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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.8 by dl, Tue Jul 1 16:29:45 2003 UTC vs.
Revision 1.114 by jsr166, Wed Nov 30 18:12:52 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()} and the Spliterator provided in method {@link #spliterator()}
58	>	* are <em>not</em> guaranteed to traverse the elements of
59	>	* the priority queue in any particular order. If you need ordered
60	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
61	>	*
62	>	* <p><strong>Note that this implementation is not synchronized.</strong>
63	>	* Multiple threads should not access a {@code PriorityQueue}
64	>	* instance concurrently if any of the threads modifies the queue.
65	>	* Instead, use the thread-safe {@link
66	>	* java.util.concurrent.PriorityBlockingQueue} class.
67	>	*
68	>	* <p>Implementation note: this implementation provides
69	>	* O(log(n)) time for the enqueuing and dequeuing methods
70	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
71	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
72	>	* methods; and constant time for the retrieval methods
73	>	* ({@code peek}, {@code element}, and {@code size}).
74		*
75		* <p>This class is a member of the
76	<	* <a href="{@docRoot}/../guide/collections/index.html">
76	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
77		* Java Collections Framework</a>.
78	+	*
79		* @since 1.5
80	<	* @author Josh Bloch
80	>	* @author Josh Bloch, Doug Lea
81	>	* @param <E> the type of elements held in this queue
82		*/
83		public class PriorityQueue<E> extends AbstractQueue<E>
84	<	implements Queue<E>,
85	<	java.io.Serializable {
84	>	implements java.io.Serializable {
85	>
86	>	private static final long serialVersionUID = -7720805057305804111L;
87	>
88		private static final int DEFAULT_INITIAL_CAPACITY = 11;
89
90		/**
91	<	* Priority queue represented as a balanced binary heap: the two children
92	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
93	<	* ordered by comparator, or by the elements' natural ordering, if
94	<	* comparator is null:  For each node n in the heap and each descendant d
95	<	* of n, n <= d.
96	<	*
45	<	* The element with the lowest value is in queue[1], assuming the queue is
46	<	* nonempty.  (A one-based array is used in preference to the traditional
47	<	* zero-based array to simplify parent and child calculations.)
48	<	*
49	<	* queue.length must be >= 2, even if size == 0.
91	>	* Priority queue represented as a balanced binary heap: the two
92	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
93	>	* priority queue is ordered by comparator, or by the elements'
94	>	* natural ordering, if comparator is null: For each node n in the
95	>	* heap and each descendant d of n, n <= d.  The element with the
96	>	* lowest value is in queue[0], assuming the queue is nonempty.
97		*/
98	<	private transient E[] queue;
98	>	transient Object[] queue; // non-private to simplify nested class access
99
100		/**
101		* The number of elements in the priority queue.
102		*/
103	<	private int size = 0;
103	>	int size;
104
105		/**
106		* The comparator, or null if priority queue uses elements'
107		* natural ordering.
108		*/
109	<	private final Comparator<E> comparator;
109	>	private final Comparator<? super E> comparator;
110
111		/**
112		* The number of times this priority queue has been
113		* <i>structurally modified</i>.  See AbstractList for gory details.
114		*/
115	<	private transient int modCount = 0;
115	>	transient int modCount;     // non-private to simplify nested class access
116
117		/**
118	<	* Create a new priority queue with the default initial capacity
119	<	* (11) that orders its elements according to their natural
120	<	* ordering (using <tt>Comparable</tt>.)
118	>	* Creates a {@code PriorityQueue} with the default initial
119	>	* capacity (11) that orders its elements according to their
120	>	* {@linkplain Comparable natural ordering}.
121		*/
122		public PriorityQueue() {
123	<	this(DEFAULT_INITIAL_CAPACITY);
123	>	this(DEFAULT_INITIAL_CAPACITY, null);
124		}
125
126		/**
127	<	* Create a new priority queue with the specified initial capacity
128	<	* that orders its elements according to their natural ordering
129	<	* (using <tt>Comparable</tt>.)
127	>	* Creates a {@code PriorityQueue} with the specified initial
128	>	* capacity that orders its elements according to their
129	>	* {@linkplain Comparable natural ordering}.
130		*
131	<	* @param initialCapacity the initial capacity for this priority queue.
131	>	* @param initialCapacity the initial capacity for this priority queue
132	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
133	>	*         than 1
134		*/
135		public PriorityQueue(int initialCapacity) {
136		this(initialCapacity, null);
137		}
138
139		/**
140	<	* Create a new priority queue with the specified initial capacity (11)
141	<	* that orders its elements according to the specified comparator.
