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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.19 by tim, Mon Aug 4 16:14:48 2003 UTC vs.
Revision 1.94 by dl, Wed Mar 13 12:38:56 2013 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* Copyright (c) 2003, 2012, Oracle and/or its affiliates. All rights reserved.
3	>	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4	>	*
5	>	* This code is free software; you can redistribute it and/or modify it
6	>	* under the terms of the GNU General Public License version 2 only, as
7	>	* published by the Free Software Foundation.  Oracle designates this
8	>	* particular file as subject to the "Classpath" exception as provided
9	>	* by Oracle in the LICENSE file that accompanied this code.
10	>	*
11	>	* This code is distributed in the hope that it will be useful, but WITHOUT
12	>	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13	>	* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
14	>	* version 2 for more details (a copy is included in the LICENSE file that
15	>	* accompanied this code).
16	>	*
17	>	* You should have received a copy of the GNU General Public License version
18	>	* 2 along with this work; if not, write to the Free Software Foundation,
19	>	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20	>	*
21	>	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22	>	* or visit www.oracle.com if you need additional information or have any
23	>	* questions.
24	>	*/
25	>
26	>	package java.util;
27	>	import java.util.function.Consumer;
28	>	import java.util.stream.Stream;
29	>	import java.util.stream.Streams;
30
31		/**
32	<	* A priority queue based on a priority heap.  This queue orders
33	<	* elements according to an order specified at construction time, which is
34	<	* specified in the same manner as {@link java.util.TreeSet} and
35	<	* {@link java.util.TreeMap}: elements are ordered
36	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
37	<	* according to a {@link java.util.Comparator}, depending on which
38	<	* constructor is used.
39	<	* <p>The <em>head</em> of this queue is the <em>least</em> element with
40	<	* respect to the specified ordering.
41	<	* If multiple elements are tied for least value, the
42	<	* head is one of those elements. A priority queue does not permit
43	<	* <tt>null</tt> elements.
44	<	*
45	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and
46	<	* return the head of the queue.
47	<	*
48	<	* <p>The {@link #element()} and {@link #peek()} methods return, but do
49	<	* not delete, the head of the queue.
50	<	*
51	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
52	<	* size of the array used internally to store the elements on the
53	<	* queue, and is limited to <tt>Integer.MAX_VALUE-1</tt>.
54	<	* It is always at least as large as the queue size.  As
55	<	* elements are added to a priority queue, its capacity grows
56	<	* automatically.  The details of the growth policy are not specified.
57	<	*
58	<	* <p>Implementation note: this implementation provides O(log(n)) time
59	<	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
60	<	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
61	<	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
62	<	* constant time for the retrieval methods (<tt>peek</tt>,
63	<	* <tt>element</tt>, and <tt>size</tt>).
32	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
33	>	* The elements of the priority queue are ordered according to their
34	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
35	>	* provided at queue construction time, depending on which constructor is
36	>	* used.  A priority queue does not permit {@code null} elements.
37	>	* A priority queue relying on natural ordering also does not permit
38	>	* insertion of non-comparable objects (doing so may result in
39	>	* {@code ClassCastException}).
40	>	*
41	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
42	>	* with respect to the specified ordering.  If multiple elements are
43	>	* tied for least value, the head is one of those elements -- ties are
44	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
45	>	* {@code remove}, {@code peek}, and {@code element} access the
46	>	* element at the head of the queue.
47	>	*
48	>	* <p>A priority queue is unbounded, but has an internal
49	>	* <i>capacity</i> governing the size of an array used to store the
50	>	* elements on the queue.  It is always at least as large as the queue
51	>	* size.  As elements are added to a priority queue, its capacity
52	>	* grows automatically.  The details of the growth policy are not
53	>	* specified.
54	>	*
55	>	* <p>This class and its iterator implement all of the
56	>	* <em>optional</em> methods of the {@link Collection} and {@link
57	>	* Iterator} interfaces.  The Iterator provided in method {@link
58	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
59	>	* the priority queue in any particular order. If you need ordered
60	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
61	>	*
62	>	* <p><strong>Note that this implementation is not synchronized.</strong>
63	>	* Multiple threads should not access a {@code PriorityQueue}
64	>	* instance concurrently if any of the threads modifies the queue.
65	>	* Instead, use the thread-safe {@link
66	>	* java.util.concurrent.PriorityBlockingQueue} class.
67	>	*
68	>	* <p>Implementation note: this implementation provides
69	>	* O(log(n)) time for the enqueing and dequeing methods
70	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
71	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
72	>	* methods; and constant time for the retrieval methods
73	>	* ({@code peek}, {@code element}, and {@code size}).
74		*
75		* <p>This class is a member of the
76	<	* <a href="{@docRoot}/../guide/collections/index.html">
76	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
77		* Java Collections Framework</a>.
78	+	*
79		* @since 1.5
80	<	* @author Josh Bloch
80	>	* @author Josh Bloch, Doug Lea
81	>	* @param <E> the type of elements held in this collection
82		*/
83		public class PriorityQueue<E> extends AbstractQueue<E>
84	<	implements Sorted, Queue<E>, java.io.Serializable {
84	>	implements java.io.Serializable {
85	>
86	>	private static final long serialVersionUID = -7720805057305804111L;
87
88		private static final int DEFAULT_INITIAL_CAPACITY = 11;
89
90		/**
91	<	* Priority queue represented as a balanced binary heap: the two children
92	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
93	<	* ordered by comparator, or by the elements' natural ordering, if
94	<	* comparator is null:  For each node n in the heap and each descendant d
95	<	* of n, n <= d.
