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revision 1.61, Tue Feb 7 20:54:24 2006 UTC revision 1.68, Sun May 18 23:47:56 2008 UTC
# Line 1  Line 1 
1  /*  /*
2   * %W% %E%   * Copyright 2003-2006 Sun Microsystems, Inc.  All Rights Reserved.
3     * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4   *   *
5   * Copyright 2006 Sun Microsystems, Inc. All rights reserved.   * This code is free software; you can redistribute it and/or modify it
6   * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.   * under the terms of the GNU General Public License version 2 only, as
7     * published by the Free Software Foundation.  Sun designates this
8     * particular file as subject to the "Classpath" exception as provided
9     * by Sun in the LICENSE file that accompanied this code.
10     *
11     * This code is distributed in the hope that it will be useful, but WITHOUT
12     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13     * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14     * version 2 for more details (a copy is included in the LICENSE file that
15     * accompanied this code).
16     *
17     * You should have received a copy of the GNU General Public License version
18     * 2 along with this work; if not, write to the Free Software Foundation,
19     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20     *
21     * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22     * CA 95054 USA or visit www.sun.com if you need additional information or
23     * have any questions.
24   */   */
25    
26  package java.util;  package java.util;
27    
28  /**  /**
29   * An unbounded priority {@linkplain Queue queue} based on a priority   * An unbounded priority {@linkplain Queue queue} based on a priority heap.
30   * heap.  The elements of the priority queue are ordered according to   * The elements of the priority queue are ordered according to their
31   * their {@linkplain Comparable natural ordering}, or by a {@link   * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
32   * Comparator} provided at queue construction time, depending on which   * provided at queue construction time, depending on which constructor is
33   * constructor is used.  A priority queue does not permit   * used.  A priority queue does not permit {@code null} elements.
34   * <tt>null</tt> elements.  A priority queue relying on natural   * A priority queue relying on natural ordering also does not permit
35   * ordering also does not permit insertion of non-comparable objects   * insertion of non-comparable objects (doing so may result in
36   * (doing so may result in <tt>ClassCastException</tt>).   * {@code ClassCastException}).
37   *   *
38   * <p>The <em>head</em> of this queue is the <em>least</em> element   * <p>The <em>head</em> of this queue is the <em>least</em> element
39   * with respect to the specified ordering.  If multiple elements are   * with respect to the specified ordering.  If multiple elements are
40   * tied for least value, the head is one of those elements -- ties are   * tied for least value, the head is one of those elements -- ties are
41   * broken arbitrarily.  The queue retrieval operations <tt>poll</tt>,   * broken arbitrarily.  The queue retrieval operations {@code poll},
42   * <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the   * {@code remove}, {@code peek}, and {@code element} access the
43   * element at the head of the queue.   * element at the head of the queue.
44   *   *
45   * <p>A priority queue is unbounded, but has an internal   * <p>A priority queue is unbounded, but has an internal
# Line 36  Line 54 
54   * Iterator} interfaces.  The Iterator provided in method {@link   * Iterator} interfaces.  The Iterator provided in method {@link
55   * #iterator()} is <em>not</em> guaranteed to traverse the elements of   * #iterator()} is <em>not</em> guaranteed to traverse the elements of
56   * the priority queue in any particular order. If you need ordered   * the priority queue in any particular order. If you need ordered
57   * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.   * traversal, consider using {@code Arrays.sort(pq.toArray())}.
58   *   *
59   * <p> <strong>Note that this implementation is not synchronized.</strong>   * <p> <strong>Note that this implementation is not synchronized.</strong>
60   * Multiple threads should not access a <tt>PriorityQueue</tt>   * Multiple threads should not access a {@code PriorityQueue}
61   * instance concurrently if any of the threads modifies the list   * instance concurrently if any of the threads modifies the queue.
62   * structurally. Instead, use the thread-safe {@link   * Instead, use the thread-safe {@link
63   * java.util.concurrent.PriorityBlockingQueue} class.   * java.util.concurrent.PriorityBlockingQueue} class.