140	>	* Creates a {@code PriorityQueue} with the default initial capacity and
141	>	* whose elements are ordered according to the specified comparator.
142		*
143	<	* @param initialCapacity the initial capacity for this priority queue.
144	<	* @param comparator the comparator used to order this priority queue.
143	>	* @param  comparator the comparator that will be used to order this
144	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
145	>	*         natural ordering} of the elements will be used.
146	>	* @since 1.8
147		*/
148	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
148	>	public PriorityQueue(Comparator<? super E> comparator) {
149	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
150	>	}
151	>
152	>	/**
153	>	* Creates a {@code PriorityQueue} with the specified initial capacity
154	>	* that orders its elements according to the specified comparator.
155	>	*
156	>	* @param  initialCapacity the initial capacity for this priority queue
157	>	* @param  comparator the comparator that will be used to order this
158	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
159	>	*         natural ordering} of the elements will be used.
160	>	* @throws IllegalArgumentException if {@code initialCapacity} is
161	>	*         less than 1
162	>	*/
163	>	public PriorityQueue(int initialCapacity,
164	>	Comparator<? super E> comparator) {
165	>	// Note: This restriction of at least one is not actually needed,
166	>	// but continues for 1.5 compatibility
167		if (initialCapacity < 1)
168	<	initialCapacity = 1;
169	<	queue = new E[initialCapacity + 1];
168	>	throw new IllegalArgumentException();
169	>	this.queue = new Object[initialCapacity];
170		this.comparator = comparator;
171		}
172
173		/**
174	<	* Create a new priority queue containing the elements in the specified
175	<	* collection.  The priority queue has an initial capacity of 110% of the
176	<	* size of the specified collection. If the specified collection
177	<	* implements the {@link Sorted} interface, the priority queue will be
178	<	* sorted according to the same comparator, or according to its elements'
179	<	* natural order if the collection is sorted according to its elements'
111	<	* natural order.  If the specified collection does not implement
112	<	* <tt>Sorted</tt>, the priority queue is ordered according to
113	<	* its elements' natural order.
174	>	* Creates a {@code PriorityQueue} containing the elements in the
175	>	* specified collection.  If the specified collection is an instance of
176	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
177	>	* priority queue will be ordered according to the same ordering.
178	>	* Otherwise, this priority queue will be ordered according to the
179	>	* {@linkplain Comparable natural ordering} of its elements.
180		*
181	<	* @param initialElements the collection whose elements are to be placed
182	<	*        into this priority queue.
181	>	* @param  c the collection whose elements are to be placed
182	>	*         into this priority queue
183		* @throws ClassCastException if elements of the specified collection
184		*         cannot be compared to one another according to the priority
185	<	*         queue's ordering.
186	<	* @throws NullPointerException if the specified collection or an
187	<	*         element of the specified collection is <tt>null</tt>.
188	<	*/
189	<	public PriorityQueue(Collection<E> initialElements) {
190	<	int sz = initialElements.size();
191	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
192	<	Integer.MAX_VALUE - 1);
193	<	if (initialCapacity < 1)
194	<	initialCapacity = 1;
195	<	queue = new E[initialCapacity + 1];
185	>	*         queue's ordering
186	>	* @throws NullPointerException if the specified collection or any
187	>	*         of its elements are null
188	>	*/
189	>	@SuppressWarnings("unchecked")
190	>	public PriorityQueue(Collection<? extends E> c) {
191	>	if (c instanceof SortedSet<?>) {
192	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
193	>	this.comparator = (Comparator<? super E>) ss.comparator();
194	>	initElementsFromCollection(ss);
195	>	}
196	>	else if (c instanceof PriorityQueue<?>) {
197	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
198	>	this.comparator = (Comparator<? super E>) pq.comparator();
199	>	initFromPriorityQueue(pq);
200	>	}
201	>	else {
202	>	this.comparator = null;
203	>	initFromCollection(c);
204	>	}
205	>	}
206
207	+	/**
208	+	* Creates a {@code PriorityQueue} containing the elements in the
209	+	* specified priority queue.  This priority queue will be
210	+	* ordered according to the same ordering as the given priority
211	+	* queue.
