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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 1.69 by jsr166, Sun May 18 23:59:57 2008 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* Copyright 2003-2006 Sun Microsystems, Inc.  All Rights Reserved.
3	>	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	>	*
5	>	* This code is free software; you can redistribute it and/or modify it
6	>	* 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	<	import java.util.*;
26	>	package java.util;
27
28		/**
29	<	* An unbounded (resizable) priority queue based on a priority
30	<	* heap.The take operation returns the least element with respect to
31	<	* the given ordering. (If more than one element is tied for least
32	<	* value, one of them is arbitrarily chosen to be returned -- no
33	<	* guarantees are made for ordering across ties.) Ordering follows the
34	<	* java.util.Collection conventions: Either the elements must be
35	<	* Comparable, or a Comparator must be supplied. Comparison failures
36	<	* throw ClassCastExceptions during insertions and extractions.
37	<	**/
38	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
39	<	public PriorityQueue(int initialCapacity) {}
40	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
29	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
30	>	* The elements of the priority queue are ordered according to their
31	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
32	>	* provided at queue construction time, depending on which constructor is
33	>	* used.  A priority queue does not permit {@code null} elements.
34	>	* A priority queue relying on natural ordering also does not permit
35	>	* insertion of non-comparable objects (doing so may result in
36	>	* {@code ClassCastException}).
37	>	*
38	>	* <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
40	>	* tied for least value, the head is one of those elements -- ties are
41	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
42	>	* {@code remove}, {@code peek}, and {@code element} access the
43	>	* element at the head of the queue.
44	>	*
45	>	* <p>A priority queue is unbounded, but has an internal
46	>	* <i>capacity</i> governing the size of an array used to store the
47	>	* elements on the queue.  It is always at least as large as the queue
48	>	* size.  As elements are added to a priority queue, its capacity
49	>	* grows automatically.  The details of the growth policy are not
50	>	* specified.
51	>	*
52	>	* <p>This class and its iterator implement all of the
53	>	* <em>optional</em> methods of the {@link Collection} and {@link
54	>	* Iterator} interfaces.  The Iterator provided in method {@link
55	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
56	>	* the priority queue in any particular order. If you need ordered
57	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
58	>	*
59	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
60	>	* Multiple threads should not access a {@code PriorityQueue}
61	>	* instance concurrently if any of the threads modifies the queue.
62	>	* Instead, use the thread-safe {@link
63	>	* java.util.concurrent.PriorityBlockingQueue} class.
64	>	*
65	>	* <p>Implementation note: this implementation provides
66	>	* O(log(n)) time for the enqueing and dequeing methods
67	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
68	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
69	>	* methods; and constant time for the retrieval methods
70	>	* ({@code peek}, {@code element}, and {@code size}).
71	>	*
72	>	* <p>This class is a member of the
73	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
74	>	* Java Collections Framework</a>.
75	>	*
76	>	* @since 1.5
77	>	* @author Josh Bloch, Doug Lea
78	>	* @param <E> the type of elements held in this collection
79	>	*/
80	>	public class PriorityQueue<E> extends AbstractQueue<E>
81	>	implements java.io.Serializable {
82
83	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
83	>	private static final long serialVersionUID = -7720805057305804111L;
84
85	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
85	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
86
87	<	public boolean add(E x) {
88	<	return false;
87	>	/**
88	>	* Priority queue represented as a balanced binary heap: the two
89	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
90	>	* priority queue is ordered by comparator, or by the elements'
91	>	* natural ordering, if comparator is null: For each node n in the
92	>	* heap and each descendant d of n, n <= d.  The element with the
93	>	* lowest value is in queue[0], assuming the queue is nonempty.
94	>	*/
95	>	private transient Object[] queue;
96	>
97	>	/**
98	>	* The number of elements in the priority queue.
99	>	*/
100	>	private int size = 0;
101	>
102	>	/**
103	>	* The comparator, or null if priority queue uses elements'
104	>	* natural ordering.
