or the given timeout period expires.

This method does not offer real-time guarantees: It schedules the timeout as if by invoking the Object#wait(long) method.