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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.4 by tim, Mon May 19 02:45:07 2003 UTC vs.
Revision 1.132 by jsr166, Fri Aug 30 18:05:39 2019 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* Copyright (c) 2003, 2019, 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	<	*   1) Make it serializable.
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.function.Consumer;
29	+	import java.util.function.Predicate;
30	+	// OPENJDK import jdk.internal.access.SharedSecrets;
31	+	import jdk.internal.util.ArraysSupport;
32	+
33		/**
34	<	* An unbounded priority queue based on a priority heap.  This queue orders
35	<	* elements according to the order specified at creation time.  This order is
36	<	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
37	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
38	<	* according to a {@link Comparator}, depending on which constructor is used.
39	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
40	<	* minimal element with respect to the specified ordering.  If multiple
41	<	* these elements are tied for least value, no guarantees are made as to
42	<	* which of elements is returned.
43	<	*
44	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
45	<	* the array used to store the elements on the queue.  It is always at least
46	<	* as large as the queue size.  As elements are added to a priority list,
47	<	* its capacity grows automatically.  The details of the growth policy are not
34	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
35	>	* The elements of the priority queue are ordered according to their
36	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
37	>	* provided at queue construction time, depending on which constructor is
38	>	* used.  A priority queue does not permit {@code null} elements.
39	>	* A priority queue relying on natural ordering also does not permit
40	>	* insertion of non-comparable objects (doing so may result in
41	>	* {@code ClassCastException}).
42	>	*
43	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
44	>	* with respect to the specified ordering.  If multiple elements are
45	>	* tied for least value, the head is one of those elements -- ties are
46	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
47	>	* {@code remove}, {@code peek}, and {@code element} access the
48	>	* element at the head of the queue.
49	>	*
50	>	* <p>A priority queue is unbounded, but has an internal
51	>	* <i>capacity</i> governing the size of an array used to store the
52	>	* elements on the queue.  It is always at least as large as the queue
53	>	* size.  As elements are added to a priority queue, its capacity
54	>	* grows automatically.  The details of the growth policy are not
55		* specified.
56		*
57	<	*<p>Implementation note: this implementation provides O(log(n)) time for
58	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
59	<	* methods; linear time for the <tt>remove(Object)</tt> and
60	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
61	<	* <tt>element</tt>, and <tt>size</tt> methods.
57	>	* <p>This class and its iterator implement all of the
58	>	* <em>optional</em> methods of the {@link Collection} and {@link
59	>	* Iterator} interfaces.  The Iterator provided in method {@link
60	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
61	>	* are <em>not</em> guaranteed to traverse the elements of
62	>	* the priority queue in any particular order. If you need ordered
63	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
64	>	*
65	>	* <p><strong>Note that this implementation is not synchronized.</strong>
66	>	* Multiple threads should not access a {@code PriorityQueue}
67	>	* instance concurrently if any of the threads modifies the queue.
68	>	* Instead, use the thread-safe {@link
69	>	* java.util.concurrent.PriorityBlockingQueue} class.
70	>	*
71	>	* <p>Implementation note: this implementation provides
72	>	* O(log(n)) time for the enqueuing and dequeuing methods
73	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
74	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
75	>	* methods; and constant time for the retrieval methods
76	>	* ({@code peek}, {@code element}, and {@code size}).
77		*
78		* <p>This class is a member of the
79	<	* <a href="{@docRoot}/../guide/collections/index.html">
79	>	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
80		* Java Collections Framework</a>.
81	+	*
82	+	* @since 1.5
83	+	* @author Josh Bloch, Doug Lea
84	+	* @param <E> the type of elements held in this queue
85		*/
86	+	@SuppressWarnings("unchecked")
87		public class PriorityQueue<E> extends AbstractQueue<E>
88	<	implements Queue<E>
89	<	{
88	>	implements java.io.Serializable {
89	>
90	>	// OPENJDK @java.io.Serial
91	>	private static final long serialVersionUID = -7720805057305804111L;
92	>
93		private static final int DEFAULT_INITIAL_CAPACITY = 11;
94
95		/**
96	<	* Priority queue represented as a balanced binary heap: the two children
97	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
98	<	* ordered by comparator, or by the elements' natural ordering, if
99	<	* comparator is null:  For each node n in the heap, and each descendant
100	<	* of n, d, n <= d.
101	<	*
48	<	* The element with the lowest value is in queue[1] (assuming the queue is
49	<	* nonempty). A one-based array is used in preference to the traditional
50	<	* zero-based array to simplify parent and child calculations.
51	<	*
52	<	* queue.length must be >= 2, even if size == 0.
96	>	* Priority queue represented as a balanced binary heap: the two
97	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
98	>	* priority queue is ordered by comparator, or by the elements'
99	>	* natural ordering, if comparator is null: For each node n in the
100	>	* heap and each descendant d of n, n <= d.  The element with the
101	>	* lowest value is in queue[0], assuming the queue is nonempty.
102		*/
103	<	private E[] queue;
103	>	transient Object[] queue; // non-private to simplify nested class access
104
105		/**
106		* The number of elements in the priority queue.
107		*/
108	<	private int size = 0;
108	>	int size;
109
110		/**
111		* The comparator, or null if priority queue uses elements'
112		* natural ordering.
113		*/
114	<	private final Comparator<E> comparator;
114	>	private final Comparator<? super E> comparator;
115
116		/**
117		* The number of times this priority queue has been
118		* <i>structurally modified</i>.  See AbstractList for gory details.
