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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.21 by dholmes, Tue Aug 5 06:49:51 2003 UTC vs.
Revision 1.73 by jsr166, Tue Jun 21 19:29:21 2011 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 java.util.TreeSet} and
32	<	* {@link java.util.TreeMap}: elements are ordered
33	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
34	<	* according to a {@link java.util.Comparator}, depending on which
35	<	* constructor is used.
36	<	* <p>The <em>head</em> of this queue is the <em>least</em> element with
37	<	* respect to the specified ordering.
38	<	* 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.
51	<	* It is always at least as large as the queue size.  As
52	<	* elements are added to a priority queue, its capacity grows
53	<	* automatically.  The details of the growth policy are not specified.
54	<	*
55	<	* <p>Implementation note: this implementation provides O(log(n)) time
56	<	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
57	<	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
58	<	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
59	<	* constant time for the retrieval methods (<tt>peek</tt>,
60	<	* <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 enqueing and dequeing 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		public class PriorityQueue<E> extends AbstractQueue<E>
81	<	implements Sorted, Queue<E>, java.io.Serializable {
81	>	implements java.io.Serializable {
82	>
83	>	private static final long serialVersionUID = -7720805057305804111L;
84
85		private static final int DEFAULT_INITIAL_CAPACITY = 11;
86
87		/**
88	<	* Priority queue represented as a balanced binary heap: the two children
89	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
90	<	* ordered by comparator, or by the elements' natural ordering, if
91	<	* comparator is null:  For each node n in the heap and each descendant d
92	<	* of n, n <= d.
93	<	*
55	<	* The element with the lowest value is in queue[1], assuming the queue is
56	<	* nonempty.  (A one-based array is used in preference to the traditional
57	<	* zero-based array to simplify parent and child calculations.)
58	<	*
59	<	* queue.length must be >= 2, even if size == 0.
88	>	* Priority queue represented as a balanced binary heap: the two
89	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
90	>	* priority queue is ordered by comparator, or by the elements'
91	>	* natural ordering, if comparator is null: For each node n in the
92	>	* heap and each descendant d of n, n <= d.  The element with the
93	>	* lowest value is in queue[0], assuming the queue is nonempty.
94		*/
95		private transient Object[] queue;
96
#	Line 78 | Line 112 | public class PriorityQueue<E> extends Ab
112		private transient int modCount = 0;
113
114		/**
115	<	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
116	<	* (11) that orders its elements according to their natural
117	<	* ordering (using <tt>Comparable</tt>.)
115	>	* Creates a {@code PriorityQueue} with the default initial
116	>	* capacity (11) that orders its elements according to their
117	>	* {@linkplain Comparable natural ordering}.
118		*/
119		public PriorityQueue() {
120		this(DEFAULT_INITIAL_CAPACITY, null);
121		}
122
123		/**
124	<	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
125	<	* that orders its elements according to their natural ordering
126	<	* (using <tt>Comparable</tt>.)
127	<	*
128	<	* @param initialCapacity the initial capacity for this priority queue.
124	>	* Creates a {@code PriorityQueue} with the specified initial
125	>	* capacity that orders its elements according to their
126	>	* {@linkplain Comparable natural ordering}.
127	>	*
128	>	* @param initialCapacity the initial capacity for this priority queue
129	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
130	>	*         than 1
131		*/
132		public PriorityQueue(int initialCapacity) {
133		this(initialCapacity, null);
134		}
135
136		/**
137	<	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
137	>	* Creates a {@code PriorityQueue} with the specified initial capacity
138		* that orders its elements according to the specified comparator.
139		*
140	<	* @param initialCapacity the initial capacity for this priority queue.
141	<	* @param comparator the comparator used to order this priority queue.
142	<	* If <tt>null</tt> then the order depends on the elements' natural
143	<	* ordering.
144	<	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
145	<	* than 1
146	<	*/
147	<	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
140	>	* @param  initialCapacity the initial capacity for this priority queue
141	>	* @param  comparator the comparator that will be used to order this
142	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
143	>	*         natural ordering} of the elements will be used.
