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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.9 by dl, Sun Jul 13 22:51:22 2003 UTC vs.
Revision 1.122 by jsr166, Sun May 6 02:08:36 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		public class PriorityQueue<E> extends AbstractQueue<E>
85	<	implements Queue<E>,
86	<	java.io.Serializable {
85	>	implements java.io.Serializable {
86	>
87	>	private static final long serialVersionUID = -7720805057305804111L;
88	>
89		private static final int DEFAULT_INITIAL_CAPACITY = 11;
90
91		/**
92	<	* Priority queue represented as a balanced binary heap: the two children
93	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
94	<	* ordered by comparator, or by the elements' natural ordering, if
95	<	* comparator is null:  For each node n in the heap and each descendant d
96	<	* of n, n <= d.
97	<	*
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.
92	>	* Priority queue represented as a balanced binary heap: the two
93	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
94	>	* priority queue is ordered by comparator, or by the elements'
95	>	* natural ordering, if comparator is null: For each node n in the
96	>	* heap and each descendant d of n, n <= d.  The element with the
97	>	* lowest value is in queue[0], assuming the queue is nonempty.
98		*/
99	<	private transient E[] queue;
99	>	transient Object[] queue; // non-private to simplify nested class access
100
101		/**
102		* The number of elements in the priority queue.
103		*/
104	<	private int size = 0;
104	>	int size;
105
106		/**
107		* The comparator, or null if priority queue uses elements'
108		* natural ordering.
109		*/
110	<	private final Comparator<E> comparator;
110	>	private final Comparator<? super E> comparator;
111
112		/**
113		* The number of times this priority queue has been
114		* <i>structurally modified</i>.  See AbstractList for gory details.
115		*/
116	<	private transient int modCount = 0;
116	>	transient int modCount;     // non-private to simplify nested class access
117
118		/**
119	<	* Create a new priority queue with the default initial capacity
120	<	* (11) that orders its elements according to their natural
121	<	* ordering (using <tt>Comparable</tt>.)
119	>	* Creates a {@code PriorityQueue} with the default initial
120	>	* capacity (11) that orders its elements according to their
121	>	* {@linkplain Comparable natural ordering}.
122		*/
123		public PriorityQueue() {
124	<	this(DEFAULT_INITIAL_CAPACITY);
124	>	this(DEFAULT_INITIAL_CAPACITY, null);
125		}
126
127		/**
128	<	* Create a new priority queue with the specified initial capacity
129	<	* that orders its elements according to their natural ordering
130	<	* (using <tt>Comparable</tt>.)
128	>	* Creates a {@code PriorityQueue} with the specified initial
129	>	* capacity that orders its elements according to their
130	>	* {@linkplain Comparable natural ordering}.
131		*
132	<	* @param initialCapacity the initial capacity for this priority queue.
132	>	* @param initialCapacity the initial capacity for this priority queue
133	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
134	>	*         than 1
135		*/
136		public PriorityQueue(int initialCapacity) {
137		this(initialCapacity, null);
138		}
139
140		/**
141	<	* Create a new priority queue with the specified initial capacity (11)
142	<	* that orders its elements according to the specified comparator.
141	>	* Creates a {@code PriorityQueue} with the default initial capacity and
142	>	* whose elements are ordered according to the specified comparator.
143		*
144	<	* @param initialCapacity the initial capacity for this priority queue.
145	<	* @param comparator the comparator used to order this priority queue.
144	>	* @param  comparator the comparator that will be used to order this
145	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
146	>	*         natural ordering} of the elements will be used.
147	>	* @since 1.8
148		*/
149	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
149	>	public PriorityQueue(Comparator<? super E> comparator) {
150	>	this(DEFAULT_INITIAL_CAPACITY, comparator);
151	>	}
152	>
153	>	/**
154	>	* Creates a {@code PriorityQueue} with the specified initial capacity
155	>	* that orders its elements according to the specified comparator.
156	>	*
157	>	* @param  initialCapacity the initial capacity for this priority queue
158	>	* @param  comparator the comparator that will be used to order this
159	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
160	>	*         natural ordering} of the elements will be used.
