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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 1.132 by jsr166, Fri Aug 30 18:05:39 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	>	// OPENJDK @java.io.Serial
91	>	private static final long serialVersionUID = -7720805057305804111L;
92	>
93	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
94	>
95	>	/**
96	>	* Priority queue represented as a balanced binary heap: the two
97	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
98	>	* priority queue is ordered by comparator, or by the elements'
99	>	* natural ordering, if comparator is null: For each node n in the
100	>	* heap and each descendant d of n, n <= d.  The element with the
101	>	* lowest value is in queue[0], assuming the queue is nonempty.
102	>	*/
103	>	transient Object[] queue; // non-private to simplify nested class access
104	>
105	>	/**
106	>	* The number of elements in the priority queue.
107	>	*/
108	>	int size;
109	>
110	>	/**
111	>	* The comparator, or null if priority queue uses elements'
112	>	* natural ordering.
113	>	*/
114	>	private final Comparator<? super E> comparator;
115	>
116	>	/**
117	>	* The number of times this priority queue has been
118	>	* <i>structurally modified</i>.  See AbstractList for gory details.
119	>	*/
120	>	transient int modCount;     // non-private to simplify nested class access
121	>
122	>	/**
123	>	* Creates a {@code PriorityQueue} with the default initial
124	>	* capacity (11) that orders its elements according to their
125	>	* {@linkplain Comparable natural ordering}.
126	>	*/
127	>	public PriorityQueue() {
128	>	this(DEFAULT_INITIAL_CAPACITY, null);
129		}
130	<	public boolean offer(E x) {
131	<	return false;
130	>
131	>	/**
132	>	* Creates a {@code PriorityQueue} with the specified initial
133	>	* capacity that orders its elements according to their
134	>	* {@linkplain Comparable natural ordering}.
135	>	*
136	>	* @param initialCapacity the initial capacity for this priority queue
137	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
138	>	*         than 1
139	>	*/
140	>	public PriorityQueue(int initialCapacity) {
141	>	this(initialCapacity, null);
142		}
143	<	public boolean remove(Object x) {
144	<	return false;
143	>
144	>	/**
145	>	* Creates a {@code PriorityQueue} with the default initial capacity and
146	>	* whose elements are ordered according to the specified comparator.
147	>	*
148	>	* @param  comparator the comparator that will be used to order this
149	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
150	>	*         natural ordering} of the elements will be used.
151	>	* @since 1.8
152	>	*/
153	>	public PriorityQueue(Comparator<? super E> comparator) {
154	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
155		}
156
157	<	public E remove() {
158	<	return null;
157	>	/**
158	>	* Creates a {@code PriorityQueue} with the specified initial capacity
159	>	* that orders its elements according to the specified comparator.
160	>	*
161	>	* @param  initialCapacity the initial capacity for this priority queue
162	>	* @param  comparator the comparator that will be used to order this
163	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
164	>	*         natural ordering} of the elements will be used.
165	>	* @throws IllegalArgumentException if {@code initialCapacity} is
166	>	*         less than 1
167	>	*/
168	>	public PriorityQueue(int initialCapacity,
169	>	Comparator<? super E> comparator) {
170	>	// Note: This restriction of at least one is not actually needed,
171	>	// but continues for 1.5 compatibility
172	>	if (initialCapacity < 1)
173	>	throw new IllegalArgumentException();
174	>	this.queue = new Object[initialCapacity];
175	>	this.comparator = comparator;
176		}
177	<	public Iterator<E> iterator() {
178	<	return null;
177	>
178	>	/**
179	>	* Creates a {@code PriorityQueue} containing the elements in the
180	>	* specified collection.  If the specified collection is an instance of
181	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
182	>	* priority queue will be ordered according to the same ordering.
183	>	* Otherwise, this priority queue will be ordered according to the
184	>	* {@linkplain Comparable natural ordering} of its elements.
