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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.4 by tim, Mon May 19 02:45:07 2003 UTC vs.
Revision 1.107 by jsr166, Sun Sep 20 16:20:21 2015 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
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	<	*   1) Make it serializable.
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 the order specified at creation time.  This order is
33	<	* specified as for {@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	<	* these elements are tied for least value, no guarantees are made as to
39	<	* which of elements is returned.
40	<	*
41	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
42	<	* the array used to store the elements on the queue.  It is always at least
43	<	* as large as the queue size.  As elements are added to a priority list,
44	<	* its capacity grows automatically.  The details of the growth policy are not
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>Implementation note: this implementation provides O(log(n)) time for
55	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
56	<	* methods; linear time for the <tt>remove(Object)</tt> and
57	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
58	<	* <tt>element</tt>, and <tt>size</tt> methods.
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, 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>
84	<	{
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
94	<	* of n, d, n <= d.
95	<	*
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.
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 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 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 (11)
118	<	* that orders its elements according to their natural ordering.
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.
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'
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.
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	>	/**
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	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	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 if
147	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
148	<	* <i>minimal</i> is defined according to this priority queue's order.
269	>	* Initializes queue array with elements from the given Collection.
270		*
271	<	* @return the minimal element from this priority queue if it contains
151	<	*         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;
156	<	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 priority queue,
280	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
281	<	* defined according to this priority queue's order.  This method returns
282	<	* the same object reference that would be returned by by the
283	<	* <tt>poll</tt> method.  The two methods differ in that this method
284	<	* does not remove the element 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
168	<	*         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	+	size = i + 1;
341	+	if (i == 0)
342	+	queue[0] = e;
343	+	else
344	+	siftUp(i, e);
345	+	return true;
346	+	}
347	+
348	+	@SuppressWarnings("unchecked")
349		public E peek() {
350	<	return queue[1];
350	>	return (size == 0) ? null : (E) queue[0];
351		}
352
353	<	// Collection Methods
353	>	private int indexOf(Object o) {
354	>	if (o != null) {
355	>	for (int i = 0; i < size; i++)
356	>	if (o.equals(queue[i]))
357	>	return i;
358	>	}
359	>	return -1;
360	>	}
361
362		/**
363	<	* Removes a single instance of the specified element from this priority
364	<	* queue, if it is present.  Returns true if this collection contained the
365	<	* specified element (or equivalently, if this collection changed as a
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 collection, if present.
371	<	* @return <tt>true</tt> if this collection changed as a result of the
184	<	*         call
185	<	* @throws ClassCastException if the specified element cannot be compared
186	<	*            with elements currently in the priority queue according
187	<	*            to the priority queue's ordering.
188	<	* @throws NullPointerException if the specified element is null.
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 element) {
374	<	if (element == null)
375	<	throw new NullPointerException();
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	<	if (comparator == null) {
384	<	for (int i = 1; i <= size; i++) {
385	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
386	<	remove(i);
387	<	return true;
388	<	}
389	<	}
390	<	} else {
391	<	for (int i = 1; i <= size; i++) {
392	<	if (comparator.compare(queue[i], (E) element) == 0) {
393	<	remove(i);
394	<	return true;
206	<	}
383	>	/**
384	>	* Version of remove using reference equality, not equals.
385	>	* Needed by iterator.remove.
386	>	*
387	>	* @param o element to be removed from this queue, if present
388	>	* @return {@code true} if removed
389	>	*/
390	>	boolean removeEq(Object o) {
391	>	for (int i = 0; i < size; i++) {
392	>	if (o == queue[i]) {
393	>	removeAt(i);
394	>	return true;
395		}
396		}
397		return false;
398		}
399
400		/**
401	<	* Returns an iterator over the elements in this priority queue.  The
402	<	* first element returned by this iterator is the same element that
403	<	* would be returned by a call to <tt>peek</tt>.
401	>	* Returns {@code true} if this queue contains the specified element.
402	>	* More formally, returns {@code true} if and only if this queue contains
403	>	* at least one element {@code e} such that {@code o.equals(e)}.
404		*
405	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
405	>	* @param o object to be checked for containment in this queue
406	>	* @return {@code true} if this queue contains the specified element
407	>	*/
408	>	public boolean contains(Object o) {
409	>	return indexOf(o) >= 0;
410	>	}
411	>
412	>	/**
413	>	* Returns an array containing all of the elements in this queue.
414	>	* The elements are in no particular order.