144	>	* @throws IllegalArgumentException if {@code initialCapacity} is
145	>	*         less than 1
146	>	*/
147	>	public PriorityQueue(int initialCapacity,
148	>	Comparator<? super E> comparator) {
149	>	// Note: This restriction of at least one is not actually needed,
150	>	// but continues for 1.5 compatibility
151		if (initialCapacity < 1)
152		throw new IllegalArgumentException();
153	<	this.queue = new Object[initialCapacity + 1];
153	>	this.queue = new Object[initialCapacity];
154		this.comparator = comparator;
155		}
156
157		/**
158	<	* Creates a <tt>PriorityQueue</tt> containing the elements in the
159	<	* specified collection.
160	<	* The priority queue has an initial capacity of 110% of the
161	<	* size of the specified collection or 1 if the collection is empty.
162	<	* If the specified collection
163	<	* implements the {@link Sorted} interface, the priority queue will be
125	<	* sorted according to the same comparator, or according to its elements'
126	<	* natural order if the collection is sorted according to its elements'
127	<	* natural order.  If the specified collection does not implement
128	<	* <tt>Sorted</tt>, the priority queue is ordered according to
129	<	* its elements' natural order.
158	>	* Creates a {@code PriorityQueue} containing the elements in the
159	>	* specified collection.  If the specified collection is an instance of
160	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
161	>	* priority queue will be ordered according to the same ordering.
162	>	* Otherwise, this priority queue will be ordered according to the
163	>	* {@linkplain Comparable natural ordering} of its elements.
164		*
165	<	* @param c the collection whose elements are to be placed
166	<	*        into this priority queue.
165	>	* @param  c the collection whose elements are to be placed
166	>	*         into this priority queue
167		* @throws ClassCastException if elements of the specified collection
168		*         cannot be compared to one another according to the priority
169	<	*         queue's ordering.
170	<	* @throws NullPointerException if <tt>c</tt> or any element within it
171	<	* is <tt>null</tt>
169	>	*         queue's ordering
170	>	* @throws NullPointerException if the specified collection or any
171	>	*         of its elements are null
172		*/
173	+	@SuppressWarnings("unchecked")
174		public PriorityQueue(Collection<? extends E> c) {
175	<	int sz = c.size();
176	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
177	<	Integer.MAX_VALUE - 1);
178	<	if (initialCapacity < 1)
179	<	initialCapacity = 1;
175	>	if (c instanceof SortedSet<?>) {
176	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
177	>	this.comparator = (Comparator<? super E>) ss.comparator();
178	>	initElementsFromCollection(ss);
179	>	}
180	>	else if (c instanceof PriorityQueue<?>) {
181	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
182	>	this.comparator = (Comparator<? super E>) pq.comparator();
183	>	initFromPriorityQueue(pq);
184	>	}
185	>	else {
186	>	this.comparator = null;
187	>	initFromCollection(c);
188	>	}
189	>	}
190
191	<	this.queue = new Object[initialCapacity + 1];
191	>	/**
192	>	* Creates a {@code PriorityQueue} containing the elements in the
193	>	* specified priority queue.  This priority queue will be
194	>	* ordered according to the same ordering as the given priority
195	>	* queue.
196	>	*
197	>	* @param  c the priority queue whose elements are to be placed
198	>	*         into this priority queue
199	>	* @throws ClassCastException if elements of {@code c} cannot be
200	>	*         compared to one another according to {@code c}'s
201	>	*         ordering
202	>	* @throws NullPointerException if the specified priority queue or any
203	>	*         of its elements are null
204	>	*/
205	>	@SuppressWarnings("unchecked")
206	>	public PriorityQueue(PriorityQueue<? extends E> c) {
207	>	this.comparator = (Comparator<? super E>) c.comparator();
208	>	initFromPriorityQueue(c);
209	>	}
210
211	<	if (c instanceof Sorted) {
212	<	comparator = (Comparator<? super E>)((Sorted)c).comparator();
211	>	/**
212	>	* Creates a {@code PriorityQueue} containing the elements in the
213	>	* specified sorted set.   This priority queue will be ordered
214	>	* according to the same ordering as the given sorted set.
