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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 1.41 by dl, Sat Sep 13 18:51:06 2003 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* %W% %E%
3		*
4	<	*   1) Make it serializable.
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
12	>	* heap.  This queue orders elements according to an order specified
13	>	* at construction time, which is specified either according to their
14	>	* <i>natural order</i> (see {@link Comparable}), or according to a
15	>	* {@link java.util.Comparator}, depending on which constructor is
16	>	* used. A priority queue does not permit <tt>null</tt> elements.
17	>	*
18	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
19	>	* with respect to the specified ordering.  If multiple elements are
20	>	* tied for least value, the head is one of those elements -- ties are
21	>	* broken arbitrarily.  The {@link #remove()} and {@link #poll()}
22	>	* methods remove and return the head of the queue, and the {@link
23	>	* #element()} and {@link #peek()} methods return, but do not delete,
24	>	* the head of the queue.
25		*
26	<	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
27	<	* the array used to store the elements on the queue.  It is always at least
28	<	* as large as the queue size.  As elements are added to a priority list,
29	<	* its capacity grows automatically.  The details of the growth policy are not
26	>	* <p>A priority queue is unbounded, but has an internal
27	>	* <i>capacity</i> governing the size of an array used to store the
28	>	* elements on the queue.  It is always at least as large as the queue
29	>	* size.  As elements are added to a priority queue, its capacity
30	>	* grows automatically.  The details of the growth policy are not
31		* specified.
32		*
33	<	*<p>Implementation note: this implementation provides O(log(n)) time for
34	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
35	<	* methods; linear time for the <tt>remove(Object)</tt> and
36	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
37	<	* <tt>element</tt>, and <tt>size</tt> methods.
33	>	* <p>This class implements all of the <em>optional</em> methods of
34	>	* the {@link Collection} and {@link Iterator} interfaces.  The
35	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
36	>	* guaranteed to traverse the elements of the PriorityQueue in any
37	>	* particular order. If you need ordered traversal, consider using
38	>	* <tt>Arrays.sort(pq.toArray())</tt>.
39	>	*
40	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
41	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
42	>	* instance concurrently if any of the threads modifies the list
43	>	* structurally. Instead, use the thread-safe {@link
44	>	* java.util.concurrent.PriorityBlockingQueue} class.
45	>	*
46	>	*
47	>	* <p>Implementation note: this implementation provides O(log(n)) time
48	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
49	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
50	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
51	>	* constant time for the retrieval methods (<tt>peek</tt>,
52	>	* <tt>element</tt>, and <tt>size</tt>).
53		*
54		* <p>This class is a member of the
55		* <a href="{@docRoot}/../guide/collections/index.html">
56		* Java Collections Framework</a>.
57	+	* @since 1.5
58	+	* @version %I%, %G%
59	+	* @author Josh Bloch
60		*/
61		public class PriorityQueue<E> extends AbstractQueue<E>
62	<	implements Queue<E>
63	<	{
62	>	implements Queue<E>, java.io.Serializable {
63	>
64	>	private static final long serialVersionUID = -7720805057305804111L;
65	>
66		private static final int DEFAULT_INITIAL_CAPACITY = 11;
67
68		/**
69		* Priority queue represented as a balanced binary heap: the two children
70		* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
71		* ordered by comparator, or by the elements' natural ordering, if
72	<	* comparator is null:  For each node n in the heap, and each descendant
73	<	* of n, d, n <= d.
72	>	* comparator is null:  For each node n in the heap and each descendant d
73	>	* of n, n <= d.
74		*
75	<	* The element with the lowest value is in queue[1] (assuming the queue is
76	<	* nonempty). A one-based array is used in preference to the traditional
77	<	* zero-based array to simplify parent and child calculations.
75	>	* The element with the lowest value is in queue[1], assuming the queue is
76	>	* nonempty.  (A one-based array is used in preference to the traditional
77	>	* zero-based array to simplify parent and child calculations.)
78		*
79		* queue.length must be >= 2, even if size == 0.