64   *   *
65   * <p>Implementation note: this implementation provides O(log(n)) time   * <p>Implementation note: this implementation provides
66   * for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,   * O(log(n)) time for the enqueing and dequeing methods
67   * <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the   * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
68   * <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and   * linear time for the {@code remove(Object)} and {@code contains(Object)}
69   * constant time for the retrieval methods (<tt>peek</tt>,   * methods; and constant time for the retrieval methods
70   * <tt>element</tt>, and <tt>size</tt>).   * ({@code peek}, {@code element}, and {@code size}).
71   *   *
72   * <p>This class is a member of the   * <p>This class is a member of the
73   * <a href="{@docRoot}/../guide/collections/index.html">   * <a href="{@docRoot}/../technotes/guides/collections/index.html">
74   * Java Collections Framework</a>.   * Java Collections Framework</a>.
75     *
76   * @since 1.5   * @since 1.5
77   * @version 1.8, 08/27/05   * @version %I%, %G%
78   * @author Josh Bloch   * @author Josh Bloch, Doug Lea
79   * @param <E> the type of elements held in this collection   * @param <E> the type of elements held in this collection
80   */   */
81  public class PriorityQueue<E> extends AbstractQueue<E>  public class PriorityQueue<E> extends AbstractQueue<E>
# Line 94  Line 113 
113      private transient int modCount = 0;      private transient int modCount = 0;
114    
115      /**      /**
116       * Creates a <tt>PriorityQueue</tt> with the default initial       * Creates a {@code PriorityQueue} with the default initial
117       * capacity (11) that orders its elements according to their       * capacity (11) that orders its elements according to their
118       * {@linkplain Comparable natural ordering}.       * {@linkplain Comparable natural ordering}.
119       */       */
# Line 103  Line 122 
122      }      }
123    
124      /**      /**
125       * Creates a <tt>PriorityQueue</tt> with the specified initial       * Creates a {@code PriorityQueue} with the specified initial
126       * capacity that orders its elements according to their       * capacity that orders its elements according to their
127       * {@linkplain Comparable natural ordering}.       * {@linkplain Comparable natural ordering}.
128       *       *
129       * @param initialCapacity the initial capacity for this priority queue       * @param initialCapacity the initial capacity for this priority queue
130       * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less       * @throws IllegalArgumentException if {@code initialCapacity} is less
131       * than 1       * than 1
132       */       */
133      public PriorityQueue(int initialCapacity) {      public PriorityQueue(int initialCapacity) {
# Line 116  Line 135 
135      }      }
136    
137      /**      /**
138       * Creates a <tt>PriorityQueue</tt> with the specified initial capacity       * Creates a {@code PriorityQueue} with the specified initial capacity
139       * that orders its elements according to the specified comparator.       * that orders its elements according to the specified comparator.
140       *       *
141       * @param  initialCapacity the initial capacity for this priority queue       * @param  initialCapacity the initial capacity for this priority queue
142       * @param  comparator the comparator that will be used to order       * @param  comparator the comparator that will be used to order this
143       *         this priority queue.  If <tt>null</tt>, the <i>natural       *         priority queue.  If {@code null}, the {@linkplain Comparable
144       *         ordering</i> of the elements will be used.       *         natural ordering} of the elements will be used.
145       * @throws IllegalArgumentException if <tt>initialCapacity</tt> is       * @throws IllegalArgumentException if {@code initialCapacity} is
146       *         less than 1       *         less than 1
147       */       */
148      public PriorityQueue(int initialCapacity,      public PriorityQueue(int initialCapacity,
# Line 137  Line 156 
156      }      }
157    
158      /**      /**
159       * Creates a <tt>PriorityQueue</tt> containing the elements in the       * Creates a {@code PriorityQueue} containing the elements in the
160       * specified collection.   If the specified collection is an       * specified collection.  If the specified collection is an instance of
161       * instance of a {@link java.util.SortedSet} or is another       * a {@link SortedSet} or is another {@code PriorityQueue}, this
162       * <tt>PriorityQueue</tt>, the priority queue will be ordered       * priority queue will be ordered according to the same ordering.
