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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 1.125 by jsr166, Sun May 6 21:07:41 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	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
246	>	private static Object[] ensureNonEmpty(Object[] es) {
247	>	return (es.length > 0) ? es : new Object[1];
248	>	}
249	>
250	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
251	>	if (c.getClass() == PriorityQueue.class) {
252	>	this.queue = ensureNonEmpty(c.toArray());
253	>	this.size = c.size();
254	>	} else {
255	>	initFromCollection(c);
256	>	}
257		}
258	+
259	+	private void initElementsFromCollection(Collection<? extends E> c) {
260	+	Object[] es = c.toArray();
261	+	int len = es.length;
262	+	// If c.toArray incorrectly doesn't return Object[], copy it.
263	+	if (es.getClass() != Object[].class)
264	+	es = Arrays.copyOf(es, len, Object[].class);
265	+	if (len == 1 || this.comparator != null)
266	+	for (Object e : es)
267	+	if (e == null)
268	+	throw new NullPointerException();
269	+	this.queue = ensureNonEmpty(es);
270	+	this.size = len;
271	+	}
272	+
273	+	/**
274	+	* Initializes queue array with elements from the given Collection.
275	+	*
276	+	* @param c the collection
277	+	*/
278	+	private void initFromCollection(Collection<? extends E> c) {
279	+	initElementsFromCollection(c);
280	+	heapify();
281	+	}
282	+
283	+	/**
284	+	* The maximum size of array to allocate.
285	+	* Some VMs reserve some header words in an array.
286	+	* Attempts to allocate larger arrays may result in
287	+	* OutOfMemoryError: Requested array size exceeds VM limit
288	+	*/
289	+	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
290	+
291	+	/**
292	+	* Increases the capacity of the array.
293	+	*
294	+	* @param minCapacity the desired minimum capacity
295	+	*/
296	+	private void grow(int minCapacity) {
297	+	int oldCapacity = queue.length;
298	+	// Double size if small; else grow by 50%
299	+	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
300	+	(oldCapacity + 2) :
301	+	(oldCapacity >> 1));
302	+	// overflow-conscious code
303	+	if (newCapacity - MAX_ARRAY_SIZE > 0)
304	+	newCapacity = hugeCapacity(minCapacity);
305	+	queue = Arrays.copyOf(queue, newCapacity);
306	+	}
307	+
308	+	private static int hugeCapacity(int minCapacity) {
309	+	if (minCapacity < 0) // overflow
310	+	throw new OutOfMemoryError();
311	+	return (minCapacity > MAX_ARRAY_SIZE) ?
312	+	Integer.MAX_VALUE :
313	+	MAX_ARRAY_SIZE;
314	+	}
315	+
316	+	/**
317	+	* Inserts the specified element into this priority queue.
318	+	*
319	+	* @return {@code true} (as specified by {@link Collection#add})
320	+	* @throws ClassCastException if the specified element cannot be
321	+	*         compared with elements currently in this priority queue
322	+	*         according to the priority queue's ordering
323	+	* @throws NullPointerException if the specified element is null
324	+	*/
325	+	public boolean add(E e) {
326	+	return offer(e);
327	+	}
328	+
329	+	/**
330	+	* Inserts the specified element into this priority queue.
