int cur = availabilityMap.nextSetBit(0);
            V next = ids.get(cur);
            @Override
            public boolean hasNext()
            {
                return next != null;
            }

            @Override
            public V next()
            {
                V ret = next;
                do {
                	cur = availabilityMap.nextSetBit(cur + 1);
                	next = ids.get(cur);
                } while (next == null && cur != -1);
                return ret;
            }