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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.50 by dl, Wed Jun 2 23:45:46 2004 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5	>	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	>	*/
7
8	<	import java.util.*;
8	>	package java.util;
9
10		/**
11	<	* An unbounded (resizable) priority queue based on a priority
12	<	* heap.The take operation returns the least element with respect to
13	<	* the given ordering. (If more than one element is tied for least
14	<	* value, one of them is arbitrarily chosen to be returned -- no
15	<	* guarantees are made for ordering across ties.) Ordering follows the
16	<	* java.util.Collection conventions: Either the elements must be
17	<	* Comparable, or a Comparator must be supplied. Comparison failures
18	<	* throw ClassCastExceptions during insertions and extractions.
19	<	**/
20	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
21	<	public PriorityQueue(int initialCapacity) {}
22	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
11	>	* An unbounded priority {@linkplain Queue queue} based on a priority
12	>	* heap.  This queue orders elements according to an order specified
13	>	* at construction time, which is specified either according to their
14	>	* <i>natural order</i> (see {@link Comparable}), or according to a
15	>	* {@link java.util.Comparator}, depending on which constructor is
16	>	* used. A priority queue does not permit <tt>null</tt> elements.
17	>	* A priority queue relying on natural ordering also does not
18	>	* permit insertion of non-comparable objects (doing so may result
19	>	* in <tt>ClassCastException</tt>).
20	>	*
21	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
22	>	* with respect to the specified ordering.  If multiple elements are
23	>	* tied for least value, the head is one of those elements -- ties are
24	>	* broken arbitrarily.  The queue retrieval operations <tt>poll</tt>,
25	>	* <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the
26	>	* element at the head of the queue.
27	>	*
28	>	* <p>A priority queue is unbounded, but has an internal
29	>	* <i>capacity</i> governing the size of an array used to store the
30	>	* elements on the queue.  It is always at least as large as the queue
31	>	* size.  As elements are added to a priority queue, its capacity
32	>	* grows automatically.  The details of the growth policy are not
33	>	* specified.
34	>	*
35	>	* <p>This class and its iterator implement all of the
36	>	* <em>optional</em> methods of the {@link Collection} and {@link
37	>	* Iterator} interfaces.
38	>	* The
39	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
40	>	* guaranteed to traverse the elements of the PriorityQueue in any
41	>	* particular order. If you need ordered traversal, consider using
42	>	* <tt>Arrays.sort(pq.toArray())</tt>.
43	>	*
44	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
45	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
46	>	* instance concurrently if any of the threads modifies the list
47	>	* structurally. Instead, use the thread-safe {@link
48	>	* java.util.concurrent.PriorityBlockingQueue} class.
49	>	*
50	>	*
51	>	* <p>Implementation note: this implementation provides O(log(n)) time
52	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
53	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
54	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
55	>	* constant time for the retrieval methods (<tt>peek</tt>,
56	>	* <tt>element</tt>, and <tt>size</tt>).
57	>	*
58	>	* <p>This class is a member of the
59	>	* <a href="{@docRoot}/../guide/collections/index.html">
60	>	* Java Collections Framework</a>.
61	>	* @since 1.5
62	>	* @version %I%, %G%
63	>	* @author Josh Bloch
64	>	* @param <E> the type of elements held in this collection
65	>	*/
66	>	public class PriorityQueue<E> extends AbstractQueue<E>
67	>	implements java.io.Serializable {
68
69	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
69	>	private static final long serialVersionUID = -7720805057305804111L;
70
71	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
71	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
72
73	<	public boolean add(E x) {
74	<	return false;
73	>	/**
74	>	* Priority queue represented as a balanced binary heap: the two children
75	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
76	>	* ordered by comparator, or by the elements' natural ordering, if
77	>	* comparator is null:  For each node n in the heap and each descendant d
78	>	* of n, n <= d.
