/**   @version 1.00 2004-08-03   @author Cay Horstmann*/import java.util.*;/**   This program demonstrates the use of a priority queue.*/public class PriorityQueueTest{     public static void main(String[] args)   {        PriorityQueue<GregorianCalendar> pq = new PriorityQueue<GregorianCalendar>();      pq.add(new GregorianCalendar(1906, Calendar.DECEMBER, 9)); // G. Hopper      pq.add(new GregorianCalendar(1815, Calendar.DECEMBER, 10)); // A. Lovelace      pq.add(new GregorianCalendar(1903, Calendar.DECEMBER, 3)); // J. von Neumann      pq.add(new GregorianCalendar(1910, Calendar.JUNE, 22)); // K. Zuse      System.out.println("Iterating over elements...");      for (GregorianCalendar date : pq)         System.out.println(date.get(Calendar.YEAR));      System.out.println("Removing elements...");      while (!pq.isEmpty())         System.out.println(pq.remove().get(Calendar.YEAR));   }}