212	+	*
213	+	* @param  c the priority queue whose elements are to be placed
214	+	*         into this priority queue
215	+	* @throws ClassCastException if elements of {@code c} cannot be
216	+	*         compared to one another according to {@code c}'s
217	+	*         ordering
218	+	* @throws NullPointerException if the specified priority queue or any
219	+	*         of its elements are null
220	+	*/
221	+	@SuppressWarnings("unchecked")
222	+	public PriorityQueue(PriorityQueue<? extends E> c) {
223	+	this.comparator = (Comparator<? super E>) c.comparator();
224	+	initFromPriorityQueue(c);
225	+	}
226
227	<	if (initialElements instanceof Sorted) {
228	<	comparator = ((Sorted)initialElements).comparator();
229	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
230	<	queue[++size] = i.next();
227	>	/**
228	>	* Creates a {@code PriorityQueue} containing the elements in the
229	>	* specified sorted set.   This priority queue will be ordered
230	>	* according to the same ordering as the given sorted set.
231	>	*
232	>	* @param  c the sorted set whose elements are to be placed
233	>	*         into this priority queue
234	>	* @throws ClassCastException if elements of the specified sorted
235	>	*         set cannot be compared to one another according to the
236	>	*         sorted set's ordering
237	>	* @throws NullPointerException if the specified sorted set or any
238	>	*         of its elements are null
239	>	*/
240	>	@SuppressWarnings("unchecked")
241	>	public PriorityQueue(SortedSet<? extends E> c) {
242	>	this.comparator = (Comparator<? super E>) c.comparator();
243	>	initElementsFromCollection(c);
244	>	}
245	>
246	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
247	>	if (c.getClass() == PriorityQueue.class) {
248	>	this.queue = c.toArray();
249	>	this.size = c.size();
250		} else {
251	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
251	>	initFromCollection(c);
252		}
253		}
254
255	<	// Queue Methods
255	>	private void initElementsFromCollection(Collection<? extends E> c) {
256	>	Object[] a = c.toArray();
257	>	// If c.toArray incorrectly doesn't return Object[], copy it.
258	>	if (a.getClass() != Object[].class)
259	>	a = Arrays.copyOf(a, a.length, Object[].class);
260	>	int len = a.length;
261	>	if (len == 1 || this.comparator != null)
262	>	for (Object e : a)
263	>	if (e == null)
264	>	throw new NullPointerException();
265	>	this.queue = a;
266	>	this.size = a.length;
267	>	}
268
269		/**
270	<	* Remove and return the minimal element from this priority queue
147	<	* if it contains one or more elements, otherwise return
148	<	* <tt>null</tt>.  The term <i>minimal</i> is defined according to
149	<	* this priority queue's order.
270	>	* Initializes queue array with elements from the given Collection.
271		*
272	<	* @return the minimal element from this priority queue if it contains
152	<	*         one or more elements, otherwise <tt>null</tt>.
272	>	* @param c the collection
273		*/
274	<	public E poll() {
275	<	if (size == 0)
276	<	return null;
157	<	return remove(1);
274	>	private void initFromCollection(Collection<? extends E> c) {
275	>	initElementsFromCollection(c);
276	>	heapify();
277		}
278
279		/**
280	<	* Return, but do not remove, the minimal element from the
281	<	* priority queue, or return <tt>null</tt> if the queue is empty.
282	<	* The term <i>minimal</i> is defined according to this priority
283	<	* queue's order.  This method returns the same object reference
284	<	* that would be returned by by the <tt>poll</tt> method.  The two
285	<	* methods differ in that this method does not remove the element
286	<	* from the priority queue.
280	>	* The maximum size of array to allocate.
281	>	* Some VMs reserve some header words in an array.
282	>	* Attempts to allocate larger arrays may result in
283	>	* OutOfMemoryError: Requested array size exceeds VM limit
284	>	*/
285	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
286	>
287	>	/**
288	>	* Increases the capacity of the array.
289		*
290	<	* @return the minimal element from this priority queue if it contains
170	<	*         one or more elements, otherwise <tt>null</tt>.
290	>	* @param minCapacity the desired minimum capacity
291		*/
292	+	private void grow(int minCapacity) {
293	+	int oldCapacity = queue.length;
294	+	// Double size if small; else grow by 50%
295	+	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
296	+	(oldCapacity + 2) :
297	+	(oldCapacity >> 1));
298	+	// overflow-conscious code
299	+	if (newCapacity - MAX_ARRAY_SIZE > 0)
300	+	newCapacity = hugeCapacity(minCapacity);
301	+	queue = Arrays.copyOf(queue, newCapacity);
302	+	}
303	+
304	+	private static int hugeCapacity(int minCapacity) {
305	+	if (minCapacity < 0) // overflow
306	+	throw new OutOfMemoryError();
307	+	return (minCapacity > MAX_ARRAY_SIZE) ?