415	>	*
416	>	* <p>The returned array will be "safe" in that no references to it are
417	>	* maintained by this queue.  (In other words, this method must allocate
418	>	* a new array).  The caller is thus free to modify the returned array.
419	>	*
420	>	* <p>This method acts as bridge between array-based and collection-based
421	>	* APIs.
422	>	*
423	>	* @return an array containing all of the elements in this queue
424	>	*/
425	>	public Object[] toArray() {
426	>	return Arrays.copyOf(queue, size);
427	>	}
428	>
429	>	/**
430	>	* Returns an array containing all of the elements in this queue; the
431	>	* runtime type of the returned array is that of the specified array.
432	>	* The returned array elements are in no particular order.
433	>	* If the queue fits in the specified array, it is returned therein.
434	>	* Otherwise, a new array is allocated with the runtime type of the
435	>	* specified array and the size of this queue.
436	>	*
437	>	* <p>If the queue fits in the specified array with room to spare
438	>	* (i.e., the array has more elements than the queue), the element in
439	>	* the array immediately following the end of the collection is set to
440	>	* {@code null}.
441	>	*
442	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
443	>	* array-based and collection-based APIs.  Further, this method allows
444	>	* precise control over the runtime type of the output array, and may,
445	>	* under certain circumstances, be used to save allocation costs.
446	>	*
447	>	* <p>Suppose {@code x} is a queue known to contain only strings.
448	>	* The following code can be used to dump the queue into a newly
449	>	* allocated array of {@code String}:
450	>	*
451	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
452	>	*
453	>	* Note that {@code toArray(new Object[0])} is identical in function to
454	>	* {@code toArray()}.
455	>	*
456	>	* @param a the array into which the elements of the queue are to
457	>	*          be stored, if it is big enough; otherwise, a new array of the
458	>	*          same runtime type is allocated for this purpose.
459	>	* @return an array containing all of the elements in this queue
460	>	* @throws ArrayStoreException if the runtime type of the specified array
461	>	*         is not a supertype of the runtime type of every element in
462	>	*         this queue
463	>	* @throws NullPointerException if the specified array is null
464	>	*/
465	>	@SuppressWarnings("unchecked")
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 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	>	* 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	>	private ArrayDeque<E> forgetMeNot;
513
514		/**
515	<	* Index of element returned by most recent call to next or
516	<	* previous.  Reset to 0 if this element is deleted by a call
233	<	* to remove.
515	>	* Element returned by the most recent call to next iff that
516	>	* element was drawn from the forgetMeNot list.
517		*/
518	<	int lastRet = 0;
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		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 = 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();
261	<
262	<	PriorityQueue.this.remove(lastRet);
263	<	if (lastRet < cursor)
264	<	cursor--;
265	<	lastRet = 0;
565	>	}
566		expectedModCount = modCount;
567		}
568	+	}
569
570	<	final void checkForComodification() {
571	<	if (modCount != expectedModCount)
271	<	throw new ConcurrentModificationException();
272	<	}
570	>	public int size() {
571	>	return size;
572		}
573
574		/**
575	<	* Returns the number of elements in this priority queue.
576	<	*
278	<	* @return the number of elements in this 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 int size() {
579	<	return size;
578	>	public void clear() {
579	>	modCount++;
580	>	for (int i = 0; i < size; i++)
581	>	queue[i] = null;
582	>	size = 0;
583	>	}
584	>
585	>	@SuppressWarnings("unchecked")
586	>	public E poll() {
587	>	if (size == 0)
588	>	return null;
589	>	int s = --size;
590	>	modCount++;
591	>	E result = (E) queue[0];
592	>	E x = (E) queue[s];
593	>	queue[s] = null;
594	>	if (s != 0)
595	>	siftDown(0, x);
596	>	return result;
597		}
598
599		/**
600	<	* Add the specified element to this priority queue.
600	>	* Removes the ith element from queue.
601		*
602	<	* @param element the element to add.
603	<	* @return true
604	<	* @throws ClassCastException if the specified element cannot be compared
605	<	*            with elements currently in the priority queue according
606	<	*            to the priority queue's ordering.
607	<	* @throws NullPointerException if the specified element is null.
608	<	*/
609	<	public boolean offer(E element) {
610	<	if (element == null)
611	<	throw new NullPointerException();
602	>	* Normally this method leaves the elements at up to i-1,
603	>	* inclusive, untouched.  Under these circumstances, it returns
604	>	* null.  Occasionally, in order to maintain the heap invariant,
605	>	* it must swap a later element of the list with one earlier than
606	>	* i.  Under these circumstances, this method returns the element
607	>	* that was previously at the end of the list and is now at some
608	>	* position before i. This fact is used by iterator.remove so as to
609	>	* avoid missing traversing elements.
