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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 1.113 by jsr166, Wed Nov 30 03:31:47 2016 UTC

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1	+	/*
2	+	* Copyright (c) 2003, 2013, 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
30		/**
31	<	* An unbounded (resizable) priority queue based on a priority
32	<	* heap.The take operation returns the least element with respect to
33	<	* the given ordering. (If more than one element is tied for least
34	<	* value, one of them is arbitrarily chosen to be returned -- no
35	<	* guarantees are made for ordering across ties.) Ordering follows the
36	<	* java.util.Collection conventions: Either the elements must be
37	<	* Comparable, or a Comparator must be supplied. Comparison failures
38	<	* throw ClassCastExceptions during insertions and extractions.
39	<	**/
40	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
41	<	public PriorityQueue(int initialCapacity) {}
42	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
31	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
32	>	* The elements of the priority queue are ordered according to their
33	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
34	>	* provided at queue construction time, depending on which constructor is
35	>	* used.  A priority queue does not permit {@code null} elements.
36	>	* A priority queue relying on natural ordering also does not permit
37	>	* insertion of non-comparable objects (doing so may result in
38	>	* {@code ClassCastException}).
39	>	*
40	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
41	>	* with respect to the specified ordering.  If multiple elements are
42	>	* tied for least value, the head is one of those elements -- ties are
43	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
44	>	* {@code remove}, {@code peek}, and {@code element} access the
45	>	* element at the head of the queue.
46	>	*
47	>	* <p>A priority queue is unbounded, but has an internal
48	>	* <i>capacity</i> governing the size of an array used to store the
49	>	* elements on the queue.  It is always at least as large as the queue
50	>	* size.  As elements are added to a priority queue, its capacity
51	>	* grows automatically.  The details of the growth policy are not
52	>	* specified.
53	>	*
54	>	* <p>This class and its iterator implement all of the
55	>	* <em>optional</em> methods of the {@link Collection} and {@link
56	>	* Iterator} interfaces.  The Iterator provided in method {@link
57	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
58	>	* are <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 enqueuing and dequeuing 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 queue
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	>	int size;
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;     // 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 default initial capacity and
141	>	* whose elements are ordered according to the specified comparator.
142	>	*
143	>	* @param  comparator the comparator that will be used to order this
144	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
145	>	*         natural ordering} of the elements will be used.
146	>	* @since 1.8
147	>	*/
148	>	public PriorityQueue(Comparator<? super E> comparator) {
149	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
150		}
151
152	<	public E remove() {
153	<	return null;
152	>	/**
153	>	* Creates a {@code PriorityQueue} with the specified initial capacity
154	>	* that orders its elements according to the specified comparator.
155	>	*
156	>	* @param  initialCapacity the initial capacity for this priority queue
157	>	* @param  comparator the comparator that will be used to order this
158	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
159	>	*         natural ordering} of the elements will be used.
160	>	* @throws IllegalArgumentException if {@code initialCapacity} is
161	>	*         less than 1
162	>	*/
163	>	public PriorityQueue(int initialCapacity,
164	>	Comparator<? super E> comparator) {
165	>	// Note: This restriction of at least one is not actually needed,
166	>	// but continues for 1.5 compatibility
167	>	if (initialCapacity < 1)
168	>	throw new IllegalArgumentException();
169	>	this.queue = new Object[initialCapacity];
170	>	this.comparator = comparator;
171		}
172	<	public Iterator<E> iterator() {
173	<	return null;
172	>
173	>	/**
174	>	* Creates a {@code PriorityQueue} containing the elements in the
175	>	* specified collection.  If the specified collection is an instance of
176	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
177	>	* priority queue will be ordered according to the same ordering.
178	>	* Otherwise, this priority queue will be ordered according to the
179	>	* {@linkplain Comparable natural ordering} of its elements.
