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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 1.109 by jsr166, Wed Jun 1 16:08:04 2016 UTC

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1	+	/*
2	+	* Copyright (c) 2003, 2013, Oracle and/or its affiliates. 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.  Oracle designates this
8	+	* particular file as subject to the "Classpath" exception as provided
9	+	* by Oracle 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 Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	+	* or visit www.oracle.com if you need additional information or have any
23	+	* questions.
24	+	*/
25	+
26		package java.util;
27
28	<	import java.util.*;
28	>	import java.util.function.Consumer;
29
30		/**
31	<	* An unbounded (resizable) priority queue based on a priority
32	<	* heap.The take operation returns the least element with respect to
33	<	* the given ordering. (If more than one element is tied for least
34	<	* value, one of them is arbitrarily chosen to be returned -- no
35	<	* guarantees are made for ordering across ties.) Ordering follows the
36	<	* java.util.Collection conventions: Either the elements must be
37	<	* Comparable, or a Comparator must be supplied. Comparison failures
38	<	* throw ClassCastExceptions during insertions and extractions.
39	<	**/
40	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
41	<	public PriorityQueue(int initialCapacity) {}
42	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
31	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
32	>	* The elements of the priority queue are ordered according to their
33	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
34	>	* provided at queue construction time, depending on which constructor is
35	>	* used.  A priority queue does not permit {@code null} elements.
36	>	* A priority queue relying on natural ordering also does not permit
37	>	* insertion of non-comparable objects (doing so may result in
38	>	* {@code ClassCastException}).
39	>	*
40	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
41	>	* with respect to the specified ordering.  If multiple elements are
42	>	* tied for least value, the head is one of those elements -- ties are
43	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
44	>	* {@code remove}, {@code peek}, and {@code element} access the
45	>	* element at the head of the queue.
46	>	*
47	>	* <p>A priority queue is unbounded, but has an internal
48	>	* <i>capacity</i> governing the size of an array used to store the
49	>	* elements on the queue.  It is always at least as large as the queue
50	>	* size.  As elements are added to a priority queue, its capacity
51	>	* grows automatically.  The details of the growth policy are not
52	>	* specified.
53	>	*
54	>	* <p>This class and its iterator implement all of the
55	>	* <em>optional</em> methods of the {@link Collection} and {@link
56	>	* Iterator} interfaces.  The Iterator provided in method {@link
57	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
58	>	* the priority queue in any particular order. If you need ordered
59	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
60	>	*
61	>	* <p><strong>Note that this implementation is not synchronized.</strong>
62	>	* Multiple threads should not access a {@code PriorityQueue}
63	>	* instance concurrently if any of the threads modifies the queue.
64	>	* Instead, use the thread-safe {@link
65	>	* java.util.concurrent.PriorityBlockingQueue} class.
66	>	*
67	>	* <p>Implementation note: this implementation provides
68	>	* O(log(n)) time for the enqueuing and dequeuing methods
69	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
70	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
71	>	* methods; and constant time for the retrieval methods
72	>	* ({@code peek}, {@code element}, and {@code size}).
73	>	*
74	>	* <p>This class is a member of the
75	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
76	>	* Java Collections Framework</a>.
77	>	*
78	>	* @since 1.5
79	>	* @author Josh Bloch, Doug Lea
80	>	* @param <E> the type of elements held in this queue
81	>	*/
82	>	public class PriorityQueue<E> extends AbstractQueue<E>
83	>	implements java.io.Serializable {
84
85	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
85	>	private static final long serialVersionUID = -7720805057305804111L;
86
87	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
87	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
88
89	<	public boolean add(E x) {
90	<	return false;
89	>	/**
90	>	* Priority queue represented as a balanced binary heap: the two
91	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
92	>	* priority queue is ordered by comparator, or by the elements'
93	>	* natural ordering, if comparator is null: For each node n in the
94	>	* heap and each descendant d of n, n <= d.  The element with the
95	>	* lowest value is in queue[0], assuming the queue is nonempty.
96	>	*/
97	>	transient Object[] queue; // non-private to simplify nested class access
98	>
99	>	/**
100	>	* The number of elements in the priority queue.
