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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 1.121 by jsr166, Wed Mar 28 02:50:41 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) {}
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	>	public class PriorityQueue<E> extends AbstractQueue<E>
85	>	implements java.io.Serializable {
86
87	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
87	>	private static final long serialVersionUID = -7720805057305804111L;
88
89	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
89	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
90
91	<	public boolean add(E x) {
92	<	return false;
91	>	/**
92	>	* Priority queue represented as a balanced binary heap: the two
93	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
94	>	* priority queue is ordered by comparator, or by the elements'
95	>	* natural ordering, if comparator is null: For each node n in the
96	>	* heap and each descendant d of n, n <= d.  The element with the
97	>	* lowest value is in queue[0], assuming the queue is nonempty.
98	>	*/
99	>	transient Object[] queue; // non-private to simplify nested class access
100	>
101	>	/**
102	>	* The number of elements in the priority queue.
103	>	*/
104	>	int size;
105	>
106	>	/**
107	>	* The comparator, or null if priority queue uses elements'
108	>	* natural ordering.
109	>	*/
110	>	private final Comparator<? super E> comparator;
111	>
112	>	/**
113	>	* The number of times this priority queue has been
114	>	* <i>structurally modified</i>.  See AbstractList for gory details.
115	>	*/
116	>	transient int modCount;     // non-private to simplify nested class access
117	>
118	>	/**
119	>	* Creates a {@code PriorityQueue} with the default initial
120	>	* capacity (11) that orders its elements according to their
121	>	* {@linkplain Comparable natural ordering}.
122	>	*/
123	>	public PriorityQueue() {
124	>	this(DEFAULT_INITIAL_CAPACITY, null);
125		}
126	<	public boolean offer(E x) {
127	<	return false;
126	>
127	>	/**
128	>	* Creates a {@code PriorityQueue} with the specified initial
129	>	* capacity that orders its elements according to their
130	>	* {@linkplain Comparable natural ordering}.
131	>	*
132	>	* @param initialCapacity the initial capacity for this priority queue
133	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
134	>	*         than 1
135	>	*/
136	>	public PriorityQueue(int initialCapacity) {
137	>	this(initialCapacity, null);
138		}
139	<	public boolean remove(Object x) {
140	<	return false;
139	>
140	>	/**
141	>	* Creates a {@code PriorityQueue} with the default initial capacity and
142	>	* whose elements are ordered according to the specified comparator.
143	>	*
144	>	* @param  comparator the comparator that will be used to order this
145	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
146	>	*         natural ordering} of the elements will be used.
147	>	* @since 1.8
148	>	*/
149	>	public PriorityQueue(Comparator<? super E> comparator) {
150	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
151		}
152
153	<	public E remove() {
154	<	return null;
153	>	/**
154	>	* Creates a {@code PriorityQueue} with the specified initial capacity
155	>	* that orders its elements according to the specified comparator.
156	>	*
157	>	* @param  initialCapacity the initial capacity for this priority queue
158	>	* @param  comparator the comparator that will be used to order this
159	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
160	>	*         natural ordering} of the elements will be used.
161	>	* @throws IllegalArgumentException if {@code initialCapacity} is
162	>	*         less than 1
163	>	*/
164	>	public PriorityQueue(int initialCapacity,
165	>	Comparator<? super E> comparator) {
166	>	// Note: This restriction of at least one is not actually needed,
167	>	// but continues for 1.5 compatibility
168	>	if (initialCapacity < 1)
169	>	throw new IllegalArgumentException();
170	>	this.queue = new Object[initialCapacity];
171	>	this.comparator = comparator;
172		}
173	<	public Iterator<E> iterator() {
174	<	return null;
173	>
174	>	/**
175	>	* Creates a {@code PriorityQueue} containing the elements in the
176	>	* specified collection.  If the specified collection is an instance of
177	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
178	>	* priority queue will be ordered according to the same ordering.
179	>	* Otherwise, this priority queue will be ordered according to the
180	>	* {@linkplain Comparable natural ordering} of its elements.