80		*/
81	<	private E[] queue;
81	>	private transient Object[] queue;
82
83		/**
84		* The number of elements in the priority queue.
#	Line 62 | Line 89 | public class PriorityQueue<E> extends Ab
89		* The comparator, or null if priority queue uses elements'
90		* natural ordering.
91		*/
92	<	private final Comparator<E> comparator;
92	>	private final Comparator<? super E> comparator;
93
94		/**
95		* The number of times this priority queue has been
96		* <i>structurally modified</i>.  See AbstractList for gory details.
97		*/
98	<	private int modCount = 0;
98	>	private transient int modCount = 0;
99
100		/**
101	<	* Create a new priority queue with the default initial capacity (11)
102	<	* that orders its elements according to their natural ordering.
101	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
102	>	* (11) that orders its elements according to their natural
103	>	* ordering (using <tt>Comparable</tt>).
104		*/
105		public PriorityQueue() {
106	<	this(DEFAULT_INITIAL_CAPACITY);
106	>	this(DEFAULT_INITIAL_CAPACITY, null);
107		}
108
109		/**
110	<	* Create a new priority queue with the specified initial capacity
111	<	* that orders its elements according to their natural ordering.
110	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
111	>	* that orders its elements according to their natural ordering
112	>	* (using <tt>Comparable</tt>).
113		*
114		* @param initialCapacity the initial capacity for this priority queue.
115	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
116	+	* than 1
117		*/
118		public PriorityQueue(int initialCapacity) {
119		this(initialCapacity, null);
120		}
121
122		/**
123	<	* Create a new priority queue with the specified initial capacity (11)
123	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
124		* that orders its elements according to the specified comparator.
125		*
126		* @param initialCapacity the initial capacity for this priority queue.
127		* @param comparator the comparator used to order this priority queue.
128	+	* If <tt>null</tt> then the order depends on the elements' natural
129	+	* ordering.
130	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
131	+	* than 1
132		*/
133	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
133	>	public PriorityQueue(int initialCapacity,
134	>	Comparator<? super E> comparator) {
135		if (initialCapacity < 1)
136	<	initialCapacity = 1;
137	<	queue = new E[initialCapacity + 1];
136	>	throw new IllegalArgumentException();
137	>	this.queue = new Object[initialCapacity + 1];
138		this.comparator = comparator;
139		}
140
141		/**
142	<	* Create a new priority queue containing the elements in the specified
143	<	* collection.  The priority queue has an initial capacity of 110% of the
108	<	* size of the specified collection. If the specified collection
109	<	* implements the {@link Sorted} interface, the priority queue will be
110	<	* sorted according to the same comparator, or according to its elements'
111	<	* 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.
115	<	*
116	<	* @param initialElements the collection whose elements are to be placed
117	<	*        into this priority queue.
118	<	* @throws ClassCastException if elements of the specified collection
119	<	*         cannot be compared to one another according to the priority
120	<	*         queue's ordering.
121	<	* @throws NullPointerException if the specified collection or an
122	<	*         element of the specified collection is <tt>null</tt>.
142	>	* Common code to initialize underlying queue array across
143	>	* constructors below.
144		*/
145	<	public PriorityQueue(Collection<E> initialElements) {
146	<	int sz = initialElements.size();
145	>	private void initializeArray(Collection<? extends E> c) {
146	>	int sz = c.size();
147		int initialCapacity = (int)Math.min((sz * 110L) / 100,
148		Integer.MAX_VALUE - 1);
149		if (initialCapacity < 1)
150		initialCapacity = 1;
130	–	queue = new E[initialCapacity + 1];
151
152	<	/* Commented out to compile with generics compiler
152	>	this.queue = new Object[initialCapacity + 1];
153	>	}
154
155	<	if (initialElements instanceof Sorted) {
156	<	comparator = ((Sorted)initialElements).comparator();
157	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
158	<	queue[++size] = i.next();
155	>	/**
156	>	* Initially fill elements of the queue array under the
157	>	* knowledge that it is sorted or is another PQ, in which
158	>	* case we can just place the elements in the order presented.