101	>	*/
102	>	int size;
103	>
104	>	/**
105	>	* The comparator, or null if priority queue uses elements'
106	>	* natural ordering.
107	>	*/
108	>	private final Comparator<? super E> comparator;
109	>
110	>	/**
111	>	* The number of times this priority queue has been
112	>	* <i>structurally modified</i>.  See AbstractList for gory details.
113	>	*/
114	>	transient int modCount;     // non-private to simplify nested class access
115	>
116	>	/**
117	>	* Creates a {@code PriorityQueue} with the default initial
118	>	* capacity (11) that orders its elements according to their
119	>	* {@linkplain Comparable natural ordering}.
120	>	*/
121	>	public PriorityQueue() {
122	>	this(DEFAULT_INITIAL_CAPACITY, null);
123		}
124	<	public boolean offer(E x) {
125	<	return false;
124	>
125	>	/**
126	>	* Creates a {@code PriorityQueue} with the specified initial
127	>	* capacity that orders its elements according to their
128	>	* {@linkplain Comparable natural ordering}.
129	>	*
130	>	* @param initialCapacity the initial capacity for this priority queue
131	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
132	>	*         than 1
133	>	*/
134	>	public PriorityQueue(int initialCapacity) {
135	>	this(initialCapacity, null);
136		}
137	<	public boolean remove(Object x) {
138	<	return false;
137	>
138	>	/**
139	>	* Creates a {@code PriorityQueue} with the default initial capacity and
140	>	* whose elements are ordered according to the specified comparator.
141	>	*
142	>	* @param  comparator the comparator that will be used to order this
143	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
144	>	*         natural ordering} of the elements will be used.
145	>	* @since 1.8
146	>	*/
147	>	public PriorityQueue(Comparator<? super E> comparator) {
148	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
149		}
150
151	<	public E remove() {
152	<	return null;
151	>	/**
152	>	* Creates a {@code PriorityQueue} with the specified initial capacity
153	>	* that orders its elements according to the specified comparator.
154	>	*
155	>	* @param  initialCapacity the initial capacity for this priority queue
156	>	* @param  comparator the comparator that will be used to order this
157	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
158	>	*         natural ordering} of the elements will be used.
159	>	* @throws IllegalArgumentException if {@code initialCapacity} is
160	>	*         less than 1
161	>	*/
162	>	public PriorityQueue(int initialCapacity,
163	>	Comparator<? super E> comparator) {
164	>	// Note: This restriction of at least one is not actually needed,
165	>	// but continues for 1.5 compatibility
166	>	if (initialCapacity < 1)
167	>	throw new IllegalArgumentException();
168	>	this.queue = new Object[initialCapacity];
169	>	this.comparator = comparator;
170		}
171	<	public Iterator<E> iterator() {
172	<	return null;
171	>
172	>	/**
173	>	* Creates a {@code PriorityQueue} containing the elements in the
174	>	* specified collection.  If the specified collection is an instance of
175	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
176	>	* priority queue will be ordered according to the same ordering.
177	>	* Otherwise, this priority queue will be ordered according to the
178	>	* {@linkplain Comparable natural ordering} of its elements.
179	>	*
180	>	* @param  c the collection whose elements are to be placed
181	>	*         into this priority queue
182	>	* @throws ClassCastException if elements of the specified collection
183	>	*         cannot be compared to one another according to the priority
184	>	*         queue's ordering
185	>	* @throws NullPointerException if the specified collection or any
186	>	*         of its elements are null
187	>	*/
188	>	@SuppressWarnings("unchecked")
189	>	public PriorityQueue(Collection<? extends E> c) {
190	>	if (c instanceof SortedSet<?>) {
191	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
192	>	this.comparator = (Comparator<? super E>) ss.comparator();
193	>	initElementsFromCollection(ss);
194	>	}
195	>	else if (c instanceof PriorityQueue<?>) {
196	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
197	>	this.comparator = (Comparator<? super E>) pq.comparator();
198	>	initFromPriorityQueue(pq);
199	>	}
200	>	else {
201	>	this.comparator = null;
202	>	initFromCollection(c);
203	>	}
204		}
205
206	<	public E element() {
207	<	return null;
206	>	/**
207	>	* Creates a {@code PriorityQueue} containing the elements in the
208	>	* specified priority queue.  This priority queue will be
209	>	* ordered according to the same ordering as the given priority
210	>	* queue.
