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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 1.58 by dl, Mon Nov 28 23:53:32 2005 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2005 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	>	import java.util.*; // for javadoc (till 6280605 is fixed)
10
11		/**
12	<	* An unbounded (resizable) priority queue based on a priority
13	<	* heap.The take operation returns the least element with respect to
14	<	* the given ordering. (If more than one element is tied for least
15	<	* value, one of them is arbitrarily chosen to be returned -- no
16	<	* guarantees are made for ordering across ties.) Ordering follows the
17	<	* java.util.Collection conventions: Either the elements must be
18	<	* Comparable, or a Comparator must be supplied. Comparison failures
19	<	* throw ClassCastExceptions during insertions and extractions.
20	<	**/
21	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
22	<	public PriorityQueue(int initialCapacity) {}
23	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
12	>	* An unbounded priority {@linkplain Queue queue} based on a priority
13	>	* heap.  The elements of the priority queue are ordered according to
14	>	* their {@linkplain Comparable natural ordering}, or by a {@link
15	>	* Comparator} provided at queue construction time, depending on which
16	>	* constructor is used.  A priority queue does not permit
17	>	* <tt>null</tt> elements.  A priority queue relying on natural
18	>	* ordering also does not permit insertion of non-comparable objects
19	>	* (doing so may result 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>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>This class and its iterator implement all of the
36	>	* <em>optional</em> methods of the {@link Collection} and {@link
37	>	* Iterator} interfaces.  The Iterator provided in method {@link
38	>	* #iterator()} is <em>not</em> guaranteed to traverse the elements of
39	>	* the priority queue in any particular order. If you need ordered
40	>	* traversal, consider using <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	>	* <p>Implementation note: this implementation provides O(log(n)) time
49	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
50	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
51	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
52	>	* constant time for the retrieval methods (<tt>peek</tt>,
53	>	* <tt>element</tt>, and <tt>size</tt>).
54	>	*
55	>	* <p>This class is a member of the
56	>	* <a href="{@docRoot}/../guide/collections/index.html">
57	>	* Java Collections Framework</a>.
58	>	* @since 1.5
59	>	* @version 1.8, 08/27/05
60	>	* @author Josh Bloch
61	>	* @param <E> the type of elements held in this collection
62	>	*/
63	>	public class PriorityQueue<E> extends AbstractQueue<E>
64	>	implements java.io.Serializable {
65
66	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
66	>	private static final long serialVersionUID = -7720805057305804111L;
67
68	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
68	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
69
70	<	public boolean add(E x) {
71	<	return false;
70	>	/**
71	>	* Priority queue represented as a balanced binary heap: the two
72	>	* children of queue[n] are queue[2*n+1] and queue[2*(n+1)].  The
73	>	* priority queue is ordered by comparator, or by the elements'
74	>	* natural ordering, if comparator is null: For each node n in the
75	>	* heap and each descendant d of n, n <= d.  The element with the
76	>	* lowest value is in queue[0], assuming the queue is nonempty.
77	>	*/
78	>	private transient Object[] queue;
79	>
80	>	/**
81	>	* The number of elements in the priority queue.
82	>	*/
83	>	private int size = 0;
84	>
85	>	/**
86	>	* The comparator, or null if priority queue uses elements'
87	>	* natural ordering.
88	>	*/
89	>	private final Comparator<? super E> comparator;
90	>
91	>	/**
92	>	* The number of times this priority queue has been
93	>	* <i>structurally modified</i>.  See AbstractList for gory details.
94	>	*/
95	>	private transient int modCount = 0;
96	>
97	>	/**
98	>	* Creates a <tt>PriorityQueue</tt> with the default initial
99	>	* capacity (11) that orders its elements according to their
100	>	* {@linkplain Comparable natural ordering}.
101	>	*/
102	>	public PriorityQueue() {
103	>	this(DEFAULT_INITIAL_CAPACITY, null);
104		}
105	<	public boolean offer(E x) {
106	<	return false;
105	>
106	>	/**
107	>	* Creates a <tt>PriorityQueue</tt> with the specified initial
108	>	* capacity that orders its elements according to their
109	>	* {@linkplain Comparable natural ordering}.