161	>	* @throws IllegalArgumentException if {@code initialCapacity} is
162	>	*         less than 1
163	>	*/
164	>	public PriorityQueue(int initialCapacity,
165	>	Comparator<? super E> comparator) {
166	>	// Note: This restriction of at least one is not actually needed,
167	>	// but continues for 1.5 compatibility
168		if (initialCapacity < 1)
169	<	initialCapacity = 1;
170	<	queue = new E[initialCapacity + 1];
169	>	throw new IllegalArgumentException();
170	>	this.queue = new Object[initialCapacity];
171		this.comparator = comparator;
172		}
173
174		/**
175	<	* Create a new priority queue containing the elements in the specified
176	<	* collection.  The priority queue has an initial capacity of 110% of the
177	<	* size of the specified collection. If the specified collection
178	<	* implements the {@link Sorted} interface, the priority queue will be
179	<	* sorted according to the same comparator, or according to its elements'
180	<	* 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.
175	>	* Creates a {@code PriorityQueue} containing the elements in the
176	>	* specified collection.  If the specified collection is an instance of
177	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
178	>	* priority queue will be ordered according to the same ordering.
179	>	* Otherwise, this priority queue will be ordered according to the
180	>	* {@linkplain Comparable natural ordering} of its elements.
181		*
182	<	* @param initialElements the collection whose elements are to be placed
183	<	*        into this priority queue.
182	>	* @param  c the collection whose elements are to be placed
183	>	*         into this priority queue
184		* @throws ClassCastException if elements of the specified collection
185		*         cannot be compared to one another according to the priority
186	<	*         queue's ordering.
187	<	* @throws NullPointerException if the specified collection or an
188	<	*         element of the specified collection is <tt>null</tt>.
189	<	*/
190	<	public PriorityQueue(Collection<E> initialElements) {
191	<	int sz = initialElements.size();
192	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
193	<	Integer.MAX_VALUE - 1);
194	<	if (initialCapacity < 1)
195	<	initialCapacity = 1;
196	<	queue = new E[initialCapacity + 1];
186	>	*         queue's ordering
187	>	* @throws NullPointerException if the specified collection or any
188	>	*         of its elements are null
189	>	*/
190	>	@SuppressWarnings("unchecked")
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	+	@SuppressWarnings("unchecked")
223	+	public PriorityQueue(PriorityQueue<? extends E> c) {
224	+	this.comparator = (Comparator<? super E>) c.comparator();
225	+	initFromPriorityQueue(c);
226	+	}
227
228	<	if (initialElements instanceof Sorted) {
229	<	comparator = ((Sorted)initialElements).comparator();
230	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
231	<	queue[++size] = i.next();
228	>	/**
229	>	* Creates a {@code PriorityQueue} containing the elements in the
230	>	* specified sorted set.   This priority queue will be ordered
231	>	* according to the same ordering as the given sorted set.
232	>	*
233	>	* @param  c the sorted set whose elements are to be placed
234	>	*         into this priority queue
235	>	* @throws ClassCastException if elements of the specified sorted
236	>	*         set cannot be compared to one another according to the
237	>	*         sorted set's ordering
238	>	* @throws NullPointerException if the specified sorted set or any
239	>	*         of its elements are null
240	>	*/
241	>	@SuppressWarnings("unchecked")
242	>	public PriorityQueue(SortedSet<? extends E> c) {
243	>	this.comparator = (Comparator<? super E>) c.comparator();
244	>	initElementsFromCollection(c);
245	>	}
246	>
247	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
248	>	if (c.getClass() == PriorityQueue.class) {
249	>	this.queue = c.toArray();
250	>	this.size = c.size();
251		} else {
252	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
252	>	initFromCollection(c);
253		}
254		}
255
256	<	// Queue Methods
256	>	private void initElementsFromCollection(Collection<? extends E> c) {
257	>	Object[] a = c.toArray();
258	>	// If c.toArray incorrectly doesn't return Object[], copy it.
259	>	if (a.getClass() != Object[].class)
260	>	a = Arrays.copyOf(a, a.length, Object[].class);
261	>	int len = a.length;
262	>	if (len == 1 || this.comparator != null)
263	>	for (Object e : a)
264	>	if (e == null)
265	>	throw new NullPointerException();
266	>	this.queue = a;
267	>	this.size = a.length;
268	>	}
269
270		/**
271	<	* 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.
271	>	* Initializes queue array with elements from the given Collection.
