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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.16 by tim, Thu Jul 31 15:44:41 2003 UTC vs.
Revision 1.123 by jsr166, Sun May 6 16:26:03 2018 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3	>	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	>	*
5	>	* This code is free software; you can redistribute it and/or modify it
6	>	* under the terms of the GNU General Public License version 2 only, as
7	>	* published by the Free Software Foundation.  Oracle designates this
8	>	* particular file as subject to the "Classpath" exception as provided
9	>	* by Oracle in the LICENSE file that accompanied this code.
10	>	*
11	>	* This code is distributed in the hope that it will be useful, but WITHOUT
12	>	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	>	* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14	>	* version 2 for more details (a copy is included in the LICENSE file that
15	>	* accompanied this code).
16	>	*
17	>	* You should have received a copy of the GNU General Public License version
18	>	* 2 along with this work; if not, write to the Free Software Foundation,
19	>	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20	>	*
21	>	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	>	* or visit www.oracle.com if you need additional information or have any
23	>	* questions.
24	>	*/
25	>
26	>	package java.util;
27	>
28	>	import java.util.function.Consumer;
29	>	import jdk.internal.misc.SharedSecrets;
30
31		/**
32	<	* An unbounded priority queue based on a priority heap.  This queue orders
33	<	* elements according to an order specified at construction time, which is
34	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}:
35	<	* 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 <em>head</em> of this queue is the least element with respect to the
39	<	* specified ordering. If multiple elements are tied for least value, the
40	<	* head is one of those elements. A priority queue does not permit
41	<	* <tt>null</tt> elements.
42	<	*
43	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and
44	<	* return the head of the queue.
45	<	*
46	<	* <p>The {@link #element()} and {@link #peek()} methods return, but do
47	<	* not delete, the head of the queue.
48	<	*
49	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
50	<	* size of the array used internally to store the elements on the
51	<	* queue.  It is always at least as large as the queue size.  As
52	<	* elements are added to a priority queue, its capacity grows
53	<	* automatically.  The details of the growth policy are not specified.
54	<	*
55	<	* <p>Implementation note: this implementation provides O(log(n)) time
56	<	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
57	<	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
58	<	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
59	<	* constant time for the retrieval methods (<tt>peek</tt>,
60	<	* <tt>element</tt>, and <tt>size</tt>).
32	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
33	>	* The elements of the priority queue are ordered according to their
34	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
35	>	* provided at queue construction time, depending on which constructor is
36	>	* used.  A priority queue does not permit {@code null} elements.
37	>	* A priority queue relying on natural ordering also does not permit
38	>	* insertion of non-comparable objects (doing so may result in
39	>	* {@code ClassCastException}).
40	>	*
41	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
42	>	* with respect to the specified ordering.  If multiple elements are
43	>	* tied for least value, the head is one of those elements -- ties are
44	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
45	>	* {@code remove}, {@code peek}, and {@code element} access the
46	>	* element at the head of the queue.
47	>	*
48	>	* <p>A priority queue is unbounded, but has an internal
49	>	* <i>capacity</i> governing the size of an array used to store the
50	>	* elements on the queue.  It is always at least as large as the queue
51	>	* size.  As elements are added to a priority queue, its capacity
52	>	* grows automatically.  The details of the growth policy are not
53	>	* specified.
54	>	*
55	>	* <p>This class and its iterator implement all of the
56	>	* <em>optional</em> methods of the {@link Collection} and {@link
57	>	* Iterator} interfaces.  The Iterator provided in method {@link
58	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
59	>	* are <em>not</em> guaranteed to traverse the elements of
60	>	* the priority queue in any particular order. If you need ordered
61	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
62	>	*
63	>	* <p><strong>Note that this implementation is not synchronized.</strong>
64	>	* Multiple threads should not access a {@code PriorityQueue}
65	>	* instance concurrently if any of the threads modifies the queue.
66	>	* Instead, use the thread-safe {@link
67	>	* java.util.concurrent.PriorityBlockingQueue} class.
68	>	*
69	>	* <p>Implementation note: this implementation provides
70	>	* O(log(n)) time for the enqueuing and dequeuing methods
71	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
72	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
73	>	* methods; and constant time for the retrieval methods
74	>	* ({@code peek}, {@code element}, and {@code size}).
75		*
76		* <p>This class is a member of the
77	<	* <a href="{@docRoot}/../guide/collections/index.html">
77	>	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
78		* Java Collections Framework</a>.
79	+	*
80		* @since 1.5
81	<	* @author Josh Bloch
81	>	* @author Josh Bloch, Doug Lea
82	>	* @param <E> the type of elements held in this queue
83		*/
84		public class PriorityQueue<E> extends AbstractQueue<E>
85	<	implements Queue<E>, java.io.Serializable {
85	>	implements java.io.Serializable {
86	>
87	>	private static final long serialVersionUID = -7720805057305804111L;
88
89		private static final int DEFAULT_INITIAL_CAPACITY = 11;
90
91		/**
92	<	* Priority queue represented as a balanced binary heap: the two children
93	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
94	<	* ordered by comparator, or by the elements' natural ordering, if
95	<	* comparator is null:  For each node n in the heap and each descendant d
96	<	* of n, n <= d.
