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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 1.85 by jsr166, Sat Jan 19 18:18:10 2013 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2012, 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	<	import java.util.*;
26	>	package java.util;
27	>	import java.util.stream.Stream;
28	>	import java.util.Spliterator;
29	>	import java.util.stream.Streams;
30	>	import java.util.function.Block;
31
32		/**
33	<	* An unbounded (resizable) priority queue based on a priority
34	<	* heap.The take operation returns the least element with respect to
35	<	* the given ordering. (If more than one element is tied for least
36	<	* value, one of them is arbitrarily chosen to be returned -- no
37	<	* guarantees are made for ordering across ties.) Ordering follows the
38	<	* java.util.Collection conventions: Either the elements must be
39	<	* Comparable, or a Comparator must be supplied. Comparison failures
40	<	* throw ClassCastExceptions during insertions and extractions.
41	<	**/
42	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
43	<	public PriorityQueue(int initialCapacity) {}
44	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
33	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
34	>	* The elements of the priority queue are ordered according to their
35	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
36	>	* provided at queue construction time, depending on which constructor is
37	>	* used.  A priority queue does not permit {@code null} elements.
38	>	* A priority queue relying on natural ordering also does not permit
39	>	* insertion of non-comparable objects (doing so may result in
40	>	* {@code ClassCastException}).
41	>	*
42	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
43	>	* with respect to the specified ordering.  If multiple elements are
44	>	* tied for least value, the head is one of those elements -- ties are
45	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
46	>	* {@code remove}, {@code peek}, and {@code element} access the
47	>	* element at the head of the queue.
48	>	*
49	>	* <p>A priority queue is unbounded, but has an internal
50	>	* <i>capacity</i> governing the size of an array used to store the
51	>	* elements on the queue.  It is always at least as large as the queue
52	>	* size.  As elements are added to a priority queue, its capacity
53	>	* grows automatically.  The details of the growth policy are not
54	>	* specified.
55	>	*
56	>	* <p>This class and its iterator implement all of the
57	>	* <em>optional</em> methods of the {@link Collection} and {@link
58	>	* Iterator} interfaces.  The Iterator provided in method {@link
59	>	* #iterator()} is <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 enqueing and dequeing 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}/../technotes/guides/collections/index.html">
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 collection
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	>	private int size = 0;
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 = 0; // 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 specified initial capacity
142	>	* that orders its elements according to the specified comparator.
143	>	*
144	>	* @param  initialCapacity the initial capacity for this priority queue
145	>	* @param  comparator the comparator that will be used to order this
146	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
147	>	*         natural ordering} of the elements will be used.
148	>	* @throws IllegalArgumentException if {@code initialCapacity} is
149	>	*         less than 1
150	>	*/
151	>	public PriorityQueue(int initialCapacity,
152	>	Comparator<? super E> comparator) {
153	>	// Note: This restriction of at least one is not actually needed,
154	>	// but continues for 1.5 compatibility
155	>	if (initialCapacity < 1)
156	>	throw new IllegalArgumentException();
157	>	this.queue = new Object[initialCapacity];
158	>	this.comparator = comparator;
159		}
160
161	<	public E remove() {
162	<	return null;
161	>	/**
162	>	* Creates a {@code PriorityQueue} containing the elements in the
163	>	* specified collection.  If the specified collection is an instance of
164	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
165	>	* priority queue will be ordered according to the same ordering.
166	>	* Otherwise, this priority queue will be ordered according to the
167	>	* {@linkplain Comparable natural ordering} of its elements.
