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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.12 by dl, Mon Jul 28 09:40:07 2003 UTC vs.
Revision 1.100 by jsr166, Fri Aug 29 21:42:37 2014 UTC

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1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2012, 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	>	import java.util.function.Consumer;
28	>	import java.util.stream.Stream;
29
30		/**
31	<	* An unbounded priority queue based on a priority heap.  This queue orders
32	<	* elements according to an order specified at construction time, which is
33	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}:
34	<	* 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 <em>head</em> of this queue is the least element with respect to the
38	<	* specified ordering. If multiple elements are tied for least value, the
39	<	* head is one of those elements. A priority queue does not permit
40	<	* <tt>null</tt> elements.
41	<	*
42	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and
43	<	* return the head of the queue.
44	<	*
45	<	* <p>The {@link #element()} and {@link #peek()} methods return, but do
46	<	* not delete, the head of the queue.
47	<	*
48	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
49	<	* size of the array used internally to store the elements on the
50	<	* queue.  It is always at least as large as the queue size.  As
51	<	* elements are added to a priority queue, its capacity grows
52	<	* automatically.  The details of the growth policy are not specified.
53	<	*
54	<	* <p>Implementation note: this implementation provides O(log(n)) time
55	<	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
56	<	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
57	<	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
58	<	* constant time for the retrieval methods (<tt>peek</tt>,
59	<	* <tt>element</tt>, and <tt>size</tt>).
31	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
32	>	* The elements of the priority queue are ordered according to their
33	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
34	>	* provided at queue construction time, depending on which constructor is
35	>	* used.  A priority queue does not permit {@code null} elements.
36	>	* A priority queue relying on natural ordering also does not permit
37	>	* insertion of non-comparable objects (doing so may result in
38	>	* {@code ClassCastException}).
39	>	*
40	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
41	>	* with respect to the specified ordering.  If multiple elements are
42	>	* tied for least value, the head is one of those elements -- ties are
43	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
44	>	* {@code remove}, {@code peek}, and {@code element} access the
45	>	* element at the head of the queue.
46	>	*
47	>	* <p>A priority queue is unbounded, but has an internal
48	>	* <i>capacity</i> governing the size of an array used to store the
49	>	* elements on the queue.  It is always at least as large as the queue
50	>	* size.  As elements are added to a priority queue, its capacity
51	>	* grows automatically.  The details of the growth policy are not
52	>	* specified.
53	>	*
54	>	* <p>This class and its iterator implement all of the
55	>	* <em>optional</em> methods of the {@link Collection} and {@link
56	>	* Iterator} interfaces.  The Iterator provided in method {@link
57	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
58	>	* the priority queue in any particular order. If you need ordered
59	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
60	>	*
61	>	* <p><strong>Note that this implementation is not synchronized.</strong>
62	>	* Multiple threads should not access a {@code PriorityQueue}
63	>	* instance concurrently if any of the threads modifies the queue.
64	>	* Instead, use the thread-safe {@link
65	>	* java.util.concurrent.PriorityBlockingQueue} class.
66	>	*
67	>	* <p>Implementation note: this implementation provides
68	>	* O(log(n)) time for the enqueuing and dequeuing methods
69	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
70	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
71	>	* methods; and constant time for the retrieval methods
72	>	* ({@code peek}, {@code element}, and {@code size}).
73		*
74		* <p>This class is a member of the
75	<	* <a href="{@docRoot}/../guide/collections/index.html">
75	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
76		* Java Collections Framework</a>.
77	+	*
78		* @since 1.5
79	<	* @author Josh Bloch
79	>	* @author Josh Bloch, Doug Lea
80	>	* @param <E> the type of elements held in this collection
81		*/
82		public class PriorityQueue<E> extends AbstractQueue<E>
83	<	implements Queue<E>, Sorted, java.io.Serializable {
83	>	implements java.io.Serializable {
84	>
85	>	private static final long serialVersionUID = -7720805057305804111L;
86
87		private static final int DEFAULT_INITIAL_CAPACITY = 11;
88
89		/**
90	<	* Priority queue represented as a balanced binary heap: the two children
91	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
92	<	* ordered by comparator, or by the elements' natural ordering, if
93	<	* comparator is null:  For each node n in the heap and each descendant d
94	<	* of n, n <= d.
95	<	*
52	<	* The element with the lowest value is in queue[1], assuming the queue is
53	<	* nonempty.  (A one-based array is used in preference to the traditional
54	<	* zero-based array to simplify parent and child calculations.)
55	<	*
56	<	* queue.length must be >= 2, even if size == 0.
90	>	* Priority queue represented as a balanced binary heap: the two
91	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
92	>	* priority queue is ordered by comparator, or by the elements'
93	>	* natural ordering, if comparator is null: For each node n in the
94	>	* heap and each descendant d of n, n <= d.  The element with the
95	>	* lowest value is in queue[0], assuming the queue is nonempty.
96		*/
97	<	private transient E[] queue;
97	>	transient Object[] queue; // non-private to simplify nested class access
98
99		/**
100		* The number of elements in the priority queue.