181	>	*
182	>	* @param  c the collection whose elements are to be placed
183	>	*         into this priority queue
184	>	* @throws ClassCastException if elements of the specified collection
185	>	*         cannot be compared to one another according to the priority
186	>	*         queue's ordering
187	>	* @throws NullPointerException if the specified collection or any
188	>	*         of its elements are null
189	>	*/
190	>	@SuppressWarnings("unchecked")
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	>	@SuppressWarnings("unchecked")
223	>	public PriorityQueue(PriorityQueue<? extends E> c) {
224	>	this.comparator = (Comparator<? super E>) c.comparator();
225	>	initFromPriorityQueue(c);
226		}
227	<	public E poll() {
228	<	return null;
227	>
228	>	/**
229	>	* Creates a {@code PriorityQueue} containing the elements in the
230	>	* specified sorted set.   This priority queue will be ordered
231	>	* according to the same ordering as the given sorted set.
232	>	*
233	>	* @param  c the sorted set whose elements are to be placed
234	>	*         into this priority queue
235	>	* @throws ClassCastException if elements of the specified sorted
236	>	*         set cannot be compared to one another according to the
237	>	*         sorted set's ordering
238	>	* @throws NullPointerException if the specified sorted set or any
239	>	*         of its elements are null
240	>	*/
241	>	@SuppressWarnings("unchecked")
242	>	public PriorityQueue(SortedSet<? extends E> c) {
243	>	this.comparator = (Comparator<? super E>) c.comparator();
244	>	initElementsFromCollection(c);
245	>	}
246	>
247	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
248	>	if (c.getClass() == PriorityQueue.class) {
249	>	this.queue = c.toArray();
250	>	this.size = c.size();
251	>	} else {
252	>	initFromCollection(c);
253	>	}
254	>	}
255	>
256	>	private void initElementsFromCollection(Collection<? extends E> c) {
257	>	Object[] a = c.toArray();
258	>	// If c.toArray incorrectly doesn't return Object[], copy it.
259	>	if (a.getClass() != Object[].class)
260	>	a = Arrays.copyOf(a, a.length, Object[].class);
261	>	int len = a.length;
262	>	if (len == 1 || this.comparator != null)
263	>	for (Object e : a)
264	>	if (e == null)
265	>	throw new NullPointerException();
266	>	this.queue = a;
267	>	this.size = a.length;
268	>	}
269	>
270	>	/**
271	>	* Initializes queue array with elements from the given Collection.
272	>	*
273	>	* @param c the collection
274	>	*/
275	>	private void initFromCollection(Collection<? extends E> c) {
276	>	initElementsFromCollection(c);
277	>	heapify();
278	>	}
279	>
280	>	/**
281	>	* The maximum size of array to allocate.
282	>	* Some VMs reserve some header words in an array.
283	>	* Attempts to allocate larger arrays may result in
284	>	* OutOfMemoryError: Requested array size exceeds VM limit
285	>	*/
286	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
287	>
288	>	/**
289	>	* Increases the capacity of the array.
290	>	*
291	>	* @param minCapacity the desired minimum capacity
292	>	*/
293	>	private void grow(int minCapacity) {
294	>	int oldCapacity = queue.length;
295	>	// Double size if small; else grow by 50%
296	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
297	>	(oldCapacity + 2) :
298	>	(oldCapacity >> 1));
299	>	// overflow-conscious code
300	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
301	>	newCapacity = hugeCapacity(minCapacity);
302	>	queue = Arrays.copyOf(queue, newCapacity);
303		}
304	+
305	+	private static int hugeCapacity(int minCapacity) {
306	+	if (minCapacity < 0) // overflow
307	+	throw new OutOfMemoryError();
308	+	return (minCapacity > MAX_ARRAY_SIZE) ?
309	+	Integer.MAX_VALUE :
310	+	MAX_ARRAY_SIZE;
311	+	}
312	+
313	+	/**
314	+	* Inserts the specified element into this priority queue.
315	+	*
316	+	* @return {@code true} (as specified by {@link Collection#add})
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 add(E e) {
323	+	return offer(e);
324	+	}
325	+
326	+	/**
327	+	* Inserts the specified element into this priority queue.