110	>	*
111	>	* @param initialCapacity the initial capacity for this priority queue
112	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
113	>	* than 1
114	>	*/
115	>	public PriorityQueue(int initialCapacity) {
116	>	this(initialCapacity, null);
117		}
118	<	public boolean remove(Object x) {
119	<	return false;
118	>
119	>	/**
120	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
121	>	* that orders its elements according to the specified comparator.
122	>	*
123	>	* @param  initialCapacity the initial capacity for this priority queue
124	>	* @param  comparator the comparator that will be used to order
125	>	*         this priority queue.  If <tt>null</tt>, the <i>natural
126	>	*         ordering</i> of the elements will be used.
127	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is
128	>	*         less than 1
129	>	*/
130	>	public PriorityQueue(int initialCapacity,
131	>	Comparator<? super E> comparator) {
132	>	// Note: This restriction of at least one is not actually needed,
133	>	// but continues for 1.5 compatibility
134	>	if (initialCapacity < 1)
135	>	throw new IllegalArgumentException();
136	>	this.queue = new Object[initialCapacity];
137	>	this.comparator = comparator;
138		}
139
140	<	public E remove() {
141	<	return null;
140	>	/**
141	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
142	>	* specified collection.   If the specified collection is an
143	>	* instance of a {@link java.util.SortedSet} or is another
144	>	* <tt>PriorityQueue</tt>, the priority queue will be ordered
145	>	* according to the same ordering.  Otherwise, this priority queue
146	>	* will be ordered according to the natural ordering of its elements.
147	>	*
148	>	* @param  c the collection whose elements are to be placed
149	>	*         into this priority queue
150	>	* @throws ClassCastException if elements of the specified collection
151	>	*         cannot be compared to one another according to the priority
152	>	*         queue's ordering
153	>	* @throws NullPointerException if the specified collection or any
154	>	*         of its elements are null
155	>	*/
156	>	public PriorityQueue(Collection<? extends E> c) {
157	>	initFromCollection(c);
158	>	if (c instanceof SortedSet)
159	>	comparator = (Comparator<? super E>)
160	>	((SortedSet<? extends E>)c).comparator();
161	>	else if (c instanceof PriorityQueue)
162	>	comparator = (Comparator<? super E>)
163	>	((PriorityQueue<? extends E>)c).comparator();
164	>	else {
165	>	comparator = null;
166	>	heapify();
167	>	}
168		}
169	<	public Iterator<E> iterator() {
170	<	return null;
169	>
170	>	/**
171	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
172	>	* specified priority queue.  This priority queue will be
173	>	* ordered according to the same ordering as the given priority
174	>	* queue.
175	>	*
176	>	* @param  c the priority queue whose elements are to be placed
177	>	*         into this priority queue
178	>	* @throws ClassCastException if elements of <tt>c</tt> cannot be
179	>	*         compared to one another according to <tt>c</tt>'s
180	>	*         ordering
181	>	* @throws NullPointerException if the specified priority queue or any
182	>	*         of its elements are null
183	>	*/
184	>	public PriorityQueue(PriorityQueue<? extends E> c) {
185	>	comparator = (Comparator<? super E>)c.comparator();
186	>	initFromCollection(c);
187		}
188
189	<	public E element() {
190	<	return null;
189	>	/**
190	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
191	>	* specified sorted set.  This priority queue will be ordered
192	>	* according to the same ordering as the given sorted set.
193	>	*
194	>	* @param  c the sorted set whose elements are to be placed
195	>	*         into this priority queue.
196	>	* @throws ClassCastException if elements of the specified sorted
197	>	*         set cannot be compared to one another according to the
198	>	*         sorted set's ordering
199	>	* @throws NullPointerException if the specified sorted set or any
200	>	*         of its elements are null
201	>	*/
202	>	public PriorityQueue(SortedSet<? extends E> c) {
203	>	comparator = (Comparator<? super E>)c.comparator();
204	>	initFromCollection(c);
205		}
206	<	public E poll() {
207	<	return null;
206	>
207	>	/**
208	>	* Initialize queue array with elements from the given Collection.
209	>	* @param c the collection
210	>	*/
211	>	private void initFromCollection(Collection<? extends E> c) {
212	>	Object[] a = c.toArray();
213	>	// If c.toArray incorrectly doesn't return Object[], copy it.
214	>	if (a.getClass() != Object[].class)
215	>	a = Arrays.copyOf(a, a.length, Object[].class);
216	>	queue = a;
217	>	size = a.length;
218		}
219	+
220	+	/**
221	+	* Increases the capacity of the array.