101		*/
102	<	private int size = 0;
102	>	private int size;
103
104		/**
105		* The comparator, or null if priority queue uses elements'
106		* natural ordering.
107		*/
108	<	private final Comparator<E> comparator;
108	>	private final Comparator<? super E> comparator;
109
110		/**
111		* The number of times this priority queue has been
112		* <i>structurally modified</i>.  See AbstractList for gory details.
113		*/
114	<	private transient int modCount = 0;
114	>	transient int modCount = 0; // non-private to simplify nested class access
115
116		/**
117	<	* Create a <tt>PriorityQueue</tt> with the default initial capacity
118	<	* (11) that orders its elements according to their natural
119	<	* ordering (using <tt>Comparable</tt>.)
117	>	* Creates a {@code PriorityQueue} with the default initial
118	>	* capacity (11) that orders its elements according to their
119	>	* {@linkplain Comparable natural ordering}.
120		*/
121		public PriorityQueue() {
122		this(DEFAULT_INITIAL_CAPACITY, null);
123		}
124
125		/**
126	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
127	<	* that orders its elements according to their natural ordering
128	<	* (using <tt>Comparable</tt>.)
129	<	*
130	<	* @param initialCapacity the initial capacity for this priority queue.
126	>	* Creates a {@code PriorityQueue} with the specified initial
127	>	* capacity that orders its elements according to their
128	>	* {@linkplain Comparable natural ordering}.
129	>	*
130	>	* @param initialCapacity the initial capacity for this priority queue
131	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
132	>	*         than 1
133		*/
134		public PriorityQueue(int initialCapacity) {
135		this(initialCapacity, null);
136		}
137
138		/**
139	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
139	>	* Creates a {@code PriorityQueue} with the specified initial capacity
140		* that orders its elements according to the specified comparator.
141		*
142	<	* @param initialCapacity the initial capacity for this priority queue.
143	<	* @param comparator the comparator used to order this priority queue.
144	<	* If <tt>null</tt> then the order depends on the elements' natural
145	<	* ordering.
146	<	*/
147	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
142	>	* @param  initialCapacity the initial capacity for this priority queue
143	>	* @param  comparator the comparator that will be used to order this
144	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
145	>	*         natural ordering} of the elements will be used.
146	>	* @throws IllegalArgumentException if {@code initialCapacity} is
147	>	*         less than 1
148	>	*/
149	>	public PriorityQueue(int initialCapacity,
150	>	Comparator<? super E> comparator) {
151	>	// Note: This restriction of at least one is not actually needed,
152	>	// but continues for 1.5 compatibility
153		if (initialCapacity < 1)
154	<	initialCapacity = 1;
155	<	queue = (E[]) new Object[initialCapacity + 1];
154	>	throw new IllegalArgumentException();
155	>	this.queue = new Object[initialCapacity];
156		this.comparator = comparator;
157		}
158
159		/**
160	<	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
161	<	* collection.  The priority queue has an initial capacity of 110% of the
162	<	* size of the specified collection. If the specified collection
163	<	* implements the {@link Sorted} interface, the priority queue will be
164	<	* sorted according to the same comparator, or according to its elements'
165	<	* natural order if the collection is sorted according to its elements'
120	<	* natural order.  If the specified collection does not implement
121	<	* <tt>Sorted</tt>, the priority queue is ordered according to
122	<	* its elements' natural order.
160	>	* Creates a {@code PriorityQueue} containing the elements in the
161	>	* specified collection.  If the specified collection is an instance of
162	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
163	>	* priority queue will be ordered according to the same ordering.
164	>	* Otherwise, this priority queue will be ordered according to the
165	>	* {@linkplain Comparable natural ordering} of its elements.
166		*
167	<	* @param initialElements the collection whose elements are to be placed
168	<	*        into this priority queue.
167	>	* @param  c the collection whose elements are to be placed
168	>	*         into this priority queue
169		* @throws ClassCastException if elements of the specified collection
170		*         cannot be compared to one another according to the priority
171	<	*         queue's ordering.
172	<	* @throws NullPointerException if the specified collection or an
173	<	*         element of the specified collection is <tt>null</tt>.
174	<	*/
175	<	public PriorityQueue(Collection<E> initialElements) {
176	<	int sz = initialElements.size();
177	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
178	<	Integer.MAX_VALUE - 1);
179	<	if (initialCapacity < 1)
180	<	initialCapacity = 1;
181	<	queue = (E[]) new Object[initialCapacity + 1];
171	>	*         queue's ordering
172	>	* @throws NullPointerException if the specified collection or any
173	>	*         of its elements are null
174	>	*/
175	>	@SuppressWarnings("unchecked")
176	>	public PriorityQueue(Collection<? extends E> c) {
177	>	if (c instanceof SortedSet<?>) {
178	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
179	>	this.comparator = (Comparator<? super E>) ss.comparator();
180	>	initElementsFromCollection(ss);
181	>	}
182	>	else if (c instanceof PriorityQueue<?>) {
183	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
184	>	this.comparator = (Comparator<? super E>) pq.comparator();
185	>	initFromPriorityQueue(pq);
186	>	}
187	>	else {
188	>	this.comparator = null;
189	>	initFromCollection(c);
190	>	}
191	>	}
192
193	<	if (initialElements instanceof Sorted) {
194	<	comparator = ((Sorted)initialElements).comparator();
195	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
196	<	queue[++size] = i.next();
193	>	/**
194	>	* Creates a {@code PriorityQueue} containing the elements in the
195	>	* specified priority queue.  This priority queue will be
196	>	* ordered according to the same ordering as the given priority
197	>	* queue.