180	>	*
181	>	* @param  c the collection whose elements are to be placed
182	>	*         into this priority queue
183	>	* @throws ClassCastException if elements of the specified collection
184	>	*         cannot be compared to one another according to the priority
185	>	*         queue's ordering
186	>	* @throws NullPointerException if the specified collection or any
187	>	*         of its elements are null
188	>	*/
189	>	@SuppressWarnings("unchecked")
190	>	public PriorityQueue(Collection<? extends E> c) {
191	>	if (c instanceof SortedSet<?>) {
192	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
193	>	this.comparator = (Comparator<? super E>) ss.comparator();
194	>	initElementsFromCollection(ss);
195	>	}
196	>	else if (c instanceof PriorityQueue<?>) {
197	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
198	>	this.comparator = (Comparator<? super E>) pq.comparator();
199	>	initFromPriorityQueue(pq);
200	>	}
201	>	else {
202	>	this.comparator = null;
203	>	initFromCollection(c);
204	>	}
205		}
206
207	<	public E element() {
208	<	return null;
207	>	/**
208	>	* Creates a {@code PriorityQueue} containing the elements in the
209	>	* specified priority queue.  This priority queue will be
210	>	* ordered according to the same ordering as the given priority
211	>	* queue.
212	>	*
213	>	* @param  c the priority queue whose elements are to be placed
214	>	*         into this priority queue
215	>	* @throws ClassCastException if elements of {@code c} cannot be
216	>	*         compared to one another according to {@code c}'s
217	>	*         ordering
218	>	* @throws NullPointerException if the specified priority queue or any
219	>	*         of its elements are null
220	>	*/
221	>	@SuppressWarnings("unchecked")
222	>	public PriorityQueue(PriorityQueue<? extends E> c) {
223	>	this.comparator = (Comparator<? super E>) c.comparator();
224	>	initFromPriorityQueue(c);
225		}
226	<	public E poll() {
227	<	return null;
226	>
227	>	/**
228	>	* Creates a {@code PriorityQueue} containing the elements in the
229	>	* specified sorted set.   This priority queue will be ordered
230	>	* according to the same ordering as the given sorted set.
231	>	*
232	>	* @param  c the sorted set whose elements are to be placed
233	>	*         into this priority queue
234	>	* @throws ClassCastException if elements of the specified sorted
235	>	*         set cannot be compared to one another according to the
236	>	*         sorted set's ordering
237	>	* @throws NullPointerException if the specified sorted set or any
238	>	*         of its elements are null
239	>	*/
240	>	@SuppressWarnings("unchecked")
241	>	public PriorityQueue(SortedSet<? extends E> c) {
242	>	this.comparator = (Comparator<? super E>) c.comparator();
243	>	initElementsFromCollection(c);
244	>	}
245	>
246	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
247	>	if (c.getClass() == PriorityQueue.class) {
248	>	this.queue = c.toArray();
249	>	this.size = c.size();
250	>	} else {
251	>	initFromCollection(c);
252	>	}
253	>	}
254	>
255	>	private void initElementsFromCollection(Collection<? extends E> c) {
256	>	Object[] a = c.toArray();
257	>	// If c.toArray incorrectly doesn't return Object[], copy it.
258	>	if (a.getClass() != Object[].class)
259	>	a = Arrays.copyOf(a, a.length, Object[].class);
260	>	int len = a.length;
261	>	if (len == 1 || this.comparator != null)
262	>	for (Object e : a)
263	>	if (e == null)
264	>	throw new NullPointerException();
265	>	this.queue = a;
266	>	this.size = a.length;
267	>	}
268	>
269	>	/**
270	>	* Initializes queue array with elements from the given Collection.
271	>	*
272	>	* @param c the collection
273	>	*/
274	>	private void initFromCollection(Collection<? extends E> c) {
275	>	initElementsFromCollection(c);
276	>	heapify();
277	>	}
278	>
279	>	/**
280	>	* The maximum size of array to allocate.
281	>	* Some VMs reserve some header words in an array.
282	>	* Attempts to allocate larger arrays may result in
283	>	* OutOfMemoryError: Requested array size exceeds VM limit
284	>	*/
285	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
286	>
287	>	/**
288	>	* Increases the capacity of the array.
