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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.2 by tim, Sun May 18 18:10:02 2003 UTC vs.
Revision 1.131 by jsr166, Wed May 22 17:36:58 2019 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* Copyright (c) 2003, 2019, 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	<	*   1) Make it serializable.
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 java.util.function.Predicate;
30	+	// OPENJDK import jdk.internal.access.SharedSecrets;
31	+	import jdk.internal.util.ArraysSupport;
32	+
33		/**
34	<	* An unbounded priority queue based on a priority heap.  This queue orders
35	<	* elements according to the order specified at creation time.  This order is
36	<	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
37	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
38	<	* according to a {@link Comparator}, depending on which constructor is used.
39	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
40	<	* minimal element with respect to the specified ordering.  If multiple
41	<	* these elements are tied for least value, no guarantees are made as to
42	<	* which of elements is returned.
43	<	*
44	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
45	<	* the array used to store the elements on the queue.  It is always at least
46	<	* as large as the queue size.  As elements are added to a priority list,
47	<	* its capacity grows automatically.  The details of the growth policy are not
34	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
35	>	* The elements of the priority queue are ordered according to their
36	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
37	>	* provided at queue construction time, depending on which constructor is
38	>	* used.  A priority queue does not permit {@code null} elements.
39	>	* A priority queue relying on natural ordering also does not permit
40	>	* insertion of non-comparable objects (doing so may result in
41	>	* {@code ClassCastException}).
42	>	*
43	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
44	>	* with respect to the specified ordering.  If multiple elements are
45	>	* tied for least value, the head is one of those elements -- ties are
46	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
47	>	* {@code remove}, {@code peek}, and {@code element} access the
48	>	* element at the head of the queue.
49	>	*
50	>	* <p>A priority queue is unbounded, but has an internal
51	>	* <i>capacity</i> governing the size of an array used to store the
52	>	* elements on the queue.  It is always at least as large as the queue
53	>	* size.  As elements are added to a priority queue, its capacity
54	>	* grows automatically.  The details of the growth policy are not
55		* specified.
56		*
57	<	*<p>Implementation note: this implementation provides O(log(n)) time for
58	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
59	<	* methods; linear time for the <tt>remove(Object)</tt> and
60	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
61	<	* <tt>element</tt>, and <tt>size</tt> methods.
57	>	* <p>This class and its iterator implement all of the
58	>	* <em>optional</em> methods of the {@link Collection} and {@link
59	>	* Iterator} interfaces.  The Iterator provided in method {@link
60	>	* #iterator()} and the Spliterator provided in method {@link #spliterator()}
61	>	* are <em>not</em> guaranteed to traverse the elements of
62	>	* the priority queue in any particular order. If you need ordered
63	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
64	>	*
65	>	* <p><strong>Note that this implementation is not synchronized.</strong>
66	>	* Multiple threads should not access a {@code PriorityQueue}
67	>	* instance concurrently if any of the threads modifies the queue.
68	>	* Instead, use the thread-safe {@link
69	>	* java.util.concurrent.PriorityBlockingQueue} class.
70	>	*
71	>	* <p>Implementation note: this implementation provides
72	>	* O(log(n)) time for the enqueuing and dequeuing methods
73	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
74	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
75	>	* methods; and constant time for the retrieval methods
76	>	* ({@code peek}, {@code element}, and {@code size}).
77		*
78		* <p>This class is a member of the
79	<	* <a href="{@docRoot}/../guide/collections/index.html">
79	>	* <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
80		* Java Collections Framework</a>.
81	+	*
82	+	* @since 1.5
83	+	* @author Josh Bloch, Doug Lea
84	+	* @param <E> the type of elements held in this queue
85		*/
86	+	@SuppressWarnings("unchecked")
87		public class PriorityQueue<E> extends AbstractQueue<E>
88	<	implements Queue<E>
89	<	{
88	>	implements java.io.Serializable {
89	>
90	>	private static final long serialVersionUID = -7720805057305804111L;
91	>
92		private static final int DEFAULT_INITIAL_CAPACITY = 11;
93
94		/**
95	<	* Priority queue represented as a balanced binary heap: the two children
96	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
97	<	* ordered by comparator, or by the elements' natural ordering, if
98	<	* comparator is null:  For each node n in the heap, and each descendant
99	<	* of n, d, n <= d.
100	<	*
48	<	* The element with the lowest value is in queue[1] (assuming the queue is
49	<	* nonempty). A one-based array is used in preference to the traditional
50	<	* zero-based array to simplify parent and child calculations.
51	<	*
52	<	* queue.length must be >= 2, even if size == 0.
95	>	* Priority queue represented as a balanced binary heap: the two
96	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
97	>	* priority queue is ordered by comparator, or by the elements'
98	>	* natural ordering, if comparator is null: For each node n in the
99	>	* heap and each descendant d of n, n <= d.  The element with the
100	>	* lowest value is in queue[0], assuming the queue is nonempty.
101		*/
102	<	private E[] queue;
102	>	transient Object[] queue; // non-private to simplify nested class access
103
104		/**
105		* The number of elements in the priority queue.
106		*/
107	<	private int size = 0;
107	>	int size;
108
109		/**
110		* The comparator, or null if priority queue uses elements'
111		* natural ordering.
112		*/
113	<	private final Comparator<E> comparator;
113	>	private final Comparator<? super E> comparator;
114
115		/**
116		* The number of times this priority queue has been
117		* <i>structurally modified</i>.  See AbstractList for gory details.