168	>	*
169	>	* @param  c the collection whose elements are to be placed
170	>	*         into this priority queue
171	>	* @throws ClassCastException if elements of the specified collection
172	>	*         cannot be compared to one another according to the priority
173	>	*         queue's ordering
174	>	* @throws NullPointerException if the specified collection or any
175	>	*         of its elements are null
176	>	*/
177	>	@SuppressWarnings("unchecked")
178	>	public PriorityQueue(Collection<? extends E> c) {
179	>	if (c instanceof SortedSet<?>) {
180	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
181	>	this.comparator = (Comparator<? super E>) ss.comparator();
182	>	initElementsFromCollection(ss);
183	>	}
184	>	else if (c instanceof PriorityQueue<?>) {
185	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
186	>	this.comparator = (Comparator<? super E>) pq.comparator();
187	>	initFromPriorityQueue(pq);
188	>	}
189	>	else {
190	>	this.comparator = null;
191	>	initFromCollection(c);
192	>	}
193		}
194	<	public Iterator<E> iterator() {
195	<	return null;
194	>
195	>	/**
196	>	* Creates a {@code PriorityQueue} containing the elements in the
197	>	* specified priority queue.  This priority queue will be
198	>	* ordered according to the same ordering as the given priority
199	>	* queue.
200	>	*
201	>	* @param  c the priority queue whose elements are to be placed
202	>	*         into this priority queue
203	>	* @throws ClassCastException if elements of {@code c} cannot be
204	>	*         compared to one another according to {@code c}'s
205	>	*         ordering
206	>	* @throws NullPointerException if the specified priority queue or any
207	>	*         of its elements are null
208	>	*/
209	>	@SuppressWarnings("unchecked")
210	>	public PriorityQueue(PriorityQueue<? extends E> c) {
211	>	this.comparator = (Comparator<? super E>) c.comparator();
212	>	initFromPriorityQueue(c);
213		}
214
215	<	public E element() {
216	<	return null;
215	>	/**
216	>	* Creates a {@code PriorityQueue} containing the elements in the
217	>	* specified sorted set.   This priority queue will be ordered
218	>	* according to the same ordering as the given sorted set.
219	>	*
220	>	* @param  c the sorted set whose elements are to be placed
221	>	*         into this priority queue
222	>	* @throws ClassCastException if elements of the specified sorted
223	>	*         set cannot be compared to one another according to the
224	>	*         sorted set's ordering
225	>	* @throws NullPointerException if the specified sorted set or any
226	>	*         of its elements are null
227	>	*/
228	>	@SuppressWarnings("unchecked")
229	>	public PriorityQueue(SortedSet<? extends E> c) {
230	>	this.comparator = (Comparator<? super E>) c.comparator();
231	>	initElementsFromCollection(c);
232		}
233	<	public E poll() {
234	<	return null;
233	>
234	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
235	>	if (c.getClass() == PriorityQueue.class) {
236	>	this.queue = c.toArray();
237	>	this.size = c.size();
238	>	} else {
239	>	initFromCollection(c);
240	>	}
241	>	}
242	>
243	>	private void initElementsFromCollection(Collection<? extends E> c) {
244	>	Object[] a = c.toArray();
245	>	// If c.toArray incorrectly doesn't return Object[], copy it.
246	>	if (a.getClass() != Object[].class)
247	>	a = Arrays.copyOf(a, a.length, Object[].class);
248	>	int len = a.length;
249	>	if (len == 1 || this.comparator != null)
250	>	for (int i = 0; i < len; i++)
251	>	if (a[i] == null)
252	>	throw new NullPointerException();
253	>	this.queue = a;
254	>	this.size = a.length;
255		}
256	+
257	+	/**
258	+	* Initializes queue array with elements from the given Collection.
259	+	*
260	+	* @param c the collection
261	+	*/
262	+	private void initFromCollection(Collection<? extends E> c) {
263	+	initElementsFromCollection(c);
264	+	heapify();
265	+	}
266	+
267	+	/**
268	+	* The maximum size of array to allocate.
269	+	* Some VMs reserve some header words in an array.
270	+	* Attempts to allocate larger arrays may result in
271	+	* OutOfMemoryError: Requested array size exceeds VM limit
272	+	*/
273	+	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
274	+
275	+	/**
276	+	* Increases the capacity of the array.