610	>	*/
611	>	@SuppressWarnings("unchecked")
612	>	E removeAt(int i) {
613	>	// assert i >= 0 && i < size;
614		modCount++;
615	+	int s = --size;
616	+	if (s == i) // removed last element
617	+	queue[i] = null;
618	+	else {
619	+	E moved = (E) queue[s];
620	+	queue[s] = null;
621	+	siftDown(i, moved);
622	+	if (queue[i] == moved) {
623	+	siftUp(i, moved);
624	+	if (queue[i] != moved)
625	+	return moved;
626	+	}
627	+	}
628	+	return null;
629	+	}
630
631	<	// Grow backing store if necessary
632	<	if (++size == queue.length) {
633	<	E[] newQueue = new E[2 * queue.length];
634	<	System.arraycopy(queue, 0, newQueue, 0, size);
635	<	queue = newQueue;
631	>	/**
632	>	* Inserts item x at position k, maintaining heap invariant by
633	>	* promoting x up the tree until it is greater than or equal to
634	>	* its parent, or is the root.
635	>	*
636	>	* To simplify and speed up coercions and comparisons. the
637	>	* Comparable and Comparator versions are separated into different
638	>	* methods that are otherwise identical. (Similarly for siftDown.)
639	>	*
640	>	* @param k the position to fill
641	>	* @param x the item to insert
642	>	*/
643	>	private void siftUp(int k, E x) {
644	>	if (comparator != null)
645	>	siftUpUsingComparator(k, x);
646	>	else
647	>	siftUpComparable(k, x);
648	>	}
649	>
650	>	@SuppressWarnings("unchecked")
651	>	private void siftUpComparable(int k, E x) {
652	>	Comparable<? super E> key = (Comparable<? super E>) x;
653	>	while (k > 0) {
654	>	int parent = (k - 1) >>> 1;
655	>	Object e = queue[parent];
656	>	if (key.compareTo((E) e) >= 0)
657	>	break;
658	>	queue[k] = e;
659	>	k = parent;
660		}
661	+	queue[k] = key;
662	+	}
663
664	<	queue[size] = element;
665	<	fixUp(size);
666	<	return true;
664	>	@SuppressWarnings("unchecked")
665	>	private void siftUpUsingComparator(int k, E x) {
666	>	while (k > 0) {
667	>	int parent = (k - 1) >>> 1;
668	>	Object e = queue[parent];
669	>	if (comparator.compare(x, (E) e) >= 0)
670	>	break;
671	>	queue[k] = e;
672	>	k = parent;
673	>	}
674	>	queue[k] = x;
675		}
676
677		/**
678	<	* Remove all elements from the priority queue.
678	>	* Inserts item x at position k, maintaining heap invariant by
679	>	* demoting x down the tree repeatedly until it is less than or
680	>	* equal to its children or is a leaf.
681	>	*
682	>	* @param k the position to fill
683	>	* @param x the item to insert
684	>	*/
685	>	private void siftDown(int k, E x) {
686	>	if (comparator != null)
687	>	siftDownUsingComparator(k, x);
688	>	else
689	>	siftDownComparable(k, x);
690	>	}
691	>
692	>	@SuppressWarnings("unchecked")
693	>	private void siftDownComparable(int k, E x) {
694	>	Comparable<? super E> key = (Comparable<? super E>)x;
695	>	int half = size >>> 1;        // loop while a non-leaf
696	>	while (k < half) {
697	>	int child = (k << 1) + 1; // assume left child is least
698	>	Object c = queue[child];
699	>	int right = child + 1;
700	>	if (right < size &&
701	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
702	>	c = queue[child = right];
703	>	if (key.compareTo((E) c) <= 0)
704	>	break;
705	>	queue[k] = c;
706	>	k = child;
707	>	}
708	>	queue[k] = key;
709	>	}
710	>
711	>	@SuppressWarnings("unchecked")
712	>	private void siftDownUsingComparator(int k, E x) {
713	>	int half = size >>> 1;
714	>	while (k < half) {
715	>	int child = (k << 1) + 1;
716	>	Object c = queue[child];
717	>	int right = child + 1;
718	>	if (right < size &&
719	>	comparator.compare((E) c, (E) queue[right]) > 0)
720	>	c = queue[child = right];
721	>	if (comparator.compare(x, (E) c) <= 0)
722	>	break;
723	>	queue[k] = c;
724	>	k = child;
725	>	}
726	>	queue[k] = x;
727	>	}
728	>
729	>	/**
730	>	* Establishes the heap invariant (described above) in the entire tree,
731	>	* assuming nothing about the order of the elements prior to the call.