79	>	*
80	>	* The element with the lowest value is in queue[1], assuming the queue is
81	>	* nonempty.  (A one-based array is used in preference to the traditional
82	>	* zero-based array to simplify parent and child calculations.)
83	>	*
84	>	* queue.length must be >= 2, even if size == 0.
85	>	*/
86	>	private transient Object[] queue;
87	>
88	>	/**
89	>	* The number of elements in the priority queue.
90	>	*/
91	>	private int size = 0;
92	>
93	>	/**
94	>	* The comparator, or null if priority queue uses elements'
95	>	* natural ordering.
96	>	*/
97	>	private final Comparator<? super E> comparator;
98	>
99	>	/**
100	>	* The number of times this priority queue has been
101	>	* <i>structurally modified</i>.  See AbstractList for gory details.
102	>	*/
103	>	private transient int modCount = 0;
104	>
105	>	/**
106	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
107	>	* (11) that orders its elements according to their natural
108	>	* ordering (using <tt>Comparable</tt>).
109	>	*/
110	>	public PriorityQueue() {
111	>	this(DEFAULT_INITIAL_CAPACITY, null);
112		}
113	<	public boolean offer(E x) {
114	<	return false;
113	>
114	>	/**
115	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
116	>	* that orders its elements according to their natural ordering
117	>	* (using <tt>Comparable</tt>).
118	>	*
119	>	* @param initialCapacity the initial capacity for this priority queue.
120	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
121	>	* than 1
122	>	*/
123	>	public PriorityQueue(int initialCapacity) {
124	>	this(initialCapacity, null);
125		}
126	<	public boolean remove(Object x) {
127	<	return false;
126	>
127	>	/**
128	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
129	>	* that orders its elements according to the specified comparator.
130	>	*
131	>	* @param initialCapacity the initial capacity for this priority queue.
132	>	* @param comparator the comparator used to order this priority queue.
133	>	* If <tt>null</tt> then the order depends on the elements' natural
134	>	* ordering.
135	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
136	>	* than 1
137	>	*/
138	>	public PriorityQueue(int initialCapacity,
139	>	Comparator<? super E> comparator) {
140	>	if (initialCapacity < 1)
141	>	throw new IllegalArgumentException();
142	>	this.queue = new Object[initialCapacity + 1];
143	>	this.comparator = comparator;
144		}
145
146	<	public E remove() {
147	<	return null;
146	>	/**
147	>	* Common code to initialize underlying queue array across
148	>	* constructors below.
149	>	*/
150	>	private void initializeArray(Collection<? extends E> c) {
151	>	int sz = c.size();
152	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
153	>	Integer.MAX_VALUE - 1);
154	>	if (initialCapacity < 1)
155	>	initialCapacity = 1;
156	>
157	>	this.queue = new Object[initialCapacity + 1];
158		}
159	<	public Iterator<E> iterator() {
160	<	return null;
159	>
160	>	/**
161	>	* Initially fill elements of the queue array under the
162	>	* knowledge that it is sorted or is another PQ, in which
163	>	* case we can just place the elements in the order presented.
164	>	*/
165	>	private void fillFromSorted(Collection<? extends E> c) {
166	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
167	>	queue[++size] = i.next();
168		}
169
170	<	public E element() {
171	<	return null;
170	>	/**
171	>	* Initially fill elements of the queue array that is not to our knowledge
172	>	* sorted, so we must rearrange the elements to guarantee the heap
173	>	* invariant.
174	>	*/
175	>	private void fillFromUnsorted(Collection<? extends E> c) {
176	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
177	>	queue[++size] = i.next();
178	>	heapify();
179		}
180	<	public E poll() {
181	<	return null;
180	>
181	>	/**
182	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
183	>	* specified collection.  The priority queue has an initial
184	>	* capacity of 110% of the size of the specified collection or 1
185	>	* if the collection is empty.  If the specified collection is an
186	>	* instance of a {@link java.util.SortedSet} or is another
187	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
188	>	* according to the same comparator, or according to its elements'
189	>	* natural order if the collection is sorted according to its
190	>	* elements' natural order.  Otherwise, the priority queue is
191	>	* ordered according to its elements' natural order.
