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root/jsr166/jsr166/src/main/java/util/PriorityQueue.java

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 1.36 by dl, Sat Aug 30 11:40:04 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
2	<
3	<	import java.util.*;
1	>	package java.util;
2
3		/**
4	<	* An unbounded (resizable) priority queue based on a priority
5	<	* heap.The take operation returns the least element with respect to
6	<	* the given ordering. (If more than one element is tied for least
7	<	* value, one of them is arbitrarily chosen to be returned -- no
8	<	* guarantees are made for ordering across ties.) Ordering follows the
9	<	* java.util.Collection conventions: Either the elements must be
10	<	* Comparable, or a Comparator must be supplied. Comparison failures
11	<	* throw ClassCastExceptions during insertions and extractions.
12	<	**/
13	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
14	<	public PriorityQueue(int initialCapacity) {}
15	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
4	>	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
5	>	* This queue orders elements according to an order specified at construction
6	>	* time, which is specified in the same manner as {@link java.util.TreeSet}
7	>	* and {@link java.util.TreeMap}: elements are ordered either according to
8	>	* their <i>natural order</i> (see {@link Comparable}), or according to a
9	>	* {@link java.util.Comparator}, depending on which constructor is used.
10	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
11	>	* respect to the specified ordering.  If multiple elements are tied for least
12	>	* value, the head is one of those elements. A priority queue does not permit
13	>	* <tt>null</tt> elements.
14	>	*
15	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
16	>	* return the head of the queue.
17	>	*
18	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
19	>	* not delete, the head of the queue.
20	>	*
21	>	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
22	>	* size of the array used internally to store the elements on the
23	>	* queue.
24	>	* It is always at least as large as the queue size.  As
25	>	* elements are added to a priority queue, its capacity grows
26	>	* automatically.  The details of the growth policy are not specified.
27	>	*
28	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
29	>	* guaranteed to traverse the elements of the PriorityQueue in any
30	>	* particular order. If you need ordered traversal, consider using
31	>	* <tt>Arrays.sort(pq.toArray())</tt>.
32	>	*
33	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
34	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
35	>	* instance concurrently if any of the threads modifies the list
36	>	* structurally. Instead, use the thread-safe {@link
37	>	* java.util.concurrent.PriorityBlockingQueue} class.
38	>	*
39	>	*
40	>	* <p>Implementation note: this implementation provides O(log(n)) time
41	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
42	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
43	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
44	>	* constant time for the retrieval methods (<tt>peek</tt>,
45	>	* <tt>element</tt>, and <tt>size</tt>).
46	>	*
47	>	* <p>This class is a member of the
48	>	* <a href="{@docRoot}/../guide/collections/index.html">
49	>	* Java Collections Framework</a>.
50	>	* @since 1.5
51	>	* @author Josh Bloch
52	>	*/
53	>	public class PriorityQueue<E> extends AbstractQueue<E>
54	>	implements Queue<E>, java.io.Serializable {
55
56	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
56	>	private static final long serialVersionUID = -7720805057305804111L;
57
58	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
58	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
59
60	<	public boolean add(E x) {
61	<	return false;
60	>	/**
61	>	* Priority queue represented as a balanced binary heap: the two children
62	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
63	>	* ordered by comparator, or by the elements' natural ordering, if
64	>	* comparator is null:  For each node n in the heap and each descendant d
65	>	* of n, n <= d.
66	>	*
67	>	* The element with the lowest value is in queue[1], assuming the queue is
68	>	* nonempty.  (A one-based array is used in preference to the traditional
69	>	* zero-based array to simplify parent and child calculations.)
70	>	*
71	>	* queue.length must be >= 2, even if size == 0.
72	>	*/
73	>	private transient Object[] queue;
74	>
75	>	/**
76	>	* The number of elements in the priority queue.
77	>	*/
78	>	private int size = 0;
79	>
80	>	/**
81	>	* The comparator, or null if priority queue uses elements'
82	>	* natural ordering.
