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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 1.40 by dl, Fri Sep 12 15:38:26 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2003 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 heap.
12	>	* This queue orders elements according to an order specified at construction
13	>	* time, which is specified in the same manner as {@link java.util.TreeSet}
14	>	* and {@link java.util.TreeMap}: elements are ordered either according to
15	>	* their <i>natural order</i> (see {@link Comparable}), or according to a
16	>	* {@link java.util.Comparator}, depending on which constructor is used.
17	>	*
18	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
19	>	* respect to the specified ordering.  If multiple elements are tied for least
20	>	* value, the head is one of those elements. A priority queue does not permit
21	>	* <tt>null</tt> elements.
22	>	*
23	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
24	>	* return the head of the queue.
25	>	*
26	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
27	>	* not delete, the head of the queue.
28	>	*
29	>	* <p>A priority queue is unbounded, but has a <i>capacity</i>.  The
30	>	* capacity is the size of the array used internally to store the
31	>	* elements on the queue.  It is always at least as large as the queue
32	>	* size.  As elements are added to a priority queue, its capacity
33	>	* grows automatically.  The details of the growth policy are not
34	>	* specified.
35	>	*
36	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
37	>	* guaranteed to traverse the elements of the PriorityQueue in any
38	>	* particular order. If you need ordered traversal, consider using
39	>	* <tt>Arrays.sort(pq.toArray())</tt>.
40	>	*
41	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
42	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
43	>	* instance concurrently if any of the threads modifies the list
44	>	* structurally. Instead, use the thread-safe {@link
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46	>	*
47	>	*
48	>	* <p>Implementation note: this implementation provides O(log(n)) time
49	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
50	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
51	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
52	>	* constant time for the retrieval methods (<tt>peek</tt>,
53	>	* <tt>element</tt>, and <tt>size</tt>).
54	>	*
55	>	* <p>This class is a member of the
56	>	* <a href="{@docRoot}/../guide/collections/index.html">
57	>	* Java Collections Framework</a>.
58	>	* @since 1.5
59	>	* @version %I%, %G%
60	>	* @author Josh Bloch
61	>	*/
62	>	public class PriorityQueue<E> extends AbstractQueue<E>
63	>	implements Queue<E>, java.io.Serializable {
64
65	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
65	>	private static final long serialVersionUID = -7720805057305804111L;
66
67	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
67	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
68
69	<	public boolean add(E x) {
70	<	return false;
69	>	/**
70	>	* Priority queue represented as a balanced binary heap: the two children
71	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
72	>	* ordered by comparator, or by the elements' natural ordering, if
73	>	* comparator is null:  For each node n in the heap and each descendant d
74	>	* of n, n <= d.
75	>	*
76	>	* The element with the lowest value is in queue[1], assuming the queue is
77	>	* nonempty.  (A one-based array is used in preference to the traditional
78	>	* zero-based array to simplify parent and child calculations.)
79	>	*
80	>	* queue.length must be >= 2, even if size == 0.
81	>	*/
82	>	private transient Object[] queue;
83	>
84	>	/**
85	>	* The number of elements in the priority queue.
86	>	*/
87	>	private int size = 0;
88	>
89	>	/**
90	>	* The comparator, or null if priority queue uses elements'
91	>	* natural ordering.
92	>	*/
93	>	private final Comparator<? super E> comparator;
94	>
95	>	/**
96	>	* The number of times this priority queue has been
97	>	* <i>structurally modified</i>.  See AbstractList for gory details.
98	>	*/
99	>	private transient int modCount = 0;
100	>
101	>	/**
102	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
103	>	* (11) that orders its elements according to their natural
104	>	* ordering (using <tt>Comparable</tt>).
105	>	*/
106	>	public PriorityQueue() {
107	>	this(DEFAULT_INITIAL_CAPACITY, null);
108		}
109	<	public boolean offer(E x) {
110	<	return false;
109	>
110	>	/**
111	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
112	>	* that orders its elements according to their natural ordering
113	>	* (using <tt>Comparable</tt>).
114	>	*
115	>	* @param initialCapacity the initial capacity for this priority queue.
116	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
117	>	* than 1
118	>	*/
119	>	public PriorityQueue(int initialCapacity) {
120	>	this(initialCapacity, null);
121		}
122	<	public boolean remove(Object x) {
123	<	return false;
122	>
123	>	/**
124	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
125	>	* that orders its elements according to the specified comparator.
126	>	*
127	>	* @param initialCapacity the initial capacity for this priority queue.
128	>	* @param comparator the comparator used to order this priority queue.