96	<	*
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.
91	>	* Priority queue represented as a balanced binary heap: the two
92	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
93	>	* priority queue is ordered by comparator, or by the elements'
94	>	* natural ordering, if comparator is null: For each node n in the
95	>	* heap and each descendant d of n, n <= d.  The element with the
96	>	* lowest value is in queue[0], assuming the queue is nonempty.
97		*/
98	<	private transient Object[] queue;
98	>	transient Object[] queue; // non-private to simplify nested class access
99
100		/**
101		* The number of elements in the priority queue.
#	Line 75 | Line 112 | public class PriorityQueue<E> extends Ab
112		* The number of times this priority queue has been
113		* <i>structurally modified</i>.  See AbstractList for gory details.
114		*/
115	<	private transient int modCount = 0;
115	>	transient int modCount = 0; // non-private to simplify nested class access
116
117		/**
118	<	* Create a <tt>PriorityQueue</tt> with the default initial capacity
119	<	* (11) that orders its elements according to their natural
120	<	* ordering (using <tt>Comparable</tt>.)
118	>	* Creates a {@code PriorityQueue} with the default initial
119	>	* capacity (11) that orders its elements according to their
120	>	* {@linkplain Comparable natural ordering}.
121		*/
122		public PriorityQueue() {
123		this(DEFAULT_INITIAL_CAPACITY, null);
124		}
125
126		/**
127	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
128	<	* that orders its elements according to their natural ordering
129	<	* (using <tt>Comparable</tt>.)
130	<	*
131	<	* @param initialCapacity the initial capacity for this priority queue.
127	>	* Creates a {@code PriorityQueue} with the specified initial
128	>	* capacity that orders its elements according to their
129	>	* {@linkplain Comparable natural ordering}.
130	>	*
131	>	* @param initialCapacity the initial capacity for this priority queue
132	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
133	>	*         than 1
134		*/
135		public PriorityQueue(int initialCapacity) {
136		this(initialCapacity, null);
137		}
138
139		/**
140	<	* Create a <tt>PriorityQueue</tt> with the specified initial capacity
140	>	* Creates a {@code PriorityQueue} with the specified initial capacity
141		* that orders its elements according to the specified comparator.
142		*
143	<	* @param initialCapacity the initial capacity for this priority queue.
144	<	* @param comparator the comparator used to order this priority queue.
145	<	* If <tt>null</tt> then the order depends on the elements' natural
146	<	* ordering.
147	<	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
148	<	* than 1
149	<	*/
150	<	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
143	>	* @param  initialCapacity the initial capacity for this priority queue
144	>	* @param  comparator the comparator that will be used to order this
145	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
146	>	*         natural ordering} of the elements will be used.
147	>	* @throws IllegalArgumentException if {@code initialCapacity} is
148	>	*         less than 1
149	>	*/
150	>	public PriorityQueue(int initialCapacity,
151	>	Comparator<? super E> comparator) {
152	>	// Note: This restriction of at least one is not actually needed,
153	>	// but continues for 1.5 compatibility
154		if (initialCapacity < 1)
155		throw new IllegalArgumentException();
156	<	this.queue = new Object[initialCapacity + 1];
156	>	this.queue = new Object[initialCapacity];
157		this.comparator = comparator;
158		}
159
160		/**
161	<	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
162	<	* collection.  The priority queue has an initial capacity of 110% of the
163	<	* size of the specified collection (bounded by
164	<	* <tt>Integer.MAX_VALUE-1</tt>); or 1 if the collection is empty.
165	<	* If the specified collection
166	<	* 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.
161	>	* Creates a {@code PriorityQueue} containing the elements in the
162	>	* specified collection.  If the specified collection is an instance of
163	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
164	>	* priority queue will be ordered according to the same ordering.
165	>	* Otherwise, this priority queue will be ordered according to the
166	>	* {@linkplain Comparable natural ordering} of its elements.
167		*
168	<	* @param c the collection whose elements are to be placed
169	<	*        into this priority queue.
168	>	* @param  c the collection whose elements are to be placed
169	>	*         into this priority queue
170		* @throws ClassCastException if elements of the specified collection
171		*         cannot be compared to one another according to the priority
172	<	*         queue's ordering.
