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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 1.128 by jsr166, Sun May 6 23:29:25 2018 UTC

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1	+	/*
2	+	* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3	+	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	+	*
5	+	* This code is free software; you can redistribute it and/or modify it
6	+	* under the terms of the GNU General Public License version 2 only, as
7	+	* published by the Free Software Foundation.  Oracle designates this
8	+	* particular file as subject to the "Classpath" exception as provided
9	+	* by Oracle in the LICENSE file that accompanied this code.
10	+	*
11	+	* This code is distributed in the hope that it will be useful, but WITHOUT
12	+	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	+	* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14	+	* version 2 for more details (a copy is included in the LICENSE file that
15	+	* accompanied this code).
16	+	*
17	+	* You should have received a copy of the GNU General Public License version
18	+	* 2 along with this work; if not, write to the Free Software Foundation,
19	+	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20	+	*
21	+	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	+	* or visit www.oracle.com if you need additional information or have any
23	+	* questions.
24	+	*/
25	+
26		package java.util;
27
28	<	import java.util.*;
28	>	import java.util.function.Consumer;
29	>	import java.util.function.Predicate;
30	>	import jdk.internal.misc.SharedSecrets;
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) {}
45	<
46	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
47	<
48	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
49	<
50	<	public boolean add(E x) {
51	<	return false;
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()} and the Spliterator provided in method {@link #spliterator()}
60	>	* are <em>not</em> guaranteed to traverse the elements of
61	>	* the priority queue in any particular order. If you need ordered
62	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
63	>	*
64	>	* <p><strong>Note that this implementation is not synchronized.</strong>
65	>	* Multiple threads should not access a {@code PriorityQueue}
66	>	* instance concurrently if any of the threads modifies the queue.
67	>	* Instead, use the thread-safe {@link
68	>	* java.util.concurrent.PriorityBlockingQueue} class.
69	>	*
70	>	* <p>Implementation note: this implementation provides
71	>	* O(log(n)) time for the enqueuing and dequeuing methods
72	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
73	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
74	>	* methods; and constant time for the retrieval methods
75	>	* ({@code peek}, {@code element}, and {@code size}).
76	>	*
77	>	* <p>This class is a member of the
78	>	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
79	>	* Java Collections Framework</a>.
80	>	*
81	>	* @since 1.5
82	>	* @author Josh Bloch, Doug Lea
83	>	* @param <E> the type of elements held in this queue
84	>	*/
85	>	@SuppressWarnings("unchecked")
86	>	public class PriorityQueue<E> extends AbstractQueue<E>
87	>	implements java.io.Serializable {
88	>
89	>	private static final long serialVersionUID = -7720805057305804111L;
90	>
91	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
92	>
93	>	/**
94	>	* Priority queue represented as a balanced binary heap: the two
95	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
96	>	* priority queue is ordered by comparator, or by the elements'
97	>	* natural ordering, if comparator is null: For each node n in the
98	>	* heap and each descendant d of n, n <= d.  The element with the
99	>	* lowest value is in queue[0], assuming the queue is nonempty.
100	>	*/
101	>	transient Object[] queue; // non-private to simplify nested class access
102	>
103	>	/**
104	>	* The number of elements in the priority queue.
105	>	*/
106	>	int size;
107	>
108	>	/**
109	>	* The comparator, or null if priority queue uses elements'
110	>	* natural ordering.
111	>	*/
112	>	private final Comparator<? super E> comparator;
113	>
114	>	/**
115	>	* The number of times this priority queue has been
116	>	* <i>structurally modified</i>.  See AbstractList for gory details.
117	>	*/
118	>	transient int modCount;     // non-private to simplify nested class access
119	>
120	>	/**
121	>	* Creates a {@code PriorityQueue} with the default initial
122	>	* capacity (11) that orders its elements according to their
123	>	* {@linkplain Comparable natural ordering}.
124	>	*/
125	>	public PriorityQueue() {
126	>	this(DEFAULT_INITIAL_CAPACITY, null);
127		}
128	<	public boolean offer(E x) {
129	<	return false;
128	>
129	>	/**
130	>	* Creates a {@code PriorityQueue} with the specified initial
131	>	* capacity that orders its elements according to their
132	>	* {@linkplain Comparable natural ordering}.