198	>	*
199	>	* @param  c the priority queue whose elements are to be placed
200	>	*         into this priority queue
201	>	* @throws ClassCastException if elements of {@code c} cannot be
202	>	*         compared to one another according to {@code c}'s
203	>	*         ordering
204	>	* @throws NullPointerException if the specified priority queue or any
205	>	*         of its elements are null
206	>	*/
207	>	@SuppressWarnings("unchecked")
208	>	public PriorityQueue(PriorityQueue<? extends E> c) {
209	>	this.comparator = (Comparator<? super E>) c.comparator();
210	>	initFromPriorityQueue(c);
211	>	}
212	>
213	>	/**
214	>	* Creates a {@code PriorityQueue} containing the elements in the
215	>	* specified sorted set.   This priority queue will be ordered
216	>	* according to the same ordering as the given sorted set.
217	>	*
218	>	* @param  c the sorted set whose elements are to be placed
219	>	*         into this priority queue
220	>	* @throws ClassCastException if elements of the specified sorted
221	>	*         set cannot be compared to one another according to the
222	>	*         sorted set's ordering
223	>	* @throws NullPointerException if the specified sorted set or any
224	>	*         of its elements are null
225	>	*/
226	>	@SuppressWarnings("unchecked")
227	>	public PriorityQueue(SortedSet<? extends E> c) {
228	>	this.comparator = (Comparator<? super E>) c.comparator();
229	>	initElementsFromCollection(c);
230	>	}
231	>
232	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
233	>	if (c.getClass() == PriorityQueue.class) {
234	>	this.queue = c.toArray();
235	>	this.size = c.size();
236		} else {
237	<	comparator = null;
146	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
147	<	add(i.next());
237	>	initFromCollection(c);
238		}
239		}
240
241	<	// Queue Methods
241	>	private void initElementsFromCollection(Collection<? extends E> c) {
242	>	Object[] a = c.toArray();
243	>	// If c.toArray incorrectly doesn't return Object[], copy it.
244	>	if (a.getClass() != Object[].class)
245	>	a = Arrays.copyOf(a, a.length, Object[].class);
246	>	int len = a.length;
247	>	if (len == 1 || this.comparator != null)
248	>	for (int i = 0; i < len; i++)
249	>	if (a[i] == null)
250	>	throw new NullPointerException();
251	>	this.queue = a;
252	>	this.size = a.length;
253	>	}
254
255		/**
256	<	* Add the specified element to this priority queue.
256	>	* Initializes queue array with elements from the given Collection.
257		*
258	<	* @param element the element to add.
157	<	* @return <tt>true</tt>
158	<	* @throws ClassCastException if the specified element cannot be compared
159	<	* with elements currently in the priority queue according
160	<	* to the priority queue's ordering.
161	<	* @throws NullPointerException if the specified element is null.
258	>	* @param c the collection
259		*/
260	<	public boolean offer(E element) {
261	<	if (element == null)
262	<	throw new NullPointerException();
263	<	modCount++;
167	<	++size;
260	>	private void initFromCollection(Collection<? extends E> c) {
261	>	initElementsFromCollection(c);
262	>	heapify();
263	>	}
264
265	<	// Grow backing store if necessary
266	<	while (size >= queue.length) {
267	<	E[] newQueue = (E[]) new Object[2 * queue.length];
268	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
269	<	queue = newQueue;
270	<	}
265	>	/**
266	>	* The maximum size of array to allocate.
267	>	* Some VMs reserve some header words in an array.
268	>	* Attempts to allocate larger arrays may result in
269	>	* OutOfMemoryError: Requested array size exceeds VM limit
270	>	*/
271	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
272
273	<	queue[size] = element;
274	<	fixUp(size);
275	<	return true;
273	>	/**
274	>	* Increases the capacity of the array.
275	>	*
276	>	* @param minCapacity the desired minimum capacity
277	>	*/
278	>	private void grow(int minCapacity) {
279	>	int oldCapacity = queue.length;
280	>	// Double size if small; else grow by 50%
281	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
282	>	(oldCapacity + 2) :
283	>	(oldCapacity >> 1));
284	>	// overflow-conscious code
285	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
286	>	newCapacity = hugeCapacity(minCapacity);
287	>	queue = Arrays.copyOf(queue, newCapacity);
288		}
289
290	<	public E poll() {
291	<	if (size == 0)
292	<	return null;
293	<	return remove(1);
290	>	private static int hugeCapacity(int minCapacity) {
291	>	if (minCapacity < 0) // overflow
292	>	throw new OutOfMemoryError();
293	>	return (minCapacity > MAX_ARRAY_SIZE) ?
