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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.7 by dl, Tue Jun 24 14:34:30 2003 UTC vs.
Revision 1.110 by jsr166, Wed Aug 24 21:46:18 2016 UTC

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1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2013, 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
30		/**
31	<	* An unbounded priority queue based on a priority heap.  This queue orders
32	<	* elements according to an order specified at construction time, which is
33	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered
34	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
35	<	* according to a {@link Comparator}, depending on which constructor is used.
36	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
37	<	* minimal element with respect to the specified ordering.  If multiple
38	<	* elements are tied for least value, no guarantees are made as to
39	<	* which of these elements is returned.
40	<	*
41	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
42	<	* size of the array used internally to store the elements on the
43	<	* queue.  It is always at least as large as the queue size.  As
44	<	* elements are added to a priority queue, its capacity grows
45	<	* automatically.  The details of the growth policy are not specified.
46	<	*
47	<	*<p>Implementation note: this implementation provides O(log(n)) time
48	<	*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
49	<	*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
50	<	*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
51	<	*constant time for the retrieval methods (<tt>peek</tt>,
52	<	*<tt>element</tt>, and <tt>size</tt>).
31	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
32	>	* The elements of the priority queue are ordered according to their
33	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
34	>	* provided at queue construction time, depending on which constructor is
35	>	* used.  A priority queue does not permit {@code null} elements.
36	>	* A priority queue relying on natural ordering also does not permit
37	>	* insertion of non-comparable objects (doing so may result in
38	>	* {@code ClassCastException}).
39	>	*
40	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
41	>	* with respect to the specified ordering.  If multiple elements are
42	>	* tied for least value, the head is one of those elements -- ties are
43	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
44	>	* {@code remove}, {@code peek}, and {@code element} access the
45	>	* element at the head of the queue.
46	>	*
47	>	* <p>A priority queue is unbounded, but has an internal
48	>	* <i>capacity</i> governing the size of an array used to store the
49	>	* elements on the queue.  It is always at least as large as the queue
50	>	* size.  As elements are added to a priority queue, its capacity
51	>	* grows automatically.  The details of the growth policy are not
52	>	* specified.
53	>	*
54	>	* <p>This class and its iterator implement all of the
55	>	* <em>optional</em> methods of the {@link Collection} and {@link
56	>	* Iterator} interfaces.  The Iterator provided in method {@link
57	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
58	>	* the priority queue in any particular order. If you need ordered
59	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
60	>	*
61	>	* <p><strong>Note that this implementation is not synchronized.</strong>
62	>	* Multiple threads should not access a {@code PriorityQueue}
63	>	* instance concurrently if any of the threads modifies the queue.
64	>	* Instead, use the thread-safe {@link
65	>	* java.util.concurrent.PriorityBlockingQueue} class.
66	>	*
67	>	* <p>Implementation note: this implementation provides
68	>	* O(log(n)) time for the enqueuing and dequeuing methods
69	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
70	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
71	>	* methods; and constant time for the retrieval methods
72	>	* ({@code peek}, {@code element}, and {@code size}).
73		*
74		* <p>This class is a member of the
75	<	* <a href="{@docRoot}/../guide/collections/index.html">
75	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
76		* Java Collections Framework</a>.
77	+	*
78		* @since 1.5
79	<	* @author Josh Bloch
79	>	* @author Josh Bloch, Doug Lea
80	>	* @param <E> the type of elements held in this queue
81		*/
82		public class PriorityQueue<E> extends AbstractQueue<E>
83	<	implements Queue<E> {
83	>	implements java.io.Serializable {
84	>
85	>	private static final long serialVersionUID = -7720805057305804111L;
86	>
87		private static final int DEFAULT_INITIAL_CAPACITY = 11;
88
89		/**
90	<	* Priority queue represented as a balanced binary heap: the two children
91	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
92	<	* ordered by comparator, or by the elements' natural ordering, if
93	<	* comparator is null:  For each node n in the heap and each descendant d
94	<	* of n, n <= d.
95	<	*
44	<	* The element with the lowest value is in queue[1], assuming the queue is
45	<	* nonempty.  (A one-based array is used in preference to the traditional
46	<	* zero-based array to simplify parent and child calculations.)
47	<	*
48	<	* queue.length must be >= 2, even if size == 0.
90	>	* Priority queue represented as a balanced binary heap: the two
91	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
92	>	* priority queue is ordered by comparator, or by the elements'
93	>	* natural ordering, if comparator is null: For each node n in the
94	>	* heap and each descendant d of n, n <= d.  The element with the
95	>	* lowest value is in queue[0], assuming the queue is nonempty.
96		*/
97	<	private transient E[] queue;
97	>	transient Object[] queue; // non-private to simplify nested class access
98
99		/**
100		* The number of elements in the priority queue.
101		*/
102	<	private int size = 0;
102	>	int size;
103
104		/**
105		* The comparator, or null if priority queue uses elements'
106		* natural ordering.
107		*/
108	<	private final Comparator<E> comparator;
108	>	private final Comparator<? super E> comparator;
109
110		/**
111		* The number of times this priority queue has been
112		* <i>structurally modified</i>.  See AbstractList for gory details.
113		*/
114	<	private transient int modCount = 0;
114	>	transient int modCount;     // non-private to simplify nested class access
115
116		/**
117	<	* Create a new priority queue with the default initial capacity
118	<	* (11) that orders its elements according to their natural
119	<	* ordering (using <tt>Comparable</tt>.)