133	>	*
134	>	* @param initialCapacity the initial capacity for this priority queue
135	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
136	>	*         than 1
137	>	*/
138	>	public PriorityQueue(int initialCapacity) {
139	>	this(initialCapacity, null);
140		}
141	<	public boolean remove(Object x) {
142	<	return false;
141	>
142	>	/**
143	>	* Creates a {@code PriorityQueue} with the default initial capacity and
144	>	* whose elements are ordered according to the specified comparator.
145	>	*
146	>	* @param  comparator the comparator that will be used to order this
147	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
148	>	*         natural ordering} of the elements will be used.
149	>	* @since 1.8
150	>	*/
151	>	public PriorityQueue(Comparator<? super E> comparator) {
152	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
153		}
154
155	<	public E remove() {
156	<	return null;
155	>	/**
156	>	* Creates a {@code PriorityQueue} with the specified initial capacity
157	>	* that orders its elements according to the specified comparator.
158	>	*
159	>	* @param  initialCapacity the initial capacity for this priority queue
160	>	* @param  comparator the comparator that will be used to order this
161	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
162	>	*         natural ordering} of the elements will be used.
163	>	* @throws IllegalArgumentException if {@code initialCapacity} is
164	>	*         less than 1
165	>	*/
166	>	public PriorityQueue(int initialCapacity,
167	>	Comparator<? super E> comparator) {
168	>	// Note: This restriction of at least one is not actually needed,
169	>	// but continues for 1.5 compatibility
170	>	if (initialCapacity < 1)
171	>	throw new IllegalArgumentException();
172	>	this.queue = new Object[initialCapacity];
173	>	this.comparator = comparator;
174		}
175	<	public Iterator<E> iterator() {
176	<	return null;
175	>
176	>	/**
177	>	* Creates a {@code PriorityQueue} containing the elements in the
178	>	* specified collection.  If the specified collection is an instance of
179	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
180	>	* priority queue will be ordered according to the same ordering.
181	>	* Otherwise, this priority queue will be ordered according to the
182	>	* {@linkplain Comparable natural ordering} of its elements.
183	>	*
184	>	* @param  c the collection whose elements are to be placed
185	>	*         into this priority queue
186	>	* @throws ClassCastException if elements of the specified collection
187	>	*         cannot be compared to one another according to the priority
188	>	*         queue's ordering
189	>	* @throws NullPointerException if the specified collection or any
190	>	*         of its elements are null
191	>	*/
192	>	public PriorityQueue(Collection<? extends E> c) {
193	>	if (c instanceof SortedSet<?>) {
194	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
195	>	this.comparator = (Comparator<? super E>) ss.comparator();
196	>	initElementsFromCollection(ss);
197	>	}
198	>	else if (c instanceof PriorityQueue<?>) {
199	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
200	>	this.comparator = (Comparator<? super E>) pq.comparator();
201	>	initFromPriorityQueue(pq);
202	>	}
203	>	else {
204	>	this.comparator = null;
205	>	initFromCollection(c);
206	>	}
207		}
208
209	<	public E element() {
210	<	return null;
209	>	/**
210	>	* Creates a {@code PriorityQueue} containing the elements in the
211	>	* specified priority queue.  This priority queue will be
212	>	* ordered according to the same ordering as the given priority
213	>	* queue.
214	>	*
215	>	* @param  c the priority queue whose elements are to be placed
216	>	*         into this priority queue
217	>	* @throws ClassCastException if elements of {@code c} cannot be
218	>	*         compared to one another according to {@code c}'s
219	>	*         ordering
220	>	* @throws NullPointerException if the specified priority queue or any
221	>	*         of its elements are null
222	>	*/
223	>	public PriorityQueue(PriorityQueue<? extends E> c) {
224	>	this.comparator = (Comparator<? super E>) c.comparator();
225	>	initFromPriorityQueue(c);
226		}
227	<	public E poll() {
228	<	return null;
227	>
228	>	/**
229	>	* Creates a {@code PriorityQueue} containing the elements in the
230	>	* specified sorted set.   This priority queue will be ordered
231	>	* according to the same ordering as the given sorted set.