328	+	*
329	+	* @return {@code true} (as specified by {@link Queue#offer})
330	+	* @throws ClassCastException if the specified element cannot be
331	+	*         compared with elements currently in this priority queue
332	+	*         according to the priority queue's ordering
333	+	* @throws NullPointerException if the specified element is null
334	+	*/
335	+	public boolean offer(E e) {
336	+	if (e == null)
337	+	throw new NullPointerException();
338	+	modCount++;
339	+	int i = size;
340	+	if (i >= queue.length)
341	+	grow(i + 1);
342	+	siftUp(i, e);
343	+	size = i + 1;
344	+	return true;
345	+	}
346	+
347	+	@SuppressWarnings("unchecked")
348		public E peek() {
349	<	return null;
349	>	return (size == 0) ? null : (E) queue[0];
350	>	}
351	>
352	>	private int indexOf(Object o) {
353	>	if (o != null) {
354	>	for (int i = 0; i < size; i++)
355	>	if (o.equals(queue[i]))
356	>	return i;
357	>	}
358	>	return -1;
359		}
360
361	<	public boolean isEmpty() {
361	>	/**
362	>	* Removes a single instance of the specified element from this queue,
363	>	* if it is present.  More formally, removes an element {@code e} such
364	>	* that {@code o.equals(e)}, if this queue contains one or more such
365	>	* elements.  Returns {@code true} if and only if this queue contained
366	>	* the specified element (or equivalently, if this queue changed as a
367	>	* result of the call).
368	>	*
369	>	* @param o element to be removed from this queue, if present
370	>	* @return {@code true} if this queue changed as a result of the call
371	>	*/
372	>	public boolean remove(Object o) {
373	>	int i = indexOf(o);
374	>	if (i == -1)
375	>	return false;
376	>	else {
377	>	removeAt(i);
378	>	return true;
379	>	}
380	>	}
381	>
382	>	/**
383	>	* Version of remove using reference equality, not equals.
384	>	* Needed by iterator.remove.
385	>	*
386	>	* @param o element to be removed from this queue, if present
387	>	* @return {@code true} if removed
388	>	*/
389	>	boolean removeEq(Object o) {
390	>	for (int i = 0; i < size; i++) {
391	>	if (o == queue[i]) {
392	>	removeAt(i);
393	>	return true;
394	>	}
395	>	}
396		return false;
397		}
398	<	public int size() {
399	<	return 0;
398	>
399	>	/**
400	>	* Returns {@code true} if this queue contains the specified element.
401	>	* More formally, returns {@code true} if and only if this queue contains
402	>	* at least one element {@code e} such that {@code o.equals(e)}.
403	>	*
404	>	* @param o object to be checked for containment in this queue
405	>	* @return {@code true} if this queue contains the specified element
406	>	*/
407	>	public boolean contains(Object o) {
408	>	return indexOf(o) >= 0;
409		}
410	+
411	+	/**
412	+	* Returns an array containing all of the elements in this queue.
413	+	* The elements are in no particular order.
414	+	*
415	+	* <p>The returned array will be "safe" in that no references to it are
416	+	* maintained by this queue.  (In other words, this method must allocate
417	+	* a new array).  The caller is thus free to modify the returned array.
418	+	*
419	+	* <p>This method acts as bridge between array-based and collection-based
420	+	* APIs.
421	+	*
422	+	* @return an array containing all of the elements in this queue
423	+	*/
424		public Object[] toArray() {
425	<	return null;
425	>	return Arrays.copyOf(queue, size);
426	>	}
427	>
428	>	/**
429	>	* Returns an array containing all of the elements in this queue; the
430	>	* runtime type of the returned array is that of the specified array.
431	>	* The returned array elements are in no particular order.
432	>	* If the queue fits in the specified array, it is returned therein.
433	>	* Otherwise, a new array is allocated with the runtime type of the
434	>	* specified array and the size of this queue.
435	>	*
436	>	* <p>If the queue fits in the specified array with room to spare
437	>	* (i.e., the array has more elements than the queue), the element in
438	>	* the array immediately following the end of the collection is set to
439	>	* {@code null}.
440	>	*
441	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
442	>	* array-based and collection-based APIs.  Further, this method allows
443	>	* precise control over the runtime type of the output array, and may,
444	>	* under certain circumstances, be used to save allocation costs.
445	>	*
446	>	* <p>Suppose {@code x} is a queue known to contain only strings.
447	>	* The following code can be used to dump the queue into a newly
448	>	* allocated array of {@code String}:
449	>	*
450	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
451	>	*
452	>	* Note that {@code toArray(new Object[0])} is identical in function to
453	>	* {@code toArray()}.