117	>	* Creates a {@code PriorityQueue} with the default initial
118	>	* capacity (11) that orders its elements according to their
119	>	* {@linkplain Comparable natural ordering}.
120		*/
121		public PriorityQueue() {
122	<	this(DEFAULT_INITIAL_CAPACITY);
122	>	this(DEFAULT_INITIAL_CAPACITY, null);
123		}
124
125		/**
126	<	* Create a new priority queue with the specified initial capacity
127	<	* that orders its elements according to their natural ordering
128	<	* (using <tt>Comparable</tt>.)
126	>	* Creates a {@code PriorityQueue} with the specified initial
127	>	* capacity that orders its elements according to their
128	>	* {@linkplain Comparable natural ordering}.
129		*
130	<	* @param initialCapacity the initial capacity for this priority queue.
130	>	* @param initialCapacity the initial capacity for this priority queue
131	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
132	>	*         than 1
133		*/
134		public PriorityQueue(int initialCapacity) {
135		this(initialCapacity, null);
136		}
137
138		/**
139	<	* Create a new priority queue with the specified initial capacity (11)
140	<	* that orders its elements according to the specified comparator.
139	>	* Creates a {@code PriorityQueue} with the default initial capacity and
140	>	* whose elements are ordered according to the specified comparator.
141		*
142	<	* @param initialCapacity the initial capacity for this priority queue.
143	<	* @param comparator the comparator used to order this priority queue.
142	>	* @param  comparator the comparator that will be used to order this
143	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
144	>	*         natural ordering} of the elements will be used.
145	>	* @since 1.8
146		*/
147	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
147	>	public PriorityQueue(Comparator<? super E> comparator) {
148	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
149	>	}
150	>
151	>	/**
152	>	* Creates a {@code PriorityQueue} with the specified initial capacity
153	>	* that orders its elements according to the specified comparator.
154	>	*
155	>	* @param  initialCapacity the initial capacity for this priority queue
156	>	* @param  comparator the comparator that will be used to order this
157	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
158	>	*         natural ordering} of the elements will be used.
159	>	* @throws IllegalArgumentException if {@code initialCapacity} is
160	>	*         less than 1
161	>	*/
162	>	public PriorityQueue(int initialCapacity,
163	>	Comparator<? super E> comparator) {
164	>	// Note: This restriction of at least one is not actually needed,
165	>	// but continues for 1.5 compatibility
166		if (initialCapacity < 1)
167	<	initialCapacity = 1;
168	<	queue = new E[initialCapacity + 1];
167	>	throw new IllegalArgumentException();
168	>	this.queue = new Object[initialCapacity];
169		this.comparator = comparator;
170		}
171
172		/**
173	<	* Create a new priority queue containing the elements in the specified
174	<	* collection.  The priority queue has an initial capacity of 110% of the
175	<	* size of the specified collection. If the specified collection
176	<	* implements the {@link Sorted} interface, the priority queue will be
177	<	* sorted according to the same comparator, or according to its elements'
178	<	* natural order if the collection is sorted according to its elements'
110	<	* natural order.  If the specified collection does not implement
111	<	* <tt>Sorted</tt>, the priority queue is ordered according to
112	<	* its elements' natural order.
173	>	* Creates a {@code PriorityQueue} containing the elements in the
174	>	* specified collection.  If the specified collection is an instance of
175	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
176	>	* priority queue will be ordered according to the same ordering.
177	>	* Otherwise, this priority queue will be ordered according to the
178	>	* {@linkplain Comparable natural ordering} of its elements.
179		*
180	<	* @param initialElements the collection whose elements are to be placed
181	<	*        into this priority queue.
180	>	* @param  c the collection whose elements are to be placed
181	>	*         into this priority queue
182		* @throws ClassCastException if elements of the specified collection
183		*         cannot be compared to one another according to the priority
184	<	*         queue's ordering.
185	<	* @throws NullPointerException if the specified collection or an
186	<	*         element of the specified collection is <tt>null</tt>.
187	<	*/
188	<	public PriorityQueue(Collection<E> initialElements) {
189	<	int sz = initialElements.size();
190	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
191	<	Integer.MAX_VALUE - 1);
192	<	if (initialCapacity < 1)
193	<	initialCapacity = 1;
194	<	queue = new E[initialCapacity + 1];
184	>	*         queue's ordering
185	>	* @throws NullPointerException if the specified collection or any
186	>	*         of its elements are null
187	>	*/
188	>	@SuppressWarnings("unchecked")
189	>	public PriorityQueue(Collection<? extends E> c) {
190	>	if (c instanceof SortedSet<?>) {
191	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
192	>	this.comparator = (Comparator<? super E>) ss.comparator();
193	>	initElementsFromCollection(ss);
194	>	}
195	>	else if (c instanceof PriorityQueue<?>) {
196	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
197	>	this.comparator = (Comparator<? super E>) pq.comparator();
198	>	initFromPriorityQueue(pq);
199	>	}
200	>	else {
201	>	this.comparator = null;
202	>	initFromCollection(c);
203	>	}
204	>	}
205
206	<	/* Commented out to compile with generics compiler
206	>	/**
207	>	* Creates a {@code PriorityQueue} containing the elements in the
208	>	* specified priority queue.  This priority queue will be
209	>	* ordered according to the same ordering as the given priority
210	>	* queue.
