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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.3 by tim, Sun May 18 20:36:01 2003 UTC vs.
Revision 1.133 by jsr166, Thu Oct 10 16:53:08 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	>	@SuppressWarnings("serial") // Conditionally serializable
115	>	private final Comparator<? super E> comparator;
116
117		/**
118		* The number of times this priority queue has been
119		* <i>structurally modified</i>.  See AbstractList for gory details.
120		*/
121	<	private int modCount = 0;
121	>	transient int modCount;     // non-private to simplify nested class access
122
123		/**
124	<	* Create a new priority queue with the default initial capacity (11)
125	<	* that orders its elements according to their natural ordering.
124	>	* Creates a {@code PriorityQueue} with the default initial
125	>	* capacity (11) that orders its elements according to their
126	>	* {@linkplain Comparable natural ordering}.
127		*/
128		public PriorityQueue() {
129	<	this(DEFAULT_INITIAL_CAPACITY);
129	>	this(DEFAULT_INITIAL_CAPACITY, null);
130		}
131
132		/**
133	<	* Create a new priority queue with the specified initial capacity
134	<	* that orders its elements according to their natural ordering.
133	>	* Creates a {@code PriorityQueue} with the specified initial
134	>	* capacity that orders its elements according to their
135	>	* {@linkplain Comparable natural ordering}.
136		*
137	<	* @param initialCapacity the initial capacity for this priority queue.
137	>	* @param initialCapacity the initial capacity for this priority queue
138	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
139	>	*         than 1
140		*/
141		public PriorityQueue(int initialCapacity) {
142		this(initialCapacity, null);
143		}
144
145		/**
146	<	* Create a new priority queue with the specified initial capacity (11)
147	<	* that orders its elements according to the specified comparator.
146	>	* Creates a {@code PriorityQueue} with the default initial capacity and
147	>	* whose elements are ordered according to the specified comparator.
148		*
149	<	* @param initialCapacity the initial capacity for this priority queue.
150	<	* @param comparator the comparator used to order this priority queue.
149	>	* @param  comparator the comparator that will be used to order this
150	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
151	>	*         natural ordering} of the elements will be used.
152	>	* @since 1.8
153		*/
154	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
154	>	public PriorityQueue(Comparator<? super E> comparator) {
155	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
156	>	}
157	>
158	>	/**
159	>	* Creates a {@code PriorityQueue} with the specified initial capacity
160	>	* that orders its elements according to the specified comparator.
161	>	*
162	>	* @param  initialCapacity the initial capacity for this priority queue
163	>	* @param  comparator the comparator that will be used to order this
164	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
165	>	*         natural ordering} of the elements will be used.
166	>	* @throws IllegalArgumentException if {@code initialCapacity} is
167	>	*         less than 1
168	>	*/
169	>	public PriorityQueue(int initialCapacity,
170	>	Comparator<? super E> comparator) {
171	>	// Note: This restriction of at least one is not actually needed,
172	>	// but continues for 1.5 compatibility
173		if (initialCapacity < 1)
174	<	initialCapacity = 1;
175	<	queue = new E[initialCapacity + 1];
174	>	throw new IllegalArgumentException();
175	>	this.queue = new Object[initialCapacity];
176		this.comparator = comparator;
177		}
178
179		/**
180	<	* Create a new priority queue containing the elements in the specified
181	<	* collection.  The priority queue has an initial capacity of 110% of the
182	<	* size of the specified collection. If the specified collection
183	<	* implements the {@link Sorted} interface, the priority queue will be
184	<	* sorted according to the same comparator, or according to its elements'
185	<	* 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.
180	>	* Creates a {@code PriorityQueue} containing the elements in the
181	>	* specified collection.  If the specified collection is an instance of
182	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
183	>	* priority queue will be ordered according to the same ordering.
184	>	* Otherwise, this priority queue will be ordered according to the
185	>	* {@linkplain Comparable natural ordering} of its elements.
186		*
187	<	* @param initialElements the collection whose elements are to be placed
188	<	*        into this priority queue.
187	>	* @param  c the collection whose elements are to be placed
188	>	*         into this priority queue
189		* @throws ClassCastException if elements of the specified collection
190		*         cannot be compared to one another according to the priority
191	<	*         queue's ordering.
192	<	* @throws NullPointerException if the specified collection or an
193	<	*         element of the specified collection is <tt>null</tt>.