105	>	*/
106	>	private final Comparator<? super E> comparator;
107	>
108	>	/**
109	>	* The number of times this priority queue has been
110	>	* <i>structurally modified</i>.  See AbstractList for gory details.
111	>	*/
112	>	private transient int modCount = 0;
113	>
114	>	/**
115	>	* Creates a {@code PriorityQueue} with the default initial
116	>	* capacity (11) that orders its elements according to their
117	>	* {@linkplain Comparable natural ordering}.
118	>	*/
119	>	public PriorityQueue() {
120	>	this(DEFAULT_INITIAL_CAPACITY, null);
121		}
122	<	public boolean offer(E x) {
123	<	return false;
122	>
123	>	/**
124	>	* Creates a {@code PriorityQueue} with the specified initial
125	>	* capacity that orders its elements according to their
126	>	* {@linkplain Comparable natural ordering}.
127	>	*
128	>	* @param initialCapacity the initial capacity for this priority queue
129	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
130	>	*         than 1
131	>	*/
132	>	public PriorityQueue(int initialCapacity) {
133	>	this(initialCapacity, null);
134		}
135	<	public boolean remove(Object x) {
136	<	return false;
135	>
136	>	/**
137	>	* Creates a {@code PriorityQueue} with the specified initial capacity
138	>	* that orders its elements according to the specified comparator.
139	>	*
140	>	* @param  initialCapacity the initial capacity for this priority queue
141	>	* @param  comparator the comparator that will be used to order this
142	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
143	>	*         natural ordering} of the elements will be used.
144	>	* @throws IllegalArgumentException if {@code initialCapacity} is
145	>	*         less than 1
146	>	*/
147	>	public PriorityQueue(int initialCapacity,
148	>	Comparator<? super E> comparator) {
149	>	// Note: This restriction of at least one is not actually needed,
150	>	// but continues for 1.5 compatibility
151	>	if (initialCapacity < 1)
152	>	throw new IllegalArgumentException();
153	>	this.queue = new Object[initialCapacity];
154	>	this.comparator = comparator;
155		}
156
157	<	public E remove() {
158	<	return null;
157	>	/**
158	>	* Creates a {@code PriorityQueue} containing the elements in the
159	>	* specified collection.  If the specified collection is an instance of
160	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
161	>	* priority queue will be ordered according to the same ordering.
162	>	* Otherwise, this priority queue will be ordered according to the
163	>	* {@linkplain Comparable natural ordering} of its elements.
164	>	*
165	>	* @param  c the collection whose elements are to be placed
166	>	*         into this priority queue
167	>	* @throws ClassCastException if elements of the specified collection
168	>	*         cannot be compared to one another according to the priority
169	>	*         queue's ordering
170	>	* @throws NullPointerException if the specified collection or any
171	>	*         of its elements are null
172	>	*/
173	>	public PriorityQueue(Collection<? extends E> c) {
174	>	initFromCollection(c);
175	>	if (c instanceof SortedSet)
176	>	comparator = (Comparator<? super E>)
177	>	((SortedSet<? extends E>)c).comparator();
178	>	else if (c instanceof PriorityQueue)
179	>	comparator = (Comparator<? super E>)
180	>	((PriorityQueue<? extends E>)c).comparator();
181	>	else {
182	>	comparator = null;
183	>	heapify();
184	>	}
185		}
186	<	public Iterator<E> iterator() {
187	<	return null;
186	>
187	>	/**
188	>	* Creates a {@code PriorityQueue} containing the elements in the
189	>	* specified priority queue.  This priority queue will be
190	>	* ordered according to the same ordering as the given priority
191	>	* queue.
