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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.3 by tim, Sun May 18 20:36:01 2003 UTC vs.
Revision 1.56 by jsr166, Mon Nov 28 02:35:46 2005 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* @(#)PriorityQueue.java       1.8 05/08/27
3		*
4	<	*   1) Make it serializable.
4	>	* Copyright 2005 Sun Microsystems, Inc. All rights reserved.
5	>	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6		*/
7
8	+	package java.util;
9	+	import java.util.*; // for javadoc (till 6280605 is fixed)
10	+
11		/**
12	<	* An unbounded priority queue based on a priority heap.  This queue orders
13	<	* elements according to the order specified at creation time.  This order is
14	<	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
15	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
16	<	* according to a {@link Comparator}, depending on which constructor is used.
17	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
18	<	* minimal element with respect to the specified ordering.  If multiple
19	<	* these elements are tied for least value, no guarantees are made as to
20	<	* which of elements is returned.
12	>	* An unbounded priority {@linkplain Queue queue} based on a priority
13	>	* heap.  The elements of the priority queue are ordered according to
14	>	* their {@linkplain Comparable natural ordering}, or by a {@link
15	>	* Comparator} provided at queue construction time, depending on which
16	>	* constructor is used.  A priority queue does not permit
17	>	* <tt>null</tt> elements.  A priority queue relying on natural
18	>	* ordering also does not permit insertion of non-comparable objects
19	>	* (doing so may result in <tt>ClassCastException</tt>).
20	>	*
21	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
22	>	* with respect to the specified ordering.  If multiple elements are
23	>	* tied for least value, the head is one of those elements -- ties are
24	>	* broken arbitrarily.  The queue retrieval operations <tt>poll</tt>,
25	>	* <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the
26	>	* element at the head of the queue.
27		*
28	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
29	<	* the array used to store the elements on the queue.  It is always at least
30	<	* as large as the queue size.  As elements are added to a priority list,
31	<	* its capacity grows automatically.  The details of the growth policy are not
28	>	* <p>A priority queue is unbounded, but has an internal
29	>	* <i>capacity</i> governing the size of an array used to store the
30	>	* elements on the queue.  It is always at least as large as the queue
31	>	* size.  As elements are added to a priority queue, its capacity
32	>	* grows automatically.  The details of the growth policy are not
33		* specified.
34		*
35	<	*<p>Implementation note: this implementation provides O(log(n)) time for
36	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
37	<	* methods; linear time for the <tt>remove(Object)</tt> and
38	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
39	<	* <tt>element</tt>, and <tt>size</tt> methods.
35	>	* <p>This class and its iterator implement all of the
36	>	* <em>optional</em> methods of the {@link Collection} and {@link
37	>	* Iterator} interfaces.  The Iterator provided in method {@link
38	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
39	>	* the priority queue in any particular order. If you need ordered
40	>	* traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
41	>	*
42	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
43	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
44	>	* instance concurrently if any of the threads modifies the list
45	>	* structurally. Instead, use the thread-safe {@link
46	>	* java.util.concurrent.PriorityBlockingQueue} class.
47	>	*
48	>	* <p>Implementation note: this implementation provides O(log(n)) time
49	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
50	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
51	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
52	>	* constant time for the retrieval methods (<tt>peek</tt>,
53	>	* <tt>element</tt>, and <tt>size</tt>).
54		*
55		* <p>This class is a member of the
56		* <a href="{@docRoot}/../guide/collections/index.html">
57		* Java Collections Framework</a>.
58	+	* @since 1.5
59	+	* @version 1.8, 08/27/05
60	+	* @author Josh Bloch
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	<	{
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
75	<	* of n, d, n <= d.
76	<	*
48	<	* The element with the lowest value is in queue[1] (assuming the queue is
49	<	* nonempty). A one-based array is used in preference to the traditional
50	<	* zero-based array to simplify parent and child calculations.
51	<	*
52	<	* queue.length must be >= 2, even if size == 0.
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 E[] queue;
78	>	private transient Object[] queue;
79
80		/**
81		* The number of elements in the priority queue.
#	Line 62 | 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
93		* <i>structurally modified</i>.  See AbstractList for gory details.
