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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.8 by dl, Tue Jul 1 16:29:45 2003 UTC vs.
Revision 1.80 by jsr166, Wed Jan 16 01:59:47 2013 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2006, 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.  Sun designates this
8	>	* particular file as subject to the "Classpath" exception as provided
9	>	* by Sun 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		/**
29	<	* An unbounded priority queue based on a priority heap.  This queue orders
30	<	* elements according to an order specified at construction time, which is
31	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered
32	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
33	<	* according to a {@link Comparator}, depending on which constructor is used.
34	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
35	<	* minimal element with respect to the specified ordering.  If multiple
36	<	* elements are tied for least value, no guarantees are made as to
37	<	* which of these elements is returned.
38	<	*
39	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
40	<	* size of the array used internally to store the elements on the
41	<	* queue.  It is always at least as large as the queue size.  As
42	<	* elements are added to a priority queue, its capacity grows
43	<	* automatically.  The details of the growth policy are not specified.
44	<	*
45	<	*<p>Implementation note: this implementation provides O(log(n)) time
46	<	*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
47	<	*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
48	<	*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
49	<	*constant time for the retrieval methods (<tt>peek</tt>,
50	<	*<tt>element</tt>, and <tt>size</tt>).
29	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
30	>	* The elements of the priority queue are ordered according to their
31	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
32	>	* provided at queue construction time, depending on which constructor is
33	>	* used.  A priority queue does not permit {@code null} elements.
34	>	* A priority queue relying on natural ordering also does not permit
35	>	* insertion of non-comparable objects (doing so may result in
36	>	* {@code ClassCastException}).
37	>	*
38	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
39	>	* with respect to the specified ordering.  If multiple elements are
40	>	* tied for least value, the head is one of those elements -- ties are
41	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
42	>	* {@code remove}, {@code peek}, and {@code element} access the
43	>	* element at the head of the queue.
44	>	*
45	>	* <p>A priority queue is unbounded, but has an internal
46	>	* <i>capacity</i> governing the size of an array used to store the
47	>	* elements on the queue.  It is always at least as large as the queue
48	>	* size.  As elements are added to a priority queue, its capacity
49	>	* grows automatically.  The details of the growth policy are not
50	>	* specified.
51	>	*
52	>	* <p>This class and its iterator implement all of the
53	>	* <em>optional</em> methods of the {@link Collection} and {@link
54	>	* Iterator} interfaces.  The Iterator provided in method {@link
55	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
56	>	* the priority queue in any particular order. If you need ordered
57	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
58	>	*
59	>	* <p><strong>Note that this implementation is not synchronized.</strong>
60	>	* Multiple threads should not access a {@code PriorityQueue}
61	>	* instance concurrently if any of the threads modifies the queue.
62	>	* Instead, use the thread-safe {@link
63	>	* java.util.concurrent.PriorityBlockingQueue} class.
64	>	*
65	>	* <p>Implementation note: this implementation provides
66	>	* O(log(n)) time for the enqueuing and dequeuing methods
67	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
68	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
69	>	* methods; and constant time for the retrieval methods
70	>	* ({@code peek}, {@code element}, and {@code size}).
71		*
72		* <p>This class is a member of the
73	<	* <a href="{@docRoot}/../guide/collections/index.html">
73	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
74		* Java Collections Framework</a>.
75	+	*
76		* @since 1.5
77	<	* @author Josh Bloch
77	>	* @author Josh Bloch, Doug Lea
78	>	* @param <E> the type of elements held in this collection
79		*/
80	+	@SuppressWarnings("unchecked")
81		public class PriorityQueue<E> extends AbstractQueue<E>
82	<	implements Queue<E>,
83	<	java.io.Serializable {
82	>	implements java.io.Serializable {
83	>
84	>	private static final long serialVersionUID = -7720805057305804111L;
85	>
86		private static final int DEFAULT_INITIAL_CAPACITY = 11;
87
88		/**
89	<	* Priority queue represented as a balanced binary heap: the two children
90	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
91	<	* ordered by comparator, or by the elements' natural ordering, if
92	<	* comparator is null:  For each node n in the heap and each descendant d
93	<	* of n, n <= d.
94	<	*
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.
89	>	* Priority queue represented as a balanced binary heap: the two
90	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
91	>	* priority queue is ordered by comparator, or by the elements'
92	>	* natural ordering, if comparator is null: For each node n in the
93	>	* heap and each descendant d of n, n <= d.  The element with the
94	>	* lowest value is in queue[0], assuming the queue is nonempty.