192	>	*
193	>	* @param  c the priority queue whose elements are to be placed
194	>	*         into this priority queue
195	>	* @throws ClassCastException if elements of {@code c} cannot be
196	>	*         compared to one another according to {@code c}'s
197	>	*         ordering
198	>	* @throws NullPointerException if the specified priority queue or any
199	>	*         of its elements are null
200	>	*/
201	>	public PriorityQueue(PriorityQueue<? extends E> c) {
202	>	comparator = (Comparator<? super E>)c.comparator();
203	>	initFromCollection(c);
204		}
205
206	<	public E element() {
207	<	return null;
206	>	/**
207	>	* Creates a {@code PriorityQueue} containing the elements in the
208	>	* specified sorted set.   This priority queue will be ordered
209	>	* according to the same ordering as the given sorted set.
210	>	*
211	>	* @param  c the sorted set whose elements are to be placed
212	>	*         into this priority queue
213	>	* @throws ClassCastException if elements of the specified sorted
214	>	*         set cannot be compared to one another according to the
215	>	*         sorted set's ordering
216	>	* @throws NullPointerException if the specified sorted set or any
217	>	*         of its elements are null
218	>	*/
219	>	public PriorityQueue(SortedSet<? extends E> c) {
220	>	comparator = (Comparator<? super E>)c.comparator();
221	>	initFromCollection(c);
222		}
223	<	public E poll() {
224	<	return null;
223	>
224	>	/**
225	>	* Initializes queue array with elements from the given Collection.
226	>	*
227	>	* @param c the collection
228	>	*/
229	>	private void initFromCollection(Collection<? extends E> c) {
230	>	Object[] a = c.toArray();
231	>	// If c.toArray incorrectly doesn't return Object[], copy it.
232	>	if (a.getClass() != Object[].class)
233	>	a = Arrays.copyOf(a, a.length, Object[].class);
234	>	queue = a;
235	>	size = a.length;
236		}
237	+
238	+	/**
239	+	* Increases the capacity of the array.
240	+	*
241	+	* @param minCapacity the desired minimum capacity
242	+	*/
243	+	private void grow(int minCapacity) {
244	+	if (minCapacity < 0) // overflow
245	+	throw new OutOfMemoryError();
246	+	int oldCapacity = queue.length;
247	+	// Double size if small; else grow by 50%
248	+	int newCapacity = ((oldCapacity < 64)?
249	+	((oldCapacity + 1) * 2):
250	+	((oldCapacity / 2) * 3));
251	+	if (newCapacity < 0) // overflow
252	+	newCapacity = Integer.MAX_VALUE;
253	+	if (newCapacity < minCapacity)
254	+	newCapacity = minCapacity;
255	+	queue = Arrays.copyOf(queue, newCapacity);
256	+	}
257	+
258	+	/**
259	+	* Inserts the specified element into this priority queue.
260	+	*
261	+	* @return {@code true} (as specified by {@link Collection#add})
262	+	* @throws ClassCastException if the specified element cannot be
263	+	*         compared with elements currently in this priority queue
264	+	*         according to the priority queue's ordering
265	+	* @throws NullPointerException if the specified element is null
266	+	*/
267	+	public boolean add(E e) {
268	+	return offer(e);
269	+	}
270	+
271	+	/**
272	+	* Inserts the specified element into this priority queue.
273	+	*
274	+	* @return {@code true} (as specified by {@link Queue#offer})
275	+	* @throws ClassCastException if the specified element cannot be
276	+	*         compared with elements currently in this priority queue
277	+	*         according to the priority queue's ordering
278	+	* @throws NullPointerException if the specified element is null
279	+	*/
280	+	public boolean offer(E e) {
281	+	if (e == null)
282	+	throw new NullPointerException();
283	+	modCount++;
284	+	int i = size;
285	+	if (i >= queue.length)
286	+	grow(i + 1);
287	+	size = i + 1;
288	+	if (i == 0)
289	+	queue[0] = e;
290	+	else
291	+	siftUp(i, e);
292	+	return true;
293	+	}
294	+
295		public E peek() {
296	<	return null;
296	>	if (size == 0)
297	>	return null;
298	>	return (E) queue[0];
299		}
300
301	<	public boolean isEmpty() {
301	>	private int indexOf(Object o) {
302	>	if (o != null) {
303	>	for (int i = 0; i < size; i++)
304	>	if (o.equals(queue[i]))
305	>	return i;
306	>	}
307	>	return -1;
308	>	}
309	>
310	>	/**
311	>	* Removes a single instance of the specified element from this queue,
312	>	* if it is present.  More formally, removes an element {@code e} such
313	>	* that {@code o.equals(e)}, if this queue contains one or more such
314	>	* elements.  Returns {@code true} if and only if this queue contained
315	>	* the specified element (or equivalently, if this queue changed as a
316	>	* result of the call).