272		*
273	<	* @return the minimal element from this priority queue if it contains
152	<	*         one or more elements, otherwise <tt>null</tt>.
273	>	* @param c the collection
274		*/
275	<	public E poll() {
276	<	if (size == 0)
277	<	return null;
278	<	return remove(1);
275	>	private void initFromCollection(Collection<? extends E> c) {
276	>	initElementsFromCollection(c);
277	>	heapify();
278	>	}
279	>
280	>	/**
281	>	* The maximum size of array to allocate.
282	>	* Some VMs reserve some header words in an array.
283	>	* Attempts to allocate larger arrays may result in
284	>	* OutOfMemoryError: Requested array size exceeds VM limit
285	>	*/
286	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
287	>
288	>	/**
289	>	* Increases the capacity of the array.
290	>	*
291	>	* @param minCapacity the desired minimum capacity
292	>	*/
293	>	private void grow(int minCapacity) {
294	>	int oldCapacity = queue.length;
295	>	// Double size if small; else grow by 50%
296	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
297	>	(oldCapacity + 2) :
298	>	(oldCapacity >> 1));
299	>	// overflow-conscious code
300	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
301	>	newCapacity = hugeCapacity(minCapacity);
302	>	queue = Arrays.copyOf(queue, newCapacity);
303	>	}
304	>
305	>	private static int hugeCapacity(int minCapacity) {
306	>	if (minCapacity < 0) // overflow
307	>	throw new OutOfMemoryError();
308	>	return (minCapacity > MAX_ARRAY_SIZE) ?
309	>	Integer.MAX_VALUE :
310	>	MAX_ARRAY_SIZE;
311	>	}
312	>
313	>	/**
314	>	* Inserts the specified element into this priority queue.
315	>	*
316	>	* @return {@code true} (as specified by {@link Collection#add})
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 add(E e) {
323	>	return offer(e);
324		}
325
326		/**
327	<	* 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.
327	>	* Inserts the specified element into this priority queue.
328		*
329	<	* @return the minimal element from this priority queue if it contains
330	<	*         one or more elements, otherwise <tt>null</tt>.
329	>	* @return {@code true} (as specified by {@link Queue#offer})
330	>	* @throws ClassCastException if the specified element cannot be
331	>	*         compared with elements currently in this priority queue
332	>	*         according to the priority queue's ordering
333	>	* @throws NullPointerException if the specified element is null
334		*/
335	+	public boolean offer(E e) {
336	+	if (e == null)
337	+	throw new NullPointerException();
338	+	modCount++;
339	+	int i = size;
340	+	if (i >= queue.length)
341	+	grow(i + 1);
342	+	siftUp(i, e);
343	+	size = i + 1;
344	+	return true;
345	+	}
346	+
347	+	@SuppressWarnings("unchecked")
348		public E peek() {
349	<	return queue[1];
349	>	return (size == 0) ? null : (E) queue[0];
350		}
351
352	<	// Collection Methods
352	>	private int indexOf(Object o) {
353	>	if (o != null) {
354	>	for (int i = 0; i < size; i++)
355	>	if (o.equals(queue[i]))
356	>	return i;
357	>	}
358	>	return -1;
359	>	}
360
361		/**
362	<	* Removes a single instance of the specified element from this priority
363	<	* queue, if it is present.  Returns true if this collection contained the
364	<	* specified element (or equivalently, if this collection changed as a
362	>	* Removes a single instance of the specified element from this queue,
363	>	* if it is present.  More formally, removes an element {@code e} such
364	>	* that {@code o.equals(e)}, if this queue contains one or more such
365	>	* elements.  Returns {@code true} if and only if this queue contained
366	>	* the specified element (or equivalently, if this queue changed as a
367		* result of the call).
368		*
369	<	* @param element the element to be removed from this collection,
370	<	* 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.
369	>	* @param o element to be removed from this queue, if present
370	>	* @return {@code true} if this queue changed as a result of the call
371		*/
372	<	public boolean remove(Object element) {
373	<	if (element == null)
374	<	throw new NullPointerException();
372	>	public boolean remove(Object o) {
373	>	int i = indexOf(o);
374	>	if (i == -1)
375	>	return false;
376	>	else {
377	>	removeAt(i);
378	>	return true;
379	>	}
380	>	}
381
382	<	if (comparator == null) {
383	<	for (int i = 1; i <= size; i++) {
384	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
385	<	remove(i);
386	<	return true;
387	<	}
388	<	}
389	<	} else {
390	<	for (int i = 1; i <= size; i++) {
391	<	if (comparator.compare(queue[i], (E) element) == 0) {
392	<	remove(i);
393	<	return true;
209	<	}
382	>	/**
383	>	* Version of remove using reference equality, not equals.
