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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.10 by tim, Sat Jul 26 13:17:51 2003 UTC vs.
Revision 1.125 by jsr166, Sun May 6 21:07:41 2018 UTC

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1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3	>	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	>	*
5	>	* This code is free software; you can redistribute it and/or modify it
6	>	* under the terms of the GNU General Public License version 2 only, as
7	>	* published by the Free Software Foundation.  Oracle designates this
8	>	* particular file as subject to the "Classpath" exception as provided
9	>	* by Oracle in the LICENSE file that accompanied this code.
10	>	*
11	>	* This code is distributed in the hope that it will be useful, but WITHOUT
12	>	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	>	* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14	>	* version 2 for more details (a copy is included in the LICENSE file that
15	>	* accompanied this code).
16	>	*
17	>	* You should have received a copy of the GNU General Public License version
18	>	* 2 along with this work; if not, write to the Free Software Foundation,
19	>	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20	>	*
21	>	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	>	* or visit www.oracle.com if you need additional information or have any
23	>	* questions.
24	>	*/
25	>
26	>	package java.util;
27	>
28	>	import java.util.function.Consumer;
29	>	import jdk.internal.misc.SharedSecrets;
30
31		/**
32	<	* An unbounded priority queue based on a priority heap.  This queue orders
33	<	* elements according to an order specified at construction time, which is
34	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered
35	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
36	<	* according to a {@link Comparator}, depending on which constructor is used.
37	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
38	<	* minimal element with respect to the specified ordering.  If multiple
39	<	* elements are tied for least value, no guarantees are made as to
40	<	* which of these elements is returned.
41	<	*
42	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
43	<	* size of the array used internally to store the elements on the
44	<	* queue.  It is always at least as large as the queue size.  As
45	<	* elements are added to a priority queue, its capacity grows
46	<	* automatically.  The details of the growth policy are not specified.
47	<	*
48	<	*<p>Implementation note: this implementation provides O(log(n)) time
49	<	*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
50	<	*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
51	<	*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
52	<	*constant time for the retrieval methods (<tt>peek</tt>,
53	<	*<tt>element</tt>, and <tt>size</tt>).
32	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
33	>	* The elements of the priority queue are ordered according to their
34	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
35	>	* provided at queue construction time, depending on which constructor is
36	>	* used.  A priority queue does not permit {@code null} elements.
37	>	* A priority queue relying on natural ordering also does not permit
38	>	* insertion of non-comparable objects (doing so may result in
39	>	* {@code ClassCastException}).
40	>	*
41	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
42	>	* with respect to the specified ordering.  If multiple elements are
43	>	* tied for least value, the head is one of those elements -- ties are
44	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
45	>	* {@code remove}, {@code peek}, and {@code element} access the
46	>	* element at the head of the queue.
47	>	*
48	>	* <p>A priority queue is unbounded, but has an internal
49	>	* <i>capacity</i> governing the size of an array used to store the
50	>	* elements on the queue.  It is always at least as large as the queue
51	>	* size.  As elements are added to a priority queue, its capacity
52	>	* grows automatically.  The details of the growth policy are not
53	>	* specified.
54	>	*
55	>	* <p>This class and its iterator implement all of the
56	>	* <em>optional</em> methods of the {@link Collection} and {@link
57	>	* Iterator} interfaces.  The Iterator provided in method {@link
58	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
59	>	* are <em>not</em> guaranteed to traverse the elements of
60	>	* the priority queue in any particular order. If you need ordered
61	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
62	>	*
63	>	* <p><strong>Note that this implementation is not synchronized.</strong>
64	>	* Multiple threads should not access a {@code PriorityQueue}
65	>	* instance concurrently if any of the threads modifies the queue.
66	>	* Instead, use the thread-safe {@link
67	>	* java.util.concurrent.PriorityBlockingQueue} class.
68	>	*
69	>	* <p>Implementation note: this implementation provides
70	>	* O(log(n)) time for the enqueuing and dequeuing methods
71	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
72	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
73	>	* methods; and constant time for the retrieval methods
74	>	* ({@code peek}, {@code element}, and {@code size}).
75		*
76		* <p>This class is a member of the
77	<	* <a href="{@docRoot}/../guide/collections/index.html">
77	>	* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
78		* Java Collections Framework</a>.
