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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 1.92 by jsr166, Mon Feb 18 03:15:10 2013 UTC

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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.function.Consumer;
28	>	import java.util.stream.Stream;
29	>	import java.util.stream.Streams;
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()} is <em>not</em> guaranteed to traverse the elements of
59	>	* the priority queue in any particular order. If you need ordered
60	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
61	>	*
62	>	* <p><strong>Note that this implementation is not synchronized.</strong>
63	>	* Multiple threads should not access a {@code PriorityQueue}
64	>	* instance concurrently if any of the threads modifies the queue.
65	>	* Instead, use the thread-safe {@link
66	>	* java.util.concurrent.PriorityBlockingQueue} class.
67	>	*
68	>	* <p>Implementation note: this implementation provides
69	>	* O(log(n)) time for the enqueing and dequeing methods
70	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
71	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
72	>	* methods; and constant time for the retrieval methods
73	>	* ({@code peek}, {@code element}, and {@code size}).
74	>	*
75	>	* <p>This class is a member of the
76	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
77	>	* Java Collections Framework</a>.
78	>	*
79	>	* @since 1.5
80	>	* @author Josh Bloch, Doug Lea
81	>	* @param <E> the type of elements held in this collection
82	>	*/
83	>	public class PriorityQueue<E> extends AbstractQueue<E>
84	>	implements java.io.Serializable {
85
86	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
86	>	private static final long serialVersionUID = -7720805057305804111L;
87
88	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
88	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
89
90	<	public boolean add(E x) {
91	<	return false;
90	>	/**
91	>	* Priority queue represented as a balanced binary heap: the two
92	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
93	>	* priority queue is ordered by comparator, or by the elements'
94	>	* natural ordering, if comparator is null: For each node n in the
95	>	* heap and each descendant d of n, n <= d.  The element with the
96	>	* lowest value is in queue[0], assuming the queue is nonempty.
97	>	*/
98	>	transient Object[] queue; // non-private to simplify nested class access
99	>
100	>	/**
101	>	* The number of elements in the priority queue.
102	>	*/
103	>	private int size = 0;
104	>
105	>	/**
106	>	* The comparator, or null if priority queue uses elements'
107	>	* natural ordering.
108	>	*/
109	>	private final Comparator<? super E> comparator;
110	>
111	>	/**
112	>	* The number of times this priority queue has been
113	>	* <i>structurally modified</i>.  See AbstractList for gory details.
114	>	*/
115	>	transient int modCount = 0; // non-private to simplify nested class access
116	>
117	>	/**
118	>	* Creates a {@code PriorityQueue} with the default initial
119	>	* capacity (11) that orders its elements according to their
120	>	* {@linkplain Comparable natural ordering}.
121	>	*/
122	>	public PriorityQueue() {
123	>	this(DEFAULT_INITIAL_CAPACITY, null);
124		}
125	<	public boolean offer(E x) {
126	<	return false;
125	>
126	>	/**
127	>	* Creates a {@code PriorityQueue} with the specified initial
128	>	* capacity that orders its elements according to their
129	>	* {@linkplain Comparable natural ordering}.
130	>	*
131	>	* @param initialCapacity the initial capacity for this priority queue
132	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
133	>	*         than 1
134	>	*/
135	>	public PriorityQueue(int initialCapacity) {
136	>	this(initialCapacity, null);
137		}
138	<	public boolean remove(Object x) {
139	<	return false;
138	>
139	>	/**
140	>	* Creates a {@code PriorityQueue} with the specified initial capacity
141	>	* that orders its elements according to the specified comparator.
142	>	*
143	>	* @param  initialCapacity the initial capacity for this priority queue
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	>	* @throws IllegalArgumentException if {@code initialCapacity} is
148	>	*         less than 1
149	>	*/
150	>	public PriorityQueue(int initialCapacity,
151	>	Comparator<? super E> comparator) {
152	>	// Note: This restriction of at least one is not actually needed,
153	>	// but continues for 1.5 compatibility
154	>	if (initialCapacity < 1)
155	>	throw new IllegalArgumentException();
156	>	this.queue = new Object[initialCapacity];
157	>	this.comparator = comparator;
158		}
159
160	<	public E remove() {
161	<	return null;
160	>	/**
161	>	* Creates a {@code PriorityQueue} containing the elements in the
162	>	* specified collection.  If the specified collection is an instance of
163	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
164	>	* priority queue will be ordered according to the same ordering.