97	<	*
52	<	* The element with the lowest value is in queue[1], assuming the queue is
53	<	* nonempty.  (A one-based array is used in preference to the traditional
54	<	* zero-based array to simplify parent and child calculations.)
55	<	*
56	<	* queue.length must be >= 2, even if size == 0.
92	>	* Priority queue represented as a balanced binary heap: the two
93	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
94	>	* priority queue is ordered by comparator, or by the elements'
95	>	* natural ordering, if comparator is null: For each node n in the
96	>	* heap and each descendant d of n, n <= d.  The element with the
97	>	* lowest value is in queue[0], assuming the queue is nonempty.
98		*/
99	<	private transient Object[] queue;
99	>	transient Object[] queue; // non-private to simplify nested class access
100
101		/**
102		* The number of elements in the priority queue.
103		*/
104	<	private int size = 0;
104	>	int size;
105
106		/**
107		* The comparator, or null if priority queue uses elements'
#	Line 72 | Line 113 | public class PriorityQueue<E> extends Ab
113		* The number of times this priority queue has been
114		* <i>structurally modified</i>.  See AbstractList for gory details.
115		*/
116	<	private transient int modCount = 0;
116	>	transient int modCount;     // non-private to simplify nested class access
117
118		/**
119	<	* Create a <tt>PriorityQueue</tt> with the default initial capacity
120	<	* (11) that orders its elements according to their natural
121	<	* ordering (using <tt>Comparable</tt>.)
119	>	* Creates a {@code PriorityQueue} with the default initial
120	>	* capacity (11) that orders its elements according to their
121	>	* {@linkplain Comparable natural ordering}.
122		*/
123		public PriorityQueue() {
124		this(DEFAULT_INITIAL_CAPACITY, null);
125		}
126
127		/**
128	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
129	<	* that orders its elements according to their natural ordering
130	<	* (using <tt>Comparable</tt>.)
131	<	*
132	<	* @param initialCapacity the initial capacity for this priority queue.
128	>	* Creates a {@code PriorityQueue} with the specified initial
129	>	* capacity that orders its elements according to their
130	>	* {@linkplain Comparable natural ordering}.
131	>	*
132	>	* @param initialCapacity the initial capacity for this priority queue
133	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
134	>	*         than 1
135		*/
136		public PriorityQueue(int initialCapacity) {
137		this(initialCapacity, null);
138		}
139
140		/**
141	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
142	<	* that orders its elements according to the specified comparator.
141	>	* Creates a {@code PriorityQueue} with the default initial capacity and
142	>	* whose elements are ordered according to the specified comparator.
143		*
144	<	* @param initialCapacity the initial capacity for this priority queue.
145	<	* @param comparator the comparator used to order this priority queue.
146	<	* If <tt>null</tt> then the order depends on the elements' natural
147	<	* ordering.
105	<	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
106	<	* than 1
144	>	* @param  comparator the comparator that will be used to order this
145	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
146	>	*         natural ordering} of the elements will be used.
147	>	* @since 1.8
148		*/
149	<	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
149	>	public PriorityQueue(Comparator<? super E> comparator) {
150	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
151	>	}
152	>
153	>	/**
154	>	* Creates a {@code PriorityQueue} with the specified initial capacity
155	>	* that orders its elements according to the specified comparator.
156	>	*
157	>	* @param  initialCapacity the initial capacity for this priority queue
158	>	* @param  comparator the comparator that will be used to order this
159	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
160	>	*         natural ordering} of the elements will be used.
161	>	* @throws IllegalArgumentException if {@code initialCapacity} is
162	>	*         less than 1
163	>	*/
164	>	public PriorityQueue(int initialCapacity,
165	>	Comparator<? super E> comparator) {
166	>	// Note: This restriction of at least one is not actually needed,
167	>	// but continues for 1.5 compatibility
168		if (initialCapacity < 1)
169		throw new IllegalArgumentException();
170	<	this.queue = new Object[initialCapacity + 1];
170	>	this.queue = new Object[initialCapacity];
171		this.comparator = comparator;
172		}
173
174		/**
175	<	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
176	<	* collection.  The priority queue has an initial capacity of 110% of the
177	<	* size of the specified collection; or 1 if the collection is empty.
178	<	* If the specified collection
179	<	* implements the {@link Sorted} interface, the priority queue will be
180	<	* sorted according to the same comparator, or according to its elements'
122	<	* natural order if the collection is sorted according to its elements'
123	<	* natural order.  If the specified collection does not implement
124	<	* <tt>Sorted</tt>, the priority queue is ordered according to
125	<	* its elements' natural order.
175	>	* Creates a {@code PriorityQueue} containing the elements in the
176	>	* specified collection.  If the specified collection is an instance of
177	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
178	>	* priority queue will be ordered according to the same ordering.
179	>	* Otherwise, this priority queue will be ordered according to the
180	>	* {@linkplain Comparable natural ordering} of its elements.
181		*
182	<	* @param c the collection whose elements are to be placed
183	<	*        into this priority queue.
182	>	* @param  c the collection whose elements are to be placed
183	>	*         into this priority queue
184		* @throws ClassCastException if elements of the specified collection
185		*         cannot be compared to one another according to the priority
186	<	*         queue's ordering.