317	>	*
318	>	* @param o element to be removed from this queue, if present
319	>	* @return {@code true} if this queue changed as a result of the call
320	>	*/
321	>	public boolean remove(Object o) {
322	>	int i = indexOf(o);
323	>	if (i == -1)
324	>	return false;
325	>	else {
326	>	removeAt(i);
327	>	return true;
328	>	}
329	>	}
330	>
331	>	/**
332	>	* Version of remove using reference equality, not equals.
333	>	* Needed by iterator.remove.
334	>	*
335	>	* @param o element to be removed from this queue, if present
336	>	* @return {@code true} if removed
337	>	*/
338	>	boolean removeEq(Object o) {
339	>	for (int i = 0; i < size; i++) {
340	>	if (o == queue[i]) {
341	>	removeAt(i);
342	>	return true;
343	>	}
344	>	}
345		return false;
346		}
347	<	public int size() {
348	<	return 0;
347	>
348	>	/**
349	>	* Returns {@code true} if this queue contains the specified element.
350	>	* More formally, returns {@code true} if and only if this queue contains
351	>	* at least one element {@code e} such that {@code o.equals(e)}.
352	>	*
353	>	* @param o object to be checked for containment in this queue
354	>	* @return {@code true} if this queue contains the specified element
355	>	*/
356	>	public boolean contains(Object o) {
357	>	return indexOf(o) != -1;
358		}
359	+
360	+	/**
361	+	* Returns an array containing all of the elements in this queue.
362	+	* The elements are in no particular order.
363	+	*
364	+	* <p>The returned array will be "safe" in that no references to it are
365	+	* maintained by this queue.  (In other words, this method must allocate
366	+	* a new array).  The caller is thus free to modify the returned array.
367	+	*
368	+	* <p>This method acts as bridge between array-based and collection-based
369	+	* APIs.
370	+	*
371	+	* @return an array containing all of the elements in this queue
372	+	*/
373		public Object[] toArray() {
374	<	return null;
374	>	return Arrays.copyOf(queue, size);
375	>	}
376	>
377	>	/**
378	>	* Returns an array containing all of the elements in this queue; the
379	>	* runtime type of the returned array is that of the specified array.
380	>	* The returned array elements are in no particular order.
381	>	* If the queue fits in the specified array, it is returned therein.
382	>	* Otherwise, a new array is allocated with the runtime type of the
383	>	* specified array and the size of this queue.
384	>	*
385	>	* <p>If the queue fits in the specified array with room to spare
386	>	* (i.e., the array has more elements than the queue), the element in
387	>	* the array immediately following the end of the collection is set to
388	>	* {@code null}.
389	>	*
390	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
391	>	* array-based and collection-based APIs.  Further, this method allows
392	>	* precise control over the runtime type of the output array, and may,
393	>	* under certain circumstances, be used to save allocation costs.
394	>	*
395	>	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
396	>	* The following code can be used to dump the queue into a newly
397	>	* allocated array of <tt>String</tt>:
398	>	*
399	>	* <pre>
400	>	*     String[] y = x.toArray(new String[0]);</pre>
401	>	*
402	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
403	>	* <tt>toArray()</tt>.