165	>	* Otherwise, this priority queue will be ordered according to the
166	>	* {@linkplain Comparable natural ordering} of its elements.
167	>	*
168	>	* @param  c the collection whose elements are to be placed
169	>	*         into this priority queue
170	>	* @throws ClassCastException if elements of the specified collection
171	>	*         cannot be compared to one another according to the priority
172	>	*         queue's ordering
173	>	* @throws NullPointerException if the specified collection or any
174	>	*         of its elements are null
175	>	*/
176	>	@SuppressWarnings("unchecked")
177	>	public PriorityQueue(Collection<? extends E> c) {
178	>	if (c instanceof SortedSet<?>) {
179	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
180	>	this.comparator = (Comparator<? super E>) ss.comparator();
181	>	initElementsFromCollection(ss);
182	>	}
183	>	else if (c instanceof PriorityQueue<?>) {
184	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
185	>	this.comparator = (Comparator<? super E>) pq.comparator();
186	>	initFromPriorityQueue(pq);
187	>	}
188	>	else {
189	>	this.comparator = null;
190	>	initFromCollection(c);
191	>	}
192		}
193	<	public Iterator<E> iterator() {
194	<	return null;
193	>
194	>	/**
195	>	* Creates a {@code PriorityQueue} containing the elements in the
196	>	* specified priority queue.  This priority queue will be
197	>	* ordered according to the same ordering as the given priority
198	>	* queue.
199	>	*
200	>	* @param  c the priority queue whose elements are to be placed
201	>	*         into this priority queue
202	>	* @throws ClassCastException if elements of {@code c} cannot be
203	>	*         compared to one another according to {@code c}'s
204	>	*         ordering
205	>	* @throws NullPointerException if the specified priority queue or any
206	>	*         of its elements are null
207	>	*/
208	>	@SuppressWarnings("unchecked")
209	>	public PriorityQueue(PriorityQueue<? extends E> c) {
210	>	this.comparator = (Comparator<? super E>) c.comparator();
211	>	initFromPriorityQueue(c);
212		}
213
214	<	public E element() {
215	<	return null;
214	>	/**
215	>	* Creates a {@code PriorityQueue} containing the elements in the
216	>	* specified sorted set.   This priority queue will be ordered
217	>	* according to the same ordering as the given sorted set.
218	>	*
219	>	* @param  c the sorted set whose elements are to be placed
220	>	*         into this priority queue
221	>	* @throws ClassCastException if elements of the specified sorted
222	>	*         set cannot be compared to one another according to the
223	>	*         sorted set's ordering
224	>	* @throws NullPointerException if the specified sorted set or any
225	>	*         of its elements are null
226	>	*/
227	>	@SuppressWarnings("unchecked")
228	>	public PriorityQueue(SortedSet<? extends E> c) {
229	>	this.comparator = (Comparator<? super E>) c.comparator();
230	>	initElementsFromCollection(c);
231		}
232	<	public E poll() {
233	<	return null;
232	>
233	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
234	>	if (c.getClass() == PriorityQueue.class) {
235	>	this.queue = c.toArray();
236	>	this.size = c.size();
237	>	} else {
238	>	initFromCollection(c);
239	>	}
240	>	}
241	>
242	>	private void initElementsFromCollection(Collection<? extends E> c) {
243	>	Object[] a = c.toArray();
244	>	// If c.toArray incorrectly doesn't return Object[], copy it.
245	>	if (a.getClass() != Object[].class)
246	>	a = Arrays.copyOf(a, a.length, Object[].class);
247	>	int len = a.length;
248	>	if (len == 1 || this.comparator != null)
249	>	for (int i = 0; i < len; i++)
250	>	if (a[i] == null)
251	>	throw new NullPointerException();
252	>	this.queue = a;
253	>	this.size = a.length;
254	>	}
255	>
256	>	/**
257	>	* Initializes queue array with elements from the given Collection.
258	>	*
259	>	* @param c the collection
260	>	*/
261	>	private void initFromCollection(Collection<? extends E> c) {
262	>	initElementsFromCollection(c);
263	>	heapify();
264	>	}
265	>
266	>	/**
267	>	* The maximum size of array to allocate.
268	>	* Some VMs reserve some header words in an array.