119		*/
120	<	private int modCount = 0;
120	>	transient int modCount;     // non-private to simplify nested class access
121
122		/**
123	<	* Create a new priority queue with the default initial capacity (11)
124	<	* that orders its elements according to their natural ordering.
123	>	* Creates a {@code PriorityQueue} with the default initial
124	>	* capacity (11) that orders its elements according to their
125	>	* {@linkplain Comparable natural ordering}.
126		*/
127		public PriorityQueue() {
128	<	this(DEFAULT_INITIAL_CAPACITY);
128	>	this(DEFAULT_INITIAL_CAPACITY, null);
129		}
130
131		/**
132	<	* Create a new priority queue with the specified initial capacity
133	<	* that orders its elements according to their natural ordering.
132	>	* Creates a {@code PriorityQueue} with the specified initial
133	>	* capacity that orders its elements according to their
134	>	* {@linkplain Comparable natural ordering}.
135		*
136	<	* @param initialCapacity the initial capacity for this priority queue.
136	>	* @param initialCapacity the initial capacity for this priority queue
137	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
138	>	*         than 1
139		*/
140		public PriorityQueue(int initialCapacity) {
141		this(initialCapacity, null);
142		}
143
144		/**
145	<	* Create a new priority queue with the specified initial capacity (11)
146	<	* that orders its elements according to the specified comparator.
145	>	* Creates a {@code PriorityQueue} with the default initial capacity and
146	>	* whose elements are ordered according to the specified comparator.
147		*
148	<	* @param initialCapacity the initial capacity for this priority queue.
149	<	* @param comparator the comparator used to order this priority queue.
148	>	* @param  comparator the comparator that will be used to order this
149	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
150	>	*         natural ordering} of the elements will be used.
151	>	* @since 1.8
152		*/
153	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
153	>	public PriorityQueue(Comparator<? super E> comparator) {
154	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
155	>	}
156	>
157	>	/**
158	>	* Creates a {@code PriorityQueue} with the specified initial capacity
159	>	* that orders its elements according to the specified comparator.
160	>	*
161	>	* @param  initialCapacity the initial capacity for this priority queue
162	>	* @param  comparator the comparator that will be used to order this
163	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
164	>	*         natural ordering} of the elements will be used.
165	>	* @throws IllegalArgumentException if {@code initialCapacity} is
166	>	*         less than 1
167	>	*/
168	>	public PriorityQueue(int initialCapacity,
169	>	Comparator<? super E> comparator) {
170	>	// Note: This restriction of at least one is not actually needed,
171	>	// but continues for 1.5 compatibility
172		if (initialCapacity < 1)
173	<	initialCapacity = 1;
174	<	queue = new E[initialCapacity + 1];
173	>	throw new IllegalArgumentException();
174	>	this.queue = new Object[initialCapacity];
175		this.comparator = comparator;
176		}
177
178		/**
179	<	* Create a new priority queue containing the elements in the specified
180	<	* collection.  The priority queue has an initial capacity of 110% of the
181	<	* size of the specified collection. If the specified collection
182	<	* implements the {@link Sorted} interface, the priority queue will be
183	<	* sorted according to the same comparator, or according to its elements'
184	<	* natural order if the collection is sorted according to its elements'
112	<	* natural order.  If the specified collection does not implement the
113	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
114	<	* its elements' natural order.
179	>	* Creates a {@code PriorityQueue} containing the elements in the
180	>	* specified collection.  If the specified collection is an instance of
181	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
182	>	* priority queue will be ordered according to the same ordering.
183	>	* Otherwise, this priority queue will be ordered according to the
184	>	* {@linkplain Comparable natural ordering} of its elements.
185		*
186	<	* @param initialElements the collection whose elements are to be placed
187	<	*        into this priority queue.
186	>	* @param  c the collection whose elements are to be placed
187	>	*         into this priority queue
188		* @throws ClassCastException if elements of the specified collection
189		*         cannot be compared to one another according to the priority
190	<	*         queue's ordering.
191	<	* @throws NullPointerException if the specified collection or an
192	<	*         element of the specified collection is <tt>null</tt>.
193	<	*/
194	<	public PriorityQueue(Collection<E> initialElements) {
195	<	int sz = initialElements.size();
196	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
197	<	Integer.MAX_VALUE - 1);
198	<	if (initialCapacity < 1)
199	<	initialCapacity = 1;
200	<	queue = new E[initialCapacity + 1];
190	>	*         queue's ordering
191	>	* @throws NullPointerException if the specified collection or any
192	>	*         of its elements are null
193	>	*/
194	>	public PriorityQueue(Collection<? extends E> c) {
195	>	if (c instanceof SortedSet<?>) {
196	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
197	>	this.comparator = (Comparator<? super E>) ss.comparator();
198	>	initElementsFromCollection(ss);
199	>	}
200	>	else if (c instanceof PriorityQueue<?>) {
201	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
202	>	this.comparator = (Comparator<? super E>) pq.comparator();
203	>	initFromPriorityQueue(pq);
204	>	}
205	>	else {
206	>	this.comparator = null;
207	>	initFromCollection(c);
208	>	}
209	>	}
210
211	<	if (initialElements instanceof Sorted) {
212	<	comparator = ((Sorted)initialElements).comparator();
213	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
214	<	queue[++size] = i.next();
211	>	/**
212	>	* Creates a {@code PriorityQueue} containing the elements in the
213	>	* specified priority queue.  This priority queue will be
214	>	* ordered according to the same ordering as the given priority
215	>	* queue.