404	>	*
405	>	* @param a the array into which the elements of the queue are to
406	>	*          be stored, if it is big enough; otherwise, a new array of the
407	>	*          same runtime type is allocated for this purpose.
408	>	* @return an array containing all of the elements in this queue
409	>	* @throws ArrayStoreException if the runtime type of the specified array
410	>	*         is not a supertype of the runtime type of every element in
411	>	*         this queue
412	>	* @throws NullPointerException if the specified array is null
413	>	*/
414	>	public <T> T[] toArray(T[] a) {
415	>	if (a.length < size)
416	>	// Make a new array of a's runtime type, but my contents:
417	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
418	>	System.arraycopy(queue, 0, a, 0, size);
419	>	if (a.length > size)
420	>	a[size] = null;
421	>	return a;
422		}
423
424	<	public <T> T[] toArray(T[] array) {
424	>	/**
425	>	* Returns an iterator over the elements in this queue. The iterator
426	>	* does not return the elements in any particular order.
427	>	*
428	>	* @return an iterator over the elements in this queue
429	>	*/
430	>	public Iterator<E> iterator() {
431	>	return new Itr();
432	>	}
433	>
434	>	private final class Itr implements Iterator<E> {
435	>	/**
436	>	* Index (into queue array) of element to be returned by
437	>	* subsequent call to next.
438	>	*/
439	>	private int cursor = 0;
440	>
441	>	/**
442	>	* Index of element returned by most recent call to next,
443	>	* unless that element came from the forgetMeNot list.
444	>	* Set to -1 if element is deleted by a call to remove.
445	>	*/
446	>	private int lastRet = -1;
447	>
448	>	/**
449	>	* A queue of elements that were moved from the unvisited portion of
450	>	* the heap into the visited portion as a result of "unlucky" element
451	>	* removals during the iteration.  (Unlucky element removals are those
452	>	* that require a siftup instead of a siftdown.)  We must visit all of
453	>	* the elements in this list to complete the iteration.  We do this
454	>	* after we've completed the "normal" iteration.
455	>	*
456	>	* We expect that most iterations, even those involving removals,
457	>	* will not need to store elements in this field.
458	>	*/
459	>	private ArrayDeque<E> forgetMeNot = null;
460	>
461	>	/**
462	>	* Element returned by the most recent call to next iff that
463	>	* element was drawn from the forgetMeNot list.
464	>	*/
465	>	private E lastRetElt = null;
466	>
467	>	/**
468	>	* The modCount value that the iterator believes that the backing
469	>	* Queue should have.  If this expectation is violated, the iterator
470	>	* has detected concurrent modification.
471	>	*/
472	>	private int expectedModCount = modCount;
473	>
474	>	public boolean hasNext() {
475	>	return cursor < size ||
476	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
477	>	}
478	>
479	>	public E next() {
480	>	if (expectedModCount != modCount)
481	>	throw new ConcurrentModificationException();
482	>	if (cursor < size)
483	>	return (E) queue[lastRet = cursor++];
484	>	if (forgetMeNot != null) {
485	>	lastRet = -1;
486	>	lastRetElt = forgetMeNot.poll();
487	>	if (lastRetElt != null)
488	>	return lastRetElt;
489	>	}
490	>	throw new NoSuchElementException();
491	>	}
492	>
493	>	public void remove() {
494	>	if (expectedModCount != modCount)
495	>	throw new ConcurrentModificationException();
496	>	if (lastRet != -1) {
497	>	E moved = PriorityQueue.this.removeAt(lastRet);
498	>	lastRet = -1;
499	>	if (moved == null)
500	>	cursor--;
501	>	else {
502	>	if (forgetMeNot == null)
503	>	forgetMeNot = new ArrayDeque<E>();
504	>	forgetMeNot.add(moved);
505	>	}
506	>	} else if (lastRetElt != null) {
507	>	PriorityQueue.this.removeEq(lastRetElt);
508	>	lastRetElt = null;
509	>	} else {
510	>	throw new IllegalStateException();
511	>	}
512	>	expectedModCount = modCount;
513	>	}
514	>	}
515	>
516	>	public int size() {
517	>	return size;
518	>	}
519	>
520	>	/**
521	>	* Removes all of the elements from this priority queue.