269	>	* Attempts to allocate larger arrays may result in
270	>	* OutOfMemoryError: Requested array size exceeds VM limit
271	>	*/
272	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
273	>
274	>	/**
275	>	* Increases the capacity of the array.
276	>	*
277	>	* @param minCapacity the desired minimum capacity
278	>	*/
279	>	private void grow(int minCapacity) {
280	>	int oldCapacity = queue.length;
281	>	// Double size if small; else grow by 50%
282	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
283	>	(oldCapacity + 2) :
284	>	(oldCapacity >> 1));
285	>	// overflow-conscious code
286	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
287	>	newCapacity = hugeCapacity(minCapacity);
288	>	queue = Arrays.copyOf(queue, newCapacity);
289	>	}
290	>
291	>	private static int hugeCapacity(int minCapacity) {
292	>	if (minCapacity < 0) // overflow
293	>	throw new OutOfMemoryError();
294	>	return (minCapacity > MAX_ARRAY_SIZE) ?
295	>	Integer.MAX_VALUE :
296	>	MAX_ARRAY_SIZE;
297	>	}
298	>
299	>	/**
300	>	* Inserts the specified element into this priority queue.
301	>	*
302	>	* @return {@code true} (as specified by {@link Collection#add})
303	>	* @throws ClassCastException if the specified element cannot be
304	>	*         compared with elements currently in this priority queue
305	>	*         according to the priority queue's ordering
306	>	* @throws NullPointerException if the specified element is null
307	>	*/
308	>	public boolean add(E e) {
309	>	return offer(e);
310		}
311	+
312	+	/**
313	+	* Inserts the specified element into this priority queue.
314	+	*
315	+	* @return {@code true} (as specified by {@link Queue#offer})
316	+	* @throws ClassCastException if the specified element cannot be
317	+	*         compared with elements currently in this priority queue
318	+	*         according to the priority queue's ordering
319	+	* @throws NullPointerException if the specified element is null
320	+	*/
321	+	public boolean offer(E e) {
322	+	if (e == null)
323	+	throw new NullPointerException();
324	+	modCount++;
325	+	int i = size;
326	+	if (i >= queue.length)
327	+	grow(i + 1);
328	+	size = i + 1;
329	+	if (i == 0)
330	+	queue[0] = e;
331	+	else
332	+	siftUp(i, e);
333	+	return true;
334	+	}
335	+
336	+	@SuppressWarnings("unchecked")
337		public E peek() {
338	<	return null;
338	>	return (size == 0) ? null : (E) queue[0];
339		}
340
341	<	public boolean isEmpty() {
341	>	private int indexOf(Object o) {
342	>	if (o != null) {
343	>	for (int i = 0; i < size; i++)
344	>	if (o.equals(queue[i]))
345	>	return i;
346	>	}
347	>	return -1;
348	>	}
349	>
350	>	/**
351	>	* Removes a single instance of the specified element from this queue,
352	>	* if it is present.  More formally, removes an element {@code e} such
353	>	* that {@code o.equals(e)}, if this queue contains one or more such
354	>	* elements.  Returns {@code true} if and only if this queue contained
355	>	* the specified element (or equivalently, if this queue changed as a
356	>	* result of the call).
357	>	*
358	>	* @param o element to be removed from this queue, if present
359	>	* @return {@code true} if this queue changed as a result of the call
360	>	*/
361	>	public boolean remove(Object o) {
362	>	int i = indexOf(o);
363	>	if (i == -1)
364	>	return false;
365	>	else {
366	>	removeAt(i);
367	>	return true;
368	>	}
369	>	}
370	>
371	>	/**
372	>	* Version of remove using reference equality, not equals.
373	>	* Needed by iterator.remove.
374	>	*
375	>	* @param o element to be removed from this queue, if present
376	>	* @return {@code true} if removed
377	>	*/
378	>	boolean removeEq(Object o) {
379	>	for (int i = 0; i < size; i++) {
380	>	if (o == queue[i]) {
381	>	removeAt(i);
382	>	return true;
383	>	}
384	>	}
385		return false;
386		}
387	<	public int size() {
388	<	return 0;
387	>
388	>	/**
389	>	* Returns {@code true} if this queue contains the specified element.
390	>	* More formally, returns {@code true} if and only if this queue contains
391	>	* at least one element {@code e} such that {@code o.equals(e)}.