118		*/
119	<	private int modCount = 0;
119	>	transient int modCount;     // non-private to simplify nested class access
120
121		/**
122	<	* Create a new priority queue with the default initial capacity (11)
123	<	* that orders its elements according to their natural ordering.
122	>	* Creates a {@code PriorityQueue} with the default initial
123	>	* capacity (11) that orders its elements according to their
124	>	* {@linkplain Comparable natural ordering}.
125		*/
126		public PriorityQueue() {
127	<	this(DEFAULT_INITIAL_CAPACITY);
127	>	this(DEFAULT_INITIAL_CAPACITY, null);
128		}
129
130		/**
131	<	* Create a new priority queue with the specified initial capacity
132	<	* that orders its elements according to their natural ordering.
131	>	* Creates a {@code PriorityQueue} with the specified initial
132	>	* capacity that orders its elements according to their
133	>	* {@linkplain Comparable natural ordering}.
134		*
135	<	* @param initialCapacity the initial capacity for this priority queue.
135	>	* @param initialCapacity the initial capacity for this priority queue
136	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
137	>	*         than 1
138		*/
139		public PriorityQueue(int initialCapacity) {
140		this(initialCapacity, null);
141		}
142
143		/**
144	<	* Create a new priority queue with the specified initial capacity (11)
145	<	* that orders its elements according to the specified comparator.
144	>	* Creates a {@code PriorityQueue} with the default initial capacity and
145	>	* whose elements are ordered according to the specified comparator.
146		*
147	<	* @param initialCapacity the initial capacity for this priority queue.
148	<	* @param comparator the comparator used to order this priority queue.
147	>	* @param  comparator the comparator that will be used to order this
148	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
149	>	*         natural ordering} of the elements will be used.
150	>	* @since 1.8
151		*/
152	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
152	>	public PriorityQueue(Comparator<? super E> comparator) {
153	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
154	>	}
155	>
156	>	/**
157	>	* Creates a {@code PriorityQueue} with the specified initial capacity
158	>	* that orders its elements according to the specified comparator.
159	>	*
160	>	* @param  initialCapacity the initial capacity for this priority queue
161	>	* @param  comparator the comparator that will be used to order this
162	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
163	>	*         natural ordering} of the elements will be used.
164	>	* @throws IllegalArgumentException if {@code initialCapacity} is
165	>	*         less than 1
166	>	*/
167	>	public PriorityQueue(int initialCapacity,
168	>	Comparator<? super E> comparator) {
169	>	// Note: This restriction of at least one is not actually needed,
170	>	// but continues for 1.5 compatibility
171		if (initialCapacity < 1)
172	<	initialCapacity = 1;
173	<	queue = new E[initialCapacity + 1];
172	>	throw new IllegalArgumentException();
173	>	this.queue = new Object[initialCapacity];
174		this.comparator = comparator;
175		}
176
177		/**
178	<	* Create a new priority queue containing the elements in the specified
179	<	* collection.  The priority queue has an initial capacity of 110% of the
180	<	* size of the specified collection. If the specified collection
181	<	* implements the {@link Sorted} interface, the priority queue will be
182	<	* sorted according to the same comparator, or according to its elements'
183	<	* natural order if the collection is sorted according to its elements'
112	<	* natural order.  If the specified collection does not implement the
113	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
114	<	* its elements' natural order.
178	>	* Creates a {@code PriorityQueue} containing the elements in the
179	>	* specified collection.  If the specified collection is an instance of
180	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
181	>	* priority queue will be ordered according to the same ordering.
182	>	* Otherwise, this priority queue will be ordered according to the
183	>	* {@linkplain Comparable natural ordering} of its elements.
184		*
185	<	* @param initialElements the collection whose elements are to be placed
186	<	*        into this priority queue.
185	>	* @param  c the collection whose elements are to be placed
186	>	*         into this priority queue
187		* @throws ClassCastException if elements of the specified collection
188		*         cannot be compared to one another according to the priority
189	<	*         queue's ordering.
190	<	* @throws NullPointerException if the specified collection or an
191	<	*         element of the specified collection is <tt>null</tt>.
192	<	*/
193	<	public PriorityQueue(Collection<E> initialElements) {
194	<	int sz = initialElements.size();
195	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
196	<	Integer.MAX_VALUE - 1);
197	<	if (initialCapacity < 1)
198	<	initialCapacity = 1;
199	<	queue = new E[initialCapacity + 1];
189	>	*         queue's ordering
190	>	* @throws NullPointerException if the specified collection or any
191	>	*         of its elements are null
192	>	*/
193	>	public PriorityQueue(Collection<? extends E> c) {
194	>	if (c instanceof SortedSet<?>) {
195	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
196	>	this.comparator = (Comparator<? super E>) ss.comparator();
197	>	initElementsFromCollection(ss);
198	>	}
199	>	else if (c instanceof PriorityQueue<?>) {
200	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
201	>	this.comparator = (Comparator<? super E>) pq.comparator();
202	>	initFromPriorityQueue(pq);
203	>	}
204	>	else {
205	>	this.comparator = null;
206	>	initFromCollection(c);
207	>	}
208	>	}
209
210	<	/* Commented out to compile with generics compiler
210	>	/**
211	>	* Creates a {@code PriorityQueue} containing the elements in the
212	>	* specified priority queue.  This priority queue will be
213	>	* ordered according to the same ordering as the given priority
214	>	* queue.
