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root/jsr166/jsr166/src/main/java/util/PriorityQueue.java

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.9 by dl, Sun Jul 13 22:51:22 2003 UTC vs.
Revision 1.64 by jsr166, Sun Mar 19 01:00:40 2006 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5	>	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	>	*/
7	>
8	>	package java.util;
9
10		/**
11	<	* An unbounded priority queue based on a priority heap.  This queue orders
12	<	* elements according to an order specified at construction time, which is
13	<	* specified in the same manner as {@link TreeSet} and {@link TreeMap}: elements are ordered
14	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
15	<	* according to a {@link Comparator}, depending on which constructor is used.
16	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
17	<	* minimal element with respect to the specified ordering.  If multiple
18	<	* elements are tied for least value, no guarantees are made as to
19	<	* which of these elements is returned.
11	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
12	>	* The elements of the priority queue are ordered according to their
13	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
14	>	* provided at queue construction time, depending on which constructor is
15	>	* used.  A priority queue does not permit {@code null} elements.
16	>	* A priority queue relying on natural ordering also does not permit
17	>	* insertion of non-comparable objects (doing so may result in
18	>	* {@code ClassCastException}).
19	>	*
20	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
21	>	* with respect to the specified ordering.  If multiple elements are
22	>	* tied for least value, the head is one of those elements -- ties are
23	>	* broken arbitrarily.  The queue retrieval operations {@code poll},
24	>	* {@code remove}, {@code peek}, and {@code element} access the
25	>	* element at the head of the queue.
26	>	*
27	>	* <p>A priority queue is unbounded, but has an internal
28	>	* <i>capacity</i> governing the size of an array used to store the
29	>	* elements on the queue.  It is always at least as large as the queue
30	>	* size.  As elements are added to a priority queue, its capacity
31	>	* grows automatically.  The details of the growth policy are not
32	>	* specified.
33		*
34	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
35	<	* size of the array used internally to store the elements on the
36	<	* queue.  It is always at least as large as the queue size.  As
37	<	* elements are added to a priority queue, its capacity grows
38	<	* automatically.  The details of the growth policy are not specified.
34	>	* <p>This class and its iterator implement all of the
35	>	* <em>optional</em> methods of the {@link Collection} and {@link
36	>	* Iterator} interfaces.  The Iterator provided in method {@link
37	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
38	>	* the priority queue in any particular order. If you need ordered
39	>	* traversal, consider using {@code Arrays.sort(pq.toArray())}.
40		*
41	<	*<p>Implementation note: this implementation provides O(log(n)) time
42	<	*for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
43	<	*<tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
44	<	*<tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
45	<	*constant time for the retrieval methods (<tt>peek</tt>,
46	<	*<tt>element</tt>, and <tt>size</tt>).
41	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
42	>	* Multiple threads should not access a {@code PriorityQueue}
43	>	* instance concurrently if any of the threads modifies the queue.
44	>	* Instead, use the thread-safe {@link
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46	>	*
47	>	* <p>Implementation note: this implementation provides
48	>	* O(log(n)) time for the enqueing and dequeing methods
49	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
50	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
51	>	* methods; and constant time for the retrieval methods
52	>	* ({@code peek}, {@code element}, and {@code size}).
53		*
54		* <p>This class is a member of the
55		* <a href="{@docRoot}/../guide/collections/index.html">
56		* Java Collections Framework</a>.
57	+	*
58		* @since 1.5
59	<	* @author Josh Bloch
59	>	* @version %I%, %G%
60	>	* @author Josh Bloch, Doug Lea
61	>	* @param <E> the type of elements held in this collection
62		*/
63		public class PriorityQueue<E> extends AbstractQueue<E>
64	<	implements Queue<E>,
65	<	java.io.Serializable {
64	>	implements java.io.Serializable {
65	>
66	>	private static final long serialVersionUID = -7720805057305804111L;
67	>
68		private static final int DEFAULT_INITIAL_CAPACITY = 11;
69
70		/**
71	<	* Priority queue represented as a balanced binary heap: the two children
72	<	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
73	<	* ordered by comparator, or by the elements' natural ordering, if
74	<	* comparator is null:  For each node n in the heap and each descendant d
75	<	* of n, n <= d.
76	<	*
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.
71	>	* Priority queue represented as a balanced binary heap: the two
72	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
73	>	* priority queue is ordered by comparator, or by the elements'
74	>	* natural ordering, if comparator is null: For each node n in the
75	>	* heap and each descendant d of n, n <= d.  The element with the
76	>	* lowest value is in queue[0], assuming the queue is nonempty.