185	>	*
186	>	* @param  c the collection whose elements are to be placed
187	>	*         into this priority queue
188	>	* @throws ClassCastException if elements of the specified collection
189	>	*         cannot be compared to one another according to the priority
190	>	*         queue's ordering
191	>	* @throws NullPointerException if the specified collection or any
192	>	*         of its elements are null
193	>	*/
194	>	public PriorityQueue(Collection<? extends E> c) {
195	>	if (c instanceof SortedSet<?>) {
196	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
197	>	this.comparator = (Comparator<? super E>) ss.comparator();
198	>	initElementsFromCollection(ss);
199	>	}
200	>	else if (c instanceof PriorityQueue<?>) {
201	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
202	>	this.comparator = (Comparator<? super E>) pq.comparator();
203	>	initFromPriorityQueue(pq);
204	>	}
205	>	else {
206	>	this.comparator = null;
207	>	initFromCollection(c);
208	>	}
209		}
210
211	<	public E element() {
212	<	return null;
211	>	/**
212	>	* Creates a {@code PriorityQueue} containing the elements in the
213	>	* specified priority queue.  This priority queue will be
214	>	* ordered according to the same ordering as the given priority
215	>	* queue.
216	>	*
217	>	* @param  c the priority queue whose elements are to be placed
218	>	*         into this priority queue
219	>	* @throws ClassCastException if elements of {@code c} cannot be
220	>	*         compared to one another according to {@code c}'s
221	>	*         ordering
222	>	* @throws NullPointerException if the specified priority queue or any
223	>	*         of its elements are null
224	>	*/
225	>	public PriorityQueue(PriorityQueue<? extends E> c) {
226	>	this.comparator = (Comparator<? super E>) c.comparator();
227	>	initFromPriorityQueue(c);
228		}
229	<	public E poll() {
230	<	return null;
229	>
230	>	/**
231	>	* Creates a {@code PriorityQueue} containing the elements in the
232	>	* specified sorted set.   This priority queue will be ordered
233	>	* according to the same ordering as the given sorted set.
234	>	*
235	>	* @param  c the sorted set whose elements are to be placed
236	>	*         into this priority queue
237	>	* @throws ClassCastException if elements of the specified sorted
238	>	*         set cannot be compared to one another according to the
239	>	*         sorted set's ordering
240	>	* @throws NullPointerException if the specified sorted set or any
241	>	*         of its elements are null
242	>	*/
243	>	public PriorityQueue(SortedSet<? extends E> c) {
244	>	this.comparator = (Comparator<? super E>) c.comparator();
245	>	initElementsFromCollection(c);
246	>	}
247	>
248	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
249	>	private static Object[] ensureNonEmpty(Object[] es) {
250	>	return (es.length > 0) ? es : new Object[1];
251	>	}
252	>
253	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
254	>	if (c.getClass() == PriorityQueue.class) {
255	>	this.queue = ensureNonEmpty(c.toArray());
256	>	this.size = c.size();
257	>	} else {
258	>	initFromCollection(c);
259	>	}
260	>	}
261	>
262	>	private void initElementsFromCollection(Collection<? extends E> c) {
263	>	Object[] es = c.toArray();
264	>	int len = es.length;
265	>	// If c.toArray incorrectly doesn't return Object[], copy it.
266	>	if (es.getClass() != Object[].class)
267	>	es = Arrays.copyOf(es, len, Object[].class);
268	>	if (len == 1 || this.comparator != null)
269	>	for (Object e : es)
270	>	if (e == null)
271	>	throw new NullPointerException();
272	>	this.queue = ensureNonEmpty(es);
273	>	this.size = len;
274	>	}
275	>
276	>	/**
277	>	* Initializes queue array with elements from the given Collection.
278	>	*
279	>	* @param c the collection
280	>	*/
281	>	private void initFromCollection(Collection<? extends E> c) {
282	>	initElementsFromCollection(c);
283	>	heapify();
284	>	}
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 = ArraysSupport.newLength(oldCapacity,
295	>	minCapacity - oldCapacity, /* minimum growth */
296	>	oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
297	>	/* preferred growth */);
298	>	queue = Arrays.copyOf(queue, newCapacity);
299	>	}
300	>
301	>	/**
302	>	* Inserts the specified element into this priority queue.