215	>	*
216	>	* @param  c the priority queue whose elements are to be placed
217	>	*         into this priority queue
218	>	* @throws ClassCastException if elements of {@code c} cannot be
219	>	*         compared to one another according to {@code c}'s
220	>	*         ordering
221	>	* @throws NullPointerException if the specified priority queue or any
222	>	*         of its elements are null
223	>	*/
224	>	public PriorityQueue(PriorityQueue<? extends E> c) {
225	>	this.comparator = (Comparator<? super E>) c.comparator();
226	>	initFromPriorityQueue(c);
227	>	}
228
229	<	if (initialElements instanceof Sorted) {
230	<	comparator = ((Sorted)initialElements).comparator();
231	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
232	<	queue[++size] = i.next();
229	>	/**
230	>	* Creates a {@code PriorityQueue} containing the elements in the
231	>	* specified sorted set.   This priority queue will be ordered
232	>	* according to the same ordering as the given sorted set.
233	>	*
234	>	* @param  c the sorted set whose elements are to be placed
235	>	*         into this priority queue
236	>	* @throws ClassCastException if elements of the specified sorted
237	>	*         set cannot be compared to one another according to the
238	>	*         sorted set's ordering
239	>	* @throws NullPointerException if the specified sorted set or any
240	>	*         of its elements are null
241	>	*/
242	>	public PriorityQueue(SortedSet<? extends E> c) {
243	>	this.comparator = (Comparator<? super E>) c.comparator();
244	>	initElementsFromCollection(c);
245	>	}
246	>
247	>	/** Ensures that queue[0] exists, helping peek() and poll(). */
248	>	private static Object[] ensureNonEmpty(Object[] es) {
249	>	return (es.length > 0) ? es : new Object[1];
250	>	}
251	>
252	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
253	>	if (c.getClass() == PriorityQueue.class) {
254	>	this.queue = ensureNonEmpty(c.toArray());
255	>	this.size = c.size();
256		} else {
257	<	*/
140	<	{
141	<	comparator = null;
142	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
257	>	initFromCollection(c);
258		}
259		}
260
261	<	// Queue Methods
261	>	private void initElementsFromCollection(Collection<? extends E> c) {
262	>	Object[] es = c.toArray();
263	>	int len = es.length;
264	>	// If c.toArray incorrectly doesn't return Object[], copy it.
265	>	if (es.getClass() != Object[].class)
266	>	es = Arrays.copyOf(es, len, Object[].class);
267	>	if (len == 1 || this.comparator != null)
268	>	for (Object e : es)
269	>	if (e == null)
270	>	throw new NullPointerException();
271	>	this.queue = ensureNonEmpty(es);
272	>	this.size = len;
273	>	}
274
275		/**
276	<	* Remove and return the minimal element from this priority queue if
151	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
152	<	* <i>minimal</i> is defined according to this priority queue's order.
276	>	* Initializes queue array with elements from the given Collection.
277		*
278	<	* @return the minimal element from this priority queue if it contains
155	<	*         one or more elements, otherwise <tt>null</tt>.
278	>	* @param c the collection
279		*/
280	<	public E poll() {
281	<	if (size == 0)
282	<	return null;
283	<	return remove(1);
280	>	private void initFromCollection(Collection<? extends E> c) {
281	>	initElementsFromCollection(c);
282	>	heapify();
283	>	}
284	>
285	>	/**
286	>	* Increases the capacity of the array.
287	>	*
288	>	* @param minCapacity the desired minimum capacity
289	>	*/
290	>	private void grow(int minCapacity) {
291	>	int oldCapacity = queue.length;
292	>	// Double size if small; else grow by 50%
293	>	int newCapacity = ArraysSupport.newLength(oldCapacity,
294	>	minCapacity - oldCapacity, /* minimum growth */
295	>	oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
296	>	/* preferred growth */);
297	>	queue = Arrays.copyOf(queue, newCapacity);
298	>	}
299	>
300	>	/**
301	>	* Inserts the specified element into this priority queue.
302	>	*
303	>	* @return {@code true} (as specified by {@link Collection#add})
304	>	* @throws ClassCastException if the specified element cannot be
305	>	*         compared with elements currently in this priority queue
306	>	*         according to the priority queue's ordering
307	>	* @throws NullPointerException if the specified element is null
308	>	*/
309	>	public boolean add(E e) {
310	>	return offer(e);
311		}
312
313		/**
314	<	* Return, but do not remove, the minimal element from the priority queue,
165	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
166	<	* defined according to this priority queue's order.  This method returns
167	<	* the same object reference that would be returned by by the
168	<	* <tt>poll</tt> method.  The two methods differ in that this method
169	<	* does not remove the element from the priority queue.
314	>	* Inserts the specified element into this priority queue.
315		*
316	<	* @return the minimal element from this priority queue if it contains
317	<	*         one or more elements, otherwise <tt>null</tt>.
