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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 1.56 by jsr166, Mon Nov 28 02:35:46 2005 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* @(#)PriorityQueue.java       1.8 05/08/27
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 * 3) / 2));
233	+	if (newCapacity < minCapacity)
234	+	newCapacity = minCapacity;
235	+	queue = Arrays.copyOf(queue, newCapacity);
236	+	}
237	+
238	+	/**
239	+	* Inserts the specified element into this priority queue.
240	+	*
241	+	* @return <tt>true</tt> (as specified by {@link Collection#add})
242	+	* @throws ClassCastException if the specified element cannot be
243	+	*         compared with elements currently in this priority queue
244	+	*         according to the priority queue's ordering
245	+	* @throws NullPointerException if the specified element is null
246	+	*/
247	+	public boolean add(E e) {
248	+	return offer(e);
249	+	}
250	+
251	+	/**
252	+	* Inserts the specified element into this priority queue.
253	+	*
254	+	* @return <tt>true</tt> (as specified by {@link Queue#offer})
255	+	* @throws ClassCastException if the specified element cannot be
256	+	*         compared with elements currently in this priority queue
257	+	*         according to the priority queue's ordering
258	+	* @throws NullPointerException if the specified element is null
259	+	*/
260	+	public boolean offer(E e) {
261	+	if (e == null)
262	+	throw new NullPointerException();
263	+	modCount++;
264	+	int i = size;
265	+	if (i >= queue.length)
266	+	grow(i + 1);
267	+	size = i + 1;
268	+	if (i == 0)
269	+	queue[0] = e;
270	+	else
271	+	siftUp(i, e);
272	+	return true;
273	+	}
274	+
275		public E peek() {
276	<	return null;
276	>	if (size == 0)
277	>	return null;
278	>	return (E) queue[0];
279		}
280
281	<	public boolean isEmpty() {
281	>	private int indexOf(Object o) {
282	>	if (o != null) {
283	>	for (int i = 0; i < size; i++)
284	>	if (o.equals(queue[i]))
285	>	return i;
286	>	}
287	>	return -1;
288	>	}
289	>
290	>	/**
291	>	* Removes a single instance of the specified element from this queue,
292	>	* if it is present.  More formally, removes an element <tt>e</tt> such
293	>	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
294	>	* elements.  Returns true if this queue contained the specified element
295	>	* (or equivalently, if this queue changed as a result of the call).
296	>	*
297	>	* @param o element to be removed from this queue, if present
298	>	* @return <tt>true</tt> if this queue changed as a result of the call
299	>	*/
300	>	public boolean remove(Object o) {
301	>	int i = indexOf(o);
302	>	if (i == -1)
303	>	return false;
304	>	else {
305	>	removeAt(i);
306	>	return true;
307	>	}
308	>	}
309	>
310	>	/**
311	>	* Version of remove using reference equality, not equals.
312	>	* Needed by iterator.remove
313	>	*
314	>	* @param o element to be removed from this queue, if present
315	>	* @return <tt>true</tt> if removed.
316	>	*/
317	>	boolean removeEq(Object o) {
318	>	for (int i = 0; i < size; i++) {
319	>	if (o == queue[i]) {
320	>	removeAt(i);
321	>	return true;
322	>	}
323	>	}
324		return false;
325		}
326	<	public int size() {
327	<	return 0;
326	>
327	>	/**
328	>	* Returns <tt>true</tt> if this queue contains the specified element.
329	>	* More formally, returns <tt>true</tt> if and only if this queue contains
330	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
331	>	*
332	>	* @param o object to be checked for containment in this queue
333	>	* @return <tt>true</tt> if this queue contains the specified element
334	>	*/
335	>	public boolean contains(Object o) {
336	>	return indexOf(o) != -1;
337		}
338	+
339	+	/**
340	+	* Returns an array containing all of the elements in this queue,
341	+	* The elements are in no particular order.
342	+	*
343	+	* <p>The returned array will be "safe" in that no references to it are
344	+	* maintained by this list.  (In other words, this method must allocate
345	+	* a new array).  The caller is thus free to modify the returned array.
346	+	*
347	+	* @return an array containing all of the elements in this queue.
