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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 1.131 by jsr166, Wed May 22 17:36:58 2019 UTC

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1	+	/*
2	+	* Copyright (c) 2003, 2019, 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 java.util.function.Predicate;
30	>	// OPENJDK import jdk.internal.access.SharedSecrets;
31	>	import jdk.internal.util.ArraysSupport;
32
33		/**
34	<	* An unbounded (resizable) priority queue based on a priority
35	<	* heap.The take operation returns the least element with respect to
36	<	* the given ordering. (If more than one element is tied for least
37	<	* value, one of them is arbitrarily chosen to be returned -- no
38	<	* guarantees are made for ordering across ties.) Ordering follows the
39	<	* java.util.Collection conventions: Either the elements must be
40	<	* Comparable, or a Comparator must be supplied. Comparison failures
41	<	* throw ClassCastExceptions during insertions and extractions.
42	<	**/
43	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
44	<	public PriorityQueue(int initialCapacity) {}
45	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
46	<
47	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
48	<
49	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
50	<
51	<	public boolean add(E x) {
52	<	return false;
34	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
35	>	* The elements of the priority queue are ordered according to their
36	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
37	>	* provided at queue construction time, depending on which constructor is
38	>	* used.  A priority queue does not permit {@code null} elements.
39	>	* A priority queue relying on natural ordering also does not permit
40	>	* insertion of non-comparable objects (doing so may result in
41	>	* {@code ClassCastException}).
42	>	*
43	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
44	>	* with respect to the specified ordering.  If multiple elements are
45	>	* tied for least value, the head is one of those elements -- ties are
46	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
47	>	* {@code remove}, {@code peek}, and {@code element} access the
48	>	* element at the head of the queue.
49	>	*
50	>	* <p>A priority queue is unbounded, but has an internal
51	>	* <i>capacity</i> governing the size of an array used to store the
52	>	* elements on the queue.  It is always at least as large as the queue
53	>	* size.  As elements are added to a priority queue, its capacity
54	>	* grows automatically.  The details of the growth policy are not
55	>	* specified.
56	>	*
57	>	* <p>This class and its iterator implement all of the
58	>	* <em>optional</em> methods of the {@link Collection} and {@link
59	>	* Iterator} interfaces.  The Iterator provided in method {@link
60	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
61	>	* are <em>not</em> guaranteed to traverse the elements of
62	>	* the priority queue in any particular order. If you need ordered
63	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
64	>	*
65	>	* <p><strong>Note that this implementation is not synchronized.</strong>
66	>	* Multiple threads should not access a {@code PriorityQueue}
67	>	* instance concurrently if any of the threads modifies the queue.
68	>	* Instead, use the thread-safe {@link
69	>	* java.util.concurrent.PriorityBlockingQueue} class.
70	>	*
71	>	* <p>Implementation note: this implementation provides
72	>	* O(log(n)) time for the enqueuing and dequeuing methods
73	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
74	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
75	>	* methods; and constant time for the retrieval methods
76	>	* ({@code peek}, {@code element}, and {@code size}).
77	>	*
78	>	* <p>This class is a member of the
79	>	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
80	>	* Java Collections Framework</a>.
81	>	*
82	>	* @since 1.5
83	>	* @author Josh Bloch, Doug Lea
84	>	* @param <E> the type of elements held in this queue
85	>	*/
86	>	@SuppressWarnings("unchecked")
87	>	public class PriorityQueue<E> extends AbstractQueue<E>
88	>	implements java.io.Serializable {
89	>
90	>	private static final long serialVersionUID = -7720805057305804111L;
91	>
92	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
93	>
94	>	/**
95	>	* Priority queue represented as a balanced binary heap: the two
96	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
97	>	* priority queue is ordered by comparator, or by the elements'
98	>	* natural ordering, if comparator is null: For each node n in the
99	>	* heap and each descendant d of n, n <= d.  The element with the
100	>	* lowest value is in queue[0], assuming the queue is nonempty.
101	>	*/
102	>	transient Object[] queue; // non-private to simplify nested class access
103	>
104	>	/**
105	>	* The number of elements in the priority queue.
106	>	*/
107	>	int size;
108	>
109	>	/**
110	>	* The comparator, or null if priority queue uses elements'
111	>	* natural ordering.