211	>	*
212	>	* @param  c the priority queue whose elements are to be placed
213	>	*         into this priority queue
214	>	* @throws ClassCastException if elements of {@code c} cannot be
215	>	*         compared to one another according to {@code c}'s
216	>	*         ordering
217	>	* @throws NullPointerException if the specified priority queue or any
218	>	*         of its elements are null
219	>	*/
220	>	@SuppressWarnings("unchecked")
221	>	public PriorityQueue(PriorityQueue<? extends E> c) {
222	>	this.comparator = (Comparator<? super E>) c.comparator();
223	>	initFromPriorityQueue(c);
224		}
225	<	public E poll() {
226	<	return null;
225	>
226	>	/**
227	>	* Creates a {@code PriorityQueue} containing the elements in the
228	>	* specified sorted set.   This priority queue will be ordered
229	>	* according to the same ordering as the given sorted set.
230	>	*
231	>	* @param  c the sorted set whose elements are to be placed
232	>	*         into this priority queue
233	>	* @throws ClassCastException if elements of the specified sorted
234	>	*         set cannot be compared to one another according to the
235	>	*         sorted set's ordering
236	>	* @throws NullPointerException if the specified sorted set or any
237	>	*         of its elements are null
238	>	*/
239	>	@SuppressWarnings("unchecked")
240	>	public PriorityQueue(SortedSet<? extends E> c) {
241	>	this.comparator = (Comparator<? super E>) c.comparator();
242	>	initElementsFromCollection(c);
243	>	}
244	>
245	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
246	>	if (c.getClass() == PriorityQueue.class) {
247	>	this.queue = c.toArray();
248	>	this.size = c.size();
249	>	} else {
250	>	initFromCollection(c);
251	>	}
252	>	}
253	>
254	>	private void initElementsFromCollection(Collection<? extends E> c) {
255	>	Object[] a = c.toArray();
256	>	// If c.toArray incorrectly doesn't return Object[], copy it.
257	>	if (a.getClass() != Object[].class)
258	>	a = Arrays.copyOf(a, a.length, Object[].class);
259	>	int len = a.length;
260	>	if (len == 1 || this.comparator != null)
261	>	for (Object e : a)
262	>	if (e == null)
263	>	throw new NullPointerException();
264	>	this.queue = a;
265	>	this.size = a.length;
266	>	}
267	>
268	>	/**
269	>	* Initializes queue array with elements from the given Collection.
270	>	*
271	>	* @param c the collection
272	>	*/
273	>	private void initFromCollection(Collection<? extends E> c) {
274	>	initElementsFromCollection(c);
275	>	heapify();
276	>	}
277	>
278	>	/**
279	>	* The maximum size of array to allocate.
280	>	* Some VMs reserve some header words in an array.
281	>	* Attempts to allocate larger arrays may result in
282	>	* OutOfMemoryError: Requested array size exceeds VM limit
283	>	*/
284	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
285	>
286	>	/**
287	>	* Increases the capacity of the array.
288	>	*
289	>	* @param minCapacity the desired minimum capacity
290	>	*/
291	>	private void grow(int minCapacity) {
292	>	int oldCapacity = queue.length;
293	>	// Double size if small; else grow by 50%
294	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
295	>	(oldCapacity + 2) :
296	>	(oldCapacity >> 1));
297	>	// overflow-conscious code
298	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
299	>	newCapacity = hugeCapacity(minCapacity);
300	>	queue = Arrays.copyOf(queue, newCapacity);
301	>	}
302	>
303	>	private static int hugeCapacity(int minCapacity) {
304	>	if (minCapacity < 0) // overflow
305	>	throw new OutOfMemoryError();
306	>	return (minCapacity > MAX_ARRAY_SIZE) ?
307	>	Integer.MAX_VALUE :
308	>	MAX_ARRAY_SIZE;
309	>	}
310	>
311	>	/**
312	>	* Inserts the specified element into this priority queue.