277	+	*
278	+	* @param minCapacity the desired minimum capacity
279	+	*/
280	+	private void grow(int minCapacity) {
281	+	int oldCapacity = queue.length;
282	+	// Double size if small; else grow by 50%
283	+	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
284	+	(oldCapacity + 2) :
285	+	(oldCapacity >> 1));
286	+	// overflow-conscious code
287	+	if (newCapacity - MAX_ARRAY_SIZE > 0)
288	+	newCapacity = hugeCapacity(minCapacity);
289	+	queue = Arrays.copyOf(queue, newCapacity);
290	+	}
291	+
292	+	private static int hugeCapacity(int minCapacity) {
293	+	if (minCapacity < 0) // overflow
294	+	throw new OutOfMemoryError();
295	+	return (minCapacity > MAX_ARRAY_SIZE) ?
296	+	Integer.MAX_VALUE :
297	+	MAX_ARRAY_SIZE;
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	+	size = i + 1;
330	+	if (i == 0)
331	+	queue[0] = e;
332	+	else
333	+	siftUp(i, e);
334	+	return true;
335	+	}
336	+
337	+	@SuppressWarnings("unchecked")
338		public E peek() {
339	<	return null;
339	>	return (size == 0) ? null : (E) queue[0];
340		}
341
342	<	public boolean isEmpty() {
342	>	private int indexOf(Object o) {
343	>	if (o != null) {
344	>	for (int i = 0; i < size; i++)
345	>	if (o.equals(queue[i]))
346	>	return i;
347	>	}
348	>	return -1;
349	>	}
350	>
351	>	/**
352	>	* Removes a single instance of the specified element from this queue,
353	>	* if it is present.  More formally, removes an element {@code e} such
354	>	* that {@code o.equals(e)}, if this queue contains one or more such
355	>	* elements.  Returns {@code true} if and only if this queue contained
356	>	* the specified element (or equivalently, if this queue changed as a
357	>	* result of the call).
358	>	*
359	>	* @param o element to be removed from this queue, if present
360	>	* @return {@code true} if this queue changed as a result of the call
361	>	*/
362	>	public boolean remove(Object o) {
363	>	int i = indexOf(o);
364	>	if (i == -1)
365	>	return false;
366	>	else {
367	>	removeAt(i);
368	>	return true;
369	>	}
370	>	}
371	>
372	>	/**
373	>	* Version of remove using reference equality, not equals.
374	>	* Needed by iterator.remove.
375	>	*
376	>	* @param o element to be removed from this queue, if present
377	>	* @return {@code true} if removed
378	>	*/
379	>	boolean removeEq(Object o) {
380	>	for (int i = 0; i < size; i++) {
381	>	if (o == queue[i]) {
382	>	removeAt(i);
383	>	return true;
384	>	}
385	>	}
386		return false;
387		}
388	<	public int size() {
389	<	return 0;
388	>
389	>	/**
390	>	* Returns {@code true} if this queue contains the specified element.
391	>	* More formally, returns {@code true} if and only if this queue contains
392	>	* at least one element {@code e} such that {@code o.equals(e)}.
393	>	*
394	>	* @param o object to be checked for containment in this queue
395	>	* @return {@code true} if this queue contains the specified element
396	>	*/
397	>	public boolean contains(Object o) {
398	>	return indexOf(o) != -1;
399		}
400	+
401	+	/**
402	+	* Returns an array containing all of the elements in this queue.
403	+	* The elements are in no particular order.
404	+	*
405	+	* <p>The returned array will be "safe" in that no references to it are
406	+	* maintained by this queue.  (In other words, this method must allocate
407	+	* a new array).  The caller is thus free to modify the returned array.
408	+	*
409	+	* <p>This method acts as bridge between array-based and collection-based
410	+	* APIs.
411	+	*
412	+	* @return an array containing all of the elements in this queue
413	+	*/
414		public Object[] toArray() {
415	<	return null;
415	>	return Arrays.copyOf(queue, size);
416	>	}
417	>
418	>	/**
419	>	* Returns an array containing all of the elements in this queue; the
420	>	* runtime type of the returned array is that of the specified array.
421	>	* The returned array elements are in no particular order.
422	>	* If the queue fits in the specified array, it is returned therein.
423	>	* Otherwise, a new array is allocated with the runtime type of the
424	>	* specified array and the size of this queue.
