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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 1.124 by jsr166, Sun May 6 19:35:51 2018 UTC

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1	+	/*
2	+	* Copyright (c) 2003, 2018, 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	>	import jdk.internal.misc.SharedSecrets;
30
31		/**
32	<	* An unbounded (resizable) priority queue based on a priority
33	<	* heap.The take operation returns the least element with respect to
34	<	* the given ordering. (If more than one element is tied for least
35	<	* value, one of them is arbitrarily chosen to be returned -- no
36	<	* guarantees are made for ordering across ties.) Ordering follows the
37	<	* java.util.Collection conventions: Either the elements must be
38	<	* Comparable, or a Comparator must be supplied. Comparison failures
39	<	* throw ClassCastExceptions during insertions and extractions.
40	<	**/
41	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
42	<	public PriorityQueue(int initialCapacity) {}
43	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
44	<
45	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
46	<
47	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
48	<
49	<	public boolean add(E x) {
50	<	return false;
32	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
33	>	* The elements of the priority queue are ordered according to their
34	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
35	>	* provided at queue construction time, depending on which constructor is
36	>	* used.  A priority queue does not permit {@code null} elements.
37	>	* A priority queue relying on natural ordering also does not permit
38	>	* insertion of non-comparable objects (doing so may result in
39	>	* {@code ClassCastException}).
40	>	*
41	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
42	>	* with respect to the specified ordering.  If multiple elements are
43	>	* tied for least value, the head is one of those elements -- ties are
44	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
45	>	* {@code remove}, {@code peek}, and {@code element} access the
46	>	* element at the head of the queue.
47	>	*
48	>	* <p>A priority queue is unbounded, but has an internal
49	>	* <i>capacity</i> governing the size of an array used to store the
50	>	* elements on the queue.  It is always at least as large as the queue
51	>	* size.  As elements are added to a priority queue, its capacity
52	>	* grows automatically.  The details of the growth policy are not
53	>	* specified.
54	>	*
55	>	* <p>This class and its iterator implement all of the
56	>	* <em>optional</em> methods of the {@link Collection} and {@link
57	>	* Iterator} interfaces.  The Iterator provided in method {@link
58	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
59	>	* are <em>not</em> guaranteed to traverse the elements of
60	>	* the priority queue in any particular order. If you need ordered
61	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
62	>	*
63	>	* <p><strong>Note that this implementation is not synchronized.</strong>
64	>	* Multiple threads should not access a {@code PriorityQueue}
65	>	* instance concurrently if any of the threads modifies the queue.
66	>	* Instead, use the thread-safe {@link
67	>	* java.util.concurrent.PriorityBlockingQueue} class.
68	>	*
69	>	* <p>Implementation note: this implementation provides
70	>	* O(log(n)) time for the enqueuing and dequeuing methods
71	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
72	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
73	>	* methods; and constant time for the retrieval methods
74	>	* ({@code peek}, {@code element}, and {@code size}).
75	>	*
76	>	* <p>This class is a member of the
77	>	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
78	>	* Java Collections Framework</a>.
79	>	*
80	>	* @since 1.5
81	>	* @author Josh Bloch, Doug Lea
82	>	* @param <E> the type of elements held in this queue
83	>	*/
84	>	@SuppressWarnings("unchecked")
85	>	public class PriorityQueue<E> extends AbstractQueue<E>
86	>	implements java.io.Serializable {
87	>
88	>	private static final long serialVersionUID = -7720805057305804111L;
89	>
90	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
91	>
92	>	/**
93	>	* Priority queue represented as a balanced binary heap: the two
94	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
95	>	* priority queue is ordered by comparator, or by the elements'
96	>	* natural ordering, if comparator is null: For each node n in the
97	>	* heap and each descendant d of n, n <= d.  The element with the
98	>	* lowest value is in queue[0], assuming the queue is nonempty.
99	>	*/
100	>	transient Object[] queue; // non-private to simplify nested class access
101	>
102	>	/**
103	>	* The number of elements in the priority queue.