192	>	*
193	>	* @param c the collection whose elements are to be placed
194	>	*        into this priority queue.
195	>	* @throws ClassCastException if elements of the specified collection
196	>	*         cannot be compared to one another according to the priority
197	>	*         queue's ordering.
198	>	* @throws NullPointerException if <tt>c</tt> or any element within it
199	>	* is <tt>null</tt>
200	>	*/
201	>	public PriorityQueue(Collection<? extends E> c) {
202	>	initializeArray(c);
203	>	if (c instanceof SortedSet) {
204	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
205	>	comparator = (Comparator<? super E>)s.comparator();
206	>	fillFromSorted(s);
207	>	} else if (c instanceof PriorityQueue) {
208	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
209	>	comparator = (Comparator<? super E>)s.comparator();
210	>	fillFromSorted(s);
211	>	} else {
212	>	comparator = null;
213	>	fillFromUnsorted(c);
214	>	}
215	>	}
216	>
217	>	/**
218	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
219	>	* specified collection.  The priority queue has an initial
220	>	* capacity of 110% of the size of the specified collection or 1
221	>	* if the collection is empty.  This priority queue will be sorted
222	>	* according to the same comparator as the given collection, or
223	>	* according to its elements' natural order if the collection is
224	>	* sorted according to its elements' natural order.
225	>	*
226	>	* @param c the collection whose elements are to be placed
227	>	*        into this priority queue.
228	>	* @throws ClassCastException if elements of the specified collection
229	>	*         cannot be compared to one another according to the priority
230	>	*         queue's ordering.
231	>	* @throws NullPointerException if <tt>c</tt> or any element within it
232	>	* is <tt>null</tt>
233	>	*/
234	>	public PriorityQueue(PriorityQueue<? extends E> c) {
235	>	initializeArray(c);
236	>	comparator = (Comparator<? super E>)c.comparator();
237	>	fillFromSorted(c);
238	>	}
239	>
240	>	/**
241	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
242	>	* specified collection.  The priority queue has an initial
243	>	* capacity of 110% of the size of the specified collection or 1
244	>	* if the collection is empty.  This priority queue will be sorted
245	>	* according to the same comparator as the given collection, or
246	>	* according to its elements' natural order if the collection is
247	>	* sorted according to its elements' natural order.
248	>	*
249	>	* @param c the collection whose elements are to be placed
250	>	*        into this priority queue.
251	>	* @throws ClassCastException if elements of the specified collection
252	>	*         cannot be compared to one another according to the priority
253	>	*         queue's ordering.
254	>	* @throws NullPointerException if <tt>c</tt> or any element within it
255	>	* is <tt>null</tt>
256	>	*/
257	>	public PriorityQueue(SortedSet<? extends E> c) {
258	>	initializeArray(c);
259	>	comparator = (Comparator<? super E>)c.comparator();
260	>	fillFromSorted(c);
261	>	}
262	>
263	>	/**
264	>	* Resize array, if necessary, to be able to hold given index
265	>	*/
266	>	private void grow(int index) {
267	>	int newlen = queue.length;
268	>	if (index < newlen) // don't need to grow
269	>	return;
270	>	if (index == Integer.MAX_VALUE)
271	>	throw new OutOfMemoryError();
272	>	while (newlen <= index) {
273	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
274	>	newlen = Integer.MAX_VALUE;
275	>	else
276	>	newlen <<= 2;
277	>	}
278	>	Object[] newQueue = new Object[newlen];
279	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
280	>	queue = newQueue;
281		}
282	+
283	+
284	+	/**
285	+	* Inserts the specified element into this priority queue.