316	>	* @return {@code true} (as specified by {@link Queue#offer})
317	>	* @throws ClassCastException if the specified element cannot be
318	>	*         compared with elements currently in this priority queue
319	>	*         according to the priority queue's ordering
320	>	* @throws NullPointerException if the specified element is null
321		*/
322	+	public boolean offer(E e) {
323	+	if (e == null)
324	+	throw new NullPointerException();
325	+	modCount++;
326	+	int i = size;
327	+	if (i >= queue.length)
328	+	grow(i + 1);
329	+	siftUp(i, e);
330	+	size = i + 1;
331	+	return true;
332	+	}
333	+
334		public E peek() {
335	<	return queue[1];
335	>	return (E) queue[0];
336		}
337
338	<	// Collection Methods
338	>	private int indexOf(Object o) {
339	>	if (o != null) {
340	>	final Object[] es = queue;
341	>	for (int i = 0, n = size; i < n; i++)
342	>	if (o.equals(es[i]))
343	>	return i;
344	>	}
345	>	return -1;
346	>	}
347
348		/**
349	<	* Removes a single instance of the specified element from this priority
350	<	* queue, if it is present.  Returns true if this collection contained the
351	<	* specified element (or equivalently, if this collection changed as a
349	>	* Removes a single instance of the specified element from this queue,
350	>	* if it is present.  More formally, removes an element {@code e} such
351	>	* that {@code o.equals(e)}, if this queue contains one or more such
352	>	* elements.  Returns {@code true} if and only if this queue contained
353	>	* the specified element (or equivalently, if this queue changed as a
354		* result of the call).
355		*
356	<	* @param o element to be removed from this collection, if present.
357	<	* @return <tt>true</tt> if this collection changed as a result of the
188	<	*         call
189	<	* @throws ClassCastException if the specified element cannot be compared
190	<	*            with elements currently in the priority queue according
191	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
356	>	* @param o element to be removed from this queue, if present
357	>	* @return {@code true} if this queue changed as a result of the call
358		*/
359	<	public boolean remove(Object element) {
360	<	if (element == null)
361	<	throw new NullPointerException();
359	>	public boolean remove(Object o) {
360	>	int i = indexOf(o);
361	>	if (i == -1)
362	>	return false;
363	>	else {
364	>	removeAt(i);
365	>	return true;
366	>	}
367	>	}
368
369	<	if (comparator == null) {
370	<	for (int i = 1; i <= size; i++) {
371	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
372	<	remove(i);
373	<	return true;
374	<	}
375	<	}
376	<	} else {
377	<	for (int i = 1; i <= size; i++) {
378	<	if (comparator.compare(queue[i], (E) element) == 0) {
379	<	remove(i);
209	<	return true;
210	<	}
369	>	/**
370	>	* Identity-based version for use in Itr.remove.
371	>	*
372	>	* @param o element to be removed from this queue, if present
373	>	*/
374	>	void removeEq(Object o) {
375	>	final Object[] es = queue;
376	>	for (int i = 0, n = size; i < n; i++) {
377	>	if (o == es[i]) {
378	>	removeAt(i);
379	>	break;
380		}
381		}
213	–	return false;
382		}
383
384		/**
385	<	* Returns an iterator over the elements in this priority queue.  The
386	<	* first element returned by this iterator is the same element that
387	<	* would be returned by a call to <tt>peek</tt>.
385	>	* Returns {@code true} if this queue contains the specified element.
386	>	* More formally, returns {@code true} if and only if this queue contains
387	>	* at least one element {@code e} such that {@code o.equals(e)}.
388	>	*
389	>	* @param o object to be checked for containment in this queue
390	>	* @return {@code true} if this queue contains the specified element
391	>	*/
392	>	public boolean contains(Object o) {
393	>	return indexOf(o) >= 0;
394	>	}
395	>
396	>	/**
397	>	* Returns an array containing all of the elements in this queue.
398	>	* The elements are in no particular order.
399	>	*
400	>	* <p>The returned array will be "safe" in that no references to it are
401	>	* maintained by this queue.  (In other words, this method must allocate
402	>	* a new array).  The caller is thus free to modify the returned array.
403	>	*
404	>	* <p>This method acts as bridge between array-based and collection-based
405	>	* APIs.
406	>	*
407	>	* @return an array containing all of the elements in this queue
408	>	*/
409	>	public Object[] toArray() {
410	>	return Arrays.copyOf(queue, size);
411	>	}
412	>
413	>	/**
414	>	* Returns an array containing all of the elements in this queue; the
415	>	* runtime type of the returned array is that of the specified array.
416	>	* The returned array elements are in no particular order.
417	>	* If the queue fits in the specified array, it is returned therein.
418	>	* Otherwise, a new array is allocated with the runtime type of the
419	>	* specified array and the size of this queue.
420	>	*
421	>	* <p>If the queue fits in the specified array with room to spare
422	>	* (i.e., the array has more elements than the queue), the element in
423	>	* the array immediately following the end of the collection is set to
424	>	* {@code null}.
425	>	*
426	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
427	>	* array-based and collection-based APIs.  Further, this method allows
428	>	* precise control over the runtime type of the output array, and may,
429	>	* under certain circumstances, be used to save allocation costs.
430	>	*
431	>	* <p>Suppose {@code x} is a queue known to contain only strings.
432	>	* The following code can be used to dump the queue into a newly
433	>	* allocated array of {@code String}:
434	>	*
435	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
436	>	*
437	>	* Note that {@code toArray(new Object[0])} is identical in function to
438	>	* {@code toArray()}.
439		*
440	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
440	>	* @param a the array into which the elements of the queue are to
441	>	*          be stored, if it is big enough; otherwise, a new array of the
442	>	*          same runtime type is allocated for this purpose.
443	>	* @return an array containing all of the elements in this queue
444	>	* @throws ArrayStoreException if the runtime type of the specified array
445	>	*         is not a supertype of the runtime type of every element in
446	>	*         this queue
447	>	* @throws NullPointerException if the specified array is null
448	>	*/
449	>	public <T> T[] toArray(T[] a) {
450	>	final int size = this.size;
451	>	if (a.length < size)
452	>	// Make a new array of a's runtime type, but my contents:
453	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
454	>	System.arraycopy(queue, 0, a, 0, size);
455	>	if (a.length > size)
456	>	a[size] = null;
457	>	return a;
458	>	}
459	>
460	>	/**
461	>	* Returns an iterator over the elements in this queue. The iterator
462	>	* does not return the elements in any particular order.