129	>	* If <tt>null</tt> then the order depends on the elements' natural
130	>	* ordering.
131	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
132	>	* than 1
133	>	*/
134	>	public PriorityQueue(int initialCapacity,
135	>	Comparator<? super E> comparator) {
136	>	if (initialCapacity < 1)
137	>	throw new IllegalArgumentException();
138	>	this.queue = new Object[initialCapacity + 1];
139	>	this.comparator = comparator;
140		}
141
142	<	public E remove() {
143	<	return null;
142	>	/**
143	>	* Common code to initialize underlying queue array across
144	>	* constructors below.
145	>	*/
146	>	private void initializeArray(Collection<? extends E> c) {
147	>	int sz = c.size();
148	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
149	>	Integer.MAX_VALUE - 1);
150	>	if (initialCapacity < 1)
151	>	initialCapacity = 1;
152	>
153	>	this.queue = new Object[initialCapacity + 1];
154		}
155	<	public Iterator<E> iterator() {
156	<	return null;
155	>
156	>	/**
157	>	* Initially fill elements of the queue array under the
158	>	* knowledge that it is sorted or is another PQ, in which
159	>	* case we can just place the elements in the order presented.
160	>	*/
161	>	private void fillFromSorted(Collection<? extends E> c) {
162	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
163	>	queue[++size] = i.next();
164		}
165
166	<	public E element() {
167	<	return null;
166	>	/**
167	>	* Initially fill elements of the queue array that is not to our knowledge
168	>	* sorted, so we must rearrange the elements to guarantee the heap
169	>	* invariant.
170	>	*/
171	>	private void fillFromUnsorted(Collection<? extends E> c) {
172	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
173	>	queue[++size] = i.next();
174	>	heapify();
175		}
176	<	public E poll() {
177	<	return null;
176	>
177	>	/**
178	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
179	>	* specified collection.  The priority queue has an initial
180	>	* capacity of 110% of the size of the specified collection or 1
181	>	* if the collection is empty.  If the specified collection is an
182	>	* instance of a {@link java.util.SortedSet} or is another
183	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
184	>	* according to the same comparator, or according to its elements'
185	>	* natural order if the collection is sorted according to its
186	>	* elements' natural order.  Otherwise, the priority queue is
187	>	* ordered according to its elements' natural order.
188	>	*
189	>	* @param c the collection whose elements are to be placed
190	>	*        into this priority queue.
191	>	* @throws ClassCastException if elements of the specified collection
192	>	*         cannot be compared to one another according to the priority
193	>	*         queue's ordering.
194	>	* @throws NullPointerException if <tt>c</tt> or any element within it
195	>	* is <tt>null</tt>
196	>	*/
197	>	public PriorityQueue(Collection<? extends E> c) {
198	>	initializeArray(c);
199	>	if (c instanceof SortedSet) {
200	>	// @fixme double-cast workaround for compiler
201	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
202	>	comparator = (Comparator<? super E>)s.comparator();
203	>	fillFromSorted(s);
204	>	} else if (c instanceof PriorityQueue) {
205	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
206	>	comparator = (Comparator<? super E>)s.comparator();
207	>	fillFromSorted(s);
208	>	} else {
209	>	comparator = null;
210	>	fillFromUnsorted(c);
211	>	}
212	>	}
213	>
214	>	/**
215	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
216	>	* specified collection.  The priority queue has an initial
217	>	* capacity of 110% of the size of the specified collection or 1
218	>	* if the collection is empty.  This priority queue will be sorted
219	>	* according to the same comparator as the given collection, or
220	>	* according to its elements' natural order if the collection is
221	>	* sorted according to its elements' natural order.
222	>	*
223	>	* @param c the collection whose elements are to be placed
224	>	*        into this priority queue.
225	>	* @throws ClassCastException if elements of the specified collection
226	>	*         cannot be compared to one another according to the priority
227	>	*         queue's ordering.
228	>	* @throws NullPointerException if <tt>c</tt> or any element within it
229	>	* is <tt>null</tt>
230	>	*/
231	>	public PriorityQueue(PriorityQueue<? extends E> c) {
232	>	initializeArray(c);
233	>	comparator = (Comparator<? super E>)c.comparator();
234	>	fillFromSorted(c);
235		}
236	+
237	+	/**
238	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
239	+	* specified collection.  The priority queue has an initial
240	+	* capacity of 110% of the size of the specified collection or 1
241	+	* if the collection is empty.  This priority queue will be sorted
242	+	* according to the same comparator as the given collection, or
243	+	* according to its elements' natural order if the collection is
244	+	* sorted according to its elements' natural order.
