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

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3	>	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	>	*
5	>	* This code is free software; you can redistribute it and/or modify it
6	>	* under the terms of the GNU General Public License version 2 only, as
7	>	* published by the Free Software Foundation.  Oracle designates this
8	>	* particular file as subject to the "Classpath" exception as provided
9	>	* by Oracle in the LICENSE file that accompanied this code.
10	>	*
11	>	* This code is distributed in the hope that it will be useful, but WITHOUT
12	>	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	>	* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14	>	* version 2 for more details (a copy is included in the LICENSE file that
15	>	* accompanied this code).
16	>	*
17	>	* You should have received a copy of the GNU General Public License version
18	>	* 2 along with this work; if not, write to the Free Software Foundation,
19	>	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20		*
21	<	*   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	+	import jdk.internal.misc.SharedSecrets;
31	+
32		/**
33	<	* An unbounded priority queue based on a priority heap.  This queue orders
34	<	* elements according to the order specified at creation time.  This order is
35	<	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
36	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
37	<	* according to a {@link Comparator}, depending on which constructor is used.
38	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
39	<	* minimal element with respect to the specified ordering.  If multiple
40	<	* these elements are tied for least value, no guarantees are made as to
41	<	* which of elements is returned.
42	<	*
43	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
44	<	* the array used to store the elements on the queue.  It is always at least
45	<	* as large as the queue size.  As elements are added to a priority list,
46	<	* its capacity grows automatically.  The details of the growth policy are not
33	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
34	>	* The elements of the priority queue are ordered according to their
35	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
36	>	* provided at queue construction time, depending on which constructor is
37	>	* used.  A priority queue does not permit {@code null} elements.
38	>	* A priority queue relying on natural ordering also does not permit
39	>	* insertion of non-comparable objects (doing so may result in
40	>	* {@code ClassCastException}).
41	>	*
42	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
43	>	* with respect to the specified ordering.  If multiple elements are
44	>	* tied for least value, the head is one of those elements -- ties are
45	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
46	>	* {@code remove}, {@code peek}, and {@code element} access the
47	>	* element at the head of the queue.
48	>	*
49	>	* <p>A priority queue is unbounded, but has an internal
50	>	* <i>capacity</i> governing the size of an array used to store the
51	>	* elements on the queue.  It is always at least as large as the queue
52	>	* size.  As elements are added to a priority queue, its capacity
53	>	* grows automatically.  The details of the growth policy are not
54		* specified.
55		*
56	<	*<p>Implementation note: this implementation provides O(log(n)) time for
57	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
58	<	* methods; linear time for the <tt>remove(Object)</tt> and
59	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
60	<	* <tt>element</tt>, and <tt>size</tt> methods.
56	>	* <p>This class and its iterator implement all of the
57	>	* <em>optional</em> methods of the {@link Collection} and {@link
58	>	* Iterator} interfaces.  The Iterator provided in method {@link
59	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
60	>	* are <em>not</em> guaranteed to traverse the elements of
61	>	* the priority queue in any particular order. If you need ordered
62	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
63	>	*
64	>	* <p><strong>Note that this implementation is not synchronized.</strong>
65	>	* Multiple threads should not access a {@code PriorityQueue}
66	>	* instance concurrently if any of the threads modifies the queue.
67	>	* Instead, use the thread-safe {@link
68	>	* java.util.concurrent.PriorityBlockingQueue} class.
69	>	*
70	>	* <p>Implementation note: this implementation provides
71	>	* O(log(n)) time for the enqueuing and dequeuing methods
72	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
73	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
74	>	* methods; and constant time for the retrieval methods
75	>	* ({@code peek}, {@code element}, and {@code size}).
76		*
77		* <p>This class is a member of the
78	<	* <a href="{@docRoot}/../guide/collections/index.html">
78	>	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
79		* Java Collections Framework</a>.
80	+	*
81	+	* @since 1.5
82	+	* @author Josh Bloch, Doug Lea
83	+	* @param <E> the type of elements held in this queue
84		*/
85	+	@SuppressWarnings("unchecked")
86		public class PriorityQueue<E> extends AbstractQueue<E>
87	<	implements Queue<E>
88	<	{
87	>	implements java.io.Serializable {
88	>
89	>	private static final long serialVersionUID = -7720805057305804111L;
90	>
91		private static final int DEFAULT_INITIAL_CAPACITY = 11;
92
93		/**
94	<	* Priority queue represented as a balanced binary heap: the two children
95	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
96	<	* ordered by comparator, or by the elements' natural ordering, if
97	<	* comparator is null:  For each node n in the heap, and each descendant
98	<	* of n, d, n <= d.
99	<	*
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.
94	>	* Priority queue represented as a balanced binary heap: the two
95	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
96	>	* priority queue is ordered by comparator, or by the elements'
97	>	* natural ordering, if comparator is null: For each node n in the
98	>	* heap and each descendant d of n, n <= d.  The element with the
99	>	* lowest value is in queue[0], assuming the queue is nonempty.
100		*/
101	<	private E[] queue;
101	>	transient Object[] queue; // non-private to simplify nested class access
102
103		/**
104		* The number of elements in the priority queue.
105		*/
106	<	private int size = 0;
106	>	int size;
107
108		/**
109		* The comparator, or null if priority queue uses elements'
110		* natural ordering.
111		*/
112	<	private final Comparator<E> comparator;
112	>	private final Comparator<? super E> comparator;
113
114		/**
115		* The number of times this priority queue has been
116		* <i>structurally modified</i>.  See AbstractList for gory details.