95		*/
96	<	private transient E[] queue;
96	>	private transient Object[] queue;
97
98		/**
99		* The number of elements in the priority queue.
#	Line 59 | Line 104 | public class PriorityQueue<E> extends Ab
104		* The comparator, or null if priority queue uses elements'
105		* natural ordering.
106		*/
107	<	private final Comparator<E> comparator;
107	>	private final Comparator<? super E> comparator;
108
109		/**
110		* The number of times this priority queue has been
#	Line 68 | Line 113 | public class PriorityQueue<E> extends Ab
113		private transient int modCount = 0;
114
115		/**
116	<	* Create a new priority queue with the default initial capacity
117	<	* (11) that orders its elements according to their natural
118	<	* ordering (using <tt>Comparable</tt>.)
116	>	* Creates a {@code PriorityQueue} with the default initial
117	>	* capacity (11) that orders its elements according to their
118	>	* {@linkplain Comparable natural ordering}.
119		*/
120		public PriorityQueue() {
121	<	this(DEFAULT_INITIAL_CAPACITY);
121	>	this(DEFAULT_INITIAL_CAPACITY, null);
122		}
123
124		/**
125	<	* Create a new priority queue with the specified initial capacity
126	<	* that orders its elements according to their natural ordering
127	<	* (using <tt>Comparable</tt>.)
125	>	* Creates a {@code PriorityQueue} with the specified initial
126	>	* capacity that orders its elements according to their
127	>	* {@linkplain Comparable natural ordering}.
128		*
129	<	* @param initialCapacity the initial capacity for this priority queue.
129	>	* @param initialCapacity the initial capacity for this priority queue
130	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
131	>	*         than 1
132		*/
133		public PriorityQueue(int initialCapacity) {
134		this(initialCapacity, null);
135		}
136
137		/**
138	<	* Create a new priority queue with the specified initial capacity (11)
138	>	* Creates a {@code PriorityQueue} with the specified initial capacity
139		* that orders its elements according to the specified comparator.
140		*
141	<	* @param initialCapacity the initial capacity for this priority queue.
142	<	* @param comparator the comparator used to order this priority queue.
143	<	*/
144	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
141	>	* @param  initialCapacity the initial capacity for this priority queue
142	>	* @param  comparator the comparator that will be used to order this
143	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
144	>	*         natural ordering} of the elements will be used.
145	>	* @throws IllegalArgumentException if {@code initialCapacity} is
146	>	*         less than 1
147	>	*/
148	>	public PriorityQueue(int initialCapacity,
149	>	Comparator<? super E> comparator) {
150	>	// Note: This restriction of at least one is not actually needed,
151	>	// but continues for 1.5 compatibility
152		if (initialCapacity < 1)
153	<	initialCapacity = 1;
154	<	queue = new E[initialCapacity + 1];
153	>	throw new IllegalArgumentException();
154	>	this.queue = new Object[initialCapacity];
155		this.comparator = comparator;
156		}
157
158		/**
159	<	* Create a new priority queue containing the elements in the specified
160	<	* collection.  The priority queue has an initial capacity of 110% of the
161	<	* size of the specified collection. If the specified collection
162	<	* implements the {@link Sorted} interface, the priority queue will be
163	<	* sorted according to the same comparator, or according to its elements'
164	<	* 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.
159	>	* Creates a {@code PriorityQueue} containing the elements in the
160	>	* specified collection.  If the specified collection is an instance of
161	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
162	>	* priority queue will be ordered according to the same ordering.
163	>	* Otherwise, this priority queue will be ordered according to the
164	>	* {@linkplain Comparable natural ordering} of its elements.
165		*
166	<	* @param initialElements the collection whose elements are to be placed
167	<	*        into this priority queue.
166	>	* @param  c the collection whose elements are to be placed
167	>	*         into this priority queue
168		* @throws ClassCastException if elements of the specified collection
169		*         cannot be compared to one another according to the priority
170	<	*         queue's ordering.
171	<	* @throws NullPointerException if the specified collection or an
172	<	*         element of the specified collection is <tt>null</tt>.
