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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 1.66 by jsr166, Sun Jan 7 07:38:27 2007 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2007 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 heap.
12	>	* The elements of the priority queue are ordered according to their
13	>	* {@linkplain Comparable natural ordering}, or by a {@link Comparator}
14	>	* provided at queue construction time, depending on which constructor is
15	>	* used.  A priority queue does not permit {@code null} elements.
16	>	* A priority queue relying on natural ordering also does not permit
17	>	* insertion of non-comparable objects (doing so may result in
18	>	* {@code ClassCastException}).
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 {@code poll},
24	>	* {@code remove}, {@code peek}, and {@code element} 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 {@code Arrays.sort(pq.toArray())}.
40	>	*
41	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
42	>	* Multiple threads should not access a {@code PriorityQueue}
43	>	* instance concurrently if any of the threads modifies the queue.
44	>	* Instead, use the thread-safe {@link
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46	>	*
47	>	* <p>Implementation note: this implementation provides
48	>	* O(log(n)) time for the enqueing and dequeing methods
49	>	* ({@code offer}, {@code poll}, {@code remove()} and {@code add});
50	>	* linear time for the {@code remove(Object)} and {@code contains(Object)}
51	>	* methods; and constant time for the retrieval methods
52	>	* ({@code peek}, {@code element}, and {@code size}).
53	>	*
54	>	* <p>This class is a member of the
55	>	* <a href="{@docRoot}/../technotes/guides/collections/index.html">
56	>	* Java Collections Framework</a>.
57	>	*
58	>	* @since 1.5
59	>	* @version %I%, %G%
60	>	* @author Josh Bloch, Doug Lea
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 {@code PriorityQueue} 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 {@code PriorityQueue} 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 {@code initialCapacity} 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 {@code PriorityQueue} 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 this
125	>	*         priority queue.  If {@code null}, the {@linkplain Comparable
126	>	*         natural ordering} of the elements will be used.
127	>	* @throws IllegalArgumentException if {@code initialCapacity} 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 {@code PriorityQueue} containing the elements in the
142	>	* specified collection.  If the specified collection is an instance of
143	>	* a {@link SortedSet} or is another {@code PriorityQueue}, this
144	>	* priority queue will be ordered according to the same ordering.
145	>	* Otherwise, this priority queue will be ordered according to the
146	>	* {@linkplain Comparable 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 {@code PriorityQueue} 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 {@code c} cannot be
179	>	*         compared to one another according to {@code c}'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 {@code PriorityQueue} 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	>	* Initializes queue array with elements from the given Collection.
209	>	*
210	>	* @param c the collection
211	>	*/
212	>	private void initFromCollection(Collection<? extends E> c) {
213	>	Object[] a = c.toArray();
214	>	// If c.toArray incorrectly doesn't return Object[], copy it.
215	>	if (a.getClass() != Object[].class)
216	>	a = Arrays.copyOf(a, a.length, Object[].class);
217	>	queue = a;
218	>	size = a.length;
219		}
220	+
221	+	/**
222	+	* Increases the capacity of the array.
223	+	*
224	+	* @param minCapacity the desired minimum capacity
225	+	*/
226	+	private void grow(int minCapacity) {
227	+	if (minCapacity < 0) // overflow
228	+	throw new OutOfMemoryError();
229	+	int oldCapacity = queue.length;
230	+	// Double size if small; else grow by 50%
231	+	int newCapacity = ((oldCapacity < 64)?
232	+	((oldCapacity + 1) * 2):
233	+	((oldCapacity / 2) * 3));
234	+	if (newCapacity < 0) // overflow
235	+	newCapacity = Integer.MAX_VALUE;
236	+	if (newCapacity < minCapacity)
237	+	newCapacity = minCapacity;
238	+	queue = Arrays.copyOf(queue, newCapacity);
239	+	}
240	+
241	+	/**
242	+	* Inserts the specified element into this priority queue.
243	+	*
244	+	* @return {@code true} (as specified by {@link Collection#add})
245	+	* @throws ClassCastException if the specified element cannot be
246	+	*         compared with elements currently in this priority queue
247	+	*         according to the priority queue's ordering
248	+	* @throws NullPointerException if the specified element is null
249	+	*/
250	+	public boolean add(E e) {
251	+	return offer(e);
252	+	}
253	+
254	+	/**
255	+	* Inserts the specified element into this priority queue.