425	>	*
426	>	* <p>If the queue fits in the specified array with room to spare
427	>	* (i.e., the array has more elements than the queue), the element in
428	>	* the array immediately following the end of the collection is set to
429	>	* {@code null}.
430	>	*
431	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
432	>	* array-based and collection-based APIs.  Further, this method allows
433	>	* precise control over the runtime type of the output array, and may,
434	>	* under certain circumstances, be used to save allocation costs.
435	>	*
436	>	* <p>Suppose {@code x} is a queue known to contain only strings.
437	>	* The following code can be used to dump the queue into a newly
438	>	* allocated array of {@code String}:
439	>	*
440	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
441	>	*
442	>	* Note that {@code toArray(new Object[0])} is identical in function to
443	>	* {@code toArray()}.
444	>	*
445	>	* @param a the array into which the elements of the queue are to
446	>	*          be stored, if it is big enough; otherwise, a new array of the
447	>	*          same runtime type is allocated for this purpose.
448	>	* @return an array containing all of the elements in this queue
449	>	* @throws ArrayStoreException if the runtime type of the specified array
450	>	*         is not a supertype of the runtime type of every element in
451	>	*         this queue
452	>	* @throws NullPointerException if the specified array is null
453	>	*/
454	>	@SuppressWarnings("unchecked")
455	>	public <T> T[] toArray(T[] a) {
456	>	final int size = this.size;
457	>	if (a.length < size)
458	>	// Make a new array of a's runtime type, but my contents:
459	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
460	>	System.arraycopy(queue, 0, a, 0, size);
461	>	if (a.length > size)
462	>	a[size] = null;
463	>	return a;
464	>	}
465	>
466	>	/**
467	>	* Returns an iterator over the elements in this queue. The iterator
468	>	* does not return the elements in any particular order.
469	>	*
470	>	* @return an iterator over the elements in this queue
471	>	*/
472	>	public Iterator<E> iterator() {
473	>	return new Itr();
474		}
475
476	<	public <T> T[] toArray(T[] array) {
476	>	private final class Itr implements Iterator<E> {
477	>	/**
478	>	* Index (into queue array) of element to be returned by
479	>	* subsequent call to next.
480	>	*/
481	>	private int cursor = 0;
482	>
483	>	/**
484	>	* Index of element returned by most recent call to next,
485	>	* unless that element came from the forgetMeNot list.
486	>	* Set to -1 if element is deleted by a call to remove.
487	>	*/
488	>	private int lastRet = -1;
489	>
490	>	/**
491	>	* A queue of elements that were moved from the unvisited portion of
492	>	* the heap into the visited portion as a result of "unlucky" element
493	>	* removals during the iteration.  (Unlucky element removals are those
494	>	* that require a siftup instead of a siftdown.)  We must visit all of
495	>	* the elements in this list to complete the iteration.  We do this
496	>	* after we've completed the "normal" iteration.
497	>	*
498	>	* We expect that most iterations, even those involving removals,
499	>	* will not need to store elements in this field.
500	>	*/
501	>	private ArrayDeque<E> forgetMeNot = null;
502	>
503	>	/**
504	>	* Element returned by the most recent call to next iff that
505	>	* element was drawn from the forgetMeNot list.
506	>	*/
507	>	private E lastRetElt = null;
508	>
509	>	/**
510	>	* The modCount value that the iterator believes that the backing
511	>	* Queue should have.  If this expectation is violated, the iterator
512	>	* has detected concurrent modification.