173	<	*/
174	<	public PriorityQueue(Collection<E> initialElements) {
175	<	int sz = initialElements.size();
176	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
177	<	Integer.MAX_VALUE - 1);
178	<	if (initialCapacity < 1)
179	<	initialCapacity = 1;
180	<	queue = new E[initialCapacity + 1];
170	>	*         queue's ordering
171	>	* @throws NullPointerException if the specified collection or any
172	>	*         of its elements are null
173	>	*/
174	>	@SuppressWarnings("unchecked")
175	>	public PriorityQueue(Collection<? extends E> c) {
176	>	if (c instanceof SortedSet<?>) {
177	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
178	>	this.comparator = (Comparator<? super E>) ss.comparator();
179	>	initElementsFromCollection(ss);
180	>	}
181	>	else if (c instanceof PriorityQueue<?>) {
182	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
183	>	this.comparator = (Comparator<? super E>) pq.comparator();
184	>	initFromPriorityQueue(pq);
185	>	}
186	>	else {
187	>	this.comparator = null;
188	>	initFromCollection(c);
189	>	}
190	>	}
191
192	+	/**
193	+	* Creates a {@code PriorityQueue} containing the elements in the
194	+	* specified priority queue.  This priority queue will be
195	+	* ordered according to the same ordering as the given priority
196	+	* queue.
197	+	*
198	+	* @param  c the priority queue whose elements are to be placed
199	+	*         into this priority queue
200	+	* @throws ClassCastException if elements of {@code c} cannot be
201	+	*         compared to one another according to {@code c}'s
202	+	*         ordering
203	+	* @throws NullPointerException if the specified priority queue or any
204	+	*         of its elements are null
205	+	*/
206	+	@SuppressWarnings("unchecked")
207	+	public PriorityQueue(PriorityQueue<? extends E> c) {
208	+	this.comparator = (Comparator<? super E>) c.comparator();
209	+	initFromPriorityQueue(c);
210	+	}
211
212	<	if (initialElements instanceof Sorted) {
213	<	comparator = ((Sorted)initialElements).comparator();
214	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
215	<	queue[++size] = i.next();
212	>	/**
213	>	* Creates a {@code PriorityQueue} containing the elements in the
214	>	* specified sorted set.   This priority queue will be ordered
215	>	* according to the same ordering as the given sorted set.
216	>	*
217	>	* @param  c the sorted set whose elements are to be placed
218	>	*         into this priority queue
219	>	* @throws ClassCastException if elements of the specified sorted
220	>	*         set cannot be compared to one another according to the
221	>	*         sorted set's ordering
222	>	* @throws NullPointerException if the specified sorted set or any
223	>	*         of its elements are null
224	>	*/
225	>	@SuppressWarnings("unchecked")
226	>	public PriorityQueue(SortedSet<? extends E> c) {
227	>	this.comparator = (Comparator<? super E>) c.comparator();
228	>	initElementsFromCollection(c);
229	>	}
230	>
231	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
232	>	if (c.getClass() == PriorityQueue.class) {
233	>	this.queue = c.toArray();
234	>	this.size = c.size();
235		} else {
236	<	comparator = null;
138	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
236	>	initFromCollection(c);
237		}
238		}
239
240	<	// Queue Methods
240	>	private void initElementsFromCollection(Collection<? extends E> c) {
241	>	Object[] a = c.toArray();
242	>	// If c.toArray incorrectly doesn't return Object[], copy it.
243	>	if (a.getClass() != Object[].class)
244	>	a = Arrays.copyOf(a, a.length, Object[].class);
245	>	int len = a.length;
246	>	if (len == 1 || this.comparator != null)
247	>	for (int i = 0; i < len; i++)
248	>	if (a[i] == null)
249	>	throw new NullPointerException();
250	>	this.queue = a;
251	>	this.size = a.length;
252	>	}
253
254		/**
255	<	* 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.
255	>	* Initializes queue array with elements from the given Collection.
256		*
257	<	* @return the minimal element from this priority queue if it contains
152	<	*         one or more elements, otherwise <tt>null</tt>.
257	>	* @param c the collection
258		*/
259	<	public E poll() {
260	<	if (size == 0)
261	<	return null;
262	<	return remove(1);
259	>	private void initFromCollection(Collection<? extends E> c) {
260	>	initElementsFromCollection(c);
261	>	heapify();
262	>	}
263	>
264	>	/**
265	>	* The maximum size of array to allocate.
266	>	* Some VMs reserve some header words in an array.
267	>	* Attempts to allocate larger arrays may result in
268	>	* OutOfMemoryError: Requested array size exceeds VM limit
269	>	*/
270	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
271	>
272	>	/**
273	>	* Increases the capacity of the array.
