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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 1.41 by dl, Sat Sep 13 18:51:06 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
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	>	*
18	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
19	>	* with respect to the specified ordering.  If multiple elements are
20	>	* tied for least value, the head is one of those elements -- ties are
21	>	* broken arbitrarily.  The {@link #remove()} and {@link #poll()}
22	>	* methods remove and return the head of the queue, and the {@link
23	>	* #element()} and {@link #peek()} methods return, but do not delete,
24	>	* the head of the queue.
25	>	*
26	>	* <p>A priority queue is unbounded, but has an internal
27	>	* <i>capacity</i> governing the size of an array used to store the
28	>	* elements on the queue.  It is always at least as large as the queue
29	>	* size.  As elements are added to a priority queue, its capacity
30	>	* grows automatically.  The details of the growth policy are not
31	>	* specified.
32	>	*
33	>	* <p>This class implements all of the <em>optional</em> methods of
34	>	* the {@link Collection} and {@link Iterator} interfaces.  The
35	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
36	>	* guaranteed to traverse the elements of the PriorityQueue in any
37	>	* particular order. If you need ordered traversal, consider using
38	>	* <tt>Arrays.sort(pq.toArray())</tt>.
39	>	*
40	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
41	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
42	>	* instance concurrently if any of the threads modifies the list
43	>	* structurally. Instead, use the thread-safe {@link
44	>	* java.util.concurrent.PriorityBlockingQueue} class.
45	>	*
46	>	*
47	>	* <p>Implementation note: this implementation provides O(log(n)) time
48	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
49	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
50	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
51	>	* constant time for the retrieval methods (<tt>peek</tt>,
52	>	* <tt>element</tt>, and <tt>size</tt>).
53	>	*
54	>	* <p>This class is a member of the
55	>	* <a href="{@docRoot}/../guide/collections/index.html">
56	>	* Java Collections Framework</a>.
57	>	* @since 1.5
58	>	* @version %I%, %G%
59	>	* @author Josh Bloch
60	>	*/
61	>	public class PriorityQueue<E> extends AbstractQueue<E>
62	>	implements Queue<E>, java.io.Serializable {
63
64	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
64	>	private static final long serialVersionUID = -7720805057305804111L;
65
66	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
66	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
67
68	<	public boolean add(E x) {
69	<	return false;
68	>	/**
69	>	* Priority queue represented as a balanced binary heap: the two children
70	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
71	>	* ordered by comparator, or by the elements' natural ordering, if
72	>	* comparator is null:  For each node n in the heap and each descendant d
73	>	* of n, n <= d.
74	>	*
75	>	* The element with the lowest value is in queue[1], assuming the queue is
76	>	* nonempty.  (A one-based array is used in preference to the traditional
77	>	* zero-based array to simplify parent and child calculations.)
78	>	*
79	>	* queue.length must be >= 2, even if size == 0.
80	>	*/
81	>	private transient Object[] queue;
82	>
83	>	/**
84	>	* The number of elements in the priority queue.
85	>	*/
86	>	private int size = 0;
87	>
88	>	/**
89	>	* The comparator, or null if priority queue uses elements'
90	>	* natural ordering.
91	>	*/
92	>	private final Comparator<? super E> comparator;
93	>
94	>	/**
95	>	* The number of times this priority queue has been
96	>	* <i>structurally modified</i>.  See AbstractList for gory details.
97	>	*/
98	>	private transient int modCount = 0;
99	>
100	>	/**
101	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
102	>	* (11) that orders its elements according to their natural
103	>	* ordering (using <tt>Comparable</tt>).
104	>	*/
105	>	public PriorityQueue() {
106	>	this(DEFAULT_INITIAL_CAPACITY, null);
107		}
108	<	public boolean offer(E x) {
109	<	return false;
108	>
109	>	/**
110	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
111	>	* that orders its elements according to their natural ordering
112	>	* (using <tt>Comparable</tt>).
113	>	*
114	>	* @param initialCapacity the initial capacity for this priority queue.
115	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
116	>	* than 1
117	>	*/
118	>	public PriorityQueue(int initialCapacity) {
119	>	this(initialCapacity, null);
120		}
121	<	public boolean remove(Object x) {
122	<	return false;
121	>
122	>	/**
123	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
124	>	* that orders its elements according to the specified comparator.
125	>	*
126	>	* @param initialCapacity the initial capacity for this priority queue.
127	>	* @param comparator the comparator used to order this priority queue.
128	>	* If <tt>null</tt> then the order depends on the elements' natural
129	>	* ordering.
