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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.61 by jsr166, Tue Feb 7 20:54:24 2006 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5	>	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	>	*/
7
8	<	import java.util.*;
8	>	package java.util;
9
10		/**
11	<	* An unbounded (resizable) priority queue based on a priority
12	<	* heap.The take operation returns the least element with respect to
13	<	* the given ordering. (If more than one element is tied for least
14	<	* value, one of them is arbitrarily chosen to be returned -- no
15	<	* guarantees are made for ordering across ties.) Ordering follows the
16	<	* java.util.Collection conventions: Either the elements must be
17	<	* Comparable, or a Comparator must be supplied. Comparison failures
18	<	* throw ClassCastExceptions during insertions and extractions.
19	<	**/
20	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
21	<	public PriorityQueue(int initialCapacity) {}
22	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
11	>	* An unbounded priority {@linkplain Queue queue} based on a priority
12	>	* heap.  The elements of the priority queue are ordered according to
13	>	* their {@linkplain Comparable natural ordering}, or by a {@link
14	>	* Comparator} provided at queue construction time, depending on which
15	>	* constructor is used.  A priority queue does not permit
16	>	* <tt>null</tt> elements.  A priority queue relying on natural
17	>	* ordering also does not permit insertion of non-comparable objects
18	>	* (doing so may result in <tt>ClassCastException</tt>).
19	>	*
20	>	* <p>The <em>head</em> of this queue is the <em>least</em> element
21	>	* with respect to the specified ordering.  If multiple elements are
22	>	* tied for least value, the head is one of those elements -- ties are
23	>	* broken arbitrarily.  The queue retrieval operations <tt>poll</tt>,
24	>	* <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the
25	>	* element at the head of the queue.
26	>	*
27	>	* <p>A priority queue is unbounded, but has an internal
28	>	* <i>capacity</i> governing the size of an array used to store the
29	>	* elements on the queue.  It is always at least as large as the queue
30	>	* size.  As elements are added to a priority queue, its capacity
31	>	* grows automatically.  The details of the growth policy are not
32	>	* specified.
33	>	*
34	>	* <p>This class and its iterator implement all of the
35	>	* <em>optional</em> methods of the {@link Collection} and {@link
36	>	* Iterator} interfaces.  The Iterator provided in method {@link
37	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
38	>	* the priority queue in any particular order. If you need ordered
39	>	* traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
40	>	*
41	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
42	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
43	>	* instance concurrently if any of the threads modifies the list
44	>	* structurally. Instead, use the thread-safe {@link
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46	>	*
47	>	* <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 1.8, 08/27/05
59	>	* @author Josh Bloch
60	>	* @param <E> the type of elements held in this collection
61	>	*/
62	>	public class PriorityQueue<E> extends AbstractQueue<E>
63	>	implements java.io.Serializable {
64
65	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
65	>	private static final long serialVersionUID = -7720805057305804111L;
66
67	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
67	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
68
69	<	public boolean add(E x) {
70	<	return false;
69	>	/**
70	>	* Priority queue represented as a balanced binary heap: the two
71	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
72	>	* priority queue is ordered by comparator, or by the elements'
73	>	* natural ordering, if comparator is null: For each node n in the
74	>	* heap and each descendant d of n, n <= d.  The element with the
75	>	* lowest value is in queue[0], assuming the queue is nonempty.
76	>	*/
77	>	private transient Object[] queue;
78	>
79	>	/**
80	>	* The number of elements in the priority queue.
81	>	*/
82	>	private int size = 0;
83	>
84	>	/**
85	>	* The comparator, or null if priority queue uses elements'
86	>	* natural ordering.
87	>	*/
88	>	private final Comparator<? super E> comparator;
89	>
90	>	/**
91	>	* The number of times this priority queue has been
92	>	* <i>structurally modified</i>.  See AbstractList for gory details.
93	>	*/
94	>	private transient int modCount = 0;
95	>
96	>	/**
97	>	* Creates a <tt>PriorityQueue</tt> with the default initial
98	>	* capacity (11) that orders its elements according to their
99	>	* {@linkplain Comparable natural ordering}.
100	>	*/
101	>	public PriorityQueue() {
102	>	this(DEFAULT_INITIAL_CAPACITY, null);
103		}
104	<	public boolean offer(E x) {
105	<	return false;
104	>
105	>	/**
106	>	* Creates a <tt>PriorityQueue</tt> with the specified initial
107	>	* capacity that orders its elements according to their
108	>	* {@linkplain Comparable natural ordering}.
