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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.5 by dl, Tue May 27 18:20:06 2003 UTC vs.
Revision 1.40 by dl, Fri Sep 12 15:38:26 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2003 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 the order specified at creation time.  This order is
13	<	* specified as for {@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	<	* these elements are tied for least value, no guarantees are made as to
19	<	* which of elements is returned.
11	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
12	>	* This queue orders elements according to an order specified at construction
13	>	* time, which is specified in the same manner as {@link java.util.TreeSet}
14	>	* and {@link java.util.TreeMap}: elements are ordered either according to
15	>	* their <i>natural order</i> (see {@link Comparable}), or according to a
16	>	* {@link java.util.Comparator}, depending on which constructor is used.
17	>	*
18	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
19	>	* respect to the specified ordering.  If multiple elements are tied for least
20	>	* value, the head is one of those elements. A priority queue does not permit
21	>	* <tt>null</tt> elements.
22		*
23	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
24	<	* the array used to store the elements on the queue.  It is always at least
25	<	* as large as the queue size.  As elements are added to a priority list,
26	<	* its capacity grows automatically.  The details of the growth policy are not
23	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
24	>	* return the head of the queue.
25	>	*
26	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
27	>	* not delete, the head of the queue.
28	>	*
29	>	* <p>A priority queue is unbounded, but has a <i>capacity</i>.  The
30	>	* capacity is the size of the array used internally to store the
31	>	* elements on the queue.  It is always at least as large as the queue
32	>	* size.  As elements are added to a priority queue, its capacity
33	>	* grows automatically.  The details of the growth policy are not
34		* specified.
35		*
36	<	*<p>Implementation note: this implementation provides O(log(n)) time for
37	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
38	<	* methods; linear time for the <tt>remove(Object)</tt> and
39	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
40	<	* <tt>element</tt>, and <tt>size</tt> methods.
36	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
37	>	* guaranteed to traverse the elements of the PriorityQueue in any
38	>	* particular order. If you need ordered traversal, consider using
39	>	* <tt>Arrays.sort(pq.toArray())</tt>.
40	>	*
41	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
42	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
43	>	* instance concurrently if any of the threads modifies the list
44	>	* structurally. Instead, use the thread-safe {@link
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46	>	*
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 %I%, %G%
60	+	* @author Josh Bloch
61		*/
62		public class PriorityQueue<E> extends AbstractQueue<E>
63	<	implements Queue<E>
64	<	{
63	>	implements Queue<E>, java.io.Serializable {
64	>
65	>	private static final long serialVersionUID = -7720805057305804111L;
66	>
67		private static final int DEFAULT_INITIAL_CAPACITY = 11;
68
69		/**
70		* Priority queue represented as a balanced binary heap: the two children
71		* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
72		* ordered by comparator, or by the elements' natural ordering, if
73	<	* comparator is null:  For each node n in the heap, and each descendant
74	<	* of n, d, n <= d.
73	>	* comparator is null:  For each node n in the heap and each descendant d
74	>	* of n, n <= d.
75		*
76	<	* The element with the lowest value is in queue[1] (assuming the queue is
77	<	* nonempty). A one-based array is used in preference to the traditional
78	<	* zero-based array to simplify parent and child calculations.
76	>	* The element with the lowest value is in queue[1], assuming the queue is
77	>	* nonempty.  (A one-based array is used in preference to the traditional
78	>	* zero-based array to simplify parent and child calculations.)
79		*
80		* queue.length must be >= 2, even if size == 0.
81		*/
82	<	private transient E[] queue;
82	>	private transient Object[] queue;
83
84		/**
85		* The number of elements in the priority queue.
#	Line 56 | Line 90 | public class PriorityQueue<E> extends Ab
90		* The comparator, or null if priority queue uses elements'
91		* natural ordering.
92		*/
93	<	private final Comparator<E> comparator;
93	>	private final Comparator<? super E> comparator;
94
95		/**
96		* The number of times this priority queue has been
#	Line 65 | Line 99 | public class PriorityQueue<E> extends Ab
99		private transient int modCount = 0;
100
101		/**
102	<	* Create a new priority queue with the default initial capacity (11)
103	<	* that orders its elements according to their natural ordering.