112	>	*/
113	>	private final Comparator<? super E> comparator;
114	>
115	>	/**
116	>	* The number of times this priority queue has been
117	>	* <i>structurally modified</i>.  See AbstractList for gory details.
118	>	*/
119	>	transient int modCount;     // non-private to simplify nested class access
120	>
121	>	/**
122	>	* Creates a {@code PriorityQueue} with the default initial
123	>	* capacity (11) that orders its elements according to their
124	>	* {@linkplain Comparable natural ordering}.
125	>	*/
126	>	public PriorityQueue() {
127	>	this(DEFAULT_INITIAL_CAPACITY, null);
128		}
129	<	public boolean offer(E x) {
130	<	return false;
129	>
130	>	/**
131	>	* Creates a {@code PriorityQueue} with the specified initial
132	>	* capacity that orders its elements according to their
133	>	* {@linkplain Comparable natural ordering}.
134	>	*
135	>	* @param initialCapacity the initial capacity for this priority queue
136	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
137	>	*         than 1
138	>	*/
139	>	public PriorityQueue(int initialCapacity) {
140	>	this(initialCapacity, null);
141		}
142	<	public boolean remove(Object x) {
143	<	return false;
142	>
143	>	/**
144	>	* Creates a {@code PriorityQueue} with the default initial capacity and
145	>	* whose elements are ordered according to the specified comparator.
146	>	*
147	>	* @param  comparator the comparator that will be used to order this
148	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
149	>	*         natural ordering} of the elements will be used.
150	>	* @since 1.8
151	>	*/
152	>	public PriorityQueue(Comparator<? super E> comparator) {
153	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
154		}
155
156	<	public E remove() {
157	<	return null;
156	>	/**
157	>	* Creates a {@code PriorityQueue} with the specified initial capacity
158	>	* that orders its elements according to the specified comparator.
159	>	*
160	>	* @param  initialCapacity the initial capacity for this priority queue
161	>	* @param  comparator the comparator that will be used to order this
162	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
163	>	*         natural ordering} of the elements will be used.
164	>	* @throws IllegalArgumentException if {@code initialCapacity} is
165	>	*         less than 1
166	>	*/
167	>	public PriorityQueue(int initialCapacity,
168	>	Comparator<? super E> comparator) {
169	>	// Note: This restriction of at least one is not actually needed,
170	>	// but continues for 1.5 compatibility
171	>	if (initialCapacity < 1)
172	>	throw new IllegalArgumentException();
173	>	this.queue = new Object[initialCapacity];
174	>	this.comparator = comparator;
175		}
176	<	public Iterator<E> iterator() {
177	<	return null;
176	>
177	>	/**
178	>	* Creates a {@code PriorityQueue} containing the elements in the
179	>	* specified collection.  If the specified collection is an instance of
180	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
181	>	* priority queue will be ordered according to the same ordering.
182	>	* Otherwise, this priority queue will be ordered according to the
183	>	* {@linkplain Comparable natural ordering} of its elements.
184	>	*
185	>	* @param  c the collection whose elements are to be placed
186	>	*         into this priority queue
187	>	* @throws ClassCastException if elements of the specified collection
188	>	*         cannot be compared to one another according to the priority
189	>	*         queue's ordering
190	>	* @throws NullPointerException if the specified collection or any
191	>	*         of its elements are null
192	>	*/
193	>	public PriorityQueue(Collection<? extends E> c) {
194	>	if (c instanceof SortedSet<?>) {
195	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
196	>	this.comparator = (Comparator<? super E>) ss.comparator();
197	>	initElementsFromCollection(ss);
198	>	}
199	>	else if (c instanceof PriorityQueue<?>) {
200	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
201	>	this.comparator = (Comparator<? super E>) pq.comparator();
202	>	initFromPriorityQueue(pq);
203	>	}
204	>	else {
205	>	this.comparator = null;
206	>	initFromCollection(c);
207	>	}
208		}
209
210	<	public E element() {
211	<	return null;
210	>	/**
211	>	* Creates a {@code PriorityQueue} containing the elements in the
212	>	* specified priority queue.  This priority queue will be
213	>	* ordered according to the same ordering as the given priority
214	>	* queue.