163       * according to the same ordering.  Otherwise, this priority queue       * Otherwise, this priority queue will be ordered according to the
164       * will be ordered according to the natural ordering of its elements.       * {@linkplain Comparable natural ordering} of its elements.
165       *       *
166       * @param  c the collection whose elements are to be placed       * @param  c the collection whose elements are to be placed
167       *         into this priority queue       *         into this priority queue
# Line 167  Line 186 
186      }      }
187    
188      /**      /**
189       * Creates a <tt>PriorityQueue</tt> containing the elements in the       * Creates a {@code PriorityQueue} containing the elements in the
190       * specified priority queue.  This priority queue will be       * specified priority queue.  This priority queue will be
191       * ordered according to the same ordering as the given priority       * ordered according to the same ordering as the given priority
192       * queue.       * queue.
193       *       *
194       * @param  c the priority queue whose elements are to be placed       * @param  c the priority queue whose elements are to be placed
195       *         into this priority queue       *         into this priority queue
196       * @throws ClassCastException if elements of <tt>c</tt> cannot be       * @throws ClassCastException if elements of {@code c} cannot be
197       *         compared to one another according to <tt>c</tt>'s       *         compared to one another according to {@code c}'s
198       *         ordering       *         ordering
199       * @throws NullPointerException if the specified priority queue or any       * @throws NullPointerException if the specified priority queue or any
200       *         of its elements are null       *         of its elements are null
# Line 186  Line 205 
205      }      }
206    
207      /**      /**
208       * Creates a <tt>PriorityQueue</tt> containing the elements in the       * Creates a {@code PriorityQueue} containing the elements in the
209       * specified sorted set.  This priority queue will be ordered       * specified sorted set.  This priority queue will be ordered
210       * according to the same ordering as the given sorted set.       * according to the same ordering as the given sorted set.
211       *       *
212       * @param  c the sorted set whose elements are to be placed       * @param  c the sorted set whose elements are to be placed
213       *         into this priority queue.       *         into this priority queue
214       * @throws ClassCastException if elements of the specified sorted       * @throws ClassCastException if elements of the specified sorted
215       *         set cannot be compared to one another according to the       *         set cannot be compared to one another according to the
216       *         sorted set's ordering       *         sorted set's ordering
# Line 204  Line 223 
223      }      }
224    
225      /**      /**
226       * Initialize queue array with elements from the given Collection.       * Initializes queue array with elements from the given Collection.
227         *
228       * @param c the collection       * @param c the collection
229       */       */
230      private void initFromCollection(Collection<? extends E> c) {      private void initFromCollection(Collection<? extends E> c) {
# Line 239  Line 259 
259      /**      /**
260       * Inserts the specified element into this priority queue.       * Inserts the specified element into this priority queue.
261       *       *
262       * @return <tt>true</tt> (as specified by {@link Collection#add})       * @return {@code true} (as specified by {@link Collection#add})
263       * @throws ClassCastException if the specified element cannot be       * @throws ClassCastException if the specified element cannot be
264       *         compared with elements currently in this priority queue       *         compared with elements currently in this priority queue
265       *         according to the priority queue's ordering       *         according to the priority queue's ordering
# Line 252  Line 272 
272      /**      /**
273       * Inserts the specified element into this priority queue.       * Inserts the specified element into this priority queue.