289	>	*
290	>	* @param minCapacity the desired minimum capacity
291	>	*/
292	>	private void grow(int minCapacity) {
293	>	int oldCapacity = queue.length;
294	>	// Double size if small; else grow by 50%
295	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
296	>	(oldCapacity + 2) :
297	>	(oldCapacity >> 1));
298	>	// overflow-conscious code
299	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
300	>	newCapacity = hugeCapacity(minCapacity);
301	>	queue = Arrays.copyOf(queue, newCapacity);
302	>	}
303	>
304	>	private static int hugeCapacity(int minCapacity) {
305	>	if (minCapacity < 0) // overflow
306	>	throw new OutOfMemoryError();
307	>	return (minCapacity > MAX_ARRAY_SIZE) ?
308	>	Integer.MAX_VALUE :
309	>	MAX_ARRAY_SIZE;
310	>	}
311	>
312	>	/**
313	>	* Inserts the specified element into this priority queue.
314	>	*
315	>	* @return {@code true} (as specified by {@link Collection#add})
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 add(E e) {
322	>	return offer(e);
323	>	}
324	>
325	>	/**
326	>	* Inserts the specified element into this priority queue.
327	>	*
328	>	* @return {@code true} (as specified by {@link Queue#offer})
329	>	* @throws ClassCastException if the specified element cannot be
330	>	*         compared with elements currently in this priority queue
331	>	*         according to the priority queue's ordering
332	>	* @throws NullPointerException if the specified element is null
333	>	*/
334	>	public boolean offer(E e) {
335	>	if (e == null)
336	>	throw new NullPointerException();
337	>	modCount++;
338	>	int i = size;
339	>	if (i >= queue.length)
340	>	grow(i + 1);
341	>	siftUp(i, e);
342	>	size = i + 1;
343	>	return true;
344		}
345	+
346	+	@SuppressWarnings("unchecked")
347		public E peek() {
348	<	return null;
348	>	return (size == 0) ? null : (E) queue[0];
349	>	}
350	>
351	>	private int indexOf(Object o) {
352	>	if (o != null) {
353	>	for (int i = 0; i < size; i++)
354	>	if (o.equals(queue[i]))
355	>	return i;
356	>	}
357	>	return -1;
358	>	}
359	>
360	>	/**
361	>	* Removes a single instance of the specified element from this queue,
362	>	* if it is present.  More formally, removes an element {@code e} such
363	>	* that {@code o.equals(e)}, if this queue contains one or more such
364	>	* elements.  Returns {@code true} if and only if this queue contained
365	>	* the specified element (or equivalently, if this queue changed as a
366	>	* result of the call).
367	>	*
368	>	* @param o element to be removed from this queue, if present
369	>	* @return {@code true} if this queue changed as a result of the call
370	>	*/
371	>	public boolean remove(Object o) {
372	>	int i = indexOf(o);
373	>	if (i == -1)
374	>	return false;
375	>	else {
376	>	removeAt(i);
377	>	return true;
378	>	}
379		}
380
381	<	public boolean isEmpty() {
381	>	/**
382	>	* Version of remove using reference equality, not equals.
383	>	* Needed by iterator.remove.
384	>	*
385	>	* @param o element to be removed from this queue, if present
386	>	* @return {@code true} if removed
387	>	*/
388	>	boolean removeEq(Object o) {
389	>	for (int i = 0; i < size; i++) {
390	>	if (o == queue[i]) {
391	>	removeAt(i);
392	>	return true;
393	>	}
394	>	}
395		return false;
396		}
397	<	public int size() {
398	<	return 0;
397	>
398	>	/**
399	>	* Returns {@code true} if this queue contains the specified element.
400	>	* More formally, returns {@code true} if and only if this queue contains
401	>	* at least one element {@code e} such that {@code o.equals(e)}.
402	>	*
403	>	* @param o object to be checked for containment in this queue
404	>	* @return {@code true} if this queue contains the specified element
405	>	*/
406	>	public boolean contains(Object o) {
407	>	return indexOf(o) >= 0;
408		}
409	+
410	+	/**
411	+	* Returns an array containing all of the elements in this queue.
412	+	* The elements are in no particular order.
413	+	*
414	+	* <p>The returned array will be "safe" in that no references to it are
415	+	* maintained by this queue.  (In other words, this method must allocate
416	+	* a new array).  The caller is thus free to modify the returned array.
417	+	*
418	+	* <p>This method acts as bridge between array-based and collection-based
419	+	* APIs.