274	>	*
275	>	* @param minCapacity the desired minimum capacity
276	>	*/
277	>	private void grow(int minCapacity) {
278	>	int oldCapacity = queue.length;
279	>	// Double size if small; else grow by 50%
280	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
281	>	(oldCapacity + 2) :
282	>	(oldCapacity >> 1));
283	>	// overflow-conscious code
284	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
285	>	newCapacity = hugeCapacity(minCapacity);
286	>	queue = Arrays.copyOf(queue, newCapacity);
287	>	}
288	>
289	>	private static int hugeCapacity(int minCapacity) {
290	>	if (minCapacity < 0) // overflow
291	>	throw new OutOfMemoryError();
292	>	return (minCapacity > MAX_ARRAY_SIZE) ?
293	>	Integer.MAX_VALUE :
294	>	MAX_ARRAY_SIZE;
295		}
296
297		/**
298	<	* 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.
298	>	* Inserts the specified element into this priority queue.
299		*
300	<	* @return the minimal element from this priority queue if it contains
301	<	*         one or more elements, otherwise <tt>null</tt>.
300	>	* @return {@code true} (as specified by {@link Collection#add})
301	>	* @throws ClassCastException if the specified element cannot be
302	>	*         compared with elements currently in this priority queue
303	>	*         according to the priority queue's ordering
304	>	* @throws NullPointerException if the specified element is null
305		*/
306	+	public boolean add(E e) {
307	+	return offer(e);
308	+	}
309	+
310	+	/**
311	+	* Inserts the specified element into this priority queue.
312	+	*
313	+	* @return {@code true} (as specified by {@link Queue#offer})
314	+	* @throws ClassCastException if the specified element cannot be
315	+	*         compared with elements currently in this priority queue
316	+	*         according to the priority queue's ordering
317	+	* @throws NullPointerException if the specified element is null
318	+	*/
319	+	public boolean offer(E e) {
320	+	if (e == null)
321	+	throw new NullPointerException();
322	+	modCount++;
323	+	int i = size;
324	+	if (i >= queue.length)
325	+	grow(i + 1);
326	+	size = i + 1;
327	+	if (i == 0)
328	+	queue[0] = e;
329	+	else
330	+	siftUp(i, e);
331	+	return true;
332	+	}
333	+
334		public E peek() {
335	<	return queue[1];
335	>	return (size == 0) ? null : (E) queue[0];
336		}
337
338	<	// Collection Methods
338	>	private int indexOf(Object o) {
339	>	if (o != null) {
340	>	for (int i = 0; i < size; i++)
341	>	if (o.equals(queue[i]))
342	>	return i;
343	>	}
344	>	return -1;
345	>	}
346
347		/**
348	<	* Removes a single instance of the specified element from this priority
349	<	* queue, if it is present.  Returns true if this collection contained the
350	<	* specified element (or equivalently, if this collection changed as a
348	>	* Removes a single instance of the specified element from this queue,
349	>	* if it is present.  More formally, removes an element {@code e} such
350	>	* that {@code o.equals(e)}, if this queue contains one or more such
351	>	* elements.  Returns {@code true} if and only if this queue contained
352	>	* the specified element (or equivalently, if this queue changed as a
353		* result of the call).
354		*
355	<	* @param element the element to be removed from this collection,
356	<	* 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.
355	>	* @param o element to be removed from this queue, if present
356	>	* @return {@code true} if this queue changed as a result of the call
357		*/
358	<	public boolean remove(Object element) {
359	<	if (element == null)
360	<	throw new NullPointerException();
358	>	public boolean remove(Object o) {
359	>	int i = indexOf(o);
360	>	if (i == -1)
361	>	return false;
362	>	else {
363	>	removeAt(i);
364	>	return true;
365	>	}
366	>	}
367
368	<	if (comparator == null) {
369	<	for (int i = 1; i <= size; i++) {
370	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
371	<	remove(i);
372	<	return true;
373	<	}
374	<	}
375	<	} else {
376	<	for (int i = 1; i <= size; i++) {
377	<	if (comparator.compare(queue[i], (E) element) == 0) {
378	<	remove(i);
379	<	return true;
209	<	}
368	>	/**
369	>	* Version of remove using reference equality, not equals.
370	>	* Needed by iterator.remove.
371	>	*
372	>	* @param o element to be removed from this queue, if present
373	>	* @return {@code true} if removed
374	>	*/
375	>	boolean removeEq(Object o) {
376	>	for (int i = 0; i < size; i++) {
377	>	if (o == queue[i]) {
378	>	removeAt(i);
379	>	return true;
380		}
381		}
382		return false;
383		}
384
385		/**
386	<	* Returns an iterator over the elements in this priority queue.  The
387	<	* elements of the priority queue will be returned by this iterator in the
388	<	* order specified by the queue, which is to say the order they would be
389	<	* returned by repeated calls to <tt>poll</tt>.