159	>	*/
160	>	private void fillFromSorted(Collection<? extends E> c) {
161	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
162	>	queue[++size] = i.next();
163	>	}
164	>
165	>	/**
166	>	* Initially fill elements of the queue array that is not to our knowledge
167	>	* sorted, so we must rearrange the elements to guarantee the heap
168	>	* invariant.
169	>	*/
170	>	private void fillFromUnsorted(Collection<? extends E> c) {
171	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
172	>	queue[++size] = i.next();
173	>	heapify();
174	>	}
175	>
176	>	/**
177	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
178	>	* specified collection.  The priority queue has an initial
179	>	* capacity of 110% of the size of the specified collection or 1
180	>	* if the collection is empty.  If the specified collection is an
181	>	* instance of a {@link java.util.SortedSet} or is another
182	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
183	>	* according to the same comparator, or according to its elements'
184	>	* natural order if the collection is sorted according to its
185	>	* elements' natural order.  Otherwise, the priority queue is
186	>	* ordered according to its elements' natural order.
187	>	*
188	>	* @param c the collection whose elements are to be placed
189	>	*        into this priority queue.
190	>	* @throws ClassCastException if elements of the specified collection
191	>	*         cannot be compared to one another according to the priority
192	>	*         queue's ordering.
193	>	* @throws NullPointerException if <tt>c</tt> or any element within it
194	>	* is <tt>null</tt>
195	>	*/
196	>	public PriorityQueue(Collection<? extends E> c) {
197	>	initializeArray(c);
198	>	if (c instanceof SortedSet) {
199	>	// @fixme double-cast workaround for compiler
200	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
201	>	comparator = (Comparator<? super E>)s.comparator();
202	>	fillFromSorted(s);
203	>	} else if (c instanceof PriorityQueue) {
204	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
205	>	comparator = (Comparator<? super E>)s.comparator();
206	>	fillFromSorted(s);
207		} else {
139	–	*/
140	–	{
208		comparator = null;
209	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
209	>	fillFromUnsorted(c);
210		}
211		}
212
213	<	// Queue Methods
213	>	/**
214	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
215	>	* specified collection.  The priority queue has an initial
216	>	* capacity of 110% of the size of the specified collection or 1
217	>	* if the collection is empty.  This priority queue will be sorted
218	>	* according to the same comparator as the given collection, or
219	>	* according to its elements' natural order if the collection is
220	>	* sorted according to its elements' natural order.
221	>	*
222	>	* @param c the collection whose elements are to be placed
223	>	*        into this priority queue.
224	>	* @throws ClassCastException if elements of the specified collection
225	>	*         cannot be compared to one another according to the priority
226	>	*         queue's ordering.
227	>	* @throws NullPointerException if <tt>c</tt> or any element within it
228	>	* is <tt>null</tt>
229	>	*/
230	>	public PriorityQueue(PriorityQueue<? extends E> c) {
231	>	initializeArray(c);
232	>	comparator = (Comparator<? super E>)c.comparator();
233	>	fillFromSorted(c);
234	>	}
235
236		/**
237	<	* Remove and return the minimal element from this priority queue if
238	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
239	<	* <i>minimal</i> is defined according to this priority queue's order.
237	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
238	>	* specified collection.  The priority queue has an initial
239	>	* capacity of 110% of the size of the specified collection or 1
240	>	* if the collection is empty.  This priority queue will be sorted
241	>	* according to the same comparator as the given collection, or
242	>	* according to its elements' natural order if the collection is
243	>	* sorted according to its elements' natural order.
244		*
245	<	* @return the minimal element from this priority queue if it contains
246	<	*         one or more elements, otherwise <tt>null</tt>.
245	>	* @param c the collection whose elements are to be placed
246	>	*        into this priority queue.
247	>	* @throws ClassCastException if elements of the specified collection
248	>	*         cannot be compared to one another according to the priority
249	>	*         queue's ordering.