94		*/
95	<	private int modCount = 0;
95	>	private transient int modCount = 0;
96
97		/**
98	<	* Create a new priority queue with the default initial capacity (11)
99	<	* that orders its elements according to their natural ordering.
98	>	* Creates a <tt>PriorityQueue</tt> 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.
107	>	* Creates a <tt>PriorityQueue</tt> 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 <tt>initialCapacity</tt> 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 <tt>PriorityQueue</tt> 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
125	>	*         this priority queue.  If <tt>null</tt>, the <i>natural
126	>	*         ordering</i> of the elements will be used.
127	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> 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'
112	<	* natural order.  If the specified collection does not implement the
113	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
114	<	* its elements' natural order.
141	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
142	>	* specified collection.   If the specified collection is an
143	>	* instance of a {@link java.util.SortedSet} or is another
144	>	* <tt>PriorityQueue</tt>, the priority queue will be ordered
145	>	* according to the same ordering.  Otherwise, this priority queue
146	>	* will be ordered according to the 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	<	/* Commented out to compile with generics compiler
133	<
134	<	if (initialElements instanceof Sorted) {
135	<	comparator = ((Sorted)initialElements).comparator();
136	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	<	queue[++size] = i.next();
138	<	} else {
139	<	*/
140	<	{
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(); )
143	<	add(i.next());
166	>	heapify();
167		}
168		}
169
170	<	// Queue Methods
170	>	/**
171	>	* Creates a <tt>PriorityQueue</tt> 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 <tt>c</tt> cannot be
179	>	*         compared to one another according to <tt>c</tt>'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 if
191	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
192	<	* <i>minimal</i> is defined according to this priority queue's order.
190	>	* Creates a <tt>PriorityQueue</tt> 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;
160	<	return remove(1);
202	>	public PriorityQueue(SortedSet<? extends E> c) {
203	>	comparator = (Comparator<? super E>)c.comparator();
204	>	initFromCollection(c);
205		}
206
207		/**
208	<	* Return, but do not remove, the minimal element from the priority queue,
209	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
210	<	* defined according to this priority queue's order.  This method returns
211	<	* the same object reference that would be returned by by the
212	<	* <tt>poll</tt> method.  The two methods differ in that this method
213	<	* does not remove the element from the priority queue.
208	>	* Initialize queue array with elements from the given Collection.
209	>	* @param c the collection
210	>	*/
211	>	private void initFromCollection(Collection<? extends E> c) {
212	>	Object[] a = c.toArray();
213	>	// If c.toArray incorrectly doesn't return Object[], copy it.
214	>	if (a.getClass() != Object[].class)
215	>	a = Arrays.copyOf(a, a.length, Object[].class);
216	>	queue = a;
217	>	size = a.length;
218	>	}
219	>
220	>	/**
221	>	* Increases the capacity of the array.
222		*
223	<	* @return the minimal element from this priority queue if it contains
172	<	*         one or more elements, otherwise <tt>null</tt>.
223	>	* @param minCapacity the desired minimum capacity
224		*/
225	<	public E peek() {
226	<	return queue[1];
225	>	private void grow(int minCapacity) {
226	>	if (minCapacity < 0) // overflow
227	>	throw new OutOfMemoryError();
228	>	int oldCapacity = queue.length;
229	>	// Double size if small; else grow by 50%
230	>	int newCapacity = ((oldCapacity < 64)?
231	>	((oldCapacity + 1) * 2):
232	>	((oldCapacity * 3) / 2));
233	>	if (newCapacity < minCapacity)
234	>	newCapacity = minCapacity;
235	>	queue = Arrays.copyOf(queue, newCapacity);
236		}
237
238	<	// Collection Methods
238	>	/**
239	>	* Inserts the specified element into this priority queue.
240	>	*
241	>	* @return <tt>true</tt> (as specified by {@link Collection#add})
242	>	* @throws ClassCastException if the specified element cannot be
243	>	*         compared with elements currently in this priority queue
244	>	*         according to the priority queue's ordering
245	>	* @throws NullPointerException if the specified element is null
246	>	*/
247	>	public boolean add(E e) {
248	>	return offer(e);
249	>	}
250
251		/**
252	<	* Removes a single instance of the specified element from this priority
182	<	* queue, if it is present.  Returns true if this collection contained the
183	<	* specified element (or equivalently, if this collection changed as a
184	<	* result of the call).
