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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 1.52 by dl, Tue Nov 22 11:44:47 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) {}
24	<
25	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
26	<
27	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
28	<
29	<	public boolean add(E x) {
30	<	return false;
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	>	private static final long serialVersionUID = -7720805057305804111L;
67	>
68	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
69	>
70	>	/**
71	>	* Priority queue represented as a balanced binary heap: the two children
72	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
73	>	* ordered by comparator, or by the elements' natural ordering, if
74	>	* comparator is null:  For each node n in the heap and each descendant d
75	>	* of n, n <= d.
76	>	*
77	>	* The element with the lowest value is in queue[1], assuming the queue is
78	>	* nonempty.  (A one-based array is used in preference to the traditional
79	>	* zero-based array to simplify parent and child calculations.)
80	>	*
81	>	* queue.length must be >= 2, even if size == 0.
82	>	*/
83	>	private transient Object[] queue;
84	>
85	>	/**
86	>	* The number of elements in the priority queue.
87	>	*/
88	>	private int size = 0;
89	>
90	>	/**
91	>	* The comparator, or null if priority queue uses elements'
92	>	* natural ordering.
93	>	*/
94	>	private final Comparator<? super E> comparator;
95	>
96	>	/**
97	>	* The number of times this priority queue has been
98	>	* <i>structurally modified</i>.  See AbstractList for gory details.
99	>	*/
100	>	private transient int modCount = 0;
101	>
102	>	/**
103	>	* Creates a <tt>PriorityQueue</tt> with the default initial
104	>	* capacity (11) that orders its elements according to their
105	>	* {@linkplain Comparable natural ordering}.
106	>	*/
107	>	public PriorityQueue() {
108	>	this(DEFAULT_INITIAL_CAPACITY, null);
109	>	}
110	>
111	>	/**
112	>	* Creates a <tt>PriorityQueue</tt> with the specified initial
113	>	* capacity that orders its elements according to their
114	>	* {@linkplain Comparable natural ordering}.
115	>	*
116	>	* @param initialCapacity the initial capacity for this priority queue
117	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
118	>	* than 1
119	>	*/
120	>	public PriorityQueue(int initialCapacity) {
121	>	this(initialCapacity, null);
122		}
123	<	public boolean offer(E x) {
124	<	return false;
123	>
124	>	/**
125	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
126	>	* that orders its elements according to the specified comparator.
127	>	*
128	>	* @param  initialCapacity the initial capacity for this priority queue
129	>	* @param  comparator the comparator that will be used to order
130	>	*         this priority queue.  If <tt>null</tt>, the <i>natural
131	>	*         ordering</i> of the elements will be used.
132	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is
133	>	*         less than 1
134	>	*/
135	>	public PriorityQueue(int initialCapacity,
136	>	Comparator<? super E> comparator) {
137	>	if (initialCapacity < 1)
138	>	throw new IllegalArgumentException();
139	>	this.queue = new Object[initialCapacity + 1];
140	>	this.comparator = comparator;
141		}
142	<	public boolean remove(Object x) {
143	<	return false;
142	>
143	>	/**
144	>	* Common code to initialize underlying queue array across
145	>	* constructors below.
146	>	*/
147	>	private void initializeArray(Collection<? extends E> c) {
148	>	int sz = c.size();
149	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
150	>	Integer.MAX_VALUE - 1);
151	>	if (initialCapacity < 1)
152	>	initialCapacity = 1;
153	>
154	>	this.queue = new Object[initialCapacity + 1];
155		}
156
157	<	public E remove() {
158	<	return null;
157	>	/**
158	>	* Initially fill elements of the queue array under the
159	>	* knowledge that it is sorted or is another PQ, in which
160	>	* case we can just place the elements in the order presented.
161	>	*/
162	>	private void fillFromSorted(Collection<? extends E> c) {
163	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) {
164	>	int k = ++size;
165	>	if (k >= queue.length)
166	>	grow(k);
167	>	queue[k] = i.next();
168	>	}
169		}
170	<	public Iterator<E> iterator() {
171	<	return null;
170	>
171	>	/**
172	>	* Initially fill elements of the queue array that is not to our knowledge
173	>	* sorted, so we must rearrange the elements to guarantee the heap
174	>	* invariant.