77		*/
78	<	private transient E[] queue;
78	>	private transient Object[] queue;
79
80		/**
81		* The number of elements in the priority queue.
#	Line 59 | Line 86 | public class PriorityQueue<E> extends Ab
86		* The comparator, or null if priority queue uses elements'
87		* natural ordering.
88		*/
89	<	private final Comparator<E> comparator;
89	>	private final Comparator<? super E> comparator;
90
91		/**
92		* The number of times this priority queue has been
#	Line 68 | Line 95 | public class PriorityQueue<E> extends Ab
95		private transient int modCount = 0;
96
97		/**
98	<	* Create a new priority queue with the default initial capacity
99	<	* (11) that orders its elements according to their natural
100	<	* ordering (using <tt>Comparable</tt>.)
98	>	* Creates a {@code PriorityQueue} with the default initial
99	>	* capacity (11) that orders its elements according to their
100	>	* {@linkplain Comparable natural ordering}.
101		*/
102		public PriorityQueue() {
103	<	this(DEFAULT_INITIAL_CAPACITY);
103	>	this(DEFAULT_INITIAL_CAPACITY, null);
104		}
105
106		/**
107	<	* Create a new priority queue with the specified initial capacity
108	<	* that orders its elements according to their natural ordering
109	<	* (using <tt>Comparable</tt>.)
107	>	* Creates a {@code PriorityQueue} with the specified initial
108	>	* capacity that orders its elements according to their
109	>	* {@linkplain Comparable natural ordering}.
110		*
111	<	* @param initialCapacity the initial capacity for this priority queue.
111	>	* @param initialCapacity the initial capacity for this priority queue
112	>	* @throws IllegalArgumentException if {@code initialCapacity} is less
113	>	*         than 1
114		*/
115		public PriorityQueue(int initialCapacity) {
116		this(initialCapacity, null);
117		}
118
119		/**
120	<	* Create a new priority queue with the specified initial capacity (11)
120	>	* Creates a {@code PriorityQueue} with the specified initial capacity
121		* that orders its elements according to the specified comparator.
122		*
123	<	* @param initialCapacity the initial capacity for this priority queue.
124	<	* @param comparator the comparator used to order this priority queue.
125	<	*/
126	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
123	>	* @param  initialCapacity the initial capacity for this priority queue
124	>	* @param  comparator the comparator that will be used to order this
125	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
126	>	*         natural ordering} of the elements will be used.
127	>	* @throws IllegalArgumentException if {@code initialCapacity} is
128	>	*         less than 1
129	>	*/
130	>	public PriorityQueue(int initialCapacity,
131	>	Comparator<? super E> comparator) {
132	>	// Note: This restriction of at least one is not actually needed,
133	>	// but continues for 1.5 compatibility
134		if (initialCapacity < 1)
135	<	initialCapacity = 1;
136	<	queue = new E[initialCapacity + 1];
135	>	throw new IllegalArgumentException();
136	>	this.queue = new Object[initialCapacity];
137		this.comparator = comparator;
138		}
139
140		/**
141	<	* Create a new priority queue containing the elements in the specified
142	<	* collection.  The priority queue has an initial capacity of 110% of the
143	<	* size of the specified collection. If the specified collection
144	<	* implements the {@link Sorted} interface, the priority queue will be
145	<	* sorted according to the same comparator, or according to its elements'
146	<	* 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.
141	>	* Creates a {@code PriorityQueue} containing the elements in the
142	>	* specified collection.  If the specified collection is an instance of
143	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
144	>	* priority queue will be ordered according to the same ordering.
145	>	* Otherwise, this priority queue will be ordered according to the
146	>	* {@linkplain Comparable natural ordering} of its elements.
147		*
148	<	* @param initialElements the collection whose elements are to be placed
149	<	*        into this priority queue.
148	>	* @param  c the collection whose elements are to be placed
149	>	*         into this priority queue
150		* @throws ClassCastException if elements of the specified collection
151		*         cannot be compared to one another according to the priority
152	<	*         queue's ordering.
153	<	* @throws NullPointerException if the specified collection or an
154	<	*         element of the specified collection is <tt>null</tt>.