173	<	* @throws NullPointerException if <tt>c</tt> or any element within it
174	<	* is <tt>null</tt>
172	>	*         queue's ordering
173	>	* @throws NullPointerException if the specified collection or any
174	>	*         of its elements are null
175		*/
176	+	@SuppressWarnings("unchecked")
177		public PriorityQueue(Collection<? extends E> c) {
178	<	int sz = c.size();
179	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
180	<	Integer.MAX_VALUE - 1);
181	<	if (initialCapacity < 1)
182	<	initialCapacity = 1;
183	<
184	<	this.queue = new Object[initialCapacity + 1];
178	>	if (c instanceof SortedSet<?>) {
179	>	SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
180	>	this.comparator = (Comparator<? super E>) ss.comparator();
181	>	initElementsFromCollection(ss);
182	>	}
183	>	else if (c instanceof PriorityQueue<?>) {
184	>	PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
185	>	this.comparator = (Comparator<? super E>) pq.comparator();
186	>	initFromPriorityQueue(pq);
187	>	}
188	>	else {
189	>	this.comparator = null;
190	>	initFromCollection(c);
191	>	}
192	>	}
193
194	<	// FIXME: if c is larger than Integer.MAX_VALUE we'll
195	<	// overflow the array
194	>	/**
195	>	* Creates a {@code PriorityQueue} containing the elements in the
196	>	* specified priority queue.  This priority queue will be
197	>	* ordered according to the same ordering as the given priority
198	>	* queue.
199	>	*
200	>	* @param  c the priority queue whose elements are to be placed
201	>	*         into this priority queue
202	>	* @throws ClassCastException if elements of {@code c} cannot be
203	>	*         compared to one another according to {@code c}'s
204	>	*         ordering
205	>	* @throws NullPointerException if the specified priority queue or any
206	>	*         of its elements are null
207	>	*/
208	>	@SuppressWarnings("unchecked")
209	>	public PriorityQueue(PriorityQueue<? extends E> c) {
210	>	this.comparator = (Comparator<? super E>) c.comparator();
211	>	initFromPriorityQueue(c);
212	>	}
213
214	<	if (c instanceof Sorted) {
215	<	comparator = (Comparator<? super E>)((Sorted)c).comparator();
214	>	/**
215	>	* Creates a {@code PriorityQueue} containing the elements in the
216	>	* specified sorted set.   This priority queue will be ordered
217	>	* according to the same ordering as the given sorted set.
218	>	*
219	>	* @param  c the sorted set whose elements are to be placed
220	>	*         into this priority queue
221	>	* @throws ClassCastException if elements of the specified sorted
222	>	*         set cannot be compared to one another according to the
223	>	*         sorted set's ordering
224	>	* @throws NullPointerException if the specified sorted set or any
225	>	*         of its elements are null
226	>	*/
227	>	@SuppressWarnings("unchecked")
228	>	public PriorityQueue(SortedSet<? extends E> c) {
229	>	this.comparator = (Comparator<? super E>) c.comparator();
230	>	initElementsFromCollection(c);
231	>	}
232	>
233	>	private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
234	>	if (c.getClass() == PriorityQueue.class) {
235	>	this.queue = c.toArray();
236	>	this.size = c.size();
237		} else {
238	<	comparator = null;
238	>	initFromCollection(c);
239		}
240	+	}
241
242	<	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
243	<	add(i.next());
242	>	private void initElementsFromCollection(Collection<? extends E> c) {
243	>	Object[] a = c.toArray();
244	>	// If c.toArray incorrectly doesn't return Object[], copy it.
245	>	if (a.getClass() != Object[].class)
246	>	a = Arrays.copyOf(a, a.length, Object[].class);
247	>	int len = a.length;
248	>	if (len == 1 || this.comparator != null)
249	>	for (int i = 0; i < len; i++)
250	>	if (a[i] == null)
251	>	throw new NullPointerException();
252	>	this.queue = a;
253	>	this.size = a.length;
254		}
255
256	<	// Queue Methods
256	>	/**
257	>	* Initializes queue array with elements from the given Collection.
258	>	*
259	>	* @param c the collection
260	>	*/
261	>	private void initFromCollection(Collection<? extends E> c) {
262	>	initElementsFromCollection(c);
263	>	heapify();
264	>	}
265	>
266	>	/**
267	>	* The maximum size of array to allocate.
268	>	* Some VMs reserve some header words in an array.
269	>	* Attempts to allocate larger arrays may result in
270	>	* OutOfMemoryError: Requested array size exceeds VM limit
271	>	*/
272	>	private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
273
274		/**
275	<	* Add the specified element to this priority queue.
275	>	* Increases the capacity of the array.
276		*
277	<	* @return <tt>true</tt>
167	<	* @throws ClassCastException if the specified element cannot be compared
168	<	* with elements currently in the priority queue according
169	<	* to the priority queue's ordering.
170	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
277	>	* @param minCapacity the desired minimum capacity
278		*/
279	<	public boolean offer(E o) {
280	<	if (o == null)
281	<	throw new NullPointerException();
282	<	modCount++;
283	<	++size;
279	>	private void grow(int minCapacity) {
280	>	int oldCapacity = queue.length;
281	>	// Double size if small; else grow by 50%
282	>	int newCapacity = oldCapacity + ((oldCapacity < 64) ?
283	>	(oldCapacity + 2) :
284	>	(oldCapacity >> 1));
285	>	// overflow-conscious code
286	>	if (newCapacity - MAX_ARRAY_SIZE > 0)
287	>	newCapacity = hugeCapacity(minCapacity);
288	>	queue = Arrays.copyOf(queue, newCapacity);
289	>	}
290
291	<	// Grow backing store if necessary
292	<	// FIXME: watch for overflow
293	<	// FIXME: what if we're full?