348	+	*/
349		public Object[] toArray() {
350	<	return null;
350	>	return Arrays.copyOf(queue, size);
351	>	}
352	>
353	>	/**
354	>	* Returns an array containing all of the elements in this queue.
355	>	* The elements are in no particular order.  The runtime type of
356	>	* the returned array is that of the specified array.  If the queue
357	>	* fits in the specified array, it is returned therein.
358	>	* Otherwise, a new array is allocated with the runtime type of
359	>	* the specified array and the size of this queue.
360	>	*
361	>	* <p>If the queue fits in the specified array with room to spare
362	>	* (i.e., the array has more elements than the queue), the element in
363	>	* the array immediately following the end of the collection is set to
364	>	* <tt>null</tt>.  (This is useful in determining the length of the
365	>	* queue <i>only</i> if the caller knows that the queue does not contain
366	>	* any null elements.)
367	>	*
368	>	* @param a the array into which the elements of the queue are to
369	>	*          be stored, if it is big enough; otherwise, a new array of the
370	>	*          same runtime type is allocated for this purpose.
371	>	* @return an array containing the elements of the queue
372	>	* @throws ArrayStoreException if the runtime type of the specified array
373	>	*         is not a supertype of the runtime type of every element in
374	>	*         this queue
375	>	* @throws NullPointerException if the specified array is null
376	>	*/
377	>	public <T> T[] toArray(T[] a) {
378	>	if (a.length < size)
379	>	// Make a new array of a's runtime type, but my contents:
380	>	return (T[]) Arrays.copyOf(queue, size, a.getClass());
381	>	System.arraycopy(queue, 0, a, 0, size);
382	>	if (a.length > size)
383	>	a[size] = null;
384	>	return a;
385		}
386
387	<	public <T> T[] toArray(T[] array) {
387	>	/**
388	>	* Returns an iterator over the elements in this queue. The iterator
389	>	* does not return the elements in any particular order.
390	>	*
391	>	* @return an iterator over the elements in this queue
392	>	*/
393	>	public Iterator<E> iterator() {
394	>	return new Itr();
395	>	}
396	>
397	>	private final class Itr implements Iterator<E> {
398	>	/**
399	>	* Index (into queue array) of element to be returned by
400	>	* subsequent call to next.
401	>	*/
402	>	private int cursor = 0;
403	>
404	>	/**
405	>	* Index of element returned by most recent call to next,
406	>	* unless that element came from the forgetMeNot list.
407	>	* Set to -1 if element is deleted by a call to remove.
408	>	*/
409	>	private int lastRet = -1;
410	>
411	>	/**
412	>	* A queue of elements that were moved from the unvisited portion of
413	>	* the heap into the visited portion as a result of "unlucky" element
414	>	* removals during the iteration.  (Unlucky element removals are those
415	>	* that require a siftup instead of a siftdown.)  We must visit all of
416	>	* the elements in this list to complete the iteration.  We do this
417	>	* after we've completed the "normal" iteration.
418	>	*
419	>	* We expect that most iterations, even those involving removals,
420	>	* will not use need to store elements in this field.
421	>	*/
422	>	private ArrayDeque<E> forgetMeNot = null;
423	>
424	>	/**
425	>	* Element returned by the most recent call to next iff that
426	>	* element was drawn from the forgetMeNot list.
427	>	*/
428	>	private E lastRetElt = null;
429	>
430	>	/**
431	>	* The modCount value that the iterator believes that the backing
432	>	* List should have.  If this expectation is violated, the iterator
433	>	* has detected concurrent modification.