303	>	*
304	>	* @return {@code true} (as specified by {@link Collection#add})
305	>	* @throws ClassCastException if the specified element cannot be
306	>	*         compared with elements currently in this priority queue
307	>	*         according to the priority queue's ordering
308	>	* @throws NullPointerException if the specified element is null
309	>	*/
310	>	public boolean add(E e) {
311	>	return offer(e);
312		}
313	+
314	+	/**
315	+	* Inserts the specified element into this priority queue.
316	+	*
317	+	* @return {@code true} (as specified by {@link Queue#offer})
318	+	* @throws ClassCastException if the specified element cannot be
319	+	*         compared with elements currently in this priority queue
320	+	*         according to the priority queue's ordering
321	+	* @throws NullPointerException if the specified element is null
322	+	*/
323	+	public boolean offer(E e) {
324	+	if (e == null)
325	+	throw new NullPointerException();
326	+	modCount++;
327	+	int i = size;
328	+	if (i >= queue.length)
329	+	grow(i + 1);
330	+	siftUp(i, e);
331	+	size = i + 1;
332	+	return true;
333	+	}
334	+
335		public E peek() {
336	<	return null;
336	>	return (E) queue[0];
337		}
338
339	<	public boolean isEmpty() {
340	<	return false;
339	>	private int indexOf(Object o) {
340	>	if (o != null) {
341	>	final Object[] es = queue;
342	>	for (int i = 0, n = size; i < n; i++)
343	>	if (o.equals(es[i]))
344	>	return i;
345	>	}
346	>	return -1;
347		}
348	<	public int size() {
349	<	return 0;
348	>
349	>	/**
350	>	* Removes a single instance of the specified element from this queue,
351	>	* if it is present.  More formally, removes an element {@code e} such
352	>	* that {@code o.equals(e)}, if this queue contains one or more such
353	>	* elements.  Returns {@code true} if and only if this queue contained
354	>	* the specified element (or equivalently, if this queue changed as a
355	>	* result of the call).
356	>	*
357	>	* @param o element to be removed from this queue, if present
358	>	* @return {@code true} if this queue changed as a result of the call
359	>	*/
360	>	public boolean remove(Object o) {
361	>	int i = indexOf(o);
362	>	if (i == -1)
363	>	return false;
364	>	else {
365	>	removeAt(i);
366	>	return true;
367	>	}
368	>	}
369	>
370	>	/**
371	>	* Identity-based version for use in Itr.remove.
372	>	*
373	>	* @param o element to be removed from this queue, if present
374	>	*/
375	>	void removeEq(Object o) {
376	>	final Object[] es = queue;
377	>	for (int i = 0, n = size; i < n; i++) {
378	>	if (o == es[i]) {
379	>	removeAt(i);
380	>	break;
381	>	}
382	>	}
383		}
384	+
385	+	/**
386	+	* Returns {@code true} if this queue contains the specified element.
387	+	* More formally, returns {@code true} if and only if this queue contains
388	+	* at least one element {@code e} such that {@code o.equals(e)}.
389	+	*
390	+	* @param o object to be checked for containment in this queue
391	+	* @return {@code true} if this queue contains the specified element
392	+	*/
393	+	public boolean contains(Object o) {
394	+	return indexOf(o) >= 0;
395	+	}
396	+
397	+	/**
398	+	* Returns an array containing all of the elements in this queue.
399	+	* The elements are in no particular order.
400	+	*
401	+	* <p>The returned array will be "safe" in that no references to it are
402	+	* maintained by this queue.  (In other words, this method must allocate
403	+	* a new array).  The caller is thus free to modify the returned array.
404	+	*
405	+	* <p>This method acts as bridge between array-based and collection-based
406	+	* APIs.