463	>	*
464	>	* @return an iterator over the elements in this queue
465		*/
466		public Iterator<E> iterator() {
467		return new Itr();
468		}
469
470	<	private class Itr implements Iterator<E> {
470	>	private final class Itr implements Iterator<E> {
471		/**
472		* Index (into queue array) of element to be returned by
473		* subsequent call to next.
474		*/
475	<	int cursor = 1;
475	>	private int cursor;
476	>
477	>	/**
478	>	* Index of element returned by most recent call to next,
479	>	* unless that element came from the forgetMeNot list.
480	>	* Set to -1 if element is deleted by a call to remove.
481	>	*/
482	>	private int lastRet = -1;
483	>
484	>	/**
485	>	* A queue of elements that were moved from the unvisited portion of
486	>	* the heap into the visited portion as a result of "unlucky" element
487	>	* removals during the iteration.  (Unlucky element removals are those
488	>	* that require a siftup instead of a siftdown.)  We must visit all of
489	>	* the elements in this list to complete the iteration.  We do this
490	>	* after we've completed the "normal" iteration.
491	>	*
492	>	* We expect that most iterations, even those involving removals,
493	>	* will not need to store elements in this field.
494	>	*/
495	>	private ArrayDeque<E> forgetMeNot;
496
497		/**
498	<	* Index of element returned by most recent call to next or
499	<	* previous.  Reset to 0 if this element is deleted by a call
237	<	* to remove.
498	>	* Element returned by the most recent call to next iff that
499	>	* element was drawn from the forgetMeNot list.
500		*/
501	<	int lastRet = 0;
501	>	private E lastRetElt;
502
503		/**
504		* The modCount value that the iterator believes that the backing
505	<	* List should have.  If this expectation is violated, the iterator
505	>	* Queue should have.  If this expectation is violated, the iterator
506		* has detected concurrent modification.
507		*/
508	<	int expectedModCount = modCount;
508	>	private int expectedModCount = modCount;
509	>
510	>	Itr() {}                        // prevent access constructor creation
511
512		public boolean hasNext() {
513	<	return cursor <= size;
513	>	return cursor < size ||
514	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
515		}
516
517		public E next() {
518	<	checkForComodification();
519	<	if (cursor > size)
520	<	throw new NoSuchElementException();
521	<	E result = queue[cursor];
522	<	lastRet = cursor++;
523	<	return result;
518	>	if (expectedModCount != modCount)
519	>	throw new ConcurrentModificationException();
520	>	if (cursor < size)
521	>	return (E) queue[lastRet = cursor++];
522	>	if (forgetMeNot != null) {
523	>	lastRet = -1;
524	>	lastRetElt = forgetMeNot.poll();
525	>	if (lastRetElt != null)
526	>	return lastRetElt;
527	>	}
528	>	throw new NoSuchElementException();
529		}
530
531		public void remove() {
532	<	if (lastRet == 0)
532	>	if (expectedModCount != modCount)
533	>	throw new ConcurrentModificationException();
534	>	if (lastRet != -1) {
535	>	E moved = PriorityQueue.this.removeAt(lastRet);
536	>	lastRet = -1;
537	>	if (moved == null)
538	>	cursor--;
539	>	else {
540	>	if (forgetMeNot == null)
541	>	forgetMeNot = new ArrayDeque<>();
542	>	forgetMeNot.add(moved);
543	>	}
544	>	} else if (lastRetElt != null) {
545	>	PriorityQueue.this.removeEq(lastRetElt);
546	>	lastRetElt = null;
547	>	} else {
548		throw new IllegalStateException();
549	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
549	>	}
550		expectedModCount = modCount;
551		}
552	+	}
553
554	<	final void checkForComodification() {
555	<	if (modCount != expectedModCount)
556	<	throw new ConcurrentModificationException();
554	>	public int size() {
555	>	return size;
556	>	}
557	>
558	>	/**
559	>	* Removes all of the elements from this priority queue.
560	>	* The queue will be empty after this call returns.
561	>	*/
562	>	public void clear() {
563	>	modCount++;
564	>	final Object[] es = queue;
565	>	for (int i = 0, n = size; i < n; i++)
566	>	es[i] = null;
567	>	size = 0;
568	>	}
569	>
570	>	public E poll() {
571	>	final Object[] es;
572	>	final E result;
573	>
574	>	if ((result = (E) ((es = queue)[0])) != null) {
575	>	modCount++;
576	>	final int n;
577	>	final E x = (E) es[(n = --size)];
578	>	es[n] = null;
579	>	if (n > 0) {
580	>	final Comparator<? super E> cmp;
581	>	if ((cmp = comparator) == null)
582	>	siftDownComparable(0, x, es, n);
583	>	else
584	>	siftDownUsingComparator(0, x, es, n, cmp);
585	>	}
586		}
587	+	return result;
588		}
589
590		/**
591	<	* Returns the number of elements in this priority queue.
591	>	* Removes the ith element from queue.
592		*
593	<	* @return the number of elements in this priority queue.