420	+	*
421	+	* @return an array containing all of the elements in this queue
422	+	*/
423		public Object[] toArray() {
424	<	return null;
424	>	return Arrays.copyOf(queue, size);
425	>	}
426	>
427	>	/**
428	>	* Returns an array containing all of the elements in this queue; the
429	>	* runtime type of the returned array is that of the specified array.
430	>	* The returned array elements are in no particular order.
431	>	* If the queue fits in the specified array, it is returned therein.
432	>	* Otherwise, a new array is allocated with the runtime type of the
433	>	* specified array and the size of this queue.
434	>	*
435	>	* <p>If the queue fits in the specified array with room to spare
436	>	* (i.e., the array has more elements than the queue), the element in
437	>	* the array immediately following the end of the collection is set to
438	>	* {@code null}.
439	>	*
440	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
441	>	* array-based and collection-based APIs.  Further, this method allows
442	>	* precise control over the runtime type of the output array, and may,
443	>	* under certain circumstances, be used to save allocation costs.
444	>	*
445	>	* <p>Suppose {@code x} is a queue known to contain only strings.
446	>	* The following code can be used to dump the queue into a newly
447	>	* allocated array of {@code String}:
448	>	*
449	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
450	>	*
451	>	* Note that {@code toArray(new Object[0])} is identical in function to
452	>	* {@code toArray()}.
453	>	*
454	>	* @param a the array into which the elements of the queue are to
455	>	*          be stored, if it is big enough; otherwise, a new array of the
456	>	*          same runtime type is allocated for this purpose.
457	>	* @return an array containing all of the elements in this queue
458	>	* @throws ArrayStoreException if the runtime type of the specified array
459	>	*         is not a supertype of the runtime type of every element in
460	>	*         this queue
461	>	* @throws NullPointerException if the specified array is null
462	>	*/
463	>	@SuppressWarnings("unchecked")
464	>	public <T> T[] toArray(T[] a) {
465	>	final int size = this.size;
466	>	if (a.length < size)
467	>	// Make a new array of a's runtime type, but my contents:
468	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
469	>	System.arraycopy(queue, 0, a, 0, size);
470	>	if (a.length > size)
471	>	a[size] = null;
472	>	return a;
473	>	}
474	>
475	>	/**
476	>	* Returns an iterator over the elements in this queue. The iterator
477	>	* does not return the elements in any particular order.
478	>	*
479	>	* @return an iterator over the elements in this queue
480	>	*/
481	>	public Iterator<E> iterator() {
482	>	return new Itr();
483	>	}
484	>
485	>	private final class Itr implements Iterator<E> {
486	>	/**
487	>	* Index (into queue array) of element to be returned by
488	>	* subsequent call to next.
489	>	*/
490	>	private int cursor;
491	>
492	>	/**
493	>	* Index of element returned by most recent call to next,
494	>	* unless that element came from the forgetMeNot list.
495	>	* Set to -1 if element is deleted by a call to remove.
496	>	*/
497	>	private int lastRet = -1;
498	>
499	>	/**
500	>	* A queue of elements that were moved from the unvisited portion of
501	>	* the heap into the visited portion as a result of "unlucky" element
502	>	* removals during the iteration.  (Unlucky element removals are those
503	>	* that require a siftup instead of a siftdown.)  We must visit all of
504	>	* the elements in this list to complete the iteration.  We do this
505	>	* after we've completed the "normal" iteration.
506	>	*
507	>	* We expect that most iterations, even those involving removals,
508	>	* will not need to store elements in this field.
509	>	*/
510	>	private ArrayDeque<E> forgetMeNot;
511	>
512	>	/**
513	>	* Element returned by the most recent call to next iff that
514	>	* element was drawn from the forgetMeNot list.
515	>	*/
516	>	private E lastRetElt;
517	>
518	>	/**
519	>	* The modCount value that the iterator believes that the backing
520	>	* Queue should have.  If this expectation is violated, the iterator
521	>	* has detected concurrent modification.