104	>	*/
105	>	int size;
106	>
107	>	/**
108	>	* The comparator, or null if priority queue uses elements'
109	>	* natural ordering.
110	>	*/
111	>	private final Comparator<? super E> comparator;
112	>
113	>	/**
114	>	* The number of times this priority queue has been
115	>	* <i>structurally modified</i>.  See AbstractList for gory details.
116	>	*/
117	>	transient int modCount;     // non-private to simplify nested class access
118	>
119	>	/**
120	>	* Creates a {@code PriorityQueue} with the default initial
121	>	* capacity (11) that orders its elements according to their
122	>	* {@linkplain Comparable natural ordering}.
123	>	*/
124	>	public PriorityQueue() {
125	>	this(DEFAULT_INITIAL_CAPACITY, null);
126		}
127	<	public boolean offer(E x) {
128	<	return false;
127	>
128	>	/**
129	>	* Creates a {@code PriorityQueue} with the specified initial
130	>	* capacity that orders its elements according to their
131	>	* {@linkplain Comparable natural ordering}.
132	>	*
133	>	* @param initialCapacity the initial capacity for this priority queue
134	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
135	>	*         than 1
136	>	*/
137	>	public PriorityQueue(int initialCapacity) {
138	>	this(initialCapacity, null);
139		}
140	<	public boolean remove(Object x) {
141	<	return false;
140	>
141	>	/**
142	>	* Creates a {@code PriorityQueue} with the default initial capacity and
143	>	* whose elements are ordered according to the specified comparator.
144	>	*
145	>	* @param  comparator the comparator that will be used to order this
146	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
147	>	*         natural ordering} of the elements will be used.
148	>	* @since 1.8
149	>	*/
150	>	public PriorityQueue(Comparator<? super E> comparator) {
151	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
152		}
153
154	<	public E remove() {
155	<	return null;
154	>	/**
155	>	* Creates a {@code PriorityQueue} with the specified initial capacity
156	>	* that orders its elements according to the specified comparator.
157	>	*
158	>	* @param  initialCapacity the initial capacity for this priority queue
159	>	* @param  comparator the comparator that will be used to order this
160	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
161	>	*         natural ordering} of the elements will be used.
162	>	* @throws IllegalArgumentException if {@code initialCapacity} is
163	>	*         less than 1
164	>	*/
165	>	public PriorityQueue(int initialCapacity,
166	>	Comparator<? super E> comparator) {
167	>	// Note: This restriction of at least one is not actually needed,
168	>	// but continues for 1.5 compatibility
169	>	if (initialCapacity < 1)
170	>	throw new IllegalArgumentException();
171	>	this.queue = new Object[initialCapacity];
172	>	this.comparator = comparator;
173		}
174	<	public Iterator<E> iterator() {
175	<	return null;
174	>
175	>	/**
176	>	* Creates a {@code PriorityQueue} containing the elements in the
177	>	* specified collection.  If the specified collection is an instance of
178	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
179	>	* priority queue will be ordered according to the same ordering.
180	>	* Otherwise, this priority queue will be ordered according to the
181	>	* {@linkplain Comparable natural ordering} of its elements.
182	>	*
183	>	* @param  c the collection whose elements are to be placed
184	>	*         into this priority queue
185	>	* @throws ClassCastException if elements of the specified collection
186	>	*         cannot be compared to one another according to the priority
187	>	*         queue's ordering
188	>	* @throws NullPointerException if the specified collection or any
189	>	*         of its elements are null
190	>	*/
191	>	public PriorityQueue(Collection<? extends E> c) {
192	>	if (c instanceof SortedSet<?>) {
193	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
194	>	this.comparator = (Comparator<? super E>) ss.comparator();
195	>	initElementsFromCollection(ss);
196	>	}
197	>	else if (c instanceof PriorityQueue<?>) {
198	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
199	>	this.comparator = (Comparator<? super E>) pq.comparator();
200	>	initFromPriorityQueue(pq);
201	>	}
202	>	else {
203	>	this.comparator = null;
204	>	initFromCollection(c);
205	>	}
206		}
207
208	<	public E element() {
209	<	return null;
208	>	/**
209	>	* Creates a {@code PriorityQueue} containing the elements in the
210	>	* specified priority queue.  This priority queue will be
211	>	* ordered according to the same ordering as the given priority
212	>	* queue.