222	+	*
223	+	* @param minCapacity the desired minimum capacity
224	+	*/
225	+	private void grow(int minCapacity) {
226	+	if (minCapacity < 0) // overflow
227	+	throw new OutOfMemoryError();
228	+	int oldCapacity = queue.length;
229	+	// Double size if small; else grow by 50%
230	+	int newCapacity = ((oldCapacity < 64)?
231	+	((oldCapacity + 1) * 2):
232	+	((oldCapacity / 2) * 3));
233	+	if (newCapacity < 0) // overflow
234	+	newCapacity = Integer.MAX_VALUE;
235	+	if (newCapacity < minCapacity)
236	+	newCapacity = minCapacity;
237	+	queue = Arrays.copyOf(queue, newCapacity);
238	+	}
239	+
240	+	/**
241	+	* Inserts the specified element into this priority queue.
242	+	*
243	+	* @return <tt>true</tt> (as specified by {@link Collection#add})
244	+	* @throws ClassCastException if the specified element cannot be
245	+	*         compared with elements currently in this priority queue
246	+	*         according to the priority queue's ordering
247	+	* @throws NullPointerException if the specified element is null
248	+	*/
249	+	public boolean add(E e) {
250	+	return offer(e);
251	+	}
252	+
253	+	/**
254	+	* Inserts the specified element into this priority queue.
255	+	*
256	+	* @return <tt>true</tt> (as specified by {@link Queue#offer})
257	+	* @throws ClassCastException if the specified element cannot be
258	+	*         compared with elements currently in this priority queue
259	+	*         according to the priority queue's ordering
260	+	* @throws NullPointerException if the specified element is null
261	+	*/
262	+	public boolean offer(E e) {
263	+	if (e == null)
264	+	throw new NullPointerException();
265	+	modCount++;
266	+	int i = size;
267	+	if (i >= queue.length)
268	+	grow(i + 1);
269	+	size = i + 1;
270	+	if (i == 0)
271	+	queue[0] = e;
272	+	else
273	+	siftUp(i, e);
274	+	return true;
275	+	}
276	+
277		public E peek() {
278	<	return null;
278	>	if (size == 0)
279	>	return null;
280	>	return (E) queue[0];
281		}
282
283	<	public boolean isEmpty() {
283	>	private int indexOf(Object o) {
284	>	if (o != null) {
285	>	for (int i = 0; i < size; i++)
286	>	if (o.equals(queue[i]))
287	>	return i;
288	>	}
289	>	return -1;
290	>	}
291	>
292	>	/**
293	>	* Removes a single instance of the specified element from this queue,
294	>	* if it is present.  More formally, removes an element <tt>e</tt> such
295	>	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
296	>	* elements.  Returns true if this queue contained the specified element
297	>	* (or equivalently, if this queue changed as a result of the call).
298	>	*
299	>	* @param o element to be removed from this queue, if present
300	>	* @return <tt>true</tt> if this queue changed as a result of the call
301	>	*/
302	>	public boolean remove(Object o) {
303	>	int i = indexOf(o);
304	>	if (i == -1)
305	>	return false;
306	>	else {
307	>	removeAt(i);
308	>	return true;
309	>	}
310	>	}
311	>
312	>	/**
313	>	* Version of remove using reference equality, not equals.
314	>	* Needed by iterator.remove
315	>	*
316	>	* @param o element to be removed from this queue, if present
317	>	* @return <tt>true</tt> if removed.
318	>	*/
319	>	boolean removeEq(Object o) {
320	>	for (int i = 0; i < size; i++) {
321	>	if (o == queue[i]) {
322	>	removeAt(i);
323	>	return true;
324	>	}
325	>	}
326		return false;
327		}
328	<	public int size() {
329	<	return 0;
328	>
329	>	/**
330	>	* Returns <tt>true</tt> if this queue contains the specified element.
331	>	* More formally, returns <tt>true</tt> if and only if this queue contains
332	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
333	>	*
334	>	* @param o object to be checked for containment in this queue
335	>	* @return <tt>true</tt> if this queue contains the specified element
336	>	*/
337	>	public boolean contains(Object o) {
338	>	return indexOf(o) != -1;
339		}
340	+
341	+	/**
342	+	* Returns an array containing all of the elements in this queue,
343	+	* The elements are in no particular order.