434	>	*/
435	>	private int expectedModCount = modCount;
436	>
437	>	public boolean hasNext() {
438	>	return cursor < size ||
439	>	(forgetMeNot != null && !forgetMeNot.isEmpty());
440	>	}
441	>
442	>	public E next() {
443	>	if (expectedModCount != modCount)
444	>	throw new ConcurrentModificationException();
445	>	if (cursor < size)
446	>	return (E) queue[lastRet = cursor++];
447	>	if (forgetMeNot != null) {
448	>	lastRet = -1;
449	>	lastRetElt = forgetMeNot.poll();
450	>	if (lastRetElt != null)
451	>	return lastRetElt;
452	>	}
453	>	throw new NoSuchElementException();
454	>	}
455	>
456	>	public void remove() {
457	>	if (expectedModCount != modCount)
458	>	throw new ConcurrentModificationException();
459	>	if (lastRet == -1 && lastRetElt == null)
460	>	throw new IllegalStateException();
461	>	if (lastRet != -1) {
462	>	E moved = PriorityQueue.this.removeAt(lastRet);
463	>	lastRet = -1;
464	>	if (moved == null)
465	>	cursor--;
466	>	else {
467	>	if (forgetMeNot == null)
468	>	forgetMeNot = new ArrayDeque<E>();
469	>	forgetMeNot.add(moved);
470	>	}
471	>	} else {
472	>	PriorityQueue.this.removeEq(lastRetElt);
473	>	lastRetElt = null;
474	>	}
475	>	expectedModCount = modCount;
476	>	}
477	>
478	>	}
479	>
480	>	public int size() {
481	>	return size;
482	>	}
483	>
484	>	/**
485	>	* Removes all of the elements from this priority queue.
486	>	* The queue will be empty after this call returns.
487	>	*/
488	>	public void clear() {
489	>	modCount++;
490	>	for (int i = 0; i < size; i++)
491	>	queue[i] = null;
492	>	size = 0;
493	>	}
494	>
495	>	public E poll() {
496	>	if (size == 0)
497	>	return null;
498	>	int s = --size;
499	>	modCount++;
500	>	E result = (E)queue[0];
501	>	E x = (E)queue[s];
502	>	queue[s] = null;
503	>	if (s != 0)
504	>	siftDown(0, x);
505	>	return result;
506	>	}
507	>
508	>	/**
509	>	* Removes the ith element from queue.
510	>	*
511	>	* Normally this method leaves the elements at up to i-1,
512	>	* inclusive, untouched.  Under these circumstances, it returns
513	>	* null.  Occasionally, in order to maintain the heap invariant,
514	>	* it must swap a later element of the list with one earlier than
515	>	* i.  Under these circumstances, this method returns the element
516	>	* that was previously at the end of the list and is now at some
517	>	* position before i. This fact is used by iterator.remove so as to
518	>	* avoid missing traverseing elements.
519	>	*/
520	>	private E removeAt(int i) {
521	>	assert i >= 0 && i < size;
522	>	modCount++;
523	>	int s = --size;
524	>	if (s == i) // removed last element
525	>	queue[i] = null;
526	>	else {
527	>	E moved = (E) queue[s];
528	>	queue[s] = null;
529	>	siftDown(i, moved);
530	>	if (queue[i] == moved) {
531	>	siftUp(i, moved);
532	>	if (queue[i] != moved)
533	>	return moved;
534	>	}
535	>	}
536		return null;
537		}
538
539	+	/**
540	+	* Inserts item x at position k, maintaining heap invariant by
541	+	* promoting x up the tree until it is greater than or equal to
542	+	* its parent, or is the root.
543	+	*
544	+	* To simplify and speed up coercions and comparisons. the
545	+	* Comparable and Comparator versions are separated into different
546	+	* methods that are otherwise identical. (Similarly for siftDown.)
547	+	*
548	+	* @param k the position to fill
549	+	* @param x the item to insert
550	+	*/
551	+	private void siftUp(int k, E x) {
552	+	if (comparator != null)
553	+	siftUpUsingComparator(k, x);
554	+	else
555	+	siftUpComparable(k, x);
556	+	}
557	+
558	+	private void siftUpComparable(int k, E x) {
559	+	Comparable<? super E> key = (Comparable<? super E>) x;
560	+	while (k > 0) {
561	+	int parent = (k - 1) >>> 1;
562	+	Object e = queue[parent];
563	+	if (key.compareTo((E)e) >= 0)
564	+	break;
565	+	queue[k] = e;
566	+	k = parent;
567	+	}
568	+	queue[k] = key;
569	+	}
570	+
571	+	private void siftUpUsingComparator(int k, E x) {
572	+	while (k > 0) {
573	+	int parent = (k - 1) >>> 1;
574	+	Object e = queue[parent];
575	+	if (comparator.compare(x, (E)e) >= 0)
576	+	break;
577	+	queue[k] = e;
578	+	k = parent;
579	+	}
580	+	queue[k] = x;
581	+	}
582	+
583	+	/**
584	+	* Inserts item x at position k, maintaining heap invariant by
585	+	* demoting x down the tree repeatedly until it is less than or
586	+	* equal to its children or is a leaf.
