/**
 * Interface for priority queue of jobs
 * @author Suzanne Balik, 9 Nov 2002
 */
public interface PriorityQueue {

  /**
   * Remove all items from queue
   */
  void clear();
  
  /**
   * Returns true if queue is empty, false otherwise
   * @return true if queue is empty, false otherwise
   */
  boolean isEmpty();
  
  /**
   * Returns maximum priority value in queue OR
   * 0 if queue is empty
   * @return maximum priority value in queue OR
   *         0 if queue is empty
   * MUST BE IMPLEMENTED RECURSIVELY IN UnorderedQueue USING 
   * private int maxPriorityHelper(Node ref) method!!
   */
  int maxPriority();
  
  /**
   * Adds job with given priority and number to queue
   * ONLY IF job is not already in the queue
   * and if the priority is > 0!!!
   * @param priority priority of job
   * @param jobNumber job number
   */
  void addJob(int priority, String jobNumber);
  
  /**
   * Removes highest priority job from queue
   * @return job number of job removed from queue OR
   *         null if queue is empty
   */       
  String removeHighestPriorityJob();
  
  /**
   * Removes the given job from queue
   * @return true if job was removed
   *         false if job was not it queue
   */
  boolean removeJob(String jobNumber);
  
  /**
   * Returns number of jobs in queue
   * @return number of jobs in queue
   * MUST BE IMPLEMENTED RECURSIVELY USING 
   * private int numberOfJobsHelper(Node ref) method!!
   */
  int numberOfJobs();
  
  /**
   * Returns list of jobs in queue
   * @return list of jobs in queue
   * MUST BE IMPLEMENTED RECURSIVELY USING 
   * private String listInOrderHelper(Node ref) method!!
   */  
  String listInOrder();
  
  /**
   * Returns list  of jobs in queue
   * @return list of jobs in queue
   * MUST BE IMPLEMENTED RECURSIVELY USING 
   * private String listInReverseHelper(Node ref) method!!
   */    
  String listInReverse();
}