155	<	*/
156	<	public PriorityQueue(Collection<E> initialElements) {
157	<	int sz = initialElements.size();
158	<	int initialCapacity = (int)Math.min((sz * 110L) / 100,
159	<	Integer.MAX_VALUE - 1);
160	<	if (initialCapacity < 1)
161	<	initialCapacity = 1;
162	<	queue = new E[initialCapacity + 1];
163	<
164	<
132	<	if (initialElements instanceof Sorted) {
133	<	comparator = ((Sorted)initialElements).comparator();
134	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
135	<	queue[++size] = i.next();
136	<	} else {
152	>	*         queue's ordering
153	>	* @throws NullPointerException if the specified collection or any
154	>	*         of its elements are null
155	>	*/
156	>	public PriorityQueue(Collection<? extends E> c) {
157	>	initFromCollection(c);
158	>	if (c instanceof SortedSet)
159	>	comparator = (Comparator<? super E>)
160	>	((SortedSet<? extends E>)c).comparator();
161	>	else if (c instanceof PriorityQueue)
162	>	comparator = (Comparator<? super E>)
163	>	((PriorityQueue<? extends E>)c).comparator();
164	>	else {
165		comparator = null;
166	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
139	<	add(i.next());
166	>	heapify();
167		}
168		}
169
170	<	// Queue Methods
170	>	/**
171	>	* Creates a {@code PriorityQueue} containing the elements in the
172	>	* specified priority queue.  This priority queue will be
173	>	* ordered according to the same ordering as the given priority
174	>	* queue.
175	>	*
176	>	* @param  c the priority queue whose elements are to be placed
177	>	*         into this priority queue
178	>	* @throws ClassCastException if elements of {@code c} cannot be
179	>	*         compared to one another according to {@code c}'s
180	>	*         ordering
181	>	* @throws NullPointerException if the specified priority queue or any
182	>	*         of its elements are null
183	>	*/
184	>	public PriorityQueue(PriorityQueue<? extends E> c) {
185	>	comparator = (Comparator<? super E>)c.comparator();
186	>	initFromCollection(c);
187	>	}
188
189		/**
190	<	* Remove and return the minimal element from this priority queue
191	<	* if it contains one or more elements, otherwise return
192	<	* <tt>null</tt>.  The term <i>minimal</i> is defined according to
149	<	* this priority queue's order.
190	>	* Creates a {@code PriorityQueue} containing the elements in the
191	>	* specified sorted set.   This priority queue will be ordered
192	>	* according to the same ordering as the given sorted set.
193		*
194	<	* @return the minimal element from this priority queue if it contains
195	<	*         one or more elements, otherwise <tt>null</tt>.
194	>	* @param  c the sorted set whose elements are to be placed
195	>	*         into this priority queue
196	>	* @throws ClassCastException if elements of the specified sorted
197	>	*         set cannot be compared to one another according to the
198	>	*         sorted set's ordering
199	>	* @throws NullPointerException if the specified sorted set or any
200	>	*         of its elements are null
201		*/
202	<	public E poll() {
203	<	if (size == 0)
204	<	return null;
205	<	return remove(1);
202	>	public PriorityQueue(SortedSet<? extends E> c) {
203	>	comparator = (Comparator<? super E>)c.comparator();
204	>	initFromCollection(c);
205	>	}
206	>
207	>	/**
208	>	* Initializes queue array with elements from the given Collection.
209	>	*
210	>	* @param c the collection
211	>	*/
212	>	private void initFromCollection(Collection<? extends E> c) {
213	>	Object[] a = c.toArray();
214	>	// If c.toArray incorrectly doesn't return Object[], copy it.
215	>	if (a.getClass() != Object[].class)
216	>	a = Arrays.copyOf(a, a.length, Object[].class);
217	>	queue = a;
218	>	size = a.length;
219	>	}
220	>
221	>	/**
222	>	* Increases the capacity of the array.
223	>	*
224	>	* @param minCapacity the desired minimum capacity
225	>	*/
226	>	private void grow(int minCapacity) {
227	>	if (minCapacity < 0) // overflow
228	>	throw new OutOfMemoryError();
229	>	int oldCapacity = queue.length;
230	>	// Double size if small; else grow by 50%
231	>	int newCapacity = ((oldCapacity < 64)?
232	>	((oldCapacity + 1) * 2):
233	>	((oldCapacity / 2) * 3));
234	>	if (newCapacity < 0) // overflow
235	>	newCapacity = Integer.MAX_VALUE;
236	>	if (newCapacity < minCapacity)
237	>	newCapacity = minCapacity;
238	>	queue = Arrays.copyOf(queue, newCapacity);
239	>	}
240	>
241	>	/**
242	>	* Inserts the specified element into this priority queue.