79	+	*
80		* @since 1.5
81	<	* @author Josh Bloch
81	>	* @author Josh Bloch, Doug Lea
82	>	* @param <E> the type of elements held in this queue
83		*/
84	+	@SuppressWarnings("unchecked")
85		public class PriorityQueue<E> extends AbstractQueue<E>
86	<	implements Queue<E>,
87	<	java.io.Serializable {
86	>	implements java.io.Serializable {
87	>
88	>	private static final long serialVersionUID = -7720805057305804111L;
89	>
90		private static final int DEFAULT_INITIAL_CAPACITY = 11;
91
92		/**
93	<	* Priority queue represented as a balanced binary heap: the two children
94	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
95	<	* ordered by comparator, or by the elements' natural ordering, if
96	<	* comparator is null:  For each node n in the heap and each descendant d
97	<	* of n, n <= d.
98	<	*
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.
93	>	* Priority queue represented as a balanced binary heap: the two
94	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
95	>	* priority queue is ordered by comparator, or by the elements'
96	>	* natural ordering, if comparator is null: For each node n in the
97	>	* heap and each descendant d of n, n <= d.  The element with the
98	>	* lowest value is in queue[0], assuming the queue is nonempty.
99		*/
100	<	private transient E[] queue;
100	>	transient Object[] queue; // non-private to simplify nested class access
101
102		/**
103		* The number of elements in the priority queue.
104		*/
105	<	private int size = 0;
105	>	int size;
106
107		/**
108		* The comparator, or null if priority queue uses elements'
109		* natural ordering.
110		*/
111	<	private final Comparator<E> comparator;
111	>	private final Comparator<? super E> comparator;
112
113		/**
114		* The number of times this priority queue has been
115		* <i>structurally modified</i>.  See AbstractList for gory details.
116		*/
117	<	private transient int modCount = 0;
117	>	transient int modCount;     // non-private to simplify nested class access
118
119		/**
120	<	* Create a new priority queue with the default initial capacity
121	<	* (11) that orders its elements according to their natural
122	<	* ordering (using <tt>Comparable</tt>.)
120	>	* Creates a {@code PriorityQueue} with the default initial
121	>	* capacity (11) that orders its elements according to their
122	>	* {@linkplain Comparable natural ordering}.
123		*/
124		public PriorityQueue() {
125	<	this(DEFAULT_INITIAL_CAPACITY);
125	>	this(DEFAULT_INITIAL_CAPACITY, null);
126		}
127
128		/**
129	<	* Create a new priority queue with the specified initial capacity
130	<	* that orders its elements according to their natural ordering
131	<	* (using <tt>Comparable</tt>.)
129	>	* Creates a {@code PriorityQueue} with the specified initial
130	>	* capacity that orders its elements according to their
131	>	* {@linkplain Comparable natural ordering}.
132		*
133	<	* @param initialCapacity the initial capacity for this priority queue.
133	>	* @param initialCapacity the initial capacity for this priority queue
134	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
135	>	*         than 1
136		*/
137		public PriorityQueue(int initialCapacity) {
138		this(initialCapacity, null);
139		}
140
141		/**
142	<	* Create a new priority queue with the specified initial capacity (11)
143	<	* that orders its elements according to the specified comparator.
142	>	* Creates a {@code PriorityQueue} with the default initial capacity and
143	>	* whose elements are ordered according to the specified comparator.
144		*
145	<	* @param initialCapacity the initial capacity for this priority queue.
146	<	* @param comparator the comparator used to order this priority queue.
145	>	* @param  comparator the comparator that will be used to order this
146	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
147	>	*         natural ordering} of the elements will be used.
148	>	* @since 1.8
149		*/
150	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
150	>	public PriorityQueue(Comparator<? super E> comparator) {
151	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
152	>	}
153	>
154	>	/**
155	>	* Creates a {@code PriorityQueue} with the specified initial capacity
156	>	* that orders its elements according to the specified comparator.
157	>	*
158	>	* @param  initialCapacity the initial capacity for this priority queue
159	>	* @param  comparator the comparator that will be used to order this
160	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
161	>	*         natural ordering} of the elements will be used.
162	>	* @throws IllegalArgumentException if {@code initialCapacity} is
163	>	*         less than 1
164	>	*/
165	>	public PriorityQueue(int initialCapacity,
166	>	Comparator<? super E> comparator) {
167	>	// Note: This restriction of at least one is not actually needed,
168	>	// but continues for 1.5 compatibility
169		if (initialCapacity < 1)
170	<	initialCapacity = 1;
171	<	queue = (E[]) new Object[initialCapacity + 1];
170	>	throw new IllegalArgumentException();
171	>	this.queue = new Object[initialCapacity];
172		this.comparator = comparator;
173		}
174
175		/**
176	<	* Create a new priority queue containing the elements in the specified
177	<	* collection.  The priority queue has an initial capacity of 110% of the
178	<	* size of the specified collection. If the specified collection
179	<	* implements the {@link Sorted} interface, the priority queue will be
180	<	* sorted according to the same comparator, or according to its elements'
181	<	* 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.