194	<	*/
195	<	public PriorityQueue(Collection<E> initialElements) {
196	<	int sz = initialElements.size();
197	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
198	<	Integer.MAX_VALUE - 1);
199	<	if (initialCapacity < 1)
200	<	initialCapacity = 1;
201	<	queue = new E[initialCapacity + 1];
191	>	*         queue's ordering
192	>	* @throws NullPointerException if the specified collection or any
193	>	*         of its elements are null
194	>	*/
195	>	public PriorityQueue(Collection<? extends E> c) {
196	>	if (c instanceof SortedSet<?>) {
197	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
198	>	this.comparator = (Comparator<? super E>) ss.comparator();
199	>	initElementsFromCollection(ss);
200	>	}
201	>	else if (c instanceof PriorityQueue<?>) {
202	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
203	>	this.comparator = (Comparator<? super E>) pq.comparator();
204	>	initFromPriorityQueue(pq);
205	>	}
206	>	else {
207	>	this.comparator = null;
208	>	initFromCollection(c);
209	>	}
210	>	}
211
212	<	/* Commented out to compile with generics compiler
212	>	/**
213	>	* Creates a {@code PriorityQueue} containing the elements in the
214	>	* specified priority queue.  This priority queue will be
215	>	* ordered according to the same ordering as the given priority
216	>	* queue.
217	>	*
218	>	* @param  c the priority queue whose elements are to be placed
219	>	*         into this priority queue
220	>	* @throws ClassCastException if elements of {@code c} cannot be
221	>	*         compared to one another according to {@code c}'s
222	>	*         ordering
223	>	* @throws NullPointerException if the specified priority queue or any
224	>	*         of its elements are null
225	>	*/
226	>	public PriorityQueue(PriorityQueue<? extends E> c) {
227	>	this.comparator = (Comparator<? super E>) c.comparator();
228	>	initFromPriorityQueue(c);
229	>	}
230
231	<	if (initialElements instanceof Sorted) {
232	<	comparator = ((Sorted)initialElements).comparator();
233	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
234	<	queue[++size] = i.next();
231	>	/**
232	>	* Creates a {@code PriorityQueue} containing the elements in the
233	>	* specified sorted set.   This priority queue will be ordered
234	>	* according to the same ordering as the given sorted set.
235	>	*
236	>	* @param  c the sorted set whose elements are to be placed
237	>	*         into this priority queue
238	>	* @throws ClassCastException if elements of the specified sorted
239	>	*         set cannot be compared to one another according to the
240	>	*         sorted set's ordering
241	>	* @throws NullPointerException if the specified sorted set or any
242	>	*         of its elements are null
243	>	*/
244	>	public PriorityQueue(SortedSet<? extends E> c) {
245	>	this.comparator = (Comparator<? super E>) c.comparator();
246	>	initElementsFromCollection(c);
247	>	}
248	>
249	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
250	>	private static Object[] ensureNonEmpty(Object[] es) {
251	>	return (es.length > 0) ? es : new Object[1];
252	>	}
253	>
254	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
255	>	if (c.getClass() == PriorityQueue.class) {
256	>	this.queue = ensureNonEmpty(c.toArray());
257	>	this.size = c.size();
258		} else {
259	<	*/
140	<	{
141	<	comparator = null;
142	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
259	>	initFromCollection(c);
260		}
261		}
262
263	<	// Queue Methods
263	>	private void initElementsFromCollection(Collection<? extends E> c) {
264	>	Object[] es = c.toArray();
265	>	int len = es.length;
266	>	// If c.toArray incorrectly doesn't return Object[], copy it.
267	>	if (es.getClass() != Object[].class)
268	>	es = Arrays.copyOf(es, len, Object[].class);
269	>	if (len == 1 || this.comparator != null)
270	>	for (Object e : es)
271	>	if (e == null)
272	>	throw new NullPointerException();
273	>	this.queue = ensureNonEmpty(es);
274	>	this.size = len;
275	>	}
276
277		/**
278	<	* Remove and return the minimal element from this priority queue if
151	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
152	<	* <i>minimal</i> is defined according to this priority queue's order.
278	>	* Initializes queue array with elements from the given Collection.
279		*
280	<	* @return the minimal element from this priority queue if it contains
155	<	*         one or more elements, otherwise <tt>null</tt>.
280	>	* @param c the collection
281		*/
282	<	public E poll() {
283	<	if (size == 0)
284	<	return null;
285	<	return remove(1);
282	>	private void initFromCollection(Collection<? extends E> c) {
283	>	initElementsFromCollection(c);
284	>	heapify();
285	>	}
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 = ArraysSupport.newLength(oldCapacity,
296	>	minCapacity - oldCapacity, /* minimum growth */
297	>	oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
298	>	/* preferred growth */);
299	>	queue = Arrays.copyOf(queue, newCapacity);
300	>	}
301	>
302	>	/**
303	>	* Inserts the specified element into this priority queue.