344	+	*
345	+	* <p>The returned array will be "safe" in that no references to it are
346	+	* maintained by this list.  (In other words, this method must allocate
347	+	* a new array).  The caller is thus free to modify the returned array.
348	+	*
349	+	* @return an array containing all of the elements in this queue.
350	+	*/
351		public Object[] toArray() {
352	<	return null;
352	>	return Arrays.copyOf(queue, size);
353	>	}
354	>
355	>	/**
356	>	* Returns an array containing all of the elements in this queue.
357	>	* The elements are in no particular order.  The runtime type of
358	>	* the returned array is that of the specified array.  If the queue
359	>	* fits in the specified array, it is returned therein.
360	>	* Otherwise, a new array is allocated with the runtime type of
361	>	* the specified array and the size of this queue.
362	>	*
363	>	* <p>If the queue fits in the specified array with room to spare
364	>	* (i.e., the array has more elements than the queue), the element in
365	>	* the array immediately following the end of the collection is set to
366	>	* <tt>null</tt>.  (This is useful in determining the length of the
367	>	* queue <i>only</i> if the caller knows that the queue does not contain
368	>	* any null elements.)
369	>	*
370	>	* @param a the array into which the elements of the queue are to
371	>	*          be stored, if it is big enough; otherwise, a new array of the
372	>	*          same runtime type is allocated for this purpose.
373	>	* @return an array containing the elements of the queue
374	>	* @throws ArrayStoreException if the runtime type of the specified array
375	>	*         is not a supertype of the runtime type of every element in
376	>	*         this queue
377	>	* @throws NullPointerException if the specified array is null
378	>	*/
379	>	public <T> T[] toArray(T[] a) {
380	>	if (a.length < size)
381	>	// Make a new array of a's runtime type, but my contents:
382	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
383	>	System.arraycopy(queue, 0, a, 0, size);
384	>	if (a.length > size)
385	>	a[size] = null;
386	>	return a;
387		}
388
389	<	public <T> T[] toArray(T[] array) {
389	>	/**
390	>	* Returns an iterator over the elements in this queue. The iterator
391	>	* does not return the elements in any particular order.
392	>	*
393	>	* @return an iterator over the elements in this queue
394	>	*/
395	>	public Iterator<E> iterator() {
396	>	return new Itr();
397	>	}
398	>
399	>	private final class Itr implements Iterator<E> {
400	>	/**
401	>	* Index (into queue array) of element to be returned by
402	>	* subsequent call to next.
403	>	*/
404	>	private int cursor = 0;
405	>
406	>	/**
407	>	* Index of element returned by most recent call to next,
408	>	* unless that element came from the forgetMeNot list.
409	>	* Set to -1 if element is deleted by a call to remove.
410	>	*/
411	>	private int lastRet = -1;
412	>
413	>	/**
414	>	* A queue of elements that were moved from the unvisited portion of
415	>	* the heap into the visited portion as a result of "unlucky" element
416	>	* removals during the iteration.  (Unlucky element removals are those
417	>	* that require a siftup instead of a siftdown.)  We must visit all of
418	>	* the elements in this list to complete the iteration.  We do this
419	>	* after we've completed the "normal" iteration.
420	>	*
421	>	* We expect that most iterations, even those involving removals,
422	>	* will not use need to store elements in this field.
423	>	*/
424	>	private ArrayDeque<E> forgetMeNot = null;
425	>
426	>	/**
427	>	* Element returned by the most recent call to next iff that
428	>	* element was drawn from the forgetMeNot list.
429	>	*/
430	>	private E lastRetElt = null;
431	>
432	>	/**
433	>	* The modCount value that the iterator believes that the backing
434	>	* List should have.  If this expectation is violated, the iterator
435	>	* has detected concurrent modification.