176	>	* Creates a {@code PriorityQueue} containing the elements in the
177	>	* specified collection.  If the specified collection is an instance of
178	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
179	>	* priority queue will be ordered according to the same ordering.
180	>	* Otherwise, this priority queue will be ordered according to the
181	>	* {@linkplain Comparable natural ordering} of its elements.
182		*
183	<	* @param initialElements the collection whose elements are to be placed
184	<	*        into this priority queue.
183	>	* @param  c the collection whose elements are to be placed
184	>	*         into this priority queue
185		* @throws ClassCastException if elements of the specified collection
186		*         cannot be compared to one another according to the priority
187	<	*         queue's ordering.
188	<	* @throws NullPointerException if the specified collection or an
189	<	*         element of the specified collection is <tt>null</tt>.
190	<	*/
191	<	public PriorityQueue(Collection<E> initialElements) {
192	<	int sz = initialElements.size();
193	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
194	<	Integer.MAX_VALUE - 1);
195	<	if (initialCapacity < 1)
196	<	initialCapacity = 1;
197	<	queue = (E[]) new Object[initialCapacity + 1];
187	>	*         queue's ordering
188	>	* @throws NullPointerException if the specified collection or any
189	>	*         of its elements are null
190	>	*/
191	>	public PriorityQueue(Collection<? extends E> c) {
192	>	if (c instanceof SortedSet<?>) {
193	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
194	>	this.comparator = (Comparator<? super E>) ss.comparator();
195	>	initElementsFromCollection(ss);
196	>	}
197	>	else if (c instanceof PriorityQueue<?>) {
198	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
199	>	this.comparator = (Comparator<? super E>) pq.comparator();
200	>	initFromPriorityQueue(pq);
201	>	}
202	>	else {
203	>	this.comparator = null;
204	>	initFromCollection(c);
205	>	}
206	>	}
207
208	+	/**
209	+	* Creates a {@code PriorityQueue} containing the elements in the
210	+	* specified priority queue.  This priority queue will be
211	+	* ordered according to the same ordering as the given priority
212	+	* queue.
213	+	*
214	+	* @param  c the priority queue whose elements are to be placed
215	+	*         into this priority queue
216	+	* @throws ClassCastException if elements of {@code c} cannot be
217	+	*         compared to one another according to {@code c}'s
218	+	*         ordering
219	+	* @throws NullPointerException if the specified priority queue or any
220	+	*         of its elements are null
221	+	*/
222	+	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	>	public PriorityQueue(SortedSet<? extends E> c) {
241	>	this.comparator = (Comparator<? super E>) c.comparator();
242	>	initElementsFromCollection(c);
243	>	}
244	>
245	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
246	>	private static Object[] ensureNonEmpty(Object[] es) {
247	>	return (es.length > 0) ? es : new Object[1];
248	>	}
249	>
250	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
251	>	if (c.getClass() == PriorityQueue.class) {
252	>	this.queue = ensureNonEmpty(c.toArray());
253	>	this.size = c.size();
254		} else {
255	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
255	>	initFromCollection(c);
256		}
257		}
258
259	<	// Queue Methods
259	>	private void initElementsFromCollection(Collection<? extends E> c) {
260	>	Object[] es = c.toArray();
261	>	int len = es.length;
262	>	// If c.toArray incorrectly doesn't return Object[], copy it.
263	>	if (es.getClass() != Object[].class)
264	>	es = Arrays.copyOf(es, len, Object[].class);
265	>	if (len == 1 || this.comparator != null)
266	>	for (Object e : es)
267	>	if (e == null)
268	>	throw new NullPointerException();
269	>	this.queue = ensureNonEmpty(es);
270	>	this.size = len;
271	>	}
272
273		/**
274	<	* 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.
274	>	* Initializes queue array with elements from the given Collection.
275		*
276	<	* @return the minimal element from this priority queue if it contains
152	<	*         one or more elements, otherwise <tt>null</tt>.
276	>	* @param c the collection
277		*/
278	<	public E poll() {
279	<	if (size == 0)
280	<	return null;
281	<	return remove(1);
278	>	private void initFromCollection(Collection<? extends E> c) {
279	>	initElementsFromCollection(c);
280	>	heapify();
281	>	}
282	>
283	>	/**
284	>	* The maximum size of array to allocate.
285	>	* Some VMs reserve some header words in an array.
286	>	* Attempts to allocate larger arrays may result in
287	>	* OutOfMemoryError: Requested array size exceeds VM limit
288	>	*/
289	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
290	>
291	>	/**
292	>	* Increases the capacity of the array.