294	<	while (size >= queue.length) {
295	<	Object[] newQueue = new Object[2 * queue.length];
296	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
297	<	queue = newQueue;
185	<	}
291	>	private static int hugeCapacity(int minCapacity) {
292	>	if (minCapacity < 0) // overflow
293	>	throw new OutOfMemoryError();
294	>	return (minCapacity > MAX_ARRAY_SIZE) ?
295	>	Integer.MAX_VALUE :
296	>	MAX_ARRAY_SIZE;
297	>	}
298
299	<	queue[size] = o;
300	<	fixUp(size);
301	<	return true;
299	>	/**
300	>	* Inserts the specified element into this priority queue.
301	>	*
302	>	* @return {@code true} (as specified by {@link Collection#add})
303	>	* @throws ClassCastException if the specified element cannot be
304	>	*         compared with elements currently in this priority queue
305	>	*         according to the priority queue's ordering
306	>	* @throws NullPointerException if the specified element is null
307	>	*/
308	>	public boolean add(E e) {
309	>	return offer(e);
310		}
311
312	<	public E poll() {
313	<	if (size == 0)
314	<	return null;
315	<	return (E) remove(1);
312	>	/**
313	>	* Inserts the specified element into this priority queue.
314	>	*
315	>	* @return {@code true} (as specified by {@link Queue#offer})
316	>	* @throws ClassCastException if the specified element cannot be
317	>	*         compared with elements currently in this priority queue
318	>	*         according to the priority queue's ordering
319	>	* @throws NullPointerException if the specified element is null
320	>	*/
321	>	public boolean offer(E e) {
322	>	if (e == null)
323	>	throw new NullPointerException();
324	>	modCount++;
325	>	int i = size;
326	>	if (i >= queue.length)
327	>	grow(i + 1);
328	>	size = i + 1;
329	>	if (i == 0)
330	>	queue[0] = e;
331	>	else
332	>	siftUp(i, e);
333	>	return true;
334		}
335
336	+	@SuppressWarnings("unchecked")
337		public E peek() {
338	<	return (E) queue[1];
338	>	return (size == 0) ? null : (E) queue[0];
339		}
340
341	<	// Collection Methods
341	>	private int indexOf(Object o) {
342	>	if (o != null) {
343	>	for (int i = 0; i < size; i++)
344	>	if (o.equals(queue[i]))
345	>	return i;
346	>	}
347	>	return -1;
348	>	}
349
350	<	// these first two override just to get the throws docs
350	>	/**
351	>	* Removes a single instance of the specified element from this queue,
352	>	* if it is present.  More formally, removes an element {@code e} such
353	>	* that {@code o.equals(e)}, if this queue contains one or more such
354	>	* elements.  Returns {@code true} if and only if this queue contained
355	>	* the specified element (or equivalently, if this queue changed as a
356	>	* result of the call).
357	>	*
358	>	* @param o element to be removed from this queue, if present
359	>	* @return {@code true} if this queue changed as a result of the call
360	>	*/
361	>	public boolean remove(Object o) {
362	>	int i = indexOf(o);
363	>	if (i == -1)
364	>	return false;
365	>	else {
366	>	removeAt(i);
367	>	return true;
368	>	}
369	>	}
370
371		/**
372	<	* @throws NullPointerException if the specified element is <tt>null</tt>.
373	<	* @throws ClassCastException if the specified element cannot be compared
374	<	* with elements currently in the priority queue according
375	<	* to the priority queue's ordering.
372	>	* Version of remove using reference equality, not equals.
373	>	* Needed by iterator.remove.
374	>	*
375	>	* @param o element to be removed from this queue, if present
376	>	* @return {@code true} if removed
377		*/
378	<	public boolean add(E o) {
379	<	return super.add(o);
378	>	boolean removeEq(Object o) {
379	>	for (int i = 0; i < size; i++) {
380	>	if (o == queue[i]) {
381	>	removeAt(i);
382	>	return true;
383	>	}
384	>	}
385	>	return false;
386		}
387
388		/**
389	<	* @throws ClassCastException if any element cannot be compared
390	<	* with elements currently in the priority queue according
391	<	* to the priority queue's ordering.
392	<	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
393	<	* is <tt>null</tt>
389	>	* Returns {@code true} if this queue contains the specified element.
390	>	* More formally, returns {@code true} if and only if this queue contains
391	>	* at least one element {@code e} such that {@code o.equals(e)}.
392	>	*
393	>	* @param o object to be checked for containment in this queue
394	>	* @return {@code true} if this queue contains the specified element
395		*/
396	<	public boolean addAll(Collection<? extends E> c) {
397	<	return super.addAll(c);
396	>	public boolean contains(Object o) {
397	>	return indexOf(o) != -1;
398		}
399
400	<	public boolean remove(Object o) {
401	<	if (o == null)
402	<	return false;
400	>	/**
401	>	* Returns an array containing all of the elements in this queue.
402	>	* The elements are in no particular order.
403	>	*
404	>	* <p>The returned array will be "safe" in that no references to it are
405	>	* maintained by this queue.  (In other words, this method must allocate
406	>	* a new array).  The caller is thus free to modify the returned array.
407	>	*
408	>	* <p>This method acts as bridge between array-based and collection-based
409	>	* APIs.