294	>	Integer.MAX_VALUE :
295	>	MAX_ARRAY_SIZE;
296		}
297
298	<	public E peek() {
299	<	return queue[1];
298	>	/**
299	>	* Inserts the specified element into this priority queue.
300	>	*
301	>	* @return {@code true} (as specified by {@link Collection#add})
302	>	* @throws ClassCastException if the specified element cannot be
303	>	*         compared with elements currently in this priority queue
304	>	*         according to the priority queue's ordering
305	>	* @throws NullPointerException if the specified element is null
306	>	*/
307	>	public boolean add(E e) {
308	>	return offer(e);
309		}
310
191	–	// Collection Methods
192	–
193	–	// these first two override just to get the throws docs
194	–
311		/**
312	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
312	>	* Inserts the specified element into this priority queue.
313	>	*
314	>	* @return {@code true} (as specified by {@link Queue#offer})
315	>	* @throws ClassCastException if the specified element cannot be
316	>	*         compared with elements currently in this priority queue
317	>	*         according to the priority queue's ordering
318	>	* @throws NullPointerException if the specified element is null
319		*/
320	<	public boolean add(E element) {
321	<	return super.add(element);
320	>	public boolean offer(E e) {
321	>	if (e == null)
322	>	throw new NullPointerException();
323	>	modCount++;
324	>	int i = size;
325	>	if (i >= queue.length)
326	>	grow(i + 1);
327	>	size = i + 1;
328	>	if (i == 0)
329	>	queue[0] = e;
330	>	else
331	>	siftUp(i, e);
332	>	return true;
333		}
334
335	<	//    /**
336	<	//     * @throws NullPointerException if any element is <tt>null</tt>.
337	<	//     */
338	<	//    public boolean addAll(Collection c) {
339	<	//        return super.addAll(c);
340	<	//    }
335	>	@SuppressWarnings("unchecked")
336	>	public E peek() {
337	>	return (size == 0) ? null : (E) queue[0];
338	>	}
339	>
340	>	private int indexOf(Object o) {
341	>	if (o != null) {
342	>	for (int i = 0; i < size; i++)
343	>	if (o.equals(queue[i]))
344	>	return i;
345	>	}
346	>	return -1;
347	>	}
348
349		/**
350	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
350	>	* Removes a single instance of the specified element from this queue,
351	>	* if it is present.  More formally, removes an element {@code e} such
352	>	* that {@code o.equals(e)}, if this queue contains one or more such
353	>	* elements.  Returns {@code true} if and only if this queue contained
354	>	* the specified element (or equivalently, if this queue changed as a
355	>	* result of the call).
356	>	*
357	>	* @param o element to be removed from this queue, if present
358	>	* @return {@code true} if this queue changed as a result of the call
359		*/
360		public boolean remove(Object o) {
361	<	if (o == null)
362	<	throw new NullPointerException();
361	>	int i = indexOf(o);
362	>	if (i == -1)
363	>	return false;
364	>	else {
365	>	removeAt(i);
366	>	return true;
367	>	}
368	>	}
369
370	<	if (comparator == null) {
371	<	for (int i = 1; i <= size; i++) {
372	<	if (((Comparable)queue[i]).compareTo(o) == 0) {
373	<	remove(i);
374	<	return true;
375	<	}
376	<	}
377	<	} else {
378	<	for (int i = 1; i <= size; i++) {
379	<	if (comparator.compare(queue[i], (E)o) == 0) {
380	<	remove(i);
381	<	return true;
228	<	}
370	>	/**
371	>	* Version of remove using reference equality, not equals.
372	>	* Needed by iterator.remove.
373	>	*
374	>	* @param o element to be removed from this queue, if present
375	>	* @return {@code true} if removed
376	>	*/
377	>	boolean removeEq(Object o) {
378	>	for (int i = 0; i < size; i++) {
379	>	if (o == queue[i]) {
380	>	removeAt(i);
381	>	return true;
382		}
383		}
384		return false;
385		}
386
387		/**
388	<	* Returns an iterator over the elements in this priority queue.  The
389	<	* elements of the priority queue will be returned by this iterator in the
390	<	* order specified by the queue, which is to say the order they would be
391	<	* returned by repeated calls to <tt>poll</tt>.
388	>	* Returns {@code true} if this queue contains the specified element.
389	>	* More formally, returns {@code true} if and only if this queue contains
390	>	* at least one element {@code e} such that {@code o.equals(e)}.
391	>	*
392	>	* @param o object to be checked for containment in this queue
393	>	* @return {@code true} if this queue contains the specified element
394	>	*/
395	>	public boolean contains(Object o) {
396	>	return indexOf(o) >= 0;
397	>	}
398	>
399	>	/**
400	>	* Returns an array containing all of the elements in this queue.
401	>	* The elements are in no particular order.
402	>	*
403	>	* <p>The returned array will be "safe" in that no references to it are
404	>	* maintained by this queue.  (In other words, this method must allocate
405	>	* a new array).  The caller is thus free to modify the returned array.
406	>	*
407	>	* <p>This method acts as bridge between array-based and collection-based
408	>	* APIs.