407	+	*
408	+	* @return an array containing all of the elements in this queue
409	+	*/
410		public Object[] toArray() {
411	<	return null;
411	>	return Arrays.copyOf(queue, size);
412	>	}
413	>
414	>	/**
415	>	* Returns an array containing all of the elements in this queue; the
416	>	* runtime type of the returned array is that of the specified array.
417	>	* The returned array elements are in no particular order.
418	>	* If the queue fits in the specified array, it is returned therein.
419	>	* Otherwise, a new array is allocated with the runtime type of the
420	>	* specified array and the size of this queue.
421	>	*
422	>	* <p>If the queue fits in the specified array with room to spare
423	>	* (i.e., the array has more elements than the queue), the element in
424	>	* the array immediately following the end of the collection is set to
425	>	* {@code null}.
426	>	*
427	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
428	>	* array-based and collection-based APIs.  Further, this method allows
429	>	* precise control over the runtime type of the output array, and may,
430	>	* under certain circumstances, be used to save allocation costs.
431	>	*
432	>	* <p>Suppose {@code x} is a queue known to contain only strings.
433	>	* The following code can be used to dump the queue into a newly
434	>	* allocated array of {@code String}:
435	>	*
436	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
437	>	*
438	>	* Note that {@code toArray(new Object[0])} is identical in function to
439	>	* {@code toArray()}.
440	>	*
441	>	* @param a the array into which the elements of the queue are to
442	>	*          be stored, if it is big enough; otherwise, a new array of the
443	>	*          same runtime type is allocated for this purpose.
444	>	* @return an array containing all of the elements in this queue
445	>	* @throws ArrayStoreException if the runtime type of the specified array
446	>	*         is not a supertype of the runtime type of every element in
447	>	*         this queue
448	>	* @throws NullPointerException if the specified array is null
449	>	*/
450	>	public <T> T[] toArray(T[] a) {
451	>	final int size = this.size;
452	>	if (a.length < size)
453	>	// Make a new array of a's runtime type, but my contents:
454	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
455	>	System.arraycopy(queue, 0, a, 0, size);
456	>	if (a.length > size)
457	>	a[size] = null;
458	>	return a;
459	>	}
460	>
461	>	/**
462	>	* Returns an iterator over the elements in this queue. The iterator
463	>	* does not return the elements in any particular order.
464	>	*
465	>	* @return an iterator over the elements in this queue
466	>	*/
467	>	public Iterator<E> iterator() {
468	>	return new Itr();
469	>	}
470	>
471	>	private final class Itr implements Iterator<E> {
472	>	/**
473	>	* Index (into queue array) of element to be returned by
474	>	* subsequent call to next.
475	>	*/
476	>	private int cursor;
477	>
478	>	/**
479	>	* Index of element returned by most recent call to next,
480	>	* unless that element came from the forgetMeNot list.
481	>	* Set to -1 if element is deleted by a call to remove.
482	>	*/
483	>	private int lastRet = -1;
484	>
485	>	/**
486	>	* A queue of elements that were moved from the unvisited portion of
487	>	* the heap into the visited portion as a result of "unlucky" element
488	>	* removals during the iteration.  (Unlucky element removals are those
489	>	* that require a siftup instead of a siftdown.)  We must visit all of
490	>	* the elements in this list to complete the iteration.  We do this
491	>	* after we've completed the "normal" iteration.
492	>	*
493	>	* We expect that most iterations, even those involving removals,
494	>	* will not need to store elements in this field.
495	>	*/
496	>	private ArrayDeque<E> forgetMeNot;
497	>
498	>	/**
499	>	* Element returned by the most recent call to next iff that
500	>	* element was drawn from the forgetMeNot list.
501	>	*/
502	>	private E lastRetElt;
503	>
504	>	/**
505	>	* The modCount value that the iterator believes that the backing
506	>	* Queue should have.  If this expectation is violated, the iterator
507	>	* has detected concurrent modification.