304	>	*
305	>	* @return {@code true} (as specified by {@link Collection#add})
306	>	* @throws ClassCastException if the specified element cannot be
307	>	*         compared with elements currently in this priority queue
308	>	*         according to the priority queue's ordering
309	>	* @throws NullPointerException if the specified element is null
310	>	*/
311	>	public boolean add(E e) {
312	>	return offer(e);
313		}
314
315		/**
316	<	* Return, but do not remove, the minimal element from the priority queue,
165	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
166	<	* defined according to this priority queue's order.  This method returns
167	<	* the same object reference that would be returned by by the
168	<	* <tt>poll</tt> method.  The two methods differ in that this method
169	<	* does not remove the element from the priority queue.
316	>	* Inserts the specified element into this priority queue.
317		*
318	<	* @return the minimal element from this priority queue if it contains
319	<	*         one or more elements, otherwise <tt>null</tt>.
318	>	* @return {@code true} (as specified by {@link Queue#offer})
319	>	* @throws ClassCastException if the specified element cannot be
320	>	*         compared with elements currently in this priority queue
321	>	*         according to the priority queue's ordering
322	>	* @throws NullPointerException if the specified element is null
323		*/
324	+	public boolean offer(E e) {
325	+	if (e == null)
326	+	throw new NullPointerException();
327	+	modCount++;
328	+	int i = size;
329	+	if (i >= queue.length)
330	+	grow(i + 1);
331	+	siftUp(i, e);
332	+	size = i + 1;
333	+	return true;
334	+	}
335	+
336		public E peek() {
337	<	return queue[1];
337	>	return (E) queue[0];
338		}
339
340	<	// Collection Methods
340	>	private int indexOf(Object o) {
341	>	if (o != null) {
342	>	final Object[] es = queue;
343	>	for (int i = 0, n = size; i < n; i++)
344	>	if (o.equals(es[i]))
345	>	return i;
346	>	}
347	>	return -1;
348	>	}
349
350		/**
351	<	* Removes a single instance of the specified element from this priority
352	<	* queue, if it is present.  Returns true if this collection contained the
353	<	* specified element (or equivalently, if this collection changed as a
351	>	* Removes a single instance of the specified element from this queue,
352	>	* if it is present.  More formally, removes an element {@code e} such
353	>	* that {@code o.equals(e)}, if this queue contains one or more such
354	>	* elements.  Returns {@code true} if and only if this queue contained
355	>	* the specified element (or equivalently, if this queue changed as a
356		* result of the call).
357		*
358	<	* @param o element to be removed from this collection, if present.
359	<	* @return <tt>true</tt> if this collection changed as a result of the
188	<	*         call
189	<	* @throws ClassCastException if the specified element cannot be compared
190	<	*            with elements currently in the priority queue according
191	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
358	>	* @param o element to be removed from this queue, if present
359	>	* @return {@code true} if this queue changed as a result of the call
360		*/
361	<	public boolean remove(Object element) {
362	<	if (element == null)
363	<	throw new NullPointerException();
361	>	public boolean remove(Object o) {
362	>	int i = indexOf(o);
363	>	if (i == -1)
364	>	return false;
365	>	else {
366	>	removeAt(i);
367	>	return true;
368	>	}
369	>	}
370
371	<	if (comparator == null) {
372	<	for (int i = 1; i <= size; i++) {
373	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
374	<	remove(i);
375	<	return true;
376	<	}
377	<	}
378	<	} else {
379	<	for (int i = 1; i <= size; i++) {
380	<	if (comparator.compare(queue[i], (E) element) == 0) {
381	<	remove(i);
209	<	return true;
210	<	}
371	>	/**
372	>	* Identity-based version for use in Itr.remove.
373	>	*
374	>	* @param o element to be removed from this queue, if present
375	>	*/
376	>	void removeEq(Object o) {
377	>	final Object[] es = queue;
378	>	for (int i = 0, n = size; i < n; i++) {
379	>	if (o == es[i]) {
380	>	removeAt(i);
381	>	break;
382		}
383		}
213	–	return false;
384		}
385
386		/**
387	<	* Returns an iterator over the elements in this priority queue.  The
388	<	* first element returned by this iterator is the same element that
389	<	* would be returned by a call to <tt>peek</tt>.
387	>	* Returns {@code true} if this queue contains the specified element.
388	>	* More formally, returns {@code true} if and only if this queue contains
389	>	* at least one element {@code e} such that {@code o.equals(e)}.