409	>	*
410	>	* @return an array containing all of the elements in this queue
411	>	*/
412	>	public Object[] toArray() {
413	>	return Arrays.copyOf(queue, size);
414	>	}
415	>
416	>	/**
417	>	* Returns an array containing all of the elements in this queue; the
418	>	* runtime type of the returned array is that of the specified array.
419	>	* The returned array elements are in no particular order.
420	>	* If the queue fits in the specified array, it is returned therein.
421	>	* Otherwise, a new array is allocated with the runtime type of the
422	>	* specified array and the size of this queue.
423	>	*
424	>	* <p>If the queue fits in the specified array with room to spare
425	>	* (i.e., the array has more elements than the queue), the element in
426	>	* the array immediately following the end of the collection is set to
427	>	* {@code null}.
428	>	*
429	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
430	>	* array-based and collection-based APIs.  Further, this method allows
431	>	* precise control over the runtime type of the output array, and may,
432	>	* under certain circumstances, be used to save allocation costs.
433	>	*
434	>	* <p>Suppose {@code x} is a queue known to contain only strings.
435	>	* The following code can be used to dump the queue into a newly
436	>	* allocated array of {@code String}:
437	>	*
438	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
439	>	*
440	>	* Note that {@code toArray(new Object[0])} is identical in function to
441	>	* {@code toArray()}.
442	>	*
443	>	* @param a the array into which the elements of the queue are to
444	>	*          be stored, if it is big enough; otherwise, a new array of the
445	>	*          same runtime type is allocated for this purpose.
446	>	* @return an array containing all of the elements in this queue
447	>	* @throws ArrayStoreException if the runtime type of the specified array
448	>	*         is not a supertype of the runtime type of every element in
449	>	*         this queue
450	>	* @throws NullPointerException if the specified array is null
451	>	*/
452	>	@SuppressWarnings("unchecked")
453	>	public <T> T[] toArray(T[] a) {
454	>	final int size = this.size;
455	>	if (a.length < size)
456	>	// Make a new array of a's runtime type, but my contents:
457	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
458	>	System.arraycopy(queue, 0, a, 0, size);
459	>	if (a.length > size)
460	>	a[size] = null;
461	>	return a;
462	>	}
463	>
464	>	/**
465	>	* Returns an iterator over the elements in this queue. The iterator
466	>	* does not return the elements in any particular order.
467		*
468	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
468	>	* @return an iterator over the elements in this queue
469		*/
470		public Iterator<E> iterator() {
471		return new Itr();
472		}
473
474	<	private class Itr implements Iterator<E> {
474	>	private final class Itr implements Iterator<E> {
475		/**
476		* Index (into queue array) of element to be returned by
477		* subsequent call to next.
478		*/
479	<	private int cursor = 1;
479	>	private int cursor;
480	>
481	>	/**
482	>	* Index of element returned by most recent call to next,
483	>	* unless that element came from the forgetMeNot list.
484	>	* Set to -1 if element is deleted by a call to remove.
485	>	*/
486	>	private int lastRet = -1;
487
488		/**
489	<	* Index of element returned by most recent call to next or
490	<	* previous.  Reset to 0 if this element is deleted by a call
491	<	* to remove.
489	>	* A queue of elements that were moved from the unvisited portion of
490	>	* the heap into the visited portion as a result of "unlucky" element
491	>	* removals during the iteration.  (Unlucky element removals are those
492	>	* that require a siftup instead of a siftdown.)  We must visit all of
493	>	* the elements in this list to complete the iteration.  We do this
494	>	* after we've completed the "normal" iteration.
495	>	*
496	>	* We expect that most iterations, even those involving removals,
497	>	* will not need to store elements in this field.
498		*/
499	<	private int lastRet = 0;
499	>	private ArrayDeque<E> forgetMeNot;
500	>
501	>	/**
502	>	* Element returned by the most recent call to next iff that
503	>	* element was drawn from the forgetMeNot list.
504	>	*/
505	>	private E lastRetElt;
506
507		/**
508		* The modCount value that the iterator believes that the backing
509	<	* List should have.  If this expectation is violated, the iterator
509	>	* Queue should have.  If this expectation is violated, the iterator
510		* has detected concurrent modification.