454	>	*
455	>	* @param a the array into which the elements of the queue are to
456	>	*          be stored, if it is big enough; otherwise, a new array of the
457	>	*          same runtime type is allocated for this purpose.
458	>	* @return an array containing all of the elements in this queue
459	>	* @throws ArrayStoreException if the runtime type of the specified array
460	>	*         is not a supertype of the runtime type of every element in
461	>	*         this queue
462	>	* @throws NullPointerException if the specified array is null
463	>	*/
464	>	@SuppressWarnings("unchecked")
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	<	public <T> T[] toArray(T[] array) {
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	>	@SuppressWarnings("unchecked")
534	>	public E next() {
535	>	if (expectedModCount != modCount)
536	>	throw new ConcurrentModificationException();
537	>	if (cursor < size)
538	>	return (E) queue[lastRet = cursor++];
539	>	if (forgetMeNot != null) {
540	>	lastRet = -1;
541	>	lastRetElt = forgetMeNot.poll();
542	>	if (lastRetElt != null)
543	>	return lastRetElt;
544	>	}
545	>	throw new NoSuchElementException();
546	>	}
547	>
548	>	public void remove() {
549	>	if (expectedModCount != modCount)
550	>	throw new ConcurrentModificationException();
551	>	if (lastRet != -1) {
552	>	E moved = PriorityQueue.this.removeAt(lastRet);
553	>	lastRet = -1;
554	>	if (moved == null)
555	>	cursor--;
556	>	else {
557	>	if (forgetMeNot == null)
558	>	forgetMeNot = new ArrayDeque<>();
559	>	forgetMeNot.add(moved);
560	>	}
561	>	} else if (lastRetElt != null) {
562	>	PriorityQueue.this.removeEq(lastRetElt);
563	>	lastRetElt = null;
564	>	} else {
565	>	throw new IllegalStateException();
566	>	}
567	>	expectedModCount = modCount;
568	>	}
569	>	}
570	>
571	>	public int size() {
572	>	return size;
573	>	}
574	>
575	>	/**
576	>	* Removes all of the elements from this priority queue.
577	>	* The queue will be empty after this call returns.
578	>	*/
579	>	public void clear() {
580	>	modCount++;
581	>	for (int i = 0; i < size; i++)
582	>	queue[i] = null;
583	>	size = 0;
584	>	}
585	>
586	>	@SuppressWarnings("unchecked")
587	>	public E poll() {
588	>	if (size == 0)
589	>	return null;
590	>	int s = --size;
591	>	modCount++;
592	>	E result = (E) queue[0];
593	>	E x = (E) queue[s];
594	>	queue[s] = null;
595	>	if (s != 0)
596	>	siftDown(0, x);
597	>	return result;
598	>	}
599	>
600	>	/**
601	>	* Removes the ith element from queue.
602	>	*
603	>	* Normally this method leaves the elements at up to i-1,
604	>	* inclusive, untouched.  Under these circumstances, it returns
605	>	* null.  Occasionally, in order to maintain the heap invariant,
606	>	* it must swap a later element of the list with one earlier than
607	>	* i.  Under these circumstances, this method returns the element
608	>	* that was previously at the end of the list and is now at some
609	>	* position before i. This fact is used by iterator.remove so as to
610	>	* avoid missing traversing elements.
611	>	*/
612	>	@SuppressWarnings("unchecked")
613	>	E removeAt(int i) {
614	>	// assert i >= 0 && i < size;
615	>	modCount++;
616	>	int s = --size;
617	>	if (s == i) // removed last element
618	>	queue[i] = null;
619	>	else {
620	>	E moved = (E) queue[s];
621	>	queue[s] = null;
622	>	siftDown(i, moved);
623	>	if (queue[i] == moved) {
624	>	siftUp(i, moved);
625	>	if (queue[i] != moved)
626	>	return moved;
627	>	}
628	>	}
629		return null;
630		}
631
632	+	/**
633	+	* Inserts item x at position k, maintaining heap invariant by
634	+	* promoting x up the tree until it is greater than or equal to
635	+	* its parent, or is the root.
636	+	*
637	+	* To simplify and speed up coercions and comparisons, the
638	+	* Comparable and Comparator versions are separated into different
639	+	* methods that are otherwise identical. (Similarly for siftDown.)