508	>	*/
509	>	private int expectedModCount = modCount;
510	>
511	>	Itr() {}                        // prevent access constructor creation
512	>
513	>	public boolean hasNext() {
514	>	return cursor < size ||
515	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
516	>	}
517	>
518	>	public E next() {
519	>	if (expectedModCount != modCount)
520	>	throw new ConcurrentModificationException();
521	>	if (cursor < size)
522	>	return (E) queue[lastRet = cursor++];
523	>	if (forgetMeNot != null) {
524	>	lastRet = -1;
525	>	lastRetElt = forgetMeNot.poll();
526	>	if (lastRetElt != null)
527	>	return lastRetElt;
528	>	}
529	>	throw new NoSuchElementException();
530	>	}
531	>
532	>	public void remove() {
533	>	if (expectedModCount != modCount)
534	>	throw new ConcurrentModificationException();
535	>	if (lastRet != -1) {
536	>	E moved = PriorityQueue.this.removeAt(lastRet);
537	>	lastRet = -1;
538	>	if (moved == null)
539	>	cursor--;
540	>	else {
541	>	if (forgetMeNot == null)
542	>	forgetMeNot = new ArrayDeque<>();
543	>	forgetMeNot.add(moved);
544	>	}
545	>	} else if (lastRetElt != null) {
546	>	PriorityQueue.this.removeEq(lastRetElt);
547	>	lastRetElt = null;
548	>	} else {
549	>	throw new IllegalStateException();
550	>	}
551	>	expectedModCount = modCount;
552	>	}
553	>	}
554	>
555	>	public int size() {
556	>	return size;
557	>	}
558	>
559	>	/**
560	>	* Removes all of the elements from this priority queue.
561	>	* The queue will be empty after this call returns.
562	>	*/
563	>	public void clear() {
564	>	modCount++;
565	>	final Object[] es = queue;
566	>	for (int i = 0, n = size; i < n; i++)
567	>	es[i] = null;
568	>	size = 0;
569	>	}
570	>
571	>	public E poll() {
572	>	final Object[] es;
573	>	final E result;
574	>
575	>	if ((result = (E) ((es = queue)[0])) != null) {
576	>	modCount++;
577	>	final int n;
578	>	final E x = (E) es[(n = --size)];
579	>	es[n] = null;
580	>	if (n > 0) {
581	>	final Comparator<? super E> cmp;
582	>	if ((cmp = comparator) == null)
583	>	siftDownComparable(0, x, es, n);
584	>	else
585	>	siftDownUsingComparator(0, x, es, n, cmp);
586	>	}
587	>	}
588	>	return result;
589		}
590
591	<	public <T> T[] toArray(T[] array) {
591	>	/**
592	>	* Removes the ith element from queue.
593	>	*
594	>	* Normally this method leaves the elements at up to i-1,
595	>	* inclusive, untouched.  Under these circumstances, it returns
596	>	* null.  Occasionally, in order to maintain the heap invariant,
597	>	* it must swap a later element of the list with one earlier than
598	>	* i.  Under these circumstances, this method returns the element
599	>	* that was previously at the end of the list and is now at some
600	>	* position before i. This fact is used by iterator.remove so as to
601	>	* avoid missing traversing elements.
602	>	*/
603	>	E removeAt(int i) {
604	>	// assert i >= 0 && i < size;
605	>	final Object[] es = queue;
606	>	modCount++;
607	>	int s = --size;
608	>	if (s == i) // removed last element
609	>	es[i] = null;
610	>	else {
611	>	E moved = (E) es[s];
612	>	es[s] = null;
613	>	siftDown(i, moved);
614	>	if (es[i] == moved) {
615	>	siftUp(i, moved);
616	>	if (es[i] != moved)
617	>	return moved;
618	>	}
619	>	}
620		return null;
621		}
622
623	+	/**
624	+	* Inserts item x at position k, maintaining heap invariant by
625	+	* promoting x up the tree until it is greater than or equal to
626	+	* its parent, or is the root.