250	>	* @throws NullPointerException if <tt>c</tt> or any element within it
251	>	* is <tt>null</tt>
252		*/
253	<	public E poll() {
254	<	if (size == 0)
255	<	return null;
256	<	return remove(1);
253	>	public PriorityQueue(SortedSet<? extends E> c) {
254	>	initializeArray(c);
255	>	comparator = (Comparator<? super E>)c.comparator();
256	>	fillFromSorted(c);
257	>	}
258	>
259	>	/**
260	>	* Resize array, if necessary, to be able to hold given index
261	>	*/
262	>	private void grow(int index) {
263	>	int newlen = queue.length;
264	>	if (index < newlen) // don't need to grow
265	>	return;
266	>	if (index == Integer.MAX_VALUE)
267	>	throw new OutOfMemoryError();
268	>	while (newlen <= index) {
269	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
270	>	newlen = Integer.MAX_VALUE;
271	>	else
272	>	newlen <<= 2;
273	>	}
274	>	Object[] newQueue = new Object[newlen];
275	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
276	>	queue = newQueue;
277		}
278	+
279
280		/**
281	<	* Return, but do not remove, the minimal element from the priority queue,
165	<	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
166	<	* defined according to this priority queue's order.  This method returns
167	<	* the same object reference that would be returned by by the
168	<	* <tt>poll</tt> method.  The two methods differ in that this method
169	<	* does not remove the element from the priority queue.
281	>	* Inserts the specified element to this priority queue.
282		*
283	<	* @return the minimal element from this priority queue if it contains
284	<	*         one or more elements, otherwise <tt>null</tt>.
283	>	* @return <tt>true</tt>
284	>	* @throws ClassCastException if the specified element cannot be compared
285	>	* with elements currently in the priority queue according
286	>	* to the priority queue's ordering.
287	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
288		*/
289	+	public boolean offer(E o) {
290	+	if (o == null)
291	+	throw new NullPointerException();
292	+	modCount++;
293	+	++size;
294	+
295	+	// Grow backing store if necessary
296	+	if (size >= queue.length)
297	+	grow(size);
298	+
299	+	queue[size] = o;
300	+	fixUp(size);
301	+	return true;
302	+	}
303	+
304		public E peek() {
305	<	return queue[1];
305	>	if (size == 0)
306	>	return null;
307	>	return (E) queue[1];
308		}
309
310	<	// Collection Methods
310	>	// Collection Methods - the first two override to update docs
311
312		/**
313	<	* Removes a single instance of the specified element from this priority
314	<	* queue, if it is present.  Returns true if this collection contained the
315	<	* specified element (or equivalently, if this collection changed as a
184	<	* result of the call).
313	>	* Adds the specified element to this queue.
314	>	* @return <tt>true</tt> (as per the general contract of
315	>	* <tt>Collection.add</tt>).
316		*
317	<	* @param o element to be removed from this collection, if present.
187	<	* @return <tt>true</tt> if this collection changed as a result of the
188	<	*         call
317	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
318		* @throws ClassCastException if the specified element cannot be compared
319	<	*            with elements currently in the priority queue according
320	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
319	>	* with elements currently in the priority queue according
320	>	* to the priority queue's ordering.
321		*/
322	<	public boolean remove(Object element) {
323	<	if (element == null)
324	<	throw new NullPointerException();
322	>	public boolean add(E o) {
323	>	return offer(o);
324	>	}
325	>
326	>
327	>	/**
328	>	* Adds all of the elements in the specified collection to this queue.
329	>	* The behavior of this operation is undefined if
330	>	* the specified collection is modified while the operation is in
331	>	* progress.  (This implies that the behavior of this call is undefined if
332	>	* the specified collection is this queue, and this queue is nonempty.)
333	>	* <p>
334	>	* This implementation iterates over the specified collection, and adds
335	>	* each object returned by the iterator to this collection, in turn.