213	>	*
214	>	* @param  c the priority queue whose elements are to be placed
215	>	*         into this priority queue
216	>	* @throws ClassCastException if elements of {@code c} cannot be
217	>	*         compared to one another according to {@code c}'s
218	>	*         ordering
219	>	* @throws NullPointerException if the specified priority queue or any
220	>	*         of its elements are null
221	>	*/
222	>	public PriorityQueue(PriorityQueue<? extends E> c) {
223	>	this.comparator = (Comparator<? super E>) c.comparator();
224	>	initFromPriorityQueue(c);
225		}
226	<	public E poll() {
227	<	return null;
226	>
227	>	/**
228	>	* Creates a {@code PriorityQueue} containing the elements in the
229	>	* specified sorted set.   This priority queue will be ordered
230	>	* according to the same ordering as the given sorted set.
231	>	*
232	>	* @param  c the sorted set whose elements are to be placed
233	>	*         into this priority queue
234	>	* @throws ClassCastException if elements of the specified sorted
235	>	*         set cannot be compared to one another according to the
236	>	*         sorted set's ordering
237	>	* @throws NullPointerException if the specified sorted set or any
238	>	*         of its elements are null
239	>	*/
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[] es = c.toArray();
256	>	int len = es.length;
257	>	// If c.toArray incorrectly doesn't return Object[], copy it.
258	>	if (es.getClass() != Object[].class)
259	>	es = Arrays.copyOf(es, len, Object[].class);
260	>	if (len == 1 || this.comparator != null)
261	>	for (Object e : es)
262	>	if (e == null)
263	>	throw new NullPointerException();
264	>	this.queue = es;
265	>	this.size = len;
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		public E peek() {
346	<	return null;
346	>	return (size == 0) ? null : (E) queue[0];
347		}
348
349	<	public boolean isEmpty() {
350	<	return false;
349	>	private int indexOf(Object o) {
350	>	if (o != null) {
351	>	final Object[] es = queue;
352	>	for (int i = 0, n = size; i < n; i++)
353	>	if (o.equals(es[i]))
354	>	return i;
355	>	}
356	>	return -1;
357		}
358	<	public int size() {
359	<	return 0;
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	>	/**
381	>	* Identity-based version for use in Itr.remove.
382	>	*
383	>	* @param o element to be removed from this queue, if present
384	>	*/
385	>	void removeEq(Object o) {
386	>	final Object[] es = queue;
387	>	for (int i = 0, n = size; i < n; i++) {
388	>	if (o == es[i]) {
389	>	removeAt(i);
390	>	break;
391	>	}
392	>	}
393	>	}
394	>
395	>	/**
396	>	* Returns {@code true} if this queue contains the specified element.
397	>	* More formally, returns {@code true} if and only if this queue contains
398	>	* at least one element {@code e} such that {@code o.equals(e)}.
399	>	*
400	>	* @param o object to be checked for containment in this queue
401	>	* @return {@code true} if this queue contains the specified element
402	>	*/
403	>	public boolean contains(Object o) {
404	>	return indexOf(o) >= 0;
405		}
406	+
407	+	/**
408	+	* Returns an array containing all of the elements in this queue.
409	+	* The elements are in no particular order.
410	+	*
411	+	* <p>The returned array will be "safe" in that no references to it are
412	+	* maintained by this queue.  (In other words, this method must allocate
413	+	* a new array).  The caller is thus free to modify the returned array.
414	+	*
415	+	* <p>This method acts as bridge between array-based and collection-based
416	+	* APIs.
417	+	*
418	+	* @return an array containing all of the elements in this queue
419	+	*/
420		public Object[] toArray() {
421	<	return null;
421	>	return Arrays.copyOf(queue, size);
422		}
423
424	<	public <T> T[] toArray(T[] array) {
424	>	/**
425	>	* Returns an array containing all of the elements in this queue; the
426	>	* runtime type of the returned array is that of the specified array.