187	<	* @throws NullPointerException if <tt>c</tt> or any element within it
188	<	* is <tt>null</tt>
186	>	*         queue's ordering
187	>	* @throws NullPointerException if the specified collection or any
188	>	*         of its elements are null
189		*/
190	+	@SuppressWarnings("unchecked")
191		public PriorityQueue(Collection<? extends E> c) {
192	<	int sz = c.size();
193	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
194	<	Integer.MAX_VALUE - 1);
195	<	if (initialCapacity < 1)
196	<	initialCapacity = 1;
192	>	if (c instanceof SortedSet<?>) {
193	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
194	>	this.comparator = (Comparator<? super E>) ss.comparator();
195	>	initElementsFromCollection(ss);
196	>	}
197	>	else if (c instanceof PriorityQueue<?>) {
198	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
199	>	this.comparator = (Comparator<? super E>) pq.comparator();
200	>	initFromPriorityQueue(pq);
201	>	}
202	>	else {
203	>	this.comparator = null;
204	>	initFromCollection(c);
205	>	}
206	>	}
207
208	<	this.queue = new Object[initialCapacity + 1];
208	>	/**
209	>	* Creates a {@code PriorityQueue} containing the elements in the
210	>	* specified priority queue.  This priority queue will be
211	>	* ordered according to the same ordering as the given priority
212	>	* queue.
213	>	*
214	>	* @param  c the priority queue whose elements are to be placed
215	>	*         into this priority queue
216	>	* @throws ClassCastException if elements of {@code c} cannot be
217	>	*         compared to one another according to {@code c}'s
218	>	*         ordering
219	>	* @throws NullPointerException if the specified priority queue or any
220	>	*         of its elements are null
221	>	*/
222	>	@SuppressWarnings("unchecked")
223	>	public PriorityQueue(PriorityQueue<? extends E> c) {
224	>	this.comparator = (Comparator<? super E>) c.comparator();
225	>	initFromPriorityQueue(c);
226	>	}
227
228	<	if (c instanceof Sorted) {
229	<	// FIXME: this code assumes too much
230	<	this.comparator = (Comparator<? super E>) ((Sorted)c).comparator();
231	<	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
232	<	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	>	@SuppressWarnings("unchecked")
242	>	public PriorityQueue(SortedSet<? extends E> c) {
243	>	this.comparator = (Comparator<? super E>) c.comparator();
244	>	initElementsFromCollection(c);
245	>	}
246	>
247	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
248	>	if (c.getClass() == PriorityQueue.class) {
249	>	this.queue = c.toArray();
250	>	this.size = c.size();
251		} else {
252	<	comparator = null;
151	<	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
152	<	add(i.next());
252	>	initFromCollection(c);
253		}
254		}
255
256	<	// Queue Methods
256	>	private void initElementsFromCollection(Collection<? extends E> c) {
257	>	Object[] a = c.toArray();
258	>	// If c.toArray incorrectly doesn't return Object[], copy it.
259	>	if (a.getClass() != Object[].class)
260	>	a = Arrays.copyOf(a, a.length, Object[].class);
261	>	int len = a.length;
262	>	if (len == 1 || this.comparator != null)
263	>	for (Object e : a)
264	>	if (e == null)
265	>	throw new NullPointerException();
266	>	this.queue = a;
267	>	this.size = a.length;
268	>	}
269
270		/**
271	<	* Add the specified element to this priority queue.
271	>	* Initializes queue array with elements from the given Collection.
272		*
273	<	* @param element the element to add.
162	<	* @return <tt>true</tt>
163	<	* @throws ClassCastException if the specified element cannot be compared
164	<	* with elements currently in the priority queue according
165	<	* to the priority queue's ordering.
166	<	* @throws NullPointerException if the specified element is null.
273	>	* @param c the collection
274		*/
275	<	public boolean offer(E element) {
276	<	if (element == null)
277	<	throw new NullPointerException();
278	<	modCount++;
172	<	++size;
275	>	private void initFromCollection(Collection<? extends E> c) {
276	>	initElementsFromCollection(c);
277	>	heapify();
278	>	}
279
280	<	// Grow backing store if necessary
281	<	while (size >= queue.length) {
282	<	Object[] newQueue = new Object[2 * queue.length];
283	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
284	<	queue = newQueue;
285	<	}
280	>	/**
281	>	* The maximum size of array to allocate.
282	>	* Some VMs reserve some header words in an array.
283	>	* Attempts to allocate larger arrays may result in
284	>	* OutOfMemoryError: Requested array size exceeds VM limit
285	>	*/
286	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
287
288	<	queue[size] = element;
289	<	fixUp(size);
290	<	return true;
288	>	/**
289	>	* Increases the capacity of the array.
290	>	*
291	>	* @param minCapacity the desired minimum capacity
292	>	*/
293	>	private void grow(int minCapacity) {
294	>	int oldCapacity = queue.length;
295	>	// Double size if small; else grow by 50%
296	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
297	>	(oldCapacity + 2) :
298	>	(oldCapacity >> 1));
299	>	// overflow-conscious code
300	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
301	>	newCapacity = hugeCapacity(minCapacity);
302	>	queue = Arrays.copyOf(queue, newCapacity);
303		}
304
305	<	public E poll() {
306	<	if (size == 0)
307	<	return null;
308	<	return (E) remove(1);
305	>	private static int hugeCapacity(int minCapacity) {
306	>	if (minCapacity < 0) // overflow
307	>	throw new OutOfMemoryError();
308	>	return (minCapacity > MAX_ARRAY_SIZE) ?