410	>	*
411	>	* @return an array containing all of the elements in this queue
412	>	*/
413	>	public Object[] toArray() {
414	>	return Arrays.copyOf(queue, size);
415	>	}
416
417	<	if (comparator == null) {
418	<	for (int i = 1; i <= size; i++) {
419	<	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
420	<	remove(i);
421	<	return true;
422	<	}
423	<	}
424	<	} else {
425	<	for (int i = 1; i <= size; i++) {
426	<	if (comparator.compare((E)queue[i], (E)o) == 0) {
427	<	remove(i);
428	<	return true;
429	<	}
430	<	}
431	<	}
432	<	return false;
417	>	/**
418	>	* Returns an array containing all of the elements in this queue; the
419	>	* runtime type of the returned array is that of the specified array.
420	>	* The returned array elements are in no particular order.
421	>	* If the queue fits in the specified array, it is returned therein.
422	>	* Otherwise, a new array is allocated with the runtime type of the
423	>	* specified array and the size of this queue.
424	>	*
425	>	* <p>If the queue fits in the specified array with room to spare
426	>	* (i.e., the array has more elements than the queue), the element in
427	>	* the array immediately following the end of the collection is set to
428	>	* {@code null}.
429	>	*
430	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
431	>	* array-based and collection-based APIs.  Further, this method allows
432	>	* precise control over the runtime type of the output array, and may,
433	>	* under certain circumstances, be used to save allocation costs.
434	>	*
435	>	* <p>Suppose {@code x} is a queue known to contain only strings.
436	>	* The following code can be used to dump the queue into a newly
437	>	* allocated array of {@code String}:
438	>	*
439	>	*  <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
440	>	*
441	>	* Note that {@code toArray(new Object[0])} is identical in function to
442	>	* {@code toArray()}.
443	>	*
444	>	* @param a the array into which the elements of the queue are to
445	>	*          be stored, if it is big enough; otherwise, a new array of the
446	>	*          same runtime type is allocated for this purpose.
447	>	* @return an array containing all of the elements in this queue
448	>	* @throws ArrayStoreException if the runtime type of the specified array
449	>	*         is not a supertype of the runtime type of every element in
450	>	*         this queue
451	>	* @throws NullPointerException if the specified array is null
452	>	*/
453	>	@SuppressWarnings("unchecked")
454	>	public <T> T[] toArray(T[] a) {
455	>	final int size = this.size;
456	>	if (a.length < size)
457	>	// Make a new array of a's runtime type, but my contents:
458	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
459	>	System.arraycopy(queue, 0, a, 0, size);
460	>	if (a.length > size)
461	>	a[size] = null;
462	>	return a;
463		}
464
465	+	/**
466	+	* Returns an iterator over the elements in this queue. The iterator
467	+	* does not return the elements in any particular order.
468	+	*
469	+	* @return an iterator over the elements in this queue
470	+	*/
471		public Iterator<E> iterator() {
472		return new Itr();
473		}
474
475	<	private class Itr implements Iterator<E> {
475	>	private final class Itr implements Iterator<E> {
476		/**
477		* Index (into queue array) of element to be returned by
478		* subsequent call to next.
479		*/
480	<	private int cursor = 1;
480	>	private int cursor = 0;
481	>
482	>	/**
483	>	* Index of element returned by most recent call to next,
484	>	* unless that element came from the forgetMeNot list.
485	>	* Set to -1 if element is deleted by a call to remove.
486	>	*/
487	>	private int lastRet = -1;
488	>
489	>	/**
490	>	* A queue of elements that were moved from the unvisited portion of
491	>	* the heap into the visited portion as a result of "unlucky" element
492	>	* removals during the iteration.  (Unlucky element removals are those
493	>	* that require a siftup instead of a siftdown.)  We must visit all of
494	>	* the elements in this list to complete the iteration.  We do this
495	>	* after we've completed the "normal" iteration.
496	>	*
497	>	* We expect that most iterations, even those involving removals,
498	>	* will not need to store elements in this field.
499	>	*/
500	>	private ArrayDeque<E> forgetMeNot = null;
501
502		/**
503	<	* Index of element returned by most recent call to next or
504	<	* previous.  Reset to 0 if this element is deleted by a call
263	<	* to remove.
503	>	* Element returned by the most recent call to next iff that
504	>	* element was drawn from the forgetMeNot list.
505		*/
506	<	private int lastRet = 0;
506	>	private E lastRetElt = null;
507
508		/**
509		* The modCount value that the iterator believes that the backing
510	<	* List should have.  If this expectation is violated, the iterator
510	>	* Queue should have.  If this expectation is violated, the iterator
511		* has detected concurrent modification.