274       *       *
275       * @return <tt>true</tt> (as specified by {@link Queue#offer})       * @return {@code true} (as specified by {@link Queue#offer})
276       * @throws ClassCastException if the specified element cannot be       * @throws ClassCastException if the specified element cannot be
277       *         compared with elements currently in this priority queue       *         compared with elements currently in this priority queue
278       *         according to the priority queue's ordering       *         according to the priority queue's ordering
# Line 290  Line 310 
310    
311      /**      /**
312       * Removes a single instance of the specified element from this queue,       * Removes a single instance of the specified element from this queue,
313       * if it is present.  More formally, removes an element <tt>e</tt> such       * if it is present.  More formally, removes an element {@code e} such
314       * that <tt>o.equals(e)</tt>, if this queue contains one or more such       * that {@code o.equals(e)}, if this queue contains one or more such
315       * elements.  Returns true if this queue contained the specified element       * elements.  Returns {@code true} if and only if this queue contained
316       * (or equivalently, if this queue changed as a result of the call).       * the specified element (or equivalently, if this queue changed as a
317         * result of the call).
318       *       *
319       * @param o element to be removed from this queue, if present       * @param o element to be removed from this queue, if present
320       * @return <tt>true</tt> if this queue changed as a result of the call       * @return {@code true} if this queue changed as a result of the call
321       */       */
322      public boolean remove(Object o) {      public boolean remove(Object o) {
323          int i = indexOf(o);          int i = indexOf(o);
# Line 313  Line 334 
334       * Needed by iterator.remove.       * Needed by iterator.remove.
335       *       *
336       * @param o element to be removed from this queue, if present       * @param o element to be removed from this queue, if present
337       * @return <tt>true</tt> if removed       * @return {@code true} if removed
338       */       */
339      boolean removeEq(Object o) {      boolean removeEq(Object o) {
340          for (int i = 0; i < size; i++) {          for (int i = 0; i < size; i++) {
# Line 326  Line 347 
347      }      }
348    
349      /**      /**
350       * Returns <tt>true</tt> if this queue contains the specified element.       * Returns {@code true} if this queue contains the specified element.
351       * More formally, returns <tt>true</tt> if and only if this queue contains       * More formally, returns {@code true} if and only if this queue contains
352       * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.       * at least one element {@code e} such that {@code o.equals(e)}.
353       *       *
354       * @param o object to be checked for containment in this queue       * @param o object to be checked for containment in this queue
355       * @return <tt>true</tt> if this queue contains the specified element       * @return {@code true} if this queue contains the specified element
356       */       */
357      public boolean contains(Object o) {      public boolean contains(Object o) {
358          return indexOf(o) != -1;          return indexOf(o) != -1;
359      }      }
360    
361      /**      /**
362       * Returns an array containing all of the elements in this queue,       * Returns an array containing all of the elements in this queue.
363       * The elements are in no particular order.       * The elements are in no particular order.
364       *       *
365       * <p>The returned array will be "safe" in that no references to it are       * <p>The returned array will be "safe" in that no references to it are
366       * maintained by this list.  (In other words, this method must allocate       * maintained by this queue.  (In other words, this method must allocate
367       * a new array).  The caller is thus free to modify the returned array.       * a new array).  The caller is thus free to modify the returned array.
368       *       *
369         * <p>This method acts as bridge between array-based and collection-based
370         * APIs.
371         *
372       * @return an array containing all of the elements in this queue       * @return an array containing all of the elements in this queue
373       */       */
374      public Object[] toArray() {      public Object[] toArray() {
# Line 352  Line 376 
376      }      }
377    
378      /**      /**
379       * Returns an array containing all of the elements in this queue.       * Returns an array containing all of the elements in this queue; the
380       * The elements are in no particular order.  The runtime type of       * runtime type of the returned array is that of the specified array.
381       * the returned array is that of the specified array.  If the queue       * The returned array elements are in no particular order.
382       * fits in the specified array, it is returned therein.       * If the queue fits in the specified array, it is returned therein.
383       * Otherwise, a new array is allocated with the runtime type of       * Otherwise, a new array is allocated with the runtime type of the
384       * the specified array and the size of this queue.       * specified array and the size of this queue.