211	>	*
212	>	* @param  c the priority queue whose elements are to be placed
213	>	*         into this priority queue
214	>	* @throws ClassCastException if elements of {@code c} cannot be
215	>	*         compared to one another according to {@code c}'s
216	>	*         ordering
217	>	* @throws NullPointerException if the specified priority queue or any
218	>	*         of its elements are null
219	>	*/
220	>	@SuppressWarnings("unchecked")
221	>	public PriorityQueue(PriorityQueue<? extends E> c) {
222	>	this.comparator = (Comparator<? super E>) c.comparator();
223	>	initFromPriorityQueue(c);
224	>	}
225
226	<	if (initialElements instanceof Sorted) {
227	<	comparator = ((Sorted)initialElements).comparator();
228	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
229	<	queue[++size] = i.next();
226	>	/**
227	>	* Creates a {@code PriorityQueue} containing the elements in the
228	>	* specified sorted set.   This priority queue will be ordered
229	>	* according to the same ordering as the given sorted set.
230	>	*
231	>	* @param  c the sorted set whose elements are to be placed
232	>	*         into this priority queue
233	>	* @throws ClassCastException if elements of the specified sorted
234	>	*         set cannot be compared to one another according to the
235	>	*         sorted set's ordering
236	>	* @throws NullPointerException if the specified sorted set or any
237	>	*         of its elements are null
238	>	*/
239	>	@SuppressWarnings("unchecked")
240	>	public PriorityQueue(SortedSet<? extends E> c) {
241	>	this.comparator = (Comparator<? super E>) c.comparator();
242	>	initElementsFromCollection(c);
243	>	}
244	>
245	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
246	>	if (c.getClass() == PriorityQueue.class) {
247	>	this.queue = c.toArray();
248	>	this.size = c.size();
249		} else {
250	<	*/
138	<	{
139	<	comparator = null;
140	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
141	<	add(i.next());
250	>	initFromCollection(c);
251		}
252		}
253
254	<	// Queue Methods
254	>	private void initElementsFromCollection(Collection<? extends E> c) {
255	>	Object[] a = c.toArray();
256	>	// If c.toArray incorrectly doesn't return Object[], copy it.
257	>	if (a.getClass() != Object[].class)
258	>	a = Arrays.copyOf(a, a.length, Object[].class);
259	>	int len = a.length;
260	>	if (len == 1 || this.comparator != null)
261	>	for (Object e : a)
262	>	if (e == null)
263	>	throw new NullPointerException();
264	>	this.queue = a;
265	>	this.size = a.length;
266	>	}
267
268		/**
269	<	* Remove and return the minimal element from this priority queue
149	<	* if it contains one or more elements, otherwise return
150	<	* <tt>null</tt>.  The term <i>minimal</i> is defined according to
151	<	* this priority queue's order.
269	>	* Initializes queue array with elements from the given Collection.
270		*
271	<	* @return the minimal element from this priority queue if it contains
154	<	*         one or more elements, otherwise <tt>null</tt>.
271	>	* @param c the collection
272		*/
273	<	public E poll() {
274	<	if (size == 0)
275	<	return null;
159	<	return remove(1);
273	>	private void initFromCollection(Collection<? extends E> c) {
274	>	initElementsFromCollection(c);
275	>	heapify();
276		}
277
278		/**
279	<	* Return, but do not remove, the minimal element from the
280	<	* priority queue, or return <tt>null</tt> if the queue is empty.
281	<	* The term <i>minimal</i> is defined according to this priority
282	<	* queue's order.  This method returns the same object reference
283	<	* that would be returned by by the <tt>poll</tt> method.  The two
284	<	* methods differ in that this method does not remove the element
285	<	* from the priority queue.
279	>	* The maximum size of array to allocate.
280	>	* Some VMs reserve some header words in an array.
281	>	* Attempts to allocate larger arrays may result in
282	>	* OutOfMemoryError: Requested array size exceeds VM limit
283	>	*/
284	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
285	>
286	>	/**
287	>	* Increases the capacity of the array.
288		*
289	<	* @return the minimal element from this priority queue if it contains
172	<	*         one or more elements, otherwise <tt>null</tt>.
289	>	* @param minCapacity the desired minimum capacity
290		*/
291	+	private void grow(int minCapacity) {
292	+	int oldCapacity = queue.length;
293	+	// Double size if small; else grow by 50%
294	+	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
295	+	(oldCapacity + 2) :
296	+	(oldCapacity >> 1));
297	+	// overflow-conscious code
298	+	if (newCapacity - MAX_ARRAY_SIZE > 0)
299	+	newCapacity = hugeCapacity(minCapacity);
300	+	queue = Arrays.copyOf(queue, newCapacity);
301	+	}
302	+
303	+	private static int hugeCapacity(int minCapacity) {
304	+	if (minCapacity < 0) // overflow
305	+	throw new OutOfMemoryError();
306	+	return (minCapacity > MAX_ARRAY_SIZE) ?
307	+	Integer.MAX_VALUE :
308	+	MAX_ARRAY_SIZE;
309	+	}
310	+
311	+	/**
312	+	* Inserts the specified element into this priority queue.