117		*/
118	<	private int modCount = 0;
118	>	transient int modCount;     // non-private to simplify nested class access
119
120		/**
121	<	* Create a new priority queue with the default initial capacity (11)
122	<	* that orders its elements according to their natural ordering.
121	>	* Creates a {@code PriorityQueue} with the default initial
122	>	* capacity (11) that orders its elements according to their
123	>	* {@linkplain Comparable natural ordering}.
124		*/
125		public PriorityQueue() {
126	<	this(DEFAULT_INITIAL_CAPACITY);
126	>	this(DEFAULT_INITIAL_CAPACITY, null);
127		}
128
129		/**
130	<	* Create a new priority queue with the specified initial capacity
131	<	* that orders its elements according to their natural ordering.
130	>	* Creates a {@code PriorityQueue} with the specified initial
131	>	* capacity that orders its elements according to their
132	>	* {@linkplain Comparable natural ordering}.
133		*
134	<	* @param initialCapacity the initial capacity for this priority queue.
134	>	* @param initialCapacity the initial capacity for this priority queue
135	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
136	>	*         than 1
137		*/
138		public PriorityQueue(int initialCapacity) {
139		this(initialCapacity, null);
140		}
141
142		/**
143	<	* Create a new priority queue with the specified initial capacity (11)
144	<	* that orders its elements according to the specified comparator.
143	>	* Creates a {@code PriorityQueue} with the default initial capacity and
144	>	* whose elements are ordered according to the specified comparator.
145		*
146	<	* @param initialCapacity the initial capacity for this priority queue.
147	<	* @param comparator the comparator used to order this priority queue.
146	>	* @param  comparator the comparator that will be used to order this
147	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
148	>	*         natural ordering} of the elements will be used.
149	>	* @since 1.8
150		*/
151	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
151	>	public PriorityQueue(Comparator<? super E> comparator) {
152	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
153	>	}
154	>
155	>	/**
156	>	* Creates a {@code PriorityQueue} with the specified initial capacity
157	>	* that orders its elements according to the specified comparator.
158	>	*
159	>	* @param  initialCapacity the initial capacity for this priority queue
160	>	* @param  comparator the comparator that will be used to order this
161	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
162	>	*         natural ordering} of the elements will be used.
163	>	* @throws IllegalArgumentException if {@code initialCapacity} is
164	>	*         less than 1
165	>	*/
166	>	public PriorityQueue(int initialCapacity,
167	>	Comparator<? super E> comparator) {
168	>	// Note: This restriction of at least one is not actually needed,
169	>	// but continues for 1.5 compatibility
170		if (initialCapacity < 1)
171	<	initialCapacity = 1;
172	<	queue = new E[initialCapacity + 1];
171	>	throw new IllegalArgumentException();
172	>	this.queue = new Object[initialCapacity];
173		this.comparator = comparator;
174		}
175
176		/**
177	<	* Create a new priority queue containing the elements in the specified
178	<	* collection.  The priority queue has an initial capacity of 110% of the
179	<	* size of the specified collection. If the specified collection
180	<	* implements the {@link Sorted} interface, the priority queue will be
181	<	* sorted according to the same comparator, or according to its elements'
182	<	* 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.
177	>	* Creates a {@code PriorityQueue} containing the elements in the
178	>	* specified collection.  If the specified collection is an instance of
179	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
180	>	* priority queue will be ordered according to the same ordering.
181	>	* Otherwise, this priority queue will be ordered according to the
182	>	* {@linkplain Comparable natural ordering} of its elements.
183		*
184	<	* @param initialElements the collection whose elements are to be placed
185	<	*        into this priority queue.
184	>	* @param  c the collection whose elements are to be placed
185	>	*         into this priority queue
186		* @throws ClassCastException if elements of the specified collection
187		*         cannot be compared to one another according to the priority
188	<	*         queue's ordering.
189	<	* @throws NullPointerException if the specified collection or an
190	<	*         element of the specified collection is <tt>null</tt>.
191	<	*/
192	<	public PriorityQueue(Collection<E> initialElements) {
193	<	int sz = initialElements.size();
194	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
195	<	Integer.MAX_VALUE - 1);
196	<	if (initialCapacity < 1)
197	<	initialCapacity = 1;
198	<	queue = new E[initialCapacity + 1];
188	>	*         queue's ordering
189	>	* @throws NullPointerException if the specified collection or any
190	>	*         of its elements are null
191	>	*/
192	>	public PriorityQueue(Collection<? extends E> c) {
193	>	if (c instanceof SortedSet<?>) {
194	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
195	>	this.comparator = (Comparator<? super E>) ss.comparator();
196	>	initElementsFromCollection(ss);
197	>	}
198	>	else if (c instanceof PriorityQueue<?>) {
199	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
200	>	this.comparator = (Comparator<? super E>) pq.comparator();
201	>	initFromPriorityQueue(pq);
202	>	}
203	>	else {
204	>	this.comparator = null;
205	>	initFromCollection(c);
206	>	}
207	>	}
208
209	<	/* Commented out to compile with generics compiler
209	>	/**
210	>	* Creates a {@code PriorityQueue} containing the elements in the
211	>	* specified priority queue.  This priority queue will be
212	>	* ordered according to the same ordering as the given priority
213	>	* queue.