390	<	*
391	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
386	>	* Returns {@code true} if this queue contains the specified element.
387	>	* More formally, returns {@code true} if and only if this queue contains
388	>	* at least one element {@code e} such that {@code o.equals(e)}.
389	>	*
390	>	* @param o object to be checked for containment in this queue
391	>	* @return {@code true} if this queue contains the specified element
392	>	*/
393	>	public boolean contains(Object o) {
394	>	return indexOf(o) != -1;
395	>	}
396	>
397	>	/**
398	>	* Returns an array containing all of the elements in this queue.
399	>	* The elements are in no particular order.
400	>	*
401	>	* <p>The returned array will be "safe" in that no references to it are
402	>	* maintained by this queue.  (In other words, this method must allocate
403	>	* a new array).  The caller is thus free to modify the returned array.
404	>	*
405	>	* <p>This method acts as bridge between array-based and collection-based
406	>	* APIs.
407	>	*
408	>	* @return an array containing all of the elements in this queue
409	>	*/
410	>	public Object[] toArray() {
411	>	return Arrays.copyOf(queue, size);
412	>	}
413	>
414	>	/**
415	>	* Returns an array containing all of the elements in this queue; the
416	>	* runtime type of the returned array is that of the specified array.
417	>	* The returned array elements are in no particular order.
418	>	* If the queue fits in the specified array, it is returned therein.
419	>	* Otherwise, a new array is allocated with the runtime type of the
420	>	* specified array and the size of this queue.
421	>	*
422	>	* <p>If the queue fits in the specified array with room to spare
423	>	* (i.e., the array has more elements than the queue), the element in
424	>	* the array immediately following the end of the collection is set to
425	>	* {@code null}.
426	>	*
427	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
428	>	* array-based and collection-based APIs.  Further, this method allows
429	>	* precise control over the runtime type of the output array, and may,
430	>	* under certain circumstances, be used to save allocation costs.
431	>	*
432	>	* <p>Suppose {@code x} is a queue known to contain only strings.
433	>	* The following code can be used to dump the queue into a newly
434	>	* allocated array of {@code String}:
435	>	*
436	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
437	>	*
438	>	* Note that {@code toArray(new Object[0])} is identical in function to
439	>	* {@code toArray()}.
440	>	*
441	>	* @param a the array into which the elements of the queue are to
442	>	*          be stored, if it is big enough; otherwise, a new array of the
443	>	*          same runtime type is allocated for this purpose.
444	>	* @return an array containing all of the elements in this queue
445	>	* @throws ArrayStoreException if the runtime type of the specified array
446	>	*         is not a supertype of the runtime type of every element in
447	>	*         this queue
448	>	* @throws NullPointerException if the specified array is null
449	>	*/
450	>	public <T> T[] toArray(T[] a) {
451	>	if (a.length < size)
452	>	// Make a new array of a's runtime type, but my contents:
453	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
454	>	System.arraycopy(queue, 0, a, 0, size);
455	>	if (a.length > size)
456	>	a[size] = null;
457	>	return a;
458	>	}
459	>
460	>	/**
461	>	* Returns an iterator over the elements in this queue. The iterator
462	>	* does not return the elements in any particular order.
463	>	*
464	>	* @return an iterator over the elements in this queue
465		*/
466		public Iterator<E> iterator() {
467		return new Itr();
468		}
469
470	<	private class Itr implements Iterator<E> {
470	>	private final class Itr implements Iterator<E> {
471		/**
472		* Index (into queue array) of element to be returned by
473		* subsequent call to next.
474		*/
475	<	private int cursor = 1;
475	>	private int cursor = 0;
476	>
477	>	/**
478	>	* Index of element returned by most recent call to next,
479	>	* unless that element came from the forgetMeNot list.
480	>	* Set to -1 if element is deleted by a call to remove.
481	>	*/
482	>	private int lastRet = -1;
483
484		/**
485	<	* Index of element returned by most recent call to next or
486	<	* previous.  Reset to 0 if this element is deleted by a call
487	<	* to remove.
485	>	* A queue of elements that were moved from the unvisited portion of
486	>	* the heap into the visited portion as a result of "unlucky" element
487	>	* removals during the iteration.  (Unlucky element removals are those
488	>	* that require a siftup instead of a siftdown.)  We must visit all of
489	>	* the elements in this list to complete the iteration.  We do this
490	>	* after we've completed the "normal" iteration.
491	>	*
492	>	* We expect that most iterations, even those involving removals,
493	>	* will not need to store elements in this field.