392	>	*
393	>	* @param o object to be checked for containment in this queue
394	>	* @return {@code true} if this queue contains the specified element
395	>	*/
396	>	public boolean contains(Object o) {
397	>	return indexOf(o) != -1;
398		}
399	+
400	+	/**
401	+	* Returns an array containing all of the elements in this queue.
402	+	* The elements are in no particular order.
403	+	*
404	+	* <p>The returned array will be "safe" in that no references to it are
405	+	* maintained by this queue.  (In other words, this method must allocate
406	+	* a new array).  The caller is thus free to modify the returned array.
407	+	*
408	+	* <p>This method acts as bridge between array-based and collection-based
409	+	* APIs.
410	+	*
411	+	* @return an array containing all of the elements in this queue
412	+	*/
413		public Object[] toArray() {
414	<	return null;
414	>	return Arrays.copyOf(queue, size);
415	>	}
416	>
417	>	/**
418	>	* Returns an array containing all of the elements in this queue; the
419	>	* runtime type of the returned array is that of the specified array.
420	>	* The returned array elements are in no particular order.
421	>	* If the queue fits in the specified array, it is returned therein.
422	>	* Otherwise, a new array is allocated with the runtime type of the
423	>	* specified array and the size of this queue.
424	>	*
425	>	* <p>If the queue fits in the specified array with room to spare
426	>	* (i.e., the array has more elements than the queue), the element in
427	>	* the array immediately following the end of the collection is set to
428	>	* {@code null}.
429	>	*
430	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
431	>	* array-based and collection-based APIs.  Further, this method allows
432	>	* precise control over the runtime type of the output array, and may,
433	>	* under certain circumstances, be used to save allocation costs.
434	>	*
435	>	* <p>Suppose {@code x} is a queue known to contain only strings.
436	>	* The following code can be used to dump the queue into a newly
437	>	* allocated array of {@code String}:
438	>	*
439	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
440	>	*
441	>	* Note that {@code toArray(new Object[0])} is identical in function to
442	>	* {@code toArray()}.
443	>	*
444	>	* @param a the array into which the elements of the queue are to
445	>	*          be stored, if it is big enough; otherwise, a new array of the
446	>	*          same runtime type is allocated for this purpose.
447	>	* @return an array containing all of the elements in this queue
448	>	* @throws ArrayStoreException if the runtime type of the specified array
449	>	*         is not a supertype of the runtime type of every element in
450	>	*         this queue
451	>	* @throws NullPointerException if the specified array is null
452	>	*/
453	>	@SuppressWarnings("unchecked")
454	>	public <T> T[] toArray(T[] a) {
455	>	final int size = this.size;
456	>	if (a.length < size)
457	>	// Make a new array of a's runtime type, but my contents:
458	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
459	>	System.arraycopy(queue, 0, a, 0, size);
460	>	if (a.length > size)
461	>	a[size] = null;
462	>	return a;
463	>	}
464	>
465	>	/**
466	>	* Returns an iterator over the elements in this queue. The iterator
467	>	* does not return the elements in any particular order.
468	>	*
469	>	* @return an iterator over the elements in this queue
470	>	*/
471	>	public Iterator<E> iterator() {
472	>	return new Itr();
473		}
474
475	<	public <T> T[] toArray(T[] array) {
475	>	private final class Itr implements Iterator<E> {
476	>	/**
477	>	* Index (into queue array) of element to be returned by
478	>	* subsequent call to next.
479	>	*/
480	>	private int cursor = 0;
481	>
482	>	/**
483	>	* Index of element returned by most recent call to next,
484	>	* unless that element came from the forgetMeNot list.
485	>	* Set to -1 if element is deleted by a call to remove.
486	>	*/
487	>	private int lastRet = -1;
488	>
489	>	/**
490	>	* A queue of elements that were moved from the unvisited portion of
491	>	* the heap into the visited portion as a result of "unlucky" element
492	>	* removals during the iteration.  (Unlucky element removals are those
493	>	* that require a siftup instead of a siftdown.)  We must visit all of
494	>	* the elements in this list to complete the iteration.  We do this
495	>	* after we've completed the "normal" iteration.
496	>	*
497	>	* We expect that most iterations, even those involving removals,
498	>	* will not need to store elements in this field.