102	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
103	>	* (11) that orders its elements according to their natural
104	>	* ordering (using <tt>Comparable</tt>).
105		*/
106		public PriorityQueue() {
107	<	this(DEFAULT_INITIAL_CAPACITY);
107	>	this(DEFAULT_INITIAL_CAPACITY, null);
108		}
109
110		/**
111	<	* Create a new priority queue with the specified initial capacity
112	<	* that orders its elements according to their natural ordering.
111	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
112	>	* that orders its elements according to their natural ordering
113	>	* (using <tt>Comparable</tt>).
114		*
115		* @param initialCapacity the initial capacity for this priority queue.
116	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
117	+	* than 1
118		*/
119		public PriorityQueue(int initialCapacity) {
120		this(initialCapacity, null);
121		}
122
123		/**
124	<	* Create a new priority queue with the specified initial capacity (11)
124	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
125		* that orders its elements according to the specified comparator.
126		*
127		* @param initialCapacity the initial capacity for this priority queue.
128		* @param comparator the comparator used to order this priority queue.
129	+	* If <tt>null</tt> then the order depends on the elements' natural
130	+	* ordering.
131	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
132	+	* than 1
133		*/
134	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
134	>	public PriorityQueue(int initialCapacity,
135	>	Comparator<? super E> comparator) {
136		if (initialCapacity < 1)
137	<	initialCapacity = 1;
138	<	queue = new E[initialCapacity + 1];
137	>	throw new IllegalArgumentException();
138	>	this.queue = new Object[initialCapacity + 1];
139		this.comparator = comparator;
140		}
141
142		/**
143	<	* Create a new priority queue containing the elements in the specified
144	<	* collection.  The priority queue has an initial capacity of 110% of the
102	<	* size of the specified collection. If the specified collection
103	<	* implements the {@link Sorted} interface, the priority queue will be
104	<	* sorted according to the same comparator, or according to its elements'
105	<	* natural order if the collection is sorted according to its elements'
106	<	* natural order.  If the specified collection does not implement the
107	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
108	<	* its elements' natural order.
109	<	*
110	<	* @param initialElements the collection whose elements are to be placed
111	<	*        into this priority queue.
112	<	* @throws ClassCastException if elements of the specified collection
113	<	*         cannot be compared to one another according to the priority
114	<	*         queue's ordering.
115	<	* @throws NullPointerException if the specified collection or an
116	<	*         element of the specified collection is <tt>null</tt>.
143	>	* Common code to initialize underlying queue array across
144	>	* constructors below.
145		*/
146	<	public PriorityQueue(Collection<E> initialElements) {
147	<	int sz = initialElements.size();
146	>	private void initializeArray(Collection<? extends E> c) {
147	>	int sz = c.size();
148		int initialCapacity = (int)Math.min((sz * 110L) / 100,
149		Integer.MAX_VALUE - 1);
150		if (initialCapacity < 1)
151		initialCapacity = 1;
124	–	queue = new E[initialCapacity + 1];
152
153	<	/* Commented out to compile with generics compiler
153	>	this.queue = new Object[initialCapacity + 1];
154	>	}
155	>
156	>	/**
157	>	* Initially fill elements of the queue array under the
158	>	* knowledge that it is sorted or is another PQ, in which
159	>	* case we can just place the elements in the order presented.
160	>	*/
161	>	private void fillFromSorted(Collection<? extends E> c) {
162	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
163	>	queue[++size] = i.next();
164	>	}
165
166	<	if (initialElements instanceof Sorted) {
167	<	comparator = ((Sorted)initialElements).comparator();
168	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
169	<	queue[++size] = i.next();
166	>	/**
167	>	* Initially fill elements of the queue array that is not to our knowledge
168	>	* sorted, so we must rearrange the elements to guarantee the heap
169	>	* invariant.
170	>	*/
171	>	private void fillFromUnsorted(Collection<? extends E> c) {
172	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
173	>	queue[++size] = i.next();
174	>	heapify();
175	>	}
176	>
177	>	/**
178	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
179	>	* specified collection.  The priority queue has an initial
180	>	* capacity of 110% of the size of the specified collection or 1
181	>	* if the collection is empty.  If the specified collection is an
182	>	* instance of a {@link java.util.SortedSet} or is another
183	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
184	>	* according to the same comparator, or according to its elements'
185	>	* natural order if the collection is sorted according to its
186	>	* elements' natural order.  Otherwise, the priority queue is
187	>	* ordered according to its elements' natural order.