256	+	*
257	+	* @return {@code true} (as specified by {@link Queue#offer})
258	+	* @throws ClassCastException if the specified element cannot be
259	+	*         compared with elements currently in this priority queue
260	+	*         according to the priority queue's ordering
261	+	* @throws NullPointerException if the specified element is null
262	+	*/
263	+	public boolean offer(E e) {
264	+	if (e == null)
265	+	throw new NullPointerException();
266	+	modCount++;
267	+	int i = size;
268	+	if (i >= queue.length)
269	+	grow(i + 1);
270	+	size = i + 1;
271	+	if (i == 0)
272	+	queue[0] = e;
273	+	else
274	+	siftUp(i, e);
275	+	return true;
276	+	}
277	+
278		public E peek() {
279	<	return null;
279	>	if (size == 0)
280	>	return null;
281	>	return (E) queue[0];
282		}
283
284	<	public boolean isEmpty() {
284	>	private int indexOf(Object o) {
285	>	if (o != null) {
286	>	for (int i = 0; i < size; i++)
287	>	if (o.equals(queue[i]))
288	>	return i;
289	>	}
290	>	return -1;
291	>	}
292	>
293	>	/**
294	>	* Removes a single instance of the specified element from this queue,
295	>	* if it is present.  More formally, removes an element {@code e} such
296	>	* that {@code o.equals(e)}, if this queue contains one or more such
297	>	* elements.  Returns {@code true} if and only if this queue contained
298	>	* the specified element (or equivalently, if this queue changed as a
299	>	* result of the call).
300	>	*
301	>	* @param o element to be removed from this queue, if present
302	>	* @return {@code true} if this queue changed as a result of the call
303	>	*/
304	>	public boolean remove(Object o) {
305	>	int i = indexOf(o);
306	>	if (i == -1)
307	>	return false;
308	>	else {
309	>	removeAt(i);
310	>	return true;
311	>	}
312	>	}
313	>
314	>	/**
315	>	* Version of remove using reference equality, not equals.
316	>	* Needed by iterator.remove.
317	>	*
318	>	* @param o element to be removed from this queue, if present
319	>	* @return {@code true} if removed
320	>	*/
321	>	boolean removeEq(Object o) {
322	>	for (int i = 0; i < size; i++) {
323	>	if (o == queue[i]) {
324	>	removeAt(i);
325	>	return true;
326	>	}
327	>	}
328		return false;
329		}
330	<	public int size() {
331	<	return 0;
330	>
331	>	/**
332	>	* Returns {@code true} if this queue contains the specified element.
333	>	* More formally, returns {@code true} if and only if this queue contains
334	>	* at least one element {@code e} such that {@code o.equals(e)}.
335	>	*
336	>	* @param o object to be checked for containment in this queue
337	>	* @return {@code true} if this queue contains the specified element
338	>	*/
339	>	public boolean contains(Object o) {
340	>	return indexOf(o) != -1;
341		}
342	+
343	+	/**
344	+	* Returns an array containing all of the elements in this queue.
345	+	* The elements are in no particular order.
346	+	*
347	+	* <p>The returned array will be "safe" in that no references to it are
348	+	* maintained by this queue.  (In other words, this method must allocate
349	+	* a new array).  The caller is thus free to modify the returned array.
350	+	*
351	+	* <p>This method acts as bridge between array-based and collection-based
352	+	* APIs.
353	+	*
354	+	* @return an array containing all of the elements in this queue
355	+	*/
356		public Object[] toArray() {
357	<	return null;
357	>	return Arrays.copyOf(queue, size);
358	>	}
359	>
360	>	/**
361	>	* Returns an array containing all of the elements in this queue; the
362	>	* runtime type of the returned array is that of the specified array.
363	>	* The returned array elements are in no particular order.
364	>	* If the queue fits in the specified array, it is returned therein.
365	>	* Otherwise, a new array is allocated with the runtime type of the
366	>	* specified array and the size of this queue.