336	>	* @param c collection whose elements are to be added to this queue
337	>	* @return <tt>true</tt> if this queue changed as a result of the
338	>	*         call.
339	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
340	>	* is <tt>null</tt>
341	>	* @throws ClassCastException if any element cannot be compared
342	>	* with elements currently in the priority queue according
343	>	* to the priority queue's ordering.
344	>	*/
345	>	public boolean addAll(Collection<? extends E> c) {
346	>	return super.addAll(c);
347	>	}
348	>
349	>	public boolean remove(Object o) {
350	>	if (o == null)
351	>	return false;
352
353		if (comparator == null) {
354		for (int i = 1; i <= size; i++) {
355	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
356	<	remove(i);
355	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
356	>	removeAt(i);
357		return true;
358		}
359		}
360		} else {
361		for (int i = 1; i <= size; i++) {
362	<	if (comparator.compare(queue[i], (E) element) == 0) {
363	<	remove(i);
362	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
363	>	removeAt(i);
364		return true;
365		}
366		}
#	Line 214 | Line 369 | public class PriorityQueue<E> extends Ab
369		}
370
371		/**
372	<	* Returns an iterator over the elements in this priority queue.  The
373	<	* first element returned by this iterator is the same element that
219	<	* would be returned by a call to <tt>peek</tt>.
372	>	* Returns an iterator over the elements in this queue. The iterator
373	>	* does not return the elements in any particular order.
374		*
375	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
375	>	* @return an iterator over the elements in this queue.
376		*/
377		public Iterator<E> iterator() {
378		return new Itr();
379		}
380
381		private class Itr implements Iterator<E> {
382	+
383		/**
384		* Index (into queue array) of element to be returned by
385		* subsequent call to next.
386		*/
387	<	int cursor = 1;
387	>	private int cursor = 1;
388
389		/**
390	<	* Index of element returned by most recent call to next or
391	<	* previous.  Reset to 0 if this element is deleted by a call
392	<	* to remove.
390	>	* Index of element returned by most recent call to next,
391	>	* unless that element came from the forgetMeNot list.
392	>	* Reset to 0 if element is deleted by a call to remove.
393		*/
394	<	int lastRet = 0;
394	>	private int lastRet = 0;
395
396		/**
397		* The modCount value that the iterator believes that the backing
398		* List should have.  If this expectation is violated, the iterator
399		* has detected concurrent modification.
400		*/
401	<	int expectedModCount = modCount;
401	>	private int expectedModCount = modCount;
402	>
403	>	/**
404	>	* A list of elements that were moved from the unvisited portion of
405	>	* the heap into the visited portion as a result of "unlucky" element
406	>	* removals during the iteration.  (Unlucky element removals are those
407	>	* that require a fixup instead of a fixdown.)  We must visit all of
408	>	* the elements in this list to complete the iteration.  We do this
409	>	* after we've completed the "normal" iteration.
410	>	*
411	>	* We expect that most iterations, even those involving removals,
412	>	* will not use need to store elements in this field.
413	>	*/
414	>	private ArrayList<E> forgetMeNot = null;
415	>
416	>	/**
417	>	* Element returned by the most recent call to next iff that
418	>	* element was drawn from the forgetMeNot list.
