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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 1.45 by dl, Sun Oct 19 13:38:29 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	>	* 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 implements all of the <em>optional</em> methods of
36	>	* the {@link Collection} and {@link Iterator} interfaces.  The
37	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
38	>	* guaranteed to traverse the elements of the PriorityQueue in any
39	>	* particular order. If you need ordered traversal, consider using
40	>	* <tt>Arrays.sort(pq.toArray())</tt>.
41	>	*
42	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
43	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
44	>	* instance concurrently if any of the threads modifies the list
45	>	* structurally. Instead, use the thread-safe {@link
46	>	* java.util.concurrent.PriorityBlockingQueue} class.
47	>	*
48	>	*
49	>	* <p>Implementation note: this implementation provides O(log(n)) time
50	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
51	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
52	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
53	>	* constant time for the retrieval methods (<tt>peek</tt>,
54	>	* <tt>element</tt>, and <tt>size</tt>).
55		*
56		* <p>This class is a member of the
57		* <a href="{@docRoot}/../guide/collections/index.html">
58		* Java Collections Framework</a>.
59	+	* @since 1.5
60	+	* @version %I%, %G%
61	+	* @author Josh Bloch
62	+	* @param <E> the type of elements held in this collection
63		*/
64		public class PriorityQueue<E> extends AbstractQueue<E>
65	<	implements Queue<E>
66	<	{
65	>	implements Queue<E>, java.io.Serializable {
66	>
67	>	private static final long serialVersionUID = -7720805057305804111L;
68	>
69		private static final int DEFAULT_INITIAL_CAPACITY = 11;
70
71		/**
72		* Priority queue represented as a balanced binary heap: the two children
73		* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
74		* ordered by comparator, or by the elements' natural ordering, if
75	<	* comparator is null:  For each node n in the heap, and each descendant
76	<	* of n, d, n <= d.
75	>	* comparator is null:  For each node n in the heap and each descendant d
76	>	* of n, n <= d.
77		*
78	<	* The element with the lowest value is in queue[1] (assuming the queue is
79	<	* nonempty). A one-based array is used in preference to the traditional
80	<	* zero-based array to simplify parent and child calculations.
78	>	* The element with the lowest value is in queue[1], assuming the queue is
79	>	* nonempty.  (A one-based array is used in preference to the traditional
80	>	* zero-based array to simplify parent and child calculations.)
81		*
82		* queue.length must be >= 2, even if size == 0.
83		*/
84	<	private E[] queue;
84	>	private transient Object[] queue;
85
86		/**
87		* The number of elements in the priority queue.
#	Line 62 | Line 92 | public class PriorityQueue<E> extends Ab
92		* The comparator, or null if priority queue uses elements'
93		* natural ordering.
94		*/
95	<	private final Comparator<E> comparator;
95	>	private final Comparator<? super E> comparator;
96
97		/**
98		* The number of times this priority queue has been
99		* <i>structurally modified</i>.  See AbstractList for gory details.
100		*/
101	<	private int modCount = 0;
101	>	private transient int modCount = 0;
102
103		/**
104	<	* Create a new priority queue with the default initial capacity (11)
105	<	* that orders its elements according to their natural ordering.
104	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
105	>	* (11) that orders its elements according to their natural
106	>	* ordering (using <tt>Comparable</tt>).
107		*/
108		public PriorityQueue() {
109	<	this(DEFAULT_INITIAL_CAPACITY);
109	>	this(DEFAULT_INITIAL_CAPACITY, null);
110		}
111
112		/**
113	<	* Create a new priority queue with the specified initial capacity
114	<	* that orders its elements according to their natural ordering.
113	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
114	>	* that orders its elements according to their natural ordering
115	>	* (using <tt>Comparable</tt>).
116		*
117		* @param initialCapacity the initial capacity for this priority queue.
118	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
119	+	* than 1
120		*/
121		public PriorityQueue(int initialCapacity) {
122		this(initialCapacity, null);
123		}
124
125		/**
126	<	* Create a new priority queue with the specified initial capacity (11)
126	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
127		* that orders its elements according to the specified comparator.
