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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 1.39 by dl, Sun Sep 7 15:06:19 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2003 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	>	* This queue orders elements according to an order specified at construction
13	>	* time, which is specified in the same manner as {@link java.util.TreeSet}
14	>	* and {@link java.util.TreeMap}: elements are ordered either according to
15	>	* their <i>natural order</i> (see {@link Comparable}), or according to a
16	>	* {@link java.util.Comparator}, depending on which constructor is used.
17	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
18	>	* respect to the specified ordering.  If multiple elements are tied for least
19	>	* value, the head is one of those elements. A priority queue does not permit
20	>	* <tt>null</tt> elements.
21	>	*
22	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
23	>	* return the head of the queue.
24	>	*
25	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
26	>	* not delete, the head of the queue.
27	>	*
28	>	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
29	>	* size of the array used internally to store the elements on the
30	>	* queue.
31	>	* It is always at least as large as the queue size.  As
32	>	* elements are added to a priority queue, its capacity grows
33	>	* automatically.  The details of the growth policy are not specified.
34	>	*
35	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
36	>	* guaranteed to traverse the elements of the PriorityQueue in any
37	>	* particular order. If you need ordered traversal, consider using
38	>	* <tt>Arrays.sort(pq.toArray())</tt>.
39	>	*
40	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
41	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
42	>	* instance concurrently if any of the threads modifies the list
43	>	* structurally. Instead, use the thread-safe {@link
44	>	* java.util.concurrent.PriorityBlockingQueue} class.
45	>	*
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 %I%, %G%
59	>	* @author Josh Bloch
60	>	*/
61	>	public class PriorityQueue<E> extends AbstractQueue<E>
62	>	implements Queue<E>, java.io.Serializable {
63
64	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
64	>	private static final long serialVersionUID = -7720805057305804111L;
65
66	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
66	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
67
68	<	public boolean add(E x) {
69	<	return false;
68	>	/**
69	>	* Priority queue represented as a balanced binary heap: the two children
70	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
71	>	* ordered by comparator, or by the elements' natural ordering, if
72	>	* comparator is null:  For each node n in the heap and each descendant d
73	>	* of n, n <= d.
74	>	*
75	>	* The element with the lowest value is in queue[1], assuming the queue is
76	>	* nonempty.  (A one-based array is used in preference to the traditional
77	>	* zero-based array to simplify parent and child calculations.)
78	>	*
79	>	* queue.length must be >= 2, even if size == 0.
80	>	*/
81	>	private transient Object[] queue;
82	>
83	>	/**
84	>	* The number of elements in the priority queue.
85	>	*/
86	>	private int size = 0;
87	>
88	>	/**
89	>	* The comparator, or null if priority queue uses elements'
90	>	* natural ordering.
91	>	*/
92	>	private final Comparator<? super E> comparator;
93	>
94	>	/**
95	>	* The number of times this priority queue has been
96	>	* <i>structurally modified</i>.  See AbstractList for gory details.
97	>	*/
98	>	private transient int modCount = 0;
99	>
100	>	/**
101	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
102	>	* (11) that orders its elements according to their natural
103	>	* ordering (using <tt>Comparable</tt>).
104	>	*/
105	>	public PriorityQueue() {
106	>	this(DEFAULT_INITIAL_CAPACITY, null);
107		}
108	<	public boolean offer(E x) {
109	<	return false;
108	>
109	>	/**
110	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
111	>	* that orders its elements according to their natural ordering
112	>	* (using <tt>Comparable</tt>).
113	>	*
114	>	* @param initialCapacity the initial capacity for this priority queue.
115	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
116	>	* than 1
117	>	*/
118	>	public PriorityQueue(int initialCapacity) {
119	>	this(initialCapacity, null);
120		}
121	<	public boolean remove(Object x) {
122	<	return false;
121	>
122	>	/**
123	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
124	>	* that orders its elements according to the specified comparator.
125	>	*
126	>	* @param initialCapacity the initial capacity for this priority queue.
127	>	* @param comparator the comparator used to order this priority queue.
128	>	* If <tt>null</tt> then the order depends on the elements' natural
129	>	* ordering.
130	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
131	>	* than 1
132	>	*/
133	>	public PriorityQueue(int initialCapacity,
134	>	Comparator<? super E> comparator) {
135	>	if (initialCapacity < 1)
136	>	throw new IllegalArgumentException();
137	>	this.queue = new Object[initialCapacity + 1];
138	>	this.comparator = comparator;
139		}
140
141	<	public E remove() {
142	<	return null;
141	>	/**
142	>	* Common code to initialize underlying queue array across
143	>	* constructors below.
