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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.2 by tim, Sun May 18 18:10:02 2003 UTC vs.
Revision 1.50 by dl, Wed Jun 2 23:45:46 2004 UTC

#	Line 1 | Line 1
1	–	package java.util;
2	–
1		/*
2	<	* Todo
2	>	* %W% %E%
3		*
4	<	*   1) Make it serializable.
4	>	* Copyright 2004 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	>	* A priority queue relying on natural ordering also does not
18	>	* permit insertion of non-comparable objects (doing so may result
19	>	* 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.
38	>	* The
39	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
40	>	* guaranteed to traverse the elements of the PriorityQueue in any
41	>	* particular order. If you need ordered traversal, consider using
42	>	* <tt>Arrays.sort(pq.toArray())</tt>.
43	>	*
44	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
45	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
46	>	* instance concurrently if any of the threads modifies the list
47	>	* structurally. Instead, use the thread-safe {@link
48	>	* java.util.concurrent.PriorityBlockingQueue} class.
49	>	*
50	>	*
51	>	* <p>Implementation note: this implementation provides O(log(n)) time
52	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
53	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
54	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
55	>	* constant time for the retrieval methods (<tt>peek</tt>,
56	>	* <tt>element</tt>, and <tt>size</tt>).
57		*
58		* <p>This class is a member of the
59		* <a href="{@docRoot}/../guide/collections/index.html">
60		* Java Collections Framework</a>.
61	+	* @since 1.5
62	+	* @version %I%, %G%
63	+	* @author Josh Bloch
64	+	* @param <E> the type of elements held in this collection
65		*/
66		public class PriorityQueue<E> extends AbstractQueue<E>
67	<	implements Queue<E>
68	<	{
67	>	implements java.io.Serializable {
68	>
69	>	private static final long serialVersionUID = -7720805057305804111L;
70	>
71		private static final int DEFAULT_INITIAL_CAPACITY = 11;
72
73		/**
74		* Priority queue represented as a balanced binary heap: the two children
75		* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
76		* ordered by comparator, or by the elements' natural ordering, if
77	<	* comparator is null:  For each node n in the heap, and each descendant
78	<	* of n, d, n <= d.
77	>	* comparator is null:  For each node n in the heap and each descendant d
78	>	* of n, n <= d.
79		*
80	<	* The element with the lowest value is in queue[1] (assuming the queue is
81	<	* nonempty). A one-based array is used in preference to the traditional
82	<	* zero-based array to simplify parent and child calculations.
80	>	* The element with the lowest value is in queue[1], assuming the queue is
81	>	* nonempty.  (A one-based array is used in preference to the traditional
82	>	* zero-based array to simplify parent and child calculations.)
83		*
84		* queue.length must be >= 2, even if size == 0.
85		*/
86	<	private E[] queue;
86	>	private transient Object[] queue;
87
88		/**
89		* The number of elements in the priority queue.
#	Line 62 | Line 94 | public class PriorityQueue<E> extends Ab
94		* The comparator, or null if priority queue uses elements'
95		* natural ordering.
96		*/
97	<	private final Comparator<E> comparator;
97	>	private final Comparator<? super E> comparator;
98
99		/**
100		* The number of times this priority queue has been
101		* <i>structurally modified</i>.  See AbstractList for gory details.
102		*/
103	<	private int modCount = 0;
103	>	private transient int modCount = 0;
104
105		/**
106	<	* Create a new priority queue with the default initial capacity (11)
107	<	* that orders its elements according to their natural ordering.
106	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
107	>	* (11) that orders its elements according to their natural
108	>	* ordering (using <tt>Comparable</tt>).
109		*/
110		public PriorityQueue() {
111	<	this(DEFAULT_INITIAL_CAPACITY);
111	>	this(DEFAULT_INITIAL_CAPACITY, null);
112		}
113
114		/**
115	<	* Create a new priority queue with the specified initial capacity
116	<	* that orders its elements according to their natural ordering.
115	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
116	>	* that orders its elements according to their natural ordering
117	>	* (using <tt>Comparable</tt>).