175	>	*/
176	>	private void fillFromUnsorted(Collection<? extends E> c) {
177	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); ) {
178	>	int k = ++size;
179	>	if (k >= queue.length)
180	>	grow(k);
181	>	queue[k] = i.next();
182	>	}
183	>	heapify();
184		}
185
186	<	public E element() {
187	<	return null;
186	>	/**
187	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
188	>	* specified collection.  The priority queue has an initial
189	>	* capacity of 110% of the size of the specified collection or 1
190	>	* if the collection is empty.  If the specified collection is an
191	>	* instance of a {@link java.util.SortedSet} or is another
192	>	* <tt>PriorityQueue</tt>, the priority queue will be ordered
193	>	* according to the same ordering.  Otherwise, this priority queue
194	>	* will be ordered according to the natural ordering of its elements.
195	>	*
196	>	* @param  c the collection whose elements are to be placed
197	>	*         into this priority queue
198	>	* @throws ClassCastException if elements of the specified collection
199	>	*         cannot be compared to one another according to the priority
200	>	*         queue's ordering
201	>	* @throws NullPointerException if the specified collection or any
202	>	*         of its elements are null
203	>	*/
204	>	public PriorityQueue(Collection<? extends E> c) {
205	>	initializeArray(c);
206	>	if (c instanceof SortedSet) {
207	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
208	>	comparator = (Comparator<? super E>)s.comparator();
209	>	fillFromSorted(s);
210	>	} else if (c instanceof PriorityQueue) {
211	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
212	>	comparator = (Comparator<? super E>)s.comparator();
213	>	fillFromSorted(s);
214	>	} else {
215	>	comparator = null;
216	>	fillFromUnsorted(c);
217	>	}
218		}
219	<	public E poll() {
220	<	return null;
219	>
220	>	/**
221	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
222	>	* specified priority queue.  The priority queue has an initial
223	>	* capacity of 110% of the size of the specified priority queue or
224	>	* 1 if the priority queue is empty.  This priority queue will be
225	>	* ordered according to the same ordering as the given priority
226	>	* queue.
227	>	*
228	>	* @param  c the priority queue whose elements are to be placed
229	>	*         into this priority queue
230	>	* @throws ClassCastException if elements of <tt>c</tt> cannot be
231	>	*         compared to one another according to <tt>c</tt>'s
232	>	*         ordering
233	>	* @throws NullPointerException if the specified priority queue or any
234	>	*         of its elements are null
235	>	*/
236	>	public PriorityQueue(PriorityQueue<? extends E> c) {
237	>	initializeArray(c);
238	>	comparator = (Comparator<? super E>)c.comparator();
239	>	fillFromSorted(c);
240	>	}
241	>
242	>	/**
243	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
244	>	* specified sorted set.  The priority queue has an initial
245	>	* capacity of 110% of the size of the specified sorted set or 1
246	>	* if the sorted set is empty.  This priority queue will be ordered
247	>	* according to the same ordering as the given sorted set.
248	>	*
249	>	* @param  c the sorted set whose elements are to be placed
250	>	*         into this priority queue.
251	>	* @throws ClassCastException if elements of the specified sorted
252	>	*         set cannot be compared to one another according to the
253	>	*         sorted set's ordering
254	>	* @throws NullPointerException if the specified sorted set or any
255	>	*         of its elements are null
256	>	*/
257	>	public PriorityQueue(SortedSet<? extends E> c) {
258	>	initializeArray(c);
259	>	comparator = (Comparator<? super E>)c.comparator();
260	>	fillFromSorted(c);
261	>	}
262	>
263	>	/**
264	>	* Resize array, if necessary, to be able to hold given index.
265	>	*/
266	>	private void grow(int index) {
267	>	int newlen = queue.length;
268	>	if (index < newlen) // don't need to grow
269	>	return;
270	>	if (index == Integer.MAX_VALUE)
271	>	throw new OutOfMemoryError();
272	>	while (newlen <= index) {
273	>	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
274	>	newlen = Integer.MAX_VALUE;
275	>	else
276	>	newlen <<= 2;
277	>	}
278	>	queue = Arrays.copyOf(queue, newlen);
279		}
280	+
281	+	/**
282	+	* Inserts the specified element into this priority queue.
283	+	*
284	+	* @return <tt>true</tt> (as specified by {@link Collection#add})
285	+	* @throws ClassCastException if the specified element cannot be
286	+	*         compared with elements currently in this priority queue
287	+	*         according to the priority queue's ordering
288	+	* @throws NullPointerException if the specified element is null
289	+	*/
290	+	public boolean add(E e) {
291	+	return offer(e);
292	+	}
293	+
294	+	/**
295	+	* Inserts the specified element into this priority queue.