522	>	* The queue will be empty after this call returns.
523	>	*/
524	>	public void clear() {
525	>	modCount++;
526	>	for (int i = 0; i < size; i++)
527	>	queue[i] = null;
528	>	size = 0;
529	>	}
530	>
531	>	public E poll() {
532	>	if (size == 0)
533	>	return null;
534	>	int s = --size;
535	>	modCount++;
536	>	E result = (E) queue[0];
537	>	E x = (E) queue[s];
538	>	queue[s] = null;
539	>	if (s != 0)
540	>	siftDown(0, x);
541	>	return result;
542	>	}
543	>
544	>	/**
545	>	* Removes the ith element from queue.
546	>	*
547	>	* Normally this method leaves the elements at up to i-1,
548	>	* inclusive, untouched.  Under these circumstances, it returns
549	>	* null.  Occasionally, in order to maintain the heap invariant,
550	>	* it must swap a later element of the list with one earlier than
551	>	* i.  Under these circumstances, this method returns the element
552	>	* that was previously at the end of the list and is now at some
553	>	* position before i. This fact is used by iterator.remove so as to
554	>	* avoid missing traversing elements.
555	>	*/
556	>	private E removeAt(int i) {
557	>	assert i >= 0 && i < size;
558	>	modCount++;
559	>	int s = --size;
560	>	if (s == i) // removed last element
561	>	queue[i] = null;
562	>	else {
563	>	E moved = (E) queue[s];
564	>	queue[s] = null;
565	>	siftDown(i, moved);
566	>	if (queue[i] == moved) {
567	>	siftUp(i, moved);
568	>	if (queue[i] != moved)
569	>	return moved;
570	>	}
571	>	}
572		return null;
573		}
574
575	+	/**
576	+	* Inserts item x at position k, maintaining heap invariant by
577	+	* promoting x up the tree until it is greater than or equal to
578	+	* its parent, or is the root.
579	+	*
580	+	* To simplify and speed up coercions and comparisons. the
581	+	* Comparable and Comparator versions are separated into different
582	+	* methods that are otherwise identical. (Similarly for siftDown.)
583	+	*
584	+	* @param k the position to fill
585	+	* @param x the item to insert
586	+	*/
587	+	private void siftUp(int k, E x) {
588	+	if (comparator != null)
589	+	siftUpUsingComparator(k, x);
590	+	else
591	+	siftUpComparable(k, x);
592	+	}
593	+
594	+	private void siftUpComparable(int k, E x) {
595	+	Comparable<? super E> key = (Comparable<? super E>) x;
596	+	while (k > 0) {
597	+	int parent = (k - 1) >>> 1;
598	+	Object e = queue[parent];
599	+	if (key.compareTo((E) e) >= 0)
600	+	break;
601	+	queue[k] = e;
602	+	k = parent;
603	+	}
604	+	queue[k] = key;
605	+	}
606	+
607	+	private void siftUpUsingComparator(int k, E x) {
608	+	while (k > 0) {
609	+	int parent = (k - 1) >>> 1;
610	+	Object e = queue[parent];
611	+	if (comparator.compare(x, (E) e) >= 0)
612	+	break;
613	+	queue[k] = e;
614	+	k = parent;
615	+	}
616	+	queue[k] = x;
617	+	}
618	+
619	+	/**
620	+	* Inserts item x at position k, maintaining heap invariant by
621	+	* demoting x down the tree repeatedly until it is less than or
622	+	* equal to its children or is a leaf.