313	+	*
314	+	* @return {@code true} (as specified by {@link Collection#add})
315	+	* @throws ClassCastException if the specified element cannot be
316	+	*         compared with elements currently in this priority queue
317	+	*         according to the priority queue's ordering
318	+	* @throws NullPointerException if the specified element is null
319	+	*/
320	+	public boolean add(E e) {
321	+	return offer(e);
322	+	}
323	+
324	+	/**
325	+	* Inserts the specified element into this priority queue.
326	+	*
327	+	* @return {@code true} (as specified by {@link Queue#offer})
328	+	* @throws ClassCastException if the specified element cannot be
329	+	*         compared with elements currently in this priority queue
330	+	*         according to the priority queue's ordering
331	+	* @throws NullPointerException if the specified element is null
332	+	*/
333	+	public boolean offer(E e) {
334	+	if (e == null)
335	+	throw new NullPointerException();
336	+	modCount++;
337	+	int i = size;
338	+	if (i >= queue.length)
339	+	grow(i + 1);
340	+	siftUp(i, e);
341	+	size = i + 1;
342	+	return true;
343	+	}
344	+
345	+	@SuppressWarnings("unchecked")
346		public E peek() {
347	<	return queue[1];
347	>	return (size == 0) ? null : (E) queue[0];
348		}
349
350	<	// Collection Methods
350	>	private int indexOf(Object o) {
351	>	if (o != null) {
352	>	for (int i = 0; i < size; i++)
353	>	if (o.equals(queue[i]))
354	>	return i;
355	>	}
356	>	return -1;
357	>	}
358
359		/**
360	<	* Removes a single instance of the specified element from this priority
361	<	* queue, if it is present.  Returns true if this collection contained the
362	<	* specified element (or equivalently, if this collection changed as a
360	>	* Removes a single instance of the specified element from this queue,
361	>	* if it is present.  More formally, removes an element {@code e} such
362	>	* that {@code o.equals(e)}, if this queue contains one or more such
363	>	* elements.  Returns {@code true} if and only if this queue contained
364	>	* the specified element (or equivalently, if this queue changed as a
365		* result of the call).
366		*
367	<	* @param element the element to be removed from this collection,
368	<	* if present.
188	<	* @return <tt>true</tt> if this collection changed as a result of the
189	<	*         call
190	<	* @throws ClassCastException if the specified element cannot be compared
191	<	*            with elements currently in the priority queue according
192	<	*            to the priority queue's ordering.
193	<	* @throws NullPointerException if the specified element is null.
367	>	* @param o element to be removed from this queue, if present
368	>	* @return {@code true} if this queue changed as a result of the call
369		*/
370	<	public boolean remove(Object element) {
371	<	if (element == null)
372	<	throw new NullPointerException();
370	>	public boolean remove(Object o) {
371	>	int i = indexOf(o);
372	>	if (i == -1)
373	>	return false;
374	>	else {
375	>	removeAt(i);
376	>	return true;
377	>	}
378	>	}
379
380	<	if (comparator == null) {
381	<	for (int i = 1; i <= size; i++) {
382	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
383	<	remove(i);
384	<	return true;
385	<	}
386	<	}
387	<	} else {
388	<	for (int i = 1; i <= size; i++) {
389	<	if (comparator.compare(queue[i], (E) element) == 0) {
390	<	remove(i);
391	<	return true;
211	<	}
380	>	/**
381	>	* Version of remove using reference equality, not equals.
382	>	* Needed by iterator.remove.
383	>	*
384	>	* @param o element to be removed from this queue, if present
385	>	* @return {@code true} if removed
386	>	*/
387	>	boolean removeEq(Object o) {
388	>	for (int i = 0; i < size; i++) {
389	>	if (o == queue[i]) {
390	>	removeAt(i);
391	>	return true;
392		}
393		}
394		return false;
395		}
396
397		/**
398	<	* Returns an iterator over the elements in this priority queue.  The
399	<	* elements of the priority queue will be returned by this iterator in the
400	<	* order specified by the queue, which is to say the order they would be
401	<	* returned by repeated calls to <tt>poll</tt>.
402	<	*
403	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
398	>	* Returns {@code true} if this queue contains the specified element.
399	>	* More formally, returns {@code true} if and only if this queue contains
400	>	* at least one element {@code e} such that {@code o.equals(e)}.
401	>	*
402	>	* @param o object to be checked for containment in this queue
403	>	* @return {@code true} if this queue contains the specified element
404	>	*/
405	>	public boolean contains(Object o) {
406	>	return indexOf(o) >= 0;
407	>	}
408	>
409	>	/**
410	>	* Returns an array containing all of the elements in this queue.
411	>	* The elements are in no particular order.
412	>	*
413	>	* <p>The returned array will be "safe" in that no references to it are
414	>	* maintained by this queue.  (In other words, this method must allocate
415	>	* a new array).  The caller is thus free to modify the returned array.
416	>	*
417	>	* <p>This method acts as bridge between array-based and collection-based
418	>	* APIs.
419	>	*
420	>	* @return an array containing all of the elements in this queue
421	>	*/
422	>	public Object[] toArray() {
423	>	return Arrays.copyOf(queue, size);
424	>	}
425	>
426	>	/**
427	>	* Returns an array containing all of the elements in this queue; the
428	>	* runtime type of the returned array is that of the specified array.
429	>	* The returned array elements are in no particular order.
430	>	* If the queue fits in the specified array, it is returned therein.
431	>	* Otherwise, a new array is allocated with the runtime type of the
432	>	* specified array and the size of this queue.