494		*/
495	<	private int lastRet = 0;
495	>	private ArrayDeque<E> forgetMeNot = null;
496	>
497	>	/**
498	>	* Element returned by the most recent call to next iff that
499	>	* element was drawn from the forgetMeNot list.
500	>	*/
501	>	private E lastRetElt = null;
502
503		/**
504		* The modCount value that the iterator believes that the backing
505	<	* List should have.  If this expectation is violated, the iterator
505	>	* Queue should have.  If this expectation is violated, the iterator
506		* has detected concurrent modification.
507		*/
508		private int expectedModCount = modCount;
509
510		public boolean hasNext() {
511	<	return cursor <= size;
511	>	return cursor < size ||
512	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
513		}
514
515		public E next() {
516	<	checkForComodification();
517	<	if (cursor > size)
518	<	throw new NoSuchElementException();
519	<	E result = queue[cursor];
520	<	lastRet = cursor++;
521	<	return result;
516	>	if (expectedModCount != modCount)
517	>	throw new ConcurrentModificationException();
518	>	if (cursor < size)
519	>	return (E) queue[lastRet = cursor++];
520	>	if (forgetMeNot != null) {
521	>	lastRet = -1;
522	>	lastRetElt = forgetMeNot.poll();
523	>	if (lastRetElt != null)
524	>	return lastRetElt;
525	>	}
526	>	throw new NoSuchElementException();
527		}
528
529		public void remove() {
530	<	if (lastRet == 0)
530	>	if (expectedModCount != modCount)
531	>	throw new ConcurrentModificationException();
532	>	if (lastRet != -1) {
533	>	E moved = PriorityQueue.this.removeAt(lastRet);
534	>	lastRet = -1;
535	>	if (moved == null)
536	>	cursor--;
537	>	else {
538	>	if (forgetMeNot == null)
539	>	forgetMeNot = new ArrayDeque<E>();
540	>	forgetMeNot.add(moved);
541	>	}
542	>	} else if (lastRetElt != null) {
543	>	PriorityQueue.this.removeEq(lastRetElt);
544	>	lastRetElt = null;
545	>	} else {
546		throw new IllegalStateException();
547	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
547	>	}
548		expectedModCount = modCount;
549		}
272	–
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
550		}
551
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
552		public int size() {
553		return size;
554		}
555
556		/**
557	<	* Add the specified element to this priority queue.
558	<	*
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.
557	>	* Removes all of the elements from this priority queue.
558	>	* The queue will be empty after this call returns.
559		*/
560	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
560	>	public void clear() {
561		modCount++;
562	+	for (int i = 0; i < size; i++)
563	+	queue[i] = null;
564	+	size = 0;
565	+	}
566
567	<	// Grow backing store if necessary
568	<	if (++size == queue.length) {
569	<	E[] newQueue = new E[2 * queue.length];
570	<	System.arraycopy(queue, 0, newQueue, 0, size);
571	<	queue = newQueue;
572	<	}
573	<
574	<	queue[size] = element;
575	<	fixUp(size);
576	<	return true;
567	>	public E poll() {
568	>	if (size == 0)
569	>	return null;
570	>	int s = --size;
571	>	modCount++;
572	>	E result = (E) queue[0];
573	>	E x = (E) queue[s];
574	>	queue[s] = null;
575	>	if (s != 0)
576	>	siftDown(0, x);
577	>	return result;
578		}
579
580		/**
581	<	* Remove all elements from the priority queue.
581	>	* Removes the ith element from queue.
582	>	*
583	>	* Normally this method leaves the elements at up to i-1,
584	>	* inclusive, untouched.  Under these circumstances, it returns
585	>	* null.  Occasionally, in order to maintain the heap invariant,
586	>	* it must swap a later element of the list with one earlier than
587	>	* i.  Under these circumstances, this method returns the element
588	>	* that was previously at the end of the list and is now at some
589	>	* position before i. This fact is used by iterator.remove so as to
590	>	* avoid missing traversing elements.
591		*/
592	<	public void clear() {
592	>	private E removeAt(int i) {
593	>	// assert i >= 0 && i < size;
594		modCount++;
595	<
596	<	// Null out element references to prevent memory leak
322	<	for (int i=1; i<=size; i++)
595	>	int s = --size;
596	>	if (s == i) // removed last element
597		queue[i] = null;
598	<
599	<	size = 0;
598	>	else {
599	>	E moved = (E) queue[s];
600	>	queue[s] = null;
601	>	siftDown(i, moved);
602	>	if (queue[i] == moved) {
603	>	siftUp(i, moved);
604	>	if (queue[i] != moved)
605	>	return moved;
606	>	}
607	>	}
608	>	return null;
609		}
610
611		/**
612	<	* Removes and returns the ith element from queue.  Recall
613	<	* that queue is one-based, so 1 <= i <= size.