308	+	Integer.MAX_VALUE :
309	+	MAX_ARRAY_SIZE;
310	+	}
311	+
312	+	/**
313	+	* Inserts the specified element into this priority queue.
314	+	*
315	+	* @return {@code true} (as specified by {@link Collection#add})
316	+	* @throws ClassCastException if the specified element cannot be
317	+	*         compared with elements currently in this priority queue
318	+	*         according to the priority queue's ordering
319	+	* @throws NullPointerException if the specified element is null
320	+	*/
321	+	public boolean add(E e) {
322	+	return offer(e);
323	+	}
324	+
325	+	/**
326	+	* Inserts the specified element into this priority queue.
327	+	*
328	+	* @return {@code true} (as specified by {@link Queue#offer})
329	+	* @throws ClassCastException if the specified element cannot be
330	+	*         compared with elements currently in this priority queue
331	+	*         according to the priority queue's ordering
332	+	* @throws NullPointerException if the specified element is null
333	+	*/
334	+	public boolean offer(E e) {
335	+	if (e == null)
336	+	throw new NullPointerException();
337	+	modCount++;
338	+	int i = size;
339	+	if (i >= queue.length)
340	+	grow(i + 1);
341	+	siftUp(i, e);
342	+	size = i + 1;
343	+	return true;
344	+	}
345	+
346	+	@SuppressWarnings("unchecked")
347		public E peek() {
348	<	return queue[1];
348	>	return (size == 0) ? null : (E) queue[0];
349		}
350
351	<	// Collection Methods
351	>	private int indexOf(Object o) {
352	>	if (o != null) {
353	>	for (int i = 0; i < size; i++)
354	>	if (o.equals(queue[i]))
355	>	return i;
356	>	}
357	>	return -1;
358	>	}
359
360		/**
361	<	* Removes a single instance of the specified element from this priority
362	<	* queue, if it is present.  Returns true if this collection contained the
363	<	* specified element (or equivalently, if this collection changed as a
361	>	* Removes a single instance of the specified element from this queue,
362	>	* if it is present.  More formally, removes an element {@code e} such
363	>	* that {@code o.equals(e)}, if this queue contains one or more such
364	>	* elements.  Returns {@code true} if and only if this queue contained
365	>	* the specified element (or equivalently, if this queue changed as a
366		* result of the call).
367		*
368	<	* @param element the element to be removed from this collection,
369	<	* if present.
186	<	* @return <tt>true</tt> if this collection changed as a result of the
187	<	*         call
188	<	* @throws ClassCastException if the specified element cannot be compared
189	<	*            with elements currently in the priority queue according
190	<	*            to the priority queue's ordering.
191	<	* @throws NullPointerException if the specified element is null.
368	>	* @param o element to be removed from this queue, if present
369	>	* @return {@code true} if this queue changed as a result of the call
370		*/
371	<	public boolean remove(Object element) {
372	<	if (element == null)
373	<	throw new NullPointerException();
371	>	public boolean remove(Object o) {
372	>	int i = indexOf(o);
373	>	if (i == -1)
374	>	return false;
375	>	else {
376	>	removeAt(i);
377	>	return true;
378	>	}
379	>	}
380
381	<	if (comparator == null) {
382	<	for (int i = 1; i <= size; i++) {
383	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
384	<	remove(i);
385	<	return true;
386	<	}
387	<	}
388	<	} else {
389	<	for (int i = 1; i <= size; i++) {
390	<	if (comparator.compare(queue[i], (E) element) == 0) {
391	<	remove(i);
392	<	return true;
209	<	}
381	>	/**
382	>	* Version of remove using reference equality, not equals.
383	>	* Needed by iterator.remove.
384	>	*
385	>	* @param o element to be removed from this queue, if present
386	>	* @return {@code true} if removed
387	>	*/
388	>	boolean removeEq(Object o) {
389	>	for (int i = 0; i < size; i++) {
390	>	if (o == queue[i]) {
391	>	removeAt(i);
392	>	return true;
393		}
394		}
395		return false;
396		}
397
398		/**
399	<	* Returns an iterator over the elements in this priority queue.  The
400	<	* elements of the priority queue will be returned by this iterator in the
401	<	* order specified by the queue, which is to say the order they would be
402	<	* returned by repeated calls to <tt>poll</tt>.