188	>	*
189	>	* @param c the collection whose elements are to be placed
190	>	*        into this priority queue.
191	>	* @throws ClassCastException if elements of the specified collection
192	>	*         cannot be compared to one another according to the priority
193	>	*         queue's ordering.
194	>	* @throws NullPointerException if <tt>c</tt> or any element within it
195	>	* is <tt>null</tt>
196	>	*/
197	>	public PriorityQueue(Collection<? extends E> c) {
198	>	initializeArray(c);
199	>	if (c instanceof SortedSet) {
200	>	// @fixme double-cast workaround for compiler
201	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
202	>	comparator = (Comparator<? super E>)s.comparator();
203	>	fillFromSorted(s);
204	>	} else if (c instanceof PriorityQueue) {
205	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
206	>	comparator = (Comparator<? super E>)s.comparator();
207	>	fillFromSorted(s);
208		} else {
133	–	*/
134	–	{
209		comparator = null;
210	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	<	add(i.next());
210	>	fillFromUnsorted(c);
211		}
212		}
213
214	<	// Queue Methods
214	>	/**
215	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
216	>	* specified collection.  The priority queue has an initial
217	>	* capacity of 110% of the size of the specified collection or 1
218	>	* if the collection is empty.  This priority queue will be sorted
219	>	* according to the same comparator as the given collection, or
220	>	* according to its elements' natural order if the collection is
221	>	* sorted according to its elements' natural order.
222	>	*
223	>	* @param c the collection whose elements are to be placed
224	>	*        into this priority queue.
225	>	* @throws ClassCastException if elements of the specified collection
226	>	*         cannot be compared to one another according to the priority
227	>	*         queue's ordering.
228	>	* @throws NullPointerException if <tt>c</tt> or any element within it
229	>	* is <tt>null</tt>
230	>	*/
231	>	public PriorityQueue(PriorityQueue<? extends E> c) {
232	>	initializeArray(c);
233	>	comparator = (Comparator<? super E>)c.comparator();
234	>	fillFromSorted(c);
235	>	}
236
237		/**
238	<	* Remove and return the minimal element from this priority queue if
239	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
240	<	* <i>minimal</i> is defined according to this priority queue's order.
238	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
239	>	* specified collection.  The priority queue has an initial
240	>	* capacity of 110% of the size of the specified collection or 1
241	>	* if the collection is empty.  This priority queue will be sorted
242	>	* according to the same comparator as the given collection, or
243	>	* according to its elements' natural order if the collection is
244	>	* sorted according to its elements' natural order.
245		*
246	<	* @return the minimal element from this priority queue if it contains
247	<	*         one or more elements, otherwise <tt>null</tt>.
246	>	* @param c the collection whose elements are to be placed
247	>	*        into this priority queue.
248	>	* @throws ClassCastException if elements of the specified collection
249	>	*         cannot be compared to one another according to the priority
250	>	*         queue's ordering.
251	>	* @throws NullPointerException if <tt>c</tt> or any element within it
252	>	* is <tt>null</tt>
253		*/
254	<	public E poll() {
255	<	if (size == 0)
256	<	return null;
257	<	return remove(1);
254	>	public PriorityQueue(SortedSet<? extends E> c) {
255	>	initializeArray(c);
256	>	comparator = (Comparator<? super E>)c.comparator();
257	>	fillFromSorted(c);
258		}
259
260		/**
261	<	* Return, but do not remove, the minimal element from the priority queue,
262	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
263	<	* defined according to this priority queue's order.  This method returns
264	<	* the same object reference that would be returned by by the
265	<	* <tt>poll</tt> method.  The two methods differ in that this method
266	<	* does not remove the element from the priority queue.