512		*/
513		private int expectedModCount = modCount;
514
515		public boolean hasNext() {
516	<	return cursor <= size;
516	>	return cursor < size ||
517	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
518		}
519
520	+	@SuppressWarnings("unchecked")
521		public E next() {
522	<	checkForComodification();
523	<	if (cursor > size)
524	<	throw new NoSuchElementException();
525	<	E result = (E) queue[cursor];
526	<	lastRet = cursor++;
527	<	return result;
522	>	if (expectedModCount != modCount)
523	>	throw new ConcurrentModificationException();
524	>	if (cursor < size)
525	>	return (E) queue[lastRet = cursor++];
526	>	if (forgetMeNot != null) {
527	>	lastRet = -1;
528	>	lastRetElt = forgetMeNot.poll();
529	>	if (lastRetElt != null)
530	>	return lastRetElt;
531	>	}
532	>	throw new NoSuchElementException();
533		}
534
535		public void remove() {
536	<	if (lastRet == 0)
536	>	if (expectedModCount != modCount)
537	>	throw new ConcurrentModificationException();
538	>	if (lastRet != -1) {
539	>	E moved = PriorityQueue.this.removeAt(lastRet);
540	>	lastRet = -1;
541	>	if (moved == null)
542	>	cursor--;
543	>	else {
544	>	if (forgetMeNot == null)
545	>	forgetMeNot = new ArrayDeque<>();
546	>	forgetMeNot.add(moved);
547	>	}
548	>	} else if (lastRetElt != null) {
549	>	PriorityQueue.this.removeEq(lastRetElt);
550	>	lastRetElt = null;
551	>	} else {
552		throw new IllegalStateException();
553	<	checkForComodification();
291	<
292	<	PriorityQueue.this.remove(lastRet);
293	<	if (lastRet < cursor)
294	<	cursor--;
295	<	lastRet = 0;
553	>	}
554		expectedModCount = modCount;
555		}
298	–
299	–	final void checkForComodification() {
300	–	if (modCount != expectedModCount)
301	–	throw new ConcurrentModificationException();
302	–	}
556		}
557
305	–	/**
306	–	* Returns the number of elements in this priority queue.
307	–	*
308	–	* @return the number of elements in this priority queue.
309	–	*/
558		public int size() {
559		return size;
560		}
561
562		/**
563	<	* Remove all elements from the priority queue.
563	>	* Removes all of the elements from this priority queue.
564	>	* The queue will be empty after this call returns.
565		*/
566		public void clear() {
567		modCount++;
568	<
320	<	// Null out element references to prevent memory leak
321	<	for (int i=1; i<=size; i++)
568	>	for (int i = 0; i < size; i++)
569		queue[i] = null;
323	–
570		size = 0;
571		}
572
573	<	/**
574	<	* Removes and returns the ith element from queue.  Recall
575	<	* that queue is one-based, so 1 <= i <= size.
576	<	*
577	<	* XXX: Could further special-case i==size, but is it worth it?
332	<	* XXX: Could special-case i==0, but is it worth it?
333	<	*/
334	<	private E remove(int i) {
335	<	assert i <= size;
573	>	@SuppressWarnings("unchecked")
574	>	public E poll() {
575	>	if (size == 0)
576	>	return null;
577	>	int s = --size;
578		modCount++;
579	<
580	<	E result = (E) queue[i];
581	<	queue[i] = queue[size];
582	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
583	<	if (i <= size)
342	<	fixDown(i);
579	>	E result = (E) queue[0];
580	>	E x = (E) queue[s];
581	>	queue[s] = null;
582	>	if (s != 0)
583	>	siftDown(0, x);
584		return result;
585		}
586
587		/**
588	<	* Establishes the heap invariant (described above) assuming the heap
589	<	* satisfies the invariant except possibly for the leaf-node indexed by k
590	<	* (which may have a nextExecutionTime less than its parent's).
591	<	*
592	<	* This method functions by "promoting" queue[k] up the hierarchy
593	<	* (by swapping it with its parent) repeatedly until queue[k]
594	<	* is greater than or equal to its parent.
595	<	*/
596	<	private void fixUp(int k) {
597	<	if (comparator == null) {
598	<	while (k > 1) {
599	<	int j = k >> 1;
600	<	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
601	<	break;
602	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
603	<	k = j;
604	<	}
605	<	} else {
606	<	while (k > 1) {
607	<	int j = k >> 1;
608	<	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
609	<	break;
610	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
611	<	k = j;
588	>	* Removes the ith element from queue.
589	>	*
590	>	* Normally this method leaves the elements at up to i-1,
591	>	* inclusive, untouched.  Under these circumstances, it returns
592	>	* null.  Occasionally, in order to maintain the heap invariant,
593	>	* it must swap a later element of the list with one earlier than
594	>	* i.  Under these circumstances, this method returns the element
595	>	* that was previously at the end of the list and is now at some
596	>	* position before i. This fact is used by iterator.remove so as to
597	>	* avoid missing traversing elements.
598	>	*/
599	>	@SuppressWarnings("unchecked")
600	>	private E removeAt(int i) {
601	>	// assert i >= 0 && i < size;
602	>	modCount++;
603	>	int s = --size;
604	>	if (s == i) // removed last element
605	>	queue[i] = null;
606	>	else {
607	>	E moved = (E) queue[s];
608	>	queue[s] = null;
609	>	siftDown(i, moved);
610	>	if (queue[i] == moved) {
611	>	siftUp(i, moved);
612	>	if (queue[i] != moved)
613	>	return moved;
614		}
615		}
616	+	return null;
617		}
618
619		/**
620	<	* Establishes the heap invariant (described above) in the subtree
621	<	* rooted at k, which is assumed to satisfy the heap invariant except
622	<	* possibly for node k itself (which may be greater than its children).