232	>	*
233	>	* @param  c the sorted set whose elements are to be placed
234	>	*         into this priority queue
235	>	* @throws ClassCastException if elements of the specified sorted
236	>	*         set cannot be compared to one another according to the
237	>	*         sorted set's ordering
238	>	* @throws NullPointerException if the specified sorted set or any
239	>	*         of its elements are null
240	>	*/
241	>	public PriorityQueue(SortedSet<? extends E> c) {
242	>	this.comparator = (Comparator<? super E>) c.comparator();
243	>	initElementsFromCollection(c);
244	>	}
245	>
246	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
247	>	private static Object[] ensureNonEmpty(Object[] es) {
248	>	return (es.length > 0) ? es : new Object[1];
249	>	}
250	>
251	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
252	>	if (c.getClass() == PriorityQueue.class) {
253	>	this.queue = ensureNonEmpty(c.toArray());
254	>	this.size = c.size();
255	>	} else {
256	>	initFromCollection(c);
257	>	}
258	>	}
259	>
260	>	private void initElementsFromCollection(Collection<? extends E> c) {
261	>	Object[] es = c.toArray();
262	>	int len = es.length;
263	>	// If c.toArray incorrectly doesn't return Object[], copy it.
264	>	if (es.getClass() != Object[].class)
265	>	es = Arrays.copyOf(es, len, Object[].class);
266	>	if (len == 1 || this.comparator != null)
267	>	for (Object e : es)
268	>	if (e == null)
269	>	throw new NullPointerException();
270	>	this.queue = ensureNonEmpty(es);
271	>	this.size = len;
272	>	}
273	>
274	>	/**
275	>	* Initializes queue array with elements from the given Collection.
276	>	*
277	>	* @param c the collection
278	>	*/
279	>	private void initFromCollection(Collection<? extends E> c) {
280	>	initElementsFromCollection(c);
281	>	heapify();
282	>	}
283	>
284	>	/**
285	>	* The maximum size of array to allocate.
286	>	* Some VMs reserve some header words in an array.
287	>	* Attempts to allocate larger arrays may result in
288	>	* OutOfMemoryError: Requested array size exceeds VM limit
289	>	*/
290	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
291	>
292	>	/**
293	>	* Increases the capacity of the array.
294	>	*
295	>	* @param minCapacity the desired minimum capacity
296	>	*/
297	>	private void grow(int minCapacity) {
298	>	int oldCapacity = queue.length;
299	>	// Double size if small; else grow by 50%
300	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
301	>	(oldCapacity + 2) :
302	>	(oldCapacity >> 1));
303	>	// overflow-conscious code
304	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
305	>	newCapacity = hugeCapacity(minCapacity);
306	>	queue = Arrays.copyOf(queue, newCapacity);
307	>	}
308	>
309	>	private static int hugeCapacity(int minCapacity) {
310	>	if (minCapacity < 0) // overflow
311	>	throw new OutOfMemoryError();
312	>	return (minCapacity > MAX_ARRAY_SIZE) ?
313	>	Integer.MAX_VALUE :
314	>	MAX_ARRAY_SIZE;
315		}
316	+
317	+	/**
318	+	* Inserts the specified element into this priority queue.
319	+	*
320	+	* @return {@code true} (as specified by {@link Collection#add})
321	+	* @throws ClassCastException if the specified element cannot be
322	+	*         compared with elements currently in this priority queue
323	+	*         according to the priority queue's ordering
324	+	* @throws NullPointerException if the specified element is null
325	+	*/
326	+	public boolean add(E e) {
327	+	return offer(e);
328	+	}
329	+
330	+	/**
331	+	* Inserts the specified element into this priority queue.
332	+	*
333	+	* @return {@code true} (as specified by {@link Queue#offer})
334	+	* @throws ClassCastException if the specified element cannot be
335	+	*         compared with elements currently in this priority queue
336	+	*         according to the priority queue's ordering
337	+	* @throws NullPointerException if the specified element is null
338	+	*/
339	+	public boolean offer(E e) {
340	+	if (e == null)
341	+	throw new NullPointerException();
342	+	modCount++;
343	+	int i = size;
344	+	if (i >= queue.length)
345	+	grow(i + 1);
346	+	siftUp(i, e);
347	+	size = i + 1;
348	+	return true;
349	+	}
350	+
351		public E peek() {
352	<	return null;
352	>	return (E) queue[0];
353		}
354
355	<	public boolean isEmpty() {
356	<	return false;
355	>	private int indexOf(Object o) {
356	>	if (o != null) {
357	>	final Object[] es = queue;
358	>	for (int i = 0, n = size; i < n; i++)
359	>	if (o.equals(es[i]))
360	>	return i;
361	>	}
362	>	return -1;
363		}
364	<	public int size() {
365	<	return 0;
364	>
365	>	/**
366	>	* Removes a single instance of the specified element from this queue,
367	>	* if it is present.  More formally, removes an element {@code e} such
368	>	* that {@code o.equals(e)}, if this queue contains one or more such
369	>	* elements.  Returns {@code true} if and only if this queue contained
370	>	* the specified element (or equivalently, if this queue changed as a
371	>	* result of the call).