261	>	* Resize array, if necessary, to be able to hold given index
262	>	*/
263	>	private void grow(int index) {
264	>	int newlen = queue.length;
265	>	if (index < newlen) // don't need to grow
266	>	return;
267	>	if (index == Integer.MAX_VALUE)
268	>	throw new OutOfMemoryError();
269	>	while (newlen <= index) {
270	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
271	>	newlen = Integer.MAX_VALUE;
272	>	else
273	>	newlen <<= 2;
274	>	}
275	>	Object[] newQueue = new Object[newlen];
276	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
277	>	queue = newQueue;
278	>	}
279	>
280	>
281	>	/**
282	>	* Inserts the specified element to this priority queue.
283		*
284	<	* @return the minimal element from this priority queue if it contains
285	<	*         one or more elements, otherwise <tt>null</tt>.
284	>	* @return <tt>true</tt>
285	>	* @throws ClassCastException if the specified element cannot be compared
286	>	* with elements currently in the priority queue according
287	>	* to the priority queue's ordering.
288	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
289		*/
290	+	public boolean offer(E o) {
291	+	if (o == null)
292	+	throw new NullPointerException();
293	+	modCount++;
294	+	++size;
295	+
296	+	// Grow backing store if necessary
297	+	if (size >= queue.length)
298	+	grow(size);
299	+
300	+	queue[size] = o;
301	+	fixUp(size);
302	+	return true;
303	+	}
304	+
305		public E peek() {
306	<	return queue[1];
306	>	if (size == 0)
307	>	return null;
308	>	return (E) queue[1];
309		}
310
311	<	// Collection Methods
311	>	// Collection Methods - the first two override to update docs
312
313		/**
314	<	* Removes a single instance of the specified element from this priority
315	<	* queue, if it is present.  Returns true if this collection contained the
316	<	* specified element (or equivalently, if this collection changed as a
178	<	* result of the call).
314	>	* Adds the specified element to this queue.
315	>	* @return <tt>true</tt> (as per the general contract of
316	>	* <tt>Collection.add</tt>).
317		*
318	<	* @param o element to be removed from this collection, if present.
181	<	* @return <tt>true</tt> if this collection changed as a result of the
182	<	*         call
318	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
319		* @throws ClassCastException if the specified element cannot be compared
320	<	*            with elements currently in the priority queue according
321	<	*            to the priority queue's ordering.
186	<	* @throws NullPointerException if the specified element is null.
320	>	* with elements currently in the priority queue according
321	>	* to the priority queue's ordering.
322		*/
323	<	public boolean remove(Object element) {
324	<	if (element == null)
325	<	throw new NullPointerException();
323	>	public boolean add(E o) {
324	>	return super.add(o);
325	>	}
326	>
327	>
328	>	/**
329	>	* Adds all of the elements in the specified collection to this queue.
330	>	* The behavior of this operation is undefined if
331	>	* the specified collection is modified while the operation is in
332	>	* progress.  (This implies that the behavior of this call is undefined if
333	>	* the specified collection is this queue, and this queue is nonempty.)
334	>	* <p>
335	>	* This implementation iterates over the specified collection, and adds
336	>	* each object returned by the iterator to this collection, in turn.
337	>	* @param c collection whose elements are to be added to this queue
338	>	* @return <tt>true</tt> if this queue changed as a result of the
339	>	*         call.
340	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
341	>	* is <tt>null</tt>
342	>	* @throws ClassCastException if any element cannot be compared
343	>	* with elements currently in the priority queue according
344	>	* to the priority queue's ordering.
345	>	*/
346	>	public boolean addAll(Collection<? extends E> c) {
347	>	return super.addAll(c);
348	>	}
349	>
350	>	public boolean remove(Object o) {
351	>	if (o == null)
352	>	return false;
353
354		if (comparator == null) {
355		for (int i = 1; i <= size; i++) {
356	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
357	<	remove(i);
356	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
357	>	removeAt(i);
358		return true;
359		}
360		}
361		} else {
362		for (int i = 1; i <= size; i++) {
363	<	if (comparator.compare(queue[i], (E) element) == 0) {
364	<	remove(i);
363	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
364	>	removeAt(i);
365		return true;
366		}
367		}
#	Line 208 | Line 370 | public class PriorityQueue<E> extends Ab
370		}
371
372		/**
373	<	* Returns an iterator over the elements in this priority queue.  The
374	<	* first element returned by this iterator is the same element that
375	<	* would be returned by a call to <tt>peek</tt>.