144	>	*/
145	>	private void initializeArray(Collection<? extends E> c) {
146	>	int sz = c.size();
147	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
148	>	Integer.MAX_VALUE - 1);
149	>	if (initialCapacity < 1)
150	>	initialCapacity = 1;
151	>
152	>	this.queue = new Object[initialCapacity + 1];
153		}
154	<	public Iterator<E> iterator() {
155	<	return null;
154	>
155	>	/**
156	>	* Initially fill elements of the queue array under the
157	>	* knowledge that it is sorted or is another PQ, in which
158	>	* case we can just place the elements in the order presented.
159	>	*/
160	>	private void fillFromSorted(Collection<? extends E> c) {
161	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
162	>	queue[++size] = i.next();
163		}
164
165	<	public E element() {
166	<	return null;
165	>	/**
166	>	* Initially fill elements of the queue array that is not to our knowledge
167	>	* sorted, so we must rearrange the elements to guarantee the heap
168	>	* invariant.
169	>	*/
170	>	private void fillFromUnsorted(Collection<? extends E> c) {
171	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
172	>	queue[++size] = i.next();
173	>	heapify();
174		}
175	+
176	+	/**
177	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
178	+	* specified collection.  The priority queue has an initial
179	+	* capacity of 110% of the size of the specified collection or 1
180	+	* if the collection is empty.  If the specified collection is an
181	+	* instance of a {@link java.util.SortedSet} or is another
182	+	* <tt>PriorityQueue</tt>, the priority queue will be sorted
183	+	* according to the same comparator, or according to its elements'
184	+	* natural order if the collection is sorted according to its
185	+	* elements' natural order.  Otherwise, the priority queue is
186	+	* ordered according to its elements' natural order.
187	+	*
188	+	* @param c the collection whose elements are to be placed
189	+	*        into this priority queue.
190	+	* @throws ClassCastException if elements of the specified collection
191	+	*         cannot be compared to one another according to the priority
192	+	*         queue's ordering.
193	+	* @throws NullPointerException if <tt>c</tt> or any element within it
194	+	* is <tt>null</tt>
195	+	*/
196	+	public PriorityQueue(Collection<? extends E> c) {
197	+	initializeArray(c);
198	+	if (c instanceof SortedSet) {
199	+	// @fixme double-cast workaround for compiler
200	+	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
201	+	comparator = (Comparator<? super E>)s.comparator();
202	+	fillFromSorted(s);
203	+	} else if (c instanceof PriorityQueue) {
204	+	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
205	+	comparator = (Comparator<? super E>)s.comparator();
206	+	fillFromSorted(s);
207	+	} else {
208	+	comparator = null;
209	+	fillFromUnsorted(c);
210	+	}
211	+	}
212	+
213	+	/**
214	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
215	+	* specified collection.  The priority queue has an initial
216	+	* capacity of 110% of the size of the specified collection or 1
217	+	* if the collection is empty.  This priority queue will be sorted
218	+	* according to the same comparator as the given collection, or
219	+	* according to its elements' natural order if the collection is
220	+	* sorted according to its elements' natural order.
221	+	*
222	+	* @param c the collection whose elements are to be placed
223	+	*        into this priority queue.
224	+	* @throws ClassCastException if elements of the specified collection
225	+	*         cannot be compared to one another according to the priority
226	+	*         queue's ordering.
227	+	* @throws NullPointerException if <tt>c</tt> or any element within it
228	+	* is <tt>null</tt>
229	+	*/
230	+	public PriorityQueue(PriorityQueue<? extends E> c) {
231	+	initializeArray(c);
232	+	comparator = (Comparator<? super E>)c.comparator();
233	+	fillFromSorted(c);
234	+	}
235	+
236	+	/**
237	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
238	+	* specified collection.  The priority queue has an initial
239	+	* capacity of 110% of the size of the specified collection or 1
240	+	* if the collection is empty.  This priority queue will be sorted
241	+	* according to the same comparator as the given collection, or
242	+	* according to its elements' natural order if the collection is
243	+	* sorted according to its elements' natural order.
244	+	*
245	+	* @param c the collection whose elements are to be placed
246	+	*        into this priority queue.
247	+	* @throws ClassCastException if elements of the specified collection
248	+	*         cannot be compared to one another according to the priority
249	+	*         queue's ordering.