372	>	*
373	>	* @param o element to be removed from this queue, if present
374	>	* @return {@code true} if this queue changed as a result of the call
375	>	*/
376	>	public boolean remove(Object o) {
377	>	int i = indexOf(o);
378	>	if (i == -1)
379	>	return false;
380	>	else {
381	>	removeAt(i);
382	>	return true;
383	>	}
384		}
385	+
386	+	/**
387	+	* Identity-based version for use in Itr.remove.
388	+	*
389	+	* @param o element to be removed from this queue, if present
390	+	*/
391	+	void removeEq(Object o) {
392	+	final Object[] es = queue;
393	+	for (int i = 0, n = size; i < n; i++) {
394	+	if (o == es[i]) {
395	+	removeAt(i);
396	+	break;
397	+	}
398	+	}
399	+	}
400	+
401	+	/**
402	+	* Returns {@code true} if this queue contains the specified element.
403	+	* More formally, returns {@code true} if and only if this queue contains
404	+	* at least one element {@code e} such that {@code o.equals(e)}.
405	+	*
406	+	* @param o object to be checked for containment in this queue
407	+	* @return {@code true} if this queue contains the specified element
408	+	*/
409	+	public boolean contains(Object o) {
410	+	return indexOf(o) >= 0;
411	+	}
412	+
413	+	/**
414	+	* Returns an array containing all of the elements in this queue.
415	+	* The elements are in no particular order.
416	+	*
417	+	* <p>The returned array will be "safe" in that no references to it are
418	+	* maintained by this queue.  (In other words, this method must allocate
419	+	* a new array).  The caller is thus free to modify the returned array.
420	+	*
421	+	* <p>This method acts as bridge between array-based and collection-based
422	+	* APIs.
423	+	*
424	+	* @return an array containing all of the elements in this queue
425	+	*/
426		public Object[] toArray() {
427	<	return null;
427	>	return Arrays.copyOf(queue, size);
428	>	}
429	>
430	>	/**
431	>	* Returns an array containing all of the elements in this queue; the
432	>	* runtime type of the returned array is that of the specified array.
433	>	* The returned array elements are in no particular order.
434	>	* If the queue fits in the specified array, it is returned therein.
435	>	* Otherwise, a new array is allocated with the runtime type of the
436	>	* specified array and the size of this queue.
437	>	*
438	>	* <p>If the queue fits in the specified array with room to spare
439	>	* (i.e., the array has more elements than the queue), the element in
440	>	* the array immediately following the end of the collection is set to
441	>	* {@code null}.
442	>	*
443	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
444	>	* array-based and collection-based APIs.  Further, this method allows
445	>	* precise control over the runtime type of the output array, and may,
446	>	* under certain circumstances, be used to save allocation costs.
447	>	*
448	>	* <p>Suppose {@code x} is a queue known to contain only strings.
449	>	* The following code can be used to dump the queue into a newly
450	>	* allocated array of {@code String}:
451	>	*
452	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
453	>	*
454	>	* Note that {@code toArray(new Object[0])} is identical in function to
455	>	* {@code toArray()}.
456	>	*
457	>	* @param a the array into which the elements of the queue are to
458	>	*          be stored, if it is big enough; otherwise, a new array of the
459	>	*          same runtime type is allocated for this purpose.
460	>	* @return an array containing all of the elements in this queue
461	>	* @throws ArrayStoreException if the runtime type of the specified array
462	>	*         is not a supertype of the runtime type of every element in
463	>	*         this queue
464	>	* @throws NullPointerException if the specified array is null
465	>	*/
466	>	public <T> T[] toArray(T[] a) {
467	>	final int size = this.size;
468	>	if (a.length < size)
469	>	// Make a new array of a's runtime type, but my contents:
470	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
471	>	System.arraycopy(queue, 0, a, 0, size);
472	>	if (a.length > size)
473	>	a[size] = null;
474	>	return a;
475	>	}
476	>
477	>	/**
478	>	* Returns an iterator over the elements in this queue. The iterator
479	>	* does not return the elements in any particular order.