313	>	*
314	>	* @return {@code true} (as specified by {@link Collection#add})
315	>	* @throws ClassCastException if the specified element cannot be
316	>	*         compared with elements currently in this priority queue
317	>	*         according to the priority queue's ordering
318	>	* @throws NullPointerException if the specified element is null
319	>	*/
320	>	public boolean add(E e) {
321	>	return offer(e);
322	>	}
323	>
324	>	/**
325	>	* Inserts the specified element into this priority queue.
326	>	*
327	>	* @return {@code true} (as specified by {@link Queue#offer})
328	>	* @throws ClassCastException if the specified element cannot be
329	>	*         compared with elements currently in this priority queue
330	>	*         according to the priority queue's ordering
331	>	* @throws NullPointerException if the specified element is null
332	>	*/
333	>	public boolean offer(E e) {
334	>	if (e == null)
335	>	throw new NullPointerException();
336	>	modCount++;
337	>	int i = size;
338	>	if (i >= queue.length)
339	>	grow(i + 1);
340	>	siftUp(i, e);
341	>	size = i + 1;
342	>	return true;
343		}
344	+
345	+	@SuppressWarnings("unchecked")
346		public E peek() {
347	<	return null;
347	>	return (size == 0) ? null : (E) queue[0];
348	>	}
349	>
350	>	private int indexOf(Object o) {
351	>	if (o != null) {
352	>	for (int i = 0; i < size; i++)
353	>	if (o.equals(queue[i]))
354	>	return i;
355	>	}
356	>	return -1;
357	>	}
358	>
359	>	/**
360	>	* Removes a single instance of the specified element from this queue,
361	>	* if it is present.  More formally, removes an element {@code e} such
362	>	* that {@code o.equals(e)}, if this queue contains one or more such
363	>	* elements.  Returns {@code true} if and only if this queue contained
364	>	* the specified element (or equivalently, if this queue changed as a
365	>	* result of the call).
366	>	*
367	>	* @param o element to be removed from this queue, if present
368	>	* @return {@code true} if this queue changed as a result of the call
369	>	*/
370	>	public boolean remove(Object o) {
371	>	int i = indexOf(o);
372	>	if (i == -1)
373	>	return false;
374	>	else {
375	>	removeAt(i);
376	>	return true;
377	>	}
378		}
379
380	<	public boolean isEmpty() {
380	>	/**
381	>	* Version of remove using reference equality, not equals.
382	>	* Needed by iterator.remove.
383	>	*
384	>	* @param o element to be removed from this queue, if present
385	>	* @return {@code true} if removed
386	>	*/
387	>	boolean removeEq(Object o) {
388	>	for (int i = 0; i < size; i++) {
389	>	if (o == queue[i]) {
390	>	removeAt(i);
391	>	return true;
392	>	}
393	>	}
394		return false;
395		}
396	<	public int size() {
397	<	return 0;
396	>
397	>	/**
398	>	* Returns {@code true} if this queue contains the specified element.
399	>	* More formally, returns {@code true} if and only if this queue contains
400	>	* at least one element {@code e} such that {@code o.equals(e)}.
401	>	*
402	>	* @param o object to be checked for containment in this queue
403	>	* @return {@code true} if this queue contains the specified element
404	>	*/
405	>	public boolean contains(Object o) {
406	>	return indexOf(o) >= 0;
407		}
408	+
409	+	/**
410	+	* Returns an array containing all of the elements in this queue.
411	+	* The elements are in no particular order.
412	+	*
413	+	* <p>The returned array will be "safe" in that no references to it are
414	+	* maintained by this queue.  (In other words, this method must allocate
415	+	* a new array).  The caller is thus free to modify the returned array.
416	+	*
417	+	* <p>This method acts as bridge between array-based and collection-based
418	+	* APIs.
419	+	*
420	+	* @return an array containing all of the elements in this queue
421	+	*/
422		public Object[] toArray() {
423	<	return null;
423	>	return Arrays.copyOf(queue, size);
424	>	}
425	>
426	>	/**
427	>	* Returns an array containing all of the elements in this queue; the
428	>	* runtime type of the returned array is that of the specified array.
429	>	* The returned array elements are in no particular order.