118		*
119		* @param initialCapacity the initial capacity for this priority queue.
120	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
121	+	* than 1
122		*/
123		public PriorityQueue(int initialCapacity) {
124		this(initialCapacity, null);
125		}
126
127		/**
128	<	* Create a new priority queue with the specified initial capacity (11)
128	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
129		* that orders its elements according to the specified comparator.
130		*
131		* @param initialCapacity the initial capacity for this priority queue.
132		* @param comparator the comparator used to order this priority queue.
133	+	* If <tt>null</tt> then the order depends on the elements' natural
134	+	* ordering.
135	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
136	+	* than 1
137		*/
138	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
138	>	public PriorityQueue(int initialCapacity,
139	>	Comparator<? super E> comparator) {
140		if (initialCapacity < 1)
141	<	initialCapacity = 1;
142	<	queue = new E[initialCapacity + 1];
141	>	throw new IllegalArgumentException();
142	>	this.queue = new Object[initialCapacity + 1];
143		this.comparator = comparator;
144		}
145
146		/**
147	<	* Create a new priority queue containing the elements in the specified
148	<	* 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>.
147	>	* Common code to initialize underlying queue array across
148	>	* constructors below.
149		*/
150	<	public PriorityQueue(Collection<E> initialElements) {
151	<	int sz = initialElements.size();
150	>	private void initializeArray(Collection<? extends E> c) {
151	>	int sz = c.size();
152		int initialCapacity = (int)Math.min((sz * 110L) / 100,
153		Integer.MAX_VALUE - 1);
154		if (initialCapacity < 1)
155		initialCapacity = 1;
130	–	queue = new E[initialCapacity + 1];
156
157	<	/* Commented out to compile with generics compiler
157	>	this.queue = new Object[initialCapacity + 1];
158	>	}
159
160	<	if (initialElements instanceof Sorted) {
161	<	comparator = ((Sorted)initialElements).comparator();
162	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
163	<	queue[++size] = i.next();
160	>	/**
161	>	* Initially fill elements of the queue array under the
162	>	* knowledge that it is sorted or is another PQ, in which
163	>	* case we can just place the elements in the order presented.
164	>	*/
165	>	private void fillFromSorted(Collection<? extends E> c) {
166	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
167	>	queue[++size] = i.next();
168	>	}
169	>
170	>	/**
171	>	* Initially fill elements of the queue array that is not to our knowledge
172	>	* sorted, so we must rearrange the elements to guarantee the heap
173	>	* invariant.
174	>	*/
175	>	private void fillFromUnsorted(Collection<? extends E> c) {
176	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
177	>	queue[++size] = i.next();
178	>	heapify();
179	>	}
180	>
181	>	/**
182	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
183	>	* specified collection.  The priority queue has an initial
184	>	* capacity of 110% of the size of the specified collection or 1
185	>	* if the collection is empty.  If the specified collection is an
186	>	* instance of a {@link java.util.SortedSet} or is another
187	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
188	>	* according to the same comparator, or according to its elements'
189	>	* natural order if the collection is sorted according to its
190	>	* elements' natural order.  Otherwise, the priority queue is
191	>	* ordered according to its elements' natural order.
192	>	*
193	>	* @param c the collection whose elements are to be placed
194	>	*        into this priority queue.
195	>	* @throws ClassCastException if elements of the specified collection
196	>	*         cannot be compared to one another according to the priority
197	>	*         queue's ordering.
198	>	* @throws NullPointerException if <tt>c</tt> or any element within it
199	>	* is <tt>null</tt>
200	>	*/
201	>	public PriorityQueue(Collection<? extends E> c) {
202	>	initializeArray(c);
203	>	if (c instanceof SortedSet) {
204	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
205	>	comparator = (Comparator<? super E>)s.comparator();
206	>	fillFromSorted(s);
207	>	} else if (c instanceof PriorityQueue) {
208	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
209	>	comparator = (Comparator<? super E>)s.comparator();
210	>	fillFromSorted(s);
211		} else {
139	–	*/
140	–	{
212		comparator = null;
213	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
213	>	fillFromUnsorted(c);
214		}
215		}
216
217	<	// Queue Methods
217	>	/**
218	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
219	>	* specified collection.  The priority queue has an initial
220	>	* capacity of 110% of the size of the specified collection or 1
221	>	* if the collection is empty.  This priority queue will be sorted
222	>	* according to the same comparator as the given collection, or
223	>	* according to its elements' natural order if the collection is
224	>	* sorted according to its elements' natural order.