384	>	* Needed by iterator.remove.
385	>	*
386	>	* @param o element to be removed from this queue, if present
387	>	* @return {@code true} if removed
388	>	*/
389	>	boolean removeEq(Object o) {
390	>	for (int i = 0; i < size; i++) {
391	>	if (o == queue[i]) {
392	>	removeAt(i);
393	>	return true;
394		}
395		}
396		return false;
397		}
398
399		/**
400	<	* Returns an iterator over the elements in this priority queue.  The
401	<	* elements of the priority queue will be returned by this iterator in the
402	<	* order specified by the queue, which is to say the order they would be
403	<	* returned by repeated calls to <tt>poll</tt>.
404	<	*
405	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
400	>	* Returns {@code true} if this queue contains the specified element.
401	>	* More formally, returns {@code true} if and only if this queue contains
402	>	* at least one element {@code e} such that {@code o.equals(e)}.
403	>	*
404	>	* @param o object to be checked for containment in this queue
405	>	* @return {@code true} if this queue contains the specified element
406	>	*/
407	>	public boolean contains(Object o) {
408	>	return indexOf(o) >= 0;
409	>	}
410	>
411	>	/**
412	>	* Returns an array containing all of the elements in this queue.
413	>	* The elements are in no particular order.
414	>	*
415	>	* <p>The returned array will be "safe" in that no references to it are
416	>	* maintained by this queue.  (In other words, this method must allocate
417	>	* a new array).  The caller is thus free to modify the returned array.
418	>	*
419	>	* <p>This method acts as bridge between array-based and collection-based
420	>	* APIs.
421	>	*
422	>	* @return an array containing all of the elements in this queue
423	>	*/
424	>	public Object[] toArray() {
425	>	return Arrays.copyOf(queue, size);
426	>	}
427	>
428	>	/**
429	>	* Returns an array containing all of the elements in this queue; the
430	>	* runtime type of the returned array is that of the specified array.
431	>	* The returned array elements are in no particular order.
432	>	* If the queue fits in the specified array, it is returned therein.
433	>	* Otherwise, a new array is allocated with the runtime type of the
434	>	* specified array and the size of this queue.
435	>	*
436	>	* <p>If the queue fits in the specified array with room to spare
437	>	* (i.e., the array has more elements than the queue), the element in
438	>	* the array immediately following the end of the collection is set to
439	>	* {@code null}.
440	>	*
441	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
442	>	* array-based and collection-based APIs.  Further, this method allows
443	>	* precise control over the runtime type of the output array, and may,
444	>	* under certain circumstances, be used to save allocation costs.
445	>	*
446	>	* <p>Suppose {@code x} is a queue known to contain only strings.
447	>	* The following code can be used to dump the queue into a newly
448	>	* allocated array of {@code String}:
449	>	*
450	>	* <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
451	>	*
452	>	* Note that {@code toArray(new Object[0])} is identical in function to
453	>	* {@code toArray()}.
454	>	*
455	>	* @param a the array into which the elements of the queue are to
456	>	*          be stored, if it is big enough; otherwise, a new array of the
457	>	*          same runtime type is allocated for this purpose.
458	>	* @return an array containing all of the elements in this queue
459	>	* @throws ArrayStoreException if the runtime type of the specified array
460	>	*         is not a supertype of the runtime type of every element in
461	>	*         this queue
462	>	* @throws NullPointerException if the specified array is null
463	>	*/
464	>	@SuppressWarnings("unchecked")
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,
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 = -1;
499
500		/**
501	<	* Index of element returned by most recent call to next or
502	<	* previous.  Reset to 0 if this element is deleted by a call
503	<	* to remove.