83	>	*/
84	>	private final Comparator<? super E> comparator;
85	>
86	>	/**
87	>	* The number of times this priority queue has been
88	>	* <i>structurally modified</i>.  See AbstractList for gory details.
89	>	*/
90	>	private transient int modCount = 0;
91	>
92	>	/**
93	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
94	>	* (11) that orders its elements according to their natural
95	>	* ordering (using <tt>Comparable</tt>).
96	>	*/
97	>	public PriorityQueue() {
98	>	this(DEFAULT_INITIAL_CAPACITY, null);
99		}
100	<	public boolean offer(E x) {
101	<	return false;
100	>
101	>	/**
102	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
103	>	* that orders its elements according to their natural ordering
104	>	* (using <tt>Comparable</tt>).
105	>	*
106	>	* @param initialCapacity the initial capacity for this priority queue.
107	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
108	>	* than 1
109	>	*/
110	>	public PriorityQueue(int initialCapacity) {
111	>	this(initialCapacity, null);
112		}
113	<	public boolean remove(Object x) {
114	<	return false;
113	>
114	>	/**
115	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
116	>	* that orders its elements according to the specified comparator.
117	>	*
118	>	* @param initialCapacity the initial capacity for this priority queue.
119	>	* @param comparator the comparator used to order this priority queue.
120	>	* If <tt>null</tt> then the order depends on the elements' natural
121	>	* ordering.
122	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
123	>	* than 1
124	>	*/
125	>	public PriorityQueue(int initialCapacity,
126	>	Comparator<? super E> comparator) {
127	>	if (initialCapacity < 1)
128	>	throw new IllegalArgumentException();
129	>	this.queue = new Object[initialCapacity + 1];
130	>	this.comparator = comparator;
131		}
132
133	<	public E remove() {
134	<	return null;
133	>	/**
134	>	* Common code to initialize underlying queue array across
135	>	* constructors below.
136	>	*/
137	>	private void initializeArray(Collection<? extends E> c) {
138	>	int sz = c.size();
139	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
140	>	Integer.MAX_VALUE - 1);
141	>	if (initialCapacity < 1)
142	>	initialCapacity = 1;
143	>
144	>	this.queue = new Object[initialCapacity + 1];
145		}
146	<	public Iterator<E> iterator() {
147	<	return null;
146	>
147	>	/**
148	>	* Initially fill elements of the queue array under the
149	>	* knowledge that it is sorted or is another PQ, in which
150	>	* case we can just place the elements in the order presented.
151	>	*/
152	>	private void fillFromSorted(Collection<? extends E> c) {
153	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154	>	queue[++size] = i.next();
155		}
156
157	<	public E element() {
158	<	return null;
157	>	/**
158	>	* Initially fill elements of the queue array that is not to our knowledge
159	>	* sorted, so we must rearrange the elements to guarantee the heap
160	>	* invariant.
161	>	*/
162	>	private void fillFromUnsorted(Collection<? extends E> c) {
163	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
164	>	queue[++size] = i.next();
165	>	heapify();
166	>	}
167	>
168	>	/**
169	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
170	>	* specified collection.  The priority queue has an initial
171	>	* capacity of 110% of the size of the specified collection or 1
172	>	* if the collection is empty.  If the specified collection is an
173	>	* instance of a {@link java.util.SortedSet} or is another
174	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
175	>	* according to the same comparator, or according to its elements'
176	>	* natural order if the collection is sorted according to its
177	>	* elements' natural order.  Otherwise, the priority queue is
178	>	* ordered according to its elements' natural order.
179	>	*
180	>	* @param c the collection whose elements are to be placed
181	>	*        into this priority queue.
182	>	* @throws ClassCastException if elements of the specified collection
183	>	*         cannot be compared to one another according to the priority
184	>	*         queue's ordering.