216	>	*
217	>	* @param  c the priority queue whose elements are to be placed
218	>	*         into this priority queue
219	>	* @throws ClassCastException if elements of {@code c} cannot be
220	>	*         compared to one another according to {@code c}'s
221	>	*         ordering
222	>	* @throws NullPointerException if the specified priority queue or any
223	>	*         of its elements are null
224	>	*/
225	>	public PriorityQueue(PriorityQueue<? extends E> c) {
226	>	this.comparator = (Comparator<? super E>) c.comparator();
227	>	initFromPriorityQueue(c);
228	>	}
229	>
230	>	/**
231	>	* Creates a {@code PriorityQueue} containing the elements in the
232	>	* specified sorted set.   This priority queue will be ordered
233	>	* according to the same ordering as the given sorted set.
234	>	*
235	>	* @param  c the sorted set whose elements are to be placed
236	>	*         into this priority queue
237	>	* @throws ClassCastException if elements of the specified sorted
238	>	*         set cannot be compared to one another according to the
239	>	*         sorted set's ordering
240	>	* @throws NullPointerException if the specified sorted set or any
241	>	*         of its elements are null
242	>	*/
243	>	public PriorityQueue(SortedSet<? extends E> c) {
244	>	this.comparator = (Comparator<? super E>) c.comparator();
245	>	initElementsFromCollection(c);
246	>	}
247	>
248	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
249	>	private static Object[] ensureNonEmpty(Object[] es) {
250	>	return (es.length > 0) ? es : new Object[1];
251	>	}
252	>
253	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
254	>	if (c.getClass() == PriorityQueue.class) {
255	>	this.queue = ensureNonEmpty(c.toArray());
256	>	this.size = c.size();
257		} else {
258	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
258	>	initFromCollection(c);
259		}
260		}
261
262	<	// Queue Methods
262	>	private void initElementsFromCollection(Collection<? extends E> c) {
263	>	Object[] es = c.toArray();
264	>	int len = es.length;
265	>	// If c.toArray incorrectly doesn't return Object[], copy it.
266	>	if (es.getClass() != Object[].class)
267	>	es = Arrays.copyOf(es, len, Object[].class);
268	>	if (len == 1 || this.comparator != null)
269	>	for (Object e : es)
270	>	if (e == null)
271	>	throw new NullPointerException();
272	>	this.queue = ensureNonEmpty(es);
273	>	this.size = len;
274	>	}
275
276		/**
277	<	* Remove and return the minimal element from this priority queue if
147	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
148	<	* <i>minimal</i> is defined according to this priority queue's order.
277	>	* Initializes queue array with elements from the given Collection.
278		*
279	<	* @return the minimal element from this priority queue if it contains
151	<	*         one or more elements, otherwise <tt>null</tt>.
279	>	* @param c the collection
280		*/
281	<	public E poll() {
282	<	if (size == 0)
283	<	return null;
284	<	return remove(1);
281	>	private void initFromCollection(Collection<? extends E> c) {
282	>	initElementsFromCollection(c);
283	>	heapify();
284	>	}
285	>
286	>	/**
287	>	* Increases the capacity of the array.
288	>	*
289	>	* @param minCapacity the desired minimum capacity
290	>	*/
291	>	private void grow(int minCapacity) {
292	>	int oldCapacity = queue.length;
293	>	// Double size if small; else grow by 50%
294	>	int newCapacity = ArraysSupport.newLength(oldCapacity,
295	>	minCapacity - oldCapacity, /* minimum growth */
296	>	oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
297	>	/* preferred growth */);
298	>	queue = Arrays.copyOf(queue, newCapacity);
299	>	}
300	>
301	>	/**
302	>	* Inserts the specified element into this priority queue.
303	>	*
304	>	* @return {@code true} (as specified by {@link Collection#add})
305	>	* @throws ClassCastException if the specified element cannot be
306	>	*         compared with elements currently in this priority queue
307	>	*         according to the priority queue's ordering
308	>	* @throws NullPointerException if the specified element is null
309	>	*/
310	>	public boolean add(E e) {
311	>	return offer(e);
312		}
313
314		/**
315	<	* Return, but do not remove, the minimal element from the priority queue,
161	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
162	<	* defined according to this priority queue's order.  This method returns
163	<	* the same object reference that would be returned by by the
164	<	* <tt>poll</tt> method.  The two methods differ in that this method
165	<	* does not remove the element from the priority queue.
315	>	* Inserts the specified element into this priority queue.
316		*
317	<	* @return the minimal element from this priority queue if it contains
318	<	*         one or more elements, otherwise <tt>null</tt>.
317	>	* @return {@code true} (as specified by {@link Queue#offer})
318	>	* @throws ClassCastException if the specified element cannot be
319	>	*         compared with elements currently in this priority queue
320	>	*         according to the priority queue's ordering
321	>	* @throws NullPointerException if the specified element is null
322		*/
323	+	public boolean offer(E e) {
324	+	if (e == null)
325	+	throw new NullPointerException();
326	+	modCount++;
327	+	int i = size;
328	+	if (i >= queue.length)
329	+	grow(i + 1);
330	+	siftUp(i, e);
331	+	size = i + 1;
332	+	return true;
333	+	}
334	+
335		public E peek() {
336	<	return queue[1];
336	>	return (E) queue[0];
337		}
338
339	<	// Collection Methods
339	>	private int indexOf(Object o) {
340	>	if (o != null) {
341	>	final Object[] es = queue;
342	>	for (int i = 0, n = size; i < n; i++)
343	>	if (o.equals(es[i]))
344	>	return i;
345	>	}
346	>	return -1;
347	>	}
348
349		/**
350	<	* Removes a single instance of the specified element from this priority
351	<	* queue, if it is present.  Returns true if this collection contained the
352	<	* specified element (or equivalently, if this collection changed as a
350	>	* Removes a single instance of the specified element from this queue,
351	>	* if it is present.  More formally, removes an element {@code e} such
352	>	* that {@code o.equals(e)}, if this queue contains one or more such
353	>	* elements.  Returns {@code true} if and only if this queue contained
354	>	* the specified element (or equivalently, if this queue changed as a
355		* result of the call).