640	+	*
641	+	* @param k the position to fill
642	+	* @param x the item to insert
643	+	*/
644	+	private void siftUp(int k, E x) {
645	+	if (comparator != null)
646	+	siftUpUsingComparator(k, x);
647	+	else
648	+	siftUpComparable(k, x);
649	+	}
650	+
651	+	@SuppressWarnings("unchecked")
652	+	private void siftUpComparable(int k, E x) {
653	+	Comparable<? super E> key = (Comparable<? super E>) x;
654	+	while (k > 0) {
655	+	int parent = (k - 1) >>> 1;
656	+	Object e = queue[parent];
657	+	if (key.compareTo((E) e) >= 0)
658	+	break;
659	+	queue[k] = e;
660	+	k = parent;
661	+	}
662	+	queue[k] = key;
663	+	}
664	+
665	+	@SuppressWarnings("unchecked")
666	+	private void siftUpUsingComparator(int k, E x) {
667	+	while (k > 0) {
668	+	int parent = (k - 1) >>> 1;
669	+	Object e = queue[parent];
670	+	if (comparator.compare(x, (E) e) >= 0)
671	+	break;
672	+	queue[k] = e;
673	+	k = parent;
674	+	}
675	+	queue[k] = x;
676	+	}
677	+
678	+	/**
679	+	* Inserts item x at position k, maintaining heap invariant by
680	+	* demoting x down the tree repeatedly until it is less than or
681	+	* equal to its children or is a leaf.
682	+	*
683	+	* @param k the position to fill
684	+	* @param x the item to insert
685	+	*/
686	+	private void siftDown(int k, E x) {
687	+	if (comparator != null)
688	+	siftDownUsingComparator(k, x);
689	+	else
690	+	siftDownComparable(k, x);
691	+	}
692	+
693	+	@SuppressWarnings("unchecked")
694	+	private void siftDownComparable(int k, E x) {
695	+	Comparable<? super E> key = (Comparable<? super E>)x;
696	+	int half = size >>> 1;        // loop while a non-leaf
697	+	while (k < half) {
698	+	int child = (k << 1) + 1; // assume left child is least
699	+	Object c = queue[child];
700	+	int right = child + 1;
701	+	if (right < size &&
702	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
703	+	c = queue[child = right];
704	+	if (key.compareTo((E) c) <= 0)
705	+	break;
706	+	queue[k] = c;
707	+	k = child;
708	+	}
709	+	queue[k] = key;
710	+	}
711	+
712	+	@SuppressWarnings("unchecked")
713	+	private void siftDownUsingComparator(int k, E x) {
714	+	int half = size >>> 1;
715	+	while (k < half) {
716	+	int child = (k << 1) + 1;
717	+	Object c = queue[child];
718	+	int right = child + 1;
719	+	if (right < size &&
720	+	comparator.compare((E) c, (E) queue[right]) > 0)
721	+	c = queue[child = right];
722	+	if (comparator.compare(x, (E) c) <= 0)
723	+	break;
724	+	queue[k] = c;
725	+	k = child;
726	+	}
727	+	queue[k] = x;
728	+	}
729	+
730	+	/**
731	+	* Establishes the heap invariant (described above) in the entire tree,
732	+	* assuming nothing about the order of the elements prior to the call.
733	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
734	+	*/
735	+	@SuppressWarnings("unchecked")
736	+	private void heapify() {
737	+	final Object[] es = queue;
738	+	int i = (size >>> 1) - 1;
739	+	if (comparator == null)
740	+	for (; i >= 0; i--)
741	+	siftDownComparable(i, (E) es[i]);
742	+	else
743	+	for (; i >= 0; i--)
744	+	siftDownUsingComparator(i, (E) es[i]);
745	+	}
746	+
747	+	/**
748	+	* Returns the comparator used to order the elements in this
749	+	* queue, or {@code null} if this queue is sorted according to
750	+	* the {@linkplain Comparable natural ordering} of its elements.
751	+	*
752	+	* @return the comparator used to order this queue, or
753	+	*         {@code null} if this queue is sorted according to the
754	+	*         natural ordering of its elements
755	+	*/
756	+	public Comparator<? super E> comparator() {
757	+	return comparator;
758	+	}
759	+
760	+	/**
761	+	* Saves this queue to a stream (that is, serializes it).