109	>	*
110	>	* @param initialCapacity the initial capacity for this priority queue
111	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
112	>	* than 1
113	>	*/
114	>	public PriorityQueue(int initialCapacity) {
115	>	this(initialCapacity, null);
116		}
117	<	public boolean remove(Object x) {
118	<	return false;
117	>
118	>	/**
119	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
120	>	* that orders its elements according to the specified comparator.
121	>	*
122	>	* @param  initialCapacity the initial capacity for this priority queue
123	>	* @param  comparator the comparator that will be used to order
124	>	*         this priority queue.  If <tt>null</tt>, the <i>natural
125	>	*         ordering</i> of the elements will be used.
126	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is
127	>	*         less than 1
128	>	*/
129	>	public PriorityQueue(int initialCapacity,
130	>	Comparator<? super E> comparator) {
131	>	// Note: This restriction of at least one is not actually needed,
132	>	// but continues for 1.5 compatibility
133	>	if (initialCapacity < 1)
134	>	throw new IllegalArgumentException();
135	>	this.queue = new Object[initialCapacity];
136	>	this.comparator = comparator;
137		}
138
139	<	public E remove() {
140	<	return null;
139	>	/**
140	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
141	>	* specified collection.   If the specified collection is an
142	>	* instance of a {@link java.util.SortedSet} or is another
143	>	* <tt>PriorityQueue</tt>, the priority queue will be ordered
144	>	* according to the same ordering.  Otherwise, this priority queue
145	>	* will be ordered according to the natural ordering of its elements.
146	>	*
147	>	* @param  c the collection whose elements are to be placed
148	>	*         into this priority queue
149	>	* @throws ClassCastException if elements of the specified collection
150	>	*         cannot be compared to one another according to the priority
151	>	*         queue's ordering
152	>	* @throws NullPointerException if the specified collection or any
153	>	*         of its elements are null
154	>	*/
155	>	public PriorityQueue(Collection<? extends E> c) {
156	>	initFromCollection(c);
157	>	if (c instanceof SortedSet)
158	>	comparator = (Comparator<? super E>)
159	>	((SortedSet<? extends E>)c).comparator();
160	>	else if (c instanceof PriorityQueue)
161	>	comparator = (Comparator<? super E>)
162	>	((PriorityQueue<? extends E>)c).comparator();
163	>	else {
164	>	comparator = null;
165	>	heapify();
166	>	}
167		}
168	<	public Iterator<E> iterator() {
169	<	return null;
168	>
169	>	/**
170	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
171	>	* specified priority queue.  This priority queue will be
172	>	* ordered according to the same ordering as the given priority
173	>	* queue.
174	>	*
175	>	* @param  c the priority queue whose elements are to be placed
176	>	*         into this priority queue
177	>	* @throws ClassCastException if elements of <tt>c</tt> cannot be
178	>	*         compared to one another according to <tt>c</tt>'s
179	>	*         ordering
180	>	* @throws NullPointerException if the specified priority queue or any
181	>	*         of its elements are null
182	>	*/
183	>	public PriorityQueue(PriorityQueue<? extends E> c) {
184	>	comparator = (Comparator<? super E>)c.comparator();
185	>	initFromCollection(c);
186		}
187
188	<	public E element() {
189	<	return null;
188	>	/**
189	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
190	>	* specified sorted set.  This priority queue will be ordered
191	>	* according to the same ordering as the given sorted set.
192	>	*
193	>	* @param  c the sorted set whose elements are to be placed
194	>	*         into this priority queue.
195	>	* @throws ClassCastException if elements of the specified sorted
196	>	*         set cannot be compared to one another according to the
197	>	*         sorted set's ordering
198	>	* @throws NullPointerException if the specified sorted set or any
199	>	*         of its elements are null
200	>	*/
201	>	public PriorityQueue(SortedSet<? extends E> c) {
202	>	comparator = (Comparator<? super E>)c.comparator();
203	>	initFromCollection(c);
204		}
205	<	public E poll() {
206	<	return null;
205	>
206	>	/**
207	>	* Initialize queue array with elements from the given Collection.
208	>	* @param c the collection
209	>	*/
210	>	private void initFromCollection(Collection<? extends E> c) {
211	>	Object[] a = c.toArray();
212	>	// If c.toArray incorrectly doesn't return Object[], copy it.