331	+	*
332	+	* @return {@code true} (as specified by {@link Queue#offer})
333	+	* @throws ClassCastException if the specified element cannot be
334	+	*         compared with elements currently in this priority queue
335	+	*         according to the priority queue's ordering
336	+	* @throws NullPointerException if the specified element is null
337	+	*/
338	+	public boolean offer(E e) {
339	+	if (e == null)
340	+	throw new NullPointerException();
341	+	modCount++;
342	+	int i = size;
343	+	if (i >= queue.length)
344	+	grow(i + 1);
345	+	siftUp(i, e);
346	+	size = i + 1;
347	+	return true;
348	+	}
349	+
350		public E peek() {
351	<	return null;
351	>	return (E) queue[0];
352		}
353
354	<	public boolean isEmpty() {
355	<	return false;
354	>	private int indexOf(Object o) {
355	>	if (o != null) {
356	>	final Object[] es = queue;
357	>	for (int i = 0, n = size; i < n; i++)
358	>	if (o.equals(es[i]))
359	>	return i;
360	>	}
361	>	return -1;
362		}
363	<	public int size() {
364	<	return 0;
363	>
364	>	/**
365	>	* Removes a single instance of the specified element from this queue,
366	>	* if it is present.  More formally, removes an element {@code e} such
367	>	* that {@code o.equals(e)}, if this queue contains one or more such
368	>	* elements.  Returns {@code true} if and only if this queue contained
369	>	* the specified element (or equivalently, if this queue changed as a
370	>	* result of the call).
371	>	*
372	>	* @param o element to be removed from this queue, if present
373	>	* @return {@code true} if this queue changed as a result of the call
374	>	*/
375	>	public boolean remove(Object o) {
376	>	int i = indexOf(o);
377	>	if (i == -1)
378	>	return false;
379	>	else {
380	>	removeAt(i);
381	>	return true;
382	>	}
383	>	}
384	>
385	>	/**
386	>	* Identity-based version for use in Itr.remove.
387	>	*
388	>	* @param o element to be removed from this queue, if present
389	>	*/
390	>	void removeEq(Object o) {
391	>	final Object[] es = queue;
392	>	for (int i = 0, n = size; i < n; i++) {
393	>	if (o == es[i]) {
394	>	removeAt(i);
395	>	break;
396	>	}
397	>	}
398		}
399	+
400	+	/**
401	+	* Returns {@code true} if this queue contains the specified element.
402	+	* More formally, returns {@code true} if and only if this queue contains
403	+	* at least one element {@code e} such that {@code o.equals(e)}.
404	+	*
405	+	* @param o object to be checked for containment in this queue
406	+	* @return {@code true} if this queue contains the specified element
407	+	*/
408	+	public boolean contains(Object o) {
409	+	return indexOf(o) >= 0;
410	+	}
411	+
412	+	/**
413	+	* Returns an array containing all of the elements in this queue.
414	+	* The elements are in no particular order.
415	+	*
416	+	* <p>The returned array will be "safe" in that no references to it are
417	+	* maintained by this queue.  (In other words, this method must allocate
418	+	* a new array).  The caller is thus free to modify the returned array.
419	+	*
420	+	* <p>This method acts as bridge between array-based and collection-based
421	+	* APIs.
422	+	*
423	+	* @return an array containing all of the elements in this queue
424	+	*/
425		public Object[] toArray() {
426	<	return null;
426	>	return Arrays.copyOf(queue, size);
427	>	}
428	>
429	>	/**
430	>	* Returns an array containing all of the elements in this queue; the
431	>	* runtime type of the returned array is that of the specified array.
432	>	* The returned array elements are in no particular order.
433	>	* If the queue fits in the specified array, it is returned therein.
434	>	* Otherwise, a new array is allocated with the runtime type of the
435	>	* specified array and the size of this queue.
436	>	*
437	>	* <p>If the queue fits in the specified array with room to spare
438	>	* (i.e., the array has more elements than the queue), the element in
439	>	* the array immediately following the end of the collection is set to
440	>	* {@code null}.
441	>	*
442	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
443	>	* array-based and collection-based APIs.  Further, this method allows
444	>	* precise control over the runtime type of the output array, and may,
445	>	* under certain circumstances, be used to save allocation costs.
446	>	*
447	>	* <p>Suppose {@code x} is a queue known to contain only strings.
448	>	* The following code can be used to dump the queue into a newly
449	>	* allocated array of {@code String}:
450	>	*
451	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
452	>	*
453	>	* Note that {@code toArray(new Object[0])} is identical in function to
454	>	* {@code toArray()}.