513	>	*/
514	>	private int expectedModCount = modCount;
515	>
516	>	public boolean hasNext() {
517	>	return cursor < size ||
518	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
519	>	}
520	>
521	>	@SuppressWarnings("unchecked")
522	>	public E next() {
523	>	if (expectedModCount != modCount)
524	>	throw new ConcurrentModificationException();
525	>	if (cursor < size)
526	>	return (E) queue[lastRet = cursor++];
527	>	if (forgetMeNot != null) {
528	>	lastRet = -1;
529	>	lastRetElt = forgetMeNot.poll();
530	>	if (lastRetElt != null)
531	>	return lastRetElt;
532	>	}
533	>	throw new NoSuchElementException();
534	>	}
535	>
536	>	public void remove() {
537	>	if (expectedModCount != modCount)
538	>	throw new ConcurrentModificationException();
539	>	if (lastRet != -1) {
540	>	E moved = PriorityQueue.this.removeAt(lastRet);
541	>	lastRet = -1;
542	>	if (moved == null)
543	>	cursor--;
544	>	else {
545	>	if (forgetMeNot == null)
546	>	forgetMeNot = new ArrayDeque<E>();
547	>	forgetMeNot.add(moved);
548	>	}
549	>	} else if (lastRetElt != null) {
550	>	PriorityQueue.this.removeEq(lastRetElt);
551	>	lastRetElt = null;
552	>	} else {
553	>	throw new IllegalStateException();
554	>	}
555	>	expectedModCount = modCount;
556	>	}
557	>	}
558	>
559	>	public int size() {
560	>	return size;
561	>	}
562	>
563	>	/**
564	>	* Removes all of the elements from this priority queue.
565	>	* The queue will be empty after this call returns.
566	>	*/
567	>	public void clear() {
568	>	modCount++;
569	>	for (int i = 0; i < size; i++)
570	>	queue[i] = null;
571	>	size = 0;
572	>	}
573	>
574	>	@SuppressWarnings("unchecked")
575	>	public E poll() {
576	>	if (size == 0)
577	>	return null;
578	>	int s = --size;
579	>	modCount++;
580	>	E result = (E) queue[0];
581	>	E x = (E) queue[s];
582	>	queue[s] = null;
583	>	if (s != 0)
584	>	siftDown(0, x);
585	>	return result;
586	>	}
587	>
588	>	/**
589	>	* Removes the ith element from queue.
590	>	*
591	>	* Normally this method leaves the elements at up to i-1,
592	>	* inclusive, untouched.  Under these circumstances, it returns
593	>	* null.  Occasionally, in order to maintain the heap invariant,
594	>	* it must swap a later element of the list with one earlier than
595	>	* i.  Under these circumstances, this method returns the element
596	>	* that was previously at the end of the list and is now at some
597	>	* position before i. This fact is used by iterator.remove so as to
598	>	* avoid missing traversing elements.
599	>	*/
600	>	@SuppressWarnings("unchecked")
601	>	private E removeAt(int i) {
602	>	// assert i >= 0 && i < size;
603	>	modCount++;
604	>	int s = --size;
605	>	if (s == i) // removed last element
606	>	queue[i] = null;
607	>	else {
608	>	E moved = (E) queue[s];
609	>	queue[s] = null;
610	>	siftDown(i, moved);
611	>	if (queue[i] == moved) {
612	>	siftUp(i, moved);
613	>	if (queue[i] != moved)
614	>	return moved;
615	>	}
616	>	}
617		return null;
618		}
619
620	+	/**
621	+	* Inserts item x at position k, maintaining heap invariant by
622	+	* promoting x up the tree until it is greater than or equal to
623	+	* its parent, or is the root.
624	+	*
625	+	* To simplify and speed up coercions and comparisons. the
626	+	* Comparable and Comparator versions are separated into different
627	+	* methods that are otherwise identical. (Similarly for siftDown.)
628	+	*
629	+	* @param k the position to fill
630	+	* @param x the item to insert
631	+	*/
632	+	private void siftUp(int k, E x) {
633	+	if (comparator != null)
634	+	siftUpUsingComparator(k, x);
635	+	else
636	+	siftUpComparable(k, x);
637	+	}
638	+
639	+	@SuppressWarnings("unchecked")
640	+	private void siftUpComparable(int k, E x) {
641	+	Comparable<? super E> key = (Comparable<? super E>) x;
642	+	while (k > 0) {
643	+	int parent = (k - 1) >>> 1;
644	+	Object e = queue[parent];
645	+	if (key.compareTo((E) e) >= 0)
646	+	break;
647	+	queue[k] = e;
648	+	k = parent;
649	+	}
650	+	queue[k] = key;
651	+	}
652	+
653	+	@SuppressWarnings("unchecked")
654	+	private void siftUpUsingComparator(int k, E x) {
655	+	while (k > 0) {
656	+	int parent = (k - 1) >>> 1;
657	+	Object e = queue[parent];
658	+	if (comparator.compare(x, (E) e) >= 0)
659	+	break;
660	+	queue[k] = e;
661	+	k = parent;
662	+	}
663	+	queue[k] = x;
664	+	}
665	+
666	+	/**
667	+	* Inserts item x at position k, maintaining heap invariant by
668	+	* demoting x down the tree repeatedly until it is less than or
669	+	* equal to its children or is a leaf.
