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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.4 by tim, Mon May 19 02:45:07 2003 UTC vs.
Revision 1.85 by jsr166, Sat Jan 19 18:18:10 2013 UTC

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

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