214	>	*
215	>	* @param  c the priority queue whose elements are to be placed
216	>	*         into this priority queue
217	>	* @throws ClassCastException if elements of {@code c} cannot be
218	>	*         compared to one another according to {@code c}'s
219	>	*         ordering
220	>	* @throws NullPointerException if the specified priority queue or any
221	>	*         of its elements are null
222	>	*/
223	>	public PriorityQueue(PriorityQueue<? extends E> c) {
224	>	this.comparator = (Comparator<? super E>) c.comparator();
225	>	initFromPriorityQueue(c);
226	>	}
227
228	<	if (initialElements instanceof Sorted) {
229	<	comparator = ((Sorted)initialElements).comparator();
230	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
231	<	queue[++size] = i.next();
228	>	/**
229	>	* Creates a {@code PriorityQueue} containing the elements in the
230	>	* specified sorted set.   This priority queue will be ordered
231	>	* according to the same ordering as the given sorted set.
232	>	*
233	>	* @param  c the sorted set whose elements are to be placed
234	>	*         into this priority queue
235	>	* @throws ClassCastException if elements of the specified sorted
236	>	*         set cannot be compared to one another according to the
237	>	*         sorted set's ordering
238	>	* @throws NullPointerException if the specified sorted set or any
239	>	*         of its elements are null
240	>	*/
241	>	public PriorityQueue(SortedSet<? extends E> c) {
242	>	this.comparator = (Comparator<? super E>) c.comparator();
243	>	initElementsFromCollection(c);
244	>	}
245	>
246	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
247	>	private static Object[] ensureNonEmpty(Object[] es) {
248	>	return (es.length > 0) ? es : new Object[1];
249	>	}
250	>
251	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
252	>	if (c.getClass() == PriorityQueue.class) {
253	>	this.queue = ensureNonEmpty(c.toArray());
254	>	this.size = c.size();
255		} else {
256	<	*/
140	<	{
141	<	comparator = null;
142	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
256	>	initFromCollection(c);
257		}
258		}
259
260	<	// Queue Methods
260	>	private void initElementsFromCollection(Collection<? extends E> c) {
261	>	Object[] es = c.toArray();
262	>	int len = es.length;
263	>	// If c.toArray incorrectly doesn't return Object[], copy it.
264	>	if (es.getClass() != Object[].class)
265	>	es = Arrays.copyOf(es, len, Object[].class);
266	>	if (len == 1 || this.comparator != null)
267	>	for (Object e : es)
268	>	if (e == null)
269	>	throw new NullPointerException();
270	>	this.queue = ensureNonEmpty(es);
271	>	this.size = len;
272	>	}
273
274		/**
275	<	* 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.
275	>	* Initializes queue array with elements from the given Collection.
276		*
277	<	* @return the minimal element from this priority queue if it contains
155	<	*         one or more elements, otherwise <tt>null</tt>.
277	>	* @param c the collection
278		*/
279	<	public E poll() {
280	<	if (size == 0)
281	<	return null;
160	<	return remove(1);
279	>	private void initFromCollection(Collection<? extends E> c) {
280	>	initElementsFromCollection(c);
281	>	heapify();
282		}
283
284		/**
285	<	* Return, but do not remove, the minimal element from the priority queue,
286	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
287	<	* defined according to this priority queue's order.  This method returns
288	<	* the same object reference that would be returned by by the
289	<	* <tt>poll</tt> method.  The two methods differ in that this method
290	<	* does not remove the element from the priority queue.
285	>	* The maximum size of array to allocate.
286	>	* Some VMs reserve some header words in an array.
287	>	* Attempts to allocate larger arrays may result in
288	>	* OutOfMemoryError: Requested array size exceeds VM limit
289	>	*/
290	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
291	>
292	>	/**
293	>	* Increases the capacity of the array.
294		*
295	<	* @return the minimal element from this priority queue if it contains
172	<	*         one or more elements, otherwise <tt>null</tt>.
295	>	* @param minCapacity the desired minimum capacity
296		*/
297	+	private void grow(int minCapacity) {
298	+	int oldCapacity = queue.length;
299	+	// Double size if small; else grow by 50%
300	+	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
301	+	(oldCapacity + 2) :
302	+	(oldCapacity >> 1));
303	+	// overflow-conscious code
304	+	if (newCapacity - MAX_ARRAY_SIZE > 0)
305	+	newCapacity = hugeCapacity(minCapacity);
306	+	queue = Arrays.copyOf(queue, newCapacity);
307	+	}
308	+
309	+	private static int hugeCapacity(int minCapacity) {
310	+	if (minCapacity < 0) // overflow
311	+	throw new OutOfMemoryError();
312	+	return (minCapacity > MAX_ARRAY_SIZE) ?
313	+	Integer.MAX_VALUE :
314	+	MAX_ARRAY_SIZE;
315	+	}
316	+
317	+	/**
318	+	* Inserts the specified element into this priority queue.
319	+	*
320	+	* @return {@code true} (as specified by {@link Collection#add})
321	+	* @throws ClassCastException if the specified element cannot be
322	+	*         compared with elements currently in this priority queue
323	+	*         according to the priority queue's ordering
324	+	* @throws NullPointerException if the specified element is null
325	+	*/
326	+	public boolean add(E e) {
327	+	return offer(e);
328	+	}
329	+
330	+	/**
331	+	* Inserts the specified element into this priority queue.