185	>	* @throws NullPointerException if <tt>c</tt> or any element within it
186	>	* is <tt>null</tt>
187	>	*/
188	>	public PriorityQueue(Collection<? extends E> c) {
189	>	initializeArray(c);
190	>	if (c instanceof SortedSet) {
191	>	// @fixme double-cast workaround for compiler
192	>	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
193	>	comparator = (Comparator<? super E>)s.comparator();
194	>	fillFromSorted(s);
195	>	} else if (c instanceof PriorityQueue) {
196	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
197	>	comparator = (Comparator<? super E>)s.comparator();
198	>	fillFromSorted(s);
199	>	} else {
200	>	comparator = null;
201	>	fillFromUnsorted(c);
202	>	}
203	>	}
204	>
205	>	/**
206	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
207	>	* specified collection.  The priority queue has an initial
208	>	* capacity of 110% of the size of the specified collection or 1
209	>	* if the collection is empty.  This priority queue will be sorted
210	>	* according to the same comparator as the given collection, or
211	>	* according to its elements' natural order if the collection is
212	>	* sorted according to its elements' natural order.
213	>	*
214	>	* @param c the collection whose elements are to be placed
215	>	*        into this priority queue.
216	>	* @throws ClassCastException if elements of the specified collection
217	>	*         cannot be compared to one another according to the priority
218	>	*         queue's ordering.
219	>	* @throws NullPointerException if <tt>c</tt> or any element within it
220	>	* is <tt>null</tt>
221	>	*/
222	>	public PriorityQueue(PriorityQueue<? extends E> c) {
223	>	initializeArray(c);
224	>	comparator = (Comparator<? super E>)c.comparator();
225	>	fillFromSorted(c);
226	>	}
227	>
228	>	/**
229	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
230	>	* specified collection.  The priority queue has an initial
231	>	* capacity of 110% of the size of the specified collection or 1
232	>	* if the collection is empty.  This priority queue will be sorted
233	>	* according to the same comparator as the given collection, or
234	>	* according to its elements' natural order if the collection is
235	>	* sorted according to its elements' natural order.
236	>	*
237	>	* @param c the collection whose elements are to be placed
238	>	*        into this priority queue.
239	>	* @throws ClassCastException if elements of the specified collection
240	>	*         cannot be compared to one another according to the priority
241	>	*         queue's ordering.
242	>	* @throws NullPointerException if <tt>c</tt> or any element within it
243	>	* is <tt>null</tt>
244	>	*/
245	>	public PriorityQueue(SortedSet<? extends E> c) {
246	>	initializeArray(c);
247	>	comparator = (Comparator<? super E>)c.comparator();
248	>	fillFromSorted(c);
249	>	}
250	>
251	>	/**
252	>	* Resize array, if necessary, to be able to hold given index
253	>	*/
254	>	private void grow(int index) {
255	>	int newlen = queue.length;
256	>	if (index < newlen) // don't need to grow
257	>	return;
258	>	if (index == Integer.MAX_VALUE)
259	>	throw new OutOfMemoryError();
260	>	while (newlen <= index) {
261	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
262	>	newlen = Integer.MAX_VALUE;
263	>	else
264	>	newlen <<= 2;
265	>	}
266	>	Object[] newQueue = new Object[newlen];
267	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
268	>	queue = newQueue;
269		}
270	+
271	+
272	+	// Queue Methods
273	+
274	+	/**
275	+	* Add the specified element to this priority queue.
276	+	*
277	+	* @return <tt>true</tt>
278	+	* @throws ClassCastException if the specified element cannot be compared
279	+	* with elements currently in the priority queue according
280	+	* to the priority queue's ordering.
281	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
282	+	*/
283	+	public boolean offer(E o) {
284	+	if (o == null)
285	+	throw new NullPointerException();
286	+	modCount++;
287	+	++size;
288	+
289	+	// Grow backing store if necessary
290	+	if (size >= queue.length)
291	+	grow(size);
292	+
293	+	queue[size] = o;
294	+	fixUp(size);
295	+	return true;
296	+	}
297	+
298		public E poll() {
299	<	return null;
299	>	if (size == 0)
300	>	return null;
301	>	return remove();
302		}
303	+
304		public E peek() {
305	<	return null;
305	>	return (E) queue[1];
306	>	}
307	>
308	>	// Collection Methods - the first two override to update docs
309	>
310	>	/**
311	>	* Adds the specified element to this queue.