455	>	*
456	>	* @param a the array into which the elements of the queue are to
457	>	*          be stored, if it is big enough; otherwise, a new array of the
458	>	*          same runtime type is allocated for this purpose.
459	>	* @return an array containing all of the elements in this queue
460	>	* @throws ArrayStoreException if the runtime type of the specified array
461	>	*         is not a supertype of the runtime type of every element in
462	>	*         this queue
463	>	* @throws NullPointerException if the specified array is null
464	>	*/
465	>	public <T> T[] toArray(T[] a) {
466	>	final int size = this.size;
467	>	if (a.length < size)
468	>	// Make a new array of a's runtime type, but my contents:
469	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
470	>	System.arraycopy(queue, 0, a, 0, size);
471	>	if (a.length > size)
472	>	a[size] = null;
473	>	return a;
474	>	}
475	>
476	>	/**
477	>	* Returns an iterator over the elements in this queue. The iterator
478	>	* does not return the elements in any particular order.
479	>	*
480	>	* @return an iterator over the elements in this queue
481	>	*/
482	>	public Iterator<E> iterator() {
483	>	return new Itr();
484	>	}
485	>
486	>	private final class Itr implements Iterator<E> {
487	>	/**
488	>	* Index (into queue array) of element to be returned by
489	>	* subsequent call to next.
490	>	*/
491	>	private int cursor;
492	>
493	>	/**
494	>	* Index of element returned by most recent call to next,
495	>	* unless that element came from the forgetMeNot list.
496	>	* Set to -1 if element is deleted by a call to remove.
497	>	*/
498	>	private int lastRet = -1;
499	>
500	>	/**
501	>	* A queue of elements that were moved from the unvisited portion of
502	>	* the heap into the visited portion as a result of "unlucky" element
503	>	* removals during the iteration.  (Unlucky element removals are those
504	>	* that require a siftup instead of a siftdown.)  We must visit all of
505	>	* the elements in this list to complete the iteration.  We do this
506	>	* after we've completed the "normal" iteration.
507	>	*
508	>	* We expect that most iterations, even those involving removals,
509	>	* will not need to store elements in this field.
510	>	*/
511	>	private ArrayDeque<E> forgetMeNot;
512	>
513	>	/**
514	>	* Element returned by the most recent call to next iff that
515	>	* element was drawn from the forgetMeNot list.
516	>	*/
517	>	private E lastRetElt;
518	>
519	>	/**
520	>	* The modCount value that the iterator believes that the backing
521	>	* Queue should have.  If this expectation is violated, the iterator
522	>	* has detected concurrent modification.
523	>	*/
524	>	private int expectedModCount = modCount;
525	>
526	>	Itr() {}                        // prevent access constructor creation
527	>
528	>	public boolean hasNext() {
529	>	return cursor < size ||
530	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
531	>	}
532	>
533	>	public E next() {
534	>	if (expectedModCount != modCount)
535	>	throw new ConcurrentModificationException();
536	>	if (cursor < size)
537	>	return (E) queue[lastRet = cursor++];
538	>	if (forgetMeNot != null) {
539	>	lastRet = -1;
540	>	lastRetElt = forgetMeNot.poll();
541	>	if (lastRetElt != null)
542	>	return lastRetElt;
543	>	}
544	>	throw new NoSuchElementException();
545	>	}
546	>
547	>	public void remove() {
548	>	if (expectedModCount != modCount)
549	>	throw new ConcurrentModificationException();
550	>	if (lastRet != -1) {
551	>	E moved = PriorityQueue.this.removeAt(lastRet);
552	>	lastRet = -1;
553	>	if (moved == null)
554	>	cursor--;
555	>	else {
556	>	if (forgetMeNot == null)
557	>	forgetMeNot = new ArrayDeque<>();
558	>	forgetMeNot.add(moved);
559	>	}
560	>	} else if (lastRetElt != null) {
561	>	PriorityQueue.this.removeEq(lastRetElt);
562	>	lastRetElt = null;
563	>	} else {
564	>	throw new IllegalStateException();
565	>	}
566	>	expectedModCount = modCount;
567	>	}
568	>	}
569	>
570	>	public int size() {
571	>	return size;
572	>	}
573	>
574	>	/**
575	>	* Removes all of the elements from this priority queue.