427	>	* The returned array elements are in no particular order.
428	>	* If the queue fits in the specified array, it is returned therein.
429	>	* Otherwise, a new array is allocated with the runtime type of the
430	>	* specified array and the size of this queue.
431	>	*
432	>	* <p>If the queue fits in the specified array with room to spare
433	>	* (i.e., the array has more elements than the queue), the element in
434	>	* the array immediately following the end of the collection is set to
435	>	* {@code null}.
436	>	*
437	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
438	>	* array-based and collection-based APIs.  Further, this method allows
439	>	* precise control over the runtime type of the output array, and may,
440	>	* under certain circumstances, be used to save allocation costs.
441	>	*
442	>	* <p>Suppose {@code x} is a queue known to contain only strings.
443	>	* The following code can be used to dump the queue into a newly
444	>	* allocated array of {@code String}:
445	>	*
446	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
447	>	*
448	>	* Note that {@code toArray(new Object[0])} is identical in function to
449	>	* {@code toArray()}.
450	>	*
451	>	* @param a the array into which the elements of the queue are to
452	>	*          be stored, if it is big enough; otherwise, a new array of the
453	>	*          same runtime type is allocated for this purpose.
454	>	* @return an array containing all of the elements in this queue
455	>	* @throws ArrayStoreException if the runtime type of the specified array
456	>	*         is not a supertype of the runtime type of every element in
457	>	*         this queue
458	>	* @throws NullPointerException if the specified array is null
459	>	*/
460	>	public <T> T[] toArray(T[] a) {
461	>	final int size = this.size;
462	>	if (a.length < size)
463	>	// Make a new array of a's runtime type, but my contents:
464	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
465	>	System.arraycopy(queue, 0, a, 0, size);
466	>	if (a.length > size)
467	>	a[size] = null;
468	>	return a;
469	>	}
470	>
471	>	/**
472	>	* Returns an iterator over the elements in this queue. The iterator
473	>	* does not return the elements in any particular order.
474	>	*
475	>	* @return an iterator over the elements in this queue
476	>	*/
477	>	public Iterator<E> iterator() {
478	>	return new Itr();
479	>	}
480	>
481	>	private final class Itr implements Iterator<E> {
482	>	/**
483	>	* Index (into queue array) of element to be returned by
484	>	* subsequent call to next.
485	>	*/
486	>	private int cursor;
487	>
488	>	/**
489	>	* Index of element returned by most recent call to next,
490	>	* unless that element came from the forgetMeNot list.
491	>	* Set to -1 if element is deleted by a call to remove.
492	>	*/
493	>	private int lastRet = -1;
494	>
495	>	/**
496	>	* A queue of elements that were moved from the unvisited portion of
497	>	* the heap into the visited portion as a result of "unlucky" element
498	>	* removals during the iteration.  (Unlucky element removals are those
499	>	* that require a siftup instead of a siftdown.)  We must visit all of
500	>	* the elements in this list to complete the iteration.  We do this
501	>	* after we've completed the "normal" iteration.
502	>	*
503	>	* We expect that most iterations, even those involving removals,
504	>	* will not need to store elements in this field.
505	>	*/
506	>	private ArrayDeque<E> forgetMeNot;
507	>
508	>	/**
509	>	* Element returned by the most recent call to next iff that
510	>	* element was drawn from the forgetMeNot list.
511	>	*/
512	>	private E lastRetElt;
513	>
514	>	/**
515	>	* The modCount value that the iterator believes that the backing
516	>	* Queue should have.  If this expectation is violated, the iterator
517	>	* has detected concurrent modification.