594	<	*/
595	<	public int size() {
596	<	return size;
593	>	* Normally this method leaves the elements at up to i-1,
594	>	* inclusive, untouched.  Under these circumstances, it returns
595	>	* null.  Occasionally, in order to maintain the heap invariant,
596	>	* it must swap a later element of the list with one earlier than
597	>	* i.  Under these circumstances, this method returns the element
598	>	* that was previously at the end of the list and is now at some
599	>	* position before i. This fact is used by iterator.remove so as to
600	>	* avoid missing traversing elements.
601	>	*/
602	>	E removeAt(int i) {
603	>	// assert i >= 0 && i < size;
604	>	final Object[] es = queue;
605	>	modCount++;
606	>	int s = --size;
607	>	if (s == i) // removed last element
608	>	es[i] = null;
609	>	else {
610	>	E moved = (E) es[s];
611	>	es[s] = null;
612	>	siftDown(i, moved);
613	>	if (es[i] == moved) {
614	>	siftUp(i, moved);
615	>	if (es[i] != moved)
616	>	return moved;
617	>	}
618	>	}
619	>	return null;
620		}
621
622		/**
623	<	* Add the specified element to this priority queue.
623	>	* Inserts item x at position k, maintaining heap invariant by
624	>	* promoting x up the tree until it is greater than or equal to
625	>	* its parent, or is the root.
626	>	*
627	>	* To simplify and speed up coercions and comparisons, the
628	>	* Comparable and Comparator versions are separated into different
629	>	* methods that are otherwise identical. (Similarly for siftDown.)
630		*
631	<	* @param element the element to add.
632	<	* @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.
631	>	* @param k the position to fill
632	>	* @param x the item to insert
633		*/
634	<	public boolean offer(E element) {
635	<	if (element == null)
636	<	throw new NullPointerException();
637	<	modCount++;
634	>	private void siftUp(int k, E x) {
635	>	if (comparator != null)
636	>	siftUpUsingComparator(k, x, queue, comparator);
637	>	else
638	>	siftUpComparable(k, x, queue);
639	>	}
640
641	<	// Grow backing store if necessary
642	<	if (++size == queue.length) {
643	<	E[] newQueue = new E[2 * queue.length];
644	<	System.arraycopy(queue, 0, newQueue, 0, size);
645	<	queue = newQueue;
641	>	private static <T> void siftUpComparable(int k, T x, Object[] es) {
642	>	Comparable<? super T> key = (Comparable<? super T>) x;
643	>	while (k > 0) {
644	>	int parent = (k - 1) >>> 1;
645	>	Object e = es[parent];
646	>	if (key.compareTo((T) e) >= 0)
647	>	break;
648	>	es[k] = e;
649	>	k = parent;
650		}
651	+	es[k] = key;
652	+	}
653
654	<	queue[size] = element;
655	<	fixUp(size);
656	<	return true;
654	>	private static <T> void siftUpUsingComparator(
655	>	int k, T x, Object[] es, Comparator<? super T> cmp) {
656	>	while (k > 0) {
657	>	int parent = (k - 1) >>> 1;
658	>	Object e = es[parent];
659	>	if (cmp.compare(x, (T) e) >= 0)
660	>	break;
661	>	es[k] = e;
662	>	k = parent;
663	>	}
664	>	es[k] = x;
665		}
666
667		/**
668	<	* Remove all elements from the priority queue.
668	>	* Inserts item x at position k, maintaining heap invariant by
669	>	* demoting x down the tree repeatedly until it is less than or
670	>	* equal to its children or is a leaf.
671	>	*
672	>	* @param k the position to fill
673	>	* @param x the item to insert
674	>	*/
675	>	private void siftDown(int k, E x) {
676	>	if (comparator != null)
677	>	siftDownUsingComparator(k, x, queue, size, comparator);
678	>	else
679	>	siftDownComparable(k, x, queue, size);
680	>	}
681	>
682	>	private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
683	>	// assert n > 0;
684	>	Comparable<? super T> key = (Comparable<? super T>)x;
685	>	int half = n >>> 1;           // loop while a non-leaf
686	>	while (k < half) {
687	>	int child = (k << 1) + 1; // assume left child is least
688	>	Object c = es[child];
689	>	int right = child + 1;
690	>	if (right < n &&
691	>	((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
692	>	c = es[child = right];
693	>	if (key.compareTo((T) c) <= 0)
694	>	break;
695	>	es[k] = c;
696	>	k = child;
697	>	}
698	>	es[k] = key;
699	>	}
700	>
701	>	private static <T> void siftDownUsingComparator(
702	>	int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
703	>	// assert n > 0;
704	>	int half = n >>> 1;
705	>	while (k < half) {
706	>	int child = (k << 1) + 1;
707	>	Object c = es[child];
708	>	int right = child + 1;
709	>	if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
710	>	c = es[child = right];
711	>	if (cmp.compare(x, (T) c) <= 0)
712	>	break;
713	>	es[k] = c;
714	>	k = child;
715	>	}
716	>	es[k] = x;
717	>	}
718	>
719	>	/**
720	>	* Establishes the heap invariant (described above) in the entire tree,
721	>	* assuming nothing about the order of the elements prior to the call.
722	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
723		*/
724	<	public void clear() {
725	<	modCount++;
724	>	private void heapify() {
725	>	final Object[] es = queue;
726	>	int n = size, i = (n >>> 1) - 1;
727	>	final Comparator<? super E> cmp;
728	>	if ((cmp = comparator) == null)
729	>	for (; i >= 0; i--)
730	>	siftDownComparable(i, (E) es[i], es, n);
731	>	else
732	>	for (; i >= 0; i--)
733	>	siftDownUsingComparator(i, (E) es[i], es, n, cmp);
734	>	}
735	>
736	>	/**
737	>	* Returns the comparator used to order the elements in this
738	>	* queue, or {@code null} if this queue is sorted according to
739	>	* the {@linkplain Comparable natural ordering} of its elements.