252	>	* Inserts the specified element into this priority queue.
253		*
254	<	* @param o element to be removed from this collection, if present.
255	<	* @return <tt>true</tt> if this collection changed as a result of the
256	<	*         call
257	<	* @throws ClassCastException if the specified element cannot be compared
258	<	*            with elements currently in the priority queue according
191	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
254	>	* @return <tt>true</tt> (as specified by {@link Queue#offer})
255	>	* @throws ClassCastException if the specified element cannot be
256	>	*         compared with elements currently in this priority queue
257	>	*         according to the priority queue's ordering
258	>	* @throws NullPointerException if the specified element is null
259		*/
260	<	public boolean remove(Object element) {
261	<	if (element == null)
260	>	public boolean offer(E e) {
261	>	if (e == null)
262		throw new NullPointerException();
263	+	modCount++;
264	+	int i = size;
265	+	if (i >= queue.length)
266	+	grow(i + 1);
267	+	size = i + 1;
268	+	if (i == 0)
269	+	queue[0] = e;
270	+	else
271	+	siftUp(i, e);
272	+	return true;
273	+	}
274
275	<	if (comparator == null) {
276	<	for (int i = 1; i <= size; i++) {
277	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
278	<	remove(i);
279	<	return true;
280	<	}
281	<	}
282	<	} else {
283	<	for (int i = 1; i <= size; i++) {
284	<	if (comparator.compare(queue[i], (E) element) == 0) {
285	<	remove(i);
286	<	return true;
287	<	}
275	>	public E peek() {
276	>	if (size == 0)
277	>	return null;
278	>	return (E) queue[0];
279	>	}
280	>
281	>	private int indexOf(Object o) {
282	>	if (o != null) {
283	>	for (int i = 0; i < size; i++)
284	>	if (o.equals(queue[i]))
285	>	return i;
286	>	}
287	>	return -1;
288	>	}
289	>
290	>	/**
291	>	* Removes a single instance of the specified element from this queue,
292	>	* if it is present.  More formally, removes an element <tt>e</tt> such
293	>	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
294	>	* elements.  Returns true if this queue contained the specified element
295	>	* (or equivalently, if this queue changed as a result of the call).
296	>	*
297	>	* @param o element to be removed from this queue, if present
298	>	* @return <tt>true</tt> if this queue changed as a result of the call
299	>	*/
300	>	public boolean remove(Object o) {
301	>	int i = indexOf(o);
302	>	if (i == -1)
303	>	return false;
304	>	else {
305	>	removeAt(i);
306	>	return true;
307	>	}
308	>	}
309	>
310	>	/**
311	>	* Version of remove using reference equality, not equals.
312	>	* Needed by iterator.remove
313	>	*
314	>	* @param o element to be removed from this queue, if present
315	>	* @return <tt>true</tt> if removed.
316	>	*/
317	>	boolean removeEq(Object o) {
318	>	for (int i = 0; i < size; i++) {
319	>	if (o == queue[i]) {
320	>	removeAt(i);
321	>	return true;
322		}
323		}
324		return false;
325		}
326
327		/**
328	<	* Returns an iterator over the elements in this priority queue.  The
329	<	* first element returned by this iterator is the same element that
330	<	* would be returned by a call to <tt>peek</tt>.
328	>	* Returns <tt>true</tt> if this queue contains the specified element.
329	>	* More formally, returns <tt>true</tt> if and only if this queue contains
330	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
331	>	*
332	>	* @param o object to be checked for containment in this queue
333	>	* @return <tt>true</tt> if this queue contains the specified element
334	>	*/
335	>	public boolean contains(Object o) {
336	>	return indexOf(o) != -1;
337	>	}
338	>
339	>	/**
340	>	* Returns an array containing all of the elements in this queue,
341	>	* The elements are in no particular order.
342	>	*
343	>	* <p>The returned array will be "safe" in that no references to it are
344	>	* maintained by this list.  (In other words, this method must allocate
345	>	* a new array).  The caller is thus free to modify the returned array.