390	>	*
391	>	* @param o object to be checked for containment in this queue
392	>	* @return {@code true} if this queue contains the specified element
393	>	*/
394	>	public boolean contains(Object o) {
395	>	return indexOf(o) >= 0;
396	>	}
397	>
398	>	/**
399	>	* Returns an array containing all of the elements in this queue.
400	>	* The elements are in no particular order.
401	>	*
402	>	* <p>The returned array will be "safe" in that no references to it are
403	>	* maintained by this queue.  (In other words, this method must allocate
404	>	* a new array).  The caller is thus free to modify the returned array.
405	>	*
406	>	* <p>This method acts as bridge between array-based and collection-based
407	>	* APIs.
408	>	*
409	>	* @return an array containing all of the elements in this queue
410	>	*/
411	>	public Object[] toArray() {
412	>	return Arrays.copyOf(queue, size);
413	>	}
414	>
415	>	/**
416	>	* Returns an array containing all of the elements in this queue; the
417	>	* runtime type of the returned array is that of the specified array.
418	>	* The returned array elements are in no particular order.
419	>	* If the queue fits in the specified array, it is returned therein.
420	>	* Otherwise, a new array is allocated with the runtime type of the
421	>	* specified array and the size of this queue.
422	>	*
423	>	* <p>If the queue fits in the specified array with room to spare
424	>	* (i.e., the array has more elements than the queue), the element in
425	>	* the array immediately following the end of the collection is set to
426	>	* {@code null}.
427	>	*
428	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
429	>	* array-based and collection-based APIs.  Further, this method allows
430	>	* precise control over the runtime type of the output array, and may,
431	>	* under certain circumstances, be used to save allocation costs.
432	>	*
433	>	* <p>Suppose {@code x} is a queue known to contain only strings.
434	>	* The following code can be used to dump the queue into a newly
435	>	* allocated array of {@code String}:
436	>	*
437	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
438	>	*
439	>	* Note that {@code toArray(new Object[0])} is identical in function to
440	>	* {@code toArray()}.
441		*
442	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
442	>	* @param a the array into which the elements of the queue are to
443	>	*          be stored, if it is big enough; otherwise, a new array of the
444	>	*          same runtime type is allocated for this purpose.
445	>	* @return an array containing all of the elements in this queue
446	>	* @throws ArrayStoreException if the runtime type of the specified array
447	>	*         is not a supertype of the runtime type of every element in
448	>	*         this queue
449	>	* @throws NullPointerException if the specified array is null
450	>	*/
451	>	public <T> T[] toArray(T[] a) {
452	>	final int size = this.size;
453	>	if (a.length < size)
454	>	// Make a new array of a's runtime type, but my contents:
455	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
456	>	System.arraycopy(queue, 0, a, 0, size);
457	>	if (a.length > size)
458	>	a[size] = null;
459	>	return a;
460	>	}
461	>
462	>	/**
463	>	* Returns an iterator over the elements in this queue. The iterator
464	>	* does not return the elements in any particular order.
465	>	*
466	>	* @return an iterator over the elements in this queue
467		*/
468		public Iterator<E> iterator() {
469		return new Itr();
470		}
471
472	<	private class Itr implements Iterator<E> {
472	>	private final class Itr implements Iterator<E> {
473		/**
474		* Index (into queue array) of element to be returned by
475		* subsequent call to next.
476		*/
477	<	int cursor = 1;
477	>	private int cursor;
478	>
479	>	/**
480	>	* Index of element returned by most recent call to next,
481	>	* unless that element came from the forgetMeNot list.
482	>	* Set to -1 if element is deleted by a call to remove.
483	>	*/
484	>	private int lastRet = -1;
485	>
486	>	/**
487	>	* A queue of elements that were moved from the unvisited portion of
488	>	* the heap into the visited portion as a result of "unlucky" element
489	>	* removals during the iteration.  (Unlucky element removals are those
490	>	* that require a siftup instead of a siftdown.)  We must visit all of
491	>	* the elements in this list to complete the iteration.  We do this
492	>	* after we've completed the "normal" iteration.
493	>	*
494	>	* We expect that most iterations, even those involving removals,
495	>	* will not need to store elements in this field.
496	>	*/
497	>	private ArrayDeque<E> forgetMeNot;
498
499		/**
500	<	* Index of element returned by most recent call to next or
501	<	* previous.  Reset to 0 if this element is deleted by a call
237	<	* to remove.
500	>	* Element returned by the most recent call to next iff that
501	>	* element was drawn from the forgetMeNot list.
502		*/
503	<	int lastRet = 0;
503	>	private E lastRetElt;
504
505		/**
506		* The modCount value that the iterator believes that the backing
507	<	* List should have.  If this expectation is violated, the iterator
507	>	* Queue should have.  If this expectation is violated, the iterator
508		* has detected concurrent modification.
