// holding/Ex29.java // TIJ4 Chapter Holding, Exercise 29, page 427 /* Fill a PriorityQueue (using offer()) with Double values created using * java.util.Random, then remove the elements using poll() and display them. */ import java.util.*; class Simple extends Object {} public class Ex29 { public static void main(String[] args) { PriorityQueue s = new PriorityQueue(); // OK to add one Simple: s.offer(new Simple()); // but no more allowed; get runtime exception: // Simple cannot be cast to Comparable: s.offer(new Simple()); } }