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 int lastRet = 0;
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	+	@SuppressWarnings("unchecked")
534		public E next() {
535	<	checkForComodification();
536	<	if (cursor > size)
537	<	throw new NoSuchElementException();
538	<	E result = queue[cursor];
539	<	lastRet = cursor++;
540	<	return result;
535	>	if (expectedModCount != modCount)
536	>	throw new ConcurrentModificationException();
537	>	if (cursor < size)
538	>	return (E) queue[lastRet = cursor++];
539	>	if (forgetMeNot != null) {
540	>	lastRet = -1;
541	>	lastRetElt = forgetMeNot.poll();
542	>	if (lastRetElt != null)
543	>	return lastRetElt;
544	>	}
545	>	throw new NoSuchElementException();
546		}
547
548		public void remove() {
549	<	if (lastRet == 0)
549	>	if (expectedModCount != modCount)
550	>	throw new ConcurrentModificationException();
551	>	if (lastRet != -1) {
552	>	E moved = PriorityQueue.this.removeAt(lastRet);
553	>	lastRet = -1;
554	>	if (moved == null)
555	>	cursor--;
556	>	else {
557	>	if (forgetMeNot == null)
558	>	forgetMeNot = new ArrayDeque<>();
559	>	forgetMeNot.add(moved);
560	>	}
561	>	} else if (lastRetElt != null) {
562	>	PriorityQueue.this.removeEq(lastRetElt);
563	>	lastRetElt = null;
564	>	} else {
565		throw new IllegalStateException();
566	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
566	>	}
567		expectedModCount = modCount;
568		}
272	–
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
569		}
570
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
571		public int size() {
572		return size;
573		}
574
575		/**
576	<	* Add the specified element to this priority queue.
577	<	*
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.
576	>	* Removes all of the elements from this priority queue.
577	>	* The queue will be empty after this call returns.
578		*/
579	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
579	>	public void clear() {
580		modCount++;
581	<	++size;
582	<
583	<	// Grow backing store if necessary
584	<	while (size >= queue.length) {
306	<	E[] newQueue = new E[2 * queue.length];
307	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
308	<	queue = newQueue;
309	<	}
581	>	for (int i = 0; i < size; i++)
582	>	queue[i] = null;
583	>	size = 0;
584	>	}
585
586	<	queue[size] = element;
587	<	fixUp(size);
588	<	return true;
586	>	@SuppressWarnings("unchecked")
587	>	public E poll() {
588	>	if (size == 0)
589	>	return null;
590	>	int s = --size;
591	>	modCount++;
592	>	E result = (E) queue[0];
593	>	E x = (E) queue[s];
594	>	queue[s] = null;
595	>	if (s != 0)
596	>	siftDown(0, x);
597	>	return result;
598		}
599
600		/**
601	<	* Remove all elements from the priority queue.
602	<	*/
603	<	public void clear() {
601	>	* Removes the ith element from queue.
602	>	*
603	>	* Normally this method leaves the elements at up to i-1,
604	>	* inclusive, untouched.  Under these circumstances, it returns
605	>	* null.  Occasionally, in order to maintain the heap invariant,
606	>	* it must swap a later element of the list with one earlier than
607	>	* i.  Under these circumstances, this method returns the element
608	>	* that was previously at the end of the list and is now at some
609	>	* position before i. This fact is used by iterator.remove so as to
610	>	* avoid missing traversing elements.
611	>	*/
612	>	@SuppressWarnings("unchecked")
613	>	E removeAt(int i) {
614	>	// assert i >= 0 && i < size;
615		modCount++;
616	<
617	<	// Null out element references to prevent memory leak
323	<	for (int i=1; i<=size; i++)
616	>	int s = --size;
617	>	if (s == i) // removed last element
618		queue[i] = null;
619	<
620	<	size = 0;
619	>	else {
620	>	E moved = (E) queue[s];
621	>	queue[s] = null;
622	>	siftDown(i, moved);
623	>	if (queue[i] == moved) {
624	>	siftUp(i, moved);
625	>	if (queue[i] != moved)
626	>	return moved;
627	>	}
628	>	}
629	>	return null;
630		}
631
632		/**
633	<	* Removes and returns the ith element from queue.  Recall
634	<	* that queue is one-based, so 1 <= i <= size.
635	<	*
636	<	* XXX: Could further special-case i==size, but is it worth it?
637	<	* XXX: Could special-case i==0, but is it worth it?