215	>	*
216	>	* @param  c the sorted set whose elements are to be placed
217	>	*         into this priority queue
218	>	* @throws ClassCastException if elements of the specified sorted
219	>	*         set cannot be compared to one another according to the
220	>	*         sorted set's ordering
221	>	* @throws NullPointerException if the specified sorted set or any
222	>	*         of its elements are null
223	>	*/
224	>	@SuppressWarnings("unchecked")
225	>	public PriorityQueue(SortedSet<? extends E> c) {
226	>	this.comparator = (Comparator<? super E>) c.comparator();
227	>	initElementsFromCollection(c);
228	>	}
229	>
230	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
231	>	if (c.getClass() == PriorityQueue.class) {
232	>	this.queue = c.toArray();
233	>	this.size = c.size();
234		} else {
235	<	comparator = null;
235	>	initFromCollection(c);
236		}
237	+	}
238
239	<	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
240	<	add(i.next());
239	>	private void initElementsFromCollection(Collection<? extends E> c) {
240	>	Object[] a = c.toArray();
241	>	// If c.toArray incorrectly doesn't return Object[], copy it.
242	>	if (a.getClass() != Object[].class)
243	>	a = Arrays.copyOf(a, a.length, Object[].class);
244	>	int len = a.length;
245	>	if (len == 1 || this.comparator != null)
246	>	for (int i = 0; i < len; i++)
247	>	if (a[i] == null)
248	>	throw new NullPointerException();
249	>	this.queue = a;
250	>	this.size = a.length;
251		}
252
253	<	// Queue Methods
253	>	/**
254	>	* Initializes queue array with elements from the given Collection.
255	>	*
256	>	* @param c the collection
257	>	*/
258	>	private void initFromCollection(Collection<? extends E> c) {
259	>	initElementsFromCollection(c);
260	>	heapify();
261	>	}
262
263		/**
264	<	* Add the specified element to this priority queue.
264	>	* The maximum size of array to allocate.
265	>	* Some VMs reserve some header words in an array.
266	>	* Attempts to allocate larger arrays may result in
267	>	* OutOfMemoryError: Requested array size exceeds VM limit
268	>	*/
269	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
270	>
271	>	/**
272	>	* Increases the capacity of the array.
273		*
274	<	* @return <tt>true</tt>
164	<	* @throws ClassCastException if the specified element cannot be compared
165	<	* with elements currently in the priority queue according
166	<	* to the priority queue's ordering.
167	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
274	>	* @param minCapacity the desired minimum capacity
275		*/
276	<	public boolean offer(E o) {
277	<	if (o == null)
278	<	throw new NullPointerException();
279	<	modCount++;
280	<	++size;
276	>	private void grow(int minCapacity) {
277	>	int oldCapacity = queue.length;
278	>	// Double size if small; else grow by 50%
279	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
280	>	(oldCapacity + 2) :
281	>	(oldCapacity >> 1));
282	>	// overflow-conscious code
283	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
284	>	newCapacity = hugeCapacity(minCapacity);
285	>	queue = Arrays.copyOf(queue, newCapacity);
286	>	}
287
288	<	// Grow backing store if necessary
289	<	while (size >= queue.length) {
290	<	Object[] newQueue = new Object[2 * queue.length];
291	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
292	<	queue = newQueue;
293	<	}
288	>	private static int hugeCapacity(int minCapacity) {
289	>	if (minCapacity < 0) // overflow
290	>	throw new OutOfMemoryError();
291	>	return (minCapacity > MAX_ARRAY_SIZE) ?
292	>	Integer.MAX_VALUE :
293	>	MAX_ARRAY_SIZE;
294	>	}
295
296	<	queue[size] = o;
297	<	fixUp(size);
298	<	return true;
296	>	/**
297	>	* Inserts the specified element into this priority queue.
298	>	*
299	>	* @return {@code true} (as specified by {@link Collection#add})
300	>	* @throws ClassCastException if the specified element cannot be
301	>	*         compared with elements currently in this priority queue
302	>	*         according to the priority queue's ordering
303	>	* @throws NullPointerException if the specified element is null
304	>	*/
305	>	public boolean add(E e) {
306	>	return offer(e);
307		}
308
309	<	public E poll() {
310	<	if (size == 0)
311	<	return null;
312	<	return (E) remove(1);
309	>	/**
310	>	* Inserts the specified element into this priority queue.