670	+	*
671	+	* @param k the position to fill
672	+	* @param x the item to insert
673	+	*/
674	+	private void siftDown(int k, E x) {
675	+	if (comparator != null)
676	+	siftDownUsingComparator(k, x);
677	+	else
678	+	siftDownComparable(k, x);
679	+	}
680	+
681	+	@SuppressWarnings("unchecked")
682	+	private void siftDownComparable(int k, E x) {
683	+	Comparable<? super E> key = (Comparable<? super E>)x;
684	+	int half = size >>> 1;        // loop while a non-leaf
685	+	while (k < half) {
686	+	int child = (k << 1) + 1; // assume left child is least
687	+	Object c = queue[child];
688	+	int right = child + 1;
689	+	if (right < size &&
690	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
691	+	c = queue[child = right];
692	+	if (key.compareTo((E) c) <= 0)
693	+	break;
694	+	queue[k] = c;
695	+	k = child;
696	+	}
697	+	queue[k] = key;
698	+	}
699	+
700	+	@SuppressWarnings("unchecked")
701	+	private void siftDownUsingComparator(int k, E x) {
702	+	int half = size >>> 1;
703	+	while (k < half) {
704	+	int child = (k << 1) + 1;
705	+	Object c = queue[child];
706	+	int right = child + 1;
707	+	if (right < size &&
708	+	comparator.compare((E) c, (E) queue[right]) > 0)
709	+	c = queue[child = right];
710	+	if (comparator.compare(x, (E) c) <= 0)
711	+	break;
712	+	queue[k] = c;
713	+	k = child;
714	+	}
715	+	queue[k] = x;
716	+	}
717	+
718	+	/**
719	+	* Establishes the heap invariant (described above) in the entire tree,
720	+	* assuming nothing about the order of the elements prior to the call.
721	+	*/
722	+	@SuppressWarnings("unchecked")
723	+	private void heapify() {
724	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
725	+	siftDown(i, (E) queue[i]);
726	+	}
727	+
728	+	/**
729	+	* Returns the comparator used to order the elements in this
730	+	* queue, or {@code null} if this queue is sorted according to
731	+	* the {@linkplain Comparable natural ordering} of its elements.
732	+	*
733	+	* @return the comparator used to order this queue, or
734	+	*         {@code null} if this queue is sorted according to the
735	+	*         natural ordering of its elements
736	+	*/
737	+	public Comparator<? super E> comparator() {
738	+	return comparator;
739	+	}
740	+
741	+	/**
742	+	* Saves this queue to a stream (that is, serializes it).
743	+	*
744	+	* @serialData The length of the array backing the instance is
745	+	*             emitted (int), followed by all of its elements
746	+	*             (each an {@code Object}) in the proper order.
747	+	* @param s the stream
748	+	*/
749	+	private void writeObject(java.io.ObjectOutputStream s)
750	+	throws java.io.IOException {
751	+	// Write out element count, and any hidden stuff
752	+	s.defaultWriteObject();
753	+
754	+	// Write out array length, for compatibility with 1.5 version
755	+	s.writeInt(Math.max(2, size + 1));
756	+
757	+	// Write out all elements in the "proper order".
758	+	for (int i = 0; i < size; i++)
759	+	s.writeObject(queue[i]);
760	+	}
761	+
762	+	/**
763	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
764	+	* (that is, deserializes it).
