package DataStructures;

/**
 * Interface for a priority queue of elements of type E. <p>
 *
 * <p>
 * Elements of type E must implement the Comparable interface 
 * in their defining class or in some superclass.
 * </p>
 *
 * The <tt>remove</tt> method returns an item of highest priority from
 * the queue.
 * If distinct items are of the same priority, an implementation is
 * not obliged to return them in any particular order, unless it
 * declares otherwise.<p>
 * 
 * @see <a href="http://java.sun.com/products/j2se/1.5/docs/api/java/lang/Comparable.html">Comparable</a>
 * @param <E> the type of elements held in this queue
 * @author Peter Williams
 */

public interface PriorityQueue<E extends Comparable<? super E>> {
    /**
     * Indicates the status of the queue.
     * @return <code>true</code> if the queue is empty.
     */
    public boolean isEmpty();

    /**
     * Returns the current size of the queue
     * @return the current size of the queue
     */
    public int size();

    /**
     * Adds an item to the queue.
     * @param item the item to be added.
     */
    public void add(E item);

    /**
     * Removes an item of highest priority from the queue.
     * @return an item of highest priority.
     * @throws NoSuchElementException if the queue is empty.
     */
    public E remove();
}