367	>	*
368	>	* <p>If the queue fits in the specified array with room to spare
369	>	* (i.e., the array has more elements than the queue), the element in
370	>	* the array immediately following the end of the collection is set to
371	>	* {@code null}.
372	>	*
373	>	* <p>Like the {@link #toArray()} method, this method acts as bridge between
374	>	* array-based and collection-based APIs.  Further, this method allows
375	>	* precise control over the runtime type of the output array, and may,
376	>	* under certain circumstances, be used to save allocation costs.
377	>	*
378	>	* <p>Suppose <tt>x</tt> is a queue known to contain only strings.
379	>	* The following code can be used to dump the queue into a newly
380	>	* allocated array of <tt>String</tt>:
381	>	*
382	>	* <pre>
383	>	*     String[] y = x.toArray(new String[0]);</pre>
384	>	*
385	>	* Note that <tt>toArray(new Object[0])</tt> is identical in function to
386	>	* <tt>toArray()</tt>.
387	>	*
388	>	* @param a the array into which the elements of the queue are to
389	>	*          be stored, if it is big enough; otherwise, a new array of the
390	>	*          same runtime type is allocated for this purpose.
391	>	* @return an array containing all of the elements in this queue
392	>	* @throws ArrayStoreException if the runtime type of the specified array
393	>	*         is not a supertype of the runtime type of every element in
394	>	*         this queue
395	>	* @throws NullPointerException if the specified array is null
396	>	*/
397	>	public <T> T[] toArray(T[] a) {
398	>	if (a.length < size)
399	>	// Make a new array of a's runtime type, but my contents:
400	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
401	>	System.arraycopy(queue, 0, a, 0, size);
402	>	if (a.length > size)
403	>	a[size] = null;
404	>	return a;
405		}
406
407	<	public <T> T[] toArray(T[] array) {
407	>	/**
408	>	* Returns an iterator over the elements in this queue. The iterator
409	>	* does not return the elements in any particular order.
410	>	*
411	>	* @return an iterator over the elements in this queue
412	>	*/
413	>	public Iterator<E> iterator() {
414	>	return new Itr();
415	>	}
416	>
417	>	private final class Itr implements Iterator<E> {
418	>	/**
419	>	* Index (into queue array) of element to be returned by
420	>	* subsequent call to next.
421	>	*/
422	>	private int cursor = 0;
423	>
424	>	/**
425	>	* Index of element returned by most recent call to next,
426	>	* unless that element came from the forgetMeNot list.
427	>	* Set to -1 if element is deleted by a call to remove.
428	>	*/
429	>	private int lastRet = -1;
430	>
431	>	/**
432	>	* A queue of elements that were moved from the unvisited portion of
433	>	* the heap into the visited portion as a result of "unlucky" element
434	>	* removals during the iteration.  (Unlucky element removals are those
435	>	* that require a siftup instead of a siftdown.)  We must visit all of
436	>	* the elements in this list to complete the iteration.  We do this
437	>	* after we've completed the "normal" iteration.
438	>	*
439	>	* We expect that most iterations, even those involving removals,
440	>	* will not need to store elements in this field.
441	>	*/
442	>	private ArrayDeque<E> forgetMeNot = null;
443	>
444	>	/**
445	>	* Element returned by the most recent call to next iff that
446	>	* element was drawn from the forgetMeNot list.
447	>	*/
448	>	private E lastRetElt = null;
449	>
450	>	/**
451	>	* The modCount value that the iterator believes that the backing
452	>	* Queue should have.  If this expectation is violated, the iterator
453	>	* has detected concurrent modification.