243	>	*
244	>	* @return {@code true} (as specified by {@link Collection#add})
245	>	* @throws ClassCastException if the specified element cannot be
246	>	*         compared with elements currently in this priority queue
247	>	*         according to the priority queue's ordering
248	>	* @throws NullPointerException if the specified element is null
249	>	*/
250	>	public boolean add(E e) {
251	>	return offer(e);
252		}
253
254		/**
255	<	* 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.
255	>	* Inserts the specified element into this priority queue.
256		*
257	<	* @return the minimal element from this priority queue if it contains
258	<	*         one or more elements, otherwise <tt>null</tt>.
257	>	* @return {@code true} (as specified by {@link Queue#offer})
258	>	* @throws ClassCastException if the specified element cannot be
259	>	*         compared with elements currently in this priority queue
260	>	*         according to the priority queue's ordering
261	>	* @throws NullPointerException if the specified element is null
262		*/
263	+	public boolean offer(E e) {
264	+	if (e == null)
265	+	throw new NullPointerException();
266	+	modCount++;
267	+	int i = size;
268	+	if (i >= queue.length)
269	+	grow(i + 1);
270	+	size = i + 1;
271	+	if (i == 0)
272	+	queue[0] = e;
273	+	else
274	+	siftUp(i, e);
275	+	return true;
276	+	}
277	+
278		public E peek() {
279	<	return queue[1];
279	>	if (size == 0)
280	>	return null;
281	>	return (E) queue[0];
282		}
283
284	<	// Collection Methods
284	>	private int indexOf(Object o) {
285	>	if (o != null) {
286	>	for (int i = 0; i < size; i++)
287	>	if (o.equals(queue[i]))
288	>	return i;
289	>	}
290	>	return -1;
291	>	}
292
293		/**
294	<	* Removes a single instance of the specified element from this priority
295	<	* queue, if it is present.  Returns true if this collection contained the
296	<	* specified element (or equivalently, if this collection changed as a
294	>	* Removes a single instance of the specified element from this queue,
295	>	* if it is present.  More formally, removes an element {@code e} such
296	>	* that {@code o.equals(e)}, if this queue contains one or more such
297	>	* elements.  Returns {@code true} if and only if this queue contained
298	>	* the specified element (or equivalently, if this queue changed as a
299		* result of the call).
300		*
301	<	* @param element the element to be removed from this collection,
302	<	* 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.
301	>	* @param o element to be removed from this queue, if present
302	>	* @return {@code true} if this queue changed as a result of the call
303		*/
304	<	public boolean remove(Object element) {
305	<	if (element == null)
306	<	throw new NullPointerException();
304	>	public boolean remove(Object o) {
305	>	int i = indexOf(o);
306	>	if (i == -1)
307	>	return false;
308	>	else {
309	>	removeAt(i);
310	>	return true;
311	>	}
312	>	}
313
314	<	if (comparator == null) {
315	<	for (int i = 1; i <= size; i++) {
316	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
317	<	remove(i);
318	<	return true;
319	<	}
320	<	}
321	<	} else {
322	<	for (int i = 1; i <= size; i++) {
323	<	if (comparator.compare(queue[i], (E) element) == 0) {
324	<	remove(i);
325	<	return true;
209	<	}
314	>	/**
315	>	* Version of remove using reference equality, not equals.
316	>	* Needed by iterator.remove.
317	>	*
318	>	* @param o element to be removed from this queue, if present
319	>	* @return {@code true} if removed
320	>	*/
321	>	boolean removeEq(Object o) {
322	>	for (int i = 0; i < size; i++) {
323	>	if (o == queue[i]) {
324	>	removeAt(i);
325	>	return true;
326		}
327		}
328		return false;
329		}
330
331		/**
332	<	* Returns an iterator over the elements in this priority queue.  The
333	<	* elements of the priority queue will be returned by this iterator in the
334	<	* order specified by the queue, which is to say the order they would be
335	<	* returned by repeated calls to <tt>poll</tt>.
336	<	*
337	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
332	>	* Returns {@code true} if this queue contains the specified element.
333	>	* More formally, returns {@code true} if and only if this queue contains
334	>	* at least one element {@code e} such that {@code o.equals(e)}.
335	>	*
336	>	* @param o object to be checked for containment in this queue
337	>	* @return {@code true} if this queue contains the specified element
338	>	*/
339	>	public boolean contains(Object o) {
340	>	return indexOf(o) != -1;
341	>	}
342	>
343	>	/**
344	>	* Returns an array containing all of the elements in this queue.