128		*
129		* @param initialCapacity the initial capacity for this priority queue.
130		* @param comparator the comparator used to order this priority queue.
131	+	* If <tt>null</tt> then the order depends on the elements' natural
132	+	* ordering.
133	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
134	+	* than 1
135		*/
136	<	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
136	>	public PriorityQueue(int initialCapacity,
137	>	Comparator<? super E> comparator) {
138		if (initialCapacity < 1)
139	<	initialCapacity = 1;
140	<	queue = new E[initialCapacity + 1];
139	>	throw new IllegalArgumentException();
140	>	this.queue = new Object[initialCapacity + 1];
141		this.comparator = comparator;
142		}
143
144		/**
145	<	* Create a new priority queue containing the elements in the specified
146	<	* 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>.
145	>	* Common code to initialize underlying queue array across
146	>	* constructors below.
147		*/
148	<	public PriorityQueue(Collection<E> initialElements) {
149	<	int sz = initialElements.size();
148	>	private void initializeArray(Collection<? extends E> c) {
149	>	int sz = c.size();
150		int initialCapacity = (int)Math.min((sz * 110L) / 100,
151		Integer.MAX_VALUE - 1);
152		if (initialCapacity < 1)
153		initialCapacity = 1;
130	–	queue = new E[initialCapacity + 1];
154
155	<	/* Commented out to compile with generics compiler
155	>	this.queue = new Object[initialCapacity + 1];
156	>	}
157
158	<	if (initialElements instanceof Sorted) {
159	<	comparator = ((Sorted)initialElements).comparator();
160	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
161	<	queue[++size] = i.next();
158	>	/**
159	>	* Initially fill elements of the queue array under the
160	>	* knowledge that it is sorted or is another PQ, in which
161	>	* case we can just place the elements in the order presented.
162	>	*/
163	>	private void fillFromSorted(Collection<? extends E> c) {
164	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
165	>	queue[++size] = i.next();
166	>	}
167	>
168	>	/**
169	>	* Initially fill elements of the queue array that is not to our knowledge
170	>	* sorted, so we must rearrange the elements to guarantee the heap
171	>	* invariant.
172	>	*/
173	>	private void fillFromUnsorted(Collection<? extends E> c) {
174	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
175	>	queue[++size] = i.next();
176	>	heapify();
177	>	}
178	>
179	>	/**
180	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
181	>	* specified collection.  The priority queue has an initial
182	>	* capacity of 110% of the size of the specified collection or 1
183	>	* if the collection is empty.  If the specified collection is an
184	>	* instance of a {@link java.util.SortedSet} or is another
185	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
186	>	* according to the same comparator, or according to its elements'
187	>	* natural order if the collection is sorted according to its
188	>	* elements' natural order.  Otherwise, the priority queue is
189	>	* ordered according to its elements' natural order.
190	>	*
191	>	* @param c the collection whose elements are to be placed
192	>	*        into this priority queue.
193	>	* @throws ClassCastException if elements of the specified collection
194	>	*         cannot be compared to one another according to the priority
195	>	*         queue's ordering.
196	>	* @throws NullPointerException if <tt>c</tt> or any element within it
197	>	* is <tt>null</tt>
198	>	*/
199	>	public PriorityQueue(Collection<? extends E> c) {
200	>	initializeArray(c);
201	>	if (c instanceof SortedSet) {
202	>	// @fixme double-cast workaround for compiler
203	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
204	>	comparator = (Comparator<? super E>)s.comparator();
205	>	fillFromSorted(s);
206	>	} else if (c instanceof PriorityQueue) {
207	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
208	>	comparator = (Comparator<? super E>)s.comparator();
209	>	fillFromSorted(s);
210		} else {
139	–	*/
140	–	{
211		comparator = null;
212	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	<	add(i.next());
212	>	fillFromUnsorted(c);
213		}
214		}
215
216	<	// Queue Methods
216	>	/**
217	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
218	>	* specified collection.  The priority queue has an initial
219	>	* capacity of 110% of the size of the specified collection or 1
220	>	* if the collection is empty.  This priority queue will be sorted
221	>	* according to the same comparator as the given collection, or
222	>	* according to its elements' natural order if the collection is
223	>	* sorted according to its elements' natural order.