480	>	*
481	>	* @return an iterator over the elements in this queue
482	>	*/
483	>	public Iterator<E> iterator() {
484	>	return new Itr();
485		}
486
487	<	public <T> T[] toArray(T[] array) {
487	>	private final class Itr implements Iterator<E> {
488	>	/**
489	>	* Index (into queue array) of element to be returned by
490	>	* subsequent call to next.
491	>	*/
492	>	private int cursor;
493	>
494	>	/**
495	>	* Index of element returned by most recent call to next,
496	>	* unless that element came from the forgetMeNot list.
497	>	* Set to -1 if element is deleted by a call to remove.
498	>	*/
499	>	private int lastRet = -1;
500	>
501	>	/**
502	>	* A queue of elements that were moved from the unvisited portion of
503	>	* the heap into the visited portion as a result of "unlucky" element
504	>	* removals during the iteration.  (Unlucky element removals are those
505	>	* that require a siftup instead of a siftdown.)  We must visit all of
506	>	* the elements in this list to complete the iteration.  We do this
507	>	* after we've completed the "normal" iteration.
508	>	*
509	>	* We expect that most iterations, even those involving removals,
510	>	* will not need to store elements in this field.
511	>	*/
512	>	private ArrayDeque<E> forgetMeNot;
513	>
514	>	/**
515	>	* Element returned by the most recent call to next iff that
516	>	* element was drawn from the forgetMeNot list.
517	>	*/
518	>	private E lastRetElt;
519	>
520	>	/**
521	>	* The modCount value that the iterator believes that the backing
522	>	* Queue should have.  If this expectation is violated, the iterator
523	>	* has detected concurrent modification.
524	>	*/
525	>	private int expectedModCount = modCount;
526	>
527	>	Itr() {}                        // prevent access constructor creation
528	>
529	>	public boolean hasNext() {
530	>	return cursor < size ||
531	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
532	>	}
533	>
534	>	public E next() {
535	>	if (expectedModCount != modCount)
536	>	throw new ConcurrentModificationException();
537	>	if (cursor < size)
538	>	return (E) queue[lastRet = cursor++];
539	>	if (forgetMeNot != null) {
540	>	lastRet = -1;
541	>	lastRetElt = forgetMeNot.poll();
542	>	if (lastRetElt != null)
543	>	return lastRetElt;
544	>	}
545	>	throw new NoSuchElementException();
546	>	}
547	>
548	>	public void remove() {
549	>	if (expectedModCount != modCount)
550	>	throw new ConcurrentModificationException();
551	>	if (lastRet != -1) {
552	>	E moved = PriorityQueue.this.removeAt(lastRet);
553	>	lastRet = -1;
554	>	if (moved == null)
555	>	cursor--;
556	>	else {
557	>	if (forgetMeNot == null)
558	>	forgetMeNot = new ArrayDeque<>();
559	>	forgetMeNot.add(moved);
560	>	}
561	>	} else if (lastRetElt != null) {
562	>	PriorityQueue.this.removeEq(lastRetElt);
563	>	lastRetElt = null;
564	>	} else {
565	>	throw new IllegalStateException();
566	>	}
567	>	expectedModCount = modCount;
568	>	}
569	>	}
570	>
571	>	public int size() {
572	>	return size;
573	>	}
574	>
575	>	/**
576	>	* Removes all of the elements from this priority queue.
577	>	* The queue will be empty after this call returns.
578	>	*/
579	>	public void clear() {
580	>	modCount++;
581	>	final Object[] es = queue;
582	>	for (int i = 0, n = size; i < n; i++)
583	>	es[i] = null;
584	>	size = 0;
585	>	}
586	>
587	>	public E poll() {
588	>	final Object[] es;
589	>	final E result;
590	>
591	>	if ((result = (E) ((es = queue)[0])) != null) {
592	>	modCount++;
593	>	final int n;
594	>	final E x = (E) es[(n = --size)];
595	>	es[n] = null;
596	>	if (n > 0) {
597	>	final Comparator<? super E> cmp;
598	>	if ((cmp = comparator) == null)
599	>	siftDownComparable(0, x, es, n);
600	>	else
601	>	siftDownUsingComparator(0, x, es, n, cmp);
602	>	}
603	>	}
604	>	return result;
605	>	}
606	>
607	>	/**
608	>	* Removes the ith element from queue.