312	>	* @return <tt>true</tt> (as per the general contract of
313	>	* <tt>Collection.add</tt>).
314	>	*
315	>	* @throws NullPointerException {@inheritDoc}
316	>	* @throws ClassCastException if the specified element cannot be compared
317	>	* with elements currently in the priority queue according
318	>	* to the priority queue's ordering.
319	>	*/
320	>	public boolean add(E o) {
321	>	return super.add(o);
322	>	}
323	>
324	>
325	>	/**
326	>	* Adds all of the elements in the specified collection to this queue.
327	>	* The behavior of this operation is undefined if
328	>	* the specified collection is modified while the operation is in
329	>	* progress.  (This implies that the behavior of this call is undefined if
330	>	* the specified collection is this queue, and this queue is nonempty.)
331	>	* <p>
332	>	* This implementation iterates over the specified collection, and adds
333	>	* each object returned by the iterator to this collection, in turn.
334	>	* @throws NullPointerException {@inheritDoc}
335	>	* @throws ClassCastException if any element cannot be compared
336	>	* with elements currently in the priority queue according
337	>	* to the priority queue's ordering.
338	>	*/
339	>	public boolean addAll(Collection<? extends E> c) {
340	>	return super.addAll(c);
341		}
342
343	<	public boolean isEmpty() {
343	>
344	>	/**
345	>	* Removes a single instance of the specified element from this
346	>	* queue, if it is present.  More formally,
347	>	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
348	>	* o.equals(e))</tt>, if the queue contains one or more such
349	>	* elements.  Returns <tt>true</tt> if the queue contained the
350	>	* specified element (or equivalently, if the queue changed as a
351	>	* result of the call).
352	>	*
353	>	* <p>This implementation iterates over the queue looking for the
354	>	* specified element.  If it finds the element, it removes the element
355	>	* from the queue using the iterator's remove method.<p>
356	>	*
357	>	*/
358	>	public boolean remove(Object o) {
359	>	if (o == null)
360	>	return false;
361	>
362	>	if (comparator == null) {
363	>	for (int i = 1; i <= size; i++) {
364	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
365	>	removeAt(i);
366	>	return true;
367	>	}
368	>	}
369	>	} else {
370	>	for (int i = 1; i <= size; i++) {
371	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
372	>	removeAt(i);
373	>	return true;
374	>	}
375	>	}
376	>	}
377		return false;
378		}
379	+
380	+	/**
381	+	* Returns an iterator over the elements in this queue. The iterator
382	+	* does not return the elements in any particular order.
383	+	*
384	+	* @return an iterator over the elements in this queue.
385	+	*/
386	+	public Iterator<E> iterator() {
387	+	return new Itr();
388	+	}
389	+
390	+	private class Itr implements Iterator<E> {
391	+
392	+	/**
393	+	* Index (into queue array) of element to be returned by
394	+	* subsequent call to next.
395	+	*/
396	+	private int cursor = 1;
397	+
398	+	/**
399	+	* Index of element returned by most recent call to next,
400	+	* unless that element came from the forgetMeNot list.
401	+	* Reset to 0 if element is deleted by a call to remove.
402	+	*/
403	+	private int lastRet = 0;
404	+
405	+	/**
406	+	* The modCount value that the iterator believes that the backing
407	+	* List should have.  If this expectation is violated, the iterator
408	+	* has detected concurrent modification.
409	+	*/
410	+	private int expectedModCount = modCount;
411	+
412	+	/**
413	+	* A list of elements that were moved from the unvisited portion of
414	+	* the heap into the visited portion as a result of "unlucky" element
415	+	* removals during the iteration.  (Unlucky element removals are those
416	+	* that require a fixup instead of a fixdown.)  We must visit all of
417	+	* the elements in this list to complete the iteration.  We do this
418	+	* after we've completed the "normal" iteration.
419	+	*
420	+	* We expect that most iterations, even those involving removals,
421	+	* will not use need to store elements in this field.
