Is there a Guava equivalent to Apache Commons CircularFifoBuffer?

Question

I need a data structure that can efficiently buffer a specific number of elements, in FIFO order.

As mentioned in this question, Apache Commons has a CircularFifoBuffer, but it is sadly not generified. Some forks exist, but I'm not sure of their maintenance status.

Since Guava is the go-to library for my collection needs, I'm wondering: is there a good alternative in Guava? If not, should I implement it in my project, based on Apache Commons' CircularFifoBuffer?

Answer 1

Starting Guava 15.0 - you can use EvictingQueue

Answer 2

I don't see anything like that in Guava, but how about a ForwardingQueue built around an ArrayDeque where you check the capacity on add(), offer(), etc. and remove() old entries if it's already full?

Answer 3

Commons-Collections with Generics (maven link) is the way to go if you want to use Apache Collections with generics (and it contains working CircularFifoBuffer<E> class).

On the other hand, as @FrankPavageau says, you can use your own ForwardingQueue implementatation. A naive approach (with place for further optimizations) would be something like this:

static class BoundedQueue<E> extends ForwardingQueue<E> {

  private final Queue<E> delegate;
  private final int capacity;

  public BoundedQueue(final int capacity) {
    this.delegate = 
        new ArrayDeque<E>(capacity); // specifying initial capacity is optional
    this.capacity = capacity;
  }

  @Override
  protected Queue<E> delegate() {
    return delegate;
  }

  @Override
  public boolean add(final E element) {
    if (size() >= capacity) {
      delegate.poll();
    }
    return delegate.add(element);
  }

  @Override
  public boolean addAll(final Collection<? extends E> collection) {
    return standardAddAll(collection);
  }

  @Override
  public boolean offer(final E o) {
    return standardOffer(o);
  }

}

Usage:

final BoundedQueue<Integer> boundedQueue = new BoundedQueue<Integer>(3);
boundedQueue.add(1);
System.out.println(boundedQueue); // [1]
boundedQueue.add(2);
System.out.println(boundedQueue); // [1, 2]
boundedQueue.add(3);
System.out.println(boundedQueue); // [1, 2, 3]
boundedQueue.add(4);
System.out.println(boundedQueue); // [2, 3, 4]
boundedQueue.addAll(Arrays.asList(5, 6, 7, 8));
System.out.println(boundedQueue); // [6, 7, 8]
((Queue<Integer>) boundedQueue).offer(9);
System.out.println(boundedQueue); // [7, 8, 9]