(E element);
                               public E poll();
                           }
                               
                           class PriorityQueueImpl&lt;E&gt; implements PriorityQueue {
                                public void add(E element) { // implementation }
                                public E poll() {// implementation }

                                private void siftDown(int k, E element) {// implementation }
                                private void siftUp(int k, 