332	+	*
333	+	* @return {@code true} (as specified by {@link Queue#offer})
334	+	* @throws ClassCastException if the specified element cannot be
335	+	*         compared with elements currently in this priority queue
336	+	*         according to the priority queue's ordering
337	+	* @throws NullPointerException if the specified element is null
338	+	*/
339	+	public boolean offer(E e) {
340	+	if (e == null)
341	+	throw new NullPointerException();
342	+	modCount++;
343	+	int i = size;
344	+	if (i >= queue.length)
345	+	grow(i + 1);
346	+	siftUp(i, e);
347	+	size = i + 1;
348	+	return true;
349	+	}
350	+
351		public E peek() {
352	<	return queue[1];
352	>	return (E) queue[0];
353		}
354
355	<	// Collection Methods
355	>	private int indexOf(Object o) {
356	>	if (o != null) {
357	>	final Object[] es = queue;
358	>	for (int i = 0, n = size; i < n; i++)
359	>	if (o.equals(es[i]))
360	>	return i;
361	>	}
362	>	return -1;
363	>	}
364
365		/**
366	<	* Removes a single instance of the specified element from this priority
367	<	* queue, if it is present.  Returns true if this collection contained the
368	<	* specified element (or equivalently, if this collection changed as a
366	>	* Removes a single instance of the specified element from this queue,
367	>	* if it is present.  More formally, removes an element {@code e} such
368	>	* that {@code o.equals(e)}, if this queue contains one or more such
369	>	* elements.  Returns {@code true} if and only if this queue contained
370	>	* the specified element (or equivalently, if this queue changed as a
371		* result of the call).
372		*
373	<	* @param o element to be removed from this collection, if present.
374	<	* @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.
373	>	* @param o element to be removed from this queue, if present
374	>	* @return {@code true} if this queue changed as a result of the call
375		*/
376	<	public boolean remove(Object element) {
377	<	if (element == null)
378	<	throw new NullPointerException();
376	>	public boolean remove(Object o) {
377	>	int i = indexOf(o);
378	>	if (i == -1)
379	>	return false;
380	>	else {
381	>	removeAt(i);
382	>	return true;
383	>	}
384	>	}
385
386	<	if (comparator == null) {
387	<	for (int i = 1; i <= size; i++) {
388	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
389	<	remove(i);
390	<	return true;
391	<	}
392	<	}
393	<	} else {
394	<	for (int i = 1; i <= size; i++) {
395	<	if (comparator.compare(queue[i], (E) element) == 0) {
396	<	remove(i);
209	<	return true;
210	<	}
386	>	/**
387	>	* Identity-based version for use in Itr.remove.
388	>	*
389	>	* @param o element to be removed from this queue, if present
390	>	*/
391	>	void removeEq(Object o) {
392	>	final Object[] es = queue;
393	>	for (int i = 0, n = size; i < n; i++) {
394	>	if (o == es[i]) {
395	>	removeAt(i);
396	>	break;
397		}
398		}
213	–	return false;
399		}
400
401		/**
402	<	* Returns an iterator over the elements in this priority queue.  The
403	<	* first element returned by this iterator is the same element that
404	<	* would be returned by a call to <tt>peek</tt>.
402	>	* Returns {@code true} if this queue contains the specified element.
403	>	* More formally, returns {@code true} if and only if this queue contains
404	>	* at least one element {@code e} such that {@code o.equals(e)}.
405	>	*
406	>	* @param o object to be checked for containment in this queue
407	>	* @return {@code true} if this queue contains the specified element
408	>	*/
409	>	public boolean contains(Object o) {
410	>	return indexOf(o) >= 0;
411	>	}
412	>
413	>	/**
414	>	* Returns an array containing all of the elements in this queue.
415	>	* The elements are in no particular order.
416	>	*
417	>	* <p>The returned array will be "safe" in that no references to it are
418	>	* maintained by this queue.  (In other words, this method must allocate
419	>	* a new array).  The caller is thus free to modify the returned array.
420	>	*
421	>	* <p>This method acts as bridge between array-based and collection-based
422	>	* APIs.
423	>	*
424	>	* @return an array containing all of the elements in this queue
425	>	*/
426	>	public Object[] toArray() {
427	>	return Arrays.copyOf(queue, size);
428	>	}
429	>
430	>	/**
431	>	* Returns an array containing all of the elements in this queue; the
432	>	* runtime type of the returned array is that of the specified array.
433	>	* The returned array elements are in no particular order.
434	>	* If the queue fits in the specified array, it is returned therein.
435	>	* Otherwise, a new array is allocated with the runtime type of the
436	>	* specified array and the size of this queue.
437	>	*
438	>	* <p>If the queue fits in the specified array with room to spare
439	>	* (i.e., the array has more elements than the queue), the element in
440	>	* the array immediately following the end of the collection is set to
441	>	* {@code null}.
442	>	*
443	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
444	>	* array-based and collection-based APIs.  Further, this method allows
445	>	* precise control over the runtime type of the output array, and may,
446	>	* under certain circumstances, be used to save allocation costs.
447	>	*
448	>	* <p>Suppose {@code x} is a queue known to contain only strings.
449	>	* The following code can be used to dump the queue into a newly
450	>	* allocated array of {@code String}:
451	>	*
452	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
453	>	*
454	>	* Note that {@code toArray(new Object[0])} is identical in function to
455	>	* {@code toArray()}.
456	>	*
457	>	* @param a the array into which the elements of the queue are to
458	>	*          be stored, if it is big enough; otherwise, a new array of the
459	>	*          same runtime type is allocated for this purpose.