740	>	*
741	>	* @return the comparator used to order this queue, or
742	>	*         {@code null} if this queue is sorted according to the
743	>	*         natural ordering of its elements
744	>	*/
745	>	public Comparator<? super E> comparator() {
746	>	return comparator;
747	>	}
748	>
749	>	/**
750	>	* Saves this queue to a stream (that is, serializes it).
751	>	*
752	>	* @param s the stream
753	>	* @throws java.io.IOException if an I/O error occurs
754	>	* @serialData The length of the array backing the instance is
755	>	*             emitted (int), followed by all of its elements
756	>	*             (each an {@code Object}) in the proper order.
757	>	*/
758	>	private void writeObject(java.io.ObjectOutputStream s)
759	>	throws java.io.IOException {
760	>	// Write out element count, and any hidden stuff
761	>	s.defaultWriteObject();
762
763	<	// Null out element references to prevent memory leak
764	<	for (int i=1; i<=size; i++)
323	<	queue[i] = null;
763	>	// Write out array length, for compatibility with 1.5 version
764	>	s.writeInt(Math.max(2, size + 1));
765
766	<	size = 0;
766	>	// Write out all elements in the "proper order".
767	>	final Object[] es = queue;
768	>	for (int i = 0, n = size; i < n; i++)
769	>	s.writeObject(es[i]);
770		}
771
772		/**
773	<	* Removes and returns the ith element from queue.  Recall
774	<	* that queue is one-based, so 1 <= i <= size.
773	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
774	>	* (that is, deserializes it).
775		*
776	<	* XXX: Could further special-case i==size, but is it worth it?
777	<	* XXX: Could special-case i==0, but is it worth it?
776	>	* @param s the stream
777	>	* @throws ClassNotFoundException if the class of a serialized object
778	>	*         could not be found
779	>	* @throws java.io.IOException if an I/O error occurs
780		*/
781	<	private E remove(int i) {
782	<	assert i <= size;
783	<	modCount++;
781	>	private void readObject(java.io.ObjectInputStream s)
782	>	throws java.io.IOException, ClassNotFoundException {
783	>	// Read in size, and any hidden stuff
784	>	s.defaultReadObject();
785
786	<	E result = queue[i];
787	<	queue[i] = queue[size];
788	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
789	<	if (i <= size)
790	<	fixDown(i);
791	<	return result;
786	>	// Read in (and discard) array length
787	>	s.readInt();
788	>
789	>	jsr166.Platform.checkArray(s, Object[].class, size);
790	>	final Object[] es = queue = new Object[Math.max(size, 1)];
791	>
792	>	// Read in all elements.
793	>	for (int i = 0, n = size; i < n; i++)
794	>	es[i] = s.readObject();
795	>
796	>	// Elements are guaranteed to be in "proper order", but the
797	>	// spec has never explained what that might be.
798	>	heapify();
799		}
800
801		/**
802	<	* Establishes the heap invariant (described above) assuming the heap
803	<	* satisfies the invariant except possibly for the leaf-node indexed by k
804	<	* (which may have a nextExecutionTime less than its parent's).
805	<	*
806	<	* This method functions by "promoting" queue[k] up the hierarchy
807	<	* (by swapping it with its parent) repeatedly until queue[k]
808	<	* is greater than or equal to its parent.
809	<	*/
810	<	private void fixUp(int k) {
811	<	if (comparator == null) {
812	<	while (k > 1) {
813	<	int j = k >> 1;
814	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
815	<	break;
816	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
817	<	k = j;
802	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
803	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
804	>	* queue. The spliterator does not traverse elements in any particular order
805	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
806	>	*
807	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
808	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
809	>	* Overriding implementations should document the reporting of additional
810	>	* characteristic values.
811	>	*
812	>	* @return a {@code Spliterator} over the elements in this queue
813	>	* @since 1.8
814	>	*/
815	>	public final Spliterator<E> spliterator() {
816	>	return new PriorityQueueSpliterator(0, -1, 0);
817	>	}
818	>
819	>	final class PriorityQueueSpliterator implements Spliterator<E> {
820	>	private int index;            // current index, modified on advance/split
821	>	private int fence;            // -1 until first use
822	>	private int expectedModCount; // initialized when fence set
823	>
824	>	/** Creates new spliterator covering the given range. */
825	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
826	>	this.index = origin;
827	>	this.fence = fence;
828	>	this.expectedModCount = expectedModCount;
829	>	}
830	>
831	>	private int getFence() { // initialize fence to size on first use
832	>	int hi;
833	>	if ((hi = fence) < 0) {
834	>	expectedModCount = modCount;
835	>	hi = fence = size;
836		}
837	<	} else {
838	<	while (k > 1) {
839	<	int j = k >> 1;
840	<	if (comparator.compare(queue[j], queue[k]) <= 0)
841	<	break;
842	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
843	<	k = j;
837	>	return hi;
838	>	}
839	>
840	>	public PriorityQueueSpliterator trySplit() {
841	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
842	>	return (lo >= mid) ? null :
843	>	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
844	>	}
845	>
846	>	public void forEachRemaining(Consumer<? super E> action) {
847	>	if (action == null)
848	>	throw new NullPointerException();
849	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
850	>	final Object[] es = queue;
851	>	int i, hi; E e;
852	>	for (i = index, index = hi = fence; i < hi; i++) {
853	>	if ((e = (E) es[i]) == null)
854	>	break;      // must be CME
855	>	action.accept(e);
856	>	}
857	>	if (modCount != expectedModCount)
858	>	throw new ConcurrentModificationException();
859	>	}
860	>
861	>	public boolean tryAdvance(Consumer<? super E> action) {
862	>	if (action == null)
863	>	throw new NullPointerException();
864	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
865	>	int i;
866	>	if ((i = index) < fence) {
867	>	index = i + 1;
868	>	E e;
869	>	if ((e = (E) queue[i]) == null
870	>	|| modCount != expectedModCount)
871	>	throw new ConcurrentModificationException();
872	>	action.accept(e);
873	>	return true;
874		}
875	+	return false;
876	+	}
877	+
878	+	public long estimateSize() {
879	+	return getFence() - index;
880	+	}
881	+
882	+	public int characteristics() {
883	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
884		}
885		}
886
887		/**
888	<	* Establishes the heap invariant (described above) in the subtree
889	<	* rooted at k, which is assumed to satisfy the heap invariant except
890	<	* possibly for node k itself (which may be greater than its children).
