PriorityQueue.java

public interface PriorityQueue<T extends Comparable<? super T>> {

    /** Adds the given item to the queue. */
    public void add(T item);

    /** Removes the first item according to compareTo from the queue, and returns it.
     * @return null if the queue is empty.
     */
    public T poll();

    /** Returns the first item according to compareTo in the queue, without removing it.
     * @return null if the queue is empty.
     */
    public T peek();

    /** Returns true if the queue is empty. */
    public boolean isEmpty();

    /** Removes all items from the queue. */
    public void clear();
}