346		*
347	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
347	>	* @return an array containing all of the elements in this queue.
348	>	*/
349	>	public Object[] toArray() {
350	>	return Arrays.copyOf(queue, size);
351	>	}
352	>
353	>	/**
354	>	* Returns an array containing all of the elements in this queue.
355	>	* The elements are in no particular order.  The runtime type of
356	>	* the returned array is that of the specified array.  If the queue
357	>	* fits in the specified array, it is returned therein.
358	>	* Otherwise, a new array is allocated with the runtime type of
359	>	* the specified array and the size of this queue.
360	>	*
361	>	* <p>If the queue fits in the specified array with room to spare
362	>	* (i.e., the array has more elements than the queue), the element in
363	>	* the array immediately following the end of the collection is set to
364	>	* <tt>null</tt>.  (This is useful in determining the length of the
365	>	* queue <i>only</i> if the caller knows that the queue does not contain
366	>	* any null elements.)
367	>	*
368	>	* @param a the array into which the elements of the queue are to
369	>	*          be stored, if it is big enough; otherwise, a new array of the
370	>	*          same runtime type is allocated for this purpose.
371	>	* @return an array containing the elements of the queue
372	>	* @throws ArrayStoreException if the runtime type of the specified array
373	>	*         is not a supertype of the runtime type of every element in
374	>	*         this queue
375	>	* @throws NullPointerException if the specified array is null
376	>	*/
377	>	public <T> T[] toArray(T[] a) {
378	>	if (a.length < size)
379	>	// Make a new array of a's runtime type, but my contents:
380	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
381	>	System.arraycopy(queue, 0, a, 0, size);
382	>	if (a.length > size)
383	>	a[size] = null;
384	>	return a;
385	>	}
386	>
387	>	/**
388	>	* Returns an iterator over the elements in this queue. The iterator
389	>	* does not return the elements in any particular order.
390	>	*
391	>	* @return an iterator over the elements in this queue
392		*/
393		public Iterator<E> iterator() {
394		return new Itr();
395		}
396
397	<	private class Itr implements Iterator<E> {
397	>	private final class Itr implements Iterator<E> {
398		/**
399		* Index (into queue array) of element to be returned by
400		* subsequent call to next.
401		*/
402	<	int cursor = 1;
402	>	private int cursor = 0;
403	>
404	>	/**
405	>	* Index of element returned by most recent call to next,
406	>	* unless that element came from the forgetMeNot list.
407	>	* Set to -1 if element is deleted by a call to remove.
408	>	*/
409	>	private int lastRet = -1;
410	>
411	>	/**
412	>	* A queue of elements that were moved from the unvisited portion of
413	>	* the heap into the visited portion as a result of "unlucky" element
414	>	* removals during the iteration.  (Unlucky element removals are those
415	>	* that require a siftup instead of a siftdown.)  We must visit all of
416	>	* the elements in this list to complete the iteration.  We do this
417	>	* after we've completed the "normal" iteration.
418	>	*
419	>	* We expect that most iterations, even those involving removals,
420	>	* will not use need to store elements in this field.
421	>	*/
422	>	private ArrayDeque<E> forgetMeNot = null;
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
237	<	* to remove.
425	>	* Element returned by the most recent call to next iff that
426	>	* element was drawn from the forgetMeNot list.
427		*/
428	<	int lastRet = 0;
428	>	private E lastRetElt = null;
429
430		/**
431		* The modCount value that the iterator believes that the backing
432		* List should have.  If this expectation is violated, the iterator
433		* has detected concurrent modification.