522	>	*/
523	>	private int expectedModCount = modCount;
524	>
525	>	public boolean hasNext() {
526	>	return cursor < size ||
527	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
528	>	}
529	>
530	>	@SuppressWarnings("unchecked")
531	>	public E next() {
532	>	if (expectedModCount != modCount)
533	>	throw new ConcurrentModificationException();
534	>	if (cursor < size)
535	>	return (E) queue[lastRet = cursor++];
536	>	if (forgetMeNot != null) {
537	>	lastRet = -1;
538	>	lastRetElt = forgetMeNot.poll();
539	>	if (lastRetElt != null)
540	>	return lastRetElt;
541	>	}
542	>	throw new NoSuchElementException();
543	>	}
544	>
545	>	public void remove() {
546	>	if (expectedModCount != modCount)
547	>	throw new ConcurrentModificationException();
548	>	if (lastRet != -1) {
549	>	E moved = PriorityQueue.this.removeAt(lastRet);
550	>	lastRet = -1;
551	>	if (moved == null)
552	>	cursor--;
553	>	else {
554	>	if (forgetMeNot == null)
555	>	forgetMeNot = new ArrayDeque<>();
556	>	forgetMeNot.add(moved);
557	>	}
558	>	} else if (lastRetElt != null) {
559	>	PriorityQueue.this.removeEq(lastRetElt);
560	>	lastRetElt = null;
561	>	} else {
562	>	throw new IllegalStateException();
563	>	}
564	>	expectedModCount = modCount;
565	>	}
566		}
567
568	<	public <T> T[] toArray(T[] array) {
568	>	public int size() {
569	>	return size;
570	>	}
571	>
572	>	/**
573	>	* Removes all of the elements from this priority queue.
574	>	* The queue will be empty after this call returns.
575	>	*/
576	>	public void clear() {
577	>	modCount++;
578	>	for (int i = 0; i < size; i++)
579	>	queue[i] = null;
580	>	size = 0;
581	>	}
582	>
583	>	@SuppressWarnings("unchecked")
584	>	public E poll() {
585	>	if (size == 0)
586	>	return null;
587	>	int s = --size;
588	>	modCount++;
589	>	E result = (E) queue[0];
590	>	E x = (E) queue[s];
591	>	queue[s] = null;
592	>	if (s != 0)
593	>	siftDown(0, x);
594	>	return result;
595	>	}
596	>
597	>	/**
598	>	* Removes the ith element from queue.
599	>	*
600	>	* Normally this method leaves the elements at up to i-1,
601	>	* inclusive, untouched.  Under these circumstances, it returns
602	>	* null.  Occasionally, in order to maintain the heap invariant,
603	>	* it must swap a later element of the list with one earlier than
604	>	* i.  Under these circumstances, this method returns the element
605	>	* that was previously at the end of the list and is now at some
606	>	* position before i. This fact is used by iterator.remove so as to
607	>	* avoid missing traversing elements.
608	>	*/
609	>	@SuppressWarnings("unchecked")
610	>	E removeAt(int i) {
611	>	// assert i >= 0 && i < size;
612	>	modCount++;
613	>	int s = --size;
614	>	if (s == i) // removed last element
615	>	queue[i] = null;
616	>	else {
617	>	E moved = (E) queue[s];
618	>	queue[s] = null;
619	>	siftDown(i, moved);
620	>	if (queue[i] == moved) {
621	>	siftUp(i, moved);
622	>	if (queue[i] != moved)
623	>	return moved;
624	>	}
625	>	}
626		return null;
627		}
628
629	+	/**
630	+	* Inserts item x at position k, maintaining heap invariant by
631	+	* promoting x up the tree until it is greater than or equal to
632	+	* its parent, or is the root.
633	+	*
634	+	* To simplify and speed up coercions and comparisons. the
635	+	* Comparable and Comparator versions are separated into different
636	+	* methods that are otherwise identical. (Similarly for siftDown.)