309	>	Integer.MAX_VALUE :
310	>	MAX_ARRAY_SIZE;
311	>	}
312	>
313	>	/**
314	>	* Inserts the specified element into this priority queue.
315	>	*
316	>	* @return {@code true} (as specified by {@link Collection#add})
317	>	* @throws ClassCastException if the specified element cannot be
318	>	*         compared with elements currently in this priority queue
319	>	*         according to the priority queue's ordering
320	>	* @throws NullPointerException if the specified element is null
321	>	*/
322	>	public boolean add(E e) {
323	>	return offer(e);
324	>	}
325	>
326	>	/**
327	>	* Inserts the specified element into this priority queue.
328	>	*
329	>	* @return {@code true} (as specified by {@link Queue#offer})
330	>	* @throws ClassCastException if the specified element cannot be
331	>	*         compared with elements currently in this priority queue
332	>	*         according to the priority queue's ordering
333	>	* @throws NullPointerException if the specified element is null
334	>	*/
335	>	public boolean offer(E e) {
336	>	if (e == null)
337	>	throw new NullPointerException();
338	>	modCount++;
339	>	int i = size;
340	>	if (i >= queue.length)
341	>	grow(i + 1);
342	>	siftUp(i, e);
343	>	size = i + 1;
344	>	return true;
345		}
346
347	+	@SuppressWarnings("unchecked")
348		public E peek() {
349	<	return (E) queue[1];
349	>	return (size == 0) ? null : (E) queue[0];
350		}
351
352	<	// Collection Methods
352	>	private int indexOf(Object o) {
353	>	if (o != null) {
354	>	final Object[] es = queue;
355	>	for (int i = 0, n = size; i < n; i++)
356	>	if (o.equals(es[i]))
357	>	return i;
358	>	}
359	>	return -1;
360	>	}
361
362	<	// these first two override just to get the throws docs
362	>	/**
363	>	* Removes a single instance of the specified element from this queue,
364	>	* if it is present.  More formally, removes an element {@code e} such
365	>	* that {@code o.equals(e)}, if this queue contains one or more such
366	>	* elements.  Returns {@code true} if and only if this queue contained
367	>	* the specified element (or equivalently, if this queue changed as a
368	>	* result of the call).
369	>	*
370	>	* @param o element to be removed from this queue, if present
371	>	* @return {@code true} if this queue changed as a result of the call
372	>	*/
373	>	public boolean remove(Object o) {
374	>	int i = indexOf(o);
375	>	if (i == -1)
376	>	return false;
377	>	else {
378	>	removeAt(i);
379	>	return true;
380	>	}
381	>	}
382
383		/**
384	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
385	<	* @throws ClassCastException if the specified element cannot be compared
386	<	* with elements currently in the priority queue according
204	<	* to the priority queue's ordering.
384	>	* Identity-based version for use in Itr.remove.
385	>	*
386	>	* @param o element to be removed from this queue, if present
387		*/
388	<	public boolean add(E element) {
389	<	return super.add(element);
388	>	void removeEq(Object o) {
389	>	final Object[] es = queue;
390	>	for (int i = 0, n = size; i < n; i++) {
391	>	if (o == es[i]) {
392	>	removeAt(i);
393	>	break;
394	>	}
395	>	}
396		}
397
398		/**
399	<	* @throws NullPointerException if any element is <tt>null</tt>.
400	<	* @throws ClassCastException if any element cannot be compared
401	<	* with elements currently in the priority queue according
402	<	* to the priority queue's ordering.
399	>	* Returns {@code true} if this queue contains the specified element.
400	>	* More formally, returns {@code true} if and only if this queue contains
401	>	* at least one element {@code e} such that {@code o.equals(e)}.
402	>	*
403	>	* @param o object to be checked for containment in this queue
404	>	* @return {@code true} if this queue contains the specified element
405		*/
406	<	public boolean addAll(Collection<? extends E> c) {
407	<	return super.addAll(c);
406	>	public boolean contains(Object o) {
407	>	return indexOf(o) >= 0;
408		}
409
410	<	public boolean remove(Object o) {
411	<	if (o == null)
412	<	return false;
410	>	/**
411	>	* Returns an array containing all of the elements in this queue.
412	>	* The elements are in no particular order.
413	>	*
414	>	* <p>The returned array will be "safe" in that no references to it are
415	>	* maintained by this queue.  (In other words, this method must allocate
416	>	* a new array).  The caller is thus free to modify the returned array.
417	>	*
418	>	* <p>This method acts as bridge between array-based and collection-based
419	>	* APIs.
420	>	*
421	>	* @return an array containing all of the elements in this queue
422	>	*/
423	>	public Object[] toArray() {
424	>	return Arrays.copyOf(queue, size);
425	>	}
426
427	<	if (comparator == null) {
428	<	for (int i = 1; i <= size; i++) {
429	<	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
430	<	remove(i);
431	<	return true;
432	<	}
433	<	}
434	<	} else {
435	<	for (int i = 1; i <= size; i++) {
436	<	if (comparator.compare((E)queue[i], (E)o) == 0) {
437	<	remove(i);
438	<	return true;
439	<	}
440	<	}
441	<	}
442	<	return false;
427	>	/**
428	>	* Returns an array containing all of the elements in this queue; the
429	>	* runtime type of the returned array is that of the specified array.