293	>	*
294	>	* @param minCapacity the desired minimum capacity
295	>	*/
296	>	private void grow(int minCapacity) {
297	>	int oldCapacity = queue.length;
298	>	// Double size if small; else grow by 50%
299	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
300	>	(oldCapacity + 2) :
301	>	(oldCapacity >> 1));
302	>	// overflow-conscious code
303	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
304	>	newCapacity = hugeCapacity(minCapacity);
305	>	queue = Arrays.copyOf(queue, newCapacity);
306	>	}
307	>
308	>	private static int hugeCapacity(int minCapacity) {
309	>	if (minCapacity < 0) // overflow
310	>	throw new OutOfMemoryError();
311	>	return (minCapacity > MAX_ARRAY_SIZE) ?
312	>	Integer.MAX_VALUE :
313	>	MAX_ARRAY_SIZE;
314	>	}
315	>
316	>	/**
317	>	* Inserts the specified element into this priority queue.
318	>	*
319	>	* @return {@code true} (as specified by {@link Collection#add})
320	>	* @throws ClassCastException if the specified element cannot be
321	>	*         compared with elements currently in this priority queue
322	>	*         according to the priority queue's ordering
323	>	* @throws NullPointerException if the specified element is null
324	>	*/
325	>	public boolean add(E e) {
326	>	return offer(e);
327		}
328
329		/**
330	<	* Return, but do not remove, the minimal element from the
162	<	* priority queue, or return <tt>null</tt> if the queue is empty.
163	<	* The term <i>minimal</i> is defined according to this priority
164	<	* queue's order.  This method returns the same object reference
165	<	* that would be returned by by the <tt>poll</tt> method.  The two
166	<	* methods differ in that this method does not remove the element
167	<	* from the priority queue.
330	>	* Inserts the specified element into this priority queue.
331		*
332	<	* @return the minimal element from this priority queue if it contains
333	<	*         one or more elements, otherwise <tt>null</tt>.
332	>	* @return {@code true} (as specified by {@link Queue#offer})
333	>	* @throws ClassCastException if the specified element cannot be
334	>	*         compared with elements currently in this priority queue
335	>	*         according to the priority queue's ordering
336	>	* @throws NullPointerException if the specified element is null
337		*/
338	+	public boolean offer(E e) {
339	+	if (e == null)
340	+	throw new NullPointerException();
341	+	modCount++;
342	+	int i = size;
343	+	if (i >= queue.length)
344	+	grow(i + 1);
345	+	siftUp(i, e);
346	+	size = i + 1;
347	+	return true;
348	+	}
349	+
350		public E peek() {
351	<	return queue[1];
351	>	return (E) queue[0];
352		}
353
354	<	// Collection Methods
354	>	private int indexOf(Object o) {
355	>	if (o != null) {
356	>	final Object[] es = queue;
357	>	for (int i = 0, n = size; i < n; i++)
358	>	if (o.equals(es[i]))
359	>	return i;
360	>	}
361	>	return -1;
362	>	}
363
364		/**
365	<	* Removes a single instance of the specified element from this priority
366	<	* queue, if it is present.  Returns true if this collection contained the
367	<	* specified element (or equivalently, if this collection changed as a
365	>	* Removes a single instance of the specified element from this queue,
366	>	* if it is present.  More formally, removes an element {@code e} such
367	>	* that {@code o.equals(e)}, if this queue contains one or more such
368	>	* elements.  Returns {@code true} if and only if this queue contained
369	>	* the specified element (or equivalently, if this queue changed as a
370		* result of the call).
371		*
372	<	* @param element the element to be removed from this collection,
373	<	* 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.
372	>	* @param o element to be removed from this queue, if present
373	>	* @return {@code true} if this queue changed as a result of the call
374		*/
375	<	public boolean remove(Object element) {
376	<	if (element == null)
377	<	throw new NullPointerException();
375	>	public boolean remove(Object o) {
376	>	int i = indexOf(o);
377	>	if (i == -1)
378	>	return false;
379	>	else {
380	>	removeAt(i);
381	>	return true;
382	>	}
383	>	}
384
385	<	if (comparator == null) {
386	<	for (int i = 1; i <= size; i++) {
387	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
388	<	remove(i);
389	<	return true;
390	<	}
391	<	}
392	<	} else {
393	<	for (int i = 1; i <= size; i++) {
394	<	if (comparator.compare(queue[i], (E) element) == 0) {
395	<	remove(i);
208	<	return true;
209	<	}
385	>	/**
386	>	* Identity-based version for use in Itr.remove.