509		*/
510	<	int expectedModCount = modCount;
510	>	private int expectedModCount = modCount;
511	>
512	>	Itr() {}                        // prevent access constructor creation
513
514		public boolean hasNext() {
515	<	return cursor <= size;
515	>	return cursor < size ||
516	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
517		}
518
519		public E next() {
520	<	checkForComodification();
521	<	if (cursor > size)
522	<	throw new NoSuchElementException();
523	<	E result = queue[cursor];
524	<	lastRet = cursor++;
525	<	return result;
520	>	if (expectedModCount != modCount)
521	>	throw new ConcurrentModificationException();
522	>	if (cursor < size)
523	>	return (E) queue[lastRet = cursor++];
524	>	if (forgetMeNot != null) {
525	>	lastRet = -1;
526	>	lastRetElt = forgetMeNot.poll();
527	>	if (lastRetElt != null)
528	>	return lastRetElt;
529	>	}
530	>	throw new NoSuchElementException();
531		}
532
533		public void remove() {
534	<	if (lastRet == 0)
534	>	if (expectedModCount != modCount)
535	>	throw new ConcurrentModificationException();
536	>	if (lastRet != -1) {
537	>	E moved = PriorityQueue.this.removeAt(lastRet);
538	>	lastRet = -1;
539	>	if (moved == null)
540	>	cursor--;
541	>	else {
542	>	if (forgetMeNot == null)
543	>	forgetMeNot = new ArrayDeque<>();
544	>	forgetMeNot.add(moved);
545	>	}
546	>	} else if (lastRetElt != null) {
547	>	PriorityQueue.this.removeEq(lastRetElt);
548	>	lastRetElt = null;
549	>	} else {
550		throw new IllegalStateException();
551	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
551	>	}
552		expectedModCount = modCount;
553		}
554	+	}
555
556	<	final void checkForComodification() {
557	<	if (modCount != expectedModCount)
558	<	throw new ConcurrentModificationException();
556	>	public int size() {
557	>	return size;
558	>	}
559	>
560	>	/**
561	>	* Removes all of the elements from this priority queue.
562	>	* The queue will be empty after this call returns.
563	>	*/
564	>	public void clear() {
565	>	modCount++;
566	>	final Object[] es = queue;
567	>	for (int i = 0, n = size; i < n; i++)
568	>	es[i] = null;
569	>	size = 0;
570	>	}
571	>
572	>	public E poll() {
573	>	final Object[] es;
574	>	final E result;
575	>
576	>	if ((result = (E) ((es = queue)[0])) != null) {
577	>	modCount++;
578	>	final int n;
579	>	final E x = (E) es[(n = --size)];
580	>	es[n] = null;
581	>	if (n > 0) {
582	>	final Comparator<? super E> cmp;
583	>	if ((cmp = comparator) == null)
584	>	siftDownComparable(0, x, es, n);
585	>	else
586	>	siftDownUsingComparator(0, x, es, n, cmp);
587	>	}
588		}
589	+	return result;
590		}
591
592		/**
593	<	* Returns the number of elements in this priority queue.
593	>	* Removes the ith element from queue.
594		*
595	<	* @return the number of elements in this priority queue.
596	<	*/
597	<	public int size() {
598	<	return size;
595	>	* Normally this method leaves the elements at up to i-1,
596	>	* inclusive, untouched.  Under these circumstances, it returns
597	>	* null.  Occasionally, in order to maintain the heap invariant,
598	>	* it must swap a later element of the list with one earlier than
599	>	* i.  Under these circumstances, this method returns the element
600	>	* that was previously at the end of the list and is now at some
601	>	* position before i. This fact is used by iterator.remove so as to
602	>	* avoid missing traversing elements.
603	>	*/
604	>	E removeAt(int i) {
605	>	// assert i >= 0 && i < size;
606	>	final Object[] es = queue;
607	>	modCount++;
608	>	int s = --size;
609	>	if (s == i) // removed last element
610	>	es[i] = null;
611	>	else {
612	>	E moved = (E) es[s];
613	>	es[s] = null;
614	>	siftDown(i, moved);
615	>	if (es[i] == moved) {
616	>	siftUp(i, moved);
617	>	if (es[i] != moved)
618	>	return moved;
619	>	}
620	>	}
621	>	return null;
622		}
623
624		/**
625	<	* Add the specified element to this priority queue.
625	>	* Inserts item x at position k, maintaining heap invariant by
626	>	* promoting x up the tree until it is greater than or equal to
627	>	* its parent, or is the root.