356		*
357	<	* @param o element to be removed from this collection, if present.
358	<	* @return <tt>true</tt> if this collection changed as a result of the
184	<	*         call
185	<	* @throws ClassCastException if the specified element cannot be compared
186	<	*            with elements currently in the priority queue according
187	<	*            to the priority queue's ordering.
188	<	* @throws NullPointerException if the specified element is null.
357	>	* @param o element to be removed from this queue, if present
358	>	* @return {@code true} if this queue changed as a result of the call
359		*/
360	<	public boolean remove(Object element) {
361	<	if (element == null)
362	<	throw new NullPointerException();
360	>	public boolean remove(Object o) {
361	>	int i = indexOf(o);
362	>	if (i == -1)
363	>	return false;
364	>	else {
365	>	removeAt(i);
366	>	return true;
367	>	}
368	>	}
369
370	<	if (comparator == null) {
371	<	for (int i = 1; i <= size; i++) {
372	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
373	<	remove(i);
374	<	return true;
375	<	}
376	<	}
377	<	} else {
378	<	for (int i = 1; i <= size; i++) {
379	<	if (comparator.compare(queue[i], (E) element) == 0) {
380	<	remove(i);
205	<	return true;
206	<	}
370	>	/**
371	>	* Identity-based version for use in Itr.remove.
372	>	*
373	>	* @param o element to be removed from this queue, if present
374	>	*/
375	>	void removeEq(Object o) {
376	>	final Object[] es = queue;
377	>	for (int i = 0, n = size; i < n; i++) {
378	>	if (o == es[i]) {
379	>	removeAt(i);
380	>	break;
381		}
382		}
209	–	return false;
383		}
384
385		/**
386	<	* Returns an iterator over the elements in this priority queue.  The
387	<	* first element returned by this iterator is the same element that
388	<	* would be returned by a call to <tt>peek</tt>.
386	>	* Returns {@code true} if this queue contains the specified element.
387	>	* More formally, returns {@code true} if and only if this queue contains
388	>	* at least one element {@code e} such that {@code o.equals(e)}.
389		*
390	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
390	>	* @param o object to be checked for containment in this queue
391	>	* @return {@code true} if this queue contains the specified element
392	>	*/
393	>	public boolean contains(Object o) {
394	>	return indexOf(o) >= 0;
395	>	}
396	>
397	>	/**
398	>	* Returns an array containing all of the elements in this queue.
399	>	* The elements are in no particular order.
400	>	*
401	>	* <p>The returned array will be "safe" in that no references to it are
402	>	* maintained by this queue.  (In other words, this method must allocate
403	>	* a new array).  The caller is thus free to modify the returned array.
404	>	*
405	>	* <p>This method acts as bridge between array-based and collection-based
406	>	* APIs.
407	>	*
408	>	* @return an array containing all of the elements in this queue
409	>	*/
410	>	public Object[] toArray() {
411	>	return Arrays.copyOf(queue, size);
412	>	}
413	>
414	>	/**
415	>	* Returns an array containing all of the elements in this queue; the
416	>	* runtime type of the returned array is that of the specified array.
417	>	* The returned array elements are in no particular order.
418	>	* If the queue fits in the specified array, it is returned therein.
419	>	* Otherwise, a new array is allocated with the runtime type of the
420	>	* specified array and the size of this queue.
421	>	*
422	>	* <p>If the queue fits in the specified array with room to spare
423	>	* (i.e., the array has more elements than the queue), the element in
424	>	* the array immediately following the end of the collection is set to
425	>	* {@code null}.
426	>	*
427	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
428	>	* array-based and collection-based APIs.  Further, this method allows
429	>	* precise control over the runtime type of the output array, and may,
430	>	* under certain circumstances, be used to save allocation costs.
431	>	*
432	>	* <p>Suppose {@code x} is a queue known to contain only strings.
433	>	* The following code can be used to dump the queue into a newly
434	>	* allocated array of {@code String}:
435	>	*
436	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
437	>	*
438	>	* Note that {@code toArray(new Object[0])} is identical in function to
439	>	* {@code toArray()}.
440	>	*
441	>	* @param a the array into which the elements of the queue are to
442	>	*          be stored, if it is big enough; otherwise, a new array of the
443	>	*          same runtime type is allocated for this purpose.
444	>	* @return an array containing all of the elements in this queue
445	>	* @throws ArrayStoreException if the runtime type of the specified array
446	>	*         is not a supertype of the runtime type of every element in
447	>	*         this queue
448	>	* @throws NullPointerException if the specified array is null
449	>	*/
450	>	public <T> T[] toArray(T[] a) {
451	>	final int size = this.size;
452	>	if (a.length < size)
453	>	// Make a new array of a's runtime type, but my contents:
454	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
455	>	System.arraycopy(queue, 0, a, 0, size);
456	>	if (a.length > size)
457	>	a[size] = null;
458	>	return a;
459	>	}
460	>
461	>	/**
462	>	* Returns an iterator over the elements in this queue. The iterator
463	>	* does not return the elements in any particular order.