511		*/
512		private int expectedModCount = modCount;
513
514		public boolean hasNext() {
515	<	return cursor <= size;
515	>	return cursor < size ||
516	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
517		}
518
519	+	@SuppressWarnings("unchecked")
520		public E next() {
521	<	checkForComodification();
522	<	if (cursor > size)
523	<	throw new NoSuchElementException();
524	<	E result = queue[cursor];
525	<	lastRet = cursor++;
526	<	return result;
521	>	if (expectedModCount != modCount)
522	>	throw new ConcurrentModificationException();
523	>	if (cursor < size)
524	>	return (E) queue[lastRet = cursor++];
525	>	if (forgetMeNot != null) {
526	>	lastRet = -1;
527	>	lastRetElt = forgetMeNot.poll();
528	>	if (lastRetElt != null)
529	>	return lastRetElt;
530	>	}
531	>	throw new NoSuchElementException();
532		}
533
534		public void remove() {
535	<	if (lastRet == 0)
535	>	if (expectedModCount != modCount)
536	>	throw new ConcurrentModificationException();
537	>	if (lastRet != -1) {
538	>	E moved = PriorityQueue.this.removeAt(lastRet);
539	>	lastRet = -1;
540	>	if (moved == null)
541	>	cursor--;
542	>	else {
543	>	if (forgetMeNot == null)
544	>	forgetMeNot = new ArrayDeque<>();
545	>	forgetMeNot.add(moved);
546	>	}
547	>	} else if (lastRetElt != null) {
548	>	PriorityQueue.this.removeEq(lastRetElt);
549	>	lastRetElt = null;
550	>	} else {
551		throw new IllegalStateException();
552	<	checkForComodification();
284	<
285	<	PriorityQueue.this.remove(lastRet);
286	<	if (lastRet < cursor)
287	<	cursor--;
288	<	lastRet = 0;
552	>	}
553		expectedModCount = modCount;
554		}
291	–
292	–	final void checkForComodification() {
293	–	if (modCount != expectedModCount)
294	–	throw new ConcurrentModificationException();
295	–	}
555		}
556
298	–	/**
299	–	* Returns the number of elements in this priority queue.
300	–	*
301	–	* @return the number of elements in this priority queue.
302	–	*/
557		public int size() {
558		return size;
559		}
560
561		/**
562	<	* Remove all elements from the priority queue.
562	>	* Removes all of the elements from this priority queue.
563	>	* The queue will be empty after this call returns.
564		*/
565		public void clear() {
566		modCount++;
567	<
313	<	// Null out element references to prevent memory leak
314	<	for (int i=1; i<=size; i++)
567	>	for (int i = 0; i < size; i++)
568		queue[i] = null;
316	–
569		size = 0;
570		}
571
572	<	/**
573	<	* Removes and returns the ith element from queue.  Recall
574	<	* that queue is one-based, so 1 <= i <= size.
575	<	*
576	<	* XXX: Could further special-case i==size, but is it worth it?
325	<	* XXX: Could special-case i==0, but is it worth it?
326	<	*/
327	<	private E remove(int i) {
328	<	assert i <= size;
572	>	@SuppressWarnings("unchecked")
573	>	public E poll() {
574	>	if (size == 0)
575	>	return null;
576	>	int s = --size;
577		modCount++;
578	<
579	<	E result = queue[i];
580	<	queue[i] = queue[size];
581	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
582	<	if (i <= size)
335	<	fixDown(i);
578	>	E result = (E) queue[0];
579	>	E x = (E) queue[s];
580	>	queue[s] = null;
581	>	if (s != 0)
582	>	siftDown(0, x);
583		return result;
584		}
585
586		/**
587	<	* Establishes the heap invariant (described above) assuming the heap
588	<	* satisfies the invariant except possibly for the leaf-node indexed by k
589	<	* (which may have a nextExecutionTime less than its parent's).
590	<	*
591	<	* This method functions by "promoting" queue[k] up the hierarchy
592	<	* (by swapping it with its parent) repeatedly until queue[k]
593	<	* is greater than or equal to its parent.
594	<	*/
595	<	private void fixUp(int k) {
596	<	if (comparator == null) {
597	<	while (k > 1) {
598	<	int j = k >> 1;
599	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
600	<	break;
601	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
602	<	k = j;
603	<	}
604	<	} else {
605	<	while (k > 1) {
606	<	int j = k >> 1;
607	<	if (comparator.compare(queue[j], queue[k]) <= 0)
608	<	break;
609	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
610	<	k = j;
587	>	* Removes the ith element from queue.
588	>	*
589	>	* Normally this method leaves the elements at up to i-1,
590	>	* inclusive, untouched.  Under these circumstances, it returns
591	>	* null.  Occasionally, in order to maintain the heap invariant,
592	>	* it must swap a later element of the list with one earlier than
593	>	* i.  Under these circumstances, this method returns the element
594	>	* that was previously at the end of the list and is now at some
595	>	* position before i. This fact is used by iterator.remove so as to
596	>	* avoid missing traversing elements.
597	>	*/
598	>	@SuppressWarnings("unchecked")
599	>	private E removeAt(int i) {
600	>	// assert i >= 0 && i < size;
601	>	modCount++;
602	>	int s = --size;
603	>	if (s == i) // removed last element
604	>	queue[i] = null;
605	>	else {
606	>	E moved = (E) queue[s];
607	>	queue[s] = null;
608	>	siftDown(i, moved);
609	>	if (queue[i] == moved) {
610	>	siftUp(i, moved);
611	>	if (queue[i] != moved)
612	>	return moved;
613		}
614		}
615	+	return null;
616		}
617
618		/**
619	<	* Establishes the heap invariant (described above) in the subtree
620	<	* rooted at k, which is assumed to satisfy the heap invariant except
621	<	* possibly for node k itself (which may be greater than its children).
622	<	*
623	<	* This method functions by "demoting" queue[k] down the hierarchy
624	<	* (by swapping it with its smaller child) repeatedly until queue[k]
625	<	* is less than or equal to its children.