215	>	*
216	>	* @param  c the priority queue whose elements are to be placed
217	>	*         into this priority queue
218	>	* @throws ClassCastException if elements of {@code c} cannot be
219	>	*         compared to one another according to {@code c}'s
220	>	*         ordering
221	>	* @throws NullPointerException if the specified priority queue or any
222	>	*         of its elements are null
223	>	*/
224	>	public PriorityQueue(PriorityQueue<? extends E> c) {
225	>	this.comparator = (Comparator<? super E>) c.comparator();
226	>	initFromPriorityQueue(c);
227		}
228	<	public E poll() {
229	<	return null;
228	>
229	>	/**
230	>	* Creates a {@code PriorityQueue} containing the elements in the
231	>	* specified sorted set.   This priority queue will be ordered
232	>	* according to the same ordering as the given sorted set.
233	>	*
234	>	* @param  c the sorted set whose elements are to be placed
235	>	*         into this priority queue
236	>	* @throws ClassCastException if elements of the specified sorted
237	>	*         set cannot be compared to one another according to the
238	>	*         sorted set's ordering
239	>	* @throws NullPointerException if the specified sorted set or any
240	>	*         of its elements are null
241	>	*/
242	>	public PriorityQueue(SortedSet<? extends E> c) {
243	>	this.comparator = (Comparator<? super E>) c.comparator();
244	>	initElementsFromCollection(c);
245	>	}
246	>
247	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
248	>	private static Object[] ensureNonEmpty(Object[] es) {
249	>	return (es.length > 0) ? es : new Object[1];
250	>	}
251	>
252	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
253	>	if (c.getClass() == PriorityQueue.class) {
254	>	this.queue = ensureNonEmpty(c.toArray());
255	>	this.size = c.size();
256	>	} else {
257	>	initFromCollection(c);
258	>	}
259	>	}
260	>
261	>	private void initElementsFromCollection(Collection<? extends E> c) {
262	>	Object[] es = c.toArray();
263	>	int len = es.length;
264	>	// If c.toArray incorrectly doesn't return Object[], copy it.
265	>	if (es.getClass() != Object[].class)
266	>	es = Arrays.copyOf(es, len, Object[].class);
267	>	if (len == 1 || this.comparator != null)
268	>	for (Object e : es)
269	>	if (e == null)
270	>	throw new NullPointerException();
271	>	this.queue = ensureNonEmpty(es);
272	>	this.size = len;
273	>	}
274	>
275	>	/**
276	>	* Initializes queue array with elements from the given Collection.
277	>	*
278	>	* @param c the collection
279	>	*/
280	>	private void initFromCollection(Collection<? extends E> c) {
281	>	initElementsFromCollection(c);
282	>	heapify();
283	>	}
284	>
285	>	/**
286	>	* Increases the capacity of the array.
287	>	*
288	>	* @param minCapacity the desired minimum capacity
289	>	*/
290	>	private void grow(int minCapacity) {
291	>	int oldCapacity = queue.length;
292	>	// Double size if small; else grow by 50%
293	>	int newCapacity = ArraysSupport.newLength(oldCapacity,
294	>	minCapacity - oldCapacity, /* minimum growth */
295	>	oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
296	>	/* preferred growth */);
297	>	queue = Arrays.copyOf(queue, newCapacity);
298	>	}
299	>
300	>	/**
301	>	* Inserts the specified element into this priority queue.
302	>	*
303	>	* @return {@code true} (as specified by {@link Collection#add})
304	>	* @throws ClassCastException if the specified element cannot be
305	>	*         compared with elements currently in this priority queue
306	>	*         according to the priority queue's ordering
307	>	* @throws NullPointerException if the specified element is null
308	>	*/
309	>	public boolean add(E e) {
310	>	return offer(e);
311		}
312	+
313	+	/**
314	+	* Inserts the specified element into this priority queue.