518	>	*/
519	>	private int expectedModCount = modCount;
520	>
521	>	Itr() {}                        // prevent access constructor creation
522	>
523	>	public boolean hasNext() {
524	>	return cursor < size ||
525	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
526	>	}
527	>
528	>	public E next() {
529	>	if (expectedModCount != modCount)
530	>	throw new ConcurrentModificationException();
531	>	if (cursor < size)
532	>	return (E) queue[lastRet = cursor++];
533	>	if (forgetMeNot != null) {
534	>	lastRet = -1;
535	>	lastRetElt = forgetMeNot.poll();
536	>	if (lastRetElt != null)
537	>	return lastRetElt;
538	>	}
539	>	throw new NoSuchElementException();
540	>	}
541	>
542	>	public void remove() {
543	>	if (expectedModCount != modCount)
544	>	throw new ConcurrentModificationException();
545	>	if (lastRet != -1) {
546	>	E moved = PriorityQueue.this.removeAt(lastRet);
547	>	lastRet = -1;
548	>	if (moved == null)
549	>	cursor--;
550	>	else {
551	>	if (forgetMeNot == null)
552	>	forgetMeNot = new ArrayDeque<>();
553	>	forgetMeNot.add(moved);
554	>	}
555	>	} else if (lastRetElt != null) {
556	>	PriorityQueue.this.removeEq(lastRetElt);
557	>	lastRetElt = null;
558	>	} else {
559	>	throw new IllegalStateException();
560	>	}
561	>	expectedModCount = modCount;
562	>	}
563	>	}
564	>
565	>	public int size() {
566	>	return size;
567	>	}
568	>
569	>	/**
570	>	* Removes all of the elements from this priority queue.
571	>	* The queue will be empty after this call returns.
572	>	*/
573	>	public void clear() {
574	>	modCount++;
575	>	final Object[] es = queue;
576	>	for (int i = 0, n = size; i < n; i++)
577	>	es[i] = null;
578	>	size = 0;
579	>	}
580	>
581	>	public E poll() {
582	>	if (size == 0)
583	>	return null;
584	>	int s = --size;
585	>	modCount++;
586	>	E result = (E) queue[0];
587	>	E x = (E) queue[s];
588	>	queue[s] = null;
589	>	if (s != 0)
590	>	siftDown(0, x);
591	>	return result;
592	>	}
593	>
594	>	/**
595	>	* Removes the ith element from queue.
596	>	*
597	>	* Normally this method leaves the elements at up to i-1,
598	>	* inclusive, untouched.  Under these circumstances, it returns
599	>	* null.  Occasionally, in order to maintain the heap invariant,
600	>	* it must swap a later element of the list with one earlier than
601	>	* i.  Under these circumstances, this method returns the element
602	>	* that was previously at the end of the list and is now at some
603	>	* position before i. This fact is used by iterator.remove so as to
604	>	* avoid missing traversing elements.
605	>	*/
606	>	E removeAt(int i) {
607	>	// assert i >= 0 && i < size;
608	>	modCount++;
609	>	int s = --size;
610	>	if (s == i) // removed last element
611	>	queue[i] = null;
612	>	else {
613	>	E moved = (E) queue[s];
614	>	queue[s] = null;
615	>	siftDown(i, moved);
616	>	if (queue[i] == moved) {
617	>	siftUp(i, moved);
618	>	if (queue[i] != moved)
619	>	return moved;
620	>	}
621	>	}
622		return null;
623		}
624
625	+	/**
626	+	* Inserts item x at position k, maintaining heap invariant by
627	+	* promoting x up the tree until it is greater than or equal to
628	+	* its parent, or is the root.
629	+	*
630	+	* To simplify and speed up coercions and comparisons, the
631	+	* Comparable and Comparator versions are separated into different
632	+	* methods that are otherwise identical. (Similarly for siftDown.)