213	>	if (a.getClass() != Object[].class)
214	>	a = Arrays.copyOf(a, a.length, Object[].class);
215	>	queue = a;
216	>	size = a.length;
217		}
218	+
219	+	/**
220	+	* Increases the capacity of the array.
221	+	*
222	+	* @param minCapacity the desired minimum capacity
223	+	*/
224	+	private void grow(int minCapacity) {
225	+	if (minCapacity < 0) // overflow
226	+	throw new OutOfMemoryError();
227	+	int oldCapacity = queue.length;
228	+	// Double size if small; else grow by 50%
229	+	int newCapacity = ((oldCapacity < 64)?
230	+	((oldCapacity + 1) * 2):
231	+	((oldCapacity / 2) * 3));
232	+	if (newCapacity < 0) // overflow
233	+	newCapacity = Integer.MAX_VALUE;
234	+	if (newCapacity < minCapacity)
235	+	newCapacity = minCapacity;
236	+	queue = Arrays.copyOf(queue, newCapacity);
237	+	}
238	+
239	+	/**
240	+	* Inserts the specified element into this priority queue.
241	+	*
242	+	* @return <tt>true</tt> (as specified by {@link Collection#add})
243	+	* @throws ClassCastException if the specified element cannot be
244	+	*         compared with elements currently in this priority queue
245	+	*         according to the priority queue's ordering
246	+	* @throws NullPointerException if the specified element is null
247	+	*/
248	+	public boolean add(E e) {
249	+	return offer(e);
250	+	}
251	+
252	+	/**
253	+	* Inserts the specified element into this priority queue.
254	+	*
255	+	* @return <tt>true</tt> (as specified by {@link Queue#offer})
256	+	* @throws ClassCastException if the specified element cannot be
257	+	*         compared with elements currently in this priority queue
258	+	*         according to the priority queue's ordering
259	+	* @throws NullPointerException if the specified element is null
260	+	*/
261	+	public boolean offer(E e) {
262	+	if (e == null)
263	+	throw new NullPointerException();
264	+	modCount++;
265	+	int i = size;
266	+	if (i >= queue.length)
267	+	grow(i + 1);
268	+	size = i + 1;
269	+	if (i == 0)
270	+	queue[0] = e;
271	+	else
272	+	siftUp(i, e);
273	+	return true;
274	+	}
275	+
276		public E peek() {
277	<	return null;
277	>	if (size == 0)
278	>	return null;
279	>	return (E) queue[0];
280		}
281
282	<	public boolean isEmpty() {
282	>	private int indexOf(Object o) {
283	>	if (o != null) {
284	>	for (int i = 0; i < size; i++)
285	>	if (o.equals(queue[i]))
286	>	return i;
287	>	}
288	>	return -1;
289	>	}
290	>
291	>	/**
292	>	* Removes a single instance of the specified element from this queue,
293	>	* if it is present.  More formally, removes an element <tt>e</tt> such
294	>	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
295	>	* elements.  Returns true if this queue contained the specified element
296	>	* (or equivalently, if this queue changed as a result of the call).
297	>	*
298	>	* @param o element to be removed from this queue, if present
299	>	* @return <tt>true</tt> if this queue changed as a result of the call
300	>	*/
301	>	public boolean remove(Object o) {
302	>	int i = indexOf(o);
303	>	if (i == -1)
304	>	return false;
305	>	else {
306	>	removeAt(i);
307	>	return true;
308	>	}
309	>	}
310	>
311	>	/**
312	>	* Version of remove using reference equality, not equals.
313	>	* Needed by iterator.remove.
314	>	*
315	>	* @param o element to be removed from this queue, if present
316	>	* @return <tt>true</tt> if removed
317	>	*/
318	>	boolean removeEq(Object o) {
319	>	for (int i = 0; i < size; i++) {
320	>	if (o == queue[i]) {
321	>	removeAt(i);
322	>	return true;
323	>	}
324	>	}
325		return false;
326		}
327	<	public int size() {
328	<	return 0;
327	>
328	>	/**
329	>	* Returns <tt>true</tt> if this queue contains the specified element.