434		*/
435	<	int expectedModCount = modCount;
435	>	private int expectedModCount = modCount;
436
437		public boolean hasNext() {
438	<	return cursor <= size;
438	>	return cursor < size ||
439	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
440		}
441
442		public E next() {
443	<	checkForComodification();
444	<	if (cursor > size)
445	<	throw new NoSuchElementException();
446	<	E result = queue[cursor];
447	<	lastRet = cursor++;
448	<	return result;
443	>	if (expectedModCount != modCount)
444	>	throw new ConcurrentModificationException();
445	>	if (cursor < size)
446	>	return (E) queue[lastRet = cursor++];
447	>	if (forgetMeNot != null) {
448	>	lastRet = -1;
449	>	lastRetElt = forgetMeNot.poll();
450	>	if (lastRetElt != null)
451	>	return lastRetElt;
452	>	}
453	>	throw new NoSuchElementException();
454		}
455
456		public void remove() {
457	<	if (lastRet == 0)
457	>	if (expectedModCount != modCount)
458	>	throw new ConcurrentModificationException();
459	>	if (lastRet == -1 && lastRetElt == null)
460		throw new IllegalStateException();
461	<	checkForComodification();
462	<
463	<	PriorityQueue.this.remove(lastRet);
464	<	if (lastRet < cursor)
465	<	cursor--;
466	<	lastRet = 0;
461	>	if (lastRet != -1) {
462	>	E moved = PriorityQueue.this.removeAt(lastRet);
463	>	lastRet = -1;
464	>	if (moved == null)
465	>	cursor--;
466	>	else {
467	>	if (forgetMeNot == null)
468	>	forgetMeNot = new ArrayDeque<E>();
469	>	forgetMeNot.add(moved);
470	>	}
471	>	} else {
472	>	PriorityQueue.this.removeEq(lastRetElt);
473	>	lastRetElt = null;
474	>	}
475		expectedModCount = modCount;
476		}
477
273	–	final void checkForComodification() {
274	–	if (modCount != expectedModCount)
275	–	throw new ConcurrentModificationException();
276	–	}
478		}
479
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
480		public int size() {
481		return size;
482		}
483
484		/**
485	<	* Add the specified element to this priority queue.
486	<	*
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.
485	>	* Removes all of the elements from this priority queue.
486	>	* The queue will be empty after this call returns.
487		*/
488	<	public boolean offer(E element) {
299	<	if (element == null)
300	<	throw new NullPointerException();
488	>	public void clear() {
489		modCount++;
490	+	for (int i = 0; i < size; i++)
491	+	queue[i] = null;
492	+	size = 0;
493	+	}
494
495	<	// Grow backing store if necessary
496	<	if (++size == queue.length) {
497	<	E[] newQueue = new E[2 * queue.length];
498	<	System.arraycopy(queue, 0, newQueue, 0, size);
499	<	queue = newQueue;
500	<	}
501	<
502	<	queue[size] = element;
503	<	fixUp(size);
504	<	return true;
495	>	public E poll() {
496	>	if (size == 0)
497	>	return null;
498	>	int s = --size;
499	>	modCount++;
500	>	E result = (E)queue[0];
501	>	E x = (E)queue[s];
502	>	queue[s] = null;
503	>	if (s != 0)
504	>	siftDown(0, x);
505	>	return result;
506		}
507
508		/**
509	<	* Remove all elements from the priority queue.
509	>	* Removes the ith element from queue.
510	>	*
511	>	* Normally this method leaves the elements at up to i-1,
512	>	* inclusive, untouched.  Under these circumstances, it returns
513	>	* null.  Occasionally, in order to maintain the heap invariant,
514	>	* it must swap a later element of the list with one earlier than
515	>	* i.  Under these circumstances, this method returns the element
516	>	* that was previously at the end of the list and is now at some
517	>	* position before i. This fact is used by iterator.remove so as to
518	>	* avoid missing traverseing elements.
519		*/
520	<	public void clear() {
520	>	private E removeAt(int i) {
521	>	assert i >= 0 && i < size;
522		modCount++;
523	<
524	<	// Null out element references to prevent memory leak
322	<	for (int i=1; i<=size; i++)
523	>	int s = --size;
524	>	if (s == i) // removed last element
525		queue[i] = null;
526	<
527	<	size = 0;
526	>	else {
527	>	E moved = (E) queue[s];
528	>	queue[s] = null;
529	>	siftDown(i, moved);
530	>	if (queue[i] == moved) {
531	>	siftUp(i, moved);
532	>	if (queue[i] != moved)
533	>	return moved;
534	>	}
535	>	}
536	>	return null;
537		}
538
539		/**
540	<	* Removes and returns the ith element from queue.  Recall
541	<	* that queue is one-based, so 1 <= i <= size.