250	+	* @throws NullPointerException if <tt>c</tt> or any element within it
251	+	* is <tt>null</tt>
252	+	*/
253	+	public PriorityQueue(SortedSet<? extends E> c) {
254	+	initializeArray(c);
255	+	comparator = (Comparator<? super E>)c.comparator();
256	+	fillFromSorted(c);
257	+	}
258	+
259	+	/**
260	+	* Resize array, if necessary, to be able to hold given index
261	+	*/
262	+	private void grow(int index) {
263	+	int newlen = queue.length;
264	+	if (index < newlen) // don't need to grow
265	+	return;
266	+	if (index == Integer.MAX_VALUE)
267	+	throw new OutOfMemoryError();
268	+	while (newlen <= index) {
269	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
270	+	newlen = Integer.MAX_VALUE;
271	+	else
272	+	newlen <<= 2;
273	+	}
274	+	Object[] newQueue = new Object[newlen];
275	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
276	+	queue = newQueue;
277	+	}
278	+
279	+
280	+	// Queue Methods
281	+
282	+	/**
283	+	* Add the specified element to this priority queue.
284	+	*
285	+	* @return <tt>true</tt>
286	+	* @throws ClassCastException if the specified element cannot be compared
287	+	* with elements currently in the priority queue according
288	+	* to the priority queue's ordering.
289	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
290	+	*/
291	+	public boolean offer(E o) {
292	+	if (o == null)
293	+	throw new NullPointerException();
294	+	modCount++;
295	+	++size;
296	+
297	+	// Grow backing store if necessary
298	+	if (size >= queue.length)
299	+	grow(size);
300	+
301	+	queue[size] = o;
302	+	fixUp(size);
303	+	return true;
304	+	}
305	+
306		public E poll() {
307	<	return null;
307	>	if (size == 0)
308	>	return null;
309	>	return remove();
310		}
311	+
312		public E peek() {
313	<	return null;
313	>	return (E) queue[1];
314	>	}
315	>
316	>	// Collection Methods - the first two override to update docs
317	>
318	>	/**
319	>	* Adds the specified element to this queue.
320	>	* @return <tt>true</tt> (as per the general contract of
321	>	* <tt>Collection.add</tt>).
322	>	*
323	>	* @throws NullPointerException {@inheritDoc}
324	>	* @throws ClassCastException if the specified element cannot be compared
325	>	* with elements currently in the priority queue according
326	>	* to the priority queue's ordering.
327	>	*/
328	>	public boolean add(E o) {
329	>	return super.add(o);
330	>	}
331	>
332	>
333	>	/**
334	>	* Adds all of the elements in the specified collection to this queue.
335	>	* The behavior of this operation is undefined if
336	>	* the specified collection is modified while the operation is in
337	>	* progress.  (This implies that the behavior of this call is undefined if
338	>	* the specified collection is this queue, and this queue is nonempty.)
339	>	* <p>
340	>	* This implementation iterates over the specified collection, and adds
341	>	* each object returned by the iterator to this collection, in turn.
342	>	* @throws NullPointerException {@inheritDoc}
343	>	* @throws ClassCastException if any element cannot be compared
344	>	* with elements currently in the priority queue according
345	>	* to the priority queue's ordering.
346	>	*/
347	>	public boolean addAll(Collection<? extends E> c) {
348	>	return super.addAll(c);
349		}
350
351	<	public boolean isEmpty() {
351	>
352	>	/**
353	>	* Removes a single instance of the specified element from this
354	>	* queue, if it is present.  More formally,
355	>	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
356	>	* o.equals(e))</tt>, if the queue contains one or more such
357	>	* elements.  Returns <tt>true</tt> if the queue contained the
358	>	* specified element (or equivalently, if the queue changed as a
359	>	* result of the call).
360	>	*
361	>	* <p>This implementation iterates over the queue looking for the
362	>	* specified element.  If it finds the element, it removes the element
363	>	* from the queue using the iterator's remove method.<p>
364	>	*
365	>	*/
366	>	public boolean remove(Object o) {
367	>	if (o == null)
368	>	return false;
369	>
370	>	if (comparator == null) {
371	>	for (int i = 1; i <= size; i++) {
372	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
373	>	removeAt(i);
374	>	return true;
375	>	}
376	>	}
377	>	} else {
378	>	for (int i = 1; i <= size; i++) {
379	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
380	>	removeAt(i);
381	>	return true;
382	>	}
383	>	}
384	>	}
385		return false;
386		}
387	+
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 class Itr implements Iterator<E> {
399	+
400	+	/**
401	+	* Index (into queue array) of element to be returned by
402	+	* subsequent call to next.
403	+	*/
404	+	private int cursor = 1;
405	+
406	+	/**
407	+	* Index of element returned by most recent call to next,
408	+	* unless that element came from the forgetMeNot list.