638	<	*/
639	<	private E remove(int i) {
640	<	assert i <= size;
641	<	modCount++;
633	>	* Inserts item x at position k, maintaining heap invariant by
634	>	* promoting x up the tree until it is greater than or equal to
635	>	* its parent, or is the root.
636	>	*
637	>	* To simplify and speed up coercions and comparisons, the
638	>	* Comparable and Comparator versions are separated into different
639	>	* methods that are otherwise identical. (Similarly for siftDown.)
640	>	*
641	>	* @param k the position to fill
642	>	* @param x the item to insert
643	>	*/
644	>	private void siftUp(int k, E x) {
645	>	if (comparator != null)
646	>	siftUpUsingComparator(k, x);
647	>	else
648	>	siftUpComparable(k, x);
649	>	}
650	>
651	>	@SuppressWarnings("unchecked")
652	>	private void siftUpComparable(int k, E x) {
653	>	Comparable<? super E> key = (Comparable<? super E>) x;
654	>	while (k > 0) {
655	>	int parent = (k - 1) >>> 1;
656	>	Object e = queue[parent];
657	>	if (key.compareTo((E) e) >= 0)
658	>	break;
659	>	queue[k] = e;
660	>	k = parent;
661	>	}
662	>	queue[k] = key;
663	>	}
664
665	<	E result = queue[i];
666	<	queue[i] = queue[size];
667	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
668	<	if (i <= size)
669	<	fixDown(i);
670	<	return result;
665	>	@SuppressWarnings("unchecked")
666	>	private void siftUpUsingComparator(int k, E x) {
667	>	while (k > 0) {
668	>	int parent = (k - 1) >>> 1;
669	>	Object e = queue[parent];
670	>	if (comparator.compare(x, (E) e) >= 0)
671	>	break;
672	>	queue[k] = e;
673	>	k = parent;
674	>	}
675	>	queue[k] = x;
676		}
677
678		/**
679	<	* Establishes the heap invariant (described above) assuming the heap
680	<	* satisfies the invariant except possibly for the leaf-node indexed by k
681	<	* (which may have a nextExecutionTime less than its parent's).
682	<	*
683	<	* This method functions by "promoting" queue[k] up the hierarchy
684	<	* (by swapping it with its parent) repeatedly until queue[k]
685	<	* is greater than or equal to its parent.
686	<	*/
687	<	private void fixUp(int k) {
688	<	if (comparator == null) {
689	<	while (k > 1) {
690	<	int j = k >> 1;
691	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
692	<	break;
693	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
694	<	k = j;
695	<	}
696	<	} else {
697	<	while (k > 1) {
698	<	int j = k >> 1;
699	<	if (comparator.compare(queue[j], queue[k]) <= 0)
700	<	break;
701	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
702	<	k = j;
703	<	}
679	>	* Inserts item x at position k, maintaining heap invariant by
680	>	* demoting x down the tree repeatedly until it is less than or
681	>	* equal to its children or is a leaf.
682	>	*
683	>	* @param k the position to fill
684	>	* @param x the item to insert
685	>	*/
686	>	private void siftDown(int k, E x) {
687	>	if (comparator != null)
688	>	siftDownUsingComparator(k, x);
689	>	else
690	>	siftDownComparable(k, x);
691	>	}
692	>
693	>	@SuppressWarnings("unchecked")
694	>	private void siftDownComparable(int k, E x) {
695	>	Comparable<? super E> key = (Comparable<? super E>)x;
696	>	int half = size >>> 1;        // loop while a non-leaf
697	>	while (k < half) {
698	>	int child = (k << 1) + 1; // assume left child is least
699	>	Object c = queue[child];
700	>	int right = child + 1;
701	>	if (right < size &&
702	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
703	>	c = queue[child = right];
704	>	if (key.compareTo((E) c) <= 0)
705	>	break;
706	>	queue[k] = c;
707	>	k = child;
708		}
709	+	queue[k] = key;
710		}
711
712	<	/**
713	<	* Establishes the heap invariant (described above) in the subtree
714	<	* rooted at k, which is assumed to satisfy the heap invariant except
715	<	* possibly for node k itself (which may be greater than its children).
716	<	*
717	<	* This method functions by "demoting" queue[k] down the hierarchy
718	<	* (by swapping it with its smaller child) repeatedly until queue[k]
719	<	* is less than or equal to its children.