612	>	* Inserts item x at position k, maintaining heap invariant by
613	>	* promoting x up the tree until it is greater than or equal to
614	>	* its parent, or is the root.
615	>	*
616	>	* To simplify and speed up coercions and comparisons. the
617	>	* Comparable and Comparator versions are separated into different
618	>	* methods that are otherwise identical. (Similarly for siftDown.)
619		*
620	<	* XXX: Could further special-case i==size, but is it worth it?
621	<	* XXX: Could special-case i==0, but is it worth it?
620	>	* @param k the position to fill
621	>	* @param x the item to insert
622		*/
623	<	private E remove(int i) {
624	<	assert i <= size;
625	<	modCount++;
623	>	private void siftUp(int k, E x) {
624	>	if (comparator != null)
625	>	siftUpUsingComparator(k, x);
626	>	else
627	>	siftUpComparable(k, x);
628	>	}
629
630	<	E result = queue[i];
631	<	queue[i] = queue[size];
632	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
633	<	if (i <= size)
634	<	fixDown(i);
635	<	return result;
630	>	private void siftUpComparable(int k, E x) {
631	>	Comparable<? super E> key = (Comparable<? super E>) x;
632	>	while (k > 0) {
633	>	int parent = (k - 1) >>> 1;
634	>	Object e = queue[parent];
635	>	if (key.compareTo((E) e) >= 0)
636	>	break;
637	>	queue[k] = e;
638	>	k = parent;
639	>	}
640	>	queue[k] = key;
641		}
642
643	<	/**
644	<	* Establishes the heap invariant (described above) assuming the heap
645	<	* satisfies the invariant except possibly for the leaf-node indexed by k
646	<	* (which may have a nextExecutionTime less than its parent's).
647	<	*
648	<	* This method functions by "promoting" queue[k] up the hierarchy
649	<	* (by swapping it with its parent) repeatedly until queue[k]
650	<	* is greater than or equal to its parent.
355	<	*/
356	<	private void fixUp(int k) {
357	<	if (comparator == null) {
358	<	while (k > 1) {
359	<	int j = k >> 1;
360	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
361	<	break;
362	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
363	<	k = j;
364	<	}
365	<	} else {
366	<	while (k > 1) {
367	<	int j = k >> 1;
368	<	if (comparator.compare(queue[j], queue[k]) <= 0)
369	<	break;
370	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
371	<	k = j;
372	<	}
643	>	private void siftUpUsingComparator(int k, E x) {
644	>	while (k > 0) {
645	>	int parent = (k - 1) >>> 1;
646	>	Object e = queue[parent];
647	>	if (comparator.compare(x, (E) e) >= 0)
648	>	break;
649	>	queue[k] = e;
650	>	k = parent;
651		}
652	+	queue[k] = x;
653		}
654
655		/**
656	<	* Establishes the heap invariant (described above) in the subtree
657	<	* rooted at k, which is assumed to satisfy the heap invariant except
658	<	* possibly for node k itself (which may be greater than its children).
659	<	*
660	<	* This method functions by "demoting" queue[k] down the hierarchy
661	<	* (by swapping it with its smaller child) repeatedly until queue[k]
662	<	* is less than or equal to its children.
663	<	*/
664	<	private void fixDown(int k) {
665	<	int j;
666	<	if (comparator == null) {
667	<	while ((j = k << 1) <= size) {
668	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
669	<	j++; // j indexes smallest kid
670	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
671	<	break;
672	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
673	<	k = j;
674	<	}
675	<	} else {
676	<	while ((j = k << 1) <= size) {
677	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
678	<	j++; // j indexes smallest kid
679	<	if (comparator.compare(queue[k], queue[j]) <= 0)
680	<	break;
681	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
682	<	k = j;
683	<	}
656	>	* Inserts item x at position k, maintaining heap invariant by
657	>	* demoting x down the tree repeatedly until it is less than or
658	>	* equal to its children or is a leaf.