419	>	*/
420	>	private Object lastRetElt = null;
421
422		public boolean hasNext() {
423	<	return cursor <= size;
423	>	return cursor <= size || forgetMeNot != null;
424		}
425
426		public E next() {
427		checkForComodification();
428	<	if (cursor > size)
428	>	E result;
429	>	if (cursor <= size) {
430	>	result = (E) queue[cursor];
431	>	lastRet = cursor++;
432	>	}
433	>	else if (forgetMeNot == null)
434		throw new NoSuchElementException();
435	<	E result = queue[cursor];
436	<	lastRet = cursor++;
435	>	else {
436	>	int remaining = forgetMeNot.size();
437	>	result = forgetMeNot.remove(remaining - 1);
438	>	if (remaining == 1)
439	>	forgetMeNot = null;
440	>	lastRet = 0;
441	>	lastRetElt = result;
442	>	}
443		return result;
444		}
445
446		public void remove() {
262	–	if (lastRet == 0)
263	–	throw new IllegalStateException();
447		checkForComodification();
448
449	<	PriorityQueue.this.remove(lastRet);
450	<	if (lastRet < cursor)
451	<	cursor--;
452	<	lastRet = 0;
449	>	if (lastRet != 0) {
450	>	E moved = PriorityQueue.this.removeAt(lastRet);
451	>	lastRet = 0;
452	>	if (moved == null) {
453	>	cursor--;
454	>	} else {
455	>	if (forgetMeNot == null)
456	>	forgetMeNot = new ArrayList<E>();
457	>	forgetMeNot.add(moved);
458	>	}
459	>	} else if (lastRetElt != null) {
460	>	PriorityQueue.this.remove(lastRetElt);
461	>	lastRetElt = null;
462	>	} else {
463	>	throw new IllegalStateException();
464	>	}
465	>
466		expectedModCount = modCount;
467		}
468
#	Line 276 | Line 472 | public class PriorityQueue<E> extends Ab
472		}
473		}
474
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
475		public int size() {
476		return size;
477		}
478
479		/**
289	–	* Add the specified element to this priority queue.
290	–	*
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.
297	–	*/
298	–	public boolean offer(E element) {
299	–	if (element == null)
300	–	throw new NullPointerException();
301	–	modCount++;
302	–
303	–	// Grow backing store if necessary
304	–	if (++size == queue.length) {
305	–	E[] newQueue = new E[2 * queue.length];
306	–	System.arraycopy(queue, 0, newQueue, 0, size);
307	–	queue = newQueue;
308	–	}
309	–
310	–	queue[size] = element;
311	–	fixUp(size);
312	–	return true;
313	–	}
314	–
315	–	/**
480		* Remove all elements from the priority queue.
481		*/
482		public void clear() {
#	Line 325 | Line 489 | public class PriorityQueue<E> extends Ab
489		size = 0;
490		}
491
492	+	public E poll() {
493	+	if (size == 0)
494	+	return null;
495	+	modCount++;
496	+
497	+	E result = (E) queue[1];
498	+	queue[1] = queue[size];
499	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
500	+	if (size > 1)
501	+	fixDown(1);
502	+
503	+	return result;
504	+	}
505	+
506		/**
507	<	* Removes and returns the ith element from queue.  Recall
508	<	* that queue is one-based, so 1 <= i <= size.
507	>	* Removes and returns the ith element from queue.  (Recall that queue
508	>	* is one-based, so 1 <= i <= size.)
509		*
510	<	* XXX: Could further special-case i==size, but is it worth it?
511	<	* XXX: Could special-case i==0, but is it worth it?
510	>	* Normally this method leaves the elements at positions from 1 up to i-1,
511	>	* inclusive, untouched.  Under these circumstances, it returns null.
512	>	* Occasionally, in order to maintain the heap invariant, it must move
513	>	* the last element of the list to some index in the range [2, i-1],
514	>	* and move the element previously at position (i/2) to position i.
515	>	* Under these circumstances, this method returns the element that was
516	>	* previously at the end of the list and is now at some position between
517	>	* 2 and i-1 inclusive.