430	>	* The returned array elements are in no particular order.
431	>	* If the queue fits in the specified array, it is returned therein.
432	>	* Otherwise, a new array is allocated with the runtime type of the
433	>	* specified array and the size of this queue.
434	>	*
435	>	* <p>If the queue fits in the specified array with room to spare
436	>	* (i.e., the array has more elements than the queue), the element in
437	>	* the array immediately following the end of the collection is set to
438	>	* {@code null}.
439	>	*
440	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
441	>	* array-based and collection-based APIs.  Further, this method allows
442	>	* precise control over the runtime type of the output array, and may,
443	>	* under certain circumstances, be used to save allocation costs.
444	>	*
445	>	* <p>Suppose {@code x} is a queue known to contain only strings.
446	>	* The following code can be used to dump the queue into a newly
447	>	* allocated array of {@code String}:
448	>	*
449	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
450	>	*
451	>	* Note that {@code toArray(new Object[0])} is identical in function to
452	>	* {@code toArray()}.
453	>	*
454	>	* @param a the array into which the elements of the queue are to
455	>	*          be stored, if it is big enough; otherwise, a new array of the
456	>	*          same runtime type is allocated for this purpose.
457	>	* @return an array containing all of the elements in this queue
458	>	* @throws ArrayStoreException if the runtime type of the specified array
459	>	*         is not a supertype of the runtime type of every element in
460	>	*         this queue
461	>	* @throws NullPointerException if the specified array is null
462	>	*/
463	>	@SuppressWarnings("unchecked")
464	>	public <T> T[] toArray(T[] a) {
465	>	final int size = this.size;
466	>	if (a.length < size)
467	>	// Make a new array of a's runtime type, but my contents:
468	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
469	>	System.arraycopy(queue, 0, a, 0, size);
470	>	if (a.length > size)
471	>	a[size] = null;
472	>	return a;
473		}
474
475	+	/**
476	+	* Returns an iterator over the elements in this queue. The iterator
477	+	* does not return the elements in any particular order.
478	+	*
479	+	* @return an iterator over the elements in this queue
480	+	*/
481		public Iterator<E> iterator() {
482		return new Itr();
483		}
484
485	<	private class Itr implements Iterator<E> {
485	>	private final class Itr implements Iterator<E> {
486		/**
487		* Index (into queue array) of element to be returned by
488		* subsequent call to next.
489		*/
490	<	private int cursor = 1;
490	>	private int cursor;
491	>
492	>	/**
493	>	* Index of element returned by most recent call to next,
494	>	* unless that element came from the forgetMeNot list.
495	>	* Set to -1 if element is deleted by a call to remove.
496	>	*/
497	>	private int lastRet = -1;
498	>
499	>	/**
500	>	* A queue of elements that were moved from the unvisited portion of
501	>	* the heap into the visited portion as a result of "unlucky" element
502	>	* removals during the iteration.  (Unlucky element removals are those
503	>	* that require a siftup instead of a siftdown.)  We must visit all of
504	>	* the elements in this list to complete the iteration.  We do this
505	>	* after we've completed the "normal" iteration.
506	>	*
507	>	* We expect that most iterations, even those involving removals,
508	>	* will not need to store elements in this field.
509	>	*/
510	>	private ArrayDeque<E> forgetMeNot;
511
512		/**
513	<	* Index of element returned by most recent call to next or
514	<	* previous.  Reset to 0 if this element is deleted by a call
256	<	* to remove.
513	>	* Element returned by the most recent call to next iff that
514	>	* element was drawn from the forgetMeNot list.
515		*/
516	<	private int lastRet = 0;
516	>	private E lastRetElt;
517
518		/**
519		* The modCount value that the iterator believes that the backing
520	<	* List should have.  If this expectation is violated, the iterator
520	>	* Queue should have.  If this expectation is violated, the iterator
521		* has detected concurrent modification.
522		*/
523		private int expectedModCount = modCount;
524
525	+	Itr() {}                        // prevent access constructor creation
526	+
527		public boolean hasNext() {
528	<	return cursor <= size;
528	>	return cursor < size ||
529	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
530		}
531
532	+	@SuppressWarnings("unchecked")
533		public E next() {
534	<	checkForComodification();
535	<	if (cursor > size)
536	<	throw new NoSuchElementException();
537	<	E result = (E) queue[cursor];
538	<	lastRet = cursor++;
539	<	return result;
534	>	if (expectedModCount != modCount)
535	>	throw new ConcurrentModificationException();
536	>	if (cursor < size)
537	>	return (E) queue[lastRet = cursor++];
538	>	if (forgetMeNot != null) {
539	>	lastRet = -1;
540	>	lastRetElt = forgetMeNot.poll();
541	>	if (lastRetElt != null)
542	>	return lastRetElt;
543	>	}
544	>	throw new NoSuchElementException();
545		}
546
547		public void remove() {
548	<	if (lastRet == 0)
548	>	if (expectedModCount != modCount)
549	>	throw new ConcurrentModificationException();
550	>	if (lastRet != -1) {
551	>	E moved = PriorityQueue.this.removeAt(lastRet);
552	>	lastRet = -1;
553	>	if (moved == null)
554	>	cursor--;
555	>	else {
556	>	if (forgetMeNot == null)
557	>	forgetMeNot = new ArrayDeque<>();
558	>	forgetMeNot.add(moved);
559	>	}
560	>	} else if (lastRetElt != null) {
561	>	PriorityQueue.this.removeEq(lastRetElt);
562	>	lastRetElt = null;
563	>	} else {
564		throw new IllegalStateException();
565	<	checkForComodification();
284	<
285	<	PriorityQueue.this.remove(lastRet);
286	<	if (lastRet < cursor)
287	<	cursor--;
288	<	lastRet = 0;
565	>	}
566		expectedModCount = modCount;
567		}
291	–
292	–	final void checkForComodification() {
293	–	if (modCount != expectedModCount)
294	–	throw new ConcurrentModificationException();
295	–	}
568		}
569
298	–	/**
299	–	* Returns the number of elements in this priority queue.
