How to iterate over a BlockingQueue.

gistfile1.java

/**
 * A BlockingQueue comes with an iterator() method which is more or less unusable because its hasNext()
 * method may return false before the last element has been placed on the queue. To indicate that the last
 * element has been put on the queue, we use the same trick used at some airports to indicate that the last 
 * piece of baggage has been placed on the baggage conveyor belt: A red suitcase marks the end.
 */
 
 public class MyClass implements Iterable<String> {
   
   private BlockingQueue<String> queue = new ArrayBlockingQueue<>(10);
   private String redSuitcase; 
   
   /** 
    * Add stuff to the queue. This method could be invoked from a separate 'producer' thread.
    */
   public void run() {
     //... Add stuff
     //...
     if(<last element on queue>) {
      queue.put(redSuitcase = new String("EOQ")); //We purposely create a *new* object to
                                                   // make sure that it is different from any
                                                   // other object on the queue which might 
                                                   // coincidently be equal to "EOQ" (yet != redSuitcase).
     }
   }
   
   /**
    * Gets an iterator
    */
   @Override
	public Iterator<String> iterator() {
		return new Iterator<String>() {
			String next = null;
			boolean consumed = true;
			@Override
			public boolean hasNext() {
				if (consumed) {
					try {
						next = queue.take();
						consumed = false;
					} catch (InterruptedException e) {
						return false;
					}
				}
				return redSuitcase == null || next != redSuitcase;  // We purposely avoid using String.equal()
			}

			@Override
			public String next() {
				if (consumed) {
					try {
						next = timeStepQueue.take();
						consumed = false;
					} catch (InterruptedException e) {
						throw new NoSuchElementException();
					}
				}
				if (redSuitcase == null || next != redSuitcase) { // We purposely avoid using String.equal()
					consumed = true;
					return next;
				} else {
					throw new NoSuchElementException();
				}
			}

			@Override
			public void remove() {
				// Not implemented
			}

		};
	}
   
   
 }