464	>	*
465	>	* @return an iterator over the elements in this queue
466		*/
467		public Iterator<E> iterator() {
468		return new Itr();
469		}
470
471	<	private class Itr implements Iterator<E> {
471	>	private final class Itr implements Iterator<E> {
472		/**
473		* Index (into queue array) of element to be returned by
474		* subsequent call to next.
475		*/
476	<	int cursor = 1;
476	>	private int cursor;
477	>
478	>	/**
479	>	* Index of element returned by most recent call to next,
480	>	* unless that element came from the forgetMeNot list.
481	>	* Set to -1 if element is deleted by a call to remove.
482	>	*/
483	>	private int lastRet = -1;
484	>
485	>	/**
486	>	* A queue of elements that were moved from the unvisited portion of
487	>	* the heap into the visited portion as a result of "unlucky" element
488	>	* removals during the iteration.  (Unlucky element removals are those
489	>	* that require a siftup instead of a siftdown.)  We must visit all of
490	>	* the elements in this list to complete the iteration.  We do this
491	>	* after we've completed the "normal" iteration.
492	>	*
493	>	* We expect that most iterations, even those involving removals,
494	>	* will not need to store elements in this field.
495	>	*/
496	>	private ArrayDeque<E> forgetMeNot;
497
498		/**
499	<	* Index of element returned by most recent call to next or
500	<	* previous.  Reset to 0 if this element is deleted by a call
233	<	* to remove.
499	>	* Element returned by the most recent call to next iff that
500	>	* element was drawn from the forgetMeNot list.
501		*/
502	<	int lastRet = 0;
502	>	private E lastRetElt;
503
504		/**
505		* The modCount value that the iterator believes that the backing
506	<	* List should have.  If this expectation is violated, the iterator
506	>	* Queue should have.  If this expectation is violated, the iterator
507		* has detected concurrent modification.
508		*/
509	<	int expectedModCount = modCount;
509	>	private int expectedModCount = modCount;
510	>
511	>	Itr() {}                        // prevent access constructor creation
512
513		public boolean hasNext() {
514	<	return cursor <= size;
514	>	return cursor < size ||
515	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
516		}
517
518		public E next() {
519	<	checkForComodification();
520	<	if (cursor > size)
521	<	throw new NoSuchElementException();
522	<	E result = queue[cursor];
523	<	lastRet = cursor++;
524	<	return result;
519	>	if (expectedModCount != modCount)
520	>	throw new ConcurrentModificationException();
521	>	if (cursor < size)
522	>	return (E) queue[lastRet = cursor++];
523	>	if (forgetMeNot != null) {
524	>	lastRet = -1;
525	>	lastRetElt = forgetMeNot.poll();
526	>	if (lastRetElt != null)
527	>	return lastRetElt;
528	>	}
529	>	throw new NoSuchElementException();
530		}
531
532		public void remove() {
533	<	if (lastRet == 0)
533	>	if (expectedModCount != modCount)
534	>	throw new ConcurrentModificationException();
535	>	if (lastRet != -1) {
536	>	E moved = PriorityQueue.this.removeAt(lastRet);
537	>	lastRet = -1;
538	>	if (moved == null)
539	>	cursor--;
540	>	else {
541	>	if (forgetMeNot == null)
542	>	forgetMeNot = new ArrayDeque<>();
543	>	forgetMeNot.add(moved);
544	>	}
545	>	} else if (lastRetElt != null) {
546	>	PriorityQueue.this.removeEq(lastRetElt);
547	>	lastRetElt = null;
548	>	} else {
549		throw new IllegalStateException();
550	<	checkForComodification();
261	<
262	<	PriorityQueue.this.remove(lastRet);
263	<	if (lastRet < cursor)
264	<	cursor--;
265	<	lastRet = 0;
550	>	}
551		expectedModCount = modCount;
552		}
553	+	}
554
555	<	final void checkForComodification() {
556	<	if (modCount != expectedModCount)
557	<	throw new ConcurrentModificationException();
555	>	public int size() {
556	>	return size;
557	>	}
558	>
559	>	/**
560	>	* Removes all of the elements from this priority queue.
561	>	* The queue will be empty after this call returns.
562	>	*/
563	>	public void clear() {
564	>	modCount++;
565	>	final Object[] es = queue;
566	>	for (int i = 0, n = size; i < n; i++)
567	>	es[i] = null;
568	>	size = 0;
569	>	}
570	>
571	>	public E poll() {
572	>	final Object[] es;
573	>	final E result;
574	>
575	>	if ((result = (E) ((es = queue)[0])) != null) {
576	>	modCount++;
577	>	final int n;
578	>	final E x = (E) es[(n = --size)];
579	>	es[n] = null;
580	>	if (n > 0) {
581	>	final Comparator<? super E> cmp;
582	>	if ((cmp = comparator) == null)
583	>	siftDownComparable(0, x, es, n);
584	>	else
585	>	siftDownUsingComparator(0, x, es, n, cmp);
586	>	}
587		}
588	+	return result;
589		}
590
591		/**
592	<	* Returns the number of elements in this priority queue.
592	>	* Removes the ith element from queue.
593		*
594	<	* @return the number of elements in this priority queue.