436	>	*/
437	>	private int expectedModCount = modCount;
438	>
439	>	public boolean hasNext() {
440	>	return cursor < size ||
441	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
442	>	}
443	>
444	>	public E next() {
445	>	if (expectedModCount != modCount)
446	>	throw new ConcurrentModificationException();
447	>	if (cursor < size)
448	>	return (E) queue[lastRet = cursor++];
449	>	if (forgetMeNot != null) {
450	>	lastRet = -1;
451	>	lastRetElt = forgetMeNot.poll();
452	>	if (lastRetElt != null)
453	>	return lastRetElt;
454	>	}
455	>	throw new NoSuchElementException();
456	>	}
457	>
458	>	public void remove() {
459	>	if (expectedModCount != modCount)
460	>	throw new ConcurrentModificationException();
461	>	if (lastRet == -1 && lastRetElt == null)
462	>	throw new IllegalStateException();
463	>	if (lastRet != -1) {
464	>	E moved = PriorityQueue.this.removeAt(lastRet);
465	>	lastRet = -1;
466	>	if (moved == null)
467	>	cursor--;
468	>	else {
469	>	if (forgetMeNot == null)
470	>	forgetMeNot = new ArrayDeque<E>();
471	>	forgetMeNot.add(moved);
472	>	}
473	>	} else {
474	>	PriorityQueue.this.removeEq(lastRetElt);
475	>	lastRetElt = null;
476	>	}
477	>	expectedModCount = modCount;
478	>	}
479	>
480	>	}
481	>
482	>	public int size() {
483	>	return size;
484	>	}
485	>
486	>	/**
487	>	* Removes all of the elements from this priority queue.
488	>	* The queue will be empty after this call returns.
489	>	*/
490	>	public void clear() {
491	>	modCount++;
492	>	for (int i = 0; i < size; i++)
493	>	queue[i] = null;
494	>	size = 0;
495	>	}
496	>
497	>	public E poll() {
498	>	if (size == 0)
499	>	return null;
500	>	int s = --size;
501	>	modCount++;
502	>	E result = (E)queue[0];
503	>	E x = (E)queue[s];
504	>	queue[s] = null;
505	>	if (s != 0)
506	>	siftDown(0, x);
507	>	return result;
508	>	}
509	>
510	>	/**
511	>	* Removes the ith element from queue.
512	>	*
513	>	* Normally this method leaves the elements at up to i-1,
514	>	* inclusive, untouched.  Under these circumstances, it returns
515	>	* null.  Occasionally, in order to maintain the heap invariant,
516	>	* it must swap a later element of the list with one earlier than
517	>	* i.  Under these circumstances, this method returns the element
518	>	* that was previously at the end of the list and is now at some
519	>	* position before i. This fact is used by iterator.remove so as to
520	>	* avoid missing traverseing elements.
521	>	*/
522	>	private E removeAt(int i) {
523	>	assert i >= 0 && i < size;
524	>	modCount++;
525	>	int s = --size;
526	>	if (s == i) // removed last element
527	>	queue[i] = null;
528	>	else {
529	>	E moved = (E) queue[s];
530	>	queue[s] = null;
531	>	siftDown(i, moved);
532	>	if (queue[i] == moved) {
533	>	siftUp(i, moved);
534	>	if (queue[i] != moved)
535	>	return moved;
536	>	}
537	>	}
538		return null;
539		}
540
541	+	/**
542	+	* Inserts item x at position k, maintaining heap invariant by
543	+	* promoting x up the tree until it is greater than or equal to
544	+	* its parent, or is the root.
545	+	*
546	+	* To simplify and speed up coercions and comparisons. the
547	+	* Comparable and Comparator versions are separated into different
548	+	* methods that are otherwise identical. (Similarly for siftDown.)
549	+	*
550	+	* @param k the position to fill
551	+	* @param x the item to insert
552	+	*/
553	+	private void siftUp(int k, E x) {
554	+	if (comparator != null)
555	+	siftUpUsingComparator(k, x);
556	+	else
557	+	siftUpComparable(k, x);
558	+	}
559	+
560	+	private void siftUpComparable(int k, E x) {
561	+	Comparable<? super E> key = (Comparable<? super E>) x;
562	+	while (k > 0) {
563	+	int parent = (k - 1) >>> 1;
564	+	Object e = queue[parent];
565	+	if (key.compareTo((E)e) >= 0)
566	+	break;
567	+	queue[k] = e;
568	+	k = parent;
569	+	}
570	+	queue[k] = key;
571	+	}
572	+
573	+	private void siftUpUsingComparator(int k, E x) {
574	+	while (k > 0) {
575	+	int parent = (k - 1) >>> 1;
576	+	Object e = queue[parent];
577	+	if (comparator.compare(x, (E)e) >= 0)
578	+	break;
579	+	queue[k] = e;
580	+	k = parent;
581	+	}
582	+	queue[k] = x;
583	+	}
584	+
585	+	/**
586	+	* Inserts item x at position k, maintaining heap invariant by
587	+	* demoting x down the tree repeatedly until it is less than or
588	+	* equal to its children or is a leaf.