433	>	*
434	>	* <p>If the queue fits in the specified array with room to spare
435	>	* (i.e., the array has more elements than the queue), the element in
436	>	* the array immediately following the end of the collection is set to
437	>	* {@code null}.
438	>	*
439	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
440	>	* array-based and collection-based APIs.  Further, this method allows
441	>	* precise control over the runtime type of the output array, and may,
442	>	* under certain circumstances, be used to save allocation costs.
443	>	*
444	>	* <p>Suppose {@code x} is a queue known to contain only strings.
445	>	* The following code can be used to dump the queue into a newly
446	>	* allocated array of {@code String}:
447	>	*
448	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
449	>	*
450	>	* Note that {@code toArray(new Object[0])} is identical in function to
451	>	* {@code toArray()}.
452	>	*
453	>	* @param a the array into which the elements of the queue are to
454	>	*          be stored, if it is big enough; otherwise, a new array of the
455	>	*          same runtime type is allocated for this purpose.
456	>	* @return an array containing all of the elements in this queue
457	>	* @throws ArrayStoreException if the runtime type of the specified array
458	>	*         is not a supertype of the runtime type of every element in
459	>	*         this queue
460	>	* @throws NullPointerException if the specified array is null
461	>	*/
462	>	@SuppressWarnings("unchecked")
463	>	public <T> T[] toArray(T[] a) {
464	>	final int size = this.size;
465	>	if (a.length < size)
466	>	// Make a new array of a's runtime type, but my contents:
467	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
468	>	System.arraycopy(queue, 0, a, 0, size);
469	>	if (a.length > size)
470	>	a[size] = null;
471	>	return a;
472	>	}
473	>
474	>	/**
475	>	* Returns an iterator over the elements in this queue. The iterator
476	>	* does not return the elements in any particular order.
477	>	*
478	>	* @return an iterator over the elements in this queue
479		*/
480		public Iterator<E> iterator() {
481		return new Itr();
482		}
483
484	<	private class Itr implements Iterator<E> {
484	>	private final class Itr implements Iterator<E> {
485		/**
486		* Index (into queue array) of element to be returned by
487		* subsequent call to next.
488		*/
489	<	private int cursor = 1;
489	>	private int cursor;
490
491		/**
492	<	* Index of element returned by most recent call to next or
493	<	* previous.  Reset to 0 if this element is deleted by a call
494	<	* to remove.
492	>	* Index of element returned by most recent call to next,
493	>	* unless that element came from the forgetMeNot list.
494	>	* Set to -1 if element is deleted by a call to remove.
495		*/
496	<	private int lastRet = 0;
496	>	private int lastRet = -1;
497	>
498	>	/**
499	>	* A queue of elements that were moved from the unvisited portion of
500	>	* the heap into the visited portion as a result of "unlucky" element
501	>	* removals during the iteration.  (Unlucky element removals are those
502	>	* that require a siftup instead of a siftdown.)  We must visit all of
503	>	* the elements in this list to complete the iteration.  We do this
504	>	* after we've completed the "normal" iteration.
505	>	*
506	>	* We expect that most iterations, even those involving removals,
507	>	* will not need to store elements in this field.
508	>	*/
509	>	private ArrayDeque<E> forgetMeNot;
510	>
511	>	/**
512	>	* Element returned by the most recent call to next iff that
513	>	* element was drawn from the forgetMeNot list.
514	>	*/
515	>	private E lastRetElt;
516
517		/**
518		* The modCount value that the iterator believes that the backing
519	<	* List should have.  If this expectation is violated, the iterator
519	>	* Queue should have.  If this expectation is violated, the iterator
520		* has detected concurrent modification.
521		*/
522		private int expectedModCount = modCount;
523
524		public boolean hasNext() {
525	<	return cursor <= size;
525	>	return cursor < size ||
526	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
527		}
528
529	+	@SuppressWarnings("unchecked")
530		public E next() {
531	<	checkForComodification();
532	<	if (cursor > size)
533	<	throw new NoSuchElementException();
534	<	E result = queue[cursor];
535	<	lastRet = cursor++;
536	<	return result;
531	>	if (expectedModCount != modCount)
532	>	throw new ConcurrentModificationException();
533	>	if (cursor < size)
534	>	return (E) queue[lastRet = cursor++];
535	>	if (forgetMeNot != null) {
536	>	lastRet = -1;
537	>	lastRetElt = forgetMeNot.poll();
538	>	if (lastRetElt != null)
539	>	return lastRetElt;
540	>	}
541	>	throw new NoSuchElementException();
542		}
543
544		public void remove() {
545	<	if (lastRet == 0)
545	>	if (expectedModCount != modCount)
546	>	throw new ConcurrentModificationException();
547	>	if (lastRet != -1) {
548	>	E moved = PriorityQueue.this.removeAt(lastRet);
549	>	lastRet = -1;
550	>	if (moved == null)
551	>	cursor--;
552	>	else {
553	>	if (forgetMeNot == null)
554	>	forgetMeNot = new ArrayDeque<>();
555	>	forgetMeNot.add(moved);
556	>	}
557	>	} else if (lastRetElt != null) {
558	>	PriorityQueue.this.removeEq(lastRetElt);
559	>	lastRetElt = null;
560	>	} else {
561		throw new IllegalStateException();
562	<	checkForComodification();
267	<
268	<	PriorityQueue.this.remove(lastRet);
269	<	if (lastRet < cursor)
270	<	cursor--;
271	<	lastRet = 0;
562	>	}
563		expectedModCount = modCount;
564		}
274	–
275	–	final void checkForComodification() {
276	–	if (modCount != expectedModCount)
277	–	throw new ConcurrentModificationException();
278	–	}
565		}
566
281	–	/**
282	–	* Returns the number of elements in this priority queue.