225	>	*
226	>	* @param c the collection whose elements are to be placed
227	>	*        into this priority queue.
228	>	* @throws ClassCastException if elements of the specified collection
229	>	*         cannot be compared to one another according to the priority
230	>	*         queue's ordering.
231	>	* @throws NullPointerException if <tt>c</tt> or any element within it
232	>	* is <tt>null</tt>
233	>	*/
234	>	public PriorityQueue(PriorityQueue<? extends E> c) {
235	>	initializeArray(c);
236	>	comparator = (Comparator<? super E>)c.comparator();
237	>	fillFromSorted(c);
238	>	}
239
240		/**
241	<	* Remove and return the minimal element from this priority queue if
242	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
243	<	* <i>minimal</i> is defined according to this priority queue's order.
241	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
242	>	* specified collection.  The priority queue has an initial
243	>	* capacity of 110% of the size of the specified collection or 1
244	>	* if the collection is empty.  This priority queue will be sorted
245	>	* according to the same comparator as the given collection, or
246	>	* according to its elements' natural order if the collection is
247	>	* sorted according to its elements' natural order.
248		*
249	<	* @return the minimal element from this priority queue if it contains
250	<	*         one or more elements, otherwise <tt>null</tt>.
249	>	* @param c the collection whose elements are to be placed
250	>	*        into this priority queue.
251	>	* @throws ClassCastException if elements of the specified collection
252	>	*         cannot be compared to one another according to the priority
253	>	*         queue's ordering.
254	>	* @throws NullPointerException if <tt>c</tt> or any element within it
255	>	* is <tt>null</tt>
256		*/
257	<	public E poll() {
258	<	if (size == 0)
259	<	return null;
260	<	return remove(1);
257	>	public PriorityQueue(SortedSet<? extends E> c) {
258	>	initializeArray(c);
259	>	comparator = (Comparator<? super E>)c.comparator();
260	>	fillFromSorted(c);
261	>	}
262	>
263	>	/**
264	>	* Resize array, if necessary, to be able to hold given index
265	>	*/
266	>	private void grow(int index) {
267	>	int newlen = queue.length;
268	>	if (index < newlen) // don't need to grow
269	>	return;
270	>	if (index == Integer.MAX_VALUE)
271	>	throw new OutOfMemoryError();
272	>	while (newlen <= index) {
273	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
274	>	newlen = Integer.MAX_VALUE;
275	>	else
276	>	newlen <<= 2;
277	>	}
278	>	Object[] newQueue = new Object[newlen];
279	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
280	>	queue = newQueue;
281		}
282	+
283
284		/**
285	<	* 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.
285	>	* Inserts the specified element into this priority queue.
286		*
287	<	* @return the minimal element from this priority queue if it contains
288	<	*         one or more elements, otherwise <tt>null</tt>.
287	>	* @return <tt>true</tt>
288	>	* @throws ClassCastException if the specified element cannot be compared
289	>	* with elements currently in the priority queue according
290	>	* to the priority queue's ordering.
291	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
292		*/
293	+	public boolean offer(E o) {
294	+	if (o == null)
295	+	throw new NullPointerException();
296	+	modCount++;
297	+	++size;
298	+
299	+	// Grow backing store if necessary
300	+	if (size >= queue.length)
301	+	grow(size);
302	+
303	+	queue[size] = o;
304	+	fixUp(size);
305	+	return true;
306	+	}
307	+
308		public E peek() {
309	<	return queue[1];
309	>	if (size == 0)
310	>	return null;
311	>	return (E) queue[1];
312		}
313
314	<	// Collection Methods
314	>	// Collection Methods - the first two override to update docs
315
316		/**
317	<	* Removes a single instance of the specified element from this priority
318	<	* queue, if it is present.  Returns true if this collection contained the
319	<	* specified element (or equivalently, if this collection changed as a
184	<	* result of the call).