311	>	*
312	>	* @return {@code true} (as specified by {@link Queue#offer})
313	>	* @throws ClassCastException if the specified element cannot be
314	>	*         compared with elements currently in this priority queue
315	>	*         according to the priority queue's ordering
316	>	* @throws NullPointerException if the specified element is null
317	>	*/
318	>	public boolean offer(E e) {
319	>	if (e == null)
320	>	throw new NullPointerException();
321	>	modCount++;
322	>	int i = size;
323	>	if (i >= queue.length)
324	>	grow(i + 1);
325	>	size = i + 1;
326	>	if (i == 0)
327	>	queue[0] = e;
328	>	else
329	>	siftUp(i, e);
330	>	return true;
331		}
332
333		public E peek() {
334	<	return (E) queue[1];
334	>	return (size == 0) ? null : (E) queue[0];
335		}
336
337	<	// Collection Methods
337	>	private int indexOf(Object o) {
338	>	if (o != null) {
339	>	for (int i = 0; i < size; i++)
340	>	if (o.equals(queue[i]))
341	>	return i;
342	>	}
343	>	return -1;
344	>	}
345
346	<	// these first two override just to get the throws docs
346	>	/**
347	>	* Removes a single instance of the specified element from this queue,
348	>	* if it is present.  More formally, removes an element {@code e} such
349	>	* that {@code o.equals(e)}, if this queue contains one or more such
350	>	* elements.  Returns {@code true} if and only if this queue contained
351	>	* the specified element (or equivalently, if this queue changed as a
352	>	* result of the call).
353	>	*
354	>	* @param o element to be removed from this queue, if present
355	>	* @return {@code true} if this queue changed as a result of the call
356	>	*/
357	>	public boolean remove(Object o) {
358	>	int i = indexOf(o);
359	>	if (i == -1)
360	>	return false;
361	>	else {
362	>	removeAt(i);
363	>	return true;
364	>	}
365	>	}
366
367		/**
368	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
369	<	* @throws ClassCastException if the specified element cannot be compared
370	<	* with elements currently in the priority queue according
371	<	* to the priority queue's ordering.
368	>	* Version of remove using reference equality, not equals.
369	>	* Needed by iterator.remove.
370	>	*
371	>	* @param o element to be removed from this queue, if present
372	>	* @return {@code true} if removed
373		*/
374	<	public boolean add(E o) {
375	<	return super.add(o);
374	>	boolean removeEq(Object o) {
375	>	for (int i = 0; i < size; i++) {
376	>	if (o == queue[i]) {
377	>	removeAt(i);
378	>	return true;
379	>	}
380	>	}
381	>	return false;
382		}
383
384		/**
385	<	* @throws ClassCastException if any element cannot be compared
386	<	* with elements currently in the priority queue according
387	<	* to the priority queue's ordering.
388	<	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
389	<	* is <tt>null</tt>
385	>	* Returns {@code true} if this queue contains the specified element.
386	>	* More formally, returns {@code true} if and only if this queue contains
387	>	* at least one element {@code e} such that {@code o.equals(e)}.
388	>	*
389	>	* @param o object to be checked for containment in this queue
390	>	* @return {@code true} if this queue contains the specified element
391		*/
392	<	public boolean addAll(Collection<? extends E> c) {
393	<	return super.addAll(c);
392	>	public boolean contains(Object o) {
393	>	return indexOf(o) != -1;
394		}
395
396	<	public boolean remove(Object o) {
397	<	if (o == null)
398	<	return false;
396	>	/**
397	>	* Returns an array containing all of the elements in this queue.
398	>	* The elements are in no particular order.
399	>	*
400	>	* <p>The returned array will be "safe" in that no references to it are
401	>	* maintained by this queue.  (In other words, this method must allocate
402	>	* a new array).  The caller is thus free to modify the returned array.
403	>	*
404	>	* <p>This method acts as bridge between array-based and collection-based
405	>	* APIs.