595	<	*/
596	<	public int size() {
597	<	return size;
594	>	* Normally this method leaves the elements at up to i-1,
595	>	* inclusive, untouched.  Under these circumstances, it returns
596	>	* null.  Occasionally, in order to maintain the heap invariant,
597	>	* it must swap a later element of the list with one earlier than
598	>	* i.  Under these circumstances, this method returns the element
599	>	* that was previously at the end of the list and is now at some
600	>	* position before i. This fact is used by iterator.remove so as to
601	>	* avoid missing traversing elements.
602	>	*/
603	>	E removeAt(int i) {
604	>	// assert i >= 0 && i < size;
605	>	final Object[] es = queue;
606	>	modCount++;
607	>	int s = --size;
608	>	if (s == i) // removed last element
609	>	es[i] = null;
610	>	else {
611	>	E moved = (E) es[s];
612	>	es[s] = null;
613	>	siftDown(i, moved);
614	>	if (es[i] == moved) {
615	>	siftUp(i, moved);
616	>	if (es[i] != moved)
617	>	return moved;
618	>	}
619	>	}
620	>	return null;
621		}
622
623		/**
624	<	* Add the specified element to this priority queue.
624	>	* Inserts item x at position k, maintaining heap invariant by
625	>	* promoting x up the tree until it is greater than or equal to
626	>	* its parent, or is the root.
627		*
628	<	* @param element the element to add.
629	<	* @return true
630	<	* @throws ClassCastException if the specified element cannot be compared
631	<	*            with elements currently in the priority queue according
632	<	*            to the priority queue's ordering.
633	<	* @throws NullPointerException if the specified element is null.
628	>	* To simplify and speed up coercions and comparisons, the
629	>	* Comparable and Comparator versions are separated into different
630	>	* methods that are otherwise identical. (Similarly for siftDown.)
631	>	*
632	>	* @param k the position to fill
633	>	* @param x the item to insert
634		*/
635	<	public boolean offer(E element) {
636	<	if (element == null)
637	<	throw new NullPointerException();
638	<	modCount++;
635	>	private void siftUp(int k, E x) {
636	>	if (comparator != null)
637	>	siftUpUsingComparator(k, x, queue, comparator);
638	>	else
639	>	siftUpComparable(k, x, queue);
640	>	}
641
642	<	// Grow backing store if necessary
643	<	if (++size == queue.length) {
644	<	E[] newQueue = new E[2 * queue.length];
645	<	System.arraycopy(queue, 0, newQueue, 0, size);
646	<	queue = newQueue;
642	>	private static <T> void siftUpComparable(int k, T x, Object[] es) {
643	>	Comparable<? super T> key = (Comparable<? super T>) x;
644	>	while (k > 0) {
645	>	int parent = (k - 1) >>> 1;
646	>	Object e = es[parent];
647	>	if (key.compareTo((T) e) >= 0)
648	>	break;
649	>	es[k] = e;
650	>	k = parent;
651		}
652	+	es[k] = key;
653	+	}
654
655	<	queue[size] = element;
656	<	fixUp(size);
657	<	return true;
655	>	private static <T> void siftUpUsingComparator(
656	>	int k, T x, Object[] es, Comparator<? super T> cmp) {
657	>	while (k > 0) {
658	>	int parent = (k - 1) >>> 1;
659	>	Object e = es[parent];
660	>	if (cmp.compare(x, (T) e) >= 0)
661	>	break;
662	>	es[k] = e;
663	>	k = parent;
664	>	}
665	>	es[k] = x;
666	>	}
667	>
668	>	/**
669	>	* Inserts item x at position k, maintaining heap invariant by
670	>	* demoting x down the tree repeatedly until it is less than or
671	>	* equal to its children or is a leaf.
672	>	*
673	>	* @param k the position to fill
674	>	* @param x the item to insert
675	>	*/
676	>	private void siftDown(int k, E x) {
677	>	if (comparator != null)
678	>	siftDownUsingComparator(k, x, queue, size, comparator);
679	>	else
680	>	siftDownComparable(k, x, queue, size);
681	>	}
682	>
683	>	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
684	>	// assert n > 0;
685	>	Comparable<? super T> key = (Comparable<? super T>)x;
686	>	int half = n >>> 1;           // loop while a non-leaf
687	>	while (k < half) {
688	>	int child = (k << 1) + 1; // assume left child is least
689	>	Object c = es[child];
690	>	int right = child + 1;
691	>	if (right < n &&
692	>	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
693	>	c = es[child = right];
694	>	if (key.compareTo((T) c) <= 0)
695	>	break;
696	>	es[k] = c;
697	>	k = child;
698	>	}
699	>	es[k] = key;
700	>	}
701	>
702	>	private static <T> void siftDownUsingComparator(
703	>	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
704	>	// assert n > 0;
705	>	int half = n >>> 1;
706	>	while (k < half) {
707	>	int child = (k << 1) + 1;
708	>	Object c = es[child];
709	>	int right = child + 1;
710	>	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
711	>	c = es[child = right];
712	>	if (cmp.compare(x, (T) c) <= 0)
713	>	break;
714	>	es[k] = c;
715	>	k = child;
716	>	}
717	>	es[k] = x;
718		}
719
720		/**
721	<	* Remove all elements from the priority queue.
721	>	* Establishes the heap invariant (described above) in the entire tree,
722	>	* assuming nothing about the order of the elements prior to the call.