576	>	* The queue will be empty after this call returns.
577	>	*/
578	>	public void clear() {
579	>	modCount++;
580	>	final Object[] es = queue;
581	>	for (int i = 0, n = size; i < n; i++)
582	>	es[i] = null;
583	>	size = 0;
584		}
585
586	<	public <T> T[] toArray(T[] array) {
586	>	public E poll() {
587	>	final Object[] es;
588	>	final E result;
589	>
590	>	if ((result = (E) ((es = queue)[0])) != null) {
591	>	modCount++;
592	>	final int n;
593	>	final E x = (E) es[(n = --size)];
594	>	es[n] = null;
595	>	if (n > 0) {
596	>	final Comparator<? super E> cmp;
597	>	if ((cmp = comparator) == null)
598	>	siftDownComparable(0, x, es, n);
599	>	else
600	>	siftDownUsingComparator(0, x, es, n, cmp);
601	>	}
602	>	}
603	>	return result;
604	>	}
605	>
606	>	/**
607	>	* Removes the ith element from queue.
608	>	*
609	>	* Normally this method leaves the elements at up to i-1,
610	>	* inclusive, untouched.  Under these circumstances, it returns
611	>	* null.  Occasionally, in order to maintain the heap invariant,
612	>	* it must swap a later element of the list with one earlier than
613	>	* i.  Under these circumstances, this method returns the element
614	>	* that was previously at the end of the list and is now at some
615	>	* position before i. This fact is used by iterator.remove so as to
616	>	* avoid missing traversing elements.
617	>	*/
618	>	E removeAt(int i) {
619	>	// assert i >= 0 && i < size;
620	>	modCount++;
621	>	int s = --size;
622	>	if (s == i) // removed last element
623	>	queue[i] = null;
624	>	else {
625	>	E moved = (E) queue[s];
626	>	queue[s] = null;
627	>	siftDown(i, moved);
628	>	if (queue[i] == moved) {
629	>	siftUp(i, moved);
630	>	if (queue[i] != moved)
631	>	return moved;
632	>	}
633	>	}
634		return null;
635		}
636
637	+	/**
638	+	* Inserts item x at position k, maintaining heap invariant by
639	+	* promoting x up the tree until it is greater than or equal to
640	+	* its parent, or is the root.
641	+	*
642	+	* To simplify and speed up coercions and comparisons, the
643	+	* Comparable and Comparator versions are separated into different
644	+	* methods that are otherwise identical. (Similarly for siftDown.)
645	+	*
646	+	* @param k the position to fill
647	+	* @param x the item to insert
648	+	*/
649	+	private void siftUp(int k, E x) {
650	+	if (comparator != null)
651	+	siftUpUsingComparator(k, x, queue, comparator);
652	+	else
653	+	siftUpComparable(k, x, queue);
654	+	}
655	+
656	+	private static <T> void siftUpComparable(int k, T x, Object[] es) {
657	+	Comparable<? super T> key = (Comparable<? super T>) x;
658	+	while (k > 0) {
659	+	int parent = (k - 1) >>> 1;
660	+	Object e = es[parent];
661	+	if (key.compareTo((T) e) >= 0)
662	+	break;
663	+	es[k] = e;
664	+	k = parent;
665	+	}
666	+	es[k] = key;
667	+	}
668	+
669	+	private static <T> void siftUpUsingComparator(
670	+	int k, T x, Object[] es, Comparator<? super T> cmp) {
671	+	while (k > 0) {
672	+	int parent = (k - 1) >>> 1;
673	+	Object e = es[parent];
674	+	if (cmp.compare(x, (T) e) >= 0)
675	+	break;
676	+	es[k] = e;
677	+	k = parent;
678	+	}
679	+	es[k] = x;
680	+	}
681	+
682	+	/**
683	+	* Inserts item x at position k, maintaining heap invariant by
684	+	* demoting x down the tree repeatedly until it is less than or
685	+	* equal to its children or is a leaf.