587	+	*
588	+	* @param k the position to fill
589	+	* @param x the item to insert
590	+	*/
591	+	private void siftDown(int k, E x) {
592	+	if (comparator != null)
593	+	siftDownUsingComparator(k, x);
594	+	else
595	+	siftDownComparable(k, x);
596	+	}
597	+
598	+	private void siftDownComparable(int k, E x) {
599	+	Comparable<? super E> key = (Comparable<? super E>)x;
600	+	int half = size >>> 1;        // loop while a non-leaf
601	+	while (k < half) {
602	+	int child = (k << 1) + 1; // assume left child is least
603	+	Object c = queue[child];
604	+	int right = child + 1;
605	+	if (right < size &&
606	+	((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
607	+	c = queue[child = right];
608	+	if (key.compareTo((E)c) <= 0)
609	+	break;
610	+	queue[k] = c;
611	+	k = child;
612	+	}
613	+	queue[k] = key;
614	+	}
615	+
616	+	private void siftDownUsingComparator(int k, E x) {
617	+	int half = size >>> 1;
618	+	while (k < half) {
619	+	int child = (k << 1) + 1;
620	+	Object c = queue[child];
621	+	int right = child + 1;
622	+	if (right < size &&
623	+	comparator.compare((E)c, (E)queue[right]) > 0)
624	+	c = queue[child = right];
625	+	if (comparator.compare(x, (E)c) <= 0)
626	+	break;
627	+	queue[k] = c;
628	+	k = child;
629	+	}
630	+	queue[k] = x;
631	+	}
632	+
633	+	/**
634	+	* Establishes the heap invariant (described above) in the entire tree,
635	+	* assuming nothing about the order of the elements prior to the call.
636	+	*/
637	+	private void heapify() {
638	+	for (int i = (size >>> 1) - 1; i >= 0; i--)
639	+	siftDown(i, (E)queue[i]);
640	+	}
641	+
642	+	/**
643	+	* Returns the comparator used to order the elements in this
644	+	* queue, or <tt>null</tt> if this queue is sorted according to
645	+	* the {@linkplain Comparable natural ordering} of its elements.
646	+	*
647	+	* @return the comparator used to order this queue, or
648	+	*         <tt>null</tt> if this queue is sorted according to the
649	+	*         natural ordering of its elements.
650	+	*/
651	+	public Comparator<? super E> comparator() {
652	+	return comparator;
653	+	}
654	+
655	+	/**
656	+	* Save the state of the instance to a stream (that
657	+	* is, serialize it).
658	+	*
659	+	* @serialData The length of the array backing the instance is
660	+	* emitted (int), followed by all of its elements (each an
661	+	* <tt>Object</tt>) in the proper order.
662	+	* @param s the stream
663	+	*/
664	+	private void writeObject(java.io.ObjectOutputStream s)
665	+	throws java.io.IOException{
666	+	// Write out element count, and any hidden stuff
667	+	s.defaultWriteObject();
668	+
669	+	// Write out array length
670	+	// For compatibility with 1.5 version, must be at least 2.
671	+	s.writeInt(Math.max(2, queue.length));
672	+
673	+	// Write out all elements in the proper order.
674	+	for (int i=0; i<size; i++)
675	+	s.writeObject(queue[i]);
676	+	}
677	+
678	+	/**
679	+	* Reconstitute the <tt>PriorityQueue</tt> instance from a stream
680	+	* (that is, deserialize it).
681	+	* @param s the stream
682	+	*/
683	+	private void readObject(java.io.ObjectInputStream s)
684	+	throws java.io.IOException, ClassNotFoundException {
685	+	// Read in size, and any hidden stuff
686	+	s.defaultReadObject();
687	+
688	+	// Read in array length and allocate array
689	+	int arrayLength = s.readInt();
690	+	queue = new Object[arrayLength];
691	+
692	+	// Read in all elements in the proper order.
693	+	for (int i=0; i<size; i++)
694	+	queue[i] = (E) s.readObject();
695	+	}
696	+
697		}

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