224	>	*
225	>	* @param c the collection whose elements are to be placed
226	>	*        into this priority queue.
227	>	* @throws ClassCastException if elements of the specified collection
228	>	*         cannot be compared to one another according to the priority
229	>	*         queue's ordering.
230	>	* @throws NullPointerException if <tt>c</tt> or any element within it
231	>	* is <tt>null</tt>
232	>	*/
233	>	public PriorityQueue(PriorityQueue<? extends E> c) {
234	>	initializeArray(c);
235	>	comparator = (Comparator<? super E>)c.comparator();
236	>	fillFromSorted(c);
237	>	}
238
239		/**
240	<	* Remove and return the minimal element from this priority queue if
241	<	* it contains one or more elements, otherwise <tt>null</tt>.  The term
242	<	* <i>minimal</i> is defined according to this priority queue's order.
240	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
241	>	* specified collection.  The priority queue has an initial
242	>	* capacity of 110% of the size of the specified collection or 1
243	>	* if the collection is empty.  This priority queue will be sorted
244	>	* according to the same comparator as the given collection, or
245	>	* according to its elements' natural order if the collection is
246	>	* sorted according to its elements' natural order.
247		*
248	<	* @return the minimal element from this priority queue if it contains
249	<	*         one or more elements, otherwise <tt>null</tt>.
248	>	* @param c the collection whose elements are to be placed
249	>	*        into this priority queue.
250	>	* @throws ClassCastException if elements of the specified collection
251	>	*         cannot be compared to one another according to the priority
252	>	*         queue's ordering.
253	>	* @throws NullPointerException if <tt>c</tt> or any element within it
254	>	* is <tt>null</tt>
255		*/
256	<	public E poll() {
257	<	if (size == 0)
258	<	return null;
259	<	return remove(1);
256	>	public PriorityQueue(SortedSet<? extends E> c) {
257	>	initializeArray(c);
258	>	comparator = (Comparator<? super E>)c.comparator();
259	>	fillFromSorted(c);
260	>	}
261	>
262	>	/**
263	>	* Resize array, if necessary, to be able to hold given index
264	>	*/
265	>	private void grow(int index) {
266	>	int newlen = queue.length;
267	>	if (index < newlen) // don't need to grow
268	>	return;
269	>	if (index == Integer.MAX_VALUE)
270	>	throw new OutOfMemoryError();
271	>	while (newlen <= index) {
272	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
273	>	newlen = Integer.MAX_VALUE;
274	>	else
275	>	newlen <<= 2;
276	>	}
277	>	Object[] newQueue = new Object[newlen];
278	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
279	>	queue = newQueue;
280		}
281	+
282
283		/**
284	<	* 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.
284	>	* Inserts the specified element into this priority queue.
285		*
286	<	* @return the minimal element from this priority queue if it contains
287	<	*         one or more elements, otherwise <tt>null</tt>.
286	>	* @return <tt>true</tt>
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 <tt>null</tt>.
291		*/
292	+	public boolean offer(E o) {
293	+	if (o == null)
294	+	throw new NullPointerException();
295	+	modCount++;
296	+	++size;
297	+
298	+	// Grow backing store if necessary
299	+	if (size >= queue.length)
300	+	grow(size);
301	+
302	+	queue[size] = o;
303	+	fixUp(size);
304	+	return true;
305	+	}
306	+
307		public E peek() {
308	<	return queue[1];
308	>	if (size == 0)
309	>	return null;
310	>	return (E) queue[1];
311		}
312
313	<	// Collection Methods
313	>	// Collection Methods - the first two override to update docs
314
315		/**
316	<	* Removes a single instance of the specified element from this priority
317	<	* queue, if it is present.  Returns true if this collection contained the
318	<	* specified element (or equivalently, if this collection changed as a
184	<	* result of the call).