345	>	* The elements are in no particular order.
346	>	*
347	>	* <p>The returned array will be "safe" in that no references to it are
348	>	* maintained by this queue.  (In other words, this method must allocate
349	>	* a new array).  The caller is thus free to modify the returned array.
350	>	*
351	>	* <p>This method acts as bridge between array-based and collection-based
352	>	* APIs.
353	>	*
354	>	* @return an array containing all of the elements in this queue
355	>	*/
356	>	public Object[] toArray() {
357	>	return Arrays.copyOf(queue, size);
358	>	}
359	>
360	>	/**
361	>	* Returns an array containing all of the elements in this queue; the
362	>	* runtime type of the returned array is that of the specified array.
363	>	* The returned array elements are in no particular order.
364	>	* If the queue fits in the specified array, it is returned therein.
365	>	* Otherwise, a new array is allocated with the runtime type of the
366	>	* specified array and the size of this queue.
367	>	*
368	>	* <p>If the queue fits in the specified array with room to spare
369	>	* (i.e., the array has more elements than the queue), the element in
370	>	* the array immediately following the end of the collection is set to
371	>	* {@code null}.
372	>	*
373	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
374	>	* array-based and collection-based APIs.  Further, this method allows
375	>	* precise control over the runtime type of the output array, and may,
376	>	* under certain circumstances, be used to save allocation costs.
377	>	*
378	>	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
379	>	* The following code can be used to dump the queue into a newly
380	>	* allocated array of <tt>String</tt>:
381	>	*
382	>	* <pre>
383	>	*     String[] y = x.toArray(new String[0]);</pre>
384	>	*
385	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
386	>	* <tt>toArray()</tt>.
387	>	*
388	>	* @param a the array into which the elements of the queue are to
389	>	*          be stored, if it is big enough; otherwise, a new array of the
390	>	*          same runtime type is allocated for this purpose.
391	>	* @return an array containing all of the elements in this queue
392	>	* @throws ArrayStoreException if the runtime type of the specified array
393	>	*         is not a supertype of the runtime type of every element in
394	>	*         this queue
395	>	* @throws NullPointerException if the specified array is null
396	>	*/
397	>	public <T> T[] toArray(T[] a) {
398	>	if (a.length < size)
399	>	// Make a new array of a's runtime type, but my contents:
400	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
401	>	System.arraycopy(queue, 0, a, 0, size);
402	>	if (a.length > size)
403	>	a[size] = null;
404	>	return a;
405	>	}
406	>
407	>	/**
408	>	* Returns an iterator over the elements in this queue. The iterator
409	>	* does not return the elements in any particular order.
410	>	*
411	>	* @return an iterator over the elements in this queue
412		*/
413		public Iterator<E> iterator() {
414		return new Itr();
415		}
416
417	<	private class Itr implements Iterator<E> {
417	>	private final class Itr implements Iterator<E> {
418		/**
419		* Index (into queue array) of element to be returned by
420		* subsequent call to next.
421		*/
422	<	private int cursor = 1;
422	>	private int cursor = 0;
423
424		/**
425	<	* Index of element returned by most recent call to next or
426	<	* previous.  Reset to 0 if this element is deleted by a call
427	<	* to remove.
425	>	* Index of element returned by most recent call to next,
426	>	* unless that element came from the forgetMeNot list.
427	>	* Set to -1 if element is deleted by a call to remove.
428		*/
429	<	private int lastRet = 0;
429	>	private int lastRet = -1;
430	>
431	>	/**
432	>	* A queue of elements that were moved from the unvisited portion of
433	>	* the heap into the visited portion as a result of "unlucky" element
434	>	* removals during the iteration.  (Unlucky element removals are those
435	>	* that require a siftup instead of a siftdown.)  We must visit all of
436	>	* the elements in this list to complete the iteration.  We do this
437	>	* after we've completed the "normal" iteration.
438	>	*
439	>	* We expect that most iterations, even those involving removals,
440	>	* will not need to store elements in this field.
441	>	*/
442	>	private ArrayDeque<E> forgetMeNot = null;
443	>
444	>	/**
445	>	* Element returned by the most recent call to next iff that
446	>	* element was drawn from the forgetMeNot list.
447	>	*/
448	>	private E lastRetElt = null;
449
450		/**
451		* The modCount value that the iterator believes that the backing
452	<	* List should have.  If this expectation is violated, the iterator
452	>	* Queue should have.  If this expectation is violated, the iterator
453		* has detected concurrent modification.