499	>	*/
500	>	private ArrayDeque<E> forgetMeNot = null;
501	>
502	>	/**
503	>	* Element returned by the most recent call to next iff that
504	>	* element was drawn from the forgetMeNot list.
505	>	*/
506	>	private E lastRetElt = null;
507	>
508	>	/**
509	>	* The modCount value that the iterator believes that the backing
510	>	* Queue should have.  If this expectation is violated, the iterator
511	>	* has detected concurrent modification.
512	>	*/
513	>	private int expectedModCount = modCount;
514	>
515	>	public boolean hasNext() {
516	>	return cursor < size ||
517	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
518	>	}
519	>
520	>	@SuppressWarnings("unchecked")
521	>	public E next() {
522	>	if (expectedModCount != modCount)
523	>	throw new ConcurrentModificationException();
524	>	if (cursor < size)
525	>	return (E) queue[lastRet = cursor++];
526	>	if (forgetMeNot != null) {
527	>	lastRet = -1;
528	>	lastRetElt = forgetMeNot.poll();
529	>	if (lastRetElt != null)
530	>	return lastRetElt;
531	>	}
532	>	throw new NoSuchElementException();
533	>	}
534	>
535	>	public void remove() {
536	>	if (expectedModCount != modCount)
537	>	throw new ConcurrentModificationException();
538	>	if (lastRet != -1) {
539	>	E moved = PriorityQueue.this.removeAt(lastRet);
540	>	lastRet = -1;
541	>	if (moved == null)
542	>	cursor--;
543	>	else {
544	>	if (forgetMeNot == null)
545	>	forgetMeNot = new ArrayDeque<>();
546	>	forgetMeNot.add(moved);
547	>	}
548	>	} else if (lastRetElt != null) {
549	>	PriorityQueue.this.removeEq(lastRetElt);
550	>	lastRetElt = null;
551	>	} else {
552	>	throw new IllegalStateException();
553	>	}
554	>	expectedModCount = modCount;
555	>	}
556	>	}
557	>
558	>	public int size() {
559	>	return size;
560	>	}
561	>
562	>	/**
563	>	* Removes all of the elements from this priority queue.
564	>	* The queue will be empty after this call returns.
565	>	*/
566	>	public void clear() {
567	>	modCount++;
568	>	for (int i = 0; i < size; i++)
569	>	queue[i] = null;
570	>	size = 0;
571	>	}
572	>
573	>	@SuppressWarnings("unchecked")
574	>	public E poll() {
575	>	if (size == 0)
576	>	return null;
577	>	int s = --size;
578	>	modCount++;
579	>	E result = (E) queue[0];
580	>	E x = (E) queue[s];
581	>	queue[s] = null;
582	>	if (s != 0)
583	>	siftDown(0, x);
584	>	return result;
585	>	}
586	>
587	>	/**
588	>	* Removes the ith element from queue.
589	>	*
590	>	* Normally this method leaves the elements at up to i-1,
591	>	* inclusive, untouched.  Under these circumstances, it returns
592	>	* null.  Occasionally, in order to maintain the heap invariant,
593	>	* it must swap a later element of the list with one earlier than
594	>	* i.  Under these circumstances, this method returns the element
595	>	* that was previously at the end of the list and is now at some
596	>	* position before i. This fact is used by iterator.remove so as to
597	>	* avoid missing traversing elements.
598	>	*/
599	>	@SuppressWarnings("unchecked")
600	>	private E removeAt(int i) {
601	>	// assert i >= 0 && i < size;
602	>	modCount++;
603	>	int s = --size;
604	>	if (s == i) // removed last element
605	>	queue[i] = null;
606	>	else {
607	>	E moved = (E) queue[s];
608	>	queue[s] = null;
609	>	siftDown(i, moved);
610	>	if (queue[i] == moved) {
611	>	siftUp(i, moved);
612	>	if (queue[i] != moved)
613	>	return moved;
614	>	}
615	>	}
616		return null;
617		}
618
619	+	/**
620	+	* Inserts item x at position k, maintaining heap invariant by
621	+	* promoting x up the tree until it is greater than or equal to
622	+	* its parent, or is the root.
623	+	*
624	+	* To simplify and speed up coercions and comparisons. the
625	+	* Comparable and Comparator versions are separated into different
626	+	* methods that are otherwise identical. (Similarly for siftDown.)