406	>	*
407	>	* @return an array containing all of the elements in this queue
408	>	*/
409	>	public Object[] toArray() {
410	>	return Arrays.copyOf(queue, size);
411	>	}
412
413	<	if (comparator == null) {
414	<	for (int i = 1; i <= size; i++) {
415	<	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
416	<	remove(i);
417	<	return true;
418	<	}
419	<	}
420	<	} else {
421	<	for (int i = 1; i <= size; i++) {
422	<	if (comparator.compare((E)queue[i], (E)o) == 0) {
423	<	remove(i);
424	<	return true;
425	<	}
426	<	}
427	<	}
428	<	return false;
413	>	/**
414	>	* Returns an array containing all of the elements in this queue; the
415	>	* runtime type of the returned array is that of the specified array.
416	>	* The returned array elements are in no particular order.
417	>	* If the queue fits in the specified array, it is returned therein.
418	>	* Otherwise, a new array is allocated with the runtime type of the
419	>	* specified array and the size of this queue.
420	>	*
421	>	* <p>If the queue fits in the specified array with room to spare
422	>	* (i.e., the array has more elements than the queue), the element in
423	>	* the array immediately following the end of the collection is set to
424	>	* {@code null}.
425	>	*
426	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
427	>	* array-based and collection-based APIs.  Further, this method allows
428	>	* precise control over the runtime type of the output array, and may,
429	>	* under certain circumstances, be used to save allocation costs.
430	>	*
431	>	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
432	>	* The following code can be used to dump the queue into a newly
433	>	* allocated array of <tt>String</tt>:
434	>	*
435	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
436	>	*
437	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
438	>	* <tt>toArray()</tt>.
439	>	*
440	>	* @param a the array into which the elements of the queue are to
441	>	*          be stored, if it is big enough; otherwise, a new array of the
442	>	*          same runtime type is allocated for this purpose.
443	>	* @return an array containing all of the elements in this queue
444	>	* @throws ArrayStoreException if the runtime type of the specified array
445	>	*         is not a supertype of the runtime type of every element in
446	>	*         this queue
447	>	* @throws NullPointerException if the specified array is null
448	>	*/
449	>	public <T> T[] toArray(T[] a) {
450	>	if (a.length < size)
451	>	// Make a new array of a's runtime type, but my contents:
452	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
453	>	System.arraycopy(queue, 0, a, 0, size);
454	>	if (a.length > size)
455	>	a[size] = null;
456	>	return a;
457		}
458
459	+	/**
460	+	* Returns an iterator over the elements in this queue. The iterator
461	+	* does not return the elements in any particular order.
462	+	*
463	+	* @return an iterator over the elements in this queue
464	+	*/
465		public Iterator<E> iterator() {
466		return new Itr();
467		}
468
469	<	private class Itr implements Iterator<E> {
469	>	private final class Itr implements Iterator<E> {
470		/**
471		* Index (into queue array) of element to be returned by
472		* subsequent call to next.
473		*/
474	<	private int cursor = 1;
474	>	private int cursor = 0;
475	>
476	>	/**
477	>	* Index of element returned by most recent call to next,
478	>	* unless that element came from the forgetMeNot list.
479	>	* Set to -1 if element is deleted by a call to remove.
480	>	*/
481	>	private int lastRet = -1;
482	>
483	>	/**
484	>	* A queue of elements that were moved from the unvisited portion of
485	>	* the heap into the visited portion as a result of "unlucky" element
486	>	* removals during the iteration.  (Unlucky element removals are those
487	>	* that require a siftup instead of a siftdown.)  We must visit all of
488	>	* the elements in this list to complete the iteration.  We do this
489	>	* after we've completed the "normal" iteration.
490	>	*
491	>	* We expect that most iterations, even those involving removals,
492	>	* will not need to store elements in this field.
493	>	*/
494	>	private ArrayDeque<E> forgetMeNot = null;
495
496		/**
497	<	* Index of element returned by most recent call to next or
498	<	* previous.  Reset to 0 if this element is deleted by a call
258	<	* to remove.
497	>	* Element returned by the most recent call to next iff that
498	>	* element was drawn from the forgetMeNot list.
499		*/
500	<	private int lastRet = 0;
500	>	private E lastRetElt = null;
501
502		/**
503		* The modCount value that the iterator believes that the backing
504	<	* List should have.  If this expectation is violated, the iterator
504	>	* Queue should have.  If this expectation is violated, the iterator
505		* has detected concurrent modification.