130	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
131	>	* than 1
132	>	*/
133	>	public PriorityQueue(int initialCapacity,
134	>	Comparator<? super E> comparator) {
135	>	if (initialCapacity < 1)
136	>	throw new IllegalArgumentException();
137	>	this.queue = new Object[initialCapacity + 1];
138	>	this.comparator = comparator;
139		}
140
141	<	public E remove() {
142	<	return null;
141	>	/**
142	>	* Common code to initialize underlying queue array across
143	>	* constructors below.
144	>	*/
145	>	private void initializeArray(Collection<? extends E> c) {
146	>	int sz = c.size();
147	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
148	>	Integer.MAX_VALUE - 1);
149	>	if (initialCapacity < 1)
150	>	initialCapacity = 1;
151	>
152	>	this.queue = new Object[initialCapacity + 1];
153		}
154	<	public Iterator<E> iterator() {
155	<	return null;
154	>
155	>	/**
156	>	* Initially fill elements of the queue array under the
157	>	* knowledge that it is sorted or is another PQ, in which
158	>	* case we can just place the elements in the order presented.
159	>	*/
160	>	private void fillFromSorted(Collection<? extends E> c) {
161	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
162	>	queue[++size] = i.next();
163		}
164
165	<	public E element() {
166	<	return null;
165	>	/**
166	>	* Initially fill elements of the queue array that is not to our knowledge
167	>	* sorted, so we must rearrange the elements to guarantee the heap
168	>	* invariant.
169	>	*/
170	>	private void fillFromUnsorted(Collection<? extends E> c) {
171	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
172	>	queue[++size] = i.next();
173	>	heapify();
174		}
175	<	public E poll() {
176	<	return null;
175	>
176	>	/**
177	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
178	>	* specified collection.  The priority queue has an initial
179	>	* capacity of 110% of the size of the specified collection or 1
180	>	* if the collection is empty.  If the specified collection is an
181	>	* instance of a {@link java.util.SortedSet} or is another
182	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
183	>	* according to the same comparator, or according to its elements'
184	>	* natural order if the collection is sorted according to its
185	>	* elements' natural order.  Otherwise, the priority queue is
186	>	* ordered according to its elements' natural order.
187	>	*
188	>	* @param c the collection whose elements are to be placed
189	>	*        into this priority queue.
190	>	* @throws ClassCastException if elements of the specified collection
191	>	*         cannot be compared to one another according to the priority
192	>	*         queue's ordering.
193	>	* @throws NullPointerException if <tt>c</tt> or any element within it
194	>	* is <tt>null</tt>
195	>	*/
196	>	public PriorityQueue(Collection<? extends E> c) {
197	>	initializeArray(c);
198	>	if (c instanceof SortedSet) {
199	>	// @fixme double-cast workaround for compiler
200	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
201	>	comparator = (Comparator<? super E>)s.comparator();
202	>	fillFromSorted(s);
203	>	} else if (c instanceof PriorityQueue) {
204	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
205	>	comparator = (Comparator<? super E>)s.comparator();
206	>	fillFromSorted(s);
207	>	} else {
208	>	comparator = null;
209	>	fillFromUnsorted(c);
210	>	}
211	>	}
212	>
213	>	/**
214	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
215	>	* specified collection.  The priority queue has an initial
216	>	* capacity of 110% of the size of the specified collection or 1
217	>	* if the collection is empty.  This priority queue will be sorted
218	>	* according to the same comparator as the given collection, or
219	>	* according to its elements' natural order if the collection is
220	>	* sorted according to its elements' natural order.
221	>	*
222	>	* @param c the collection whose elements are to be placed
223	>	*        into this priority queue.
224	>	* @throws ClassCastException if elements of the specified collection
225	>	*         cannot be compared to one another according to the priority
226	>	*         queue's ordering.
227	>	* @throws NullPointerException if <tt>c</tt> or any element within it
228	>	* is <tt>null</tt>
229	>	*/
230	>	public PriorityQueue(PriorityQueue<? extends E> c) {
231	>	initializeArray(c);
232	>	comparator = (Comparator<? super E>)c.comparator();
233	>	fillFromSorted(c);
234		}
235	+
236	+	/**
237	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
238	+	* specified collection.  The priority queue has an initial
239	+	* capacity of 110% of the size of the specified collection or 1
240	+	* if the collection is empty.  This priority queue will be sorted
241	+	* according to the same comparator as the given collection, or
242	+	* according to its elements' natural order if the collection is
243	+	* sorted according to its elements' natural order.
244	+	*
245	+	* @param c the collection whose elements are to be placed
246	+	*        into this priority queue.
