Bounded PriorityBlockingQueue

Question

PriorityBlockingQueue is unbounded, but I need to bound it somehow. What is the best way to achieve that?

For information, the bounded PriorityBlo

Answer 1

Of the top of my head, I'd subclass it and overwrite the put method to enforce this. If it goes over throw an exception or do whatever seems appropriate.

Something like:

public class LimitedPBQ extends PriorityBlockingQueue {

    private int maxItems;
    public LimitedPBQ(int maxItems){
        this.maxItems = maxItems;
    }

    @Override
    public boolean offer(Object e) {
        boolean success = super.offer(e);
        if(!success){
            return false;
        } else if (this.size()>maxItems){
            // Need to drop last item in queue
            // The array is not guaranteed to be in order, 
            // so you should sort it to be sure, even though Sun's Java 6 
            // version will return it in order
            this.remove(this.toArray()[this.size()-1]);
        }
        return true;
    }
}

Edit: Both add and put invoke offer, so overriding it should be enough

Edit 2: Should now remove the last element if over maxItems. There may be a more elegant way of doing it though.