723	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
724		*/
725	<	public void clear() {
726	<	modCount++;
725	>	private void heapify() {
726	>	final Object[] es = queue;
727	>	int n = size, i = (n >>> 1) - 1;
728	>	final Comparator<? super E> cmp;
729	>	if ((cmp = comparator) == null)
730	>	for (; i >= 0; i--)
731	>	siftDownComparable(i, (E) es[i], es, n);
732	>	else
733	>	for (; i >= 0; i--)
734	>	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
735	>	}
736	>
737	>	/**
738	>	* Returns the comparator used to order the elements in this
739	>	* queue, or {@code null} if this queue is sorted according to
740	>	* the {@linkplain Comparable natural ordering} of its elements.
741	>	*
742	>	* @return the comparator used to order this queue, or
743	>	*         {@code null} if this queue is sorted according to the
744	>	*         natural ordering of its elements
745	>	*/
746	>	public Comparator<? super E> comparator() {
747	>	return comparator;
748	>	}
749	>
750	>	/**
751	>	* Saves this queue to a stream (that is, serializes it).
752	>	*
753	>	* @param s the stream
754	>	* @throws java.io.IOException if an I/O error occurs
755	>	* @serialData The length of the array backing the instance is
756	>	*             emitted (int), followed by all of its elements
757	>	*             (each an {@code Object}) in the proper order.
758	>	*/
759	>	// OPENJDK @java.io.Serial
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	<	// Null out element references to prevent memory leak
766	<	for (int i=1; i<=size; i++)
319	<	queue[i] = null;
765	>	// Write out array length, for compatibility with 1.5 version
766	>	s.writeInt(Math.max(2, size + 1));
767
768	<	size = 0;
768	>	// Write out all elements in the "proper order".
769	>	final Object[] es = queue;
770	>	for (int i = 0, n = size; i < n; i++)
771	>	s.writeObject(es[i]);
772		}
773
774		/**
775	<	* Removes and returns the ith element from queue.  Recall
776	<	* that queue is one-based, so 1 <= i <= size.
775	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
776	>	* (that is, deserializes it).
777		*
778	<	* XXX: Could further special-case i==size, but is it worth it?
779	<	* XXX: Could special-case i==0, but is it worth it?
778	>	* @param s the stream
779	>	* @throws ClassNotFoundException if the class of a serialized object
780	>	*         could not be found
781	>	* @throws java.io.IOException if an I/O error occurs
782		*/
783	<	private E remove(int i) {
784	<	assert i <= size;
785	<	modCount++;
783	>	// OPENJDK @java.io.Serial
784	>	private void readObject(java.io.ObjectInputStream s)
785	>	throws java.io.IOException, ClassNotFoundException {
786	>	// Read in size, and any hidden stuff
787	>	s.defaultReadObject();
788
789	<	E result = queue[i];
790	<	queue[i] = queue[size];
791	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
792	<	if (i <= size)
793	<	fixDown(i);
794	<	return result;
789	>	// Read in (and discard) array length
790	>	s.readInt();
791	>
792	>	jsr166.Platform.checkArray(s, Object[].class, size);
793	>	final Object[] es = queue = new Object[Math.max(size, 1)];
794	>
795	>	// Read in all elements.
796	>	for (int i = 0, n = size; i < n; i++)
797	>	es[i] = s.readObject();
798	>
799	>	// Elements are guaranteed to be in "proper order", but the
800	>	// spec has never explained what that might be.
801	>	heapify();
802		}
803
804		/**
805	<	* Establishes the heap invariant (described above) assuming the heap
806	<	* satisfies the invariant except possibly for the leaf-node indexed by k
807	<	* (which may have a nextExecutionTime less than its parent's).
808	<	*
809	<	* This method functions by "promoting" queue[k] up the hierarchy
810	<	* (by swapping it with its parent) repeatedly until queue[k]
811	<	* is greater than or equal to its parent.
812	<	*/
813	<	private void fixUp(int k) {
814	<	if (comparator == null) {
815	<	while (k > 1) {
816	<	int j = k >> 1;
817	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
818	<	break;
819	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
820	<	k = j;
805	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
806	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
807	>	* queue. The spliterator does not traverse elements in any particular order
808	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
809	>	*
810	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
811	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
812	>	* Overriding implementations should document the reporting of additional
813	>	* characteristic values.
814	>	*
815	>	* @return a {@code Spliterator} over the elements in this queue
816	>	* @since 1.8
817	>	*/
818	>	public final Spliterator<E> spliterator() {
819	>	return new PriorityQueueSpliterator(0, -1, 0);
820	>	}
821	>
822	>	final class PriorityQueueSpliterator implements Spliterator<E> {
823	>	private int index;            // current index, modified on advance/split
824	>	private int fence;            // -1 until first use
825	>	private int expectedModCount; // initialized when fence set
826	>
827	>	/** Creates new spliterator covering the given range. */
828	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
829	>	this.index = origin;
830	>	this.fence = fence;
831	>	this.expectedModCount = expectedModCount;
832	>	}
833	>
834	>	private int getFence() { // initialize fence to size on first use
835	>	int hi;
836	>	if ((hi = fence) < 0) {
837	>	expectedModCount = modCount;
838	>	hi = fence = size;
839		}
840	<	} else {
841	<	while (k > 1) {
842	<	int j = k >> 1;
843	<	if (comparator.compare(queue[j], queue[k]) <= 0)
844	<	break;
845	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
846	<	k = j;
840	>	return hi;
841	>	}
842	>
843	>	public PriorityQueueSpliterator trySplit() {
844	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
845	>	return (lo >= mid) ? null :
846	>	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
847	>	}
848	>
849	>	public void forEachRemaining(Consumer<? super E> action) {
850	>	if (action == null)
851	>	throw new NullPointerException();
852	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
853	>	final Object[] es = queue;
854	>	int i, hi; E e;
855	>	for (i = index, index = hi = fence; i < hi; i++) {
856	>	if ((e = (E) es[i]) == null)
857	>	break;      // must be CME
858	>	action.accept(e);
859	>	}
860	>	if (modCount != expectedModCount)
861	>	throw new ConcurrentModificationException();
862	>	}
863	>
864	>	public boolean tryAdvance(Consumer<? super E> action) {
865	>	if (action == null)
866	>	throw new NullPointerException();
867	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
868	>	int i;
869	>	if ((i = index) < fence) {
870	>	index = i + 1;
871	>	E e;
872	>	if ((e = (E) queue[i]) == null
873	>	|| modCount != expectedModCount)
874	>	throw new ConcurrentModificationException();
875	>	action.accept(e);
876	>	return true;
877		}
878	+	return false;
879	+	}
880	+
881	+	public long estimateSize() {
882	+	return getFence() - index;
883	+	}
884	+
885	+	public int characteristics() {
886	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
887		}
888		}
889
890		/**
891	<	* Establishes the heap invariant (described above) in the subtree
892	<	* rooted at k, which is assumed to satisfy the heap invariant except
893	<	* possibly for node k itself (which may be greater than its children).