659	>	*
660	>	* @param k the position to fill
661	>	* @param x the item to insert
662	>	*/
663	>	private void siftDown(int k, E x) {
664	>	if (comparator != null)
665	>	siftDownUsingComparator(k, x);
666	>	else
667	>	siftDownComparable(k, x);
668	>	}
669	>
670	>	private void siftDownComparable(int k, E x) {
671	>	Comparable<? super E> key = (Comparable<? super E>)x;
672	>	int half = size >>> 1;        // loop while a non-leaf
673	>	while (k < half) {
674	>	int child = (k << 1) + 1; // assume left child is least
675	>	Object c = queue[child];
676	>	int right = child + 1;
677	>	if (right < size &&
678	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
679	>	c = queue[child = right];
680	>	if (key.compareTo((E) c) <= 0)
681	>	break;
682	>	queue[k] = c;
683	>	k = child;
684		}
685	+	queue[k] = key;
686	+	}
687	+
688	+	private void siftDownUsingComparator(int k, E x) {
689	+	int half = size >>> 1;
690	+	while (k < half) {
691	+	int child = (k << 1) + 1;
692	+	Object c = queue[child];
693	+	int right = child + 1;
694	+	if (right < size &&
695	+	comparator.compare((E) c, (E) queue[right]) > 0)
696	+	c = queue[child = right];
697	+	if (comparator.compare(x, (E) c) <= 0)
698	+	break;
699	+	queue[k] = c;
700	+	k = child;
701	+	}
702	+	queue[k] = x;
703	+	}
704	+
705	+	/**
706	+	* Establishes the heap invariant (described above) in the entire tree,
707	+	* assuming nothing about the order of the elements prior to the call.
708	+	*/
709	+	private void heapify() {
710	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
711	+	siftDown(i, (E) queue[i]);
712		}
713
714		/**
715	<	* Returns the comparator associated with this priority queue, or
716	<	* <tt>null</tt> if it uses its elements' natural ordering.
715	>	* Returns the comparator used to order the elements in this
716	>	* queue, or {@code null} if this queue is sorted according to
717	>	* the {@linkplain Comparable natural ordering} of its elements.
718		*
719	<	* @return the comparator associated with this priority queue, or
720	<	*         <tt>null</tt> if it uses its elements' natural ordering.
719	>	* @return the comparator used to order this queue, or
720	>	*         {@code null} if this queue is sorted according to the
721	>	*         natural ordering of its elements
722		*/
723	<	public Comparator comparator() {
723	>	public Comparator<? super E> comparator() {
724		return comparator;
725		}
726
727		/**
728	<	* Save the state of the instance to a stream (that
421	<	* is, serialize it).
728	>	* Saves this queue to a stream (that is, serializes it).
729		*
730		* @serialData The length of the array backing the instance is
731	<	* emitted (int), followed by all of its elements (each an
732	<	* <tt>Object</tt>) in the proper order.
426	<	* @param s the stream
731	>	*             emitted (int), followed by all of its elements
732	>	*             (each an {@code Object}) in the proper order.
733		*/
734	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
735	<	throws java.io.IOException{
734	>	private void writeObject(java.io.ObjectOutputStream s)
735	>	throws java.io.IOException {
736		// Write out element count, and any hidden stuff
737		s.defaultWriteObject();
738
739	<	// Write out array length
740	<	s.writeInt(queue.length);
739	>	// Write out array length, for compatibility with 1.5 version
740	>	s.writeInt(Math.max(2, size + 1));
741
742	<	// Write out all elements in the proper order.
743	<	for (int i=0; i<size; i++)
742	>	// Write out all elements in the "proper order".
743	>	for (int i = 0; i < size; i++)
744		s.writeObject(queue[i]);
745		}
746
747		/**
748	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
443	<	* deserialize it).
444	<	* @param s the stream
748	>	* Reconstitutes this queue from a stream (that is, deserializes it).
749		*/
750	<	private synchronized void readObject(java.io.ObjectInputStream s)
750	>	private void readObject(java.io.ObjectInputStream s)
751		throws java.io.IOException, ClassNotFoundException {
752		// Read in size, and any hidden stuff
753		s.defaultReadObject();
754
755	<	// Read in array length and allocate array
756	<	int arrayLength = s.readInt();
453	<	queue = new E[arrayLength];
454	<
455	<	// Read in all elements in the proper order.
456	<	for (int i=0; i<size; i++)
457	<	queue[i] = (E)s.readObject();
458	<	}
755	>	// Read in (and discard) array length
756	>	s.readInt();
757
758	+	queue = new Object[size];
759	+
760	+	// Read in all elements.
761	+	for (int i = 0; i < size; i++)
762	+	queue[i] = s.readObject();
763	+
764	+	// Elements are guaranteed to be in "proper order", but the
765	+	// spec has never explained what that might be.
766	+	heapify();
767	+	}
768		}

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