422	+	*/
423	+	private ArrayList<E> forgetMeNot = null;
424	+
425	+	/**
426	+	* Element returned by the most recent call to next iff that
427	+	* element was drawn from the forgetMeNot list.
428	+	*/
429	+	private Object lastRetElt = null;
430	+
431	+	public boolean hasNext() {
432	+	return cursor <= size || forgetMeNot != null;
433	+	}
434	+
435	+	public E next() {
436	+	checkForComodification();
437	+	E result;
438	+	if (cursor <= size) {
439	+	result = (E) queue[cursor];
440	+	lastRet = cursor++;
441	+	}
442	+	else if (forgetMeNot == null)
443	+	throw new NoSuchElementException();
444	+	else {
445	+	int remaining = forgetMeNot.size();
446	+	result = forgetMeNot.remove(remaining - 1);
447	+	if (remaining == 1)
448	+	forgetMeNot = null;
449	+	lastRet = 0;
450	+	lastRetElt = result;
451	+	}
452	+	return result;
453	+	}
454	+
455	+	public void remove() {
456	+	checkForComodification();
457	+
458	+	if (lastRet != 0) {
459	+	E moved = PriorityQueue.this.removeAt(lastRet);
460	+	lastRet = 0;
461	+	if (moved == null) {
462	+	cursor--;
463	+	} else {
464	+	if (forgetMeNot == null)
465	+	forgetMeNot = new ArrayList();
466	+	forgetMeNot.add(moved);
467	+	}
468	+	} else if (lastRetElt != null) {
469	+	PriorityQueue.this.remove(lastRetElt);
470	+	lastRetElt = null;
471	+	} else {
472	+	throw new IllegalStateException();
473	+	}
474	+
475	+	expectedModCount = modCount;
476	+	}
477	+
478	+	final void checkForComodification() {
479	+	if (modCount != expectedModCount)
480	+	throw new ConcurrentModificationException();
481	+	}
482	+	}
483	+
484		public int size() {
485	<	return 0;
485	>	return size;
486		}
487	<	public Object[] toArray() {
488	<	return null;
487	>
488	>	/**
489	>	* Remove all elements from the priority queue.
490	>	*/
491	>	public void clear() {
492	>	modCount++;
493	>
494	>	// Null out element references to prevent memory leak
495	>	for (int i=1; i<=size; i++)
496	>	queue[i] = null;
497	>
498	>	size = 0;
499	>	}
500	>
501	>	/**
502	>	* Removes and returns the first element from queue.
503	>	*/
504	>	public E remove() {
505	>	if (size == 0)
506	>	throw new NoSuchElementException();
507	>	modCount++;
508	>
509	>	E result = (E) queue[1];
510	>	queue[1] = queue[size];
511	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
512	>	if (size > 1)
513	>	fixDown(1);
514	>
515	>	return result;
516		}
517
518	<	public <T> T[] toArray(T[] array) {
518	>	/**
519	>	* Removes and returns the ith element from queue.  (Recall that queue
520	>	* is one-based, so 1 <= i <= size.)
521	>	*
522	>	* Normally this method leaves the elements at positions from 1 up to i-1,
523	>	* inclusive, untouched.  Under these circumstances, it returns null.
524	>	* Occasionally, in order to maintain the heap invariant, it must move
525	>	* the last element of the list to some index in the range [2, i-1],
526	>	* and move the element previously at position (i/2) to position i.
527	>	* Under these circumstances, this method returns the element that was
528	>	* previously at the end of the list and is now at some position between
529	>	* 2 and i-1 inclusive.
530	>	*/
531	>	private E removeAt(int i) {
532	>	assert i > 0 && i <= size;
533	>	modCount++;
534	>
535	>	E moved = (E) queue[size];
536	>	queue[i] = moved;
537	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
538	>	if (i <= size) {
539	>	fixDown(i);
540	>	if (queue[i] == moved) {
541	>	fixUp(i);
542	>	if (queue[i] != moved)
543	>	return moved;
544	>	}
545	>	}
546		return null;
547		}
548
549	+	/**
550	+	* Establishes the heap invariant (described above) assuming the heap
551	+	* satisfies the invariant except possibly for the leaf-node indexed by k
552	+	* (which may have a nextExecutionTime less than its parent's).