623	<	*
624	<	* This method functions by "demoting" queue[k] down the hierarchy
625	<	* (by swapping it with its smaller child) repeatedly until queue[k]
626	<	* is less than or equal to its children.
627	<	*/
628	<	private void fixDown(int k) {
629	<	int j;
630	<	if (comparator == null) {
631	<	while ((j = k << 1) <= size) {
632	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
633	<	j++; // j indexes smallest kid
634	<	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
635	<	break;
636	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
637	<	k = j;
638	<	}
639	<	} else {
640	<	while ((j = k << 1) <= size) {
641	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
642	<	j++; // j indexes smallest kid
643	<	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
644	<	break;
645	<	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
646	<	k = j;
647	<	}
620	>	* Inserts item x at position k, maintaining heap invariant by
621	>	* promoting x up the tree until it is greater than or equal to
622	>	* its parent, or is the root.
623	>	*
624	>	* To simplify and speed up coercions and comparisons. the
625	>	* Comparable and Comparator versions are separated into different
626	>	* methods that are otherwise identical. (Similarly for siftDown.)
627	>	*
628	>	* @param k the position to fill
629	>	* @param x the item to insert
630	>	*/
631	>	private void siftUp(int k, E x) {
632	>	if (comparator != null)
633	>	siftUpUsingComparator(k, x);
634	>	else
635	>	siftUpComparable(k, x);
636	>	}
637	>
638	>	@SuppressWarnings("unchecked")
639	>	private void siftUpComparable(int k, E x) {
640	>	Comparable<? super E> key = (Comparable<? super E>) x;
641	>	while (k > 0) {
642	>	int parent = (k - 1) >>> 1;
643	>	Object e = queue[parent];
644	>	if (key.compareTo((E) e) >= 0)
645	>	break;
646	>	queue[k] = e;
647	>	k = parent;
648	>	}
649	>	queue[k] = key;
650	>	}
651	>
652	>	@SuppressWarnings("unchecked")
653	>	private void siftUpUsingComparator(int k, E x) {
654	>	while (k > 0) {
655	>	int parent = (k - 1) >>> 1;
656	>	Object e = queue[parent];
657	>	if (comparator.compare(x, (E) e) >= 0)
658	>	break;
659	>	queue[k] = e;
660	>	k = parent;
661		}
662	+	queue[k] = x;
663		}
664
665	+	/**
666	+	* Inserts item x at position k, maintaining heap invariant by
667	+	* demoting x down the tree repeatedly until it is less than or
668	+	* equal to its children or is a leaf.
669	+	*
670	+	* @param k the position to fill
671	+	* @param x the item to insert
672	+	*/
673	+	private void siftDown(int k, E x) {
674	+	if (comparator != null)
675	+	siftDownUsingComparator(k, x);
676	+	else
677	+	siftDownComparable(k, x);
678	+	}
679	+
680	+	@SuppressWarnings("unchecked")
681	+	private void siftDownComparable(int k, E x) {
682	+	Comparable<? super E> key = (Comparable<? super E>)x;
683	+	int half = size >>> 1;        // loop while a non-leaf
684	+	while (k < half) {
685	+	int child = (k << 1) + 1; // assume left child is least
686	+	Object c = queue[child];
687	+	int right = child + 1;
688	+	if (right < size &&
689	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
690	+	c = queue[child = right];
691	+	if (key.compareTo((E) c) <= 0)
692	+	break;
693	+	queue[k] = c;
694	+	k = child;
695	+	}
696	+	queue[k] = key;
697	+	}
698	+
699	+	@SuppressWarnings("unchecked")
700	+	private void siftDownUsingComparator(int k, E x) {
701	+	int half = size >>> 1;
702	+	while (k < half) {
703	+	int child = (k << 1) + 1;
704	+	Object c = queue[child];
705	+	int right = child + 1;
706	+	if (right < size &&
707	+	comparator.compare((E) c, (E) queue[right]) > 0)
708	+	c = queue[child = right];
709	+	if (comparator.compare(x, (E) c) <= 0)
710	+	break;
711	+	queue[k] = c;
712	+	k = child;
713	+	}
714	+	queue[k] = x;
715	+	}
716	+
717	+	/**
718	+	* Establishes the heap invariant (described above) in the entire tree,
719	+	* assuming nothing about the order of the elements prior to the call.
720	+	*/
721	+	@SuppressWarnings("unchecked")
722	+	private void heapify() {
723	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
724	+	siftDown(i, (E) queue[i]);
725	+	}
726	+
727	+	/**
728	+	* Returns the comparator used to order the elements in this
729	+	* queue, or {@code null} if this queue is sorted according to
730	+	* the {@linkplain Comparable natural ordering} of its elements.
731	+	*
732	+	* @return the comparator used to order this queue, or
733	+	*         {@code null} if this queue is sorted according to the
734	+	*         natural ordering of its elements
735	+	*/
736		public Comparator<? super E> comparator() {
737		return comparator;
738		}
739
740		/**
741	<	* Save the state of the instance to a stream (that
413	<	* is, serialize it).
741	>	* Saves this queue to a stream (that is, serializes it).
742		*
743		* @serialData The length of the array backing the instance is
744	<	* emitted (int), followed by all of its elements (each an
745	<	* <tt>Object</tt>) in the proper order.