387	>	*
388	>	* @param o element to be removed from this queue, if present
389	>	*/
390	>	void removeEq(Object o) {
391	>	final Object[] es = queue;
392	>	for (int i = 0, n = size; i < n; i++) {
393	>	if (o == es[i]) {
394	>	removeAt(i);
395	>	break;
396		}
397		}
212	–	return false;
398		}
399
400		/**
401	<	* Returns an iterator over the elements in this priority queue.  The
402	<	* elements of the priority queue will be returned by this iterator in the
403	<	* order specified by the queue, which is to say the order they would be
219	<	* returned by repeated calls to <tt>poll</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	>	public <T> T[] toArray(T[] a) {
466	>	final int size = this.size;
467	>	if (a.length < size)
468	>	// Make a new array of a's runtime type, but my contents:
469	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
470	>	System.arraycopy(queue, 0, a, 0, size);
471	>	if (a.length > size)
472	>	a[size] = null;
473	>	return a;
474	>	}
475	>
476	>	/**
477	>	* Returns an iterator over the elements in this queue. The iterator
478	>	* does not return the elements in any particular order.
479	>	*
480	>	* @return an iterator over the elements in this queue
481		*/
482		public Iterator<E> iterator() {
483		return new Itr();
484		}
485
486	<	private class Itr implements Iterator<E> {
486	>	private final class Itr implements Iterator<E> {
487		/**
488		* Index (into queue array) of element to be returned by
489		* subsequent call to next.
490		*/
491	<	private int cursor = 1;
491	>	private int cursor;
492
493		/**
494	<	* Index of element returned by most recent call to next or
495	<	* previous.  Reset to 0 if this element is deleted by a call
496	<	* to remove.
494	>	* Index of element returned by most recent call to next,
495	>	* unless that element came from the forgetMeNot list.
496	>	* Set to -1 if element is deleted by a call to remove.
497		*/
498	<	private int lastRet = 0;
498	>	private int lastRet = -1;
499	>
500	>	/**
501	>	* A queue of elements that were moved from the unvisited portion of
502	>	* the heap into the visited portion as a result of "unlucky" element
503	>	* removals during the iteration.  (Unlucky element removals are those
504	>	* that require a siftup instead of a siftdown.)  We must visit all of
505	>	* the elements in this list to complete the iteration.  We do this
506	>	* after we've completed the "normal" iteration.
507	>	*
508	>	* We expect that most iterations, even those involving removals,
509	>	* will not need to store elements in this field.
510	>	*/
511	>	private ArrayDeque<E> forgetMeNot;
512	>
513	>	/**
514	>	* Element returned by the most recent call to next iff that
515	>	* element was drawn from the forgetMeNot list.
516	>	*/
517	>	private E lastRetElt;
518
519		/**
520		* The modCount value that the iterator believes that the backing
521	<	* List should have.  If this expectation is violated, the iterator
521	>	* Queue should have.  If this expectation is violated, the iterator
522		* has detected concurrent modification.
523		*/
524		private int expectedModCount = modCount;
525
526	+	Itr() {}                        // prevent access constructor creation
527	+
528		public boolean hasNext() {
529	<	return cursor <= size;
529	>	return cursor < size ||
530	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
531		}
532
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();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
565	>	}
566		expectedModCount = modCount;
567		}
272	–
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
568		}
569
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
570		public int size() {
571		return size;
572		}
573
574		/**
575	<	* Add the specified element to this priority queue.
576	<	*
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.
575	>	* Removes all of the elements from this priority queue.
576	>	* The queue will be empty after this call returns.
577		*/
578	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
578	>	public void clear() {
579		modCount++;
580	<	++size;
580	>	final Object[] es = queue;
581	>	for (int i = 0, n = size; i < n; i++)
582	>	es[i] = null;
583	>	size = 0;
584	>	}
585
586	<	// Grow backing store if necessary
587	<	while (size >= queue.length) {
588	<	E[] newQueue = (E[]) new Object[2 * queue.length];
307	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
308	<	queue = newQueue;
309	<	}
586	>	public E poll() {
587	>	final Object[] es;
588	>	final E result;
589
590	<	queue[size] = element;
591	<	fixUp(size);
592	<	return true;
590	>	if ((result = (E) ((es = queue)[0])) != null) {
591	>	modCount++;
592	>	final int n;
593	>	final E x = (E) es[(n = --size)];
594	>	es[n] = null;
595	>	if (n > 0) {
596	>	final Comparator<? super E> cmp;
597	>	if ((cmp = comparator) == null)
598	>	siftDownComparable(0, x, es, n);
599	>	else
600	>	siftDownUsingComparator(0, x, es, n, cmp);
601	>	}
602	>	}
603	>	return result;
604		}
605
606		/**
607	<	* Remove all elements from the priority queue.
607	>	* Removes the ith element from queue.