317	>	* Adds the specified element to this queue.
318	>	* @return <tt>true</tt> (as per the general contract of
319	>	* <tt>Collection.add</tt>).
320		*
321	<	* @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
321	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
322		* @throws ClassCastException if the specified element cannot be compared
323	<	*            with elements currently in the priority queue according
324	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
323	>	* with elements currently in the priority queue according
324	>	* to the priority queue's ordering.
325		*/
326	<	public boolean remove(Object element) {
327	<	if (element == null)
328	<	throw new NullPointerException();
326	>	public boolean add(E o) {
327	>	return offer(o);
328	>	}
329	>
330	>	/**
331	>	* Removes a single instance of the specified element from this
332	>	* queue, if it is present.
333	>	*/
334	>	public boolean remove(Object o) {
335	>	if (o == null)
336	>	return false;
337
338		if (comparator == null) {
339		for (int i = 1; i <= size; i++) {
340	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
341	<	remove(i);
340	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
341	>	removeAt(i);
342		return true;
343		}
344		}
345		} else {
346		for (int i = 1; i <= size; i++) {
347	<	if (comparator.compare(queue[i], (E) element) == 0) {
348	<	remove(i);
347	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
348	>	removeAt(i);
349		return true;
350		}
351		}
#	Line 214 | Line 354 | public class PriorityQueue<E> extends Ab
354		}
355
356		/**
357	<	* Returns an iterator over the elements in this priority queue.  The
358	<	* first element returned by this iterator is the same element that
219	<	* would be returned by a call to <tt>peek</tt>.
357	>	* Returns an iterator over the elements in this queue. The iterator
358	>	* does not return the elements in any particular order.
359		*
360	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
360	>	* @return an iterator over the elements in this queue.
361		*/
362		public Iterator<E> iterator() {
363		return new Itr();
364		}
365
366		private class Itr implements Iterator<E> {
367	+
368		/**
369		* Index (into queue array) of element to be returned by
370		* subsequent call to next.
371		*/
372	<	int cursor = 1;
372	>	private int cursor = 1;
373
374		/**
375	<	* Index of element returned by most recent call to next or
376	<	* previous.  Reset to 0 if this element is deleted by a call
377	<	* to remove.
375	>	* Index of element returned by most recent call to next,
376	>	* unless that element came from the forgetMeNot list.
377	>	* Reset to 0 if element is deleted by a call to remove.
378		*/
379	<	int lastRet = 0;
379	>	private int lastRet = 0;
380
381		/**
382		* The modCount value that the iterator believes that the backing
383		* List should have.  If this expectation is violated, the iterator
384		* has detected concurrent modification.
385		*/
386	<	int expectedModCount = modCount;
386	>	private int expectedModCount = modCount;
387	>
388	>	/**
389	>	* A list of elements that were moved from the unvisited portion of
390	>	* the heap into the visited portion as a result of "unlucky" element
391	>	* removals during the iteration.  (Unlucky element removals are those
392	>	* that require a fixup instead of a fixdown.)  We must visit all of
393	>	* the elements in this list to complete the iteration.  We do this
394	>	* after we've completed the "normal" iteration.
395	>	*
396	>	* We expect that most iterations, even those involving removals,
397	>	* will not use need to store elements in this field.
398	>	*/
399	>	private ArrayList<E> forgetMeNot = null;
400	>
401	>	/**
402	>	* Element returned by the most recent call to next iff that
403	>	* element was drawn from the forgetMeNot list.