286	+	*
287	+	* @return <tt>true</tt>
288	+	* @throws ClassCastException if the specified element cannot be compared
289	+	* with elements currently in the priority queue according
290	+	* to the priority queue's ordering.
291	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
292	+	*/
293	+	public boolean offer(E o) {
294	+	if (o == null)
295	+	throw new NullPointerException();
296	+	modCount++;
297	+	++size;
298	+
299	+	// Grow backing store if necessary
300	+	if (size >= queue.length)
301	+	grow(size);
302	+
303	+	queue[size] = o;
304	+	fixUp(size);
305	+	return true;
306	+	}
307	+
308		public E peek() {
309	<	return null;
309	>	if (size == 0)
310	>	return null;
311	>	return (E) queue[1];
312		}
313
314	<	public boolean isEmpty() {
314	>	// Collection Methods - the first two override to update docs
315	>
316	>	/**
317	>	* Adds the specified element to this queue.
318	>	* @return <tt>true</tt> (as per the general contract of
319	>	* <tt>Collection.add</tt>).
320	>	*
321	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
322	>	* @throws ClassCastException if the specified element cannot be compared
323	>	* with elements currently in the priority queue according
324	>	* to the priority queue's ordering.
325	>	*/
326	>	public boolean add(E o) {
327	>	return offer(o);
328	>	}
329	>
330	>	/**
331	>	* Removes a single instance of the specified element from this
332	>	* queue, if it is present.
333	>	*/
334	>	public boolean remove(Object o) {
335	>	if (o == null)
336	>	return false;
337	>
338	>	if (comparator == null) {
339	>	for (int i = 1; i <= size; i++) {
340	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
341	>	removeAt(i);
342	>	return true;
343	>	}
344	>	}
345	>	} else {
346	>	for (int i = 1; i <= size; i++) {
347	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
348	>	removeAt(i);
349	>	return true;
350	>	}
351	>	}
352	>	}
353		return false;
354		}
355	+
356	+	/**
357	+	* Returns an iterator over the elements in this queue. The iterator
358	+	* does not return the elements in any particular order.
359	+	*
360	+	* @return an iterator over the elements in this queue.
361	+	*/
362	+	public Iterator<E> iterator() {
363	+	return new Itr();
364	+	}
365	+
366	+	private class Itr implements Iterator<E> {
367	+
368	+	/**
369	+	* Index (into queue array) of element to be returned by
370	+	* subsequent call to next.
371	+	*/
372	+	private int cursor = 1;
373	+
374	+	/**
375	+	* Index of element returned by most recent call to next,
376	+	* unless that element came from the forgetMeNot list.
377	+	* Reset to 0 if element is deleted by a call to remove.
378	+	*/
379	+	private int lastRet = 0;
380	+
381	+	/**
382	+	* The modCount value that the iterator believes that the backing
383	+	* List should have.  If this expectation is violated, the iterator
384	+	* has detected concurrent modification.
385	+	*/
386	+	private int expectedModCount = modCount;
387	+
388	+	/**
389	+	* A list of elements that were moved from the unvisited portion of
390	+	* the heap into the visited portion as a result of "unlucky" element
391	+	* removals during the iteration.  (Unlucky element removals are those
392	+	* that require a fixup instead of a fixdown.)  We must visit all of
393	+	* the elements in this list to complete the iteration.  We do this
394	+	* after we've completed the "normal" iteration.
395	+	*
396	+	* We expect that most iterations, even those involving removals,
397	+	* will not use need to store elements in this field.
398	+	*/
399	+	private ArrayList<E> forgetMeNot = null;
400	+
401	+	/**
402	+	* Element returned by the most recent call to next iff that
403	+	* element was drawn from the forgetMeNot list.