506		*/
507		private int expectedModCount = modCount;
508
509		public boolean hasNext() {
510	<	return cursor <= size;
510	>	return cursor < size ||
511	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
512		}
513
514		public E next() {
515	<	checkForComodification();
516	<	if (cursor > size)
517	<	throw new NoSuchElementException();
518	<	E result = (E) queue[cursor];
519	<	lastRet = cursor++;
520	<	return result;
515	>	if (expectedModCount != modCount)
516	>	throw new ConcurrentModificationException();
517	>	if (cursor < size)
518	>	return (E) queue[lastRet = cursor++];
519	>	if (forgetMeNot != null) {
520	>	lastRet = -1;
521	>	lastRetElt = forgetMeNot.poll();
522	>	if (lastRetElt != null)
523	>	return lastRetElt;
524	>	}
525	>	throw new NoSuchElementException();
526		}
527
528		public void remove() {
529	<	if (lastRet == 0)
529	>	if (expectedModCount != modCount)
530	>	throw new ConcurrentModificationException();
531	>	if (lastRet != -1) {
532	>	E moved = PriorityQueue.this.removeAt(lastRet);
533	>	lastRet = -1;
534	>	if (moved == null)
535	>	cursor--;
536	>	else {
537	>	if (forgetMeNot == null)
538	>	forgetMeNot = new ArrayDeque<E>();
539	>	forgetMeNot.add(moved);
540	>	}
541	>	} else if (lastRetElt != null) {
542	>	PriorityQueue.this.removeEq(lastRetElt);
543	>	lastRetElt = null;
544	>	} else {
545		throw new IllegalStateException();
546	<	checkForComodification();
286	<
287	<	PriorityQueue.this.remove(lastRet);
288	<	if (lastRet < cursor)
289	<	cursor--;
290	<	lastRet = 0;
546	>	}
547		expectedModCount = modCount;
548		}
293	–
294	–	final void checkForComodification() {
295	–	if (modCount != expectedModCount)
296	–	throw new ConcurrentModificationException();
297	–	}
549		}
550
300	–	/**
301	–	* Returns the number of elements in this priority queue.
302	–	*
303	–	* @return the number of elements in this priority queue.
304	–	*/
551		public int size() {
552		return size;
553		}
554
555		/**
556	<	* Remove all elements from the priority queue.
556	>	* Removes all of the elements from this priority queue.
557	>	* The queue will be empty after this call returns.
558		*/
559		public void clear() {
560		modCount++;
561	<
315	<	// Null out element references to prevent memory leak
316	<	for (int i=1; i<=size; i++)
561	>	for (int i = 0; i < size; i++)
562		queue[i] = null;
318	–
563		size = 0;
564		}
565
566	+	public E poll() {
567	+	if (size == 0)
568	+	return null;
569	+	int s = --size;
570	+	modCount++;
571	+	E result = (E) queue[0];
572	+	E x = (E) queue[s];
573	+	queue[s] = null;
574	+	if (s != 0)
575	+	siftDown(0, x);
576	+	return result;
577	+	}
578	+
579		/**
580	<	* Removes and returns the ith element from queue.  Recall
324	<	* that queue is one-based, so 1 <= i <= size.
580	>	* Removes the ith element from queue.
581		*
582	<	* XXX: Could further special-case i==size, but is it worth it?
583	<	* XXX: Could special-case i==0, but is it worth it?
582	>	* Normally this method leaves the elements at up to i-1,
583	>	* inclusive, untouched.  Under these circumstances, it returns
584	>	* null.  Occasionally, in order to maintain the heap invariant,
585	>	* it must swap a later element of the list with one earlier than
586	>	* i.  Under these circumstances, this method returns the element
587	>	* that was previously at the end of the list and is now at some
588	>	* position before i. This fact is used by iterator.remove so as to
589	>	* avoid missing traversing elements.