454		*/
455		private int expectedModCount = modCount;
456
457		public boolean hasNext() {
458	<	return cursor <= size;
458	>	return cursor < size ||
459	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
460		}
461
462		public E next() {
463	<	checkForComodification();
464	<	if (cursor > size)
465	<	throw new NoSuchElementException();
466	<	E result = queue[cursor];
467	<	lastRet = cursor++;
468	<	return result;
463	>	if (expectedModCount != modCount)
464	>	throw new ConcurrentModificationException();
465	>	if (cursor < size)
466	>	return (E) queue[lastRet = cursor++];
467	>	if (forgetMeNot != null) {
468	>	lastRet = -1;
469	>	lastRetElt = forgetMeNot.poll();
470	>	if (lastRetElt != null)
471	>	return lastRetElt;
472	>	}
473	>	throw new NoSuchElementException();
474		}
475
476		public void remove() {
477	<	if (lastRet == 0)
477	>	if (expectedModCount != modCount)
478	>	throw new ConcurrentModificationException();
479	>	if (lastRet != -1) {
480	>	E moved = PriorityQueue.this.removeAt(lastRet);
481	>	lastRet = -1;
482	>	if (moved == null)
483	>	cursor--;
484	>	else {
485	>	if (forgetMeNot == null)
486	>	forgetMeNot = new ArrayDeque<E>();
487	>	forgetMeNot.add(moved);
488	>	}
489	>	} else if (lastRetElt != null) {
490	>	PriorityQueue.this.removeEq(lastRetElt);
491	>	lastRetElt = null;
492	>	} else {
493		throw new IllegalStateException();
494	<	checkForComodification();
265	<
266	<	PriorityQueue.this.remove(lastRet);
267	<	if (lastRet < cursor)
268	<	cursor--;
269	<	lastRet = 0;
494	>	}
495		expectedModCount = modCount;
496		}
272	–
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
497		}
498
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
499		public int size() {
500		return size;
501		}
502
503		/**
504	<	* Add the specified element to this priority queue.
505	<	*
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.
504	>	* Removes all of the elements from this priority queue.
505	>	* The queue will be empty after this call returns.
506		*/
507	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
507	>	public void clear() {
508		modCount++;
509	<	++size;
510	<
511	<	// Grow backing store if necessary
512	<	while (size >= queue.length) {
306	<	E[] newQueue = new E[2 * queue.length];
307	<	System.arraycopy(queue, 0, newQueue, 0, queue.length);
308	<	queue = newQueue;
309	<	}
509	>	for (int i = 0; i < size; i++)
510	>	queue[i] = null;
511	>	size = 0;
512	>	}
513
514	<	queue[size] = element;
515	<	fixUp(size);
516	<	return true;
514	>	public E poll() {
515	>	if (size == 0)
516	>	return null;
517	>	int s = --size;
518	>	modCount++;
519	>	E result = (E) queue[0];
520	>	E x = (E) queue[s];
521	>	queue[s] = null;
522	>	if (s != 0)
523	>	siftDown(0, x);
524	>	return result;
525		}
526
527		/**
528	<	* Remove all elements from the priority queue.
528	>	* Removes the ith element from queue.
529	>	*
530	>	* Normally this method leaves the elements at up to i-1,
531	>	* inclusive, untouched.  Under these circumstances, it returns
532	>	* null.  Occasionally, in order to maintain the heap invariant,
533	>	* it must swap a later element of the list with one earlier than
534	>	* i.  Under these circumstances, this method returns the element
535	>	* that was previously at the end of the list and is now at some
536	>	* position before i. This fact is used by iterator.remove so as to
537	>	* avoid missing traversing elements.
538		*/
539	<	public void clear() {
539	>	private E removeAt(int i) {
540	>	assert i >= 0 && i < size;
541		modCount++;
542	<
543	<	// Null out element references to prevent memory leak
323	<	for (int i=1; i<=size; i++)
542	>	int s = --size;
543	>	if (s == i) // removed last element
544		queue[i] = null;
545	<
546	<	size = 0;
545	>	else {
546	>	E moved = (E) queue[s];
547	>	queue[s] = null;
548	>	siftDown(i, moved);
549	>	if (queue[i] == moved) {
550	>	siftUp(i, moved);
551	>	if (queue[i] != moved)
552	>	return moved;
553	>	}
554	>	}
555	>	return null;
556		}
557
558		/**
559	<	* Removes and returns the ith element from queue.  Recall
560	<	* that queue is one-based, so 1 <= i <= size.