518		*/
519	<	private E remove(int i) {
520	<	assert i <= size;
519	>	private E removeAt(int i) {
520	>	assert i > 0 && i <= size;
521		modCount++;
522
523	<	E result = queue[i];
524	<	queue[i] = queue[size];
523	>	E moved = (E) queue[size];
524	>	queue[i] = moved;
525		queue[size--] = null;  // Drop extra ref to prevent memory leak
526	<	if (i <= size)
526	>	if (i <= size) {
527		fixDown(i);
528	<	return result;
528	>	if (queue[i] == moved) {
529	>	fixUp(i);
530	>	if (queue[i] != moved)
531	>	return moved;
532	>	}
533	>	}
534	>	return null;
535		}
536
537		/**
#	Line 357 | Line 547 | public class PriorityQueue<E> extends Ab
547		if (comparator == null) {
548		while (k > 1) {
549		int j = k >> 1;
550	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
550	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
551		break;
552	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
552	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
553		k = j;
554		}
555		} else {
556		while (k > 1) {
557	<	int j = k >> 1;
558	<	if (comparator.compare(queue[j], queue[k]) <= 0)
557	>	int j = k >>> 1;
558	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
559		break;
560	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
560	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
561		k = j;
562		}
563		}
#	Line 385 | Line 575 | public class PriorityQueue<E> extends Ab
575		private void fixDown(int k) {
576		int j;
577		if (comparator == null) {
578	<	while ((j = k << 1) <= size) {
579	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
578	>	while ((j = k << 1) <= size && (j > 0)) {
579	>	if (j<size &&
580	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
581		j++; // j indexes smallest kid
582	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
582	>
583	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
584		break;
585	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
585	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
586		k = j;
587		}
588		} else {
589	<	while ((j = k << 1) <= size) {
590	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
589	>	while ((j = k << 1) <= size && (j > 0)) {
590	>	if (j<size &&
591	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
592		j++; // j indexes smallest kid
593	<	if (comparator.compare(queue[k], queue[j]) <= 0)
593	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
594		break;
595	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
595	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
596		k = j;
597		}
598		}
599		}
600
601		/**
602	<	* Returns the comparator associated with this priority queue, or
603	<	* <tt>null</tt> if it uses its elements' natural ordering.
602	>	* Establishes the heap invariant (described above) in the entire tree,
603	>	* assuming nothing about the order of the elements prior to the call.
604	>	*/
605	>	private void heapify() {
606	>	for (int i = size/2; i >= 1; i--)
607	>	fixDown(i);
608	>	}
609	>
610	>	/**
611	>	* Returns the comparator used to order this collection, or <tt>null</tt>
612	>	* if this collection is sorted according to its elements natural ordering
613	>	* (using <tt>Comparable</tt>).
614		*
615	<	* @return the comparator associated with this priority queue, or
616	<	*         <tt>null</tt> if it uses its elements' natural ordering.
615	>	* @return the comparator used to order this collection, or <tt>null</tt>
616	>	* if this collection is sorted according to its elements natural ordering.
617		*/
618	<	Comparator<E> comparator() {
618	>	public Comparator<? super E> comparator() {
619		return comparator;
620		}
621	+
622	+	/**
623	+	* Save the state of the instance to a stream (that
624	+	* is, serialize it).
625	+	*
626	+	* @serialData The length of the array backing the instance is
627	+	* emitted (int), followed by all of its elements (each an
628	+	* <tt>Object</tt>) in the proper order.
629	+	* @param s the stream
630	+	*/
631	+	private void writeObject(java.io.ObjectOutputStream s)
632	+	throws java.io.IOException{
633	+	// Write out element count, and any hidden stuff
634	+	s.defaultWriteObject();
635	+
636	+	// Write out array length
637	+	s.writeInt(queue.length);
638	+
639	+	// Write out all elements in the proper order.
640	+	for (int i=1; i<=size; i++)
641	+	s.writeObject(queue[i]);
642	+	}
643	+
644	+	/**
645	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
646	+	* deserialize it).
647	+	* @param s the stream
648	+	*/
649	+	private void readObject(java.io.ObjectInputStream s)
650	+	throws java.io.IOException, ClassNotFoundException {
651	+	// Read in size, and any hidden stuff
652	+	s.defaultReadObject();
653	+
654	+	// Read in array length and allocate array
655	+	int arrayLength = s.readInt();
656	+	queue = new Object[arrayLength];
657	+
658	+	// Read in all elements in the proper order.
659	+	for (int i=1; i<=size; i++)
660	+	queue[i] = (E) s.readObject();
661	+	}
662	+
663		}

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