609	>	*
610	>	* Normally this method leaves the elements at up to i-1,
611	>	* inclusive, untouched.  Under these circumstances, it returns
612	>	* null.  Occasionally, in order to maintain the heap invariant,
613	>	* it must swap a later element of the list with one earlier than
614	>	* i.  Under these circumstances, this method returns the element
615	>	* that was previously at the end of the list and is now at some
616	>	* position before i. This fact is used by iterator.remove so as to
617	>	* avoid missing traversing elements.
618	>	*/
619	>	E removeAt(int i) {
620	>	// assert i >= 0 && i < size;
621	>	final Object[] es = queue;
622	>	modCount++;
623	>	int s = --size;
624	>	if (s == i) // removed last element
625	>	es[i] = null;
626	>	else {
627	>	E moved = (E) es[s];
628	>	es[s] = null;
629	>	siftDown(i, moved);
630	>	if (es[i] == moved) {
631	>	siftUp(i, moved);
632	>	if (es[i] != moved)
633	>	return moved;
634	>	}
635	>	}
636		return null;
637		}
638
639	+	/**
640	+	* Inserts item x at position k, maintaining heap invariant by
641	+	* promoting x up the tree until it is greater than or equal to
642	+	* its parent, or is the root.
643	+	*
644	+	* To simplify and speed up coercions and comparisons, the
645	+	* Comparable and Comparator versions are separated into different
646	+	* methods that are otherwise identical. (Similarly for siftDown.)
647	+	*
648	+	* @param k the position to fill
649	+	* @param x the item to insert
650	+	*/
651	+	private void siftUp(int k, E x) {
652	+	if (comparator != null)
653	+	siftUpUsingComparator(k, x, queue, comparator);
654	+	else
655	+	siftUpComparable(k, x, queue);
656	+	}
657	+
658	+	private static <T> void siftUpComparable(int k, T x, Object[] es) {
659	+	Comparable<? super T> key = (Comparable<? super T>) x;
660	+	while (k > 0) {
661	+	int parent = (k - 1) >>> 1;
662	+	Object e = es[parent];
663	+	if (key.compareTo((T) e) >= 0)
664	+	break;
665	+	es[k] = e;
666	+	k = parent;
667	+	}
668	+	es[k] = key;
669	+	}
670	+
671	+	private static <T> void siftUpUsingComparator(
672	+	int k, T x, Object[] es, Comparator<? super T> cmp) {
673	+	while (k > 0) {
674	+	int parent = (k - 1) >>> 1;
675	+	Object e = es[parent];
676	+	if (cmp.compare(x, (T) e) >= 0)
677	+	break;
678	+	es[k] = e;
679	+	k = parent;
680	+	}
681	+	es[k] = x;
682	+	}
683	+
684	+	/**
685	+	* Inserts item x at position k, maintaining heap invariant by
686	+	* demoting x down the tree repeatedly until it is less than or
687	+	* equal to its children or is a leaf.
688	+	*
689	+	* @param k the position to fill
690	+	* @param x the item to insert
691	+	*/
692	+	private void siftDown(int k, E x) {
693	+	if (comparator != null)
694	+	siftDownUsingComparator(k, x, queue, size, comparator);
695	+	else
696	+	siftDownComparable(k, x, queue, size);
697	+	}
698	+
699	+	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
700	+	// assert n > 0;
701	+	Comparable<? super T> key = (Comparable<? super T>)x;
702	+	int half = n >>> 1;           // loop while a non-leaf
703	+	while (k < half) {
704	+	int child = (k << 1) + 1; // assume left child is least
705	+	Object c = es[child];
706	+	int right = child + 1;
707	+	if (right < n &&
708	+	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
709	+	c = es[child = right];
710	+	if (key.compareTo((T) c) <= 0)
711	+	break;
712	+	es[k] = c;
713	+	k = child;
714	+	}
715	+	es[k] = key;
716	+	}
717	+
718	+	private static <T> void siftDownUsingComparator(
719	+	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
720	+	// assert n > 0;
721	+	int half = n >>> 1;
722	+	while (k < half) {
723	+	int child = (k << 1) + 1;
724	+	Object c = es[child];
725	+	int right = child + 1;
726	+	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
727	+	c = es[child = right];
728	+	if (cmp.compare(x, (T) c) <= 0)
729	+	break;
730	+	es[k] = c;
731	+	k = child;
732	+	}
733	+	es[k] = x;
734	+	}
735	+
736	+	/**
737	+	* Establishes the heap invariant (described above) in the entire tree,
738	+	* assuming nothing about the order of the elements prior to the call.