590		*/
591	<	private E remove(int i) {
592	<	assert i <= size;
591	>	private E removeAt(int i) {
592	>	assert i >= 0 && i < size;
593		modCount++;
594	<
595	<	E result = (E) queue[i];
596	<	queue[i] = queue[size];
597	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
598	<	if (i <= size)
599	<	fixDown(i);
600	<	return result;
594	>	int s = --size;
595	>	if (s == i) // removed last element
596	>	queue[i] = null;
597	>	else {
598	>	E moved = (E) queue[s];
599	>	queue[s] = null;
600	>	siftDown(i, moved);
601	>	if (queue[i] == moved) {
602	>	siftUp(i, moved);
603	>	if (queue[i] != moved)
604	>	return moved;
605	>	}
606	>	}
607	>	return null;
608		}
609
610		/**
611	<	* Establishes the heap invariant (described above) assuming the heap
612	<	* satisfies the invariant except possibly for the leaf-node indexed by k
613	<	* (which may have a nextExecutionTime less than its parent's).
614	<	*
615	<	* This method functions by "promoting" queue[k] up the hierarchy
616	<	* (by swapping it with its parent) repeatedly until queue[k]
617	<	* is greater than or equal to its parent.
618	<	*/
619	<	private void fixUp(int k) {
620	<	if (comparator == null) {
621	<	while (k > 1) {
622	<	int j = k >> 1;
623	<	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
624	<	break;
625	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
626	<	k = j;
627	<	}
628	<	} else {
629	<	while (k > 1) {
630	<	int j = k >> 1;
631	<	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
632	<	break;
633	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
634	<	k = j;
635	<	}
611	>	* Inserts item x at position k, maintaining heap invariant by
612	>	* promoting x up the tree until it is greater than or equal to
613	>	* its parent, or is the root.
614	>	*
615	>	* To simplify and speed up coercions and comparisons. the
616	>	* Comparable and Comparator versions are separated into different
617	>	* methods that are otherwise identical. (Similarly for siftDown.)
618	>	*
619	>	* @param k the position to fill
620	>	* @param x the item to insert
621	>	*/
622	>	private void siftUp(int k, E x) {
623	>	if (comparator != null)
624	>	siftUpUsingComparator(k, x);
625	>	else
626	>	siftUpComparable(k, x);
627	>	}
628	>
629	>	private void siftUpComparable(int k, E x) {
630	>	Comparable<? super E> key = (Comparable<? super E>) x;
631	>	while (k > 0) {
632	>	int parent = (k - 1) >>> 1;
633	>	Object e = queue[parent];
634	>	if (key.compareTo((E) e) >= 0)
635	>	break;
636	>	queue[k] = e;
637	>	k = parent;
638	>	}
639	>	queue[k] = key;
640	>	}
641	>
642	>	private void siftUpUsingComparator(int k, E x) {
643	>	while (k > 0) {
644	>	int parent = (k - 1) >>> 1;
645	>	Object e = queue[parent];
646	>	if (comparator.compare(x, (E) e) >= 0)
647	>	break;
648	>	queue[k] = e;
649	>	k = parent;
650		}
651	+	queue[k] = x;
652		}
653
654		/**
655	<	* Establishes the heap invariant (described above) in the subtree
656	<	* rooted at k, which is assumed to satisfy the heap invariant except
657	<	* possibly for node k itself (which may be greater than its children).
658	<	*
659	<	* This method functions by "demoting" queue[k] down the hierarchy
660	<	* (by swapping it with its smaller child) repeatedly until queue[k]
661	<	* is less than or equal to its children.
662	<	*/
663	<	private void fixDown(int k) {
664	<	int j;
665	<	if (comparator == null) {
666	<	while ((j = k << 1) <= size) {
667	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
668	<	j++; // j indexes smallest kid
669	<	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
670	<	break;
671	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
672	<	k = j;
673	<	}
674	<	} else {
675	<	while ((j = k << 1) <= size) {
676	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
677	<	j++; // j indexes smallest kid
678	<	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
679	<	break;
680	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
681	<	k = j;
682	<	}
655	>	* Inserts item x at position k, maintaining heap invariant by
656	>	* demoting x down the tree repeatedly until it is less than or
657	>	* equal to its children or is a leaf.