404	>	*/
405	>	private Object lastRetElt = null;
406
407		public boolean hasNext() {
408	<	return cursor <= size;
408	>	return cursor <= size || forgetMeNot != null;
409		}
410
411		public E next() {
412		checkForComodification();
413	<	if (cursor > size)
413	>	E result;
414	>	if (cursor <= size) {
415	>	result = (E) queue[cursor];
416	>	lastRet = cursor++;
417	>	}
418	>	else if (forgetMeNot == null)
419		throw new NoSuchElementException();
420	<	E result = queue[cursor];
421	<	lastRet = cursor++;
420	>	else {
421	>	int remaining = forgetMeNot.size();
422	>	result = forgetMeNot.remove(remaining - 1);
423	>	if (remaining == 1)
424	>	forgetMeNot = null;
425	>	lastRet = 0;
426	>	lastRetElt = result;
427	>	}
428		return result;
429		}
430
431		public void remove() {
262	–	if (lastRet == 0)
263	–	throw new IllegalStateException();
432		checkForComodification();
433
434	<	PriorityQueue.this.remove(lastRet);
435	<	if (lastRet < cursor)
436	<	cursor--;
437	<	lastRet = 0;
434	>	if (lastRet != 0) {
435	>	E moved = PriorityQueue.this.removeAt(lastRet);
436	>	lastRet = 0;
437	>	if (moved == null) {
438	>	cursor--;
439	>	} else {
440	>	if (forgetMeNot == null)
441	>	forgetMeNot = new ArrayList<E>();
442	>	forgetMeNot.add(moved);
443	>	}
444	>	} else if (lastRetElt != null) {
445	>	PriorityQueue.this.remove(lastRetElt);
446	>	lastRetElt = null;
447	>	} else {
448	>	throw new IllegalStateException();
449	>	}
450	>
451		expectedModCount = modCount;
452		}
453
#	Line 276 | Line 457 | public class PriorityQueue<E> extends Ab
457		}
458		}
459
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
460		public int size() {
461		return size;
462		}
463
464		/**
465	<	* Add the specified element to this priority queue.
466	<	*
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	<	/**
316	<	* Remove all elements from the priority queue.
465	>	* Removes all elements from the priority queue.
466	>	* The queue will be empty after this call returns.
467		*/
468		public void clear() {
469		modCount++;
#	Line 325 | Line 475 | public class PriorityQueue<E> extends Ab
475		size = 0;
476		}
477
478	+	public E poll() {
479	+	if (size == 0)
480	+	return null;
481	+	modCount++;
482	+
483	+	E result = (E) queue[1];
484	+	queue[1] = queue[size];
485	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
486	+	if (size > 1)
487	+	fixDown(1);
488	+
489	+	return result;
490	+	}
491	+
492		/**
493	<	* Removes and returns the ith element from queue.  Recall
494	<	* that queue is one-based, so 1 <= i <= size.
493	>	* Removes and returns the ith element from queue.  (Recall that queue
494	>	* is one-based, so 1 <= i <= size.)
495		*
496	<	* XXX: Could further special-case i==size, but is it worth it?
497	<	* XXX: Could special-case i==0, but is it worth it?
496	>	* Normally this method leaves the elements at positions from 1 up to i-1,
497	>	* inclusive, untouched.  Under these circumstances, it returns null.
498	>	* Occasionally, in order to maintain the heap invariant, it must move
499	>	* the last element of the list to some index in the range [2, i-1],
500	>	* and move the element previously at position (i/2) to position i.
501	>	* Under these circumstances, this method returns the element that was
502	>	* previously at the end of the list and is now at some position between
503	>	* 2 and i-1 inclusive.
