/**
 * Definition of our own private interface, Priority Queue
 *
 * Methods:
 *   isEmpty  are there any entries in the queue
 *   isValid  is this a valid priority queue (cf. append)
 *   remove   remove the minimal entry
 *   peek     examine the minimal entry without removing it
 *   enter    make an entry, restoring the priority queue propery
 *   append   add entries at the end, voiding priority queue
 *   correct  turn this into a valid priority queue
 *   clear    remove all elements from this priority queue
 *
 * Author:  Timothy Rolfe
 */
public interface PriorityQueue
{  public boolean isEmpty();
   public boolean isValid();
   public Comparable remove();
   public Comparable peek();
   public void enter(Comparable item);
   public void append(Comparable item);
   public void correct();
   public void clear();
}