315	+	*
316	+	* @return {@code true} (as specified by {@link Queue#offer})
317	+	* @throws ClassCastException if the specified element cannot be
318	+	*         compared with elements currently in this priority queue
319	+	*         according to the priority queue's ordering
320	+	* @throws NullPointerException if the specified element is null
321	+	*/
322	+	public boolean offer(E e) {
323	+	if (e == null)
324	+	throw new NullPointerException();
325	+	modCount++;
326	+	int i = size;
327	+	if (i >= queue.length)
328	+	grow(i + 1);
329	+	siftUp(i, e);
330	+	size = i + 1;
331	+	return true;
332	+	}
333	+
334		public E peek() {
335	<	return null;
335	>	return (E) queue[0];
336		}
337
338	<	public boolean isEmpty() {
339	<	return false;
338	>	private int indexOf(Object o) {
339	>	if (o != null) {
340	>	final Object[] es = queue;
341	>	for (int i = 0, n = size; i < n; i++)
342	>	if (o.equals(es[i]))
343	>	return i;
344	>	}
345	>	return -1;
346		}
347	<	public int size() {
348	<	return 0;
347	>
348	>	/**
349	>	* Removes a single instance of the specified element from this queue,
350	>	* if it is present.  More formally, removes an element {@code e} such
351	>	* that {@code o.equals(e)}, if this queue contains one or more such
352	>	* elements.  Returns {@code true} if and only if this queue contained
353	>	* the specified element (or equivalently, if this queue changed as a
354	>	* result of the call).
355	>	*
356	>	* @param o element to be removed from this queue, if present
357	>	* @return {@code true} if this queue changed as a result of the call
358	>	*/
359	>	public boolean remove(Object o) {
360	>	int i = indexOf(o);
361	>	if (i == -1)
362	>	return false;
363	>	else {
364	>	removeAt(i);
365	>	return true;
366	>	}
367	>	}
368	>
369	>	/**
370	>	* Identity-based version for use in Itr.remove.
371	>	*
372	>	* @param o element to be removed from this queue, if present
373	>	*/
374	>	void removeEq(Object o) {
375	>	final Object[] es = queue;
376	>	for (int i = 0, n = size; i < n; i++) {
377	>	if (o == es[i]) {
378	>	removeAt(i);
379	>	break;
380	>	}
381	>	}
382		}
383	+
384	+	/**
385	+	* Returns {@code true} if this queue contains the specified element.
386	+	* More formally, returns {@code true} if and only if this queue contains
387	+	* at least one element {@code e} such that {@code o.equals(e)}.
388	+	*
389	+	* @param o object to be checked for containment in this queue
390	+	* @return {@code true} if this queue contains the specified element
391	+	*/
392	+	public boolean contains(Object o) {
393	+	return indexOf(o) >= 0;
394	+	}
395	+
396	+	/**
397	+	* Returns an array containing all of the elements in this queue.
398	+	* The elements are in no particular order.
399	+	*
400	+	* <p>The returned array will be "safe" in that no references to it are
401	+	* maintained by this queue.  (In other words, this method must allocate
402	+	* a new array).  The caller is thus free to modify the returned array.
403	+	*
404	+	* <p>This method acts as bridge between array-based and collection-based
405	+	* APIs.
406	+	*
407	+	* @return an array containing all of the elements in this queue
408	+	*/
409		public Object[] toArray() {
410	<	return null;
410	>	return Arrays.copyOf(queue, size);
411	>	}
412	>
413	>	/**
414	>	* Returns an array containing all of the elements in this queue; the
415	>	* runtime type of the returned array is that of the specified array.
416	>	* The returned array elements are in no particular order.
417	>	* If the queue fits in the specified array, it is returned therein.
418	>	* Otherwise, a new array is allocated with the runtime type of the
419	>	* specified array and the size of this queue.
420	>	*
421	>	* <p>If the queue fits in the specified array with room to spare
422	>	* (i.e., the array has more elements than the queue), the element in
423	>	* the array immediately following the end of the collection is set to
424	>	* {@code null}.
425	>	*
426	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
427	>	* array-based and collection-based APIs.  Further, this method allows
428	>	* precise control over the runtime type of the output array, and may,
429	>	* under certain circumstances, be used to save allocation costs.
430	>	*
431	>	* <p>Suppose {@code x} is a queue known to contain only strings.
432	>	* The following code can be used to dump the queue into a newly
433	>	* allocated array of {@code String}:
434	>	*
435	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
436	>	*
437	>	* Note that {@code toArray(new Object[0])} is identical in function to
438	>	* {@code toArray()}.
439	>	*
440	>	* @param a the array into which the elements of the queue are to
441	>	*          be stored, if it is big enough; otherwise, a new array of the
442	>	*          same runtime type is allocated for this purpose.