247	+	* @throws ClassCastException if elements of the specified collection
248	+	*         cannot be compared to one another according to the priority
249	+	*         queue's ordering.
250	+	* @throws NullPointerException if <tt>c</tt> or any element within it
251	+	* is <tt>null</tt>
252	+	*/
253	+	public PriorityQueue(SortedSet<? extends E> c) {
254	+	initializeArray(c);
255	+	comparator = (Comparator<? super E>)c.comparator();
256	+	fillFromSorted(c);
257	+	}
258	+
259	+	/**
260	+	* Resize array, if necessary, to be able to hold given index
261	+	*/
262	+	private void grow(int index) {
263	+	int newlen = queue.length;
264	+	if (index < newlen) // don't need to grow
265	+	return;
266	+	if (index == Integer.MAX_VALUE)
267	+	throw new OutOfMemoryError();
268	+	while (newlen <= index) {
269	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
270	+	newlen = Integer.MAX_VALUE;
271	+	else
272	+	newlen <<= 2;
273	+	}
274	+	Object[] newQueue = new Object[newlen];
275	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
276	+	queue = newQueue;
277	+	}
278	+
279	+
280	+	/**
281	+	* Inserts the specified element to this priority queue.
282	+	*
283	+	* @return <tt>true</tt>
284	+	* @throws ClassCastException if the specified element cannot be compared
285	+	* with elements currently in the priority queue according
286	+	* to the priority queue's ordering.
287	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
288	+	*/
289	+	public boolean offer(E o) {
290	+	if (o == null)
291	+	throw new NullPointerException();
292	+	modCount++;
293	+	++size;
294	+
295	+	// Grow backing store if necessary
296	+	if (size >= queue.length)
297	+	grow(size);
298	+
299	+	queue[size] = o;
300	+	fixUp(size);
301	+	return true;
302	+	}
303	+
304		public E peek() {
305	<	return null;
305	>	if (size == 0)
306	>	return null;
307	>	return (E) queue[1];
308		}
309
310	<	public boolean isEmpty() {
310	>	// Collection Methods - the first two override to update docs
311	>
312	>	/**
313	>	* Adds the specified element to this queue.
314	>	* @return <tt>true</tt> (as per the general contract of
315	>	* <tt>Collection.add</tt>).
316	>	*
317	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
318	>	* @throws ClassCastException if the specified element cannot be compared
319	>	* with elements currently in the priority queue according
320	>	* to the priority queue's ordering.
321	>	*/
322	>	public boolean add(E o) {
323	>	return offer(o);
324	>	}
325	>
326	>
327	>	/**
328	>	* Adds all of the elements in the specified collection to this queue.
329	>	* The behavior of this operation is undefined if
330	>	* the specified collection is modified while the operation is in
331	>	* progress.  (This implies that the behavior of this call is undefined if
332	>	* the specified collection is this queue, and this queue is nonempty.)
333	>	* <p>
334	>	* This implementation iterates over the specified collection, and adds
335	>	* each object returned by the iterator to this collection, in turn.
336	>	* @param c collection whose elements are to be added to this queue
337	>	* @return <tt>true</tt> if this queue changed as a result of the
338	>	*         call.
339	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
340	>	* is <tt>null</tt>
341	>	* @throws ClassCastException if any element cannot be compared
342	>	* with elements currently in the priority queue according
343	>	* to the priority queue's ordering.
344	>	*/
345	>	public boolean addAll(Collection<? extends E> c) {
346	>	return super.addAll(c);
347	>	}
348	>
349	>	public boolean remove(Object o) {
350	>	if (o == null)
351	>	return false;
352	>
353	>	if (comparator == null) {
354	>	for (int i = 1; i <= size; i++) {
355	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
356	>	removeAt(i);
357	>	return true;
358	>	}
359	>	}
360	>	} else {
361	>	for (int i = 1; i <= size; i++) {
362	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
363	>	removeAt(i);
364	>	return true;
365	>	}
366	>	}
367	>	}
368		return false;
369		}
370	+
371	+	/**
372	+	* Returns an iterator over the elements in this queue. The iterator
373	+	* does not return the elements in any particular order.
374	+	*
375	+	* @return an iterator over the elements in this queue.
376	+	*/
377	+	public Iterator<E> iterator() {
378	+	return new Itr();
379	+	}
380	+
381	+	private class Itr implements Iterator<E> {
382	+
383	+	/**
384	+	* Index (into queue array) of element to be returned by
385	+	* subsequent call to next.
