Is there a Queue (PriorityQueue) implementation which is also a Set?

Question

I'm looking for a PriorityQueue implementation which is also a Set.

The compareTo implementation if its elements must not have the requirement to be consistent with the implementation of equals.

Is there somewhere such a implementation for java?

Update: I implemented it now using a SortedSet as the internal collection. So I only had to implement the missing methods to satisfy the queue interface. I also forgot to mention that it also had to be a bounded queue, so it features a capacity and discards the last element of the set if capacity is reached.

Answer 1

If it's sufficient to have a queue with a 'Set-like' behaviour, iaw you just don't want to accept duplicate entries, then I think, an easy solution could be to subclass PriorityQueue and override the add(), addAll() and offer() methods like:

@Override
public boolean offer(E e) {
  if (contains(e)) {
    return false; 
  } else {
    return super.offer(e);
  }
}

BTW - add() calls offer() internally, so maybe it's even enough to just override the offer() method and do the check there.

Answer 2

TreeSet is a set that provides an ordered iterator. It implements the SortedSet interface, which guarantees that the iterator returned by the iterator method will return the set's elements in ascending order as determined either by their natural ordering (through Comparable), or as determined by a comparator given to the set at its creation.