454	>	*/
455	>	private int expectedModCount = modCount;
456	>
457	>	public boolean hasNext() {
458	>	return cursor < size ||
459	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
460	>	}
461	>
462	>	public E next() {
463	>	if (expectedModCount != modCount)
464	>	throw new ConcurrentModificationException();
465	>	if (cursor < size)
466	>	return (E) queue[lastRet = cursor++];
467	>	if (forgetMeNot != null) {
468	>	lastRet = -1;
469	>	lastRetElt = forgetMeNot.poll();
470	>	if (lastRetElt != null)
471	>	return lastRetElt;
472	>	}
473	>	throw new NoSuchElementException();
474	>	}
475	>
476	>	public void remove() {
477	>	if (expectedModCount != modCount)
478	>	throw new ConcurrentModificationException();
479	>	if (lastRet != -1) {
480	>	E moved = PriorityQueue.this.removeAt(lastRet);
481	>	lastRet = -1;
482	>	if (moved == null)
483	>	cursor--;
484	>	else {
485	>	if (forgetMeNot == null)
486	>	forgetMeNot = new ArrayDeque<E>();
487	>	forgetMeNot.add(moved);
488	>	}
489	>	} else if (lastRetElt != null) {
490	>	PriorityQueue.this.removeEq(lastRetElt);
491	>	lastRetElt = null;
492	>	} else {
493	>	throw new IllegalStateException();
494	>	}
495	>	expectedModCount = modCount;
496	>	}
497	>	}
498	>
499	>	public int size() {
500	>	return size;
501	>	}
502	>
503	>	/**
504	>	* Removes all of the elements from this priority queue.
505	>	* The queue will be empty after this call returns.
506	>	*/
507	>	public void clear() {
508	>	modCount++;
509	>	for (int i = 0; i < size; i++)
510	>	queue[i] = null;
511	>	size = 0;
512	>	}
513	>
514	>	public E poll() {
515	>	if (size == 0)
516	>	return null;
517	>	int s = --size;
518	>	modCount++;
519	>	E result = (E) queue[0];
520	>	E x = (E) queue[s];
521	>	queue[s] = null;
522	>	if (s != 0)
523	>	siftDown(0, x);
524	>	return result;
525	>	}
526	>
527	>	/**
528	>	* Removes the ith element from queue.
529	>	*
530	>	* Normally this method leaves the elements at up to i-1,
531	>	* inclusive, untouched.  Under these circumstances, it returns
532	>	* null.  Occasionally, in order to maintain the heap invariant,
533	>	* it must swap a later element of the list with one earlier than
534	>	* i.  Under these circumstances, this method returns the element
535	>	* that was previously at the end of the list and is now at some
536	>	* position before i. This fact is used by iterator.remove so as to
537	>	* avoid missing traversing elements.
538	>	*/
539	>	private E removeAt(int i) {
540	>	assert i >= 0 && i < size;
541	>	modCount++;
542	>	int s = --size;
543	>	if (s == i) // removed last element
544	>	queue[i] = null;
545	>	else {
546	>	E moved = (E) queue[s];
547	>	queue[s] = null;
548	>	siftDown(i, moved);
549	>	if (queue[i] == moved) {
550	>	siftUp(i, moved);
551	>	if (queue[i] != moved)
552	>	return moved;
553	>	}
554	>	}
555		return null;
556		}
557
558	+	/**
559	+	* Inserts item x at position k, maintaining heap invariant by
560	+	* promoting x up the tree until it is greater than or equal to
561	+	* its parent, or is the root.
562	+	*
563	+	* To simplify and speed up coercions and comparisons. the
564	+	* Comparable and Comparator versions are separated into different
565	+	* methods that are otherwise identical. (Similarly for siftDown.)
566	+	*
567	+	* @param k the position to fill
568	+	* @param x the item to insert
569	+	*/
570	+	private void siftUp(int k, E x) {
571	+	if (comparator != null)
572	+	siftUpUsingComparator(k, x);
573	+	else
574	+	siftUpComparable(k, x);
575	+	}
576	+
577	+	private void siftUpComparable(int k, E x) {
578	+	Comparable<? super E> key = (Comparable<? super E>) x;
579	+	while (k > 0) {
580	+	int parent = (k - 1) >>> 1;
581	+	Object e = queue[parent];
582	+	if (key.compareTo((E) e) >= 0)
583	+	break;
584	+	queue[k] = e;
585	+	k = parent;
586	+	}
587	+	queue[k] = key;
588	+	}
589	+
590	+	private void siftUpUsingComparator(int k, E x) {
591	+	while (k > 0) {
592	+	int parent = (k - 1) >>> 1;
593	+	Object e = queue[parent];
594	+	if (comparator.compare(x, (E) e) >= 0)
595	+	break;
596	+	queue[k] = e;
597	+	k = parent;
598	+	}
599	+	queue[k] = x;
600	+	}
601	+
602	+	/**
603	+	* Inserts item x at position k, maintaining heap invariant by
604	+	* demoting x down the tree repeatedly until it is less than or
605	+	* equal to its children or is a leaf.