633	+	*
634	+	* @param k the position to fill
635	+	* @param x the item to insert
636	+	*/
637	+	private void siftUp(int k, E x) {
638	+	if (comparator != null)
639	+	siftUpUsingComparator(k, x, queue, comparator);
640	+	else
641	+	siftUpComparable(k, x, queue);
642	+	}
643	+
644	+	private static <T> void siftUpComparable(int k, T x, Object[] es) {
645	+	Comparable<? super T> key = (Comparable<? super T>) x;
646	+	while (k > 0) {
647	+	int parent = (k - 1) >>> 1;
648	+	Object e = es[parent];
649	+	if (key.compareTo((T) e) >= 0)
650	+	break;
651	+	es[k] = e;
652	+	k = parent;
653	+	}
654	+	es[k] = key;
655	+	}
656	+
657	+	private static <T> void siftUpUsingComparator(
658	+	int k, T x, Object[] es, Comparator<? super T> cmp) {
659	+	while (k > 0) {
660	+	int parent = (k - 1) >>> 1;
661	+	Object e = es[parent];
662	+	if (cmp.compare(x, (T) e) >= 0)
663	+	break;
664	+	es[k] = e;
665	+	k = parent;
666	+	}
667	+	es[k] = x;
668	+	}
669	+
670	+	/**
671	+	* Inserts item x at position k, maintaining heap invariant by
672	+	* demoting x down the tree repeatedly until it is less than or
673	+	* equal to its children or is a leaf.
674	+	*
675	+	* @param k the position to fill
676	+	* @param x the item to insert
677	+	*/
678	+	private void siftDown(int k, E x) {
679	+	if (comparator != null)
680	+	siftDownUsingComparator(k, x, queue, size, comparator);
681	+	else
682	+	siftDownComparable(k, x, queue, size);
683	+	}
684	+
685	+	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
686	+	// assert n > 0;
687	+	Comparable<? super T> key = (Comparable<? super T>)x;
688	+	int half = n >>> 1;           // loop while a non-leaf
689	+	while (k < half) {
690	+	int child = (k << 1) + 1; // assume left child is least
691	+	Object c = es[child];
692	+	int right = child + 1;
693	+	if (right < n &&
694	+	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
695	+	c = es[child = right];
696	+	if (key.compareTo((T) c) <= 0)
697	+	break;
698	+	es[k] = c;
699	+	k = child;
700	+	}
701	+	es[k] = key;
702	+	}
703	+
704	+	private static <T> void siftDownUsingComparator(
705	+	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
706	+	// assert n > 0;
707	+	int half = n >>> 1;
708	+	while (k < half) {
709	+	int child = (k << 1) + 1;
710	+	Object c = es[child];
711	+	int right = child + 1;
712	+	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
713	+	c = es[child = right];
714	+	if (cmp.compare(x, (T) c) <= 0)
715	+	break;
716	+	es[k] = c;
717	+	k = child;
718	+	}
719	+	es[k] = x;
720	+	}
721	+
722	+	/**
723	+	* Establishes the heap invariant (described above) in the entire tree,
724	+	* assuming nothing about the order of the elements prior to the call.
725	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
726	+	*/
727	+	private void heapify() {
728	+	final Object[] es = queue;
729	+	int n = size, i = (n >>> 1) - 1;
730	+	Comparator<? super E> cmp = comparator;
731	+	if (cmp == null)
732	+	for (; i >= 0; i--)
733	+	siftDownComparable(i, (E) es[i], es, n);
734	+	else
735	+	for (; i >= 0; i--)
736	+	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
737	+	}
738	+
739	+	/**
740	+	* Returns the comparator used to order the elements in this
741	+	* queue, or {@code null} if this queue is sorted according to
742	+	* the {@linkplain Comparable natural ordering} of its elements.
743	+	*
744	+	* @return the comparator used to order this queue, or
745	+	*         {@code null} if this queue is sorted according to the
746	+	*         natural ordering of its elements
747	+	*/
748	+	public Comparator<? super E> comparator() {
749	+	return comparator;
750	+	}
751	+
752	+	/**
753	+	* Saves this queue to a stream (that is, serializes it).
754	+	*
755	+	* @param s the stream
756	+	* @throws java.io.IOException if an I/O error occurs
757	+	* @serialData The length of the array backing the instance is
758	+	*             emitted (int), followed by all of its elements
759	+	*             (each an {@code Object}) in the proper order.
760	+	*/
761	+	private void writeObject(java.io.ObjectOutputStream s)
762	+	throws java.io.IOException {
763	+	// Write out element count, and any hidden stuff
764	+	s.defaultWriteObject();
765	+
766	+	// Write out array length, for compatibility with 1.5 version
767	+	s.writeInt(Math.max(2, size + 1));
768	+
769	+	// Write out all elements in the "proper order".