376	<	*
215	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
373	>	* Returns an iterator over the elements in this queue. The iterator
374	>	* does not return the elements in any particular order.
375	>	*
376	>	* @return an iterator over the elements in this queue.
377		*/
378		public Iterator<E> iterator() {
379	<	return new Itr();
379	>	return new Itr();
380		}
381
382		private class Itr implements Iterator<E> {
383	<	/**
384	<	* Index (into queue array) of element to be returned by
383	>
384	>	/**
385	>	* Index (into queue array) of element to be returned by
386		* subsequent call to next.
387	<	*/
388	<	int cursor = 1;
387	>	*/
388	>	private int cursor = 1;
389
390	<	/**
391	<	* Index of element returned by most recent call to next or
392	<	* previous.  Reset to 0 if this element is deleted by a call
393	<	* to remove.
394	<	*/
395	<	int lastRet = 0;
396	<
397	<	/**
398	<	* The modCount value that the iterator believes that the backing
399	<	* List should have.  If this expectation is violated, the iterator
400	<	* has detected concurrent modification.
401	<	*/
402	<	int expectedModCount = modCount;
403	<
404	<	public boolean hasNext() {
405	<	return cursor <= size;
406	<	}
390	>	/**
391	>	* Index of element returned by most recent call to next,
392	>	* unless that element came from the forgetMeNot list.
393	>	* Reset to 0 if element is deleted by a call to remove.
394	>	*/
395	>	private int lastRet = 0;
396	>
397	>	/**
398	>	* The modCount value that the iterator believes that the backing
399	>	* List should have.  If this expectation is violated, the iterator
400	>	* has detected concurrent modification.
401	>	*/
402	>	private int expectedModCount = modCount;
403	>
404	>	/**
405	>	* A list of elements that were moved from the unvisited portion of
406	>	* the heap into the visited portion as a result of "unlucky" element
407	>	* removals during the iteration.  (Unlucky element removals are those
408	>	* that require a fixup instead of a fixdown.)  We must visit all of
409	>	* the elements in this list to complete the iteration.  We do this
410	>	* after we've completed the "normal" iteration.
411	>	*
412	>	* We expect that most iterations, even those involving removals,
413	>	* will not use need to store elements in this field.
414	>	*/
415	>	private ArrayList<E> forgetMeNot = null;
416	>
417	>	/**
418	>	* Element returned by the most recent call to next iff that
419	>	* element was drawn from the forgetMeNot list.
420	>	*/
421	>	private Object lastRetElt = null;
422	>
423	>	public boolean hasNext() {
424	>	return cursor <= size || forgetMeNot != null;
425	>	}
426
427	<	public E next() {
427	>	public E next() {
428		checkForComodification();
429	<	if (cursor > size)
430	<	throw new NoSuchElementException();
431	<	E result = queue[cursor];
432	<	lastRet = cursor++;
429	>	E result;
430	>	if (cursor <= size) {
431	>	result = (E) queue[cursor];
432	>	lastRet = cursor++;
433	>	}
434	>	else if (forgetMeNot == null)
435	>	throw new NoSuchElementException();
436	>	else {
437	>	int remaining = forgetMeNot.size();
438	>	result = forgetMeNot.remove(remaining - 1);
439	>	if (remaining == 1)
440	>	forgetMeNot = null;
441	>	lastRet = 0;
442	>	lastRetElt = result;
443	>	}
444		return result;
445	<	}
445	>	}
446
447	<	public void remove() {
256	<	if (lastRet == 0)
257	<	throw new IllegalStateException();
447	>	public void remove() {
448		checkForComodification();
449
450	<	PriorityQueue.this.remove(lastRet);
451	<	if (lastRet < cursor)
452	<	cursor--;
453	<	lastRet = 0;
450	>	if (lastRet != 0) {
451	>	E moved = PriorityQueue.this.removeAt(lastRet);
452	>	lastRet = 0;
453	>	if (moved == null) {
454	>	cursor--;
455	>	} else {
456	>	if (forgetMeNot == null)
457	>	forgetMeNot = new ArrayList<E>();
458	>	forgetMeNot.add(moved);
459	>	}
460	>	} else if (lastRetElt != null) {
461	>	PriorityQueue.this.remove(lastRetElt);
462	>	lastRetElt = null;
463	>	} else {
464	>	throw new IllegalStateException();
465	>	}
466	>
467		expectedModCount = modCount;
468	<	}
468	>	}
469
470	<	final void checkForComodification() {
471	<	if (modCount != expectedModCount)
472	<	throw new ConcurrentModificationException();
473	<	}
470	>	final void checkForComodification() {
471	>	if (modCount != expectedModCount)
472	>	throw new ConcurrentModificationException();
473	>	}
474		}
475
273	–	/**
274	–	* Returns the number of elements in this priority queue.