637	+	*
638	+	* @param k the position to fill
639	+	* @param x the item to insert
640	+	*/
641	+	private void siftUp(int k, E x) {
642	+	if (comparator != null)
643	+	siftUpUsingComparator(k, x);
644	+	else
645	+	siftUpComparable(k, x);
646	+	}
647	+
648	+	@SuppressWarnings("unchecked")
649	+	private void siftUpComparable(int k, E x) {
650	+	Comparable<? super E> key = (Comparable<? super E>) x;
651	+	while (k > 0) {
652	+	int parent = (k - 1) >>> 1;
653	+	Object e = queue[parent];
654	+	if (key.compareTo((E) e) >= 0)
655	+	break;
656	+	queue[k] = e;
657	+	k = parent;
658	+	}
659	+	queue[k] = key;
660	+	}
661	+
662	+	@SuppressWarnings("unchecked")
663	+	private void siftUpUsingComparator(int k, E x) {
664	+	while (k > 0) {
665	+	int parent = (k - 1) >>> 1;
666	+	Object e = queue[parent];
667	+	if (comparator.compare(x, (E) e) >= 0)
668	+	break;
669	+	queue[k] = e;
670	+	k = parent;
671	+	}
672	+	queue[k] = x;
673	+	}
674	+
675	+	/**
676	+	* Inserts item x at position k, maintaining heap invariant by
677	+	* demoting x down the tree repeatedly until it is less than or
678	+	* equal to its children or is a leaf.
679	+	*
680	+	* @param k the position to fill
681	+	* @param x the item to insert
682	+	*/
683	+	private void siftDown(int k, E x) {
684	+	if (comparator != null)
685	+	siftDownUsingComparator(k, x);
686	+	else
687	+	siftDownComparable(k, x);
688	+	}
689	+
690	+	@SuppressWarnings("unchecked")
691	+	private void siftDownComparable(int k, E x) {
692	+	Comparable<? super E> key = (Comparable<? super E>)x;
693	+	int half = size >>> 1;        // loop while a non-leaf
694	+	while (k < half) {
695	+	int child = (k << 1) + 1; // assume left child is least
696	+	Object c = queue[child];
697	+	int right = child + 1;
698	+	if (right < size &&
699	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
700	+	c = queue[child = right];
701	+	if (key.compareTo((E) c) <= 0)
702	+	break;
703	+	queue[k] = c;
704	+	k = child;
705	+	}
706	+	queue[k] = key;
707	+	}
708	+
709	+	@SuppressWarnings("unchecked")
710	+	private void siftDownUsingComparator(int k, E x) {
711	+	int half = size >>> 1;
712	+	while (k < half) {
713	+	int child = (k << 1) + 1;
714	+	Object c = queue[child];
715	+	int right = child + 1;
716	+	if (right < size &&
717	+	comparator.compare((E) c, (E) queue[right]) > 0)
718	+	c = queue[child = right];
719	+	if (comparator.compare(x, (E) c) <= 0)
720	+	break;
721	+	queue[k] = c;
722	+	k = child;
723	+	}
724	+	queue[k] = x;
725	+	}
726	+
727	+	/**
728	+	* Establishes the heap invariant (described above) in the entire tree,
729	+	* assuming nothing about the order of the elements prior to the call.
730	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
731	+	*/
732	+	@SuppressWarnings("unchecked")
733	+	private void heapify() {
734	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
735	+	siftDown(i, (E) queue[i]);
736	+	}
737	+
738	+	/**
739	+	* Returns the comparator used to order the elements in this
740	+	* queue, or {@code null} if this queue is sorted according to
741	+	* the {@linkplain Comparable natural ordering} of its elements.
742	+	*
743	+	* @return the comparator used to order this queue, or
744	+	*         {@code null} if this queue is sorted according to the
745	+	*         natural ordering of its elements
746	+	*/
747	+	public Comparator<? super E> comparator() {
748	+	return comparator;
749	+	}
750	+
751	+	/**
752	+	* Saves this queue to a stream (that is, serializes it).
753	+	*
754	+	* @param s the stream
755	+	* @throws java.io.IOException if an I/O error occurs
756	+	* @serialData The length of the array backing the instance is
757	+	*             emitted (int), followed by all of its elements
758	+	*             (each an {@code Object}) in the proper order.
759	+	*/
760	+	private void writeObject(java.io.ObjectOutputStream s)
761	+	throws java.io.IOException {
762	+	// Write out element count, and any hidden stuff
763	+	s.defaultWriteObject();
764	+
765	+	// Write out array length, for compatibility with 1.5 version
766	+	s.writeInt(Math.max(2, size + 1));
767	+
768	+	// Write out all elements in the "proper order".