608	>	*
609	>	* Normally this method leaves the elements at up to i-1,
610	>	* inclusive, untouched.  Under these circumstances, it returns
611	>	* null.  Occasionally, in order to maintain the heap invariant,
612	>	* it must swap a later element of the list with one earlier than
613	>	* i.  Under these circumstances, this method returns the element
614	>	* that was previously at the end of the list and is now at some
615	>	* position before i. This fact is used by iterator.remove so as to
616	>	* avoid missing traversing elements.
617		*/
618	<	public void clear() {
618	>	E removeAt(int i) {
619	>	// assert i >= 0 && i < size;
620		modCount++;
621	<
622	<	// Null out element references to prevent memory leak
323	<	for (int i=1; i<=size; i++)
621	>	int s = --size;
622	>	if (s == i) // removed last element
623		queue[i] = null;
624	<
625	<	size = 0;
624	>	else {
625	>	E moved = (E) queue[s];
626	>	queue[s] = null;
627	>	siftDown(i, moved);
628	>	if (queue[i] == moved) {
629	>	siftUp(i, moved);
630	>	if (queue[i] != moved)
631	>	return moved;
632	>	}
633	>	}
634	>	return null;
635		}
636
637		/**
638	<	* Removes and returns the ith element from queue.  Recall
639	<	* that queue is one-based, so 1 <= i <= size.
638	>	* Inserts item x at position k, maintaining heap invariant by
639	>	* promoting x up the tree until it is greater than or equal to
640	>	* its parent, or is the root.
641		*
642	<	* XXX: Could further special-case i==size, but is it worth it?
643	<	* XXX: Could special-case i==0, but is it worth it?
642	>	* To simplify and speed up coercions and comparisons, the
643	>	* Comparable and Comparator versions are separated into different
644	>	* methods that are otherwise identical. (Similarly for siftDown.)
645	>	*
646	>	* @param k the position to fill
647	>	* @param x the item to insert
648		*/
649	<	private E remove(int i) {
650	<	assert i <= size;
651	<	modCount++;
649	>	private void siftUp(int k, E x) {
650	>	if (comparator != null)
651	>	siftUpUsingComparator(k, x, queue, comparator);
652	>	else
653	>	siftUpComparable(k, x, queue);
654	>	}
655
656	<	E result = queue[i];
657	<	queue[i] = queue[size];
658	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
659	<	if (i <= size)
660	<	fixDown(i);
661	<	return result;
656	>	private static <T> void siftUpComparable(int k, T x, Object[] es) {
657	>	Comparable<? super T> key = (Comparable<? super T>) x;
658	>	while (k > 0) {
659	>	int parent = (k - 1) >>> 1;
660	>	Object e = es[parent];
661	>	if (key.compareTo((T) e) >= 0)
662	>	break;
663	>	es[k] = e;
664	>	k = parent;
665	>	}
666	>	es[k] = key;
667		}
668
669	<	/**
670	<	* Establishes the heap invariant (described above) assuming the heap
671	<	* satisfies the invariant except possibly for the leaf-node indexed by k
672	<	* (which may have a nextExecutionTime less than its parent's).
673	<	*
674	<	* This method functions by "promoting" queue[k] up the hierarchy
675	<	* (by swapping it with its parent) repeatedly until queue[k]
676	<	* is greater than or equal to its parent.
677	<	*/
357	<	private void fixUp(int k) {
358	<	if (comparator == null) {
359	<	while (k > 1) {
360	<	int j = k >> 1;
361	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
362	<	break;
363	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
364	<	k = j;
365	<	}
366	<	} else {
367	<	while (k > 1) {
368	<	int j = k >> 1;
369	<	if (comparator.compare(queue[j], queue[k]) <= 0)
370	<	break;
371	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
372	<	k = j;
373	<	}
669	>	private static <T> void siftUpUsingComparator(
670	>	int k, T x, Object[] es, Comparator<? super T> cmp) {
671	>	while (k > 0) {
672	>	int parent = (k - 1) >>> 1;
673	>	Object e = es[parent];
674	>	if (cmp.compare(x, (T) e) >= 0)
675	>	break;
676	>	es[k] = e;
677	>	k = parent;
678		}
679	+	es[k] = x;
680		}
681
682		/**
683	<	* Establishes the heap invariant (described above) in the subtree
684	<	* rooted at k, which is assumed to satisfy the heap invariant except
685	<	* possibly for node k itself (which may be greater than its children).
686	<	*
687	<	* This method functions by "demoting" queue[k] down the hierarchy
688	<	* (by swapping it with its smaller child) repeatedly until queue[k]
689	<	* is less than or equal to its children.