275	–	*
276	–	* @return the number of elements in this priority queue.
277	–	*/
476		public int size() {
477		return size;
478		}
479
480		/**
283	–	* Add the specified element to this priority queue.
284	–	*
285	–	* @param element the element to add.
286	–	* @return true
287	–	* @throws ClassCastException if the specified element cannot be compared
288	–	*            with elements currently in the priority queue according
289	–	*            to the priority queue's ordering.
290	–	* @throws NullPointerException if the specified element is null.
291	–	*/
292	–	public boolean offer(E element) {
293	–	if (element == null)
294	–	throw new NullPointerException();
295	–	modCount++;
296	–
297	–	// Grow backing store if necessary
298	–	if (++size == queue.length) {
299	–	E[] newQueue = new E[2 * queue.length];
300	–	System.arraycopy(queue, 0, newQueue, 0, size);
301	–	queue = newQueue;
302	–	}
303	–
304	–	queue[size] = element;
305	–	fixUp(size);
306	–	return true;
307	–	}
308	–
309	–	/**
481		* Remove all elements from the priority queue.
482		*/
483		public void clear() {
#	Line 319 | Line 490 | public class PriorityQueue<E> extends Ab
490		size = 0;
491		}
492
493	+	public E poll() {
494	+	if (size == 0)
495	+	return null;
496	+	modCount++;
497	+
498	+	E result = (E) queue[1];
499	+	queue[1] = queue[size];
500	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
501	+	if (size > 1)
502	+	fixDown(1);
503	+
504	+	return result;
505	+	}
506	+
507		/**
508	<	* Removes and returns the ith element from queue.  Recall
509	<	* that queue is one-based, so 1 <= i <= size.
508	>	* Removes and returns the ith element from queue.  (Recall that queue
509	>	* is one-based, so 1 <= i <= size.)
510		*
511	<	* XXX: Could further special-case i==size, but is it worth it?
512	<	* XXX: Could special-case i==0, but is it worth it?
511	>	* Normally this method leaves the elements at positions from 1 up to i-1,
512	>	* inclusive, untouched.  Under these circumstances, it returns null.
513	>	* Occasionally, in order to maintain the heap invariant, it must move
514	>	* the last element of the list to some index in the range [2, i-1],
515	>	* and move the element previously at position (i/2) to position i.
516	>	* Under these circumstances, this method returns the element that was
517	>	* previously at the end of the list and is now at some position between
518	>	* 2 and i-1 inclusive.