553	+	*
554	+	* This method functions by "promoting" queue[k] up the hierarchy
555	+	* (by swapping it with its parent) repeatedly until queue[k]
556	+	* is greater than or equal to its parent.
557	+	*/
558	+	private void fixUp(int k) {
559	+	if (comparator == null) {
560	+	while (k > 1) {
561	+	int j = k >> 1;
562	+	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
563	+	break;
564	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
565	+	k = j;
566	+	}
567	+	} else {
568	+	while (k > 1) {
569	+	int j = k >>> 1;
570	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
571	+	break;
572	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
573	+	k = j;
574	+	}
575	+	}
576	+	}
577	+
578	+	/**
579	+	* Establishes the heap invariant (described above) in the subtree
580	+	* rooted at k, which is assumed to satisfy the heap invariant except
581	+	* possibly for node k itself (which may be greater than its children).
582	+	*
583	+	* This method functions by "demoting" queue[k] down the hierarchy
584	+	* (by swapping it with its smaller child) repeatedly until queue[k]
585	+	* is less than or equal to its children.
586	+	*/
587	+	private void fixDown(int k) {
588	+	int j;
589	+	if (comparator == null) {
590	+	while ((j = k << 1) <= size && (j > 0)) {
591	+	if (j<size &&
592	+	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
593	+	j++; // j indexes smallest kid
594	+
595	+	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
596	+	break;
597	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
598	+	k = j;
599	+	}
600	+	} else {
601	+	while ((j = k << 1) <= size && (j > 0)) {
602	+	if (j<size &&
603	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
604	+	j++; // j indexes smallest kid
605	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
606	+	break;
607	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
608	+	k = j;
609	+	}
610	+	}
611	+	}
612	+
613	+	/**
614	+	* Establishes the heap invariant (described above) in the entire tree,
615	+	* assuming nothing about the order of the elements prior to the call.
616	+	*/
617	+	private void heapify() {
618	+	for (int i = size/2; i >= 1; i--)
619	+	fixDown(i);
620	+	}
621	+
622	+	/**
623	+	* Returns the comparator used to order this collection, or <tt>null</tt>
624	+	* if this collection is sorted according to its elements natural ordering
625	+	* (using <tt>Comparable</tt>).
626	+	*
627	+	* @return the comparator used to order this collection, or <tt>null</tt>
628	+	* if this collection is sorted according to its elements natural ordering.
629	+	*/
630	+	public Comparator<? super E> comparator() {
631	+	return comparator;
632	+	}
633	+
634	+	/**
635	+	* Save the state of the instance to a stream (that
636	+	* is, serialize it).
637	+	*
638	+	* @serialData The length of the array backing the instance is
639	+	* emitted (int), followed by all of its elements (each an
640	+	* <tt>Object</tt>) in the proper order.
641	+	* @param s the stream
642	+	*/
643	+	private void writeObject(java.io.ObjectOutputStream s)
644	+	throws java.io.IOException{
645	+	// Write out element count, and any hidden stuff
646	+	s.defaultWriteObject();
647	+
648	+	// Write out array length
649	+	s.writeInt(queue.length);
650	+
651	+	// Write out all elements in the proper order.
652	+	for (int i=0; i<size; i++)
653	+	s.writeObject(queue[i]);
654	+	}
655	+
656	+	/**
657	+	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
658	+	* deserialize it).
659	+	* @param s the stream
660	+	*/
661	+	private void readObject(java.io.ObjectInputStream s)
662	+	throws java.io.IOException, ClassNotFoundException {
663	+	// Read in size, and any hidden stuff
664	+	s.defaultReadObject();
665	+
666	+	// Read in array length and allocate array
667	+	int arrayLength = s.readInt();
668	+	queue = new Object[arrayLength];
669	+
670	+	// Read in all elements in the proper order.
671	+	for (int i=0; i<size; i++)
672	+	queue[i] = s.readObject();
673	+	}
674	+
675		}

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