628	>	*
629	>	* To simplify and speed up coercions and comparisons, the
630	>	* Comparable and Comparator versions are separated into different
631	>	* methods that are otherwise identical. (Similarly for siftDown.)
632		*
633	<	* @param element the element to add.
634	<	* @return true
293	<	* @throws ClassCastException if the specified element cannot be compared
294	<	*            with elements currently in the priority queue according
295	<	*            to the priority queue's ordering.
296	<	* @throws NullPointerException if the specified element is null.
633	>	* @param k the position to fill
634	>	* @param x the item to insert
635		*/
636	<	public boolean offer(E element) {
637	<	if (element == null)
638	<	throw new NullPointerException();
639	<	modCount++;
636	>	private void siftUp(int k, E x) {
637	>	if (comparator != null)
638	>	siftUpUsingComparator(k, x, queue, comparator);
639	>	else
640	>	siftUpComparable(k, x, queue);
641	>	}
642
643	<	// Grow backing store if necessary
644	<	if (++size == queue.length) {
645	<	E[] newQueue = new E[2 * queue.length];
646	<	System.arraycopy(queue, 0, newQueue, 0, size);
647	<	queue = newQueue;
643	>	private static <T> void siftUpComparable(int k, T x, Object[] es) {
644	>	Comparable<? super T> key = (Comparable<? super T>) x;
645	>	while (k > 0) {
646	>	int parent = (k - 1) >>> 1;
647	>	Object e = es[parent];
648	>	if (key.compareTo((T) e) >= 0)
649	>	break;
650	>	es[k] = e;
651	>	k = parent;
652		}
653	+	es[k] = key;
654	+	}
655
656	<	queue[size] = element;
657	<	fixUp(size);
658	<	return true;
656	>	private static <T> void siftUpUsingComparator(
657	>	int k, T x, Object[] es, Comparator<? super T> cmp) {
658	>	while (k > 0) {
659	>	int parent = (k - 1) >>> 1;
660	>	Object e = es[parent];
661	>	if (cmp.compare(x, (T) e) >= 0)
662	>	break;
663	>	es[k] = e;
664	>	k = parent;
665	>	}
666	>	es[k] = x;
667		}
668
669		/**
670	<	* Remove all elements from the priority queue.
670	>	* Inserts item x at position k, maintaining heap invariant by
671	>	* demoting x down the tree repeatedly until it is less than or
672	>	* equal to its children or is a leaf.
673	>	*
674	>	* @param k the position to fill
675	>	* @param x the item to insert
676	>	*/
677	>	private void siftDown(int k, E x) {
678	>	if (comparator != null)
679	>	siftDownUsingComparator(k, x, queue, size, comparator);
680	>	else
681	>	siftDownComparable(k, x, queue, size);
682	>	}
683	>
684	>	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
685	>	// assert n > 0;
686	>	Comparable<? super T> key = (Comparable<? super T>)x;
687	>	int half = n >>> 1;           // loop while a non-leaf
688	>	while (k < half) {
689	>	int child = (k << 1) + 1; // assume left child is least
690	>	Object c = es[child];
691	>	int right = child + 1;
692	>	if (right < n &&
693	>	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
694	>	c = es[child = right];
695	>	if (key.compareTo((T) c) <= 0)
696	>	break;
697	>	es[k] = c;
698	>	k = child;
699	>	}
700	>	es[k] = key;
701	>	}
702	>
703	>	private static <T> void siftDownUsingComparator(
704	>	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
705	>	// assert n > 0;
706	>	int half = n >>> 1;
707	>	while (k < half) {
708	>	int child = (k << 1) + 1;
709	>	Object c = es[child];
710	>	int right = child + 1;
711	>	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
712	>	c = es[child = right];
713	>	if (cmp.compare(x, (T) c) <= 0)
714	>	break;
715	>	es[k] = c;
716	>	k = child;
717	>	}
718	>	es[k] = x;
719	>	}
720	>
721	>	/**
722	>	* Establishes the heap invariant (described above) in the entire tree,
723	>	* assuming nothing about the order of the elements prior to the call.
724	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
725		*/
726	<	public void clear() {
727	<	modCount++;
726	>	private void heapify() {
727	>	final Object[] es = queue;
728	>	int n = size, i = (n >>> 1) - 1;
729	>	final Comparator<? super E> cmp;
730	>	if ((cmp = comparator) == null)
731	>	for (; i >= 0; i--)
732	>	siftDownComparable(i, (E) es[i], es, n);
733	>	else
734	>	for (; i >= 0; i--)
735	>	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
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	>	// OPENJDK @java.io.Serial
761	>	private void writeObject(java.io.ObjectOutputStream s)
762	>	throws java.io.IOException {
763	>	// Write out element count, and any hidden stuff
764	>	s.defaultWriteObject();
765
766	<	// Null out element references to prevent memory leak
767	<	for (int i=1; i<=size; i++)
323	<	queue[i] = null;
766	>	// Write out array length, for compatibility with 1.5 version
767	>	s.writeInt(Math.max(2, size + 1));
768
769	<	size = 0;
769	>	// Write out all elements in the "proper order".