739	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
740	+	*/
741	+	private void heapify() {
742	+	final Object[] es = queue;
743	+	int n = size, i = (n >>> 1) - 1;
744	+	final Comparator<? super E> cmp;
745	+	if ((cmp = comparator) == null)
746	+	for (; i >= 0; i--)
747	+	siftDownComparable(i, (E) es[i], es, n);
748	+	else
749	+	for (; i >= 0; i--)
750	+	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
751	+	}
752	+
753	+	/**
754	+	* Returns the comparator used to order the elements in this
755	+	* queue, or {@code null} if this queue is sorted according to
756	+	* the {@linkplain Comparable natural ordering} of its elements.
757	+	*
758	+	* @return the comparator used to order this queue, or
759	+	*         {@code null} if this queue is sorted according to the
760	+	*         natural ordering of its elements
761	+	*/
762	+	public Comparator<? super E> comparator() {
763	+	return comparator;
764	+	}
765	+
766	+	/**
767	+	* Saves this queue to a stream (that is, serializes it).
768	+	*
769	+	* @param s the stream
770	+	* @throws java.io.IOException if an I/O error occurs
771	+	* @serialData The length of the array backing the instance is
772	+	*             emitted (int), followed by all of its elements
773	+	*             (each an {@code Object}) in the proper order.
774	+	*/
775	+	private void writeObject(java.io.ObjectOutputStream s)
776	+	throws java.io.IOException {
777	+	// Write out element count, and any hidden stuff
778	+	s.defaultWriteObject();
779	+
780	+	// Write out array length, for compatibility with 1.5 version
781	+	s.writeInt(Math.max(2, size + 1));
782	+
783	+	// Write out all elements in the "proper order".
784	+	final Object[] es = queue;
785	+	for (int i = 0, n = size; i < n; i++)
786	+	s.writeObject(es[i]);
787	+	}
788	+
789	+	/**
790	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
791	+	* (that is, deserializes it).
792	+	*
793	+	* @param s the stream
794	+	* @throws ClassNotFoundException if the class of a serialized object
795	+	*         could not be found
796	+	* @throws java.io.IOException if an I/O error occurs
797	+	*/
798	+	private void readObject(java.io.ObjectInputStream s)
799	+	throws java.io.IOException, ClassNotFoundException {
800	+	// Read in size, and any hidden stuff
801	+	s.defaultReadObject();
802	+
803	+	// Read in (and discard) array length
804	+	s.readInt();
805	+
806	+	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
807	+	final Object[] es = queue = new Object[Math.max(size, 1)];
808	+
809	+	// Read in all elements.
810	+	for (int i = 0, n = size; i < n; i++)
811	+	es[i] = s.readObject();
812	+
813	+	// Elements are guaranteed to be in "proper order", but the
814	+	// spec has never explained what that might be.
815	+	heapify();
816	+	}
817	+
818	+	/**
819	+	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
820	+	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
821	+	* queue. The spliterator does not traverse elements in any particular order
822	+	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
823	+	*
824	+	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
825	+	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
826	+	* Overriding implementations should document the reporting of additional
827	+	* characteristic values.