769	+	for (int i = 0; i < size; i++)
770	+	s.writeObject(queue[i]);
771	+	}
772	+
773	+	/**
774	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
775	+	* (that is, deserializes it).
776	+	*
777	+	* @param s the stream
778	+	* @throws ClassNotFoundException if the class of a serialized object
779	+	*         could not be found
780	+	* @throws java.io.IOException if an I/O error occurs
781	+	*/
782	+	private void readObject(java.io.ObjectInputStream s)
783	+	throws java.io.IOException, ClassNotFoundException {
784	+	// Read in size, and any hidden stuff
785	+	s.defaultReadObject();
786	+
787	+	// Read in (and discard) array length
788	+	s.readInt();
789	+
790	+	queue = new Object[size];
791	+
792	+	// Read in all elements.
793	+	for (int i = 0; i < size; i++)
794	+	queue[i] = s.readObject();
795	+
796	+	// Elements are guaranteed to be in "proper order", but the
797	+	// spec has never explained what that might be.
798	+	heapify();
799	+	}
800	+
801	+	/**
802	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
803	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
804	+	* queue. The spliterator does not traverse elements in any particular order
805	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
806	+	*
807	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
808	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
809	+	* Overriding implementations should document the reporting of additional
810	+	* characteristic values.
811	+	*
812	+	* @return a {@code Spliterator} over the elements in this queue
813	+	* @since 1.8
814	+	*/
815	+	public final Spliterator<E> spliterator() {
816	+	return new PriorityQueueSpliterator(0, -1, 0);
817	+	}
818	+
819	+	final class PriorityQueueSpliterator implements Spliterator<E> {
820	+	/*
821	+	* This is very similar to ArrayList Spliterator, except for
822	+	* extra null checks.
823	+	*/
824	+	private int index;            // current index, modified on advance/split
825	+	private int fence;            // -1 until first use
826	+	private int expectedModCount; // initialized when fence set
827	+
828	+	/** Creates new spliterator covering the given range. */
829	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
830	+	this.index = origin;
831	+	this.fence = fence;
832	+	this.expectedModCount = expectedModCount;
833	+	}
834	+
835	+	private int getFence() { // initialize fence to size on first use
836	+	int hi;
837	+	if ((hi = fence) < 0) {
838	+	expectedModCount = modCount;
839	+	hi = fence = size;
840	+	}
841	+	return hi;
842	+	}
843	+
844	+	public PriorityQueueSpliterator trySplit() {
845	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
846	+	return (lo >= mid) ? null :
847	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
848	+	}
849	+
850	+	@SuppressWarnings("unchecked")
851	+	public void forEachRemaining(Consumer<? super E> action) {
852	+	int i, hi, mc; // hoist accesses and checks from loop
853	+	final Object[] a;
854	+	if (action == null)
855	+	throw new NullPointerException();
856	+	if ((a = queue) != null) {
857	+	if ((hi = fence) < 0) {
858	+	mc = modCount;
859	+	hi = size;
860	+	}
861	+	else
862	+	mc = expectedModCount;
863	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
864	+	for (E e;; ++i) {
865	+	if (i < hi) {
866	+	if ((e = (E) a[i]) == null) // must be CME
867	+	break;
868	+	action.accept(e);
869	+	}
870	+	else if (modCount != mc)
871	+	break;
872	+	else
873	+	return;
874	+	}
875	+	}
876	+	}
877	+	throw new ConcurrentModificationException();
878	+	}
879	+
880	+	public boolean tryAdvance(Consumer<? super E> action) {
881	+	if (action == null)
882	+	throw new NullPointerException();
883	+	int hi = getFence(), lo = index;
884	+	if (lo >= 0 && lo < hi) {
885	+	index = lo + 1;
886	+	@SuppressWarnings("unchecked") E e = (E)queue[lo];
887	+	if (e == null)
888	+	throw new ConcurrentModificationException();
889	+	action.accept(e);
890	+	if (modCount != expectedModCount)
891	+	throw new ConcurrentModificationException();
892	+	return true;
893	+	}
894	+	return false;
895	+	}
896	+
897	+	public long estimateSize() {
898	+	return getFence() - index;
899	+	}
900	+
901	+	public int characteristics() {
902	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
903	+	}
904	+	}
905		}

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