762	+	*
763	+	* @param s the stream
764	+	* @throws java.io.IOException if an I/O error occurs
765	+	* @serialData The length of the array backing the instance is
766	+	*             emitted (int), followed by all of its elements
767	+	*             (each an {@code Object}) in the proper order.
768	+	*/
769	+	private void writeObject(java.io.ObjectOutputStream s)
770	+	throws java.io.IOException {
771	+	// Write out element count, and any hidden stuff
772	+	s.defaultWriteObject();
773	+
774	+	// Write out array length, for compatibility with 1.5 version
775	+	s.writeInt(Math.max(2, size + 1));
776	+
777	+	// Write out all elements in the "proper order".
778	+	for (int i = 0; i < size; i++)
779	+	s.writeObject(queue[i]);
780	+	}
781	+
782	+	/**
783	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
784	+	* (that is, deserializes it).
785	+	*
786	+	* @param s the stream
787	+	* @throws ClassNotFoundException if the class of a serialized object
788	+	*         could not be found
789	+	* @throws java.io.IOException if an I/O error occurs
790	+	*/
791	+	private void readObject(java.io.ObjectInputStream s)
792	+	throws java.io.IOException, ClassNotFoundException {
793	+	// Read in size, and any hidden stuff
794	+	s.defaultReadObject();
795	+
796	+	// Read in (and discard) array length
797	+	s.readInt();
798	+
799	+	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
800	+	queue = new Object[size];
801	+
802	+	// Read in all elements.
803	+	for (int i = 0; i < size; i++)
804	+	queue[i] = s.readObject();
805	+
806	+	// Elements are guaranteed to be in "proper order", but the
807	+	// spec has never explained what that might be.
808	+	heapify();
809	+	}
810	+
811	+	/**
812	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
813	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
814	+	* queue. The spliterator does not traverse elements in any particular order
815	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
816	+	*
817	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
818	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
819	+	* Overriding implementations should document the reporting of additional
820	+	* characteristic values.
821	+	*
822	+	* @return a {@code Spliterator} over the elements in this queue
823	+	* @since 1.8
824	+	*/
825	+	public final Spliterator<E> spliterator() {
826	+	return new PriorityQueueSpliterator(0, -1, 0);
827	+	}
828	+
829	+	final class PriorityQueueSpliterator implements Spliterator<E> {
830	+	private int index;            // current index, modified on advance/split
831	+	private int fence;            // -1 until first use
832	+	private int expectedModCount; // initialized when fence set
833	+
834	+	/** Creates new spliterator covering the given range. */
835	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
836	+	this.index = origin;
837	+	this.fence = fence;
838	+	this.expectedModCount = expectedModCount;
839	+	}
840	+
841	+	private int getFence() { // initialize fence to size on first use
842	+	int hi;
843	+	if ((hi = fence) < 0) {
844	+	expectedModCount = modCount;
845	+	hi = fence = size;
846	+	}
847	+	return hi;
848	+	}
849	+
850	+	public PriorityQueueSpliterator trySplit() {
851	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
852	+	return (lo >= mid) ? null :
853	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
854	+	}
855	+
856	+	@SuppressWarnings("unchecked")
857	+	public void forEachRemaining(Consumer<? super E> action) {
858	+	if (action == null)
859	+	throw new NullPointerException();
860	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
861	+	final Object[] a = queue;
862	+	int i, hi; E e;
863	+	for (i = index, index = hi = fence; i < hi; i++) {
864	+	if ((e = (E) a[i]) == null)
865	+	break;      // must be CME
866	+	action.accept(e);
867	+	}
868	+	if (modCount != expectedModCount)
869	+	throw new ConcurrentModificationException();
870	+	}
871	+
872	+	@SuppressWarnings("unchecked")
873	+	public boolean tryAdvance(Consumer<? super E> action) {
874	+	if (action == null)
875	+	throw new NullPointerException();
876	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
877	+	int i;
878	+	if ((i = index) < fence) {
879	+	index = i + 1;
880	+	E e;
881	+	if ((e = (E) queue[i]) == null
882	+	|| modCount != expectedModCount)
883	+	throw new ConcurrentModificationException();
884	+	action.accept(e);
885	+	return true;
886	+	}
887	+	return false;
888	+	}
889	+
890	+	public long estimateSize() {
891	+	return getFence() - index;
892	+	}
893	+
894	+	public int characteristics() {
895	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
896	+	}
897	+	}
898		}

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