283	–	*
284	–	* @return the number of elements in this priority queue.
285	–	*/
567		public int size() {
568		return size;
569		}
570
571		/**
572	<	* Add the specified element to this priority queue.
573	<	*
293	<	* @param element the element to add.
294	<	* @return true
295	<	* @throws ClassCastException if the specified element cannot be compared
296	<	*            with elements currently in the priority queue according
297	<	*            to the priority queue's ordering.
298	<	* @throws NullPointerException if the specified element is null.
572	>	* Removes all of the elements from this priority queue.
573	>	* The queue will be empty after this call returns.
574		*/
575	<	public boolean offer(E element) {
301	<	if (element == null)
302	<	throw new NullPointerException();
575	>	public void clear() {
576		modCount++;
577	+	for (int i = 0; i < size; i++)
578	+	queue[i] = null;
579	+	size = 0;
580	+	}
581
582	<	// Grow backing store if necessary
583	<	if (++size == queue.length) {
584	<	E[] newQueue = new E[2 * queue.length];
585	<	System.arraycopy(queue, 0, newQueue, 0, size);
586	<	queue = newQueue;
587	<	}
588	<
589	<	queue[size] = element;
590	<	fixUp(size);
591	<	return true;
582	>	@SuppressWarnings("unchecked")
583	>	public E poll() {
584	>	if (size == 0)
585	>	return null;
586	>	int s = --size;
587	>	modCount++;
588	>	E result = (E) queue[0];
589	>	E x = (E) queue[s];
590	>	queue[s] = null;
591	>	if (s != 0)
592	>	siftDown(0, x);
593	>	return result;
594		}
595
596		/**
597	<	* Remove all elements from the priority queue.
598	<	*/
599	<	public void clear() {
597	>	* Removes the ith element from queue.
598	>	*
599	>	* Normally this method leaves the elements at up to i-1,
600	>	* inclusive, untouched.  Under these circumstances, it returns
601	>	* null.  Occasionally, in order to maintain the heap invariant,
602	>	* it must swap a later element of the list with one earlier than
603	>	* i.  Under these circumstances, this method returns the element
604	>	* that was previously at the end of the list and is now at some
605	>	* position before i. This fact is used by iterator.remove so as to
606	>	* avoid missing traversing elements.
607	>	*/
608	>	@SuppressWarnings("unchecked")
609	>	E removeAt(int i) {
610	>	// assert i >= 0 && i < size;
611		modCount++;
612	<
613	<	// Null out element references to prevent memory leak
324	<	for (int i=1; i<=size; i++)
612	>	int s = --size;
613	>	if (s == i) // removed last element
614		queue[i] = null;
615	<
616	<	size = 0;
615	>	else {
616	>	E moved = (E) queue[s];
617	>	queue[s] = null;
618	>	siftDown(i, moved);
619	>	if (queue[i] == moved) {
620	>	siftUp(i, moved);
621	>	if (queue[i] != moved)
622	>	return moved;
623	>	}
624	>	}
625	>	return null;
626		}
627
628		/**
629	<	* Removes and returns the ith element from queue.  Recall
630	<	* that queue is one-based, so 1 <= i <= size.
631	<	*
632	<	* XXX: Could further special-case i==size, but is it worth it?
633	<	* XXX: Could special-case i==0, but is it worth it?
634	<	*/
635	<	private E remove(int i) {
636	<	assert i <= size;
637	<	modCount++;
629	>	* Inserts item x at position k, maintaining heap invariant by
630	>	* promoting x up the tree until it is greater than or equal to
631	>	* its parent, or is the root.
632	>	*
633	>	* To simplify and speed up coercions and comparisons. the
634	>	* Comparable and Comparator versions are separated into different
635	>	* methods that are otherwise identical. (Similarly for siftDown.)
636	>	*
637	>	* @param k the position to fill
638	>	* @param x the item to insert
639	>	*/
640	>	private void siftUp(int k, E x) {
641	>	if (comparator != null)
642	>	siftUpUsingComparator(k, x);
643	>	else
644	>	siftUpComparable(k, x);
645	>	}
646	>
647	>	@SuppressWarnings("unchecked")
648	>	private void siftUpComparable(int k, E x) {
649	>	Comparable<? super E> key = (Comparable<? super E>) x;
650	>	while (k > 0) {
651	>	int parent = (k - 1) >>> 1;
652	>	Object e = queue[parent];
653	>	if (key.compareTo((E) e) >= 0)
654	>	break;
655	>	queue[k] = e;
656	>	k = parent;
657	>	}
658	>	queue[k] = key;
659	>	}
660
661	<	E result = queue[i];
662	<	queue[i] = queue[size];
663	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
664	<	if (i <= size)
665	<	fixDown(i);
666	<	return result;
661	>	@SuppressWarnings("unchecked")
662	>	private void siftUpUsingComparator(int k, E x) {
663	>	while (k > 0) {
664	>	int parent = (k - 1) >>> 1;
665	>	Object e = queue[parent];
666	>	if (comparator.compare(x, (E) e) >= 0)
667	>	break;
668	>	queue[k] = e;
669	>	k = parent;
670	>	}
671	>	queue[k] = x;
672		}
673
674		/**
675	<	* Establishes the heap invariant (described above) assuming the heap
676	<	* satisfies the invariant except possibly for the leaf-node indexed by k
677	<	* (which may have a nextExecutionTime less than its parent's).