385       *       *
386       * <p>If the queue fits in the specified array with room to spare       * <p>If the queue fits in the specified array with room to spare
387       * (i.e., the array has more elements than the queue), the element in       * (i.e., the array has more elements than the queue), the element in
388       * the array immediately following the end of the collection is set to       * the array immediately following the end of the collection is set to
389       * <tt>null</tt>.  (This is useful in determining the length of the       * {@code null}.
390       * queue <i>only</i> if the caller knows that the queue does not contain       *
391       * any null elements.)       * <p>Like the {@link #toArray()} method, this method acts as bridge between
392         * array-based and collection-based APIs.  Further, this method allows
393         * precise control over the runtime type of the output array, and may,
394         * under certain circumstances, be used to save allocation costs.
395         *
396         * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
397         * The following code can be used to dump the queue into a newly
398         * allocated array of <tt>String</tt>:
399         *
400         * <pre>
401         *     String[] y = x.toArray(new String[0]);</pre>
402         *
403         * Note that <tt>toArray(new Object[0])</tt> is identical in function to
404         * <tt>toArray()</tt>.
405       *       *
406       * @param a the array into which the elements of the queue are to       * @param a the array into which the elements of the queue are to
407       *          be stored, if it is big enough; otherwise, a new array of the       *          be stored, if it is big enough; otherwise, a new array of the
408       *          same runtime type is allocated for this purpose.       *          same runtime type is allocated for this purpose.
409       * @return an array containing the elements of the queue       * @return an array containing all of the elements in this queue
410       * @throws ArrayStoreException if the runtime type of the specified array       * @throws ArrayStoreException if the runtime type of the specified array
411       *         is not a supertype of the runtime type of every element in       *         is not a supertype of the runtime type of every element in
412       *         this queue       *         this queue
# Line 418  Line 455 
455           * after we've completed the "normal" iteration.           * after we've completed the "normal" iteration.
456           *           *
457           * We expect that most iterations, even those involving removals,           * We expect that most iterations, even those involving removals,
458           * will not use need to store elements in this field.           * will not need to store elements in this field.
459           */           */
460          private ArrayDeque<E> forgetMeNot = null;          private ArrayDeque<E> forgetMeNot = null;
461    
# Line 430  Line 467 
467    
468          /**          /**
469           * The modCount value that the iterator believes that the backing           * The modCount value that the iterator believes that the backing
470           * List should have.  If this expectation is violated, the iterator           * Queue should have.  If this expectation is violated, the iterator
471           * has detected concurrent modification.           * has detected concurrent modification.
472           */           */
473          private int expectedModCount = modCount;          private int expectedModCount = modCount;
# Line 457  Line 494 
494          public void remove() {          public void remove() {
495              if (expectedModCount != modCount)              if (expectedModCount != modCount)
496                  throw new ConcurrentModificationException();                  throw new ConcurrentModificationException();
             if (lastRet == -1 && lastRetElt == null)  
                 throw new IllegalStateException();  
497              if (lastRet != -1) {              if (lastRet != -1) {
498                  E moved = PriorityQueue.this.removeAt(lastRet);                  E moved = PriorityQueue.this.removeAt(lastRet);
499                  lastRet = -1;                  lastRet = -1;
# Line 469  Line 504 
504                          forgetMeNot = new ArrayDeque<E>();                          forgetMeNot = new ArrayDeque<E>();
505                      forgetMeNot.add(moved);                      forgetMeNot.add(moved);
506                  }                  }
507              } else {              } else if (lastRetElt != null) {
508                  PriorityQueue.this.removeEq(lastRetElt);                  PriorityQueue.this.removeEq(lastRetElt);
509                  lastRetElt = null;                  lastRetElt = null;
510                } else {
511                    throw new IllegalStateException();
512              }              }
513              expectedModCount = modCount;              expectedModCount = modCount;
514          }          }
   
515      }      }
516    
517      public int size() {      public int size() {
# Line 516  Line 552 
552       * i.  Under these circumstances, this method returns the element       * i.  Under these circumstances, this method returns the element
553       * that was previously at the end of the list and is now at some       * that was previously at the end of the list and is now at some
554       * position before i. This fact is used by iterator.remove so as to       * position before i. This fact is used by iterator.remove so as to
555       * avoid missing traverseing elements.       * avoid missing traversing elements.