720	<	*/
721	<	private void fixDown(int k) {
722	<	int j;
723	<	if (comparator == null) {
724	<	while ((j = k << 1) <= size) {
725	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
391	<	j++; // j indexes smallest kid
392	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
393	<	break;
394	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
395	<	k = j;
396	<	}
397	<	} else {
398	<	while ((j = k << 1) <= size) {
399	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
400	<	j++; // j indexes smallest kid
401	<	if (comparator.compare(queue[k], queue[j]) <= 0)
402	<	break;
403	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
404	<	k = j;
405	<	}
712	>	@SuppressWarnings("unchecked")
713	>	private void siftDownUsingComparator(int k, E x) {
714	>	int half = size >>> 1;
715	>	while (k < half) {
716	>	int child = (k << 1) + 1;
717	>	Object c = queue[child];
718	>	int right = child + 1;
719	>	if (right < size &&
720	>	comparator.compare((E) c, (E) queue[right]) > 0)
721	>	c = queue[child = right];
722	>	if (comparator.compare(x, (E) c) <= 0)
723	>	break;
724	>	queue[k] = c;
725	>	k = child;
726		}
727	+	queue[k] = x;
728		}
729
730		/**
731	<	* Returns the comparator associated with this priority queue, or
732	<	* <tt>null</tt> if it uses its elements' natural ordering.
731	>	* Establishes the heap invariant (described above) in the entire tree,
732	>	* assuming nothing about the order of the elements prior to the call.
733	>	* This classic algorithm due to Floyd (1964) is known to be O(size).
734	>	*/
735	>	@SuppressWarnings("unchecked")
736	>	private void heapify() {
737	>	final Object[] es = queue;
738	>	int i = (size >>> 1) - 1;
739	>	if (comparator == null)
740	>	for (; i >= 0; i--)
741	>	siftDownComparable(i, (E) es[i]);
742	>	else
743	>	for (; i >= 0; i--)
744	>	siftDownUsingComparator(i, (E) es[i]);
745	>	}
746	>
747	>	/**
748	>	* Returns the comparator used to order the elements in this
749	>	* queue, or {@code null} if this queue is sorted according to
750	>	* the {@linkplain Comparable natural ordering} of its elements.
751		*
752	<	* @return the comparator associated with this priority queue, or
753	<	*         <tt>null</tt> if it uses its elements' natural ordering.
752	>	* @return the comparator used to order this queue, or
753	>	*         {@code null} if this queue is sorted according to the
754	>	*         natural ordering of its elements
755		*/
756	<	public Comparator comparator() {
756	>	public Comparator<? super E> comparator() {
757		return comparator;
758		}
759
760		/**
761	<	* Save the state of the instance to a stream (that
422	<	* is, serialize it).
761	>	* Saves this queue to a stream (that is, serializes it).
762		*
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.
763		* @param s the stream
764	+	* @throws java.io.IOException if an I/O error occurs
765	+	* @serialData The length of the array backing the instance is
766	+	*             emitted (int), followed by all of its elements
767	+	*             (each an {@code Object}) in the proper order.
768		*/
769	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
770	<	throws java.io.IOException{
769	>	private void writeObject(java.io.ObjectOutputStream s)
770	>	throws java.io.IOException {
771		// Write out element count, and any hidden stuff
772		s.defaultWriteObject();
773
774	<	// Write out array length
775	<	s.writeInt(queue.length);
774	>	// Write out array length, for compatibility with 1.5 version
775	>	s.writeInt(Math.max(2, size + 1));
776
777	<	// Write out all elements in the proper order.
778	<	for (int i=0; i<size; i++)
777	>	// Write out all elements in the "proper order".
778	>	for (int i = 0; i < size; i++)
779		s.writeObject(queue[i]);
780		}
781
782		/**
783	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
784	<	* deserialize it).
783	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
784	>	* (that is, deserializes it).
785	>	*
786		* @param s the stream
787	+	* @throws ClassNotFoundException if the class of a serialized object
788	+	*         could not be found
789	+	* @throws java.io.IOException if an I/O error occurs
790		*/
791	<	private synchronized void readObject(java.io.ObjectInputStream s)
791	>	private void readObject(java.io.ObjectInputStream s)
792		throws java.io.IOException, ClassNotFoundException {
793		// Read in size, and any hidden stuff
794		s.defaultReadObject();
795
796	<	// Read in array length and allocate array
797	<	int arrayLength = s.readInt();
798	<	queue = new E[arrayLength];
799	<
800	<	// Read in all elements in the proper order.