245	+	*
246	+	* @param c the collection whose elements are to be placed
247	+	*        into this priority queue.
248	+	* @throws ClassCastException if elements of the specified collection
249	+	*         cannot be compared to one another according to the priority
250	+	*         queue's ordering.
251	+	* @throws NullPointerException if <tt>c</tt> or any element within it
252	+	* is <tt>null</tt>
253	+	*/
254	+	public PriorityQueue(SortedSet<? extends E> c) {
255	+	initializeArray(c);
256	+	comparator = (Comparator<? super E>)c.comparator();
257	+	fillFromSorted(c);
258	+	}
259	+
260	+	/**
261	+	* Resize array, if necessary, to be able to hold given index
262	+	*/
263	+	private void grow(int index) {
264	+	int newlen = queue.length;
265	+	if (index < newlen) // don't need to grow
266	+	return;
267	+	if (index == Integer.MAX_VALUE)
268	+	throw new OutOfMemoryError();
269	+	while (newlen <= index) {
270	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
271	+	newlen = Integer.MAX_VALUE;
272	+	else
273	+	newlen <<= 2;
274	+	}
275	+	Object[] newQueue = new Object[newlen];
276	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
277	+	queue = newQueue;
278	+	}
279	+
280	+
281	+	/**
282	+	* Inserts the specified element to this priority queue.
283	+	*
284	+	* @return <tt>true</tt>
285	+	* @throws ClassCastException if the specified element cannot be compared
286	+	* with elements currently in the priority queue according
287	+	* to the priority queue's ordering.
288	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
289	+	*/
290	+	public boolean offer(E o) {
291	+	if (o == null)
292	+	throw new NullPointerException();
293	+	modCount++;
294	+	++size;
295	+
296	+	// Grow backing store if necessary
297	+	if (size >= queue.length)
298	+	grow(size);
299	+
300	+	queue[size] = o;
301	+	fixUp(size);
302	+	return true;
303	+	}
304	+
305		public E peek() {
306	<	return null;
306	>	if (size == 0)
307	>	return null;
308	>	return (E) queue[1];
309		}
310
311	<	public boolean isEmpty() {
311	>	// Collection Methods - the first two override to update docs
312	>
313	>	/**
314	>	* Adds the specified element to this queue.
315	>	* @return <tt>true</tt> (as per the general contract of
316	>	* <tt>Collection.add</tt>).
317	>	*
318	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
319	>	* @throws ClassCastException if the specified element cannot be compared
320	>	* with elements currently in the priority queue according
321	>	* to the priority queue's ordering.
322	>	*/
323	>	public boolean add(E o) {
324	>	return super.add(o);
325	>	}
326	>
327	>
328	>	/**
329	>	* Adds all of the elements in the specified collection to this queue.
330	>	* The behavior of this operation is undefined if
331	>	* the specified collection is modified while the operation is in
332	>	* progress.  (This implies that the behavior of this call is undefined if
333	>	* the specified collection is this queue, and this queue is nonempty.)
334	>	* <p>
335	>	* This implementation iterates over the specified collection, and adds
336	>	* each object returned by the iterator to this collection, in turn.
337	>	* @param c collection whose elements are to be added to this queue
338	>	* @return <tt>true</tt> if this queue changed as a result of the
339	>	*         call.
340	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
341	>	* is <tt>null</tt>
342	>	* @throws ClassCastException if any element cannot be compared
343	>	* with elements currently in the priority queue according
344	>	* to the priority queue's ordering.
345	>	*/
346	>	public boolean addAll(Collection<? extends E> c) {
347	>	return super.addAll(c);
348	>	}
349	>
350	>	public boolean remove(Object o) {
351	>	if (o == null)
352	>	return false;
353	>
354	>	if (comparator == null) {
355	>	for (int i = 1; i <= size; i++) {
356	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
357	>	removeAt(i);
358	>	return true;
359	>	}
360	>	}
361	>	} else {
362	>	for (int i = 1; i <= size; i++) {
363	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
364	>	removeAt(i);
365	>	return true;
366	>	}
367	>	}
368	>	}
369		return false;
370		}
371	+
372	+	/**
373	+	* Returns an iterator over the elements in this queue. The iterator
374	+	* does not return the elements in any particular order.
375	+	*
376	+	* @return an iterator over the elements in this queue.
377	+	*/
378	+	public Iterator<E> iterator() {
379	+	return new Itr();
380	+	}
381	+
382	+	private class Itr implements Iterator<E> {
383	+
384	+	/**
385	+	* Index (into queue array) of element to be returned by
386	+	* subsequent call to next.