627	+	*
628	+	* To simplify and speed up coercions and comparisons, the
629	+	* Comparable and Comparator versions are separated into different
630	+	* methods that are otherwise identical. (Similarly for siftDown.)
631	+	*
632	+	* @param k the position to fill
633	+	* @param x the item to insert
634	+	*/
635	+	private void siftUp(int k, E x) {
636	+	if (comparator != null)
637	+	siftUpUsingComparator(k, x, queue, comparator);
638	+	else
639	+	siftUpComparable(k, x, queue);
640	+	}
641	+
642	+	private static <T> void siftUpComparable(int k, T x, Object[] es) {
643	+	Comparable<? super T> key = (Comparable<? super T>) x;
644	+	while (k > 0) {
645	+	int parent = (k - 1) >>> 1;
646	+	Object e = es[parent];
647	+	if (key.compareTo((T) e) >= 0)
648	+	break;
649	+	es[k] = e;
650	+	k = parent;
651	+	}
652	+	es[k] = key;
653	+	}
654	+
655	+	private static <T> void siftUpUsingComparator(
656	+	int k, T x, Object[] es, Comparator<? super T> cmp) {
657	+	while (k > 0) {
658	+	int parent = (k - 1) >>> 1;
659	+	Object e = es[parent];
660	+	if (cmp.compare(x, (T) e) >= 0)
661	+	break;
662	+	es[k] = e;
663	+	k = parent;
664	+	}
665	+	es[k] = x;
666	+	}
667	+
668	+	/**
669	+	* Inserts item x at position k, maintaining heap invariant by
670	+	* demoting x down the tree repeatedly until it is less than or
671	+	* equal to its children or is a leaf.
672	+	*
673	+	* @param k the position to fill
674	+	* @param x the item to insert
675	+	*/
676	+	private void siftDown(int k, E x) {
677	+	if (comparator != null)
678	+	siftDownUsingComparator(k, x, queue, size, comparator);
679	+	else
680	+	siftDownComparable(k, x, queue, size);
681	+	}
682	+
683	+	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
684	+	// assert n > 0;
685	+	Comparable<? super T> key = (Comparable<? super T>)x;
686	+	int half = n >>> 1;           // loop while a non-leaf
687	+	while (k < half) {
688	+	int child = (k << 1) + 1; // assume left child is least
689	+	Object c = es[child];
690	+	int right = child + 1;
691	+	if (right < n &&
692	+	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
693	+	c = es[child = right];
694	+	if (key.compareTo((T) c) <= 0)
695	+	break;
696	+	es[k] = c;
697	+	k = child;
698	+	}
699	+	es[k] = key;
700	+	}
701	+
702	+	private static <T> void siftDownUsingComparator(
703	+	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
704	+	// assert n > 0;
705	+	int half = n >>> 1;
706	+	while (k < half) {
707	+	int child = (k << 1) + 1;
708	+	Object c = es[child];
709	+	int right = child + 1;
710	+	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
711	+	c = es[child = right];
712	+	if (cmp.compare(x, (T) c) <= 0)
713	+	break;
714	+	es[k] = c;
715	+	k = child;
716	+	}
717	+	es[k] = x;
718	+	}
719	+
720	+	/**
721	+	* Establishes the heap invariant (described above) in the entire tree,
722	+	* assuming nothing about the order of the elements prior to the call.
723	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
724	+	*/
725	+	private void heapify() {
726	+	final Object[] es = queue;
727	+	int n = size, i = (n >>> 1) - 1;
728	+	final Comparator<? super E> cmp;
729	+	if ((cmp = comparator) == null)
730	+	for (; i >= 0; i--)
731	+	siftDownComparable(i, (E) es[i], es, n);
732	+	else
733	+	for (; i >= 0; i--)
734	+	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
735	+	}
736	+
737	+	/**
738	+	* Returns the comparator used to order the elements in this
739	+	* queue, or {@code null} if this queue is sorted according to
740	+	* the {@linkplain Comparable natural ordering} of its elements.