519		*/
520	<	private E remove(int i) {
521	<	assert i <= size;
520	>	private E removeAt(int i) {
521	>	assert i > 0 && i <= size;
522		modCount++;
523
524	<	E result = queue[i];
525	<	queue[i] = queue[size];
524	>	E moved = (E) queue[size];
525	>	queue[i] = moved;
526		queue[size--] = null;  // Drop extra ref to prevent memory leak
527	<	if (i <= size)
527	>	if (i <= size) {
528		fixDown(i);
529	<	return result;
529	>	if (queue[i] == moved) {
530	>	fixUp(i);
531	>	if (queue[i] != moved)
532	>	return moved;
533	>	}
534	>	}
535	>	return null;
536		}
537
538		/**
#	Line 351 | Line 548 | public class PriorityQueue<E> extends Ab
548		if (comparator == null) {
549		while (k > 1) {
550		int j = k >> 1;
551	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
551	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
552		break;
553	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
553	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
554		k = j;
555		}
556		} else {
557		while (k > 1) {
558	<	int j = k >> 1;
559	<	if (comparator.compare(queue[j], queue[k]) <= 0)
558	>	int j = k >>> 1;
559	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
560		break;
561	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
561	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
562		k = j;
563		}
564		}
#	Line 379 | Line 576 | public class PriorityQueue<E> extends Ab
576		private void fixDown(int k) {
577		int j;
578		if (comparator == null) {
579	<	while ((j = k << 1) <= size) {
580	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
579	>	while ((j = k << 1) <= size && (j > 0)) {
580	>	if (j<size &&
581	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
582		j++; // j indexes smallest kid
583	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
583	>
584	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
585		break;
586	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
586	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
587		k = j;
588		}
589		} else {
590	<	while ((j = k << 1) <= size) {
591	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
590	>	while ((j = k << 1) <= size && (j > 0)) {
591	>	if (j<size &&
592	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
593		j++; // j indexes smallest kid
594	<	if (comparator.compare(queue[k], queue[j]) <= 0)
594	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
595		break;
596	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
596	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
597		k = j;
598		}
599		}
600		}
601
602		/**
603	<	* Returns the comparator associated with this priority queue, or
604	<	* <tt>null</tt> if it uses its elements' natural ordering.
603	>	* Establishes the heap invariant (described above) in the entire tree,
604	>	* assuming nothing about the order of the elements prior to the call.
605	>	*/
606	>	private void heapify() {
607	>	for (int i = size/2; i >= 1; i--)
608	>	fixDown(i);
609	>	}
610	>
611	>	/**
612	>	* Returns the comparator used to order this collection, or <tt>null</tt>
613	>	* if this collection is sorted according to its elements natural ordering
614	>	* (using <tt>Comparable</tt>).
615		*
616	<	* @return the comparator associated with this priority queue, or
617	<	*         <tt>null</tt> if it uses its elements' natural ordering.
616	>	* @return the comparator used to order this collection, or <tt>null</tt>
617	>	* if this collection is sorted according to its elements natural ordering.
618		*/
619	<	Comparator comparator() {
619	>	public Comparator<? super E> comparator() {
620		return comparator;
621		}
622
#	Line 417 | Line 627 | public class PriorityQueue<E> extends Ab
627		* @serialData The length of the array backing the instance is
628		* emitted (int), followed by all of its elements (each an
629		* <tt>Object</tt>) in the proper order.
630	+	* @param s the stream
631		*/
632	<	private synchronized void writeObject(java.io.ObjectOutputStream s)
632	>	private void writeObject(java.io.ObjectOutputStream s)
633		throws java.io.IOException{
634	<	// Write out element count, and any hidden stuff
635	<	s.defaultWriteObject();
634	>	// Write out element count, and any hidden stuff
635	>	s.defaultWriteObject();
636
637		// Write out array length
638		s.writeInt(queue.length);
639
640	<	// Write out all elements in the proper order.
641	<	for (int i=0; i<size; i++)
640	>	// Write out all elements in the proper order.
641	>	for (int i=1; i<=size; i++)
642		s.writeObject(queue[i]);
643		}
644
645		/**
646		* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
647		* deserialize it).
648	+	* @param s the stream
649		*/
650	<	private synchronized void readObject(java.io.ObjectInputStream s)
650	>	private void readObject(java.io.ObjectInputStream s)
651		throws java.io.IOException, ClassNotFoundException {
652	<	// Read in size, and any hidden stuff
653	<	s.defaultReadObject();
652	>	// Read in size, and any hidden stuff
653	>	s.defaultReadObject();
654
655		// Read in array length and allocate array
656		int arrayLength = s.readInt();
657	<	queue = new E[arrayLength];
657	>	queue = new Object[arrayLength];
658
659	<	// Read in all elements in the proper order.
660	<	for (int i=0; i<size; i++)
661	<	queue[i] = (E)s.readObject();
659	>	// Read in all elements in the proper order.
660	>	for (int i=1; i<=size; i++)
661	>	queue[i] = (E) s.readObject();
662		}
663
664		}

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