387	+	*/
388	+	private int cursor = 1;
389	+
390	+	/**
391	+	* Index of element returned by most recent call to next,
392	+	* unless that element came from the forgetMeNot list.
393	+	* Reset to 0 if element is deleted by a call to remove.
394	+	*/
395	+	private int lastRet = 0;
396	+
397	+	/**
398	+	* The modCount value that the iterator believes that the backing
399	+	* List should have.  If this expectation is violated, the iterator
400	+	* has detected concurrent modification.
401	+	*/
402	+	private int expectedModCount = modCount;
403	+
404	+	/**
405	+	* A list of elements that were moved from the unvisited portion of
406	+	* the heap into the visited portion as a result of "unlucky" element
407	+	* removals during the iteration.  (Unlucky element removals are those
408	+	* that require a fixup instead of a fixdown.)  We must visit all of
409	+	* the elements in this list to complete the iteration.  We do this
410	+	* after we've completed the "normal" iteration.
411	+	*
412	+	* We expect that most iterations, even those involving removals,
413	+	* will not use need to store elements in this field.
414	+	*/
415	+	private ArrayList<E> forgetMeNot = null;
416	+
417	+	/**
418	+	* Element returned by the most recent call to next iff that
419	+	* element was drawn from the forgetMeNot list.
420	+	*/
421	+	private Object lastRetElt = null;
422	+
423	+	public boolean hasNext() {
424	+	return cursor <= size || forgetMeNot != null;
425	+	}
426	+
427	+	public E next() {
428	+	checkForComodification();
429	+	E result;
430	+	if (cursor <= size) {
431	+	result = (E) queue[cursor];
432	+	lastRet = cursor++;
433	+	}
434	+	else if (forgetMeNot == null)
435	+	throw new NoSuchElementException();
436	+	else {
437	+	int remaining = forgetMeNot.size();
438	+	result = forgetMeNot.remove(remaining - 1);
439	+	if (remaining == 1)
440	+	forgetMeNot = null;
441	+	lastRet = 0;
442	+	lastRetElt = result;
443	+	}
444	+	return result;
445	+	}
446	+
447	+	public void remove() {
448	+	checkForComodification();
449	+
450	+	if (lastRet != 0) {
451	+	E moved = PriorityQueue.this.removeAt(lastRet);
452	+	lastRet = 0;
453	+	if (moved == null) {
454	+	cursor--;
455	+	} else {
456	+	if (forgetMeNot == null)
457	+	forgetMeNot = new ArrayList<E>();
458	+	forgetMeNot.add(moved);
459	+	}
460	+	} else if (lastRetElt != null) {
461	+	PriorityQueue.this.remove(lastRetElt);
462	+	lastRetElt = null;
463	+	} else {
464	+	throw new IllegalStateException();
465	+	}
466	+
467	+	expectedModCount = modCount;
468	+	}
469	+
470	+	final void checkForComodification() {
471	+	if (modCount != expectedModCount)
472	+	throw new ConcurrentModificationException();
473	+	}
474	+	}
475	+
476		public int size() {
477	<	return 0;
477	>	return size;
478		}
479	<	public Object[] toArray() {
480	<	return null;
479	>
480	>	/**
481	>	* Remove all elements from the priority queue.
482	>	*/
483	>	public void clear() {
484	>	modCount++;
485	>
486	>	// Null out element references to prevent memory leak
487	>	for (int i=1; i<=size; i++)
488	>	queue[i] = null;
489	>
490	>	size = 0;
491	>	}
492	>
493	>	public E poll() {
494	>	if (size == 0)
495	>	return null;
496	>	modCount++;
497	>
498	>	E result = (E) queue[1];
499	>	queue[1] = queue[size];
500	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
501	>	if (size > 1)
502	>	fixDown(1);
503	>
504	>	return result;
505		}
506
507	<	public <T> T[] toArray(T[] array) {
507	>	/**
508	>	* Removes and returns the ith element from queue.  (Recall that queue
509	>	* is one-based, so 1 <= i <= size.)
510	>	*
511	>	* Normally this method leaves the elements at positions from 1 up to i-1,
512	>	* inclusive, untouched.  Under these circumstances, it returns null.
513	>	* Occasionally, in order to maintain the heap invariant, it must move
514	>	* the last element of the list to some index in the range [2, i-1],
515	>	* and move the element previously at position (i/2) to position i.
516	>	* Under these circumstances, this method returns the element that was
517	>	* previously at the end of the list and is now at some position between
518	>	* 2 and i-1 inclusive.