300	–	*
301	–	* @return the number of elements in this priority queue.
302	–	*/
570		public int size() {
571		return size;
572		}
573
574		/**
575	<	* Remove all elements from the priority queue.
575	>	* Removes all of the elements from this priority queue.
576	>	* The queue will be empty after this call returns.
577		*/
578		public void clear() {
579		modCount++;
580	<
581	<	// Null out element references to prevent memory leak
582	<	for (int i=1; i<=size; i++)
315	<	queue[i] = null;
316	<
580	>	final Object[] es = queue;
581	>	for (int i = 0, n = size; i < n; i++)
582	>	es[i] = null;
583		size = 0;
584		}
585
586	<	/**
587	<	* Removes and returns the ith element from queue.  Recall
588	<	* that queue is one-based, so 1 <= i <= size.
589	<	*
590	<	* XXX: Could further special-case i==size, but is it worth it?
325	<	* XXX: Could special-case i==0, but is it worth it?
326	<	*/
327	<	private E remove(int i) {
328	<	assert i <= size;
586	>	@SuppressWarnings("unchecked")
587	>	public E poll() {
588	>	if (size == 0)
589	>	return null;
590	>	int s = --size;
591		modCount++;
592	<
593	<	E result = (E) queue[i];
594	<	queue[i] = queue[size];
595	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
596	<	if (i <= size)
335	<	fixDown(i);
592	>	E result = (E) queue[0];
593	>	E x = (E) queue[s];
594	>	queue[s] = null;
595	>	if (s != 0)
596	>	siftDown(0, x);
597		return result;
598		}
599
600		/**
601	<	* Establishes the heap invariant (described above) assuming the heap
602	<	* satisfies the invariant except possibly for the leaf-node indexed by k
603	<	* (which may have a nextExecutionTime less than its parent's).
604	<	*
605	<	* This method functions by "promoting" queue[k] up the hierarchy
606	<	* (by swapping it with its parent) repeatedly until queue[k]
607	<	* is greater than or equal to its parent.
608	<	*/
609	<	private void fixUp(int k) {
610	<	if (comparator == null) {
611	<	while (k > 1) {
612	<	int j = k >> 1;
613	<	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
614	<	break;
615	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
616	<	k = j;
617	<	}
618	<	} else {
619	<	while (k > 1) {
620	<	int j = k >> 1;
621	<	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
622	<	break;
623	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
624	<	k = j;
601	>	* Removes the ith element from queue.
602	>	*
603	>	* Normally this method leaves the elements at up to i-1,
604	>	* inclusive, untouched.  Under these circumstances, it returns
605	>	* null.  Occasionally, in order to maintain the heap invariant,
606	>	* it must swap a later element of the list with one earlier than
607	>	* i.  Under these circumstances, this method returns the element
608	>	* that was previously at the end of the list and is now at some
609	>	* position before i. This fact is used by iterator.remove so as to
610	>	* avoid missing traversing elements.
611	>	*/
612	>	@SuppressWarnings("unchecked")
613	>	E removeAt(int i) {
614	>	// assert i >= 0 && i < size;
615	>	modCount++;
616	>	int s = --size;
617	>	if (s == i) // removed last element
618	>	queue[i] = null;
619	>	else {
620	>	E moved = (E) queue[s];
621	>	queue[s] = null;
622	>	siftDown(i, moved);
623	>	if (queue[i] == moved) {
624	>	siftUp(i, moved);
625	>	if (queue[i] != moved)
626	>	return moved;
627		}
628		}
629	+	return null;
630		}
631
632		/**
633	<	* Establishes the heap invariant (described above) in the subtree
634	<	* rooted at k, which is assumed to satisfy the heap invariant except
635	<	* possibly for node k itself (which may be greater than its children).
636	<	*
637	<	* This method functions by "demoting" queue[k] down the hierarchy
638	<	* (by swapping it with its smaller child) repeatedly until queue[k]
639	<	* is less than or equal to its children.
640	<	*/
641	<	private void fixDown(int k) {
642	<	int j;
643	<	if (comparator == null) {
644	<	while ((j = k << 1) <= size) {
645	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
646	<	j++; // j indexes smallest kid
647	<	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
648	<	break;
649	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
650	<	k = j;
651	<	}
652	<	} else {
653	<	while ((j = k << 1) <= size) {
654	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
655	<	j++; // j indexes smallest kid
656	<	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
657	<	break;
658	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
659	<	k = j;
660	<	}
633	>	* Inserts item x at position k, maintaining heap invariant by
634	>	* promoting x up the tree until it is greater than or equal to
635	>	* its parent, or is the root.