330	>	* More formally, returns <tt>true</tt> if and only if this queue contains
331	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
332	>	*
333	>	* @param o object to be checked for containment in this queue
334	>	* @return <tt>true</tt> if this queue contains the specified element
335	>	*/
336	>	public boolean contains(Object o) {
337	>	return indexOf(o) != -1;
338		}
339	+
340	+	/**
341	+	* Returns an array containing all of the elements in this queue,
342	+	* The elements are in no particular order.
343	+	*
344	+	* <p>The returned array will be "safe" in that no references to it are
345	+	* maintained by this list.  (In other words, this method must allocate
346	+	* a new array).  The caller is thus free to modify the returned array.
347	+	*
348	+	* @return an array containing all of the elements in this queue
349	+	*/
350		public Object[] toArray() {
351	<	return null;
351	>	return Arrays.copyOf(queue, size);
352	>	}
353	>
354	>	/**
355	>	* Returns an array containing all of the elements in this queue.
356	>	* The elements are in no particular order.  The runtime type of
357	>	* the returned array is that of the specified array.  If the queue
358	>	* fits in the specified array, it is returned therein.
359	>	* Otherwise, a new array is allocated with the runtime type of
360	>	* the specified array and the size of this queue.
361	>	*
362	>	* <p>If the queue fits in the specified array with room to spare
363	>	* (i.e., the array has more elements than the queue), the element in
364	>	* the array immediately following the end of the collection is set to
365	>	* <tt>null</tt>.  (This is useful in determining the length of the
366	>	* queue <i>only</i> if the caller knows that the queue does not contain
367	>	* any null elements.)
368	>	*
369	>	* @param a the array into which the elements of the queue are to
370	>	*          be stored, if it is big enough; otherwise, a new array of the
371	>	*          same runtime type is allocated for this purpose.
372	>	* @return an array containing the elements of the queue
373	>	* @throws ArrayStoreException if the runtime type of the specified array
374	>	*         is not a supertype of the runtime type of every element in
375	>	*         this queue
376	>	* @throws NullPointerException if the specified array is null
377	>	*/
378	>	public <T> T[] toArray(T[] a) {
379	>	if (a.length < size)
380	>	// Make a new array of a's runtime type, but my contents:
381	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
382	>	System.arraycopy(queue, 0, a, 0, size);
383	>	if (a.length > size)
384	>	a[size] = null;
385	>	return a;
386		}
387
388	<	public <T> T[] toArray(T[] array) {
388	>	/**
389	>	* Returns an iterator over the elements in this queue. The iterator
390	>	* does not return the elements in any particular order.
391	>	*
392	>	* @return an iterator over the elements in this queue
393	>	*/
394	>	public Iterator<E> iterator() {
395	>	return new Itr();
396	>	}
397	>
398	>	private final class Itr implements Iterator<E> {
399	>	/**
400	>	* Index (into queue array) of element to be returned by
401	>	* subsequent call to next.
402	>	*/
403	>	private int cursor = 0;
404	>
405	>	/**
406	>	* Index of element returned by most recent call to next,
407	>	* unless that element came from the forgetMeNot list.
408	>	* Set to -1 if element is deleted by a call to remove.
409	>	*/
410	>	private int lastRet = -1;
411	>
412	>	/**
413	>	* A queue of elements that were moved from the unvisited portion of
414	>	* the heap into the visited portion as a result of "unlucky" element
415	>	* removals during the iteration.  (Unlucky element removals are those
416	>	* that require a siftup instead of a siftdown.)  We must visit all of
417	>	* the elements in this list to complete the iteration.  We do this
418	>	* after we've completed the "normal" iteration.
419	>	*
420	>	* We expect that most iterations, even those involving removals,
421	>	* will not use need to store elements in this field.
422	>	*/
423	>	private ArrayDeque<E> forgetMeNot = null;
424	>
425	>	/**
426	>	* Element returned by the most recent call to next iff that
427	>	* element was drawn from the forgetMeNot list.
428	>	*/
429	>	private E lastRetElt = null;
430	>
431	>	/**
432	>	* The modCount value that the iterator believes that the backing
433	>	* List should have.  If this expectation is violated, the iterator
434	>	* has detected concurrent modification.