894	<	*
895	<	* This method functions by "demoting" queue[k] down the hierarchy
896	<	* (by swapping it with its smaller child) repeatedly until queue[k]
897	<	* is less than or equal to its children.
898	<	*/
899	<	private void fixDown(int k) {
900	<	int j;
901	<	if (comparator == null) {
902	<	while ((j = k << 1) <= size) {
903	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
904	<	j++; // j indexes smallest kid
905	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
906	<	break;
907	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
908	<	k = j;
909	<	}
910	<	} else {
911	<	while ((j = k << 1) <= size) {
912	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
913	<	j++; // j indexes smallest kid
914	<	if (comparator.compare(queue[k], queue[j]) <= 0)
915	<	break;
916	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
917	<	k = j;
918	<	}
891	>	* @throws NullPointerException {@inheritDoc}
892	>	*/
893	>	public boolean removeIf(Predicate<? super E> filter) {
894	>	Objects.requireNonNull(filter);
895	>	return bulkRemove(filter);
896	>	}
897	>
898	>	/**
899	>	* @throws NullPointerException {@inheritDoc}
900	>	*/
901	>	public boolean removeAll(Collection<?> c) {
902	>	Objects.requireNonNull(c);
903	>	return bulkRemove(e -> c.contains(e));
904	>	}
905	>
906	>	/**
907	>	* @throws NullPointerException {@inheritDoc}
908	>	*/
909	>	public boolean retainAll(Collection<?> c) {
910	>	Objects.requireNonNull(c);
911	>	return bulkRemove(e -> !c.contains(e));
912	>	}
913	>
914	>	// A tiny bit set implementation
915	>
916	>	private static long[] nBits(int n) {
917	>	return new long[((n - 1) >> 6) + 1];
918	>	}
919	>	private static void setBit(long[] bits, int i) {
920	>	bits[i >> 6] |= 1L << i;
921	>	}
922	>	private static boolean isClear(long[] bits, int i) {
923	>	return (bits[i >> 6] & (1L << i)) == 0;
924	>	}
925	>
926	>	/** Implementation of bulk remove methods. */
927	>	private boolean bulkRemove(Predicate<? super E> filter) {
928	>	final int expectedModCount = ++modCount;
929	>	final Object[] es = queue;
930	>	final int end = size;
931	>	int i;
932	>	// Optimize for initial run of survivors
933	>	for (i = 0; i < end && !filter.test((E) es[i]); i++)
934	>	;
935	>	if (i >= end) {
936	>	if (modCount != expectedModCount)
937	>	throw new ConcurrentModificationException();
938	>	return false;
939		}
940	+	// Tolerate predicates that reentrantly access the collection for
941	+	// read (but writers still get CME), so traverse once to find
942	+	// elements to delete, a second pass to physically expunge.
943	+	final int beg = i;
944	+	final long[] deathRow = nBits(end - beg);
945	+	deathRow[0] = 1L;   // set bit 0
946	+	for (i = beg + 1; i < end; i++)
947	+	if (filter.test((E) es[i]))
948	+	setBit(deathRow, i - beg);
949	+	if (modCount != expectedModCount)
950	+	throw new ConcurrentModificationException();
951	+	int w = beg;
952	+	for (i = beg; i < end; i++)
953	+	if (isClear(deathRow, i - beg))
954	+	es[w++] = es[i];
955	+	for (i = size = w; i < end; i++)
956	+	es[i] = null;
957	+	heapify();
958	+	return true;
959		}
960
961		/**
962	<	* Returns the comparator associated with this priority queue, or
406	<	* <tt>null</tt> if it uses its elements' natural ordering.
407	<	*
408	<	* @return the comparator associated with this priority queue, or
409	<	*         <tt>null</tt> if it uses its elements' natural ordering.
962	>	* @throws NullPointerException {@inheritDoc}
963		*/
964	<	Comparator<E> comparator() {
965	<	return comparator;
964	>	public void forEach(Consumer<? super E> action) {
965	>	Objects.requireNonNull(action);
966	>	final int expectedModCount = modCount;
967	>	final Object[] es = queue;
968	>	for (int i = 0, n = size; i < n; i++)
969	>	action.accept((E) es[i]);
970	>	if (expectedModCount != modCount)
971	>	throw new ConcurrentModificationException();
972		}
973		}

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