636	>	*
637	>	* To simplify and speed up coercions and comparisons, the
638	>	* Comparable and Comparator versions are separated into different
639	>	* methods that are otherwise identical. (Similarly for siftDown.)
640	>	*
641	>	* @param k the position to fill
642	>	* @param x the item to insert
643	>	*/
644	>	private void siftUp(int k, E x) {
645	>	if (comparator != null)
646	>	siftUpUsingComparator(k, x);
647	>	else
648	>	siftUpComparable(k, x);
649	>	}
650	>
651	>	@SuppressWarnings("unchecked")
652	>	private void siftUpComparable(int k, E x) {
653	>	Comparable<? super E> key = (Comparable<? super E>) x;
654	>	while (k > 0) {
655	>	int parent = (k - 1) >>> 1;
656	>	Object e = queue[parent];
657	>	if (key.compareTo((E) e) >= 0)
658	>	break;
659	>	queue[k] = e;
660	>	k = parent;
661	>	}
662	>	queue[k] = key;
663	>	}
664	>
665	>	@SuppressWarnings("unchecked")
666	>	private void siftUpUsingComparator(int k, E x) {
667	>	while (k > 0) {
668	>	int parent = (k - 1) >>> 1;
669	>	Object e = queue[parent];
670	>	if (comparator.compare(x, (E) e) >= 0)
671	>	break;
672	>	queue[k] = e;
673	>	k = parent;
674	>	}
675	>	queue[k] = x;
676	>	}
677	>
678	>	/**
679	>	* Inserts item x at position k, maintaining heap invariant by
680	>	* demoting x down the tree repeatedly until it is less than or
681	>	* equal to its children or is a leaf.
682	>	*
683	>	* @param k the position to fill
684	>	* @param x the item to insert
685	>	*/
686	>	private void siftDown(int k, E x) {
687	>	if (comparator != null)
688	>	siftDownUsingComparator(k, x);
689	>	else
690	>	siftDownComparable(k, x);
691	>	}
692	>
693	>	@SuppressWarnings("unchecked")
694	>	private void siftDownComparable(int k, E x) {
695	>	Comparable<? super E> key = (Comparable<? super E>)x;
696	>	int half = size >>> 1;        // loop while a non-leaf
697	>	while (k < half) {
698	>	int child = (k << 1) + 1; // assume left child is least
699	>	Object c = queue[child];
700	>	int right = child + 1;
701	>	if (right < size &&
702	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
703	>	c = queue[child = right];
704	>	if (key.compareTo((E) c) <= 0)
705	>	break;
706	>	queue[k] = c;
707	>	k = child;
708	>	}
709	>	queue[k] = key;
710	>	}
711	>
712	>	@SuppressWarnings("unchecked")
713	>	private void siftDownUsingComparator(int k, E x) {
714	>	int half = size >>> 1;
715	>	while (k < half) {
716	>	int child = (k << 1) + 1;
717	>	Object c = queue[child];
718	>	int right = child + 1;
719	>	if (right < size &&
720	>	comparator.compare((E) c, (E) queue[right]) > 0)
721	>	c = queue[child = right];
722	>	if (comparator.compare(x, (E) c) <= 0)
723	>	break;
724	>	queue[k] = c;
725	>	k = child;
726		}
727	+	queue[k] = x;
728	+	}
729	+
730	+	/**
731	+	* Establishes the heap invariant (described above) in the entire tree,
732	+	* assuming nothing about the order of the elements prior to the call.
733	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
734	+	*/
735	+	@SuppressWarnings("unchecked")
736	+	private void heapify() {
737	+	final Object[] es = queue;
738	+	int i = (size >>> 1) - 1;
739	+	if (comparator == null)
740	+	for (; i >= 0; i--)
741	+	siftDownComparable(i, (E) es[i]);
742	+	else
743	+	for (; i >= 0; i--)
744	+	siftDownUsingComparator(i, (E) es[i]);
745		}
746
747	+	/**
748	+	* Returns the comparator used to order the elements in this
749	+	* queue, or {@code null} if this queue is sorted according to
750	+	* the {@linkplain Comparable natural ordering} of its elements.
751	+	*
752	+	* @return the comparator used to order this queue, or
753	+	*         {@code null} if this queue is sorted according to the
754	+	*         natural ordering of its elements
755	+	*/
756		public Comparator<? super E> comparator() {
757		return comparator;
758		}
759
760		/**
761	<	* Save the state of the instance to a stream (that
406	<	* is, serialize it).
761	>	* Saves this queue to a stream (that is, serializes it).
762		*
408	–	* @serialData The length of the array backing the instance is
409	–	* emitted (int), followed by all of its elements (each an
410	–	* <tt>Object</tt>) in the proper order.
763		* @param s the stream
764	+	* @throws java.io.IOException if an I/O error occurs
765	+	* @serialData The length of the array backing the instance is
766	+	*             emitted (int), followed by all of its elements
767	+	*             (each an {@code Object}) in the proper order.