403	<	*
404	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
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 contains(Object o) {
407	>	return indexOf(o) >= 0;
408	>	}
409	>
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	>	/**
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 or
494	<	* previous.  Reset to 0 if this element is deleted by a call
495	<	* to remove.
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 = 0;
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	>	* Element returned by the most recent call to next iff that
514	>	* element was drawn from the forgetMeNot list.
515	>	*/
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		public boolean hasNext() {
526	<	return cursor <= size;
526	>	return cursor < size ||
527	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
528		}
529
530	+	@SuppressWarnings("unchecked")
531		public E next() {
532	<	checkForComodification();
533	<	if (cursor > size)
534	<	throw new NoSuchElementException();
535	<	E result = queue[cursor];
536	<	lastRet = cursor++;
537	<	return result;
532	>	if (expectedModCount != modCount)
533	>	throw new ConcurrentModificationException();
534	>	if (cursor < size)
535	>	return (E) queue[lastRet = cursor++];
536	>	if (forgetMeNot != null) {
537	>	lastRet = -1;
538	>	lastRetElt = forgetMeNot.poll();
539	>	if (lastRetElt != null)
540	>	return lastRetElt;
541	>	}
542	>	throw new NoSuchElementException();
543		}
544
545		public void remove() {
546	<	if (lastRet == 0)
546	>	if (expectedModCount != modCount)
547	>	throw new ConcurrentModificationException();
548	>	if (lastRet != -1) {
549	>	E moved = PriorityQueue.this.removeAt(lastRet);
550	>	lastRet = -1;
551	>	if (moved == null)
552	>	cursor--;
553	>	else {
554	>	if (forgetMeNot == null)
555	>	forgetMeNot = new ArrayDeque<>();
556	>	forgetMeNot.add(moved);
557	>	}
558	>	} else if (lastRetElt != null) {
559	>	PriorityQueue.this.removeEq(lastRetElt);
560	>	lastRetElt = null;
561	>	} else {
562		throw new IllegalStateException();
563	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
563	>	}
564		expectedModCount = modCount;
565		}
272	–
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
566		}
567
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
568		public int size() {
569		return size;
570		}
571
572		/**
573	<	* Add the specified element to this priority queue.
574	<	*
291	<	* @param element the element to add.
292	<	* @return true
293	<	* @throws ClassCastException if the specified element cannot be compared
294	<	*            with elements currently in the priority queue according
295	<	*            to the priority queue's ordering.
296	<	* @throws NullPointerException if the specified element is null.
573	>	* Removes all of the elements from this priority queue.
574	>	* The queue will be empty after this call returns.
575		*/
576	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
576	>	public void clear() {
577		modCount++;
578	+	for (int i = 0; i < size; i++)
579	+	queue[i] = null;
580	+	size = 0;
581	+	}
582
583	<	// Grow backing store if necessary
584	<	if (++size == queue.length) {
585	<	E[] newQueue = new E[2 * queue.length];
586	<	System.arraycopy(queue, 0, newQueue, 0, size);
587	<	queue = newQueue;
588	<	}
589	<
590	<	queue[size] = element;
591	<	fixUp(size);
592	<	return true;
583	>	@SuppressWarnings("unchecked")
584	>	public E poll() {
585	>	if (size == 0)
586	>	return null;
587	>	int s = --size;
588	>	modCount++;
589	>	E result = (E) queue[0];
590	>	E x = (E) queue[s];
591	>	queue[s] = null;
592	>	if (s != 0)
593	>	siftDown(0, x);
594	>	return result;
595		}
596
597		/**
598	<	* Remove all elements from the priority queue.
599	<	*/
600	<	public void clear() {
598	>	* Removes the ith element from queue.
599	>	*
600	>	* Normally this method leaves the elements at up to i-1,
601	>	* inclusive, untouched.  Under these circumstances, it returns
602	>	* null.  Occasionally, in order to maintain the heap invariant,
603	>	* it must swap a later element of the list with one earlier than
604	>	* i.  Under these circumstances, this method returns the element
605	>	* that was previously at the end of the list and is now at some
606	>	* position before i. This fact is used by iterator.remove so as to
607	>	* avoid missing traversing elements.