732		*/
733	<	public void clear() {
734	<	modCount++;
733	>	@SuppressWarnings("unchecked")
734	>	private void heapify() {
735	>	for (int i = (size >>> 1) - 1; i >= 0; i--)
736	>	siftDown(i, (E) queue[i]);
737	>	}
738
739	<	// Null out element references to prevent memory leak
740	<	for (int i=1; i<=size; i++)
741	<	queue[i] = null;
739	>	/**
740	>	* Returns the comparator used to order the elements in this
741	>	* queue, or {@code null} if this queue is sorted according to
742	>	* the {@linkplain Comparable natural ordering} of its elements.
743	>	*
744	>	* @return the comparator used to order this queue, or
745	>	*         {@code null} if this queue is sorted according to the
746	>	*         natural ordering of its elements
747	>	*/
748	>	public Comparator<? super E> comparator() {
749	>	return comparator;
750	>	}
751
752	<	size = 0;
752	>	/**
753	>	* Saves this queue to a stream (that is, serializes it).
754	>	*
755	>	* @serialData The length of the array backing the instance is
756	>	*             emitted (int), followed by all of its elements
757	>	*             (each an {@code Object}) in the proper order.
758	>	* @param s the stream
759	>	* @throws java.io.IOException if an I/O error occurs
760	>	*/
761	>	private void writeObject(java.io.ObjectOutputStream s)
762	>	throws java.io.IOException {
763	>	// Write out element count, and any hidden stuff
764	>	s.defaultWriteObject();
765	>
766	>	// Write out array length, for compatibility with 1.5 version
767	>	s.writeInt(Math.max(2, size + 1));
768	>
769	>	// Write out all elements in the "proper order".
770	>	for (int i = 0; i < size; i++)
771	>	s.writeObject(queue[i]);
772		}
773
774		/**
775	<	* Removes and returns the ith element from queue.  Recall
776	<	* that queue is one-based, so 1 <= i <= size.
775	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
776	>	* (that is, deserializes it).
777		*
778	<	* XXX: Could further special-case i==size, but is it worth it?
779	<	* XXX: Could special-case i==0, but is it worth it?
778	>	* @param s the stream
779	>	* @throws ClassNotFoundException if the class of a serialized object
780	>	*         could not be found
781	>	* @throws java.io.IOException if an I/O error occurs
782		*/
783	<	private E remove(int i) {
784	<	assert i <= size;
785	<	modCount++;
783	>	private void readObject(java.io.ObjectInputStream s)
784	>	throws java.io.IOException, ClassNotFoundException {
785	>	// Read in size, and any hidden stuff
786	>	s.defaultReadObject();
787
788	<	E result = queue[i];
789	<	queue[i] = queue[size];
790	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
791	<	if (i <= size)
792	<	fixDown(i);
793	<	return result;
788	>	// Read in (and discard) array length
789	>	s.readInt();
790	>
791	>	queue = new Object[size];
792	>
793	>	// Read in all elements.
794	>	for (int i = 0; i < size; i++)
795	>	queue[i] = s.readObject();
796	>
797	>	// Elements are guaranteed to be in "proper order", but the
798	>	// spec has never explained what that might be.
799	>	heapify();
800		}
801
802		/**
803	<	* Establishes the heap invariant (described above) assuming the heap
804	<	* satisfies the invariant except possibly for the leaf-node indexed by k
805	<	* (which may have a nextExecutionTime less than its parent's).
806	<	*
807	<	* This method functions by "promoting" queue[k] up the hierarchy
808	<	* (by swapping it with its parent) repeatedly until queue[k]
809	<	* is greater than or equal to its parent.
810	<	*/
811	<	private void fixUp(int k) {
812	<	if (comparator == null) {
813	<	while (k > 1) {
814	<	int j = k >> 1;
815	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
816	<	break;
817	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
818	<	k = j;
819	<	}
820	<	} else {
821	<	while (k > 1) {
822	<	int j = k >> 1;
823	<	if (comparator.compare(queue[j], queue[k]) <= 0)
824	<	break;
825	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
826	<	k = j;
803	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
804	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
805	>	* queue.
806	>	*
807	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
808	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
809	>	* Overriding implementations should document the reporting of additional
810	>	* characteristic values.