443	>	* @return an array containing all of the elements in this queue
444	>	* @throws ArrayStoreException if the runtime type of the specified array
445	>	*         is not a supertype of the runtime type of every element in
446	>	*         this queue
447	>	* @throws NullPointerException if the specified array is null
448	>	*/
449	>	public <T> T[] toArray(T[] a) {
450	>	final int size = this.size;
451	>	if (a.length < size)
452	>	// Make a new array of a's runtime type, but my contents:
453	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
454	>	System.arraycopy(queue, 0, a, 0, size);
455	>	if (a.length > size)
456	>	a[size] = null;
457	>	return a;
458	>	}
459	>
460	>	/**
461	>	* Returns an iterator over the elements in this queue. The iterator
462	>	* does not return the elements in any particular order.
463	>	*
464	>	* @return an iterator over the elements in this queue
465	>	*/
466	>	public Iterator<E> iterator() {
467	>	return new Itr();
468	>	}
469	>
470	>	private final class Itr implements Iterator<E> {
471	>	/**
472	>	* Index (into queue array) of element to be returned by
473	>	* subsequent call to next.
474	>	*/
475	>	private int cursor;
476	>
477	>	/**
478	>	* Index of element returned by most recent call to next,
479	>	* unless that element came from the forgetMeNot list.
480	>	* Set to -1 if element is deleted by a call to remove.
481	>	*/
482	>	private int lastRet = -1;
483	>
484	>	/**
485	>	* A queue of elements that were moved from the unvisited portion of
486	>	* the heap into the visited portion as a result of "unlucky" element
487	>	* removals during the iteration.  (Unlucky element removals are those
488	>	* that require a siftup instead of a siftdown.)  We must visit all of
489	>	* the elements in this list to complete the iteration.  We do this
490	>	* after we've completed the "normal" iteration.
491	>	*
492	>	* We expect that most iterations, even those involving removals,
493	>	* will not need to store elements in this field.
494	>	*/
495	>	private ArrayDeque<E> forgetMeNot;
496	>
497	>	/**
498	>	* Element returned by the most recent call to next iff that
499	>	* element was drawn from the forgetMeNot list.
500	>	*/
501	>	private E lastRetElt;
502	>
503	>	/**
504	>	* The modCount value that the iterator believes that the backing
505	>	* Queue should have.  If this expectation is violated, the iterator
506	>	* has detected concurrent modification.
507	>	*/
508	>	private int expectedModCount = modCount;
509	>
510	>	Itr() {}                        // prevent access constructor creation
511	>
512	>	public boolean hasNext() {
513	>	return cursor < size ||
514	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
515	>	}
516	>
517	>	public E next() {
518	>	if (expectedModCount != modCount)
519	>	throw new ConcurrentModificationException();
520	>	if (cursor < size)
521	>	return (E) queue[lastRet = cursor++];
522	>	if (forgetMeNot != null) {
523	>	lastRet = -1;
524	>	lastRetElt = forgetMeNot.poll();
525	>	if (lastRetElt != null)
526	>	return lastRetElt;
527	>	}
528	>	throw new NoSuchElementException();
529	>	}
530	>
531	>	public void remove() {
532	>	if (expectedModCount != modCount)
533	>	throw new ConcurrentModificationException();
534	>	if (lastRet != -1) {
535	>	E moved = PriorityQueue.this.removeAt(lastRet);
536	>	lastRet = -1;
537	>	if (moved == null)
538	>	cursor--;
539	>	else {
540	>	if (forgetMeNot == null)
541	>	forgetMeNot = new ArrayDeque<>();
542	>	forgetMeNot.add(moved);
543	>	}
544	>	} else if (lastRetElt != null) {
545	>	PriorityQueue.this.removeEq(lastRetElt);
546	>	lastRetElt = null;
547	>	} else {
548	>	throw new IllegalStateException();
549	>	}
550	>	expectedModCount = modCount;
551	>	}
552	>	}
553	>
554	>	public int size() {
555	>	return size;
556	>	}
557	>
558	>	/**
559	>	* Removes all of the elements from this priority queue.
560	>	* The queue will be empty after this call returns.