316	>	* Adds the specified element to this queue.
317	>	* @return <tt>true</tt> (as per the general contract of
318	>	* <tt>Collection.add</tt>).
319		*
320	<	* @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
320	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
321		* @throws ClassCastException if the specified element cannot be compared
322	<	*            with elements currently in the priority queue according
323	<	*            to the priority queue's ordering.
192	<	* @throws NullPointerException if the specified element is null.
322	>	* with elements currently in the priority queue according
323	>	* to the priority queue's ordering.
324		*/
325	<	public boolean remove(Object element) {
326	<	if (element == null)
327	<	throw new NullPointerException();
325	>	public boolean add(E o) {
326	>	return offer(o);
327	>	}
328	>
329	>	public boolean remove(Object o) {
330	>	if (o == null)
331	>	return false;
332
333		if (comparator == null) {
334		for (int i = 1; i <= size; i++) {
335	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
336	<	remove(i);
335	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
336	>	removeAt(i);
337		return true;
338		}
339		}
340		} else {
341		for (int i = 1; i <= size; i++) {
342	<	if (comparator.compare(queue[i], (E) element) == 0) {
343	<	remove(i);
342	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
343	>	removeAt(i);
344		return true;
345		}
346		}
#	Line 214 | Line 349 | public class PriorityQueue<E> extends Ab
349		}
350
351		/**
352	<	* Returns an iterator over the elements in this priority queue.  The
353	<	* first element returned by this iterator is the same element that
219	<	* would be returned by a call to <tt>peek</tt>.
352	>	* Returns an iterator over the elements in this queue. The iterator
353	>	* does not return the elements in any particular order.
354		*
355	<	* @return an <tt>Iterator</tt> over the elements in this priority queue.
355	>	* @return an iterator over the elements in this queue.
356		*/
357		public Iterator<E> iterator() {
358		return new Itr();
359		}
360
361		private class Itr implements Iterator<E> {
362	+
363		/**
364		* Index (into queue array) of element to be returned by
365		* subsequent call to next.
366		*/
367	<	int cursor = 1;
367	>	private int cursor = 1;
368
369		/**
370	<	* Index of element returned by most recent call to next or
371	<	* previous.  Reset to 0 if this element is deleted by a call
372	<	* to remove.
370	>	* Index of element returned by most recent call to next,
371	>	* unless that element came from the forgetMeNot list.
372	>	* Reset to 0 if element is deleted by a call to remove.
373		*/
374	<	int lastRet = 0;
374	>	private int lastRet = 0;
375
376		/**
377		* The modCount value that the iterator believes that the backing
378		* List should have.  If this expectation is violated, the iterator
379		* has detected concurrent modification.
380		*/
381	<	int expectedModCount = modCount;
381	>	private int expectedModCount = modCount;
382	>
383	>	/**
384	>	* A list of elements that were moved from the unvisited portion of
385	>	* the heap into the visited portion as a result of "unlucky" element
386	>	* removals during the iteration.  (Unlucky element removals are those
387	>	* that require a fixup instead of a fixdown.)  We must visit all of
388	>	* the elements in this list to complete the iteration.  We do this
389	>	* after we've completed the "normal" iteration.
390	>	*
391	>	* We expect that most iterations, even those involving removals,
392	>	* will not use need to store elements in this field.
393	>	*/
394	>	private ArrayList<E> forgetMeNot = null;
395	>
396	>	/**
397	>	* Element returned by the most recent call to next iff that
398	>	* element was drawn from the forgetMeNot list.