626	<	*/
627	<	private void fixDown(int k) {
628	<	int j;
629	<	if (comparator == null) {
630	<	while ((j = k << 1) <= size) {
631	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
632	<	j++; // j indexes smallest kid
633	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
634	<	break;
635	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
636	<	k = j;
637	<	}
638	<	} else {
639	<	while ((j = k << 1) <= size) {
640	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
641	<	j++; // j indexes smallest kid
642	<	if (comparator.compare(queue[k], queue[j]) <= 0)
643	<	break;
644	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
645	<	k = j;
646	<	}
619	>	* Inserts item x at position k, maintaining heap invariant by
620	>	* promoting x up the tree until it is greater than or equal to
621	>	* its parent, or is the root.
622	>	*
623	>	* To simplify and speed up coercions and comparisons. the
624	>	* Comparable and Comparator versions are separated into different
625	>	* methods that are otherwise identical. (Similarly for siftDown.)
626	>	*
627	>	* @param k the position to fill
628	>	* @param x the item to insert
629	>	*/
630	>	private void siftUp(int k, E x) {
631	>	if (comparator != null)
632	>	siftUpUsingComparator(k, x);
633	>	else
634	>	siftUpComparable(k, x);
635	>	}
636	>
637	>	@SuppressWarnings("unchecked")
638	>	private void siftUpComparable(int k, E x) {
639	>	Comparable<? super E> key = (Comparable<? super E>) x;
640	>	while (k > 0) {
641	>	int parent = (k - 1) >>> 1;
642	>	Object e = queue[parent];
643	>	if (key.compareTo((E) e) >= 0)
644	>	break;
645	>	queue[k] = e;
646	>	k = parent;
647	>	}
648	>	queue[k] = key;
649	>	}
650	>
651	>	@SuppressWarnings("unchecked")
652	>	private void siftUpUsingComparator(int k, E x) {
653	>	while (k > 0) {
654	>	int parent = (k - 1) >>> 1;
655	>	Object e = queue[parent];
656	>	if (comparator.compare(x, (E) e) >= 0)
657	>	break;
658	>	queue[k] = e;
659	>	k = parent;
660	>	}
661	>	queue[k] = x;
662	>	}
663	>
664	>	/**
665	>	* Inserts item x at position k, maintaining heap invariant by
666	>	* demoting x down the tree repeatedly until it is less than or
667	>	* equal to its children or is a leaf.
668	>	*
669	>	* @param k the position to fill
670	>	* @param x the item to insert
671	>	*/
672	>	private void siftDown(int k, E x) {
673	>	if (comparator != null)
674	>	siftDownUsingComparator(k, x);
675	>	else
676	>	siftDownComparable(k, x);
677	>	}
678	>
679	>	@SuppressWarnings("unchecked")
680	>	private void siftDownComparable(int k, E x) {
681	>	Comparable<? super E> key = (Comparable<? super E>)x;
682	>	int half = size >>> 1;        // loop while a non-leaf
683	>	while (k < half) {
684	>	int child = (k << 1) + 1; // assume left child is least
685	>	Object c = queue[child];
686	>	int right = child + 1;
687	>	if (right < size &&
688	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
689	>	c = queue[child = right];
690	>	if (key.compareTo((E) c) <= 0)
691	>	break;
692	>	queue[k] = c;
693	>	k = child;
694	>	}
695	>	queue[k] = key;
696	>	}
697	>
698	>	@SuppressWarnings("unchecked")
699	>	private void siftDownUsingComparator(int k, E x) {
700	>	int half = size >>> 1;
701	>	while (k < half) {
702	>	int child = (k << 1) + 1;
703	>	Object c = queue[child];
704	>	int right = child + 1;
705	>	if (right < size &&
706	>	comparator.compare((E) c, (E) queue[right]) > 0)
707	>	c = queue[child = right];
708	>	if (comparator.compare(x, (E) c) <= 0)
709	>	break;
710	>	queue[k] = c;
711	>	k = child;
712		}
713	+	queue[k] = x;
714		}
715
716	<	public Comparator comparator() {
716	>	/**
717	>	* Establishes the heap invariant (described above) in the entire tree,
718	>	* assuming nothing about the order of the elements prior to the call.
719	>	*/
720	>	@SuppressWarnings("unchecked")
721	>	private void heapify() {
722	>	for (int i = (size >>> 1) - 1; i >= 0; i--)
723	>	siftDown(i, (E) queue[i]);
724	>	}
725	>
726	>	/**
727	>	* Returns the comparator used to order the elements in this
728	>	* queue, or {@code null} if this queue is sorted according to
729	>	* the {@linkplain Comparable natural ordering} of its elements.
730	>	*
731	>	* @return the comparator used to order this queue, or
732	>	*         {@code null} if this queue is sorted according to the
733	>	*         natural ordering of its elements
734	>	*/
735	>	public Comparator<? super E> comparator() {
736		return comparator;
737		}
738
739		/**
740	<	* Save the state of the instance to a stream (that
406	<	* is, serialize it).
740	>	* Saves this queue to a stream (that is, serializes it).
741		*
742		* @serialData The length of the array backing the instance is
743	<	* emitted (int), followed by all of its elements (each an
744	<	* <tt>Object</tt>) in the proper order.