741	+	*
742	+	* @return the comparator used to order this queue, or
743	+	*         {@code null} if this queue is sorted according to the
744	+	*         natural ordering of its elements
745	+	*/
746	+	public Comparator<? super E> comparator() {
747	+	return comparator;
748	+	}
749	+
750	+	/**
751	+	* Saves this queue to a stream (that is, serializes it).
752	+	*
753	+	* @param s the stream
754	+	* @throws java.io.IOException if an I/O error occurs
755	+	* @serialData The length of the array backing the instance is
756	+	*             emitted (int), followed by all of its elements
757	+	*             (each an {@code Object}) in the proper order.
758	+	*/
759	+	// OPENJDK @java.io.Serial
760	+	private void writeObject(java.io.ObjectOutputStream s)
761	+	throws java.io.IOException {
762	+	// Write out element count, and any hidden stuff
763	+	s.defaultWriteObject();
764	+
765	+	// Write out array length, for compatibility with 1.5 version
766	+	s.writeInt(Math.max(2, size + 1));
767	+
768	+	// Write out all elements in the "proper order".
769	+	final Object[] es = queue;
770	+	for (int i = 0, n = size; i < n; i++)
771	+	s.writeObject(es[i]);
772	+	}
773	+
774	+	/**
775	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
776	+	* (that is, deserializes it).
777	+	*
778	+	* @param s the stream
779	+	* @throws ClassNotFoundException if the class of a serialized object
780	+	*         could not be found
781	+	* @throws java.io.IOException if an I/O error occurs
782	+	*/
783	+	// OPENJDK @java.io.Serial
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	+	jsr166.Platform.checkArray(s, Object[].class, size);
793	+	final Object[] es = queue = new Object[Math.max(size, 1)];
794	+
795	+	// Read in all elements.
796	+	for (int i = 0, n = size; i < n; i++)
797	+	es[i] = s.readObject();
798	+
799	+	// Elements are guaranteed to be in "proper order", but the
800	+	// spec has never explained what that might be.
801	+	heapify();
802	+	}
803	+
804	+	/**
805	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
806	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
807	+	* queue. The spliterator does not traverse elements in any particular order
808	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
809	+	*
810	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
811	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
812	+	* Overriding implementations should document the reporting of additional
813	+	* characteristic values.
814	+	*
815	+	* @return a {@code Spliterator} over the elements in this queue
816	+	* @since 1.8
817	+	*/
818	+	public final Spliterator<E> spliterator() {
819	+	return new PriorityQueueSpliterator(0, -1, 0);
820	+	}
821	+
822	+	final class PriorityQueueSpliterator implements Spliterator<E> {
823	+	private int index;            // current index, modified on advance/split
824	+	private int fence;            // -1 until first use
825	+	private int expectedModCount; // initialized when fence set
826	+
827	+	/** Creates new spliterator covering the given range. */
828	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
829	+	this.index = origin;
830	+	this.fence = fence;
831	+	this.expectedModCount = expectedModCount;
832	+	}
833	+
834	+	private int getFence() { // initialize fence to size on first use
835	+	int hi;
836	+	if ((hi = fence) < 0) {
837	+	expectedModCount = modCount;
838	+	hi = fence = size;
839	+	}
840	+	return hi;
841	+	}
842	+
843	+	public PriorityQueueSpliterator trySplit() {
844	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
845	+	return (lo >= mid) ? null :
846	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
847	+	}
848	+
849	+	public void forEachRemaining(Consumer<? super E> action) {
850	+	if (action == null)
851	+	throw new NullPointerException();