744	>	*             emitted (int), followed by all of its elements
745	>	*             (each an {@code Object}) in the proper order.
746		* @param s the stream
747		*/
748	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
749	<	throws java.io.IOException{
748	>	private void writeObject(java.io.ObjectOutputStream s)
749	>	throws java.io.IOException {
750		// Write out element count, and any hidden stuff
751		s.defaultWriteObject();
752
753	<	// Write out array length
754	<	s.writeInt(queue.length);
753	>	// Write out array length, for compatibility with 1.5 version
754	>	s.writeInt(Math.max(2, size + 1));
755
756	<	// Write out all elements in the proper order.
757	<	for (int i=0; i<size; i++)
756	>	// Write out all elements in the "proper order".
757	>	for (int i = 0; i < size; i++)
758		s.writeObject(queue[i]);
759		}
760
761		/**
762	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
763	<	* deserialize it).
762	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
763	>	* (that is, deserializes it).
764	>	*
765		* @param s the stream
766		*/
767	<	private synchronized void readObject(java.io.ObjectInputStream s)
767	>	private void readObject(java.io.ObjectInputStream s)
768		throws java.io.IOException, ClassNotFoundException {
769		// Read in size, and any hidden stuff
770		s.defaultReadObject();
771
772	<	// Read in array length and allocate array
773	<	int arrayLength = s.readInt();
774	<	queue = new Object[arrayLength];
772	>	// Read in (and discard) array length
773	>	s.readInt();
774	>
775	>	queue = new Object[size];
776
777	<	// Read in all elements in the proper order.
778	<	for (int i=0; i<size; i++)
777	>	// Read in all elements.
778	>	for (int i = 0; i < size; i++)
779		queue[i] = s.readObject();
780	+
781	+	// Elements are guaranteed to be in "proper order", but the
782	+	// spec has never explained what that might be.
783	+	heapify();
784		}
785
786	<	}
786	>	public Spliterator<E> spliterator() {
787	>	return new PriorityQueueSpliterator<E>(this, 0, -1, 0);
788	>	}
789	>
790	>	/**
791	>	* This is very similar to ArrayList Spliterator, except for extra
792	>	* null checks.
793	>	*/
794	>	static final class PriorityQueueSpliterator<E> implements Spliterator<E> {
795	>	private final PriorityQueue<E> pq;
796	>	private int index;            // current index, modified on advance/split
797	>	private int fence;            // -1 until first use
798	>	private int expectedModCount; // initialized when fence set
799
800	+	/** Creates new spliterator covering the given range */
801	+	PriorityQueueSpliterator(PriorityQueue<E> pq, int origin, int fence,
802	+	int expectedModCount) {
803	+	this.pq = pq;
804	+	this.index = origin;
805	+	this.fence = fence;
806	+	this.expectedModCount = expectedModCount;
807	+	}
808	+
809	+	private int getFence() { // initialize fence to size on first use
810	+	int hi;
811	+	if ((hi = fence) < 0) {
812	+	expectedModCount = pq.modCount;
813	+	hi = fence = pq.size;
814	+	}
815	+	return hi;
816	+	}
817	+
818	+	public Spliterator<E> trySplit() {
819	+	int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
820	+	return (lo >= mid) ? null :
821	+	new PriorityQueueSpliterator<E>(pq, lo, index = mid,
822	+	expectedModCount);
823	+	}
824	+
825	+	@SuppressWarnings("unchecked")
826	+	public void forEach(Consumer<? super E> action) {
827	+	int i, hi, mc; // hoist accesses and checks from loop
828	+	PriorityQueue<E> q; Object[] a;
829	+	if (action == null)
830	+	throw new NullPointerException();
831	+	if ((q = pq) != null && (a = q.queue) != null) {
832	+	if ((hi = fence) < 0) {
833	+	mc = q.modCount;
834	+	hi = q.size;
835	+	}
836	+	else
837	+	mc = expectedModCount;
838	+	if ((i = index) >= 0 && (index = hi) <= a.length) {
839	+	for (E e;; ++i) {
840	+	if (i < hi) {
841	+	if ((e = (E) a[i]) == null) // must be CME
842	+	break;
843	+	action.accept(e);
844	+	}
845	+	else if (q.modCount != mc)
846	+	break;
847	+	else
848	+	return;
849	+	}
850	+	}
851	+	}
852	+	throw new ConcurrentModificationException();
853	+	}
854	+
855	+	public boolean tryAdvance(Consumer<? super E> action) {
856	+	int hi = getFence(), lo = index;
857	+	if (lo >= 0 && lo < hi) {
858	+	index = lo + 1;
859	+	@SuppressWarnings("unchecked") E e = (E)pq.queue[lo];
860	+	if (e == null)
861	+	throw new ConcurrentModificationException();
862	+	action.accept(e);
863	+	if (pq.modCount != expectedModCount)
864	+	throw new ConcurrentModificationException();
865	+	return true;
866	+	}
867	+	return false;
868	+	}
869	+
870	+	public long estimateSize() {
871	+	return (long) (getFence() - index);
872	+	}
873	+
874	+	public int characteristics() {
875	+	return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
876	+	}
877	+	}
878	+	}

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