460	>	* @return an array containing all of the elements in this queue
461	>	* @throws ArrayStoreException if the runtime type of the specified array
462	>	*         is not a supertype of the runtime type of every element in
463	>	*         this queue
464	>	* @throws NullPointerException if the specified array is null
465	>	*/
466	>	public <T> T[] toArray(T[] a) {
467	>	final int size = this.size;
468	>	if (a.length < size)
469	>	// Make a new array of a's runtime type, but my contents:
470	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
471	>	System.arraycopy(queue, 0, a, 0, size);
472	>	if (a.length > size)
473	>	a[size] = null;
474	>	return a;
475	>	}
476	>
477	>	/**
478	>	* Returns an iterator over the elements in this queue. The iterator
479	>	* does not return the elements in any particular order.
480		*
481	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
481	>	* @return an iterator over the elements in this queue
482		*/
483		public Iterator<E> iterator() {
484		return new Itr();
485		}
486
487	<	private class Itr implements Iterator<E> {
487	>	private final class Itr implements Iterator<E> {
488		/**
489		* Index (into queue array) of element to be returned by
490		* subsequent call to next.
491		*/
492	<	int cursor = 1;
492	>	private int cursor;
493	>
494	>	/**
495	>	* Index of element returned by most recent call to next,
496	>	* unless that element came from the forgetMeNot list.
497	>	* Set to -1 if element is deleted by a call to remove.
498	>	*/
499	>	private int lastRet = -1;
500
501		/**
502	<	* Index of element returned by most recent call to next or
503	<	* previous.  Reset to 0 if this element is deleted by a call
504	<	* to remove.
502	>	* A queue of elements that were moved from the unvisited portion of
503	>	* the heap into the visited portion as a result of "unlucky" element
504	>	* removals during the iteration.  (Unlucky element removals are those
505	>	* that require a siftup instead of a siftdown.)  We must visit all of
506	>	* the elements in this list to complete the iteration.  We do this
507	>	* after we've completed the "normal" iteration.
508	>	*
509	>	* We expect that most iterations, even those involving removals,
510	>	* will not need to store elements in this field.
511		*/
512	<	int lastRet = 0;
512	>	private ArrayDeque<E> forgetMeNot;
513	>
514	>	/**
515	>	* Element returned by the most recent call to next iff that
516	>	* element was drawn from the forgetMeNot list.
517	>	*/
518	>	private E lastRetElt;
519
520		/**
521		* The modCount value that the iterator believes that the backing
522	<	* List should have.  If this expectation is violated, the iterator
522	>	* Queue should have.  If this expectation is violated, the iterator
523		* has detected concurrent modification.
524		*/
525	<	int expectedModCount = modCount;
525	>	private int expectedModCount = modCount;
526	>
527	>	Itr() {}                        // prevent access constructor creation
528
529		public boolean hasNext() {
530	<	return cursor <= size;
530	>	return cursor < size ||
531	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
532		}
533
534		public E next() {
535	<	checkForComodification();
536	<	if (cursor > size)
537	<	throw new NoSuchElementException();
538	<	E result = queue[cursor];
539	<	lastRet = cursor++;
540	<	return result;
535	>	if (expectedModCount != modCount)
536	>	throw new ConcurrentModificationException();
537	>	if (cursor < size)
538	>	return (E) queue[lastRet = cursor++];
539	>	if (forgetMeNot != null) {
540	>	lastRet = -1;
541	>	lastRetElt = forgetMeNot.poll();
542	>	if (lastRetElt != null)
543	>	return lastRetElt;
544	>	}
545	>	throw new NoSuchElementException();
546		}
547
548		public void remove() {
549	<	if (lastRet == 0)
549	>	if (expectedModCount != modCount)
550	>	throw new ConcurrentModificationException();
551	>	if (lastRet != -1) {
552	>	E moved = PriorityQueue.this.removeAt(lastRet);
553	>	lastRet = -1;
554	>	if (moved == null)
555	>	cursor--;
556	>	else {
557	>	if (forgetMeNot == null)
558	>	forgetMeNot = new ArrayDeque<>();
559	>	forgetMeNot.add(moved);
560	>	}
561	>	} else if (lastRetElt != null) {
562	>	PriorityQueue.this.removeEq(lastRetElt);
563	>	lastRetElt = null;
564	>	} else {
565		throw new IllegalStateException();
566	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
566	>	}
567		expectedModCount = modCount;
568		}
569	+	}
570
571	<	final void checkForComodification() {
572	<	if (modCount != expectedModCount)
573	<	throw new ConcurrentModificationException();
571	>	public int size() {
572	>	return size;
573	>	}
574	>
575	>	/**
576	>	* Removes all of the elements from this priority queue.
577	>	* The queue will be empty after this call returns.
578	>	*/
579	>	public void clear() {
580	>	modCount++;
581	>	final Object[] es = queue;
582	>	for (int i = 0, n = size; i < n; i++)
583	>	es[i] = null;
584	>	size = 0;
585	>	}
586	>
587	>	public E poll() {
588	>	final Object[] es;
589	>	final E result;
590	>
591	>	if ((result = (E) ((es = queue)[0])) != null) {
592	>	modCount++;
593	>	final int n;
594	>	final E x = (E) es[(n = --size)];
595	>	es[n] = null;
596	>	if (n > 0) {
597	>	final Comparator<? super E> cmp;
598	>	if ((cmp = comparator) == null)
599	>	siftDownComparable(0, x, es, n);
600	>	else
601	>	siftDownUsingComparator(0, x, es, n, cmp);
602	>	}
603		}
604	+	return result;
605		}
606
607		/**
608	<	* Returns the number of elements in this priority queue.