768		*/
769	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
770	<	throws java.io.IOException{
769	>	private void writeObject(java.io.ObjectOutputStream s)
770	>	throws java.io.IOException {
771		// Write out element count, and any hidden stuff
772		s.defaultWriteObject();
773
774	<	// Write out array length
775	<	s.writeInt(queue.length);
774	>	// Write out array length, for compatibility with 1.5 version
775	>	s.writeInt(Math.max(2, size + 1));
776
777	<	// Write out all elements in the proper order.
778	<	for (int i=0; i<size; i++)
779	<	s.writeObject(queue[i]);
777	>	// Write out all elements in the "proper order".
778	>	final Object[] es = queue;
779	>	for (int i = 0, n = size; i < n; i++)
780	>	s.writeObject(es[i]);
781		}
782
783		/**
784	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
785	<	* deserialize it).
784	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
785	>	* (that is, deserializes it).
786	>	*
787		* @param s the stream
788	+	* @throws ClassNotFoundException if the class of a serialized object
789	+	*         could not be found
790	+	* @throws java.io.IOException if an I/O error occurs
791		*/
792	<	private synchronized void readObject(java.io.ObjectInputStream s)
792	>	private void readObject(java.io.ObjectInputStream s)
793		throws java.io.IOException, ClassNotFoundException {
794		// Read in size, and any hidden stuff
795		s.defaultReadObject();
796
797	<	// Read in array length and allocate array
798	<	int arrayLength = s.readInt();
799	<	queue = new Object[arrayLength];
800	<
801	<	// Read in all elements in the proper order.
802	<	for (int i=0; i<size; i++)
803	<	queue[i] = s.readObject();
797	>	// Read in (and discard) array length
798	>	s.readInt();
799	>
800	>	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
801	>	queue = new Object[size];
802	>
803	>	// Read in all elements.
804	>	final Object[] es = queue;
805	>	for (int i = 0, n = size; i < n; i++)
806	>	es[i] = s.readObject();
807	>
808	>	// Elements are guaranteed to be in "proper order", but the
809	>	// spec has never explained what that might be.
810	>	heapify();
811		}
812
813	<	}
813	>	/**
814	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
815	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
816	>	* queue. The spliterator does not traverse elements in any particular order
817	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
818	>	*
819	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
820	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
821	>	* Overriding implementations should document the reporting of additional
822	>	* characteristic values.
823	>	*
824	>	* @return a {@code Spliterator} over the elements in this queue
825	>	* @since 1.8
826	>	*/
827	>	public final Spliterator<E> spliterator() {
828	>	return new PriorityQueueSpliterator(0, -1, 0);
829	>	}
830	>
831	>	final class PriorityQueueSpliterator implements Spliterator<E> {
832	>	private int index;            // current index, modified on advance/split
833	>	private int fence;            // -1 until first use
834	>	private int expectedModCount; // initialized when fence set
835	>
836	>	/** Creates new spliterator covering the given range. */
837	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
838	>	this.index = origin;
839	>	this.fence = fence;
840	>	this.expectedModCount = expectedModCount;
841	>	}
842
843	+	private int getFence() { // initialize fence to size on first use
844	+	int hi;
845	+	if ((hi = fence) < 0) {
846	+	expectedModCount = modCount;
847	+	hi = fence = size;
848	+	}
849	+	return hi;
850	+	}
851	+
852	+	public PriorityQueueSpliterator trySplit() {
853	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
854	+	return (lo >= mid) ? null :
855	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
856	+	}
857	+
858	+	@SuppressWarnings("unchecked")
859	+	public void forEachRemaining(Consumer<? super E> action) {
860	+	if (action == null)
861	+	throw new NullPointerException();
862	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
863	+	final Object[] a = queue;
864	+	int i, hi; E e;
865	+	for (i = index, index = hi = fence; i < hi; i++) {
866	+	if ((e = (E) a[i]) == null)
867	+	break;      // must be CME
868	+	action.accept(e);
869	+	}
870	+	if (modCount != expectedModCount)
871	+	throw new ConcurrentModificationException();
872	+	}
873	+
874	+	@SuppressWarnings("unchecked")
875	+	public boolean tryAdvance(Consumer<? super E> action) {
876	+	if (action == null)
877	+	throw new NullPointerException();
878	+	if (fence < 0) { fence = size; expectedModCount = modCount; }
879	+	int i;
880	+	if ((i = index) < fence) {
881	+	index = i + 1;
882	+	E e;
883	+	if ((e = (E) queue[i]) == null
884	+	|| modCount != expectedModCount)
885	+	throw new ConcurrentModificationException();
886	+	action.accept(e);
887	+	return true;
888	+	}
889	+	return false;
890	+	}
891	+
892	+	public long estimateSize() {
893	+	return getFence() - index;
894	+	}
895	+
896	+	public int characteristics() {
897	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
898	+	}
899	+	}
900	+
901	+	/**
902	+	* @throws NullPointerException {@inheritDoc}
903	+	*/
904	+	@SuppressWarnings("unchecked")
905	+	public void forEach(Consumer<? super E> action) {
906	+	Objects.requireNonNull(action);
907	+	final int expectedModCount = modCount;
908	+	final Object[] es = queue;
909	+	for (int i = 0, n = size; i < n; i++)
910	+	action.accept((E) es[i]);
911	+	if (expectedModCount != modCount)
912	+	throw new ConcurrentModificationException();
913	+	}
914	+	}

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