828	+	*
829	+	* @return a {@code Spliterator} over the elements in this queue
830	+	* @since 1.8
831	+	*/
832	+	public final Spliterator<E> spliterator() {
833	+	return new PriorityQueueSpliterator(0, -1, 0);
834	+	}
835	+
836	+	final class PriorityQueueSpliterator implements Spliterator<E> {
837	+	private int index;            // current index, modified on advance/split
838	+	private int fence;            // -1 until first use
839	+	private int expectedModCount; // initialized when fence set
840	+
841	+	/** Creates new spliterator covering the given range. */
842	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
843	+	this.index = origin;
844	+	this.fence = fence;
845	+	this.expectedModCount = expectedModCount;
846	+	}
847	+
848	+	private int getFence() { // initialize fence to size on first use
849	+	int hi;
850	+	if ((hi = fence) < 0) {
851	+	expectedModCount = modCount;
852	+	hi = fence = size;
853	+	}
854	+	return hi;
855	+	}
856	+
857	+	public PriorityQueueSpliterator trySplit() {
858	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
859	+	return (lo >= mid) ? null :
860	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
861	+	}
862	+
863	+	public void forEachRemaining(Consumer<? super E> action) {
864	+	if (action == null)
865	+	throw new NullPointerException();
866	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
867	+	final Object[] es = queue;
868	+	int i, hi; E e;
869	+	for (i = index, index = hi = fence; i < hi; i++) {
870	+	if ((e = (E) es[i]) == null)
871	+	break;      // must be CME
872	+	action.accept(e);
873	+	}
874	+	if (modCount != expectedModCount)
875	+	throw new ConcurrentModificationException();
876	+	}
877	+
878	+	public boolean tryAdvance(Consumer<? super E> action) {
879	+	if (action == null)
880	+	throw new NullPointerException();
881	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
882	+	int i;
883	+	if ((i = index) < fence) {
884	+	index = i + 1;
885	+	E e;
886	+	if ((e = (E) queue[i]) == null
887	+	|| modCount != expectedModCount)
888	+	throw new ConcurrentModificationException();
889	+	action.accept(e);
890	+	return true;
891	+	}
892	+	return false;
893	+	}
894	+
895	+	public long estimateSize() {
896	+	return getFence() - index;
897	+	}
898	+
899	+	public int characteristics() {
900	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
901	+	}
902	+	}
903	+
904	+	/**
905	+	* @throws NullPointerException {@inheritDoc}
906	+	*/
907	+	public boolean removeIf(Predicate<? super E> filter) {
908	+	Objects.requireNonNull(filter);
909	+	return bulkRemove(filter);
910	+	}
911	+
912	+	/**
913	+	* @throws NullPointerException {@inheritDoc}
914	+	*/
915	+	public boolean removeAll(Collection<?> c) {
916	+	Objects.requireNonNull(c);
917	+	return bulkRemove(e -> c.contains(e));
918	+	}
919	+
920	+	/**
921	+	* @throws NullPointerException {@inheritDoc}
922	+	*/
923	+	public boolean retainAll(Collection<?> c) {
924	+	Objects.requireNonNull(c);
925	+	return bulkRemove(e -> !c.contains(e));
926	+	}
927	+
928	+	// A tiny bit set implementation
929	+
930	+	private static long[] nBits(int n) {
931	+	return new long[((n - 1) >> 6) + 1];
932	+	}
933	+	private static void setBit(long[] bits, int i) {
934	+	bits[i >> 6] |= 1L << i;
935	+	}
936	+	private static boolean isClear(long[] bits, int i) {
937	+	return (bits[i >> 6] & (1L << i)) == 0;
938	+	}
939	+
940	+	/** Implementation of bulk remove methods. */
941	+	private boolean bulkRemove(Predicate<? super E> filter) {
942	+	final int expectedModCount = ++modCount;
943	+	final Object[] es = queue;
944	+	final int end = size;
945	+	int i;
946	+	// Optimize for initial run of survivors
947	+	for (i = 0; i < end && !filter.test((E) es[i]); i++)
948	+	;
949	+	if (i >= end) {
950	+	if (modCount != expectedModCount)
951	+	throw new ConcurrentModificationException();
952	+	return false;
953	+	}
954	+	// Tolerate predicates that reentrantly access the collection for
955	+	// read (but writers still get CME), so traverse once to find
956	+	// elements to delete, a second pass to physically expunge.
957	+	final int beg = i;
958	+	final long[] deathRow = nBits(end - beg);
959	+	deathRow[0] = 1L;   // set bit 0
960	+	for (i = beg + 1; i < end; i++)
961	+	if (filter.test((E) es[i]))
962	+	setBit(deathRow, i - beg);
963	+	if (modCount != expectedModCount)
964	+	throw new ConcurrentModificationException();
965	+	int w = beg;
966	+	for (i = beg; i < end; i++)
967	+	if (isClear(deathRow, i - beg))
968	+	es[w++] = es[i];
969	+	for (i = size = w; i < end; i++)
970	+	es[i] = null;
971	+	heapify();
972	+	return true;
973	+	}
974	+
975	+	/**
976	+	* @throws NullPointerException {@inheritDoc}
977	+	*/
978	+	public void forEach(Consumer<? super E> action) {
979	+	Objects.requireNonNull(action);
980	+	final int expectedModCount = modCount;
981	+	final Object[] es = queue;
982	+	for (int i = 0, n = size; i < n; i++)
983	+	action.accept((E) es[i]);
984	+	if (expectedModCount != modCount)
985	+	throw new ConcurrentModificationException();
986	+	}
987		}

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