386	+	*/
387	+	private int cursor = 1;
388	+
389	+	/**
390	+	* Index of element returned by most recent call to next,
391	+	* unless that element came from the forgetMeNot list.
392	+	* Reset to 0 if element is deleted by a call to remove.
393	+	*/
394	+	private int lastRet = 0;
395	+
396	+	/**
397	+	* The modCount value that the iterator believes that the backing
398	+	* List should have.  If this expectation is violated, the iterator
399	+	* has detected concurrent modification.
400	+	*/
401	+	private int expectedModCount = modCount;
402	+
403	+	/**
404	+	* A list of elements that were moved from the unvisited portion of
405	+	* the heap into the visited portion as a result of "unlucky" element
406	+	* removals during the iteration.  (Unlucky element removals are those
407	+	* that require a fixup instead of a fixdown.)  We must visit all of
408	+	* the elements in this list to complete the iteration.  We do this
409	+	* after we've completed the "normal" iteration.
410	+	*
411	+	* We expect that most iterations, even those involving removals,
412	+	* will not use need to store elements in this field.
413	+	*/
414	+	private ArrayList<E> forgetMeNot = null;
415	+
416	+	/**
417	+	* Element returned by the most recent call to next iff that
418	+	* element was drawn from the forgetMeNot list.
419	+	*/
420	+	private Object lastRetElt = null;
421	+
422	+	public boolean hasNext() {
423	+	return cursor <= size || forgetMeNot != null;
424	+	}
425	+
426	+	public E next() {
427	+	checkForComodification();
428	+	E result;
429	+	if (cursor <= size) {
430	+	result = (E) queue[cursor];
431	+	lastRet = cursor++;
432	+	}
433	+	else if (forgetMeNot == null)
434	+	throw new NoSuchElementException();
435	+	else {
436	+	int remaining = forgetMeNot.size();
437	+	result = forgetMeNot.remove(remaining - 1);
438	+	if (remaining == 1)
439	+	forgetMeNot = null;
440	+	lastRet = 0;
441	+	lastRetElt = result;
442	+	}
443	+	return result;
444	+	}
445	+
446	+	public void remove() {
447	+	checkForComodification();
448	+
449	+	if (lastRet != 0) {
450	+	E moved = PriorityQueue.this.removeAt(lastRet);
451	+	lastRet = 0;
452	+	if (moved == null) {
453	+	cursor--;
454	+	} else {
455	+	if (forgetMeNot == null)
456	+	forgetMeNot = new ArrayList<E>();
457	+	forgetMeNot.add(moved);
458	+	}
459	+	} else if (lastRetElt != null) {
460	+	PriorityQueue.this.remove(lastRetElt);
461	+	lastRetElt = null;
462	+	} else {
463	+	throw new IllegalStateException();
464	+	}
465	+
466	+	expectedModCount = modCount;
467	+	}
468	+
469	+	final void checkForComodification() {
470	+	if (modCount != expectedModCount)
471	+	throw new ConcurrentModificationException();
472	+	}
473	+	}
474	+
475		public int size() {
476	<	return 0;
476	>	return size;
477		}
478	<	public Object[] toArray() {
479	<	return null;
478	>
479	>	/**
480	>	* Remove all elements from the priority queue.
481	>	*/
482	>	public void clear() {
483	>	modCount++;
484	>
485	>	// Null out element references to prevent memory leak
486	>	for (int i=1; i<=size; i++)
487	>	queue[i] = null;
488	>
489	>	size = 0;
490	>	}
491	>
492	>	public E poll() {
493	>	if (size == 0)
494	>	return null;
495	>	modCount++;
496	>
497	>	E result = (E) queue[1];
498	>	queue[1] = queue[size];
499	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
500	>	if (size > 1)
501	>	fixDown(1);
502	>
503	>	return result;
504		}
505
506	<	public <T> T[] toArray(T[] array) {
506	>	/**
507	>	* Removes and returns the ith element from queue.  (Recall that queue
508	>	* is one-based, so 1 <= i <= size.)
509	>	*
510	>	* Normally this method leaves the elements at positions from 1 up to i-1,
511	>	* inclusive, untouched.  Under these circumstances, it returns null.
512	>	* Occasionally, in order to maintain the heap invariant, it must move
513	>	* the last element of the list to some index in the range [2, i-1],
514	>	* and move the element previously at position (i/2) to position i.
515	>	* Under these circumstances, this method returns the element that was
516	>	* previously at the end of the list and is now at some position between
517	>	* 2 and i-1 inclusive.