540	>	* Inserts item x at position k, maintaining heap invariant by
541	>	* promoting x up the tree until it is greater than or equal to
542	>	* its parent, or is the root.
543		*
544	<	* XXX: Could further special-case i==size, but is it worth it?
545	<	* XXX: Could special-case i==0, but is it worth it?
544	>	* To simplify and speed up coercions and comparisons. the
545	>	* Comparable and Comparator versions are separated into different
546	>	* methods that are otherwise identical. (Similarly for siftDown.)
547	>	*
548	>	* @param k the position to fill
549	>	* @param x the item to insert
550		*/
551	<	private E remove(int i) {
552	<	assert i <= size;
553	<	modCount++;
551	>	private void siftUp(int k, E x) {
552	>	if (comparator != null)
553	>	siftUpUsingComparator(k, x);
554	>	else
555	>	siftUpComparable(k, x);
556	>	}
557
558	<	E result = queue[i];
559	<	queue[i] = queue[size];
560	<	queue[size--] = null;  // Drop extra ref to prevent memory leak
561	<	if (i <= size)
562	<	fixDown(i);
563	<	return result;
558	>	private void siftUpComparable(int k, E x) {
559	>	Comparable<? super E> key = (Comparable<? super E>) x;
560	>	while (k > 0) {
561	>	int parent = (k - 1) >>> 1;
562	>	Object e = queue[parent];
563	>	if (key.compareTo((E)e) >= 0)
564	>	break;
565	>	queue[k] = e;
566	>	k = parent;
567	>	}
568	>	queue[k] = key;
569		}
570
571	<	/**
572	<	* Establishes the heap invariant (described above) assuming the heap
573	<	* satisfies the invariant except possibly for the leaf-node indexed by k
574	<	* (which may have a nextExecutionTime less than its parent's).
575	<	*
576	<	* This method functions by "promoting" queue[k] up the hierarchy
577	<	* (by swapping it with its parent) repeatedly until queue[k]
578	<	* is greater than or equal to its parent.
355	<	*/
356	<	private void fixUp(int k) {
357	<	if (comparator == null) {
358	<	while (k > 1) {
359	<	int j = k >> 1;
360	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
361	<	break;
362	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
363	<	k = j;
364	<	}
365	<	} else {
366	<	while (k > 1) {
367	<	int j = k >> 1;
368	<	if (comparator.compare(queue[j], queue[k]) <= 0)
369	<	break;
370	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
371	<	k = j;
372	<	}
571	>	private void siftUpUsingComparator(int k, E x) {
572	>	while (k > 0) {
573	>	int parent = (k - 1) >>> 1;
574	>	Object e = queue[parent];
575	>	if (comparator.compare(x, (E)e) >= 0)
576	>	break;
577	>	queue[k] = e;
578	>	k = parent;
579		}
580	+	queue[k] = x;
581		}
582
583		/**
584	<	* Establishes the heap invariant (described above) in the subtree
585	<	* rooted at k, which is assumed to satisfy the heap invariant except
586	<	* possibly for node k itself (which may be greater than its children).
587	<	*
588	<	* This method functions by "demoting" queue[k] down the hierarchy
589	<	* (by swapping it with its smaller child) repeatedly until queue[k]
590	<	* is less than or equal to its children.
591	<	*/
592	<	private void fixDown(int k) {
593	<	int j;
594	<	if (comparator == null) {
595	<	while ((j = k << 1) <= size) {
596	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
597	<	j++; // j indexes smallest kid
598	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
599	<	break;
600	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
601	<	k = j;
602	<	}
603	<	} else {
604	<	while ((j = k << 1) <= size) {
605	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
606	<	j++; // j indexes smallest kid
607	<	if (comparator.compare(queue[k], queue[j]) <= 0)
608	<	break;
609	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
610	<	k = j;
611	<	}
584	>	* Inserts item x at position k, maintaining heap invariant by
585	>	* demoting x down the tree repeatedly until it is less than or
586	>	* equal to its children or is a leaf.