589	+	*
590	+	* @param k the position to fill
591	+	* @param x the item to insert
592	+	*/
593	+	private void siftDown(int k, E x) {
594	+	if (comparator != null)
595	+	siftDownUsingComparator(k, x);
596	+	else
597	+	siftDownComparable(k, x);
598	+	}
599	+
600	+	private void siftDownComparable(int k, E x) {
601	+	Comparable<? super E> key = (Comparable<? super E>)x;
602	+	int half = size >>> 1;        // loop while a non-leaf
603	+	while (k < half) {
604	+	int child = (k << 1) + 1; // assume left child is least
605	+	Object c = queue[child];
606	+	int right = child + 1;
607	+	if (right < size &&
608	+	((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
609	+	c = queue[child = right];
610	+	if (key.compareTo((E)c) <= 0)
611	+	break;
612	+	queue[k] = c;
613	+	k = child;
614	+	}
615	+	queue[k] = key;
616	+	}
617	+
618	+	private void siftDownUsingComparator(int k, E x) {
619	+	int half = size >>> 1;
620	+	while (k < half) {
621	+	int child = (k << 1) + 1;
622	+	Object c = queue[child];
623	+	int right = child + 1;
624	+	if (right < size &&
625	+	comparator.compare((E)c, (E)queue[right]) > 0)
626	+	c = queue[child = right];
627	+	if (comparator.compare(x, (E)c) <= 0)
628	+	break;
629	+	queue[k] = c;
630	+	k = child;
631	+	}
632	+	queue[k] = x;
633	+	}
634	+
635	+	/**
636	+	* Establishes the heap invariant (described above) in the entire tree,
637	+	* assuming nothing about the order of the elements prior to the call.
638	+	*/
639	+	private void heapify() {
640	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
641	+	siftDown(i, (E)queue[i]);
642	+	}
643	+
644	+	/**
645	+	* Returns the comparator used to order the elements in this
646	+	* queue, or <tt>null</tt> if this queue is sorted according to
647	+	* the {@linkplain Comparable natural ordering} of its elements.
648	+	*
649	+	* @return the comparator used to order this queue, or
650	+	*         <tt>null</tt> if this queue is sorted according to the
651	+	*         natural ordering of its elements.
652	+	*/
653	+	public Comparator<? super E> comparator() {
654	+	return comparator;
655	+	}
656	+
657	+	/**
658	+	* Save the state of the instance to a stream (that
659	+	* is, serialize it).
660	+	*
661	+	* @serialData The length of the array backing the instance is
662	+	* emitted (int), followed by all of its elements (each an
663	+	* <tt>Object</tt>) in the proper order.
664	+	* @param s the stream
665	+	*/
666	+	private void writeObject(java.io.ObjectOutputStream s)
667	+	throws java.io.IOException{
668	+	// Write out element count, and any hidden stuff
669	+	s.defaultWriteObject();
670	+
671	+	// Write out array length
672	+	// For compatibility with 1.5 version, must be at least 2.
673	+	s.writeInt(Math.max(2, queue.length));
674	+
675	+	// Write out all elements in the proper order.
676	+	for (int i=0; i<size; i++)
677	+	s.writeObject(queue[i]);
678	+	}
679	+
680	+	/**
681	+	* Reconstitute the <tt>PriorityQueue</tt> instance from a stream
682	+	* (that is, deserialize it).
683	+	* @param s the stream
684	+	*/
685	+	private void readObject(java.io.ObjectInputStream s)
686	+	throws java.io.IOException, ClassNotFoundException {
687	+	// Read in size, and any hidden stuff
688	+	s.defaultReadObject();
689	+
690	+	// Read in array length and allocate array
691	+	int arrayLength = s.readInt();
692	+	queue = new Object[arrayLength];
693	+
694	+	// Read in all elements in the proper order.
695	+	for (int i=0; i<size; i++)
696	+	queue[i] = (E) s.readObject();
697	+	}
698	+
699		}

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