770	+	final Object[] es = queue;
771	+	for (int i = 0, n = size; i < n; i++)
772	+	s.writeObject(es[i]);
773	+	}
774	+
775	+	/**
776	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
777	+	* (that is, deserializes it).
778	+	*
779	+	* @param s the stream
780	+	* @throws ClassNotFoundException if the class of a serialized object
781	+	*         could not be found
782	+	* @throws java.io.IOException if an I/O error occurs
783	+	*/
784	+	private void readObject(java.io.ObjectInputStream s)
785	+	throws java.io.IOException, ClassNotFoundException {
786	+	// Read in size, and any hidden stuff
787	+	s.defaultReadObject();
788	+
789	+	// Read in (and discard) array length
790	+	s.readInt();
791	+
792	+	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
793	+	queue = new Object[size];
794	+
795	+	// Read in all elements.
796	+	final Object[] es = queue;
797	+	for (int i = 0, n = size; i < n; i++)
798	+	es[i] = s.readObject();
799	+
800	+	// Elements are guaranteed to be in "proper order", but the
801	+	// spec has never explained what that might be.
802	+	heapify();
803	+	}
804	+
805	+	/**
806	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
807	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
808	+	* queue. The spliterator does not traverse elements in any particular order
809	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
810	+	*
811	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
812	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
813	+	* Overriding implementations should document the reporting of additional
814	+	* characteristic values.
815	+	*
816	+	* @return a {@code Spliterator} over the elements in this queue
817	+	* @since 1.8
818	+	*/
819	+	public final Spliterator<E> spliterator() {
820	+	return new PriorityQueueSpliterator(0, -1, 0);
821	+	}
822	+
823	+	final class PriorityQueueSpliterator implements Spliterator<E> {
824	+	private int index;            // current index, modified on advance/split
825	+	private int fence;            // -1 until first use
826	+	private int expectedModCount; // initialized when fence set
827	+
828	+	/** Creates new spliterator covering the given range. */
829	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
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 = modCount;
839	+	hi = fence = size;
840	+	}
841	+	return hi;
842	+	}
843	+
844	+	public PriorityQueueSpliterator trySplit() {
845	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
846	+	return (lo >= mid) ? null :
847	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
848	+	}
849	+
850	+	public void forEachRemaining(Consumer<? super E> action) {
851	+	if (action == null)
852	+	throw new NullPointerException();
853	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
854	+	final Object[] es = queue;
855	+	int i, hi; E e;
856	+	for (i = index, index = hi = fence; i < hi; i++) {
857	+	if ((e = (E) es[i]) == null)
858	+	break;      // must be CME
859	+	action.accept(e);
860	+	}
861	+	if (modCount != expectedModCount)
862	+	throw new ConcurrentModificationException();
863	+	}
864	+
865	+	public boolean tryAdvance(Consumer<? super E> action) {
866	+	if (action == null)
867	+	throw new NullPointerException();
868	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
869	+	int i;
870	+	if ((i = index) < fence) {
871	+	index = i + 1;
872	+	E e;
873	+	if ((e = (E) queue[i]) == null
874	+	|| modCount != expectedModCount)
875	+	throw new ConcurrentModificationException();
876	+	action.accept(e);
877	+	return true;
878	+	}
879	+	return false;
880	+	}
881	+
882	+	public long estimateSize() {
883	+	return getFence() - index;
884	+	}
885	+
886	+	public int characteristics() {
887	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
888	+	}
889	+	}
890	+
891	+	/**
892	+	* @throws NullPointerException {@inheritDoc}
893	+	*/
894	+	public void forEach(Consumer<? super E> action) {
895	+	Objects.requireNonNull(action);
896	+	final int expectedModCount = modCount;
897	+	final Object[] es = queue;
898	+	for (int i = 0, n = size; i < n; i++)
899	+	action.accept((E) es[i]);
900	+	if (expectedModCount != modCount)
901	+	throw new ConcurrentModificationException();
902	+	}
903		}

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