409	+	* Reset to 0 if element is deleted by a call to remove.
410	+	*/
411	+	private int lastRet = 0;
412	+
413	+	/**
414	+	* The modCount value that the iterator believes that the backing
415	+	* List should have.  If this expectation is violated, the iterator
416	+	* has detected concurrent modification.
417	+	*/
418	+	private int expectedModCount = modCount;
419	+
420	+	/**
421	+	* A list of elements that were moved from the unvisited portion of
422	+	* the heap into the visited portion as a result of "unlucky" element
423	+	* removals during the iteration.  (Unlucky element removals are those
424	+	* that require a fixup instead of a fixdown.)  We must visit all of
425	+	* the elements in this list to complete the iteration.  We do this
426	+	* after we've completed the "normal" iteration.
427	+	*
428	+	* We expect that most iterations, even those involving removals,
429	+	* will not use need to store elements in this field.
430	+	*/
431	+	private ArrayList<E> forgetMeNot = null;
432	+
433	+	/**
434	+	* Element returned by the most recent call to next iff that
435	+	* element was drawn from the forgetMeNot list.
436	+	*/
437	+	private Object lastRetElt = null;
438	+
439	+	public boolean hasNext() {
440	+	return cursor <= size || forgetMeNot != null;
441	+	}
442	+
443	+	public E next() {
444	+	checkForComodification();
445	+	E result;
446	+	if (cursor <= size) {
447	+	result = (E) queue[cursor];
448	+	lastRet = cursor++;
449	+	}
450	+	else if (forgetMeNot == null)
451	+	throw new NoSuchElementException();
452	+	else {
453	+	int remaining = forgetMeNot.size();
454	+	result = forgetMeNot.remove(remaining - 1);
455	+	if (remaining == 1)
456	+	forgetMeNot = null;
457	+	lastRet = 0;
458	+	lastRetElt = result;
459	+	}
460	+	return result;
461	+	}
462	+
463	+	public void remove() {
464	+	checkForComodification();
465	+
466	+	if (lastRet != 0) {
467	+	E moved = PriorityQueue.this.removeAt(lastRet);
468	+	lastRet = 0;
469	+	if (moved == null) {
470	+	cursor--;
471	+	} else {
472	+	if (forgetMeNot == null)
473	+	forgetMeNot = new ArrayList<E>();
474	+	forgetMeNot.add(moved);
475	+	}
476	+	} else if (lastRetElt != null) {
477	+	PriorityQueue.this.remove(lastRetElt);
478	+	lastRetElt = null;
479	+	} else {
480	+	throw new IllegalStateException();
481	+	}
482	+
483	+	expectedModCount = modCount;
484	+	}
485	+
486	+	final void checkForComodification() {
487	+	if (modCount != expectedModCount)
488	+	throw new ConcurrentModificationException();
489	+	}
490	+	}
491	+
492		public int size() {
493	<	return 0;
493	>	return size;
494		}
495	<	public Object[] toArray() {
496	<	return null;
495	>
496	>	/**
497	>	* Remove all elements from the priority queue.
498	>	*/
499	>	public void clear() {
500	>	modCount++;
501	>
502	>	// Null out element references to prevent memory leak
503	>	for (int i=1; i<=size; i++)
504	>	queue[i] = null;
505	>
506	>	size = 0;
507	>	}
508	>
509	>	/**
510	>	* Removes and returns the first element from queue.
511	>	*/
512	>	public E remove() {
513	>	if (size == 0)
514	>	throw new NoSuchElementException();
515	>	modCount++;
516	>
517	>	E result = (E) queue[1];
518	>	queue[1] = queue[size];
519	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
520	>	if (size > 1)
521	>	fixDown(1);
522	>
523	>	return result;
524		}
525
526	<	public <T> T[] toArray(T[] array) {
526	>	/**
527	>	* Removes and returns the ith element from queue.  (Recall that queue
528	>	* is one-based, so 1 <= i <= size.)
529	>	*
530	>	* Normally this method leaves the elements at positions from 1 up to i-1,
531	>	* inclusive, untouched.  Under these circumstances, it returns null.
532	>	* Occasionally, in order to maintain the heap invariant, it must move
533	>	* the last element of the list to some index in the range [2, i-1],
534	>	* and move the element previously at position (i/2) to position i.
535	>	* Under these circumstances, this method returns the element that was
536	>	* previously at the end of the list and is now at some position between
537	>	* 2 and i-1 inclusive.