627	+	*
628	+	* @param k the position to fill
629	+	* @param x the item to insert
630	+	*/
631	+	private void siftUp(int k, E x) {
632	+	if (comparator != null)
633	+	siftUpUsingComparator(k, x);
634	+	else
635	+	siftUpComparable(k, x);
636	+	}
637	+
638	+	@SuppressWarnings("unchecked")
639	+	private void siftUpComparable(int k, E x) {
640	+	Comparable<? super E> key = (Comparable<? super E>) x;
641	+	while (k > 0) {
642	+	int parent = (k - 1) >>> 1;
643	+	Object e = queue[parent];
644	+	if (key.compareTo((E) e) >= 0)
645	+	break;
646	+	queue[k] = e;
647	+	k = parent;
648	+	}
649	+	queue[k] = key;
650	+	}
651	+
652	+	@SuppressWarnings("unchecked")
653	+	private void siftUpUsingComparator(int k, E x) {
654	+	while (k > 0) {
655	+	int parent = (k - 1) >>> 1;
656	+	Object e = queue[parent];
657	+	if (comparator.compare(x, (E) e) >= 0)
658	+	break;
659	+	queue[k] = e;
660	+	k = parent;
661	+	}
662	+	queue[k] = x;
663	+	}
664	+
665	+	/**
666	+	* Inserts item x at position k, maintaining heap invariant by
667	+	* demoting x down the tree repeatedly until it is less than or
668	+	* equal to its children or is a leaf.
669	+	*
670	+	* @param k the position to fill
671	+	* @param x the item to insert
672	+	*/
673	+	private void siftDown(int k, E x) {
674	+	if (comparator != null)
675	+	siftDownUsingComparator(k, x);
676	+	else
677	+	siftDownComparable(k, x);
678	+	}
679	+
680	+	@SuppressWarnings("unchecked")
681	+	private void siftDownComparable(int k, E x) {
682	+	Comparable<? super E> key = (Comparable<? super E>)x;
683	+	int half = size >>> 1;        // loop while a non-leaf
684	+	while (k < half) {
685	+	int child = (k << 1) + 1; // assume left child is least
686	+	Object c = queue[child];
687	+	int right = child + 1;
688	+	if (right < size &&
689	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
690	+	c = queue[child = right];
691	+	if (key.compareTo((E) c) <= 0)
692	+	break;
693	+	queue[k] = c;
694	+	k = child;
695	+	}
696	+	queue[k] = key;
697	+	}
698	+
699	+	@SuppressWarnings("unchecked")
700	+	private void siftDownUsingComparator(int k, E x) {
701	+	int half = size >>> 1;
702	+	while (k < half) {
703	+	int child = (k << 1) + 1;
704	+	Object c = queue[child];
705	+	int right = child + 1;
706	+	if (right < size &&
707	+	comparator.compare((E) c, (E) queue[right]) > 0)
708	+	c = queue[child = right];
709	+	if (comparator.compare(x, (E) c) <= 0)
710	+	break;
711	+	queue[k] = c;
712	+	k = child;
713	+	}
714	+	queue[k] = x;
715	+	}
716	+
717	+	/**
718	+	* Establishes the heap invariant (described above) in the entire tree,
719	+	* assuming nothing about the order of the elements prior to the call.
720	+	*/
721	+	@SuppressWarnings("unchecked")
722	+	private void heapify() {
723	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
724	+	siftDown(i, (E) queue[i]);
725	+	}
726	+
727	+	/**
728	+	* Returns the comparator used to order the elements in this
729	+	* queue, or {@code null} if this queue is sorted according to
730	+	* the {@linkplain Comparable natural ordering} of its elements.
731	+	*
732	+	* @return the comparator used to order this queue, or
733	+	*         {@code null} if this queue is sorted according to the
734	+	*         natural ordering of its elements
735	+	*/
736	+	public Comparator<? super E> comparator() {
737	+	return comparator;
738	+	}
739	+
740	+	/**
741	+	* Saves this queue to a stream (that is, serializes it).
742	+	*
743	+	* @serialData The length of the array backing the instance is
744	+	*             emitted (int), followed by all of its elements
745	+	*             (each an {@code Object}) in the proper order.
746	+	* @param s the stream
747	+	*/
748	+	private void writeObject(java.io.ObjectOutputStream s)
749	+	throws java.io.IOException {
750	+	// Write out element count, and any hidden stuff
751	+	s.defaultWriteObject();
752	+
753	+	// Write out array length, for compatibility with 1.5 version
754	+	s.writeInt(Math.max(2, size + 1));
755	+
756	+	// Write out all elements in the "proper order".