678	<	*
679	<	* This method functions by "promoting" queue[k] up the hierarchy
680	<	* (by swapping it with its parent) repeatedly until queue[k]
681	<	* is greater than or equal to its parent.
682	<	*/
683	<	private void fixUp(int k) {
684	<	if (comparator == null) {
685	<	while (k > 1) {
686	<	int j = k >> 1;
687	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
688	<	break;
689	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
690	<	k = j;
691	<	}
692	<	} else {
693	<	while (k > 1) {
694	<	int j = k >> 1;
695	<	if (comparator.compare(queue[j], queue[k]) <= 0)
696	<	break;
697	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
698	<	k = j;
699	<	}
675	>	* Inserts item x at position k, maintaining heap invariant by
676	>	* demoting x down the tree repeatedly until it is less than or
677	>	* equal to its children or is a leaf.
678	>	*
679	>	* @param k the position to fill
680	>	* @param x the item to insert
681	>	*/
682	>	private void siftDown(int k, E x) {
683	>	if (comparator != null)
684	>	siftDownUsingComparator(k, x);
685	>	else
686	>	siftDownComparable(k, x);
687	>	}
688	>
689	>	@SuppressWarnings("unchecked")
690	>	private void siftDownComparable(int k, E x) {
691	>	Comparable<? super E> key = (Comparable<? super E>)x;
692	>	int half = size >>> 1;        // loop while a non-leaf
693	>	while (k < half) {
694	>	int child = (k << 1) + 1; // assume left child is least
695	>	Object c = queue[child];
696	>	int right = child + 1;
697	>	if (right < size &&
698	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
699	>	c = queue[child = right];
700	>	if (key.compareTo((E) c) <= 0)
701	>	break;
702	>	queue[k] = c;
703	>	k = child;
704		}
705	+	queue[k] = key;
706		}
707
708	<	/**
709	<	* Establishes the heap invariant (described above) in the subtree
710	<	* rooted at k, which is assumed to satisfy the heap invariant except
711	<	* possibly for node k itself (which may be greater than its children).
712	<	*
713	<	* This method functions by "demoting" queue[k] down the hierarchy
714	<	* (by swapping it with its smaller child) repeatedly until queue[k]
715	<	* is less than or equal to its children.
716	<	*/
717	<	private void fixDown(int k) {
718	<	int j;
719	<	if (comparator == null) {
720	<	while ((j = k << 1) <= size) {
721	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
392	<	j++; // j indexes smallest kid
393	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
394	<	break;
395	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
396	<	k = j;
397	<	}
398	<	} else {
399	<	while ((j = k << 1) <= size) {
400	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
401	<	j++; // j indexes smallest kid
402	<	if (comparator.compare(queue[k], queue[j]) <= 0)
403	<	break;
404	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
405	<	k = j;
406	<	}
708	>	@SuppressWarnings("unchecked")
709	>	private void siftDownUsingComparator(int k, E x) {
710	>	int half = size >>> 1;
711	>	while (k < half) {
712	>	int child = (k << 1) + 1;
713	>	Object c = queue[child];
714	>	int right = child + 1;
715	>	if (right < size &&
716	>	comparator.compare((E) c, (E) queue[right]) > 0)
717	>	c = queue[child = right];
718	>	if (comparator.compare(x, (E) c) <= 0)
719	>	break;
720	>	queue[k] = c;
721	>	k = child;
722		}
723	+	queue[k] = x;
724	+	}
725	+
726	+	/**
727	+	* Establishes the heap invariant (described above) in the entire tree,
728	+	* assuming nothing about the order of the elements prior to the call.
729	+	*/
730	+	@SuppressWarnings("unchecked")
731	+	private void heapify() {
732	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
733	+	siftDown(i, (E) queue[i]);
734		}
735
736		/**
737	<	* Returns the comparator associated with this priority queue, or
738	<	* <tt>null</tt> if it uses its elements' natural ordering.
737	>	* Returns the comparator used to order the elements in this
738	>	* queue, or {@code null} if this queue is sorted according to
739	>	* the {@linkplain Comparable natural ordering} of its elements.
740		*
741	<	* @return the comparator associated with this priority queue, or
742	<	*         <tt>null</tt> if it uses its elements' natural ordering.
741	>	* @return the comparator used to order this queue, or
742	>	*         {@code null} if this queue is sorted according to the
743	>	*         natural ordering of its elements
744		*/
745	<	Comparator comparator() {
745	>	public Comparator<? super E> comparator() {
746		return comparator;
747		}
748
749		/**
750	<	* Save the state of the instance to a stream (that
423	<	* is, serialize it).
750	>	* Saves this queue to a stream (that is, serializes it).
751		*
425	–	* @serialData The length of the array backing the instance is
426	–	* emitted (int), followed by all of its elements (each an
427	–	* <tt>Object</tt>) in the proper order.
752		* @param s the stream
753	+	* @throws java.io.IOException if an I/O error occurs
754	+	* @serialData The length of the array backing the instance is
755	+	*             emitted (int), followed by all of its elements
756	+	*             (each an {@code Object}) in the proper order.