608	>	* Removes the ith element from queue.
609		*
610	<	* @return the number of elements in this priority queue.
611	<	*/
612	<	public int size() {
613	<	return size;
610	>	* Normally this method leaves the elements at up to i-1,
611	>	* inclusive, untouched.  Under these circumstances, it returns
612	>	* null.  Occasionally, in order to maintain the heap invariant,
613	>	* it must swap a later element of the list with one earlier than
614	>	* i.  Under these circumstances, this method returns the element
615	>	* that was previously at the end of the list and is now at some
616	>	* position before i. This fact is used by iterator.remove so as to
617	>	* avoid missing traversing elements.
618	>	*/
619	>	E removeAt(int i) {
620	>	// assert i >= 0 && i < size;
621	>	final Object[] es = queue;
622	>	modCount++;
623	>	int s = --size;
624	>	if (s == i) // removed last element
625	>	es[i] = null;
626	>	else {
627	>	E moved = (E) es[s];
628	>	es[s] = null;
629	>	siftDown(i, moved);
630	>	if (es[i] == moved) {
631	>	siftUp(i, moved);
632	>	if (es[i] != moved)
633	>	return moved;
634	>	}
635	>	}
636	>	return null;
637		}
638
639		/**
640	<	* Add the specified element to this priority queue.
640	>	* Inserts item x at position k, maintaining heap invariant by
641	>	* promoting x up the tree until it is greater than or equal to
642	>	* its parent, or is the root.
643	>	*
644	>	* To simplify and speed up coercions and comparisons, the
645	>	* Comparable and Comparator versions are separated into different
646	>	* methods that are otherwise identical. (Similarly for siftDown.)
647		*
648	<	* @param element the element to add.
649	<	* @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.
648	>	* @param k the position to fill
649	>	* @param x the item to insert
650		*/
651	<	public boolean offer(E element) {
652	<	if (element == null)
653	<	throw new NullPointerException();
654	<	modCount++;
651	>	private void siftUp(int k, E x) {
652	>	if (comparator != null)
653	>	siftUpUsingComparator(k, x, queue, comparator);
654	>	else
655	>	siftUpComparable(k, x, queue);
656	>	}
657
658	<	// Grow backing store if necessary
659	<	if (++size == queue.length) {
660	<	E[] newQueue = new E[2 * queue.length];
661	<	System.arraycopy(queue, 0, newQueue, 0, size);
662	<	queue = newQueue;
658	>	private static <T> void siftUpComparable(int k, T x, Object[] es) {
659	>	Comparable<? super T> key = (Comparable<? super T>) x;
660	>	while (k > 0) {
661	>	int parent = (k - 1) >>> 1;
662	>	Object e = es[parent];
663	>	if (key.compareTo((T) e) >= 0)
664	>	break;
665	>	es[k] = e;
666	>	k = parent;
667		}
668	+	es[k] = key;
669	+	}
670
671	<	queue[size] = element;
672	<	fixUp(size);
673	<	return true;
671	>	private static <T> void siftUpUsingComparator(
672	>	int k, T x, Object[] es, Comparator<? super T> cmp) {
673	>	while (k > 0) {
674	>	int parent = (k - 1) >>> 1;
675	>	Object e = es[parent];
676	>	if (cmp.compare(x, (T) e) >= 0)
677	>	break;
678	>	es[k] = e;
679	>	k = parent;
680	>	}
681	>	es[k] = x;
682		}
683
684		/**
685	<	* Remove all elements from the priority queue.
685	>	* Inserts item x at position k, maintaining heap invariant by
686	>	* demoting x down the tree repeatedly until it is less than or
687	>	* equal to its children or is a leaf.
688	>	*
689	>	* @param k the position to fill
690	>	* @param x the item to insert
691	>	*/
692	>	private void siftDown(int k, E x) {
693	>	if (comparator != null)
694	>	siftDownUsingComparator(k, x, queue, size, comparator);
695	>	else
696	>	siftDownComparable(k, x, queue, size);
697	>	}
698	>
699	>	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
700	>	// assert n > 0;
701	>	Comparable<? super T> key = (Comparable<? super T>)x;
702	>	int half = n >>> 1;           // loop while a non-leaf
703	>	while (k < half) {
704	>	int child = (k << 1) + 1; // assume left child is least
705	>	Object c = es[child];
706	>	int right = child + 1;
707	>	if (right < n &&
708	>	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
709	>	c = es[child = right];
710	>	if (key.compareTo((T) c) <= 0)
711	>	break;
712	>	es[k] = c;
713	>	k = child;
714	>	}
715	>	es[k] = key;
716	>	}
717	>
718	>	private static <T> void siftDownUsingComparator(
719	>	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
720	>	// assert n > 0;
721	>	int half = n >>> 1;
722	>	while (k < half) {
723	>	int child = (k << 1) + 1;
724	>	Object c = es[child];
725	>	int right = child + 1;
726	>	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
727	>	c = es[child = right];
728	>	if (cmp.compare(x, (T) c) <= 0)
729	>	break;
730	>	es[k] = c;
731	>	k = child;
732	>	}
733	>	es[k] = x;
734	>	}
735	>
736	>	/**
737	>	* Establishes the heap invariant (described above) in the entire tree,
738	>	* assuming nothing about the order of the elements prior to the call.