757	+	for (int i = 0; i < size; i++)
758	+	s.writeObject(queue[i]);
759	+	}
760	+
761	+	/**
762	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
763	+	* (that is, deserializes it).
764	+	*
765	+	* @param s the stream
766	+	*/
767	+	private void readObject(java.io.ObjectInputStream s)
768	+	throws java.io.IOException, ClassNotFoundException {
769	+	// Read in size, and any hidden stuff
770	+	s.defaultReadObject();
771	+
772	+	// Read in (and discard) array length
773	+	s.readInt();
774	+
775	+	queue = new Object[size];
776	+
777	+	// Read in all elements.
778	+	for (int i = 0; i < size; i++)
779	+	queue[i] = s.readObject();
780	+
781	+	// Elements are guaranteed to be in "proper order", but the
782	+	// spec has never explained what that might be.
783	+	heapify();
784	+	}
785	+
786	+	final Spliterator<E> spliterator() {
787	+	return new PriorityQueueSpliterator<E>(this, 0, -1, 0);
788	+	}
789	+
790	+	public Stream<E> stream() {
791	+	return Streams.stream(spliterator());
792	+	}
793	+
794	+	public Stream<E> parallelStream() {
795	+	return Streams.parallelStream(spliterator());
796	+	}
797	+
798	+	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
799	+	/*
800	+	* This is very similar to ArrayList Spliterator, except for
801	+	* extra null checks.
802	+	*/
803	+	private final PriorityQueue<E> pq;
804	+	private int index;            // current index, modified on advance/split
805	+	private int fence;            // -1 until first use
806	+	private int expectedModCount; // initialized when fence set
807	+
808	+	/** Creates new spliterator covering the given range */
809	+	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
810	+	int expectedModCount) {
811	+	this.pq = pq;
812	+	this.index = origin;
813	+	this.fence = fence;
814	+	this.expectedModCount = expectedModCount;
815	+	}
816	+
817	+	private int getFence() { // initialize fence to size on first use
818	+	int hi;
819	+	if ((hi = fence) < 0) {
820	+	expectedModCount = pq.modCount;
821	+	hi = fence = pq.size;
822	+	}
823	+	return hi;
824	+	}
825	+
826	+	public PriorityQueueSpliterator<E> trySplit() {
827	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
828	+	return (lo >= mid) ? null :
829	+	new PriorityQueueSpliterator<E>(pq, lo, index = mid,
830	+	expectedModCount);
831	+	}
832	+
833	+	@SuppressWarnings("unchecked")
834	+	public void forEach(Consumer<? super E> action) {
835	+	int i, hi, mc; // hoist accesses and checks from loop
836	+	PriorityQueue<E> q; Object[] a;
837	+	if (action == null)
838	+	throw new NullPointerException();
839	+	if ((q = pq) != null && (a = q.queue) != null) {
840	+	if ((hi = fence) < 0) {
841	+	mc = q.modCount;
842	+	hi = q.size;
843	+	}
844	+	else
845	+	mc = expectedModCount;
846	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
847	+	for (E e;; ++i) {
848	+	if (i < hi) {
849	+	if ((e = (E) a[i]) == null) // must be CME
850	+	break;
851	+	action.accept(e);
852	+	}
853	+	else if (q.modCount != mc)
854	+	break;
855	+	else
856	+	return;
857	+	}
858	+	}
859	+	}
860	+	throw new ConcurrentModificationException();
861	+	}
862	+
863	+	public boolean tryAdvance(Consumer<? super E> action) {
864	+	int hi = getFence(), lo = index;
865	+	if (lo >= 0 && lo < hi) {
866	+	index = lo + 1;
867	+	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
868	+	if (e == null)
869	+	throw new ConcurrentModificationException();
870	+	action.accept(e);
871	+	if (pq.modCount != expectedModCount)
872	+	throw new ConcurrentModificationException();
873	+	return true;
874	+	}
875	+	return false;
876	+	}
877	+
878	+	public long estimateSize() {
879	+	return (long) (getFence() - index);
880	+	}
881	+
882	+	public int characteristics() {
883	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
884	+	}
885	+	}
886		}

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