801	<	for (int i=0; i<size; i++)
802	<	queue[i] = (E)s.readObject();
796	>	// Read in (and discard) array length
797	>	s.readInt();
798	>
799	>	SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
800	>	queue = new Object[size];
801	>
802	>	// Read in all elements.
803	>	for (int i = 0; i < size; i++)
804	>	queue[i] = s.readObject();
805	>
806	>	// Elements are guaranteed to be in "proper order", but the
807	>	// spec has never explained what that might be.
808	>	heapify();
809	>	}
810	>
811	>	/**
812	>	* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
813	>	* and <em>fail-fast</em> {@link Spliterator} over the elements in this
814	>	* queue. The spliterator does not traverse elements in any particular order
815	>	* (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
816	>	*
817	>	* <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
818	>	* {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
819	>	* Overriding implementations should document the reporting of additional
820	>	* characteristic values.
821	>	*
822	>	* @return a {@code Spliterator} over the elements in this queue
823	>	* @since 1.8
824	>	*/
825	>	public final Spliterator<E> spliterator() {
826	>	return new PriorityQueueSpliterator(0, -1, 0);
827	>	}
828	>
829	>	final class PriorityQueueSpliterator implements Spliterator<E> {
830	>	private int index;            // current index, modified on advance/split
831	>	private int fence;            // -1 until first use
832	>	private int expectedModCount; // initialized when fence set
833	>
834	>	/** Creates new spliterator covering the given range. */
835	>	PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
836	>	this.index = origin;
837	>	this.fence = fence;
838	>	this.expectedModCount = expectedModCount;
839	>	}
840	>
841	>	private int getFence() { // initialize fence to size on first use
842	>	int hi;
843	>	if ((hi = fence) < 0) {
844	>	expectedModCount = modCount;
845	>	hi = fence = size;
846	>	}
847	>	return hi;
848	>	}
849	>
850	>	public PriorityQueueSpliterator trySplit() {
851	>	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
852	>	return (lo >= mid) ? null :
853	>	new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
854	>	}
855	>
856	>	@SuppressWarnings("unchecked")
857	>	public void forEachRemaining(Consumer<? super E> action) {
858	>	if (action == null)
859	>	throw new NullPointerException();
860	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
861	>	final Object[] a = queue;
862	>	int i, hi; E e;
863	>	for (i = index, index = hi = fence; i < hi; i++) {
864	>	if ((e = (E) a[i]) == null)
865	>	break;      // must be CME
866	>	action.accept(e);
867	>	}
868	>	if (modCount != expectedModCount)
869	>	throw new ConcurrentModificationException();
870	>	}
871	>
872	>	@SuppressWarnings("unchecked")
873	>	public boolean tryAdvance(Consumer<? super E> action) {
874	>	if (action == null)
875	>	throw new NullPointerException();
876	>	if (fence < 0) { fence = size; expectedModCount = modCount; }
877	>	int i;
878	>	if ((i = index) < fence) {
879	>	index = i + 1;
880	>	E e;
881	>	if ((e = (E) queue[i]) == null
882	>	|| modCount != expectedModCount)
883	>	throw new ConcurrentModificationException();
884	>	action.accept(e);
885	>	return true;
886	>	}
887	>	return false;
888	>	}
889	>
890	>	public long estimateSize() {
891	>	return getFence() - index;
892	>	}
893	>
894	>	public int characteristics() {
895	>	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
896	>	}
897		}
898
899	+	/**
900	+	* @throws NullPointerException {@inheritDoc}
901	+	*/
902	+	@SuppressWarnings("unchecked")
903	+	public void forEach(Consumer<? super E> action) {
904	+	Objects.requireNonNull(action);
905	+	final int expectedModCount = modCount;
906	+	final Object[] es = queue;
907	+	for (int i = 0, n = size; i < n; i++)
908	+	action.accept((E) es[i]);
909	+	if (expectedModCount != modCount)
910	+	throw new ConcurrentModificationException();
911	+	}
912		}

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