430	>	* If the queue fits in the specified array, it is returned therein.
431	>	* Otherwise, a new array is allocated with the runtime type of the
432	>	* specified array and the size of this queue.
433	>	*
434	>	* <p>If the queue fits in the specified array with room to spare
435	>	* (i.e., the array has more elements than the queue), the element in
436	>	* the array immediately following the end of the collection is set to
437	>	* {@code null}.
438	>	*
439	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
440	>	* array-based and collection-based APIs.  Further, this method allows
441	>	* precise control over the runtime type of the output array, and may,
442	>	* under certain circumstances, be used to save allocation costs.
443	>	*
444	>	* <p>Suppose {@code x} is a queue known to contain only strings.
445	>	* The following code can be used to dump the queue into a newly
446	>	* allocated array of {@code String}:
447	>	*
448	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
449	>	*
450	>	* Note that {@code toArray(new Object[0])} is identical in function to
451	>	* {@code toArray()}.
452	>	*
453	>	* @param a the array into which the elements of the queue are to
454	>	*          be stored, if it is big enough; otherwise, a new array of the
455	>	*          same runtime type is allocated for this purpose.
456	>	* @return an array containing all of the elements in this queue
457	>	* @throws ArrayStoreException if the runtime type of the specified array
458	>	*         is not a supertype of the runtime type of every element in
459	>	*         this queue
460	>	* @throws NullPointerException if the specified array is null
461	>	*/
462	>	@SuppressWarnings("unchecked")
463	>	public <T> T[] toArray(T[] a) {
464	>	final int size = this.size;
465	>	if (a.length < size)
466	>	// Make a new array of a's runtime type, but my contents:
467	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
468	>	System.arraycopy(queue, 0, a, 0, size);
469	>	if (a.length > size)
470	>	a[size] = null;
471	>	return a;
472	>	}
473	>
474	>	/**
475	>	* Returns an iterator over the elements in this queue. The iterator
476	>	* does not return the elements in any particular order.
477	>	*
478	>	* @return an iterator over the elements in this queue
479	>	*/
480	>	public Iterator<E> iterator() {
481	>	return new Itr();
482	>	}
483	>
484	>	private final class Itr implements Iterator<E> {
485	>	/**
486	>	* Index (into queue array) of element to be returned by
487	>	* subsequent call to next.
488	>	*/
489	>	private int cursor;
490	>
491	>	/**
492	>	* Index of element returned by most recent call to next,
493	>	* unless that element came from the forgetMeNot list.
494	>	* Set to -1 if element is deleted by a call to remove.
495	>	*/
496	>	private int lastRet = -1;
497	>
498	>	/**
499	>	* A queue of elements that were moved from the unvisited portion of
500	>	* the heap into the visited portion as a result of "unlucky" element
501	>	* removals during the iteration.  (Unlucky element removals are those
502	>	* that require a siftup instead of a siftdown.)  We must visit all of
503	>	* the elements in this list to complete the iteration.  We do this
504	>	* after we've completed the "normal" iteration.
505	>	*
506	>	* We expect that most iterations, even those involving removals,
507	>	* will not need to store elements in this field.
508	>	*/
509	>	private ArrayDeque<E> forgetMeNot;
510	>
511	>	/**
512	>	* Element returned by the most recent call to next iff that
513	>	* element was drawn from the forgetMeNot list.
514	>	*/
515	>	private E lastRetElt;
516	>
517	>	/**
518	>	* The modCount value that the iterator believes that the backing
519	>	* Queue should have.  If this expectation is violated, the iterator
520	>	* has detected concurrent modification.