608	>	*/
609	>	@SuppressWarnings("unchecked")
610	>	E removeAt(int i) {
611	>	// assert i >= 0 && i < size;
612		modCount++;
613	<
614	<	// Null out element references to prevent memory leak
322	<	for (int i=1; i<=size; i++)
613	>	int s = --size;
614	>	if (s == i) // removed last element
615		queue[i] = null;
616	<
617	<	size = 0;
616	>	else {
617	>	E moved = (E) queue[s];
618	>	queue[s] = null;
619	>	siftDown(i, moved);
620	>	if (queue[i] == moved) {
621	>	siftUp(i, moved);
622	>	if (queue[i] != moved)
623	>	return moved;
624	>	}
625	>	}
626	>	return null;
627		}
628
629		/**
630	<	* Removes and returns the ith element from queue.  Recall
631	<	* that queue is one-based, so 1 <= i <= size.
632	<	*
633	<	* XXX: Could further special-case i==size, but is it worth it?
634	<	* XXX: Could special-case i==0, but is it worth it?
635	<	*/
636	<	private E remove(int i) {
637	<	assert i <= size;
638	<	modCount++;
630	>	* Inserts item x at position k, maintaining heap invariant by
631	>	* promoting x up the tree until it is greater than or equal to
632	>	* its parent, or is the root.
633	>	*
634	>	* To simplify and speed up coercions and comparisons. the
635	>	* Comparable and Comparator versions are separated into different
636	>	* methods that are otherwise identical. (Similarly for siftDown.)
637	>	*
638	>	* @param k the position to fill
639	>	* @param x the item to insert
640	>	*/
641	>	private void siftUp(int k, E x) {
642	>	if (comparator != null)
643	>	siftUpUsingComparator(k, x);
644	>	else
645	>	siftUpComparable(k, x);
646	>	}
647	>
648	>	@SuppressWarnings("unchecked")
649	>	private void siftUpComparable(int k, E x) {
650	>	Comparable<? super E> key = (Comparable<? super E>) x;
651	>	while (k > 0) {
652	>	int parent = (k - 1) >>> 1;
653	>	Object e = queue[parent];
654	>	if (key.compareTo((E) e) >= 0)
655	>	break;
656	>	queue[k] = e;
657	>	k = parent;
658	>	}
659	>	queue[k] = key;
660	>	}
661
662	<	E result = queue[i];
663	<	queue[i] = queue[size];
664	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
665	<	if (i <= size)
666	<	fixDown(i);
667	<	return result;
662	>	@SuppressWarnings("unchecked")
663	>	private void siftUpUsingComparator(int k, E x) {
664	>	while (k > 0) {
665	>	int parent = (k - 1) >>> 1;
666	>	Object e = queue[parent];
667	>	if (comparator.compare(x, (E) e) >= 0)
668	>	break;
669	>	queue[k] = e;
670	>	k = parent;
671	>	}
672	>	queue[k] = x;
673		}
674
675		/**
676	<	* Establishes the heap invariant (described above) assuming the heap
677	<	* satisfies the invariant except possibly for the leaf-node indexed by k
678	<	* (which may have a nextExecutionTime less than its parent's).
679	<	*
680	<	* This method functions by "promoting" queue[k] up the hierarchy
681	<	* (by swapping it with its parent) repeatedly until queue[k]
682	<	* is greater than or equal to its parent.
683	<	*/
684	<	private void fixUp(int k) {
685	<	if (comparator == null) {
686	<	while (k > 1) {
687	<	int j = k >> 1;
688	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
689	<	break;
690	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
691	<	k = j;
692	<	}
693	<	} else {
694	<	while (k > 1) {
695	<	int j = k >> 1;
696	<	if (comparator.compare(queue[j], queue[k]) <= 0)
697	<	break;
698	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
699	<	k = j;
700	<	}
676	>	* Inserts item x at position k, maintaining heap invariant by
677	>	* demoting x down the tree repeatedly until it is less than or
678	>	* equal to its children or is a leaf.
679	>	*
680	>	* @param k the position to fill
681	>	* @param x the item to insert
682	>	*/
683	>	private void siftDown(int k, E x) {
684	>	if (comparator != null)
685	>	siftDownUsingComparator(k, x);
686	>	else
687	>	siftDownComparable(k, x);
688	>	}
689	>
690	>	@SuppressWarnings("unchecked")
691	>	private void siftDownComparable(int k, E x) {
692	>	Comparable<? super E> key = (Comparable<? super E>)x;
693	>	int half = size >>> 1;        // loop while a non-leaf
694	>	while (k < half) {
695	>	int child = (k << 1) + 1; // assume left child is least
696	>	Object c = queue[child];
697	>	int right = child + 1;
698	>	if (right < size &&
699	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
700	>	c = queue[child = right];
701	>	if (key.compareTo((E) c) <= 0)
702	>	break;
703	>	queue[k] = c;
704	>	k = child;
705		}
706	+	queue[k] = key;
707		}
708
709	<	/**
710	<	* Establishes the heap invariant (described above) in the subtree
711	<	* rooted at k, which is assumed to satisfy the heap invariant except
712	<	* possibly for node k itself (which may be greater than its children).