770	>	final Object[] es = queue;
771	>	for (int i = 0, n = size; i < n; i++)
772	>	s.writeObject(es[i]);
773		}
774
775		/**
776	<	* Removes and returns the ith element from queue.  Recall
777	<	* that queue is one-based, so 1 <= i <= size.
776	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
777	>	* (that is, deserializes it).
778		*
779	<	* XXX: Could further special-case i==size, but is it worth it?
780	<	* XXX: Could special-case i==0, but is it worth it?
779	>	* @param s the stream
780	>	* @throws ClassNotFoundException if the class of a serialized object
781	>	*         could not be found
782	>	* @throws java.io.IOException if an I/O error occurs
783		*/
784	<	private E remove(int i) {
785	<	assert i <= size;
786	<	modCount++;
784	>	// OPENJDK @java.io.Serial
785	>	private void readObject(java.io.ObjectInputStream s)
786	>	throws java.io.IOException, ClassNotFoundException {
787	>	// Read in size, and any hidden stuff
788	>	s.defaultReadObject();
789
790	<	E result = queue[i];
791	<	queue[i] = queue[size];
792	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
793	<	if (i <= size)
794	<	fixDown(i);
795	<	return result;
790	>	// Read in (and discard) array length
791	>	s.readInt();
792	>
793	>	jsr166.Platform.checkArray(s, Object[].class, size);
794	>	final Object[] es = queue = new Object[Math.max(size, 1)];
795	>
796	>	// Read in all elements.
797	>	for (int i = 0, n = size; i < n; i++)
798	>	es[i] = s.readObject();
799	>
800	>	// Elements are guaranteed to be in "proper order", but the
801	>	// spec has never explained what that might be.
802	>	heapify();
803		}
804
805		/**
806	<	* Establishes the heap invariant (described above) assuming the heap
807	<	* satisfies the invariant except possibly for the leaf-node indexed by k
808	<	* (which may have a nextExecutionTime less than its parent's).
809	<	*
810	<	* This method functions by "promoting" queue[k] up the hierarchy
811	<	* (by swapping it with its parent) repeatedly until queue[k]
812	<	* is greater than or equal to its parent.
813	<	*/
814	<	private void fixUp(int k) {
815	<	if (comparator == null) {
816	<	while (k > 1) {
817	<	int j = k >> 1;
818	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
819	<	break;
820	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
821	<	k = j;
806	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
807	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
808	>	* queue. The spliterator does not traverse elements in any particular order
809	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
810	>	*
811	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
812	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
813	>	* Overriding implementations should document the reporting of additional
814	>	* characteristic values.
815	>	*
816	>	* @return a {@code Spliterator} over the elements in this queue
817	>	* @since 1.8
818	>	*/
819	>	public final Spliterator<E> spliterator() {
820	>	return new PriorityQueueSpliterator(0, -1, 0);
821	>	}
822	>
823	>	final class PriorityQueueSpliterator implements Spliterator<E> {
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	<	} else {
842	<	while (k > 1) {
843	<	int j = k >> 1;
844	<	if (comparator.compare(queue[j], queue[k]) <= 0)
845	<	break;
846	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
847	<	k = j;
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	>	public void forEachRemaining(Consumer<? super E> action) {
851	>	if (action == null)
852	>	throw new NullPointerException();
853	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
854	>	final Object[] es = queue;
855	>	int i, hi; E e;
856	>	for (i = index, index = hi = fence; i < hi; i++) {
857	>	if ((e = (E) es[i]) == null)
858	>	break;      // must be CME
859	>	action.accept(e);
860	>	}
861	>	if (modCount != expectedModCount)
862	>	throw new ConcurrentModificationException();
863	>	}
864	>
865	>	public boolean tryAdvance(Consumer<? super E> action) {
866	>	if (action == null)
867	>	throw new NullPointerException();
868	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
869	>	int i;
870	>	if ((i = index) < fence) {
871	>	index = i + 1;
872	>	E e;
873	>	if ((e = (E) queue[i]) == null
874	>	|| modCount != expectedModCount)
875	>	throw new ConcurrentModificationException();
876	>	action.accept(e);
877	>	return true;
878		}
879	+	return false;
880	+	}
881	+
882	+	public long estimateSize() {
883	+	return getFence() - index;
884	+	}
885	+
886	+	public int characteristics() {
887	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
888		}
889		}
890
891		/**
892	<	* Establishes the heap invariant (described above) in the subtree
893	<	* rooted at k, which is assumed to satisfy the heap invariant except
894	<	* possibly for node k itself (which may be greater than its children).