521	>	*/
522	>	private int expectedModCount = modCount;
523	>
524	>	public boolean hasNext() {
525	>	return cursor < size ||
526	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
527	>	}
528	>
529	>	@SuppressWarnings("unchecked")
530	>	public E next() {
531	>	if (expectedModCount != modCount)
532	>	throw new ConcurrentModificationException();
533	>	if (cursor < size)
534	>	return (E) queue[lastRet = cursor++];
535	>	if (forgetMeNot != null) {
536	>	lastRet = -1;
537	>	lastRetElt = forgetMeNot.poll();
538	>	if (lastRetElt != null)
539	>	return lastRetElt;
540	>	}
541	>	throw new NoSuchElementException();
542	>	}
543	>
544	>	public void remove() {
545	>	if (expectedModCount != modCount)
546	>	throw new ConcurrentModificationException();
547	>	if (lastRet != -1) {
548	>	E moved = PriorityQueue.this.removeAt(lastRet);
549	>	lastRet = -1;
550	>	if (moved == null)
551	>	cursor--;
552	>	else {
553	>	if (forgetMeNot == null)
554	>	forgetMeNot = new ArrayDeque<>();
555	>	forgetMeNot.add(moved);
556	>	}
557	>	} else if (lastRetElt != null) {
558	>	PriorityQueue.this.removeEq(lastRetElt);
559	>	lastRetElt = null;
560	>	} else {
561	>	throw new IllegalStateException();
562	>	}
563	>	expectedModCount = modCount;
564	>	}
565		}
566
567	<	public <T> T[] toArray(T[] array) {
567	>	public int size() {
568	>	return size;
569	>	}
570	>
571	>	/**
572	>	* Removes all of the elements from this priority queue.
573	>	* The queue will be empty after this call returns.
574	>	*/
575	>	public void clear() {
576	>	modCount++;
577	>	for (int i = 0; i < size; i++)
578	>	queue[i] = null;
579	>	size = 0;
580	>	}
581	>
582	>	@SuppressWarnings("unchecked")
583	>	public E poll() {
584	>	if (size == 0)
585	>	return null;
586	>	int s = --size;
587	>	modCount++;
588	>	E result = (E) queue[0];
589	>	E x = (E) queue[s];
590	>	queue[s] = null;
591	>	if (s != 0)
592	>	siftDown(0, x);
593	>	return result;
594	>	}
595	>
596	>	/**
597	>	* Removes the ith element from queue.
598	>	*
599	>	* Normally this method leaves the elements at up to i-1,
600	>	* inclusive, untouched.  Under these circumstances, it returns
601	>	* null.  Occasionally, in order to maintain the heap invariant,
602	>	* it must swap a later element of the list with one earlier than
603	>	* i.  Under these circumstances, this method returns the element
604	>	* that was previously at the end of the list and is now at some
605	>	* position before i. This fact is used by iterator.remove so as to
606	>	* avoid missing traversing elements.
607	>	*/
608	>	@SuppressWarnings("unchecked")
609	>	E removeAt(int i) {
610	>	// assert i >= 0 && i < size;
611	>	modCount++;
612	>	int s = --size;
613	>	if (s == i) // removed last element
614	>	queue[i] = null;
615	>	else {
616	>	E moved = (E) queue[s];
617	>	queue[s] = null;
618	>	siftDown(i, moved);
619	>	if (queue[i] == moved) {
620	>	siftUp(i, moved);
621	>	if (queue[i] != moved)
622	>	return moved;
623	>	}
624	>	}
625		return null;
626		}
627
628	+	/**
629	+	* Inserts item x at position k, maintaining heap invariant by
630	+	* promoting x up the tree until it is greater than or equal to
631	+	* its parent, or is the root.
632	+	*
633	+	* To simplify and speed up coercions and comparisons. the
634	+	* Comparable and Comparator versions are separated into different
635	+	* methods that are otherwise identical. (Similarly for siftDown.)
636	+	*
637	+	* @param k the position to fill
638	+	* @param x the item to insert
639	+	*/
640	+	private void siftUp(int k, E x) {
641	+	if (comparator != null)
642	+	siftUpUsingComparator(k, x);
643	+	else
644	+	siftUpComparable(k, x);
645	+	}
646	+
647	+	@SuppressWarnings("unchecked")
648	+	private void siftUpComparable(int k, E x) {
649	+	Comparable<? super E> key = (Comparable<? super E>) x;
650	+	while (k > 0) {
651	+	int parent = (k - 1) >>> 1;
652	+	Object e = queue[parent];
653	+	if (key.compareTo((E) e) >= 0)
654	+	break;
655	+	queue[k] = e;
656	+	k = parent;
657	+	}
658	+	queue[k] = key;
659	+	}
660	+
661	+	@SuppressWarnings("unchecked")
662	+	private void siftUpUsingComparator(int k, E x) {
663	+	while (k > 0) {
664	+	int parent = (k - 1) >>> 1;
665	+	Object e = queue[parent];
666	+	if (comparator.compare(x, (E) e) >= 0)
667	+	break;
668	+	queue[k] = e;
669	+	k = parent;
670	+	}
671	+	queue[k] = x;
672	+	}
673	+
674	+	/**
675	+	* Inserts item x at position k, maintaining heap invariant by
676	+	* demoting x down the tree repeatedly until it is less than or
677	+	* equal to its children or is a leaf.