559	>	* Inserts item x at position k, maintaining heap invariant by
560	>	* promoting x up the tree until it is greater than or equal to
561	>	* its parent, or is the root.
562	>	*
563	>	* To simplify and speed up coercions and comparisons. the
564	>	* Comparable and Comparator versions are separated into different
565	>	* methods that are otherwise identical. (Similarly for siftDown.)
566		*
567	<	* XXX: Could further special-case i==size, but is it worth it?
568	<	* XXX: Could special-case i==0, but is it worth it?
567	>	* @param k the position to fill
568	>	* @param x the item to insert
569		*/
570	<	private E remove(int i) {
571	<	assert i <= size;
572	<	modCount++;
570	>	private void siftUp(int k, E x) {
571	>	if (comparator != null)
572	>	siftUpUsingComparator(k, x);
573	>	else
574	>	siftUpComparable(k, x);
575	>	}
576
577	<	E result = queue[i];
578	<	queue[i] = queue[size];
579	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
580	<	if (i <= size)
581	<	fixDown(i);
582	<	return result;
577	>	private void siftUpComparable(int k, E x) {
578	>	Comparable<? super E> key = (Comparable<? super E>) x;
579	>	while (k > 0) {
580	>	int parent = (k - 1) >>> 1;
581	>	Object e = queue[parent];
582	>	if (key.compareTo((E) e) >= 0)
583	>	break;
584	>	queue[k] = e;
585	>	k = parent;
586	>	}
587	>	queue[k] = key;
588		}
589
590	<	/**
591	<	* Establishes the heap invariant (described above) assuming the heap
592	<	* satisfies the invariant except possibly for the leaf-node indexed by k
593	<	* (which may have a nextExecutionTime less than its parent's).
594	<	*
595	<	* This method functions by "promoting" queue[k] up the hierarchy
596	<	* (by swapping it with its parent) repeatedly until queue[k]
597	<	* is greater than or equal to its parent.
356	<	*/
357	<	private void fixUp(int k) {
358	<	if (comparator == null) {
359	<	while (k > 1) {
360	<	int j = k >> 1;
361	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
362	<	break;
363	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
364	<	k = j;
365	<	}
366	<	} else {
367	<	while (k > 1) {
368	<	int j = k >> 1;
369	<	if (comparator.compare(queue[j], queue[k]) <= 0)
370	<	break;
371	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
372	<	k = j;
373	<	}
590	>	private void siftUpUsingComparator(int k, E x) {
591	>	while (k > 0) {
592	>	int parent = (k - 1) >>> 1;
593	>	Object e = queue[parent];
594	>	if (comparator.compare(x, (E) e) >= 0)
595	>	break;
596	>	queue[k] = e;
597	>	k = parent;
598		}
599	+	queue[k] = x;
600		}
601
602		/**
603	<	* Establishes the heap invariant (described above) in the subtree
604	<	* rooted at k, which is assumed to satisfy the heap invariant except
605	<	* possibly for node k itself (which may be greater than its children).
606	<	*
607	<	* This method functions by "demoting" queue[k] down the hierarchy
608	<	* (by swapping it with its smaller child) repeatedly until queue[k]
609	<	* is less than or equal to its children.
610	<	*/
611	<	private void fixDown(int k) {
612	<	int j;
613	<	if (comparator == null) {
614	<	while ((j = k << 1) <= size) {
615	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
616	<	j++; // j indexes smallest kid
617	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
618	<	break;
619	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
620	<	k = j;
621	<	}
622	<	} else {
623	<	while ((j = k << 1) <= size) {
624	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
625	<	j++; // j indexes smallest kid
626	<	if (comparator.compare(queue[k], queue[j]) <= 0)
627	<	break;
628	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
629	<	k = j;
630	<	}
603	>	* Inserts item x at position k, maintaining heap invariant by
604	>	* demoting x down the tree repeatedly until it is less than or
605	>	* equal to its children or is a leaf.