519	>	*/
520	>	private E removeAt(int i) {
521	>	assert i > 0 && i <= size;
522	>	modCount++;
523	>
524	>	E moved = (E) queue[size];
525	>	queue[i] = moved;
526	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
527	>	if (i <= size) {
528	>	fixDown(i);
529	>	if (queue[i] == moved) {
530	>	fixUp(i);
531	>	if (queue[i] != moved)
532	>	return moved;
533	>	}
534	>	}
535		return null;
536		}
537
538	+	/**
539	+	* Establishes the heap invariant (described above) assuming the heap
540	+	* satisfies the invariant except possibly for the leaf-node indexed by k
541	+	* (which may have a nextExecutionTime less than its parent's).
542	+	*
543	+	* This method functions by "promoting" queue[k] up the hierarchy
544	+	* (by swapping it with its parent) repeatedly until queue[k]
545	+	* is greater than or equal to its parent.
546	+	*/
547	+	private void fixUp(int k) {
548	+	if (comparator == null) {
549	+	while (k > 1) {
550	+	int j = k >> 1;
551	+	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
552	+	break;
553	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
554	+	k = j;
555	+	}
556	+	} else {
557	+	while (k > 1) {
558	+	int j = k >>> 1;
559	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
560	+	break;
561	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
562	+	k = j;
563	+	}
564	+	}
565	+	}
566	+
567	+	/**
568	+	* Establishes the heap invariant (described above) in the subtree
569	+	* rooted at k, which is assumed to satisfy the heap invariant except
570	+	* possibly for node k itself (which may be greater than its children).
571	+	*
572	+	* This method functions by "demoting" queue[k] down the hierarchy
573	+	* (by swapping it with its smaller child) repeatedly until queue[k]
574	+	* is less than or equal to its children.
575	+	*/
576	+	private void fixDown(int k) {
577	+	int j;
578	+	if (comparator == null) {
579	+	while ((j = k << 1) <= size && (j > 0)) {
580	+	if (j<size &&
581	+	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
582	+	j++; // j indexes smallest kid
583	+
584	+	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
585	+	break;
586	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
587	+	k = j;
588	+	}
589	+	} else {
590	+	while ((j = k << 1) <= size && (j > 0)) {
591	+	if (j<size &&
592	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
593	+	j++; // j indexes smallest kid
594	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
595	+	break;
596	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
597	+	k = j;
598	+	}
599	+	}
600	+	}
601	+
602	+	/**
603	+	* Establishes the heap invariant (described above) in the entire tree,
604	+	* assuming nothing about the order of the elements prior to the call.
605	+	*/
606	+	private void heapify() {
607	+	for (int i = size/2; i >= 1; i--)
608	+	fixDown(i);
609	+	}
610	+
611	+	/**
612	+	* Returns the comparator used to order this collection, or <tt>null</tt>
613	+	* if this collection is sorted according to its elements natural ordering
614	+	* (using <tt>Comparable</tt>).
615	+	*
616	+	* @return the comparator used to order this collection, or <tt>null</tt>
617	+	* if this collection is sorted according to its elements natural ordering.
618	+	*/
619	+	public Comparator<? super E> comparator() {
620	+	return comparator;
621	+	}
622	+
623	+	/**
624	+	* Save the state of the instance to a stream (that
625	+	* is, serialize it).
626	+	*
627	+	* @serialData The length of the array backing the instance is
628	+	* emitted (int), followed by all of its elements (each an
629	+	* <tt>Object</tt>) in the proper order.
630	+	* @param s the stream
631	+	*/
632	+	private void writeObject(java.io.ObjectOutputStream s)
633	+	throws java.io.IOException{
634	+	// Write out element count, and any hidden stuff
635	+	s.defaultWriteObject();
636	+
637	+	// Write out array length
638	+	s.writeInt(queue.length);
639	+
640	+	// Write out all elements in the proper order.
641	+	for (int i=1; i<=size; i++)
642	+	s.writeObject(queue[i]);
643	+	}
644	+
645	+	/**
646	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
647	+	* deserialize it).
648	+	* @param s the stream
649	+	*/
650	+	private void readObject(java.io.ObjectInputStream s)
651	+	throws java.io.IOException, ClassNotFoundException {
652	+	// Read in size, and any hidden stuff
653	+	s.defaultReadObject();
654	+
655	+	// Read in array length and allocate array
656	+	int arrayLength = s.readInt();
657	+	queue = new Object[arrayLength];
658	+
659	+	// Read in all elements in the proper order.
660	+	for (int i=1; i<=size; i++)
661	+	queue[i] = (E) s.readObject();
662	+	}
663	+
664		}

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