518	>	*/
519	>	private E removeAt(int i) {
520	>	assert i > 0 && i <= size;
521	>	modCount++;
522	>
523	>	E moved = (E) queue[size];
524	>	queue[i] = moved;
525	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
526	>	if (i <= size) {
527	>	fixDown(i);
528	>	if (queue[i] == moved) {
529	>	fixUp(i);
530	>	if (queue[i] != moved)
531	>	return moved;
532	>	}
533	>	}
534		return null;
535		}
536
537	+	/**
538	+	* Establishes the heap invariant (described above) assuming the heap
539	+	* satisfies the invariant except possibly for the leaf-node indexed by k
540	+	* (which may have a nextExecutionTime less than its parent's).
541	+	*
542	+	* This method functions by "promoting" queue[k] up the hierarchy
543	+	* (by swapping it with its parent) repeatedly until queue[k]
544	+	* is greater than or equal to its parent.
545	+	*/
546	+	private void fixUp(int k) {
547	+	if (comparator == null) {
548	+	while (k > 1) {
549	+	int j = k >> 1;
550	+	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
551	+	break;
552	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
553	+	k = j;
554	+	}
555	+	} else {
556	+	while (k > 1) {
557	+	int j = k >>> 1;
558	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
559	+	break;
560	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
561	+	k = j;
562	+	}
563	+	}
564	+	}
565	+
566	+	/**
567	+	* Establishes the heap invariant (described above) in the subtree
568	+	* rooted at k, which is assumed to satisfy the heap invariant except
569	+	* possibly for node k itself (which may be greater than its children).
570	+	*
571	+	* This method functions by "demoting" queue[k] down the hierarchy
572	+	* (by swapping it with its smaller child) repeatedly until queue[k]
573	+	* is less than or equal to its children.
574	+	*/
575	+	private void fixDown(int k) {
576	+	int j;
577	+	if (comparator == null) {
578	+	while ((j = k << 1) <= size && (j > 0)) {
579	+	if (j<size &&
580	+	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
581	+	j++; // j indexes smallest kid
582	+
583	+	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
584	+	break;
585	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
586	+	k = j;
587	+	}
588	+	} else {
589	+	while ((j = k << 1) <= size && (j > 0)) {
590	+	if (j<size &&
591	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
592	+	j++; // j indexes smallest kid
593	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
594	+	break;
595	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
596	+	k = j;
597	+	}
598	+	}
599	+	}
600	+
601	+	/**
602	+	* Establishes the heap invariant (described above) in the entire tree,
603	+	* assuming nothing about the order of the elements prior to the call.
604	+	*/
605	+	private void heapify() {
606	+	for (int i = size/2; i >= 1; i--)
607	+	fixDown(i);
608	+	}
609	+
610	+	/**
611	+	* Returns the comparator used to order this collection, or <tt>null</tt>
612	+	* if this collection is sorted according to its elements natural ordering
613	+	* (using <tt>Comparable</tt>).
614	+	*
615	+	* @return the comparator used to order this collection, or <tt>null</tt>
616	+	* if this collection is sorted according to its elements natural ordering.
617	+	*/
618	+	public Comparator<? super E> comparator() {
619	+	return comparator;
620	+	}
621	+
622	+	/**
623	+	* Save the state of the instance to a stream (that
624	+	* is, serialize it).
625	+	*
626	+	* @serialData The length of the array backing the instance is
627	+	* emitted (int), followed by all of its elements (each an
628	+	* <tt>Object</tt>) in the proper order.
629	+	* @param s the stream
630	+	*/
631	+	private void writeObject(java.io.ObjectOutputStream s)
632	+	throws java.io.IOException{
633	+	// Write out element count, and any hidden stuff
634	+	s.defaultWriteObject();
635	+
636	+	// Write out array length
637	+	s.writeInt(queue.length);
638	+
639	+	// Write out all elements in the proper order.
640	+	for (int i=1; i<=size; i++)
641	+	s.writeObject(queue[i]);
642	+	}
643	+
644	+	/**
645	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
646	+	* deserialize it).
647	+	* @param s the stream
648	+	*/
649	+	private void readObject(java.io.ObjectInputStream s)
650	+	throws java.io.IOException, ClassNotFoundException {
651	+	// Read in size, and any hidden stuff
652	+	s.defaultReadObject();
653	+
654	+	// Read in array length and allocate array
655	+	int arrayLength = s.readInt();
656	+	queue = new Object[arrayLength];
657	+
658	+	// Read in all elements in the proper order.
659	+	for (int i=1; i<=size; i++)
660	+	queue[i] = (E) s.readObject();
661	+	}
662	+
663		}

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