556       */       */
557      private E removeAt(int i) {      private E removeAt(int i) {
558          assert i >= 0 && i < size;          assert i >= 0 && i < size;
# Line 642  Line 678 
678    
679      /**      /**
680       * Returns the comparator used to order the elements in this       * Returns the comparator used to order the elements in this
681       * queue, or <tt>null</tt> if this queue is sorted according to       * queue, or {@code null} if this queue is sorted according to
682       * the {@linkplain Comparable natural ordering} of its elements.       * the {@linkplain Comparable natural ordering} of its elements.
683       *       *
684       * @return the comparator used to order this queue, or       * @return the comparator used to order this queue, or
685       *         <tt>null</tt> if this queue is sorted according to the       *         {@code null} if this queue is sorted according to the
686       *         natural ordering of its elements.       *         natural ordering of its elements
687       */       */
688      public Comparator<? super E> comparator() {      public Comparator<? super E> comparator() {
689          return comparator;          return comparator;
690      }      }
691    
692      /**      /**
693       * Save the state of the instance to a stream (that       * Saves the state of the instance to a stream (that
694       * is, serialize it).       * is, serializes it).
695       *       *
696       * @serialData The length of the array backing the instance is       * @serialData The length of the array backing the instance is
697       * emitted (int), followed by all of its elements (each an       *             emitted (int), followed by all of its elements
698       * <tt>Object</tt>) in the proper order.       *             (each an {@code Object}) in the proper order.
699       * @param s the stream       * @param s the stream
700       */       */
701      private void writeObject(java.io.ObjectOutputStream s)      private void writeObject(java.io.ObjectOutputStream s)
# Line 667  Line 703 
703          // Write out element count, and any hidden stuff          // Write out element count, and any hidden stuff
704          s.defaultWriteObject();          s.defaultWriteObject();
705    
706          // Write out array length          // Write out array length, for compatibility with 1.5 version
707          // For compatibility with 1.5 version, must be at least 2.          s.writeInt(Math.max(2, size + 1));
         s.writeInt(Math.max(2, queue.length));  
708    
709          // Write out all elements in the proper order.          // Write out all elements in the "proper order".
710          for (int i=0; i<size; i++)          for (int i=0; i<size; i++)
711              s.writeObject(queue[i]);              s.writeObject(queue[i]);
712      }      }
713    
714      /**      /**
715       * Reconstitute the <tt>PriorityQueue</tt> instance from a stream       * Reconstitutes the {@code PriorityQueue} instance from a stream
716       * (that is, deserialize it).       * (that is, deserializes it).
717         *
718       * @param s the stream       * @param s the stream
719       */       */
720      private void readObject(java.io.ObjectInputStream s)      private void readObject(java.io.ObjectInputStream s)
# Line 686  Line 722 
722          // Read in size, and any hidden stuff          // Read in size, and any hidden stuff
723          s.defaultReadObject();          s.defaultReadObject();
724    
725          // Read in array length and allocate array          // Read in (and discard) array length
726          int arrayLength = s.readInt();          s.readInt();
727          queue = new Object[arrayLength];  
728            queue = new Object[size];
729    
730          // Read in all elements in the proper order.          // Read in all elements.
731          for (int i=0; i<size; i++)          for (int i=0; i<size; i++)
732              queue[i] = (E) s.readObject();              queue[i] = s.readObject();
     }  
733    
734            // Elements are guaranteed to be in "proper order", but the
735            // spec has never explained what that might be.
736            heapify();
737        }
738  }  }

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Doug Lea
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