404	+	*/
405	+	private Object lastRetElt = null;
406	+
407	+	public boolean hasNext() {
408	+	return cursor <= size || forgetMeNot != null;
409	+	}
410	+
411	+	public E next() {
412	+	checkForComodification();
413	+	E result;
414	+	if (cursor <= size) {
415	+	result = (E) queue[cursor];
416	+	lastRet = cursor++;
417	+	}
418	+	else if (forgetMeNot == null)
419	+	throw new NoSuchElementException();
420	+	else {
421	+	int remaining = forgetMeNot.size();
422	+	result = forgetMeNot.remove(remaining - 1);
423	+	if (remaining == 1)
424	+	forgetMeNot = null;
425	+	lastRet = 0;
426	+	lastRetElt = result;
427	+	}
428	+	return result;
429	+	}
430	+
431	+	public void remove() {
432	+	checkForComodification();
433	+
434	+	if (lastRet != 0) {
435	+	E moved = PriorityQueue.this.removeAt(lastRet);
436	+	lastRet = 0;
437	+	if (moved == null) {
438	+	cursor--;
439	+	} else {
440	+	if (forgetMeNot == null)
441	+	forgetMeNot = new ArrayList<E>();
442	+	forgetMeNot.add(moved);
443	+	}
444	+	} else if (lastRetElt != null) {
445	+	PriorityQueue.this.remove(lastRetElt);
446	+	lastRetElt = null;
447	+	} else {
448	+	throw new IllegalStateException();
449	+	}
450	+
451	+	expectedModCount = modCount;
452	+	}
453	+
454	+	final void checkForComodification() {
455	+	if (modCount != expectedModCount)
456	+	throw new ConcurrentModificationException();
457	+	}
458	+	}
459	+
460		public int size() {
461	<	return 0;
461	>	return size;
462		}
463	<	public Object[] toArray() {
464	<	return null;
463	>
464	>	/**
465	>	* Removes all elements from the priority queue.
466	>	* The queue will be empty after this call returns.
467	>	*/
468	>	public void clear() {
469	>	modCount++;
470	>
471	>	// Null out element references to prevent memory leak
472	>	for (int i=1; i<=size; i++)
473	>	queue[i] = null;
474	>
475	>	size = 0;
476		}
477
478	<	public <T> T[] toArray(T[] array) {
478	>	public E poll() {
479	>	if (size == 0)
480	>	return null;
481	>	modCount++;
482	>
483	>	E result = (E) queue[1];
484	>	queue[1] = queue[size];
485	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
486	>	if (size > 1)
487	>	fixDown(1);
488	>
489	>	return result;
490	>	}
491	>
492	>	/**
493	>	* Removes and returns the ith element from queue.  (Recall that queue
494	>	* is one-based, so 1 <= i <= size.)
495	>	*
496	>	* Normally this method leaves the elements at positions from 1 up to i-1,
497	>	* inclusive, untouched.  Under these circumstances, it returns null.
498	>	* Occasionally, in order to maintain the heap invariant, it must move
499	>	* the last element of the list to some index in the range [2, i-1],
500	>	* and move the element previously at position (i/2) to position i.
501	>	* Under these circumstances, this method returns the element that was
502	>	* previously at the end of the list and is now at some position between
503	>	* 2 and i-1 inclusive.
504	>	*/
505	>	private E removeAt(int i) {
506	>	assert i > 0 && i <= size;
507	>	modCount++;
508	>
509	>	E moved = (E) queue[size];
510	>	queue[i] = moved;
511	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
512	>	if (i <= size) {
513	>	fixDown(i);
514	>	if (queue[i] == moved) {
515	>	fixUp(i);
516	>	if (queue[i] != moved)
517	>	return moved;
518	>	}
519	>	}
520		return null;
521		}
522
523	+	/**
524	+	* Establishes the heap invariant (described above) assuming the heap
525	+	* satisfies the invariant except possibly for the leaf-node indexed by k
526	+	* (which may have a nextExecutionTime less than its parent's).