623	+	*
624	+	* @param k the position to fill
625	+	* @param x the item to insert
626	+	*/
627	+	private void siftDown(int k, E x) {
628	+	if (comparator != null)
629	+	siftDownUsingComparator(k, x);
630	+	else
631	+	siftDownComparable(k, x);
632	+	}
633	+
634	+	private void siftDownComparable(int k, E x) {
635	+	Comparable<? super E> key = (Comparable<? super E>)x;
636	+	int half = size >>> 1;        // loop while a non-leaf
637	+	while (k < half) {
638	+	int child = (k << 1) + 1; // assume left child is least
639	+	Object c = queue[child];
640	+	int right = child + 1;
641	+	if (right < size &&
642	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
643	+	c = queue[child = right];
644	+	if (key.compareTo((E) c) <= 0)
645	+	break;
646	+	queue[k] = c;
647	+	k = child;
648	+	}
649	+	queue[k] = key;
650	+	}
651	+
652	+	private void siftDownUsingComparator(int k, E x) {
653	+	int half = size >>> 1;
654	+	while (k < half) {
655	+	int child = (k << 1) + 1;
656	+	Object c = queue[child];
657	+	int right = child + 1;
658	+	if (right < size &&
659	+	comparator.compare((E) c, (E) queue[right]) > 0)
660	+	c = queue[child = right];
661	+	if (comparator.compare(x, (E) c) <= 0)
662	+	break;
663	+	queue[k] = c;
664	+	k = child;
665	+	}
666	+	queue[k] = x;
667	+	}
668	+
669	+	/**
670	+	* Establishes the heap invariant (described above) in the entire tree,
671	+	* assuming nothing about the order of the elements prior to the call.
672	+	*/
673	+	private void heapify() {
674	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
675	+	siftDown(i, (E) queue[i]);
676	+	}
677	+
678	+	/**
679	+	* Returns the comparator used to order the elements in this
680	+	* queue, or {@code null} if this queue is sorted according to
681	+	* the {@linkplain Comparable natural ordering} of its elements.
682	+	*
683	+	* @return the comparator used to order this queue, or
684	+	*         {@code null} if this queue is sorted according to the
685	+	*         natural ordering of its elements
686	+	*/
687	+	public Comparator<? super E> comparator() {
688	+	return comparator;
689	+	}
690	+
691	+	/**
692	+	* Saves the state of the instance to a stream (that
693	+	* is, serializes it).
694	+	*
695	+	* @serialData The length of the array backing the instance is
696	+	*             emitted (int), followed by all of its elements
697	+	*             (each an {@code Object}) in the proper order.
698	+	* @param s the stream
699	+	*/
700	+	private void writeObject(java.io.ObjectOutputStream s)
701	+	throws java.io.IOException{
702	+	// Write out element count, and any hidden stuff
703	+	s.defaultWriteObject();
704	+
705	+	// Write out array length, for compatibility with 1.5 version
706	+	s.writeInt(Math.max(2, size + 1));
707	+
708	+	// Write out all elements in the "proper order".
709	+	for (int i = 0; i < size; i++)
710	+	s.writeObject(queue[i]);
711	+	}
712	+
713	+	/**
714	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
715	+	* (that is, deserializes it).
716	+	*
717	+	* @param s the stream
718	+	*/
719	+	private void readObject(java.io.ObjectInputStream s)
720	+	throws java.io.IOException, ClassNotFoundException {
721	+	// Read in size, and any hidden stuff
722	+	s.defaultReadObject();
723	+
724	+	// Read in (and discard) array length
725	+	s.readInt();
726	+
727	+	queue = new Object[size];
728	+
729	+	// Read in all elements.
730	+	for (int i = 0; i < size; i++)
731	+	queue[i] = s.readObject();
732	+
733	+	// Elements are guaranteed to be in "proper order", but the
734	+	// spec has never explained what that might be.
735	+	heapify();
736	+	}
737		}

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