561	>	*/
562	>	public void clear() {
563	>	modCount++;
564	>	final Object[] es = queue;
565	>	for (int i = 0, n = size; i < n; i++)
566	>	es[i] = null;
567	>	size = 0;
568	>	}
569	>
570	>	public E poll() {
571	>	final Object[] es;
572	>	final E result;
573	>
574	>	if ((result = (E) ((es = queue)[0])) != null) {
575	>	modCount++;
576	>	final int n;
577	>	final E x = (E) es[(n = --size)];
578	>	es[n] = null;
579	>	if (n > 0) {
580	>	final Comparator<? super E> cmp;
581	>	if ((cmp = comparator) == null)
582	>	siftDownComparable(0, x, es, n);
583	>	else
584	>	siftDownUsingComparator(0, x, es, n, cmp);
585	>	}
586	>	}
587	>	return result;
588		}
589
590	<	public <T> T[] toArray(T[] array) {
590	>	/**
591	>	* Removes the ith element from queue.
592	>	*
593	>	* Normally this method leaves the elements at up to i-1,
594	>	* inclusive, untouched.  Under these circumstances, it returns
595	>	* null.  Occasionally, in order to maintain the heap invariant,
596	>	* it must swap a later element of the list with one earlier than
597	>	* i.  Under these circumstances, this method returns the element
598	>	* that was previously at the end of the list and is now at some
599	>	* position before i. This fact is used by iterator.remove so as to
600	>	* avoid missing traversing elements.
601	>	*/
602	>	E removeAt(int i) {
603	>	// assert i >= 0 && i < size;
604	>	final Object[] es = queue;
605	>	modCount++;
606	>	int s = --size;
607	>	if (s == i) // removed last element
608	>	es[i] = null;
609	>	else {
610	>	E moved = (E) es[s];
611	>	es[s] = null;
612	>	siftDown(i, moved);
613	>	if (es[i] == moved) {
614	>	siftUp(i, moved);
615	>	if (es[i] != moved)
616	>	return moved;
617	>	}
618	>	}
619		return null;
620		}
621
622	+	/**
623	+	* Inserts item x at position k, maintaining heap invariant by
624	+	* promoting x up the tree until it is greater than or equal to
625	+	* its parent, or is the root.
626	+	*
627	+	* To simplify and speed up coercions and comparisons, the
628	+	* Comparable and Comparator versions are separated into different
629	+	* methods that are otherwise identical. (Similarly for siftDown.)
630	+	*
631	+	* @param k the position to fill
632	+	* @param x the item to insert
633	+	*/
634	+	private void siftUp(int k, E x) {
635	+	if (comparator != null)
636	+	siftUpUsingComparator(k, x, queue, comparator);
637	+	else
638	+	siftUpComparable(k, x, queue);
639	+	}
640	+
641	+	private static <T> void siftUpComparable(int k, T x, Object[] es) {
642	+	Comparable<? super T> key = (Comparable<? super T>) x;
643	+	while (k > 0) {
644	+	int parent = (k - 1) >>> 1;
645	+	Object e = es[parent];
646	+	if (key.compareTo((T) e) >= 0)
647	+	break;
648	+	es[k] = e;
649	+	k = parent;
650	+	}
651	+	es[k] = key;
652	+	}
653	+
654	+	private static <T> void siftUpUsingComparator(
655	+	int k, T x, Object[] es, Comparator<? super T> cmp) {
656	+	while (k > 0) {
657	+	int parent = (k - 1) >>> 1;
658	+	Object e = es[parent];
659	+	if (cmp.compare(x, (T) e) >= 0)
660	+	break;
661	+	es[k] = e;
662	+	k = parent;
663	+	}
664	+	es[k] = x;
665	+	}
666	+
667	+	/**
668	+	* Inserts item x at position k, maintaining heap invariant by
669	+	* demoting x down the tree repeatedly until it is less than or
670	+	* equal to its children or is a leaf.