743	>	*             emitted (int), followed by all of its elements
744	>	*             (each an {@code Object}) in the proper order.
745		* @param s the stream
746	+	* @throws java.io.IOException if an I/O error occurs
747		*/
748	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
749	<	throws java.io.IOException{
748	>	private void writeObject(java.io.ObjectOutputStream s)
749	>	throws java.io.IOException {
750		// Write out element count, and any hidden stuff
751		s.defaultWriteObject();
752
753	<	// Write out array length
754	<	s.writeInt(queue.length);
753	>	// Write out array length, for compatibility with 1.5 version
754	>	s.writeInt(Math.max(2, size + 1));
755
756	<	// Write out all elements in the proper order.
757	<	for (int i=0; i<size; i++)
756	>	// Write out all elements in the "proper order".
757	>	for (int i = 0; i < size; i++)
758		s.writeObject(queue[i]);
759		}
760
761		/**
762	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
763	<	* deserialize it).
762	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
763	>	* (that is, deserializes it).
764	>	*
765		* @param s the stream
766	+	* @throws ClassNotFoundException if the class of a serialized object
767	+	*         could not be found
768	+	* @throws java.io.IOException if an I/O error occurs
769		*/
770	<	private synchronized void readObject(java.io.ObjectInputStream s)
770	>	private void readObject(java.io.ObjectInputStream s)
771		throws java.io.IOException, ClassNotFoundException {
772		// Read in size, and any hidden stuff
773		s.defaultReadObject();
774
775	<	// Read in array length and allocate array
776	<	int arrayLength = s.readInt();
777	<	queue = (E[]) new Object[arrayLength];
778	<
779	<	// Read in all elements in the proper order.
780	<	for (int i=0; i<size; i++)
781	<	queue[i] = (E)s.readObject();
775	>	// Read in (and discard) array length
776	>	s.readInt();
777	>
778	>	queue = new Object[size];
779	>
780	>	// Read in all elements.
781	>	for (int i = 0; i < size; i++)
782	>	queue[i] = s.readObject();
783	>
784	>	// Elements are guaranteed to be in "proper order", but the
785	>	// spec has never explained what that might be.
786	>	heapify();
787		}
788
789	<	}
789	>	public Spliterator<E> spliterator() {
790	>	return new PriorityQueueSpliterator<E>(this, 0, -1, 0);
791	>	}
792	>
793	>	/**
794	>	* This is very similar to ArrayList Spliterator, except for extra
795	>	* null checks.
796	>	*/
797	>	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
798	>	private final PriorityQueue<E> pq;
799	>	private int index;            // current index, modified on advance/split
800	>	private int fence;            // -1 until first use
801	>	private int expectedModCount; // initialized when fence set
802	>
803	>	/** Creates new spliterator covering the given range */
804	>	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
805	>	int expectedModCount) {
806	>	this.pq = pq;
807	>	this.index = origin;
808	>	this.fence = fence;
809	>	this.expectedModCount = expectedModCount;
810	>	}
811	>
812	>	private int getFence() { // initialize fence to size on first use
813	>	int hi;
814	>	if ((hi = fence) < 0) {
815	>	expectedModCount = pq.modCount;
816	>	hi = fence = pq.size;
817	>	}
818	>	return hi;
819	>	}
820
821	+	public Spliterator<E> trySplit() {
822	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
823	+	return (lo >= mid) ? null :
824	+	new PriorityQueueSpliterator<E>(pq, lo, index = mid,
825	+	expectedModCount);
826	+	}
827	+
828	+	@SuppressWarnings("unchecked")
829	+	public void forEachRemaining(Consumer<? super E> action) {
830	+	int i, hi, mc; // hoist accesses and checks from loop
831	+	PriorityQueue<E> q; Object[] a;
832	+	if (action == null)
833	+	throw new NullPointerException();
834	+	if ((q = pq) != null && (a = q.queue) != null) {
835	+	if ((hi = fence) < 0) {
836	+	mc = q.modCount;
837	+	hi = q.size;
838	+	}
839	+	else
840	+	mc = expectedModCount;
841	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
842	+	for (E e;; ++i) {
843	+	if (i < hi) {
844	+	if ((e = (E) a[i]) == null) // must be CME
845	+	break;
846	+	action.accept(e);
847	+	}
848	+	else if (q.modCount != mc)
849	+	break;
850	+	else
851	+	return;
852	+	}
853	+	}
854	+	}
855	+	throw new ConcurrentModificationException();
856	+	}
857	+
858	+	public boolean tryAdvance(Consumer<? super E> action) {
859	+	int hi = getFence(), lo = index;
860	+	if (lo >= 0 && lo < hi) {
861	+	index = lo + 1;
862	+	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
863	+	if (e == null)
864	+	throw new ConcurrentModificationException();
865	+	action.accept(e);
866	+	if (pq.modCount != expectedModCount)
867	+	throw new ConcurrentModificationException();
868	+	return true;
869	+	}
870	+	return false;
871	+	}
872	+
873	+	public long estimateSize() {
874	+	return (long) (getFence() - index);
875	+	}
876	+
877	+	public int characteristics() {
878	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
879	+	}
880	+	}
881	+	}

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