435	>	*/
436	>	private int expectedModCount = modCount;
437	>
438	>	public boolean hasNext() {
439	>	return cursor < size ||
440	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
441	>	}
442	>
443	>	public E next() {
444	>	if (expectedModCount != modCount)
445	>	throw new ConcurrentModificationException();
446	>	if (cursor < size)
447	>	return (E) queue[lastRet = cursor++];
448	>	if (forgetMeNot != null) {
449	>	lastRet = -1;
450	>	lastRetElt = forgetMeNot.poll();
451	>	if (lastRetElt != null)
452	>	return lastRetElt;
453	>	}
454	>	throw new NoSuchElementException();
455	>	}
456	>
457	>	public void remove() {
458	>	if (expectedModCount != modCount)
459	>	throw new ConcurrentModificationException();
460	>	if (lastRet == -1 && lastRetElt == null)
461	>	throw new IllegalStateException();
462	>	if (lastRet != -1) {
463	>	E moved = PriorityQueue.this.removeAt(lastRet);
464	>	lastRet = -1;
465	>	if (moved == null)
466	>	cursor--;
467	>	else {
468	>	if (forgetMeNot == null)
469	>	forgetMeNot = new ArrayDeque<E>();
470	>	forgetMeNot.add(moved);
471	>	}
472	>	} else {
473	>	PriorityQueue.this.removeEq(lastRetElt);
474	>	lastRetElt = null;
475	>	}
476	>	expectedModCount = modCount;
477	>	}
478	>
479	>	}
480	>
481	>	public int size() {
482	>	return size;
483	>	}
484	>
485	>	/**
486	>	* Removes all of the elements from this priority queue.
487	>	* The queue will be empty after this call returns.
488	>	*/
489	>	public void clear() {
490	>	modCount++;
491	>	for (int i = 0; i < size; i++)
492	>	queue[i] = null;
493	>	size = 0;
494	>	}
495	>
496	>	public E poll() {
497	>	if (size == 0)
498	>	return null;
499	>	int s = --size;
500	>	modCount++;
501	>	E result = (E)queue[0];
502	>	E x = (E)queue[s];
503	>	queue[s] = null;
504	>	if (s != 0)
505	>	siftDown(0, x);
506	>	return result;
507	>	}
508	>
509	>	/**
510	>	* Removes the ith element from queue.
511	>	*
512	>	* Normally this method leaves the elements at up to i-1,
513	>	* inclusive, untouched.  Under these circumstances, it returns
514	>	* null.  Occasionally, in order to maintain the heap invariant,
515	>	* it must swap a later element of the list with one earlier than
516	>	* i.  Under these circumstances, this method returns the element
517	>	* that was previously at the end of the list and is now at some
518	>	* position before i. This fact is used by iterator.remove so as to
519	>	* avoid missing traverseing elements.
520	>	*/
521	>	private E removeAt(int i) {
522	>	assert i >= 0 && i < size;
523	>	modCount++;
524	>	int s = --size;
525	>	if (s == i) // removed last element
526	>	queue[i] = null;
527	>	else {
528	>	E moved = (E) queue[s];
529	>	queue[s] = null;
530	>	siftDown(i, moved);
531	>	if (queue[i] == moved) {
532	>	siftUp(i, moved);
533	>	if (queue[i] != moved)
534	>	return moved;
535	>	}
536	>	}
537		return null;
538		}
539
540	+	/**
541	+	* Inserts item x at position k, maintaining heap invariant by
542	+	* promoting x up the tree until it is greater than or equal to
543	+	* its parent, or is the root.
544	+	*
545	+	* To simplify and speed up coercions and comparisons. the
546	+	* Comparable and Comparator versions are separated into different
547	+	* methods that are otherwise identical. (Similarly for siftDown.)
548	+	*
549	+	* @param k the position to fill
550	+	* @param x the item to insert
551	+	*/
552	+	private void siftUp(int k, E x) {
553	+	if (comparator != null)
554	+	siftUpUsingComparator(k, x);
555	+	else
556	+	siftUpComparable(k, x);
557	+	}
558	+
559	+	private void siftUpComparable(int k, E x) {
560	+	Comparable<? super E> key = (Comparable<? super E>) x;
561	+	while (k > 0) {
562	+	int parent = (k - 1) >>> 1;
563	+	Object e = queue[parent];
564	+	if (key.compareTo((E)e) >= 0)
565	+	break;
566	+	queue[k] = e;
567	+	k = parent;
568	+	}
569	+	queue[k] = key;
570	+	}
571	+
572	+	private void siftUpUsingComparator(int k, E x) {
573	+	while (k > 0) {
574	+	int parent = (k - 1) >>> 1;
575	+	Object e = queue[parent];
576	+	if (comparator.compare(x, (E)e) >= 0)
577	+	break;
578	+	queue[k] = e;
579	+	k = parent;
580	+	}
581	+	queue[k] = x;
582	+	}
583	+
584	+	/**
585	+	* Inserts item x at position k, maintaining heap invariant by
586	+	* demoting x down the tree repeatedly until it is less than or
587	+	* equal to its children or is a leaf.