686	+	*
687	+	* @param k the position to fill
688	+	* @param x the item to insert
689	+	*/
690	+	private void siftDown(int k, E x) {
691	+	if (comparator != null)
692	+	siftDownUsingComparator(k, x, queue, size, comparator);
693	+	else
694	+	siftDownComparable(k, x, queue, size);
695	+	}
696	+
697	+	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
698	+	// assert n > 0;
699	+	Comparable<? super T> key = (Comparable<? super T>)x;
700	+	int half = n >>> 1;           // loop while a non-leaf
701	+	while (k < half) {
702	+	int child = (k << 1) + 1; // assume left child is least
703	+	Object c = es[child];
704	+	int right = child + 1;
705	+	if (right < n &&
706	+	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
707	+	c = es[child = right];
708	+	if (key.compareTo((T) c) <= 0)
709	+	break;
710	+	es[k] = c;
711	+	k = child;
712	+	}
713	+	es[k] = key;
714	+	}
715	+
716	+	private static <T> void siftDownUsingComparator(
717	+	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
718	+	// assert n > 0;
719	+	int half = n >>> 1;
720	+	while (k < half) {
721	+	int child = (k << 1) + 1;
722	+	Object c = es[child];
723	+	int right = child + 1;
724	+	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
725	+	c = es[child = right];
726	+	if (cmp.compare(x, (T) c) <= 0)
727	+	break;
728	+	es[k] = c;
729	+	k = child;
730	+	}
731	+	es[k] = x;
732	+	}
733	+
734	+	/**
735	+	* Establishes the heap invariant (described above) in the entire tree,
736	+	* assuming nothing about the order of the elements prior to the call.
737	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
738	+	*/
739	+	private void heapify() {
740	+	final Object[] es = queue;
741	+	int n = size, i = (n >>> 1) - 1;
742	+	final Comparator<? super E> cmp;
743	+	if ((cmp = comparator) == null)
744	+	for (; i >= 0; i--)
745	+	siftDownComparable(i, (E) es[i], es, n);
746	+	else
747	+	for (; i >= 0; i--)
748	+	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
749	+	}
750	+
751	+	/**
752	+	* Returns the comparator used to order the elements in this
753	+	* queue, or {@code null} if this queue is sorted according to
754	+	* the {@linkplain Comparable natural ordering} of its elements.
755	+	*
756	+	* @return the comparator used to order this queue, or
757	+	*         {@code null} if this queue is sorted according to the
758	+	*         natural ordering of its elements
759	+	*/
760	+	public Comparator<? super E> comparator() {
761	+	return comparator;
762	+	}
763	+
764	+	/**
765	+	* Saves this queue to a stream (that is, serializes it).
766	+	*
767	+	* @param s the stream
768	+	* @throws java.io.IOException if an I/O error occurs
769	+	* @serialData The length of the array backing the instance is
770	+	*             emitted (int), followed by all of its elements
771	+	*             (each an {@code Object}) in the proper order.
772	+	*/
773	+	private void writeObject(java.io.ObjectOutputStream s)
774	+	throws java.io.IOException {
775	+	// Write out element count, and any hidden stuff
776	+	s.defaultWriteObject();
777	+
778	+	// Write out array length, for compatibility with 1.5 version
779	+	s.writeInt(Math.max(2, size + 1));
780	+
781	+	// Write out all elements in the "proper order".
782	+	final Object[] es = queue;
783	+	for (int i = 0, n = size; i < n; i++)
784	+	s.writeObject(es[i]);
785	+	}
786	+
787	+	/**
788	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
789	+	* (that is, deserializes it).