606	+	*
607	+	* @param k the position to fill
608	+	* @param x the item to insert
609	+	*/
610	+	private void siftDown(int k, E x) {
611	+	if (comparator != null)
612	+	siftDownUsingComparator(k, x);
613	+	else
614	+	siftDownComparable(k, x);
615	+	}
616	+
617	+	private void siftDownComparable(int k, E x) {
618	+	Comparable<? super E> key = (Comparable<? super E>)x;
619	+	int half = size >>> 1;        // loop while a non-leaf
620	+	while (k < half) {
621	+	int child = (k << 1) + 1; // assume left child is least
622	+	Object c = queue[child];
623	+	int right = child + 1;
624	+	if (right < size &&
625	+	((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
626	+	c = queue[child = right];
627	+	if (key.compareTo((E) c) <= 0)
628	+	break;
629	+	queue[k] = c;
630	+	k = child;
631	+	}
632	+	queue[k] = key;
633	+	}
634	+
635	+	private void siftDownUsingComparator(int k, E x) {
636	+	int half = size >>> 1;
637	+	while (k < half) {
638	+	int child = (k << 1) + 1;
639	+	Object c = queue[child];
640	+	int right = child + 1;
641	+	if (right < size &&
642	+	comparator.compare((E) c, (E) queue[right]) > 0)
643	+	c = queue[child = right];
644	+	if (comparator.compare(x, (E) c) <= 0)
645	+	break;
646	+	queue[k] = c;
647	+	k = child;
648	+	}
649	+	queue[k] = x;
650	+	}
651	+
652	+	/**
653	+	* Establishes the heap invariant (described above) in the entire tree,
654	+	* assuming nothing about the order of the elements prior to the call.
655	+	*/
656	+	private void heapify() {
657	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
658	+	siftDown(i, (E) queue[i]);
659	+	}
660	+
661	+	/**
662	+	* Returns the comparator used to order the elements in this
663	+	* queue, or {@code null} if this queue is sorted according to
664	+	* the {@linkplain Comparable natural ordering} of its elements.
665	+	*
666	+	* @return the comparator used to order this queue, or
667	+	*         {@code null} if this queue is sorted according to the
668	+	*         natural ordering of its elements
669	+	*/
670	+	public Comparator<? super E> comparator() {
671	+	return comparator;
672	+	}
673	+
674	+	/**
675	+	* Saves the state of the instance to a stream (that
676	+	* is, serializes it).
677	+	*
678	+	* @serialData The length of the array backing the instance is
679	+	*             emitted (int), followed by all of its elements
680	+	*             (each an {@code Object}) in the proper order.
681	+	* @param s the stream
682	+	*/
683	+	private void writeObject(java.io.ObjectOutputStream s)
684	+	throws java.io.IOException{
685	+	// Write out element count, and any hidden stuff
686	+	s.defaultWriteObject();
687	+
688	+	// Write out array length, for compatibility with 1.5 version
689	+	s.writeInt(Math.max(2, size + 1));
690	+
691	+	// Write out all elements in the "proper order".
692	+	for (int i = 0; i < size; i++)
693	+	s.writeObject(queue[i]);
694	+	}
695	+
696	+	/**
697	+	* Reconstitutes the {@code PriorityQueue} instance from a stream
698	+	* (that is, deserializes it).
699	+	*
700	+	* @param s the stream
701	+	*/
702	+	private void readObject(java.io.ObjectInputStream s)
703	+	throws java.io.IOException, ClassNotFoundException {
704	+	// Read in size, and any hidden stuff
705	+	s.defaultReadObject();
706	+
707	+	// Read in (and discard) array length
708	+	s.readInt();
709	+
710	+	queue = new Object[size];
711	+
712	+	// Read in all elements.
713	+	for (int i = 0; i < size; i++)
714	+	queue[i] = s.readObject();
715	+
716	+	// Elements are guaranteed to be in "proper order", but the
717	+	// spec has never explained what that might be.
718	+	heapify();
719	+	}
720		}

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