399	>	*/
400	>	private Object lastRetElt = null;
401
402		public boolean hasNext() {
403	<	return cursor <= size;
403	>	return cursor <= size || forgetMeNot != null;
404		}
405
406		public E next() {
407		checkForComodification();
408	<	if (cursor > size)
408	>	E result;
409	>	if (cursor <= size) {
410	>	result = (E) queue[cursor];
411	>	lastRet = cursor++;
412	>	}
413	>	else if (forgetMeNot == null)
414		throw new NoSuchElementException();
415	<	E result = queue[cursor];
416	<	lastRet = cursor++;
415	>	else {
416	>	int remaining = forgetMeNot.size();
417	>	result = forgetMeNot.remove(remaining - 1);
418	>	if (remaining == 1)
419	>	forgetMeNot = null;
420	>	lastRet = 0;
421	>	lastRetElt = result;
422	>	}
423		return result;
424		}
425
426		public void remove() {
262	–	if (lastRet == 0)
263	–	throw new IllegalStateException();
427		checkForComodification();
428
429	<	PriorityQueue.this.remove(lastRet);
430	<	if (lastRet < cursor)
431	<	cursor--;
432	<	lastRet = 0;
429	>	if (lastRet != 0) {
430	>	E moved = PriorityQueue.this.removeAt(lastRet);
431	>	lastRet = 0;
432	>	if (moved == null) {
433	>	cursor--;
434	>	} else {
435	>	if (forgetMeNot == null)
436	>	forgetMeNot = new ArrayList<E>();
437	>	forgetMeNot.add(moved);
438	>	}
439	>	} else if (lastRetElt != null) {
440	>	PriorityQueue.this.remove(lastRetElt);
441	>	lastRetElt = null;
442	>	} else {
443	>	throw new IllegalStateException();
444	>	}
445	>
446		expectedModCount = modCount;
447		}
448
#	Line 276 | Line 452 | public class PriorityQueue<E> extends Ab
452		}
453		}
454
279	–	/**
280	–	* Returns the number of elements in this priority queue.
281	–	*
282	–	* @return the number of elements in this priority queue.
283	–	*/
455		public int size() {
456		return size;
457		}
458
459		/**
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	–	/**
460		* Remove all elements from the priority queue.
461		*/
462		public void clear() {
#	Line 325 | Line 469 | public class PriorityQueue<E> extends Ab
469		size = 0;
470		}
471
472	+	public E poll() {
473	+	if (size == 0)
474	+	return null;
475	+	modCount++;
476	+
477	+	E result = (E) queue[1];
478	+	queue[1] = queue[size];
479	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
480	+	if (size > 1)
481	+	fixDown(1);
482	+
483	+	return result;
484	+	}
485	+
486		/**
487	<	* Removes and returns the ith element from queue.  Recall
488	<	* that queue is one-based, so 1 <= i <= size.
487	>	* Removes and returns the ith element from queue.  (Recall that queue
488	>	* is one-based, so 1 <= i <= size.)
489		*
490	<	* XXX: Could further special-case i==size, but is it worth it?
491	<	* XXX: Could special-case i==0, but is it worth it?
490	>	* Normally this method leaves the elements at positions from 1 up to i-1,
491	>	* inclusive, untouched.  Under these circumstances, it returns null.
492	>	* Occasionally, in order to maintain the heap invariant, it must move
493	>	* the last element of the list to some index in the range [2, i-1],
494	>	* and move the element previously at position (i/2) to position i.
495	>	* Under these circumstances, this method returns the element that was
496	>	* previously at the end of the list and is now at some position between
497	>	* 2 and i-1 inclusive.