713	<	*
714	<	* This method functions by "demoting" queue[k] down the hierarchy
715	<	* (by swapping it with its smaller child) repeatedly until queue[k]
716	<	* is less than or equal to its children.
717	<	*/
718	<	private void fixDown(int k) {
719	<	int j;
720	<	if (comparator == null) {
721	<	while ((j = k << 1) <= size) {
722	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
390	<	j++; // j indexes smallest kid
391	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
392	<	break;
393	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
394	<	k = j;
395	<	}
396	<	} else {
397	<	while ((j = k << 1) <= size) {
398	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
399	<	j++; // j indexes smallest kid
400	<	if (comparator.compare(queue[k], queue[j]) <= 0)
401	<	break;
402	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
403	<	k = j;
404	<	}
709	>	@SuppressWarnings("unchecked")
710	>	private void siftDownUsingComparator(int k, E x) {
711	>	int half = size >>> 1;
712	>	while (k < half) {
713	>	int child = (k << 1) + 1;
714	>	Object c = queue[child];
715	>	int right = child + 1;
716	>	if (right < size &&
717	>	comparator.compare((E) c, (E) queue[right]) > 0)
718	>	c = queue[child = right];
719	>	if (comparator.compare(x, (E) c) <= 0)
720	>	break;
721	>	queue[k] = c;
722	>	k = child;
723		}
724	+	queue[k] = x;
725	+	}
726	+
727	+	/**
728	+	* Establishes the heap invariant (described above) in the entire tree,
729	+	* assuming nothing about the order of the elements prior to the call.
730	+	* This classic algorithm due to Floyd (1964) is known to be O(size).
731	+	*/
732	+	@SuppressWarnings("unchecked")
733	+	private void heapify() {
734	+	final Object[] es = queue;
735	+	final int half = (size >>> 1) - 1;
736	+	if (comparator == null)
737	+	for (int i = half; i >= 0; i--)
738	+	siftDownComparable(i, (E) es[i]);
739	+	else
740	+	for (int i = half; i >= 0; i--)
741	+	siftDownUsingComparator(i, (E) es[i]);
742		}
743
744		/**
745	<	* Returns the comparator associated with this priority queue, or
746	<	* <tt>null</tt> if it uses its elements' natural ordering.
745	>	* Returns the comparator used to order the elements in this
746	>	* queue, or {@code null} if this queue is sorted according to
747	>	* the {@linkplain Comparable natural ordering} of its elements.
748		*
749	<	* @return the comparator associated with this priority queue, or
750	<	*         <tt>null</tt> if it uses its elements' natural ordering.
749	>	* @return the comparator used to order this queue, or
750	>	*         {@code null} if this queue is sorted according to the
751	>	*         natural ordering of its elements
752		*/
753	<	public Comparator comparator() {
753	>	public Comparator<? super E> comparator() {
754		return comparator;
755		}
756
757		/**
758	<	* Save the state of the instance to a stream (that
421	<	* is, serialize it).
758	>	* Saves this queue to a stream (that is, serializes it).
759		*
423	–	* @serialData The length of the array backing the instance is
424	–	* emitted (int), followed by all of its elements (each an
425	–	* <tt>Object</tt>) in the proper order.
760		* @param s the stream
761	+	* @throws java.io.IOException if an I/O error occurs
762	+	* @serialData The length of the array backing the instance is
763	+	*             emitted (int), followed by all of its elements
764	+	*             (each an {@code Object}) in the proper order.
765		*/
766	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
767	<	throws java.io.IOException{
766	>	private void writeObject(java.io.ObjectOutputStream s)
767	>	throws java.io.IOException {
768		// Write out element count, and any hidden stuff
769		s.defaultWriteObject();
770
771	<	// Write out array length
772	<	s.writeInt(queue.length);
771	>	// Write out array length, for compatibility with 1.5 version
772	>	s.writeInt(Math.max(2, size + 1));
773
774	<	// Write out all elements in the proper order.
775	<	for (int i=0; i<size; i++)
774	>	// Write out all elements in the "proper order".
775	>	for (int i = 0; i < size; i++)
776		s.writeObject(queue[i]);
777		}
778
779		/**
780	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
781	<	* deserialize it).