790	+	*
791	+	* @param s the stream
792	+	* @throws ClassNotFoundException if the class of a serialized object
793	+	*         could not be found
794	+	* @throws java.io.IOException if an I/O error occurs
795	+	*/
796	+	private void readObject(java.io.ObjectInputStream s)
797	+	throws java.io.IOException, ClassNotFoundException {
798	+	// Read in size, and any hidden stuff
799	+	s.defaultReadObject();
800	+
801	+	// Read in (and discard) array length
802	+	s.readInt();
803	+
804	+	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
805	+	final Object[] es = queue = new Object[Math.max(size, 1)];
806	+
807	+	// Read in all elements.
808	+	for (int i = 0, n = size; i < n; i++)
809	+	es[i] = s.readObject();
810	+
811	+	// Elements are guaranteed to be in "proper order", but the
812	+	// spec has never explained what that might be.
813	+	heapify();
814	+	}
815	+
816	+	/**
817	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
818	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
819	+	* queue. The spliterator does not traverse elements in any particular order
820	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
821	+	*
822	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
823	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
824	+	* Overriding implementations should document the reporting of additional
825	+	* characteristic values.
826	+	*
827	+	* @return a {@code Spliterator} over the elements in this queue
828	+	* @since 1.8
829	+	*/
830	+	public final Spliterator<E> spliterator() {
831	+	return new PriorityQueueSpliterator(0, -1, 0);
832	+	}
833	+
834	+	final class PriorityQueueSpliterator implements Spliterator<E> {
835	+	private int index;            // current index, modified on advance/split
836	+	private int fence;            // -1 until first use
837	+	private int expectedModCount; // initialized when fence set
838	+
839	+	/** Creates new spliterator covering the given range. */
840	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
841	+	this.index = origin;
842	+	this.fence = fence;
843	+	this.expectedModCount = expectedModCount;
844	+	}
845	+
846	+	private int getFence() { // initialize fence to size on first use
847	+	int hi;
848	+	if ((hi = fence) < 0) {
849	+	expectedModCount = modCount;
850	+	hi = fence = size;
851	+	}
852	+	return hi;
853	+	}
854	+
855	+	public PriorityQueueSpliterator trySplit() {
856	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
857	+	return (lo >= mid) ? null :
858	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
859	+	}
860	+
861	+	public void forEachRemaining(Consumer<? super E> action) {
862	+	if (action == null)
863	+	throw new NullPointerException();
864	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
865	+	final Object[] es = queue;
866	+	int i, hi; E e;
867	+	for (i = index, index = hi = fence; i < hi; i++) {
868	+	if ((e = (E) es[i]) == null)
869	+	break;      // must be CME
870	+	action.accept(e);
871	+	}
872	+	if (modCount != expectedModCount)
873	+	throw new ConcurrentModificationException();
874	+	}
875	+
876	+	public boolean tryAdvance(Consumer<? super E> action) {
877	+	if (action == null)
878	+	throw new NullPointerException();
879	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
880	+	int i;
881	+	if ((i = index) < fence) {
882	+	index = i + 1;
883	+	E e;
884	+	if ((e = (E) queue[i]) == null
885	+	|| modCount != expectedModCount)
886	+	throw new ConcurrentModificationException();
887	+	action.accept(e);
888	+	return true;
889	+	}
890	+	return false;
891	+	}
892	+
893	+	public long estimateSize() {
894	+	return getFence() - index;
895	+	}
896	+
897	+	public int characteristics() {
898	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
899	+	}
900	+	}
901	+
902	+	/**
903	+	* @throws NullPointerException {@inheritDoc}
904	+	*/
905	+	public void forEach(Consumer<? super E> action) {
906	+	Objects.requireNonNull(action);
907	+	final int expectedModCount = modCount;
908	+	final Object[] es = queue;
909	+	for (int i = 0, n = size; i < n; i++)
910	+	action.accept((E) es[i]);
911	+	if (expectedModCount != modCount)
912	+	throw new ConcurrentModificationException();
913	+	}
914		}

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