739	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
740		*/
741	<	public void clear() {
742	<	modCount++;
741	>	private void heapify() {
742	>	final Object[] es = queue;
743	>	int n = size, i = (n >>> 1) - 1;
744	>	final Comparator<? super E> cmp;
745	>	if ((cmp = comparator) == null)
746	>	for (; i >= 0; i--)
747	>	siftDownComparable(i, (E) es[i], es, n);
748	>	else
749	>	for (; i >= 0; i--)
750	>	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
751	>	}
752
753	<	// Null out element references to prevent memory leak
754	<	for (int i=1; i<=size; i++)
755	<	queue[i] = null;
753	>	/**
754	>	* Returns the comparator used to order the elements in this
755	>	* queue, or {@code null} if this queue is sorted according to
756	>	* the {@linkplain Comparable natural ordering} of its elements.
757	>	*
758	>	* @return the comparator used to order this queue, or
759	>	*         {@code null} if this queue is sorted according to the
760	>	*         natural ordering of its elements
761	>	*/
762	>	public Comparator<? super E> comparator() {
763	>	return comparator;
764	>	}
765
766	<	size = 0;
766	>	/**
767	>	* Saves this queue to a stream (that is, serializes it).
768	>	*
769	>	* @param s the stream
770	>	* @throws java.io.IOException if an I/O error occurs
771	>	* @serialData The length of the array backing the instance is
772	>	*             emitted (int), followed by all of its elements
773	>	*             (each an {@code Object}) in the proper order.
774	>	*/
775	>	private void writeObject(java.io.ObjectOutputStream s)
776	>	throws java.io.IOException {
777	>	// Write out element count, and any hidden stuff
778	>	s.defaultWriteObject();
779	>
780	>	// Write out array length, for compatibility with 1.5 version
781	>	s.writeInt(Math.max(2, size + 1));
782	>
783	>	// Write out all elements in the "proper order".
784	>	final Object[] es = queue;
785	>	for (int i = 0, n = size; i < n; i++)
786	>	s.writeObject(es[i]);
787		}
788
789		/**
790	<	* Removes and returns the ith element from queue.  Recall
791	<	* that queue is one-based, so 1 <= i <= size.
790	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
791	>	* (that is, deserializes it).
792		*
793	<	* XXX: Could further special-case i==size, but is it worth it?
794	<	* XXX: Could special-case i==0, but is it worth it?
793	>	* @param s the stream
794	>	* @throws ClassNotFoundException if the class of a serialized object
795	>	*         could not be found
796	>	* @throws java.io.IOException if an I/O error occurs
797		*/
798	<	private E remove(int i) {
799	<	assert i <= size;
800	<	modCount++;
798	>	private void readObject(java.io.ObjectInputStream s)
799	>	throws java.io.IOException, ClassNotFoundException {
800	>	// Read in size, and any hidden stuff
801	>	s.defaultReadObject();
802
803	<	E result = queue[i];
804	<	queue[i] = queue[size];
805	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
806	<	if (i <= size)
807	<	fixDown(i);
808	<	return result;
803	>	// Read in (and discard) array length
804	>	s.readInt();
805	>
806	>	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
807	>	final Object[] es = queue = new Object[Math.max(size, 1)];
808	>
809	>	// Read in all elements.
810	>	for (int i = 0, n = size; i < n; i++)
811	>	es[i] = s.readObject();
812	>
813	>	// Elements are guaranteed to be in "proper order", but the
814	>	// spec has never explained what that might be.
815	>	heapify();
816		}
817
818		/**
819	<	* Establishes the heap invariant (described above) assuming the heap
820	<	* satisfies the invariant except possibly for the leaf-node indexed by k
821	<	* (which may have a nextExecutionTime less than its parent's).
822	<	*
823	<	* This method functions by "promoting" queue[k] up the hierarchy
824	<	* (by swapping it with its parent) repeatedly until queue[k]
825	<	* is greater than or equal to its parent.
826	<	*/
827	<	private void fixUp(int k) {
828	<	if (comparator == null) {
829	<	while (k > 1) {
830	<	int j = k >> 1;
831	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
832	<	break;
833	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
834	<	k = j;
819	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
820	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
821	>	* queue. The spliterator does not traverse elements in any particular order
822	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
823	>	*
824	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
825	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
826	>	* Overriding implementations should document the reporting of additional
827	>	* characteristic values.