498		*/
499	<	private E remove(int i) {
500	<	assert i <= size;
499	>	private E removeAt(int i) {
500	>	assert i > 0 && i <= size;
501		modCount++;
502
503	<	E result = queue[i];
504	<	queue[i] = queue[size];
503	>	E moved = (E) queue[size];
504	>	queue[i] = moved;
505		queue[size--] = null;  // Drop extra ref to prevent memory leak
506	<	if (i <= size)
506	>	if (i <= size) {
507		fixDown(i);
508	<	return result;
508	>	if (queue[i] == moved) {
509	>	fixUp(i);
510	>	if (queue[i] != moved)
511	>	return moved;
512	>	}
513	>	}
514	>	return null;
515		}
516
517		/**
#	Line 357 | Line 527 | public class PriorityQueue<E> extends Ab
527		if (comparator == null) {
528		while (k > 1) {
529		int j = k >> 1;
530	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
530	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
531		break;
532	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
532	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
533		k = j;
534		}
535		} else {
536		while (k > 1) {
537	<	int j = k >> 1;
538	<	if (comparator.compare(queue[j], queue[k]) <= 0)
537	>	int j = k >>> 1;
538	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
539		break;
540	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
540	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
541		k = j;
542		}
543		}
#	Line 385 | Line 555 | public class PriorityQueue<E> extends Ab
555		private void fixDown(int k) {
556		int j;
557		if (comparator == null) {
558	<	while ((j = k << 1) <= size) {
559	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
558	>	while ((j = k << 1) <= size && (j > 0)) {
559	>	if (j<size &&
560	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
561		j++; // j indexes smallest kid
562	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
562	>
563	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
564		break;
565	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
565	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
566		k = j;
567		}
568		} else {
569	<	while ((j = k << 1) <= size) {
570	<	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
569	>	while ((j = k << 1) <= size && (j > 0)) {
570	>	if (j<size &&
571	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
572		j++; // j indexes smallest kid
573	<	if (comparator.compare(queue[k], queue[j]) <= 0)
573	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
574		break;
575	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
575	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
576		k = j;
577		}
578		}
579		}
580
581		/**
582	<	* Returns the comparator associated with this priority queue, or
583	<	* <tt>null</tt> if it uses its elements' natural ordering.
582	>	* Establishes the heap invariant (described above) in the entire tree,
583	>	* assuming nothing about the order of the elements prior to the call.
584	>	*/
585	>	private void heapify() {
586	>	for (int i = size/2; i >= 1; i--)
587	>	fixDown(i);
588	>	}
589	>
590	>	/**
591	>	* Returns the comparator used to order this collection, or <tt>null</tt>
592	>	* if this collection is sorted according to its elements natural ordering
593	>	* (using <tt>Comparable</tt>).
594		*
595	<	* @return the comparator associated with this priority queue, or
596	<	*         <tt>null</tt> if it uses its elements' natural ordering.
595	>	* @return the comparator used to order this collection, or <tt>null</tt>
596	>	* if this collection is sorted according to its elements natural ordering.
597		*/
598	<	Comparator comparator() {
598	>	public Comparator<? super E> comparator() {
599		return comparator;
600		}
601	+
602	+	/**
603	+	* Save the state of the instance to a stream (that
604	+	* is, serialize it).
605	+	*
606	+	* @serialData The length of the array backing the instance is
607	+	* emitted (int), followed by all of its elements (each an
608	+	* <tt>Object</tt>) in the proper order.
609	+	* @param s the stream
610	+	*/
611	+	private void writeObject(java.io.ObjectOutputStream s)
612	+	throws java.io.IOException{
613	+	// Write out element count, and any hidden stuff
614	+	s.defaultWriteObject();
615	+
616	+	// Write out array length
617	+	s.writeInt(queue.length);
618	+
619	+	// Write out all elements in the proper order.
620	+	for (int i=1; i<=size; i++)
621	+	s.writeObject(queue[i]);
622	+	}
623	+
624	+	/**
625	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
626	+	* deserialize it).
627	+	* @param s the stream
628	+	*/
629	+	private void readObject(java.io.ObjectInputStream s)
630	+	throws java.io.IOException, ClassNotFoundException {
631	+	// Read in size, and any hidden stuff
632	+	s.defaultReadObject();
633	+
634	+	// Read in array length and allocate array
635	+	int arrayLength = s.readInt();
636	+	queue = new Object[arrayLength];
637	+
638	+	// Read in all elements in the proper order.
639	+	for (int i=1; i<=size; i++)
640	+	queue[i] = (E) s.readObject();
641	+	}
642	+
643		}

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