811	>	*
812	>	* @return a {@code Spliterator} over the elements in this queue
813	>	* @since 1.8
814	>	*/
815	>	public final Spliterator<E> spliterator() {
816	>	return new PriorityQueueSpliterator<>(this, 0, -1, 0);
817	>	}
818	>
819	>	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
820	>	/*
821	>	* This is very similar to ArrayList Spliterator, except for
822	>	* extra null checks.
823	>	*/
824	>	private final PriorityQueue<E> pq;
825	>	private int index;            // current index, modified on advance/split
826	>	private int fence;            // -1 until first use
827	>	private int expectedModCount; // initialized when fence set
828	>
829	>	/** Creates new spliterator covering the given range */
830	>	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
831	>	int expectedModCount) {
832	>	this.pq = pq;
833	>	this.index = origin;
834	>	this.fence = fence;
835	>	this.expectedModCount = expectedModCount;
836	>	}
837	>
838	>	private int getFence() { // initialize fence to size on first use
839	>	int hi;
840	>	if ((hi = fence) < 0) {
841	>	expectedModCount = pq.modCount;
842	>	hi = fence = pq.size;
843		}
844	+	return hi;
845		}
370	–	}
846
847	<	/**
848	<	* Establishes the heap invariant (described above) in the subtree
849	<	* rooted at k, which is assumed to satisfy the heap invariant except
850	<	* possibly for node k itself (which may be greater than its children).
851	<	*
852	<	* This method functions by "demoting" queue[k] down the hierarchy
853	<	* (by swapping it with its smaller child) repeatedly until queue[k]
854	<	* is less than or equal to its children.
855	<	*/
856	<	private void fixDown(int k) {
857	<	int j;
858	<	if (comparator == null) {
859	<	while ((j = k << 1) <= size) {
860	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
861	<	j++; // j indexes smallest kid
862	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
863	<	break;
864	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
865	<	k = j;
847	>	public PriorityQueueSpliterator<E> trySplit() {
848	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
849	>	return (lo >= mid) ? null :
850	>	new PriorityQueueSpliterator<>(pq, lo, index = mid,
851	>	expectedModCount);
852	>	}
853	>
854	>	@SuppressWarnings("unchecked")
855	>	public void forEachRemaining(Consumer<? super E> action) {
856	>	int i, hi, mc; // hoist accesses and checks from loop
857	>	PriorityQueue<E> q; Object[] a;
858	>	if (action == null)
859	>	throw new NullPointerException();
860	>	if ((q = pq) != null && (a = q.queue) != null) {
861	>	if ((hi = fence) < 0) {
862	>	mc = q.modCount;
863	>	hi = q.size;
864	>	}
865	>	else
866	>	mc = expectedModCount;
867	>	if ((i = index) >= 0 && (index = hi) <= a.length) {
868	>	for (E e;; ++i) {
869	>	if (i < hi) {
870	>	if ((e = (E) a[i]) == null) // must be CME
871	>	break;
872	>	action.accept(e);
873	>	}
874	>	else if (q.modCount != mc)
875	>	break;
876	>	else
877	>	return;
878	>	}
879	>	}
880		}
881	<	} else {
882	<	while ((j = k << 1) <= size) {
883	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
884	<	j++; // j indexes smallest kid
885	<	if (comparator.compare(queue[k], queue[j]) <= 0)
886	<	break;
887	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
888	<	k = j;
881	>	throw new ConcurrentModificationException();
882	>	}
883	>
884	>	public boolean tryAdvance(Consumer<? super E> action) {
885	>	if (action == null)
886	>	throw new NullPointerException();
887	>	int hi = getFence(), lo = index;
888	>	if (lo >= 0 && lo < hi) {
889	>	index = lo + 1;
890	>	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
891	>	if (e == null)
892	>	throw new ConcurrentModificationException();
893	>	action.accept(e);
894	>	if (pq.modCount != expectedModCount)
895	>	throw new ConcurrentModificationException();
896	>	return true;
897		}
898	+	return false;
899		}
402	–	}
900
901	<	/**
902	<	* Returns the comparator associated with this priority queue, or
903	<	* <tt>null</tt> if it uses its elements' natural ordering.
904	<	*
905	<	* @return the comparator associated with this priority queue, or
906	<	*         <tt>null</tt> if it uses its elements' natural ordering.
907	<	*/
411	<	Comparator<E> comparator() {
412	<	return comparator;
901	>	public long estimateSize() {
902	>	return (long) (getFence() - index);
903	>	}
904	>
905	>	public int characteristics() {
906	>	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
907	>	}
908		}
909		}

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