606	>	*
607	>	* @param k the position to fill
608	>	* @param x the item to insert
609	>	*/
610	>	private void siftDown(int k, E x) {
611	>	if (comparator != null)
612	>	siftDownUsingComparator(k, x);
613	>	else
614	>	siftDownComparable(k, x);
615	>	}
616	>
617	>	private void siftDownComparable(int k, E x) {
618	>	Comparable<? super E> key = (Comparable<? super E>)x;
619	>	int half = size >>> 1;        // loop while a non-leaf
620	>	while (k < half) {
621	>	int child = (k << 1) + 1; // assume left child is least
622	>	Object c = queue[child];
623	>	int right = child + 1;
624	>	if (right < size &&
625	>	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
626	>	c = queue[child = right];
627	>	if (key.compareTo((E) c) <= 0)
628	>	break;
629	>	queue[k] = c;
630	>	k = child;
631	>	}
632	>	queue[k] = key;
633	>	}
634	>
635	>	private void siftDownUsingComparator(int k, E x) {
636	>	int half = size >>> 1;
637	>	while (k < half) {
638	>	int child = (k << 1) + 1;
639	>	Object c = queue[child];
640	>	int right = child + 1;
641	>	if (right < size &&
642	>	comparator.compare((E) c, (E) queue[right]) > 0)
643	>	c = queue[child = right];
644	>	if (comparator.compare(x, (E) c) <= 0)
645	>	break;
646	>	queue[k] = c;
647	>	k = child;
648		}
649	+	queue[k] = x;
650		}
651
652		/**
653	<	* Returns the comparator associated with this priority queue, or
654	<	* <tt>null</tt> if it uses its elements' natural ordering.
653	>	* Establishes the heap invariant (described above) in the entire tree,
654	>	* assuming nothing about the order of the elements prior to the call.
655	>	*/
656	>	private void heapify() {
657	>	for (int i = (size >>> 1) - 1; i >= 0; i--)
658	>	siftDown(i, (E) queue[i]);
659	>	}
660	>
661	>	/**
662	>	* Returns the comparator used to order the elements in this
663	>	* queue, or {@code null} if this queue is sorted according to
664	>	* the {@linkplain Comparable natural ordering} of its elements.
665		*
666	<	* @return the comparator associated with this priority queue, or
667	<	*         <tt>null</tt> if it uses its elements' natural ordering.
666	>	* @return the comparator used to order this queue, or
667	>	*         {@code null} if this queue is sorted according to the
668	>	*         natural ordering of its elements
669		*/
670	<	public Comparator comparator() {
670	>	public Comparator<? super E> comparator() {
671		return comparator;
672		}
673
674		/**
675	<	* Save the state of the instance to a stream (that
676	<	* is, serialize it).
675	>	* Saves the state of the instance to a stream (that
676	>	* is, serializes it).
677		*
678		* @serialData The length of the array backing the instance is
679	<	* emitted (int), followed by all of its elements (each an
680	<	* <tt>Object</tt>) in the proper order.
679	>	*             emitted (int), followed by all of its elements
680	>	*             (each an {@code Object}) in the proper order.
681		* @param s the stream
682		*/
683	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
683	>	private void writeObject(java.io.ObjectOutputStream s)
684		throws java.io.IOException{
685		// Write out element count, and any hidden stuff
686		s.defaultWriteObject();
687
688	<	// Write out array length
689	<	s.writeInt(queue.length);
688	>	// Write out array length, for compatibility with 1.5 version
689	>	s.writeInt(Math.max(2, size + 1));
690
691	<	// Write out all elements in the proper order.
692	<	for (int i=0; i<size; i++)
691	>	// Write out all elements in the "proper order".
692	>	for (int i = 0; i < size; i++)
693		s.writeObject(queue[i]);
694		}
695
696		/**
697	<	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
698	<	* deserialize it).
697	>	* Reconstitutes the {@code PriorityQueue} instance from a stream
698	>	* (that is, deserializes it).
699	>	*
700		* @param s the stream
701		*/
702	<	private synchronized void readObject(java.io.ObjectInputStream s)
702	>	private void readObject(java.io.ObjectInputStream s)
703		throws java.io.IOException, ClassNotFoundException {
704		// Read in size, and any hidden stuff
705		s.defaultReadObject();
706
707	<	// Read in array length and allocate array
708	<	int arrayLength = s.readInt();
454	<	queue = new E[arrayLength];
455	<
456	<	// Read in all elements in the proper order.
457	<	for (int i=0; i<size; i++)
458	<	queue[i] = (E)s.readObject();
459	<	}
707	>	// Read in (and discard) array length
708	>	s.readInt();
709
710	+	queue = new Object[size];
711	+
712	+	// Read in all elements.
713	+	for (int i = 0; i < size; i++)
714	+	queue[i] = s.readObject();
715	+
716	+	// Elements are guaranteed to be in "proper order", but the
717	+	// spec has never explained what that might be.
718	+	heapify();
719	+	}
720		}

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