780	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
781	>	* (that is, deserializes it).
782	>	*
783		* @param s the stream
784	+	* @throws ClassNotFoundException if the class of a serialized object
785	+	*         could not be found
786	+	* @throws java.io.IOException if an I/O error occurs
787		*/
788	<	private synchronized void readObject(java.io.ObjectInputStream s)
788	>	private void readObject(java.io.ObjectInputStream s)
789		throws java.io.IOException, ClassNotFoundException {
790		// Read in size, and any hidden stuff
791		s.defaultReadObject();
792
793	<	// Read in array length and allocate array
794	<	int arrayLength = s.readInt();
795	<	queue = new E[arrayLength];
796	<
797	<	// Read in all elements in the proper order.
798	<	for (int i=0; i<size; i++)
799	<	queue[i] = (E)s.readObject();
793	>	// Read in (and discard) array length
794	>	s.readInt();
795	>
796	>	queue = new Object[size];
797	>
798	>	// Read in all elements.
799	>	for (int i = 0; i < size; i++)
800	>	queue[i] = s.readObject();
801	>
802	>	// Elements are guaranteed to be in "proper order", but the
803	>	// spec has never explained what that might be.
804	>	heapify();
805	>	}
806	>
807	>	/**
808	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
809	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
810	>	* queue. The spliterator does not traverse elements in any particular order
811	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
812	>	*
813	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
814	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
815	>	* Overriding implementations should document the reporting of additional
816	>	* characteristic values.
817	>	*
818	>	* @return a {@code Spliterator} over the elements in this queue
819	>	* @since 1.8
820	>	*/
821	>	public final Spliterator<E> spliterator() {
822	>	return new PriorityQueueSpliterator(0, -1, 0);
823		}
824
825	+	final class PriorityQueueSpliterator implements Spliterator<E> {
826	+	/*
827	+	* This is very similar to ArrayList Spliterator, except for
828	+	* extra null checks.
829	+	*/
830	+	private int index;            // current index, modified on advance/split
831	+	private int fence;            // -1 until first use
832	+	private int expectedModCount; // initialized when fence set
833	+
834	+	/** Creates new spliterator covering the given range. */
835	+	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
836	+	this.index = origin;
837	+	this.fence = fence;
838	+	this.expectedModCount = expectedModCount;
839	+	}
840	+
841	+	private int getFence() { // initialize fence to size on first use
842	+	int hi;
843	+	if ((hi = fence) < 0) {
844	+	expectedModCount = modCount;
845	+	hi = fence = size;
846	+	}
847	+	return hi;
848	+	}
849	+
850	+	public PriorityQueueSpliterator trySplit() {
851	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
852	+	return (lo >= mid) ? null :
853	+	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
854	+	}
855	+
856	+	@SuppressWarnings("unchecked")
857	+	public void forEachRemaining(Consumer<? super E> action) {
858	+	int i, hi, mc; // hoist accesses and checks from loop
859	+	final Object[] a;
860	+	if (action == null)
861	+	throw new NullPointerException();
862	+	if ((a = queue) != null) {
863	+	if ((hi = fence) < 0) {
864	+	mc = modCount;
865	+	hi = size;
866	+	}
867	+	else
868	+	mc = expectedModCount;
869	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
870	+	for (E e;; ++i) {
871	+	if (i < hi) {
872	+	if ((e = (E) a[i]) == null) // must be CME
873	+	break;
874	+	action.accept(e);
875	+	}
876	+	else if (modCount != mc)
877	+	break;
878	+	else
879	+	return;
880	+	}
881	+	}
882	+	}
883	+	throw new ConcurrentModificationException();
884	+	}
885	+
886	+	public boolean tryAdvance(Consumer<? super E> action) {
887	+	if (action == null)
888	+	throw new NullPointerException();
889	+	int hi = getFence(), lo = index;
890	+	if (lo >= 0 && lo < hi) {
891	+	index = lo + 1;
892	+	@SuppressWarnings("unchecked") E e = (E)queue[lo];
893	+	if (e == null)
894	+	throw new ConcurrentModificationException();
895	+	action.accept(e);
896	+	if (modCount != expectedModCount)
897	+	throw new ConcurrentModificationException();
898	+	return true;
899	+	}
900	+	return false;
901	+	}
902	+
903	+	public long estimateSize() {
904	+	return getFence() - index;
905	+	}
906	+
907	+	public int characteristics() {
908	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
909	+	}
910	+	}
911		}

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