828	>	*
829	>	* @return a {@code Spliterator} over the elements in this queue
830	>	* @since 1.8
831	>	*/
832	>	public final Spliterator<E> spliterator() {
833	>	return new PriorityQueueSpliterator(0, -1, 0);
834	>	}
835	>
836	>	final class PriorityQueueSpliterator implements Spliterator<E> {
837	>	private int index;            // current index, modified on advance/split
838	>	private int fence;            // -1 until first use
839	>	private int expectedModCount; // initialized when fence set
840	>
841	>	/** Creates new spliterator covering the given range. */
842	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
843	>	this.index = origin;
844	>	this.fence = fence;
845	>	this.expectedModCount = expectedModCount;
846	>	}
847	>
848	>	private int getFence() { // initialize fence to size on first use
849	>	int hi;
850	>	if ((hi = fence) < 0) {
851	>	expectedModCount = modCount;
852	>	hi = fence = size;
853		}
854	<	} else {
855	<	while (k > 1) {
856	<	int j = k >> 1;
857	<	if (comparator.compare(queue[j], queue[k]) <= 0)
858	<	break;
859	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
860	<	k = j;
854	>	return hi;
855	>	}
856	>
857	>	public PriorityQueueSpliterator trySplit() {
858	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
859	>	return (lo >= mid) ? null :
860	>	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
861	>	}
862	>
863	>	public void forEachRemaining(Consumer<? super E> action) {
864	>	if (action == null)
865	>	throw new NullPointerException();
866	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
867	>	final Object[] es = queue;
868	>	int i, hi; E e;
869	>	for (i = index, index = hi = fence; i < hi; i++) {
870	>	if ((e = (E) es[i]) == null)
871	>	break;      // must be CME
872	>	action.accept(e);
873	>	}
874	>	if (modCount != expectedModCount)
875	>	throw new ConcurrentModificationException();
876	>	}
877	>
878	>	public boolean tryAdvance(Consumer<? super E> action) {
879	>	if (action == null)
880	>	throw new NullPointerException();
881	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
882	>	int i;
883	>	if ((i = index) < fence) {
884	>	index = i + 1;
885	>	E e;
886	>	if ((e = (E) queue[i]) == null
887	>	|| modCount != expectedModCount)
888	>	throw new ConcurrentModificationException();
889	>	action.accept(e);
890	>	return true;
891		}
892	+	return false;
893	+	}
894	+
895	+	public long estimateSize() {
896	+	return getFence() - index;
897	+	}
898	+
899	+	public int characteristics() {
900	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
901		}
902		}
903
904		/**
905	<	* Establishes the heap invariant (described above) in the subtree
906	<	* rooted at k, which is assumed to satisfy the heap invariant except
907	<	* possibly for node k itself (which may be greater than its children).
908	<	*
909	<	* This method functions by "demoting" queue[k] down the hierarchy
910	<	* (by swapping it with its smaller child) repeatedly until queue[k]
911	<	* is less than or equal to its children.
912	<	*/
913	<	private void fixDown(int k) {
914	<	int j;
915	<	if (comparator == null) {
916	<	while ((j = k << 1) <= size) {
917	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
918	<	j++; // j indexes smallest kid
919	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
920	<	break;
921	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
922	<	k = j;
923	<	}
924	<	} else {
925	<	while ((j = k << 1) <= size) {
926	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
927	<	j++; // j indexes smallest kid
928	<	if (comparator.compare(queue[k], queue[j]) <= 0)
929	<	break;
930	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
931	<	k = j;
932	<	}
905	>	* @throws NullPointerException {@inheritDoc}
906	>	*/
907	>	public boolean removeIf(Predicate<? super E> filter) {
908	>	Objects.requireNonNull(filter);
909	>	return bulkRemove(filter);
910	>	}
911	>
912	>	/**
913	>	* @throws NullPointerException {@inheritDoc}
914	>	*/
915	>	public boolean removeAll(Collection<?> c) {
916	>	Objects.requireNonNull(c);
917	>	return bulkRemove(e -> c.contains(e));
918	>	}
919	>
920	>	/**
921	>	* @throws NullPointerException {@inheritDoc}
922	>	*/
923	>	public boolean retainAll(Collection<?> c) {
924	>	Objects.requireNonNull(c);
925	>	return bulkRemove(e -> !c.contains(e));
926	>	}
927	>
928	>	// A tiny bit set implementation
929	>
930	>	private static long[] nBits(int n) {
931	>	return new long[((n - 1) >> 6) + 1];
932	>	}
933	>	private static void setBit(long[] bits, int i) {
934	>	bits[i >> 6] |= 1L << i;
935	>	}
936	>	private static boolean isClear(long[] bits, int i) {
937	>	return (bits[i >> 6] & (1L << i)) == 0;
938	>	}
939	>
940	>	/** Implementation of bulk remove methods. */
941	>	private boolean bulkRemove(Predicate<? super E> filter) {
942	>	final int expectedModCount = ++modCount;
943	>	final Object[] es = queue;
944	>	final int end = size;
945	>	int i;
946	>	// Optimize for initial run of survivors
947	>	for (i = 0; i < end && !filter.test((E) es[i]); i++)
948	>	;
949	>	if (i >= end) {
950	>	if (modCount != expectedModCount)
951	>	throw new ConcurrentModificationException();
952	>	return false;
953		}
954	+	// Tolerate predicates that reentrantly access the collection for
955	+	// read (but writers still get CME), so traverse once to find
956	+	// elements to delete, a second pass to physically expunge.
957	+	final int beg = i;
958	+	final long[] deathRow = nBits(end - beg);
959	+	deathRow[0] = 1L;   // set bit 0
960	+	for (i = beg + 1; i < end; i++)
961	+	if (filter.test((E) es[i]))
962	+	setBit(deathRow, i - beg);
963	+	if (modCount != expectedModCount)
964	+	throw new ConcurrentModificationException();
965	+	int w = beg;
966	+	for (i = beg; i < end; i++)
967	+	if (isClear(deathRow, i - beg))
968	+	es[w++] = es[i];
969	+	for (i = size = w; i < end; i++)
970	+	es[i] = null;
971	+	heapify();
972	+	return true;
973		}
974
975		/**
976	<	* 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.
976	>	* @throws NullPointerException {@inheritDoc}
977		*/
978	<	Comparator<E> comparator() {
979	<	return comparator;
978	>	public void forEach(Consumer<? super E> action) {
979	>	Objects.requireNonNull(action);
980	>	final int expectedModCount = modCount;
981	>	final Object[] es = queue;
982	>	for (int i = 0, n = size; i < n; i++)
983	>	action.accept((E) es[i]);
984	>	if (expectedModCount != modCount)
985	>	throw new ConcurrentModificationException();
986		}
987		}

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