690	<	*/
691	<	private void fixDown(int k) {
692	<	int j;
693	<	if (comparator == null) {
694	<	while ((j = k << 1) <= size) {
695	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
696	<	j++; // j indexes smallest kid
697	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
698	<	break;
699	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
700	<	k = j;
701	<	}
702	<	} else {
703	<	while ((j = k << 1) <= size) {
704	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
705	<	j++; // j indexes smallest kid
706	<	if (comparator.compare(queue[k], queue[j]) <= 0)
707	<	break;
708	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
709	<	k = j;
710	<	}
683	>	* Inserts item x at position k, maintaining heap invariant by
684	>	* demoting x down the tree repeatedly until it is less than or
685	>	* equal to its children or is a leaf.
686	>	*
687	>	* @param k the position to fill
688	>	* @param x the item to insert
689	>	*/
690	>	private void siftDown(int k, E x) {
691	>	if (comparator != null)
692	>	siftDownUsingComparator(k, x, queue, size, comparator);
693	>	else
694	>	siftDownComparable(k, x, queue, size);
695	>	}
696	>
697	>	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
698	>	// assert n > 0;
699	>	Comparable<? super T> key = (Comparable<? super T>)x;
700	>	int half = n >>> 1;           // loop while a non-leaf
701	>	while (k < half) {
702	>	int child = (k << 1) + 1; // assume left child is least
703	>	Object c = es[child];
704	>	int right = child + 1;
705	>	if (right < n &&
706	>	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
707	>	c = es[child = right];
708	>	if (key.compareTo((T) c) <= 0)
709	>	break;
710	>	es[k] = c;
711	>	k = child;
712	>	}
713	>	es[k] = key;
714	>	}
715	>
716	>	private static <T> void siftDownUsingComparator(
717	>	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
718	>	// assert n > 0;
719	>	int half = n >>> 1;
720	>	while (k < half) {
721	>	int child = (k << 1) + 1;
722	>	Object c = es[child];
723	>	int right = child + 1;
724	>	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
725	>	c = es[child = right];
726	>	if (cmp.compare(x, (T) c) <= 0)
727	>	break;
728	>	es[k] = c;
729	>	k = child;
730		}
731	+	es[k] = x;
732		}
733
734		/**
735	<	* Returns the comparator associated with this priority queue, or
736	<	* <tt>null</tt> if it uses its elements' natural ordering.
735	>	* Establishes the heap invariant (described above) in the entire tree,
736	>	* assuming nothing about the order of the elements prior to the call.
737	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
738	>	*/
739	>	private void heapify() {
740	>	final Object[] es = queue;
741	>	int n = size, i = (n >>> 1) - 1;
742	>	final Comparator<? super E> cmp;
743	>	if ((cmp = comparator) == null)
744	>	for (; i >= 0; i--)
745	>	siftDownComparable(i, (E) es[i], es, n);
746	>	else
747	>	for (; i >= 0; i--)
748	>	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
749	>	}
750	>
751	>	/**
752	>	* Returns the comparator used to order the elements in this
753	>	* queue, or {@code null} if this queue is sorted according to
754	>	* the {@linkplain Comparable natural ordering} of its elements.
755		*
756	<	* @return the comparator associated with this priority queue, or
757	<	*         <tt>null</tt> if it uses its elements' natural ordering.
756	>	* @return the comparator used to order this queue, or
757	>	*         {@code null} if this queue is sorted according to the
758	>	*         natural ordering of its elements
759		*/
760	<	public Comparator comparator() {
760	>	public Comparator<? super E> comparator() {
761		return comparator;
762		}
763
764		/**
765	<	* Save the state of the instance to a stream (that
422	<	* is, serialize it).
765	>	* Saves this queue to a stream (that is, serializes it).
766		*
424	–	* @serialData The length of the array backing the instance is
425	–	* emitted (int), followed by all of its elements (each an
426	–	* <tt>Object</tt>) in the proper order.
767		* @param s the stream
768	+	* @throws java.io.IOException if an I/O error occurs
769	+	* @serialData The length of the array backing the instance is
770	+	*             emitted (int), followed by all of its elements
771	+	*             (each an {@code Object}) in the proper order.
772		*/
773	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
774	<	throws java.io.IOException{
773	>	private void writeObject(java.io.ObjectOutputStream s)
774	>	throws java.io.IOException {
775		// Write out element count, and any hidden stuff
776		s.defaultWriteObject();
777
778	<	// Write out array length
779	<	s.writeInt(queue.length);
778	>	// Write out array length, for compatibility with 1.5 version
779	>	s.writeInt(Math.max(2, size + 1));
780
781	<	// Write out all elements in the proper order.
782	<	for (int i=0; i<size; i++)
783	<	s.writeObject(queue[i]);
781	>	// Write out all elements in the "proper order".