658	>	*
659	>	* @param k the position to fill
660	>	* @param x the item to insert
661	>	*/
662	>	private void siftDown(int k, E x) {
663	>	if (comparator != null)
664	>	siftDownUsingComparator(k, x);
665	>	else
666	>	siftDownComparable(k, x);
667	>	}
668	>
669	>	private void siftDownComparable(int k, E x) {
670	>	Comparable<? super E> key = (Comparable<? super E>)x;
671	>	int half = size >>> 1;        // loop while a non-leaf
672	>	while (k < half) {
673	>	int child = (k << 1) + 1; // assume left child is least
674	>	Object c = queue[child];
675	>	int right = child + 1;
676	>	if (right < size &&
677	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
678	>	c = queue[child = right];
679	>	if (key.compareTo((E) c) <= 0)
680	>	break;
681	>	queue[k] = c;
682	>	k = child;
683		}
684	+	queue[k] = key;
685	+	}
686	+
687	+	private void siftDownUsingComparator(int k, E x) {
688	+	int half = size >>> 1;
689	+	while (k < half) {
690	+	int child = (k << 1) + 1;
691	+	Object c = queue[child];
692	+	int right = child + 1;
693	+	if (right < size &&
694	+	comparator.compare((E) c, (E) queue[right]) > 0)
695	+	c = queue[child = right];
696	+	if (comparator.compare(x, (E) c) <= 0)
697	+	break;
698	+	queue[k] = c;
699	+	k = child;
700	+	}
701	+	queue[k] = x;
702	+	}
703	+
704	+	/**
705	+	* Establishes the heap invariant (described above) in the entire tree,
706	+	* assuming nothing about the order of the elements prior to the call.
707	+	*/
708	+	private void heapify() {
709	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
710	+	siftDown(i, (E) queue[i]);
711		}
712
713	+	/**
714	+	* Returns the comparator used to order the elements in this
715	+	* queue, or {@code null} if this queue is sorted according to
716	+	* the {@linkplain Comparable natural ordering} of its elements.
717	+	*
718	+	* @return the comparator used to order this queue, or
719	+	*         {@code null} if this queue is sorted according to the
720	+	*         natural ordering of its elements
721	+	*/
722		public Comparator<? super E> comparator() {
723		return comparator;
724		}
725
726		/**
727	<	* Save the state of the instance to a stream (that
728	<	* is, serialize it).
727	>	* Saves the state of the instance to a stream (that
728	>	* 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.
731	>	*             emitted (int), followed by all of its elements
732	>	*             (each an {@code Object}) in the proper order.
733		* @param s the stream
734		*/
735	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
735	>	private void writeObject(java.io.ObjectOutputStream s)
736		throws java.io.IOException{
737		// Write out element count, and any hidden stuff
738		s.defaultWriteObject();
739
740	<	// Write out array length
741	<	s.writeInt(queue.length);
740	>	// Write out array length, for compatibility with 1.5 version
741	>	s.writeInt(Math.max(2, size + 1));
742
743	<	// Write out all elements in the proper order.
744	<	for (int i=0; i<size; i++)
743	>	// Write out all elements in the "proper order".
744	>	for (int i = 0; i < size; i++)
745		s.writeObject(queue[i]);
746		}
747
748		/**
749	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
750	<	* deserialize it).
749	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
750	>	* (that is, deserializes it).
751	>	*
752		* @param s the stream
753		*/
754	<	private synchronized void readObject(java.io.ObjectInputStream s)
754	>	private void readObject(java.io.ObjectInputStream s)
755		throws java.io.IOException, ClassNotFoundException {
756		// Read in size, and any hidden stuff
757		s.defaultReadObject();
758
759	<	// Read in array length and allocate array
760	<	int arrayLength = s.readInt();
440	<	queue = new Object[arrayLength];
759	>	// Read in (and discard) array length
760	>	s.readInt();
761
762	<	// Read in all elements in the proper order.
763	<	for (int i=0; i<size; i++)
762	>	queue = new Object[size];
763	>
764	>	// Read in all elements.
765	>	for (int i = 0; i < size; i++)
766		queue[i] = s.readObject();
445	–	}
767
768	+	// Elements are guaranteed to be in "proper order", but the
769	+	// spec has never explained what that might be.
770	+	heapify();
771	+	}
772		}
448	–

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