588	+	*
589	+	* @param k the position to fill
590	+	* @param x the item to insert
591	+	*/
592	+	private void siftDown(int k, E x) {
593	+	if (comparator != null)
594	+	siftDownUsingComparator(k, x);
595	+	else
596	+	siftDownComparable(k, x);
597	+	}
598	+
599	+	private void siftDownComparable(int k, E x) {
600	+	Comparable<? super E> key = (Comparable<? super E>)x;
601	+	int half = size >>> 1;        // loop while a non-leaf
602	+	while (k < half) {
603	+	int child = (k << 1) + 1; // assume left child is least
604	+	Object c = queue[child];
605	+	int right = child + 1;
606	+	if (right < size &&
607	+	((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
608	+	c = queue[child = right];
609	+	if (key.compareTo((E)c) <= 0)
610	+	break;
611	+	queue[k] = c;
612	+	k = child;
613	+	}
614	+	queue[k] = key;
615	+	}
616	+
617	+	private void siftDownUsingComparator(int k, E x) {
618	+	int half = size >>> 1;
619	+	while (k < half) {
620	+	int child = (k << 1) + 1;
621	+	Object c = queue[child];
622	+	int right = child + 1;
623	+	if (right < size &&
624	+	comparator.compare((E)c, (E)queue[right]) > 0)
625	+	c = queue[child = right];
626	+	if (comparator.compare(x, (E)c) <= 0)
627	+	break;
628	+	queue[k] = c;
629	+	k = child;
630	+	}
631	+	queue[k] = x;
632	+	}
633	+
634	+	/**
635	+	* Establishes the heap invariant (described above) in the entire tree,
636	+	* assuming nothing about the order of the elements prior to the call.
637	+	*/
638	+	private void heapify() {
639	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
640	+	siftDown(i, (E)queue[i]);
641	+	}
642	+
643	+	/**
644	+	* Returns the comparator used to order the elements in this
645	+	* queue, or <tt>null</tt> if this queue is sorted according to
646	+	* the {@linkplain Comparable natural ordering} of its elements.
647	+	*
648	+	* @return the comparator used to order this queue, or
649	+	*         <tt>null</tt> if this queue is sorted according to the
650	+	*         natural ordering of its elements.
651	+	*/
652	+	public Comparator<? super E> comparator() {
653	+	return comparator;
654	+	}
655	+
656	+	/**
657	+	* Save the state of the instance to a stream (that
658	+	* is, serialize it).
659	+	*
660	+	* @serialData The length of the array backing the instance is
661	+	* emitted (int), followed by all of its elements (each an
662	+	* <tt>Object</tt>) in the proper order.
663	+	* @param s the stream
664	+	*/
665	+	private void writeObject(java.io.ObjectOutputStream s)
666	+	throws java.io.IOException{
667	+	// Write out element count, and any hidden stuff
668	+	s.defaultWriteObject();
669	+
670	+	// Write out array length
671	+	// For compatibility with 1.5 version, must be at least 2.
672	+	s.writeInt(Math.max(2, queue.length));
673	+
674	+	// Write out all elements in the proper order.
675	+	for (int i=0; i<size; i++)
676	+	s.writeObject(queue[i]);
677	+	}
678	+
679	+	/**
680	+	* Reconstitute the <tt>PriorityQueue</tt> instance from a stream
681	+	* (that is, deserialize it).
682	+	* @param s the stream
683	+	*/
684	+	private void readObject(java.io.ObjectInputStream s)
685	+	throws java.io.IOException, ClassNotFoundException {
686	+	// Read in size, and any hidden stuff
687	+	s.defaultReadObject();
688	+
689	+	// Read in array length and allocate array
690	+	int arrayLength = s.readInt();
691	+	queue = new Object[arrayLength];
692	+
693	+	// Read in all elements in the proper order.
694	+	for (int i=0; i<size; i++)
695	+	queue[i] = (E) s.readObject();
696	+	}
697	+
698		}

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