538	>	*/
539	>	private E removeAt(int i) {
540	>	assert i > 0 && i <= size;
541	>	modCount++;
542	>
543	>	E moved = (E) queue[size];
544	>	queue[i] = moved;
545	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
546	>	if (i <= size) {
547	>	fixDown(i);
548	>	if (queue[i] == moved) {
549	>	fixUp(i);
550	>	if (queue[i] != moved)
551	>	return moved;
552	>	}
553	>	}
554		return null;
555		}
556
557	+	/**
558	+	* Establishes the heap invariant (described above) assuming the heap
559	+	* satisfies the invariant except possibly for the leaf-node indexed by k
560	+	* (which may have a nextExecutionTime less than its parent's).
561	+	*
562	+	* This method functions by "promoting" queue[k] up the hierarchy
563	+	* (by swapping it with its parent) repeatedly until queue[k]
564	+	* is greater than or equal to its parent.
565	+	*/
566	+	private void fixUp(int k) {
567	+	if (comparator == null) {
568	+	while (k > 1) {
569	+	int j = k >> 1;
570	+	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
571	+	break;
572	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
573	+	k = j;
574	+	}
575	+	} else {
576	+	while (k > 1) {
577	+	int j = k >>> 1;
578	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
579	+	break;
580	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
581	+	k = j;
582	+	}
583	+	}
584	+	}
585	+
586	+	/**
587	+	* Establishes the heap invariant (described above) in the subtree
588	+	* rooted at k, which is assumed to satisfy the heap invariant except
589	+	* possibly for node k itself (which may be greater than its children).
590	+	*
591	+	* This method functions by "demoting" queue[k] down the hierarchy
592	+	* (by swapping it with its smaller child) repeatedly until queue[k]
593	+	* is less than or equal to its children.
594	+	*/
595	+	private void fixDown(int k) {
596	+	int j;
597	+	if (comparator == null) {
598	+	while ((j = k << 1) <= size && (j > 0)) {
599	+	if (j<size &&
600	+	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
601	+	j++; // j indexes smallest kid
602	+
603	+	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
604	+	break;
605	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
606	+	k = j;
607	+	}
608	+	} else {
609	+	while ((j = k << 1) <= size && (j > 0)) {
610	+	if (j<size &&
611	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
612	+	j++; // j indexes smallest kid
613	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
614	+	break;
615	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
616	+	k = j;
617	+	}
618	+	}
619	+	}
620	+
621	+	/**
622	+	* Establishes the heap invariant (described above) in the entire tree,
623	+	* assuming nothing about the order of the elements prior to the call.
624	+	*/
625	+	private void heapify() {
626	+	for (int i = size/2; i >= 1; i--)
627	+	fixDown(i);
628	+	}
629	+
630	+	/**
631	+	* Returns the comparator used to order this collection, or <tt>null</tt>
632	+	* if this collection is sorted according to its elements natural ordering
633	+	* (using <tt>Comparable</tt>).
634	+	*
635	+	* @return the comparator used to order this collection, or <tt>null</tt>
636	+	* if this collection is sorted according to its elements natural ordering.
637	+	*/
638	+	public Comparator<? super E> comparator() {
639	+	return comparator;
640	+	}
641	+
642	+	/**
643	+	* Save the state of the instance to a stream (that
644	+	* is, serialize it).
645	+	*
646	+	* @serialData The length of the array backing the instance is
647	+	* emitted (int), followed by all of its elements (each an
648	+	* <tt>Object</tt>) in the proper order.
649	+	* @param s the stream
650	+	*/
651	+	private void writeObject(java.io.ObjectOutputStream s)
652	+	throws java.io.IOException{
653	+	// Write out element count, and any hidden stuff
654	+	s.defaultWriteObject();
655	+
656	+	// Write out array length
657	+	s.writeInt(queue.length);
658	+
659	+	// Write out all elements in the proper order.
660	+	for (int i=1; i<=size; i++)
661	+	s.writeObject(queue[i]);
662	+	}
663	+
664	+	/**
665	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
666	+	* deserialize it).
667	+	* @param s the stream
668	+	*/
669	+	private void readObject(java.io.ObjectInputStream s)
670	+	throws java.io.IOException, ClassNotFoundException {
671	+	// Read in size, and any hidden stuff
672	+	s.defaultReadObject();
673	+
674	+	// Read in array length and allocate array
675	+	int arrayLength = s.readInt();
676	+	queue = new Object[arrayLength];
677	+
678	+	// Read in all elements in the proper order.
679	+	for (int i=1; i<=size; i++)
680	+	queue[i] = (E) s.readObject();
681	+	}
682	+
683		}

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