782	>	final Object[] es = queue;
783	>	for (int i = 0, n = size; i < n; i++)
784	>	s.writeObject(es[i]);
785		}
786
787		/**
788	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
789	<	* deserialize it).
788	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
789	>	* (that is, deserializes it).
790	>	*
791		* @param s the stream
792	+	* @throws ClassNotFoundException if the class of a serialized object
793	+	*         could not be found
794	+	* @throws java.io.IOException if an I/O error occurs
795		*/
796	<	private synchronized void readObject(java.io.ObjectInputStream s)
796	>	private void readObject(java.io.ObjectInputStream s)
797		throws java.io.IOException, ClassNotFoundException {
798		// Read in size, and any hidden stuff
799		s.defaultReadObject();
800
801	<	// Read in array length and allocate array
802	<	int arrayLength = s.readInt();
803	<	queue = (E[]) new Object[arrayLength];
804	<
805	<	// Read in all elements in the proper order.
806	<	for (int i=0; i<size; i++)
807	<	queue[i] = (E)s.readObject();
801	>	// Read in (and discard) array length
802	>	s.readInt();
803	>
804	>	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
805	>	final Object[] es = queue = new Object[Math.max(size, 1)];
806	>
807	>	// Read in all elements.
808	>	for (int i = 0, n = size; i < n; i++)
809	>	es[i] = s.readObject();
810	>
811	>	// Elements are guaranteed to be in "proper order", but the
812	>	// spec has never explained what that might be.
813	>	heapify();
814	>	}
815	>
816	>	/**
817	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
818	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
819	>	* queue. The spliterator does not traverse elements in any particular order
820	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
821	>	*
822	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
823	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
824	>	* Overriding implementations should document the reporting of additional
825	>	* characteristic values.
826	>	*
827	>	* @return a {@code Spliterator} over the elements in this queue
828	>	* @since 1.8
829	>	*/
830	>	public final Spliterator<E> spliterator() {
831	>	return new PriorityQueueSpliterator(0, -1, 0);
832	>	}
833	>
834	>	final class PriorityQueueSpliterator implements Spliterator<E> {
835	>	private int index;            // current index, modified on advance/split
836	>	private int fence;            // -1 until first use
837	>	private int expectedModCount; // initialized when fence set
838	>
839	>	/** Creates new spliterator covering the given range. */
840	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
841	>	this.index = origin;
842	>	this.fence = fence;
843	>	this.expectedModCount = expectedModCount;
844	>	}
845	>
846	>	private int getFence() { // initialize fence to size on first use
847	>	int hi;
848	>	if ((hi = fence) < 0) {
849	>	expectedModCount = modCount;
850	>	hi = fence = size;
851	>	}
852	>	return hi;
853	>	}
854	>
855	>	public PriorityQueueSpliterator trySplit() {
856	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
857	>	return (lo >= mid) ? null :
858	>	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
859	>	}
860	>
861	>	public void forEachRemaining(Consumer<? super E> action) {
862	>	if (action == null)
863	>	throw new NullPointerException();
864	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
865	>	final Object[] es = queue;
866	>	int i, hi; E e;
867	>	for (i = index, index = hi = fence; i < hi; i++) {
868	>	if ((e = (E) es[i]) == null)
869	>	break;      // must be CME
870	>	action.accept(e);
871	>	}
872	>	if (modCount != expectedModCount)
873	>	throw new ConcurrentModificationException();
874	>	}
875	>
876	>	public boolean tryAdvance(Consumer<? super E> action) {
877	>	if (action == null)
878	>	throw new NullPointerException();
879	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
880	>	int i;
881	>	if ((i = index) < fence) {
882	>	index = i + 1;
883	>	E e;
884	>	if ((e = (E) queue[i]) == null
885	>	|| modCount != expectedModCount)
886	>	throw new ConcurrentModificationException();
887	>	action.accept(e);
888	>	return true;
889	>	}
890	>	return false;
891	>	}
892	>
893	>	public long estimateSize() {
894	>	return getFence() - index;
895	>	}
896	>
897	>	public int characteristics() {
898	>	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
899	>	}
900		}
901
902	+	/**
903	+	* @throws NullPointerException {@inheritDoc}
904	+	*/
905	+	public void forEach(Consumer<? super E> action) {
906	+	Objects.requireNonNull(action);
907	+	final int expectedModCount = modCount;
908	+	final Object[] es = queue;
909	+	for (int i = 0, n = size; i < n; i++)
910	+	action.accept((E) es[i]);
911	+	if (expectedModCount != modCount)
912	+	throw new ConcurrentModificationException();
913	+	}
914		}

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