765	+	*
766	+	* @param s the stream
767	+	*/
768	+	private void readObject(java.io.ObjectInputStream s)
769	+	throws java.io.IOException, ClassNotFoundException {
770	+	// Read in size, and any hidden stuff
771	+	s.defaultReadObject();
772	+
773	+	// Read in (and discard) array length
774	+	s.readInt();
775	+
776	+	queue = new Object[size];
777	+
778	+	// Read in all elements.
779	+	for (int i = 0; i < size; i++)
780	+	queue[i] = s.readObject();
781	+
782	+	// Elements are guaranteed to be in "proper order", but the
783	+	// spec has never explained what that might be.
784	+	heapify();
785	+	}
786	+
787	+	// wrapping constructor in method avoids transient javac problems
788	+	final PriorityQueueSpliterator<E> spliterator(int origin, int fence,
789	+	int expectedModCount) {
790	+	return new PriorityQueueSpliterator<E>(this, origin, fence,
791	+	expectedModCount);
792	+	}
793	+
794	+	public Stream<E> stream() {
795	+	int flags = Streams.STREAM_IS_SIZED;
796	+	return Streams.stream
797	+	(() -> spliterator(0, size, modCount), flags);
798	+	}
799	+	public Stream<E> parallelStream() {
800	+	int flags = Streams.STREAM_IS_SIZED;
801	+	return Streams.parallelStream
802	+	(() -> spliterator(0, size, modCount), flags);
803	+	}
804	+
805	+	/** Index-based split-by-two Spliterator */
806	+	static final class PriorityQueueSpliterator<E>
807	+	implements Spliterator<E>, Iterator<E> {
808	+	private final PriorityQueue<E> pq;
809	+	private int index;           // current index, modified on advance/split
810	+	private final int fence;     // one past last index
811	+	private final int expectedModCount; // for comodification checks
812	+
813	+	/** Create new spliterator covering the given  range */
814	+	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
815	+	int expectedModCount) {
816	+	this.pq = pq; this.index = origin; this.fence = fence;
817	+	this.expectedModCount = expectedModCount;
818	+	}
819	+
820	+	public PriorityQueueSpliterator<E> trySplit() {
821	+	int lo = index, mid = (lo + fence) >>> 1;
822	+	return (lo >= mid) ? null :
823	+	new PriorityQueueSpliterator<E>(pq, lo, index = mid,
824	+	expectedModCount);
825	+	}
826	+
827	+	public void forEach(Block<? super E> block) {
828	+	Object[] a; int i, hi; // hoist accesses and checks from loop
829	+	if (block == null)
830	+	throw new NullPointerException();
831	+	if ((a = pq.queue).length >= (hi = fence) &&
832	+	(i = index) >= 0 && i < hi) {
833	+	index = hi;
834	+	do {
835	+	@SuppressWarnings("unchecked") E e = (E) a[i];
836	+	block.accept(e);
837	+	} while (++i < hi);
838	+	if (pq.modCount != expectedModCount)
839	+	throw new ConcurrentModificationException();
840	+	}
841	+	}
842	+
843	+	public boolean tryAdvance(Block<? super E> block) {
844	+	if (index >= 0 && index < fence) {
845	+	if (pq.modCount != expectedModCount)
846	+	throw new ConcurrentModificationException();
847	+	@SuppressWarnings("unchecked") E e =
848	+	(E)pq.queue[index++];
849	+	block.accept(e);
850	+	return true;
851	+	}
852	+	return false;
853	+	}
854	+
855	+	public long estimateSize() { return (long)(fence - index); }
856	+	public boolean hasExactSize() { return true; }
857	+	public boolean hasExactSplits() { return true; }
858	+
859	+	// Iterator support
860	+	public Iterator<E> iterator() { return this; }
861	+	public void remove() { throw new UnsupportedOperationException(); }
862	+	public boolean hasNext() { return index >= 0 && index < fence; }
863	+
864	+	public E next() {
865	+	if (index < 0 || index >= fence)
866	+	throw new NoSuchElementException();
867	+	if (pq.modCount != expectedModCount)
868	+	throw new ConcurrentModificationException();
869	+	@SuppressWarnings("unchecked") E e =
870	+	(E) pq.queue[index++];
871	+	return e;
872	+	}
873	+	}
874		}

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