527	+	*
528	+	* This method functions by "promoting" queue[k] up the hierarchy
529	+	* (by swapping it with its parent) repeatedly until queue[k]
530	+	* is greater than or equal to its parent.
531	+	*/
532	+	private void fixUp(int k) {
533	+	if (comparator == null) {
534	+	while (k > 1) {
535	+	int j = k >> 1;
536	+	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
537	+	break;
538	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
539	+	k = j;
540	+	}
541	+	} else {
542	+	while (k > 1) {
543	+	int j = k >>> 1;
544	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
545	+	break;
546	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
547	+	k = j;
548	+	}
549	+	}
550	+	}
551	+
552	+	/**
553	+	* Establishes the heap invariant (described above) in the subtree
554	+	* rooted at k, which is assumed to satisfy the heap invariant except
555	+	* possibly for node k itself (which may be greater than its children).
556	+	*
557	+	* This method functions by "demoting" queue[k] down the hierarchy
558	+	* (by swapping it with its smaller child) repeatedly until queue[k]
559	+	* is less than or equal to its children.
560	+	*/
561	+	private void fixDown(int k) {
562	+	int j;
563	+	if (comparator == null) {
564	+	while ((j = k << 1) <= size && (j > 0)) {
565	+	if (j<size &&
566	+	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
567	+	j++; // j indexes smallest kid
568	+
569	+	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
570	+	break;
571	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
572	+	k = j;
573	+	}
574	+	} else {
575	+	while ((j = k << 1) <= size && (j > 0)) {
576	+	if (j<size &&
577	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
578	+	j++; // j indexes smallest kid
579	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
580	+	break;
581	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
582	+	k = j;
583	+	}
584	+	}
585	+	}
586	+
587	+	/**
588	+	* Establishes the heap invariant (described above) in the entire tree,
589	+	* assuming nothing about the order of the elements prior to the call.
590	+	*/
591	+	private void heapify() {
592	+	for (int i = size/2; i >= 1; i--)
593	+	fixDown(i);
594	+	}
595	+
596	+	/**
597	+	* Returns the comparator used to order this collection, or <tt>null</tt>
598	+	* if this collection is sorted according to its elements natural ordering
599	+	* (using <tt>Comparable</tt>).
600	+	*
601	+	* @return the comparator used to order this collection, or <tt>null</tt>
602	+	* if this collection is sorted according to its elements natural ordering.
603	+	*/
604	+	public Comparator<? super E> comparator() {
605	+	return comparator;
606	+	}
607	+
608	+	/**
609	+	* Save the state of the instance to a stream (that
610	+	* is, serialize it).
611	+	*
612	+	* @serialData The length of the array backing the instance is
613	+	* emitted (int), followed by all of its elements (each an
614	+	* <tt>Object</tt>) in the proper order.
615	+	* @param s the stream
616	+	*/
617	+	private void writeObject(java.io.ObjectOutputStream s)
618	+	throws java.io.IOException{
619	+	// Write out element count, and any hidden stuff
620	+	s.defaultWriteObject();
621	+
622	+	// Write out array length
623	+	s.writeInt(queue.length);
624	+
625	+	// Write out all elements in the proper order.
626	+	for (int i=1; i<=size; i++)
627	+	s.writeObject(queue[i]);
628	+	}
629	+
630	+	/**
631	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
632	+	* deserialize it).
633	+	* @param s the stream
634	+	*/
635	+	private void readObject(java.io.ObjectInputStream s)
636	+	throws java.io.IOException, ClassNotFoundException {
637	+	// Read in size, and any hidden stuff
638	+	s.defaultReadObject();
639	+
640	+	// Read in array length and allocate array
641	+	int arrayLength = s.readInt();
642	+	queue = new Object[arrayLength];
643	+
644	+	// Read in all elements in the proper order.
645	+	for (int i=1; i<=size; i++)
646	+	queue[i] = (E) s.readObject();
647	+	}
648	+
649		}

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