757		*/
758	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
759	<	throws java.io.IOException{
758	>	private void writeObject(java.io.ObjectOutputStream s)
759	>	throws java.io.IOException {
760		// Write out element count, and any hidden stuff
761		s.defaultWriteObject();
762
763	<	// Write out array length
764	<	s.writeInt(queue.length);
763	>	// Write out array length, for compatibility with 1.5 version
764	>	s.writeInt(Math.max(2, size + 1));
765
766	<	// Write out all elements in the proper order.
767	<	for (int i=0; i<size; i++)
766	>	// Write out all elements in the "proper order".
767	>	for (int i = 0; i < size; i++)
768		s.writeObject(queue[i]);
769		}
770
771		/**
772	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
773	<	* deserialize it).
772	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
773	>	* (that is, deserializes it).
774	>	*
775		* @param s the stream
776	+	* @throws ClassNotFoundException if the class of a serialized object
777	+	*         could not be found
778	+	* @throws java.io.IOException if an I/O error occurs
779		*/
780	<	private synchronized void readObject(java.io.ObjectInputStream s)
780	>	private void readObject(java.io.ObjectInputStream s)
781		throws java.io.IOException, ClassNotFoundException {
782		// Read in size, and any hidden stuff
783		s.defaultReadObject();
784
785	<	// Read in array length and allocate array
786	<	int arrayLength = s.readInt();
787	<	queue = new E[arrayLength];
788	<
789	<	// Read in all elements in the proper order.
790	<	for (int i=0; i<size; i++)
791	<	queue[i] = (E)s.readObject();
785	>	// Read in (and discard) array length
786	>	s.readInt();
787	>
788	>	queue = new Object[size];
789	>
790	>	// Read in all elements.
791	>	for (int i = 0; i < size; i++)
792	>	queue[i] = s.readObject();
793	>
794	>	// Elements are guaranteed to be in "proper order", but the
795	>	// spec has never explained what that might be.
796	>	heapify();
797	>	}
798	>
799	>	/**
800	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
801	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
802	>	* queue.
803	>	*
804	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
805	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
806	>	* Overriding implementations should document the reporting of additional
807	>	* characteristic values.
808	>	*
809	>	* @return a {@code Spliterator} over the elements in this queue
810	>	* @since 1.8
811	>	*/
812	>	public final Spliterator<E> spliterator() {
813	>	return new PriorityQueueSpliterator<>(this, 0, -1, 0);
814		}
815
816	+	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
817	+	/*
818	+	* This is very similar to ArrayList Spliterator, except for
819	+	* extra null checks.
820	+	*/
821	+	private final PriorityQueue<E> pq;
822	+	private int index;            // current index, modified on advance/split
823	+	private int fence;            // -1 until first use
824	+	private int expectedModCount; // initialized when fence set
825	+
826	+	/** Creates new spliterator covering the given range. */
827	+	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
828	+	int expectedModCount) {
829	+	this.pq = pq;
830	+	this.index = origin;
831	+	this.fence = fence;
832	+	this.expectedModCount = expectedModCount;
833	+	}
834	+
835	+	private int getFence() { // initialize fence to size on first use
836	+	int hi;
837	+	if ((hi = fence) < 0) {
838	+	expectedModCount = pq.modCount;
839	+	hi = fence = pq.size;
840	+	}
841	+	return hi;
842	+	}
843	+
844	+	public PriorityQueueSpliterator<E> trySplit() {
845	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
846	+	return (lo >= mid) ? null :
847	+	new PriorityQueueSpliterator<>(pq, lo, index = mid,
848	+	expectedModCount);
849	+	}
850	+
851	+	@SuppressWarnings("unchecked")
852	+	public void forEachRemaining(Consumer<? super E> action) {
853	+	int i, hi, mc; // hoist accesses and checks from loop
854	+	PriorityQueue<E> q; Object[] a;
855	+	if (action == null)
856	+	throw new NullPointerException();
857	+	if ((q = pq) != null && (a = q.queue) != null) {
858	+	if ((hi = fence) < 0) {
859	+	mc = q.modCount;
860	+	hi = q.size;
861	+	}
862	+	else
863	+	mc = expectedModCount;
864	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
865	+	for (E e;; ++i) {
866	+	if (i < hi) {
867	+	if ((e = (E) a[i]) == null) // must be CME
868	+	break;
869	+	action.accept(e);
870	+	}
871	+	else if (q.modCount != mc)
872	+	break;
873	+	else
874	+	return;
875	+	}
876	+	}
877	+	}
878	+	throw new ConcurrentModificationException();
879	+	}
880	+
881	+	public boolean tryAdvance(Consumer<? super E> action) {
882	+	if (action == null)
883	+	throw new NullPointerException();
884	+	int hi = getFence(), lo = index;
885	+	if (lo >= 0 && lo < hi) {
886	+	index = lo + 1;
887	+	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
888	+	if (e == null)
889	+	throw new ConcurrentModificationException();
890	+	action.accept(e);
891	+	if (pq.modCount != expectedModCount)
892	+	throw new ConcurrentModificationException();
893	+	return true;
894	+	}
895	+	return false;
896	+	}
897	+
898	+	public long estimateSize() {
899	+	return (long) (getFence() - index);
900	+	}
901	+
902	+	public int characteristics() {
903	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
904	+	}
905	+	}
906		}

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