891	<	*
892	<	* This method functions by "demoting" queue[k] down the hierarchy
893	<	* (by swapping it with its smaller child) repeatedly until queue[k]
894	<	* is less than or equal to its children.
895	<	*/
896	<	private void fixDown(int k) {
897	<	int j;
898	<	if (comparator == null) {
899	<	while ((j = k << 1) <= size) {
900	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
901	<	j++; // j indexes smallest kid
902	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
903	<	break;
904	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
905	<	k = j;
906	<	}
907	<	} else {
908	<	while ((j = k << 1) <= size) {
909	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
910	<	j++; // j indexes smallest kid
911	<	if (comparator.compare(queue[k], queue[j]) <= 0)
912	<	break;
913	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
914	<	k = j;
915	<	}
888	>	* @throws NullPointerException {@inheritDoc}
889	>	*/
890	>	public boolean removeIf(Predicate<? super E> filter) {
891	>	Objects.requireNonNull(filter);
892	>	return bulkRemove(filter);
893	>	}
894	>
895	>	/**
896	>	* @throws NullPointerException {@inheritDoc}
897	>	*/
898	>	public boolean removeAll(Collection<?> c) {
899	>	Objects.requireNonNull(c);
900	>	return bulkRemove(e -> c.contains(e));
901	>	}
902	>
903	>	/**
904	>	* @throws NullPointerException {@inheritDoc}
905	>	*/
906	>	public boolean retainAll(Collection<?> c) {
907	>	Objects.requireNonNull(c);
908	>	return bulkRemove(e -> !c.contains(e));
909	>	}
910	>
911	>	// A tiny bit set implementation
912	>
913	>	private static long[] nBits(int n) {
914	>	return new long[((n - 1) >> 6) + 1];
915	>	}
916	>	private static void setBit(long[] bits, int i) {
917	>	bits[i >> 6] |= 1L << i;
918	>	}
919	>	private static boolean isClear(long[] bits, int i) {
920	>	return (bits[i >> 6] & (1L << i)) == 0;
921	>	}
922	>
923	>	/** Implementation of bulk remove methods. */
924	>	private boolean bulkRemove(Predicate<? super E> filter) {
925	>	final int expectedModCount = ++modCount;
926	>	final Object[] es = queue;
927	>	final int end = size;
928	>	int i;
929	>	// Optimize for initial run of survivors
930	>	for (i = 0; i < end && !filter.test((E) es[i]); i++)
931	>	;
932	>	if (i >= end) {
933	>	if (modCount != expectedModCount)
934	>	throw new ConcurrentModificationException();
935	>	return false;
936		}
937	+	// Tolerate predicates that reentrantly access the collection for
938	+	// read (but writers still get CME), so traverse once to find
939	+	// elements to delete, a second pass to physically expunge.
940	+	final int beg = i;
941	+	final long[] deathRow = nBits(end - beg);
942	+	deathRow[0] = 1L;   // set bit 0
943	+	for (i = beg + 1; i < end; i++)
944	+	if (filter.test((E) es[i]))
945	+	setBit(deathRow, i - beg);
946	+	if (modCount != expectedModCount)
947	+	throw new ConcurrentModificationException();
948	+	int w = beg;
949	+	for (i = beg; i < end; i++)
950	+	if (isClear(deathRow, i - beg))
951	+	es[w++] = es[i];
952	+	for (i = size = w; i < end; i++)
953	+	es[i] = null;
954	+	heapify();
955	+	return true;
956		}
957
958		/**
959	<	* Returns the comparator associated with this priority queue, or
410	<	* <tt>null</tt> if it uses its elements' natural ordering.
411	<	*
412	<	* @return the comparator associated with this priority queue, or
413	<	*         <tt>null</tt> if it uses its elements' natural ordering.
959	>	* @throws NullPointerException {@inheritDoc}
960		*/
961	<	Comparator comparator() {
962	<	return comparator;
961	>	public void forEach(Consumer<? super E> action) {
962	>	Objects.requireNonNull(action);
963	>	final int expectedModCount = modCount;
964	>	final Object[] es = queue;
965	>	for (int i = 0, n = size; i < n; i++)
966	>	action.accept((E) es[i]);
967	>	if (expectedModCount != modCount)
968	>	throw new ConcurrentModificationException();
969		}
970		}

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