671	+	*
672	+	* @param k the position to fill
673	+	* @param x the item to insert
674	+	*/
675	+	private void siftDown(int k, E x) {
676	+	if (comparator != null)
677	+	siftDownUsingComparator(k, x, queue, size, comparator);
678	+	else
679	+	siftDownComparable(k, x, queue, size);
680	+	}
681	+
682	+	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
683	+	// assert n > 0;
684	+	Comparable<? super T> key = (Comparable<? super T>)x;
685	+	int half = n >>> 1;           // loop while a non-leaf
686	+	while (k < half) {
687	+	int child = (k << 1) + 1; // assume left child is least
688	+	Object c = es[child];
689	+	int right = child + 1;
690	+	if (right < n &&
691	+	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
692	+	c = es[child = right];
693	+	if (key.compareTo((T) c) <= 0)
694	+	break;
695	+	es[k] = c;
696	+	k = child;
697	+	}
698	+	es[k] = key;
699	+	}
700	+
701	+	private static <T> void siftDownUsingComparator(
702	+	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
703	+	// assert n > 0;
704	+	int half = n >>> 1;
705	+	while (k < half) {
706	+	int child = (k << 1) + 1;
707	+	Object c = es[child];
708	+	int right = child + 1;
709	+	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
710	+	c = es[child = right];
711	+	if (cmp.compare(x, (T) c) <= 0)
712	+	break;
713	+	es[k] = c;
714	+	k = child;
715	+	}
716	+	es[k] = x;
717	+	}
718	+
719	+	/**
720	+	* Establishes the heap invariant (described above) in the entire tree,
721	+	* assuming nothing about the order of the elements prior to the call.
722	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
723	+	*/
724	+	private void heapify() {
725	+	final Object[] es = queue;
726	+	int n = size, i = (n >>> 1) - 1;
727	+	final Comparator<? super E> cmp;
728	+	if ((cmp = comparator) == null)
729	+	for (; i >= 0; i--)
730	+	siftDownComparable(i, (E) es[i], es, n);
731	+	else
732	+	for (; i >= 0; i--)
733	+	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
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	+	* @param s the stream
753	+	* @throws java.io.IOException if an I/O error occurs
754	+	* @serialData The length of the array backing the instance is
755	+	*             emitted (int), followed by all of its elements
756	+	*             (each an {@code Object}) in the proper order.
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	+	final Object[] es = queue;
768	+	for (int i = 0, n = size; i < n; i++)
769	+	s.writeObject(es[i]);
770	+	}
771	+
772	+	/**
773	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
774	+	* (that is, deserializes it).
775	+	*
776	+	* @param s the stream
777	+	* @throws ClassNotFoundException if the class of a serialized object
778	+	*         could not be found
779	+	* @throws java.io.IOException if an I/O error occurs
780	+	*/
781	+	private void readObject(java.io.ObjectInputStream s)
782	+	throws java.io.IOException, ClassNotFoundException {
783	+	// Read in size, and any hidden stuff
784	+	s.defaultReadObject();
785	+
786	+	// Read in (and discard) array length
787	+	s.readInt();
788	+
789	+	jsr166.Platform.checkArray(s, Object[].class, size);
790	+	final Object[] es = queue = new Object[Math.max(size, 1)];
791	+
792	+	// Read in all elements.
793	+	for (int i = 0, n = size; i < n; i++)
794	+	es[i] = s.readObject();
795	+
796	+	// Elements are guaranteed to be in "proper order", but the
797	+	// spec has never explained what that might be.
798	+	heapify();
799	+	}
800	+
801	+	/**
802	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
803	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
804	+	* queue. The spliterator does not traverse elements in any particular order
805	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
806	+	*
807	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
808	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
809	+	* Overriding implementations should document the reporting of additional
810	+	* characteristic values.
811	+	*
812	+	* @return a {@code Spliterator} over the elements in this queue
813	+	* @since 1.8
814	+	*/
815	+	public final Spliterator<E> spliterator() {
816	+	return new PriorityQueueSpliterator(0, -1, 0);
817	+	}
818	+
819	+	final class PriorityQueueSpliterator implements Spliterator<E> {
820	+	private int index;            // current index, modified on advance/split
821	+	private int fence;            // -1 until first use
822	+	private int expectedModCount; // initialized when fence set
823	+
824	+	/** Creates new spliterator covering the given range. */