587	>	*
588	>	* @param k the position to fill
589	>	* @param x the item to insert
590	>	*/
591	>	private void siftDown(int k, E x) {
592	>	if (comparator != null)
593	>	siftDownUsingComparator(k, x);
594	>	else
595	>	siftDownComparable(k, x);
596	>	}
597	>
598	>	private void siftDownComparable(int k, E x) {
599	>	Comparable<? super E> key = (Comparable<? super E>)x;
600	>	int half = size >>> 1;        // loop while a non-leaf
601	>	while (k < half) {
602	>	int child = (k << 1) + 1; // assume left child is least
603	>	Object c = queue[child];
604	>	int right = child + 1;
605	>	if (right < size &&
606	>	((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
607	>	c = queue[child = right];
608	>	if (key.compareTo((E)c) <= 0)
609	>	break;
610	>	queue[k] = c;
611	>	k = child;
612		}
613	+	queue[k] = key;
614	+	}
615	+
616	+	private void siftDownUsingComparator(int k, E x) {
617	+	int half = size >>> 1;
618	+	while (k < half) {
619	+	int child = (k << 1) + 1;
620	+	Object c = queue[child];
621	+	int right = child + 1;
622	+	if (right < size &&
623	+	comparator.compare((E)c, (E)queue[right]) > 0)
624	+	c = queue[child = right];
625	+	if (comparator.compare(x, (E)c) <= 0)
626	+	break;
627	+	queue[k] = c;
628	+	k = child;
629	+	}
630	+	queue[k] = x;
631	+	}
632	+
633	+	/**
634	+	* Establishes the heap invariant (described above) in the entire tree,
635	+	* assuming nothing about the order of the elements prior to the call.
636	+	*/
637	+	private void heapify() {
638	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
639	+	siftDown(i, (E)queue[i]);
640		}
641
642		/**
643	<	* Returns the comparator associated with this priority queue, or
644	<	* <tt>null</tt> if it uses its elements' natural ordering.
643	>	* Returns the comparator used to order the elements in this
644	>	* queue, or <tt>null</tt> if this queue is sorted according to
645	>	* the {@linkplain Comparable natural ordering} of its elements.
646		*
647	<	* @return the comparator associated with this priority queue, or
648	<	*         <tt>null</tt> if it uses its elements' natural ordering.
647	>	* @return the comparator used to order this queue, or
648	>	*         <tt>null</tt> if this queue is sorted according to the
649	>	*         natural ordering of its elements.
650		*/
651	<	Comparator<E> comparator() {
651	>	public Comparator<? super E> comparator() {
652		return comparator;
653		}
654	+
655	+	/**
656	+	* Save the state of the instance to a stream (that
657	+	* is, serialize it).
658	+	*
659	+	* @serialData The length of the array backing the instance is
660	+	* emitted (int), followed by all of its elements (each an
661	+	* <tt>Object</tt>) in the proper order.
662	+	* @param s the stream
663	+	*/
664	+	private void writeObject(java.io.ObjectOutputStream s)
665	+	throws java.io.IOException{
666	+	// Write out element count, and any hidden stuff
667	+	s.defaultWriteObject();
668	+
669	+	// Write out array length
670	+	// For compatibility with 1.5 version, must be at least 2.
671	+	s.writeInt(Math.max(2, queue.length));
672	+
673	+	// Write out all elements in the proper order.
674	+	for (int i=0; i<size; i++)
675	+	s.writeObject(queue[i]);
676	+	}
677	+
678	+	/**
679	+	* Reconstitute the <tt>PriorityQueue</tt> instance from a stream
680	+	* (that is, deserialize it).
681	+	* @param s the stream
682	+	*/
683	+	private void readObject(java.io.ObjectInputStream s)
684	+	throws java.io.IOException, ClassNotFoundException {
685	+	// Read in size, and any hidden stuff
686	+	s.defaultReadObject();
687	+
688	+	// Read in array length and allocate array
689	+	int arrayLength = s.readInt();
690	+	queue = new Object[arrayLength];
691	+
692	+	// Read in all elements in the proper order.
693	+	for (int i=0; i<size; i++)
694	+	queue[i] = (E) s.readObject();
695	+	}
696	+
697		}

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