895	<	*
896	<	* This method functions by "demoting" queue[k] down the hierarchy
897	<	* (by swapping it with its smaller child) repeatedly until queue[k]
898	<	* is less than or equal to its children.
899	<	*/
900	<	private void fixDown(int k) {
901	<	int j;
902	<	if (comparator == null) {
903	<	while ((j = k << 1) <= size) {
904	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
905	<	j++; // j indexes smallest kid
906	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
907	<	break;
908	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
909	<	k = j;
910	<	}
911	<	} else {
912	<	while ((j = k << 1) <= size) {
913	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
914	<	j++; // j indexes smallest kid
915	<	if (comparator.compare(queue[k], queue[j]) <= 0)
916	<	break;
917	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
918	<	k = j;
919	<	}
892	>	* @throws NullPointerException {@inheritDoc}
893	>	*/
894	>	public boolean removeIf(Predicate<? super E> filter) {
895	>	Objects.requireNonNull(filter);
896	>	return bulkRemove(filter);
897	>	}
898	>
899	>	/**
900	>	* @throws NullPointerException {@inheritDoc}
901	>	*/
902	>	public boolean removeAll(Collection<?> c) {
903	>	Objects.requireNonNull(c);
904	>	return bulkRemove(e -> c.contains(e));
905	>	}
906	>
907	>	/**
908	>	* @throws NullPointerException {@inheritDoc}
909	>	*/
910	>	public boolean retainAll(Collection<?> c) {
911	>	Objects.requireNonNull(c);
912	>	return bulkRemove(e -> !c.contains(e));
913	>	}
914	>
915	>	// A tiny bit set implementation
916	>
917	>	private static long[] nBits(int n) {
918	>	return new long[((n - 1) >> 6) + 1];
919	>	}
920	>	private static void setBit(long[] bits, int i) {
921	>	bits[i >> 6] |= 1L << i;
922	>	}
923	>	private static boolean isClear(long[] bits, int i) {
924	>	return (bits[i >> 6] & (1L << i)) == 0;
925	>	}
926	>
927	>	/** Implementation of bulk remove methods. */
928	>	private boolean bulkRemove(Predicate<? super E> filter) {
929	>	final int expectedModCount = ++modCount;
930	>	final Object[] es = queue;
931	>	final int end = size;
932	>	int i;
933	>	// Optimize for initial run of survivors
934	>	for (i = 0; i < end && !filter.test((E) es[i]); i++)
935	>	;
936	>	if (i >= end) {
937	>	if (modCount != expectedModCount)
938	>	throw new ConcurrentModificationException();
939	>	return false;
940		}
941	+	// Tolerate predicates that reentrantly access the collection for
942	+	// read (but writers still get CME), so traverse once to find
943	+	// elements to delete, a second pass to physically expunge.
944	+	final int beg = i;
945	+	final long[] deathRow = nBits(end - beg);
946	+	deathRow[0] = 1L;   // set bit 0
947	+	for (i = beg + 1; i < end; i++)
948	+	if (filter.test((E) es[i]))
949	+	setBit(deathRow, i - beg);
950	+	if (modCount != expectedModCount)
951	+	throw new ConcurrentModificationException();
952	+	int w = beg;
953	+	for (i = beg; i < end; i++)
954	+	if (isClear(deathRow, i - beg))
955	+	es[w++] = es[i];
956	+	for (i = size = w; i < end; i++)
957	+	es[i] = null;
958	+	heapify();
959	+	return true;
960		}
961
962		/**
963	<	* Returns the comparator associated with this priority queue, or
410	<	* <tt>null</tt> if it uses its elements' natural ordering.
411	<	*
412	<	* @return the comparator associated with this priority queue, or
413	<	*         <tt>null</tt> if it uses its elements' natural ordering.
963	>	* @throws NullPointerException {@inheritDoc}
964		*/
965	<	Comparator<E> comparator() {
966	<	return comparator;
965	>	public void forEach(Consumer<? super E> action) {
966	>	Objects.requireNonNull(action);
967	>	final int expectedModCount = modCount;
968	>	final Object[] es = queue;
969	>	for (int i = 0, n = size; i < n; i++)
970	>	action.accept((E) es[i]);
971	>	if (expectedModCount != modCount)
972	>	throw new ConcurrentModificationException();
973		}
974		}

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