504		*/
505	<	private E remove(int i) {
506	<	assert i <= size;
505	>	private E removeAt(int i) {
506	>	assert i > 0 && i <= size;
507		modCount++;
508
509	<	E result = queue[i];
510	<	queue[i] = queue[size];
509	>	E moved = (E) queue[size];
510	>	queue[i] = moved;
511		queue[size--] = null;  // Drop extra ref to prevent memory leak
512	<	if (i <= size)
512	>	if (i <= size) {
513		fixDown(i);
514	<	return result;
514	>	if (queue[i] == moved) {
515	>	fixUp(i);
516	>	if (queue[i] != moved)
517	>	return moved;
518	>	}
519	>	}
520	>	return null;
521		}
522
523		/**
#	Line 357 | Line 533 | public class PriorityQueue<E> extends Ab
533		if (comparator == null) {
534		while (k > 1) {
535		int j = k >> 1;
536	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
536	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
537		break;
538	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
538	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
539		k = j;
540		}
541		} else {
542		while (k > 1) {
543	<	int j = k >> 1;
544	<	if (comparator.compare(queue[j], queue[k]) <= 0)
543	>	int j = k >>> 1;
544	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
545		break;
546	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
546	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
547		k = j;
548		}
549		}
#	Line 385 | Line 561 | public class PriorityQueue<E> extends Ab
561		private void fixDown(int k) {
562		int j;
563		if (comparator == null) {
564	<	while ((j = k << 1) <= size) {
565	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
564	>	while ((j = k << 1) <= size && (j > 0)) {
565	>	if (j<size &&
566	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
567		j++; // j indexes smallest kid
568	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
568	>
569	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
570		break;
571	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
571	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
572		k = j;
573		}
574		} else {
575	<	while ((j = k << 1) <= size) {
576	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
575	>	while ((j = k << 1) <= size && (j > 0)) {
576	>	if (j<size &&
577	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
578		j++; // j indexes smallest kid
579	<	if (comparator.compare(queue[k], queue[j]) <= 0)
579	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
580		break;
581	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
581	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
582		k = j;
583		}
584		}
585		}
586
587		/**
588	<	* Returns the comparator associated with this priority queue, or
589	<	* <tt>null</tt> if it uses its elements' natural ordering.
588	>	* Establishes the heap invariant (described above) in the entire tree,
589	>	* assuming nothing about the order of the elements prior to the call.
590	>	*/
591	>	private void heapify() {
592	>	for (int i = size/2; i >= 1; i--)
593	>	fixDown(i);
594	>	}
595	>
596	>	/**
597	>	* Returns the comparator used to order this collection, or <tt>null</tt>
598	>	* if this collection is sorted according to its elements natural ordering
599	>	* (using <tt>Comparable</tt>).
600		*
601	<	* @return the comparator associated with this priority queue, or
602	<	*         <tt>null</tt> if it uses its elements' natural ordering.
601	>	* @return the comparator used to order this collection, or <tt>null</tt>
602	>	* if this collection is sorted according to its elements natural ordering.
603		*/
604	<	Comparator comparator() {
604	>	public Comparator<? super E> comparator() {
605		return comparator;
606		}
607	+
608	+	/**
609	+	* Save the state of the instance to a stream (that
610	+	* is, serialize it).
611	+	*
612	+	* @serialData The length of the array backing the instance is
613	+	* emitted (int), followed by all of its elements (each an
614	+	* <tt>Object</tt>) in the proper order.
615	+	* @param s the stream
616	+	*/
617	+	private void writeObject(java.io.ObjectOutputStream s)
618	+	throws java.io.IOException{
619	+	// Write out element count, and any hidden stuff
620	+	s.defaultWriteObject();
621	+
622	+	// Write out array length
623	+	s.writeInt(queue.length);
624	+
625	+	// Write out all elements in the proper order.
626	+	for (int i=1; i<=size; i++)
627	+	s.writeObject(queue[i]);
628	+	}
629	+
630	+	/**
631	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
632	+	* deserialize it).
633	+	* @param s the stream
634	+	*/
635	+	private void readObject(java.io.ObjectInputStream s)
636	+	throws java.io.IOException, ClassNotFoundException {
637	+	// Read in size, and any hidden stuff
638	+	s.defaultReadObject();
639	+
640	+	// Read in array length and allocate array
641	+	int arrayLength = s.readInt();
642	+	queue = new Object[arrayLength];
643	+
644	+	// Read in all elements in the proper order.
645	+	for (int i=1; i<=size; i++)
646	+	queue[i] = (E) s.readObject();
647	+	}
648	+
649		}

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