678	+	*
679	+	* @param k the position to fill
680	+	* @param x the item to insert
681	+	*/
682	+	private void siftDown(int k, E x) {
683	+	if (comparator != null)
684	+	siftDownUsingComparator(k, x);
685	+	else
686	+	siftDownComparable(k, x);
687	+	}
688	+
689	+	@SuppressWarnings("unchecked")
690	+	private void siftDownComparable(int k, E x) {
691	+	Comparable<? super E> key = (Comparable<? super E>)x;
692	+	int half = size >>> 1;        // loop while a non-leaf
693	+	while (k < half) {
694	+	int child = (k << 1) + 1; // assume left child is least
695	+	Object c = queue[child];
696	+	int right = child + 1;
697	+	if (right < size &&
698	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
699	+	c = queue[child = right];
700	+	if (key.compareTo((E) c) <= 0)
701	+	break;
702	+	queue[k] = c;
703	+	k = child;
704	+	}
705	+	queue[k] = key;
706	+	}
707	+
708	+	@SuppressWarnings("unchecked")
709	+	private void siftDownUsingComparator(int k, E x) {
710	+	int half = size >>> 1;
711	+	while (k < half) {
712	+	int child = (k << 1) + 1;
713	+	Object c = queue[child];
714	+	int right = child + 1;
715	+	if (right < size &&
716	+	comparator.compare((E) c, (E) queue[right]) > 0)
717	+	c = queue[child = right];
718	+	if (comparator.compare(x, (E) c) <= 0)
719	+	break;
720	+	queue[k] = c;
721	+	k = child;
722	+	}
723	+	queue[k] = x;
724	+	}
725	+
726	+	/**
727	+	* Establishes the heap invariant (described above) in the entire tree,
728	+	* assuming nothing about the order of the elements prior to the call.
729	+	*/
730	+	@SuppressWarnings("unchecked")
731	+	private void heapify() {
732	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
733	+	siftDown(i, (E) queue[i]);
734	+	}
735	+
736	+	/**
737	+	* Returns the comparator used to order the elements in this
738	+	* queue, or {@code null} if this queue is sorted according to
739	+	* the {@linkplain Comparable natural ordering} of its elements.
740	+	*
741	+	* @return the comparator used to order this queue, or
742	+	*         {@code null} if this queue is sorted according to the
743	+	*         natural ordering of its elements
744	+	*/
745	+	public Comparator<? super E> comparator() {
746	+	return comparator;
747	+	}
748	+
749	+	/**
750	+	* Saves this queue to a stream (that is, serializes it).
751	+	*
752	+	* @serialData The length of the array backing the instance is
753	+	*             emitted (int), followed by all of its elements
754	+	*             (each an {@code Object}) in the proper order.
755	+	* @param s the stream
756	+	* @throws java.io.IOException if an I/O error occurs
757	+	*/
758	+	private void writeObject(java.io.ObjectOutputStream s)
759	+	throws java.io.IOException {
760	+	// Write out element count, and any hidden stuff
761	+	s.defaultWriteObject();
762	+
763	+	// Write out array length, for compatibility with 1.5 version
764	+	s.writeInt(Math.max(2, size + 1));
765	+
766	+	// Write out all elements in the "proper order".
767	+	for (int i = 0; i < size; i++)
768	+	s.writeObject(queue[i]);
769	+	}
770	+
771	+	/**
772	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
773	+	* (that is, deserializes it).