825	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
826	+	this.index = origin;
827	+	this.fence = fence;
828	+	this.expectedModCount = expectedModCount;
829	+	}
830	+
831	+	private int getFence() { // initialize fence to size on first use
832	+	int hi;
833	+	if ((hi = fence) < 0) {
834	+	expectedModCount = modCount;
835	+	hi = fence = size;
836	+	}
837	+	return hi;
838	+	}
839	+
840	+	public PriorityQueueSpliterator trySplit() {
841	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
842	+	return (lo >= mid) ? null :
843	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
844	+	}
845	+
846	+	public void forEachRemaining(Consumer<? super E> action) {
847	+	if (action == null)
848	+	throw new NullPointerException();
849	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
850	+	final Object[] es = queue;
851	+	int i, hi; E e;
852	+	for (i = index, index = hi = fence; i < hi; i++) {
853	+	if ((e = (E) es[i]) == null)
854	+	break;      // must be CME
855	+	action.accept(e);
856	+	}
857	+	if (modCount != expectedModCount)
858	+	throw new ConcurrentModificationException();
859	+	}
860	+
861	+	public boolean tryAdvance(Consumer<? super E> action) {
862	+	if (action == null)
863	+	throw new NullPointerException();
864	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
865	+	int i;
866	+	if ((i = index) < fence) {
867	+	index = i + 1;
868	+	E e;
869	+	if ((e = (E) queue[i]) == null
870	+	|| modCount != expectedModCount)
871	+	throw new ConcurrentModificationException();
872	+	action.accept(e);
873	+	return true;
874	+	}
875	+	return false;
876	+	}
877	+
878	+	public long estimateSize() {
879	+	return getFence() - index;
880	+	}
881	+
882	+	public int characteristics() {
883	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
884	+	}
885	+	}
886	+
887	+	/**
888	+	* @throws NullPointerException {@inheritDoc}
889	+	*/
890	+	public boolean removeIf(Predicate<? super E> filter) {
891	+	Objects.requireNonNull(filter);
892	+	return bulkRemove(filter);
893	+	}
894	+
895	+	/**
896	+	* @throws NullPointerException {@inheritDoc}
897	+	*/
898	+	public boolean removeAll(Collection<?> c) {
899	+	Objects.requireNonNull(c);
900	+	return bulkRemove(e -> c.contains(e));
901	+	}
902	+
903	+	/**
904	+	* @throws NullPointerException {@inheritDoc}
905	+	*/
906	+	public boolean retainAll(Collection<?> c) {
907	+	Objects.requireNonNull(c);
908	+	return bulkRemove(e -> !c.contains(e));
909	+	}
910	+
911	+	// A tiny bit set implementation
912	+
913	+	private static long[] nBits(int n) {
914	+	return new long[((n - 1) >> 6) + 1];
915	+	}
916	+	private static void setBit(long[] bits, int i) {
917	+	bits[i >> 6] |= 1L << i;
918	+	}
919	+	private static boolean isClear(long[] bits, int i) {
920	+	return (bits[i >> 6] & (1L << i)) == 0;
921	+	}
922	+
923	+	/** Implementation of bulk remove methods. */
924	+	private boolean bulkRemove(Predicate<? super E> filter) {
925	+	final int expectedModCount = ++modCount;
926	+	final Object[] es = queue;
927	+	final int end = size;
928	+	int i;
929	+	// Optimize for initial run of survivors
930	+	for (i = 0; i < end && !filter.test((E) es[i]); i++)
931	+	;
932	+	if (i >= end) {
933	+	if (modCount != expectedModCount)
934	+	throw new ConcurrentModificationException();
935	+	return false;
936	+	}
937	+	// Tolerate predicates that reentrantly access the collection for
938	+	// read (but writers still get CME), so traverse once to find
939	+	// elements to delete, a second pass to physically expunge.
940	+	final int beg = i;
941	+	final long[] deathRow = nBits(end - beg);
942	+	deathRow[0] = 1L;   // set bit 0
943	+	for (i = beg + 1; i < end; i++)
944	+	if (filter.test((E) es[i]))
945	+	setBit(deathRow, i - beg);
946	+	if (modCount != expectedModCount)
947	+	throw new ConcurrentModificationException();
948	+	int w = beg;
949	+	for (i = beg; i < end; i++)
950	+	if (isClear(deathRow, i - beg))
951	+	es[w++] = es[i];
952	+	for (i = size = w; i < end; i++)
953	+	es[i] = null;
954	+	heapify();
955	+	return true;
956	+	}
957	+
958	+	/**
959	+	* @throws NullPointerException {@inheritDoc}
960	+	*/
961	+	public void forEach(Consumer<? super E> action) {
962	+	Objects.requireNonNull(action);
963	+	final int expectedModCount = modCount;
964	+	final Object[] es = queue;
965	+	for (int i = 0, n = size; i < n; i++)
966	+	action.accept((E) es[i]);
967	+	if (expectedModCount != modCount)
968	+	throw new ConcurrentModificationException();
969	+	}
970		}

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