852	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
853	+	final Object[] es = queue;
854	+	int i, hi; E e;
855	+	for (i = index, index = hi = fence; i < hi; i++) {
856	+	if ((e = (E) es[i]) == null)
857	+	break;      // must be CME
858	+	action.accept(e);
859	+	}
860	+	if (modCount != expectedModCount)
861	+	throw new ConcurrentModificationException();
862	+	}
863	+
864	+	public boolean tryAdvance(Consumer<? super E> action) {
865	+	if (action == null)
866	+	throw new NullPointerException();
867	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
868	+	int i;
869	+	if ((i = index) < fence) {
870	+	index = i + 1;
871	+	E e;
872	+	if ((e = (E) queue[i]) == null
873	+	|| modCount != expectedModCount)
874	+	throw new ConcurrentModificationException();
875	+	action.accept(e);
876	+	return true;
877	+	}
878	+	return false;
879	+	}
880	+
881	+	public long estimateSize() {
882	+	return getFence() - index;
883	+	}
884	+
885	+	public int characteristics() {
886	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
887	+	}
888	+	}
889	+
890	+	/**
891	+	* @throws NullPointerException {@inheritDoc}
892	+	*/
893	+	public boolean removeIf(Predicate<? super E> filter) {
894	+	Objects.requireNonNull(filter);
895	+	return bulkRemove(filter);
896	+	}
897	+
898	+	/**
899	+	* @throws NullPointerException {@inheritDoc}
900	+	*/
901	+	public boolean removeAll(Collection<?> c) {
902	+	Objects.requireNonNull(c);
903	+	return bulkRemove(e -> c.contains(e));
904	+	}
905	+
906	+	/**
907	+	* @throws NullPointerException {@inheritDoc}
908	+	*/
909	+	public boolean retainAll(Collection<?> c) {
910	+	Objects.requireNonNull(c);
911	+	return bulkRemove(e -> !c.contains(e));
912	+	}
913	+
914	+	// A tiny bit set implementation
915	+
916	+	private static long[] nBits(int n) {
917	+	return new long[((n - 1) >> 6) + 1];
918	+	}
919	+	private static void setBit(long[] bits, int i) {
920	+	bits[i >> 6] |= 1L << i;
921	+	}
922	+	private static boolean isClear(long[] bits, int i) {
923	+	return (bits[i >> 6] & (1L << i)) == 0;
924	+	}
925	+
926	+	/** Implementation of bulk remove methods. */
927	+	private boolean bulkRemove(Predicate<? super E> filter) {
928	+	final int expectedModCount = ++modCount;
929	+	final Object[] es = queue;
930	+	final int end = size;
931	+	int i;
932	+	// Optimize for initial run of survivors
933	+	for (i = 0; i < end && !filter.test((E) es[i]); i++)
934	+	;
935	+	if (i >= end) {
936	+	if (modCount != expectedModCount)
937	+	throw new ConcurrentModificationException();
938	+	return false;
939	+	}
940	+	// Tolerate predicates that reentrantly access the collection for
941	+	// read (but writers still get CME), so traverse once to find
942	+	// elements to delete, a second pass to physically expunge.
943	+	final int beg = i;
944	+	final long[] deathRow = nBits(end - beg);
945	+	deathRow[0] = 1L;   // set bit 0
946	+	for (i = beg + 1; i < end; i++)
947	+	if (filter.test((E) es[i]))
948	+	setBit(deathRow, i - beg);
949	+	if (modCount != expectedModCount)
950	+	throw new ConcurrentModificationException();
951	+	int w = beg;
952	+	for (i = beg; i < end; i++)
953	+	if (isClear(deathRow, i - beg))
954	+	es[w++] = es[i];
955	+	for (i = size = w; i < end; i++)
956	+	es[i] = null;
957	+	heapify();
958	+	return true;
959	+	}
960	+
961	+	/**
962	+	* @throws NullPointerException {@inheritDoc}
963	+	*/
964	+	public void forEach(Consumer<? super E> action) {
965	+	Objects.requireNonNull(action);
966	+	final int expectedModCount = modCount;
967	+	final Object[] es = queue;
968	+	for (int i = 0, n = size; i < n; i++)
969	+	action.accept((E) es[i]);
970	+	if (expectedModCount != modCount)
971	+	throw new ConcurrentModificationException();
972	+	}
973		}

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