774	+	*
775	+	* @param s the stream
776	+	* @throws ClassNotFoundException if the class of a serialized object
777	+	*         could not be found
778	+	* @throws java.io.IOException if an I/O error occurs
779	+	*/
780	+	private void readObject(java.io.ObjectInputStream s)
781	+	throws java.io.IOException, ClassNotFoundException {
782	+	// Read in size, and any hidden stuff
783	+	s.defaultReadObject();
784	+
785	+	// Read in (and discard) array length
786	+	s.readInt();
787	+
788	+	queue = new Object[size];
789	+
790	+	// Read in all elements.
791	+	for (int i = 0; i < size; i++)
792	+	queue[i] = s.readObject();
793	+
794	+	// Elements are guaranteed to be in "proper order", but the
795	+	// spec has never explained what that might be.
796	+	heapify();
797	+	}
798	+
799	+	/**
800	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
801	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
802	+	* queue.
803	+	*
804	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
805	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
806	+	* Overriding implementations should document the reporting of additional
807	+	* characteristic values.
808	+	*
809	+	* @return a {@code Spliterator} over the elements in this queue
810	+	* @since 1.8
811	+	*/
812	+	public final Spliterator<E> spliterator() {
813	+	return new PriorityQueueSpliterator<>(this, 0, -1, 0);
814	+	}
815	+
816	+	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
817	+	/*
818	+	* This is very similar to ArrayList Spliterator, except for
819	+	* extra null checks.
820	+	*/
821	+	private final PriorityQueue<E> pq;
822	+	private int index;            // current index, modified on advance/split
823	+	private int fence;            // -1 until first use
824	+	private int expectedModCount; // initialized when fence set
825	+
826	+	/** Creates new spliterator covering the given range. */
827	+	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
828	+	int expectedModCount) {
829	+	this.pq = pq;
830	+	this.index = origin;
831	+	this.fence = fence;
832	+	this.expectedModCount = expectedModCount;
833	+	}
834	+
835	+	private int getFence() { // initialize fence to size on first use
836	+	int hi;
837	+	if ((hi = fence) < 0) {
838	+	expectedModCount = pq.modCount;
839	+	hi = fence = pq.size;
840	+	}
841	+	return hi;
842	+	}
843	+
844	+	public PriorityQueueSpliterator<E> trySplit() {
845	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
846	+	return (lo >= mid) ? null :
847	+	new PriorityQueueSpliterator<>(pq, lo, index = mid,
848	+	expectedModCount);
849	+	}
850	+
851	+	@SuppressWarnings("unchecked")
852	+	public void forEachRemaining(Consumer<? super E> action) {
853	+	int i, hi, mc; // hoist accesses and checks from loop
854	+	PriorityQueue<E> q; Object[] a;
855	+	if (action == null)
856	+	throw new NullPointerException();
857	+	if ((q = pq) != null && (a = q.queue) != null) {
858	+	if ((hi = fence) < 0) {
859	+	mc = q.modCount;
860	+	hi = q.size;
861	+	}
862	+	else
863	+	mc = expectedModCount;
864	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
865	+	for (E e;; ++i) {
866	+	if (i < hi) {
867	+	if ((e = (E) a[i]) == null) // must be CME
868	+	break;
869	+	action.accept(e);
870	+	}
871	+	else if (q.modCount != mc)
872	+	break;
873	+	else
874	+	return;
875	+	}
876	+	}
877	+	}
878	+	throw new ConcurrentModificationException();
879	+	}
880	+
881	+	public boolean tryAdvance(Consumer<? super E> action) {
882	+	if (action == null)
883	+	throw new NullPointerException();
884	+	int hi = getFence(), lo = index;
885	+	if (lo >= 0 && lo < hi) {
886	+	index = lo + 1;
887	+	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
888	+	if (e == null)
889	+	throw new ConcurrentModificationException();
890	+	action.accept(e);
891	+	if (pq.modCount != expectedModCount)
892	+	throw new ConcurrentModificationException();
893	+	return true;
894	+	}
895	+	return false;
896	+	}
897	+
898	+	public long estimateSize() {
899	+	return (long) (getFence() - index);
900	+	}
901	+
902	+	public int characteristics() {
903	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
904	+	}
905	+	}
906		}

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