296	+	*
297	+	* @return <tt>true</tt> (as specified by {@link Queue#offer})
298	+	* @throws ClassCastException if the specified element cannot be
299	+	*         compared with elements currently in this priority queue
300	+	*         according to the priority queue's ordering
301	+	* @throws NullPointerException if the specified element is null
302	+	*/
303	+	public boolean offer(E e) {
304	+	if (e == null)
305	+	throw new NullPointerException();
306	+	modCount++;
307	+	++size;
308	+
309	+	// Grow backing store if necessary
310	+	if (size >= queue.length)
311	+	grow(size);
312	+
313	+	queue[size] = e;
314	+	fixUp(size);
315	+	return true;
316	+	}
317	+
318		public E peek() {
319	<	return null;
319	>	if (size == 0)
320	>	return null;
321	>	return (E) queue[1];
322		}
323
324	<	public boolean isEmpty() {
325	<	return false;
324	>	private int indexOf(Object o) {
325	>	if (o == null)
326	>	return -1;
327	>	for (int i = 1; i <= size; i++)
328	>	if (o.equals(queue[i]))
329	>	return i;
330	>	return -1;
331		}
332	<	public int size() {
333	<	return 0;
332	>
333	>	/**
334	>	* Removes a single instance of the specified element from this queue,
335	>	* if it is present.  More formally, removes an element <tt>e</tt> such
336	>	* that <tt>o.equals(e)</tt>, if this queue contains one or more such
337	>	* elements.  Returns true if this queue contained the specified element
338	>	* (or equivalently, if this queue changed as a result of the call).
339	>	*
340	>	* @param o element to be removed from this queue, if present
341	>	* @return <tt>true</tt> if this queue changed as a result of the call
342	>	*/
343	>	public boolean remove(Object o) {
344	>	int i = indexOf(o);
345	>	if (i == -1)
346	>	return false;
347	>	else {
348	>	removeAt(i);
349	>	return true;
350	>	}
351	>	}
352	>
353	>	/**
354	>	* Returns <tt>true</tt> if this queue contains the specified element.
355	>	* More formally, returns <tt>true</tt> if and only if this queue contains
356	>	* at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
357	>	*
358	>	* @param o object to be checked for containment in this queue
359	>	* @return <tt>true</tt> if this queue contains the specified element
360	>	*/
361	>	public boolean contains(Object o) {
362	>	return indexOf(o) != -1;
363		}
364	+
365	+	/**
366	+	* Returns an array containing all of the elements in this queue,
367	+	* The elements are in no particular order.
368	+	*
369	+	* <p>The returned array will be "safe" in that no references to it are
370	+	* maintained by this list.  (In other words, this method must allocate
371	+	* a new array).  The caller is thus free to modify the returned array.
372	+	*
373	+	* @return an array containing all of the elements in this queue.
374	+	*/
375		public Object[] toArray() {
376	<	return null;
376	>	return Arrays.copyOfRange(queue, 1, size+1);
377	>	}
378	>
379	>	/**
380	>	* Returns an array containing all of the elements in this queue.
381	>	* The elements are in no particular order.  The runtime type of
382	>	* the returned array is that of the specified array.  If the queue
383	>	* fits in the specified array, it is returned therein.
384	>	* Otherwise, a new array is allocated with the runtime type of
385	>	* the specified array and the size of this queue.
386	>	*
387	>	* <p>If the queue fits in the specified array with room to spare
388	>	* (i.e., the array has more elements than the queue), the element in
389	>	* the array immediately following the end of the collection is set to
390	>	* <tt>null</tt>.  (This is useful in determining the length of the
391	>	* queue <i>only</i> if the caller knows that the queue does not contain
392	>	* any null elements.)
393	>	*
394	>	* @param a the array into which the elements of the queue are to
395	>	*          be stored, if it is big enough; otherwise, a new array of the
396	>	*          same runtime type is allocated for this purpose.
397	>	* @return an array containing the elements of the queue
398	>	* @throws ArrayStoreException if the runtime type of the specified array
399	>	*         is not a supertype of the runtime type of every element in
400	>	*         this queue
401	>	* @throws NullPointerException if the specified array is null
402	>	*/
403	>	public <T> T[] toArray(T[] a) {
404	>	if (a.length < size)
405	>	// Make a new array of a's runtime type, but my contents:
406	>	return (T[]) Arrays.copyOfRange(queue, 1, size+1, a.getClass());
407	>	System.arraycopy(queue, 1, a, 0, size);
408	>	if (a.length > size)
409	>	a[size] = null;
410	>	return a;
411	>	}
412	>
413	>	/**
414	>	* Returns an iterator over the elements in this queue. The iterator
415	>	* does not return the elements in any particular order.
416	>	*
417	>	* @return an iterator over the elements in this queue
418	>	*/
419	>	public Iterator<E> iterator() {
420	>	return new Itr();
421		}
422
423	<	public <T> T[] toArray(T[] array) {
423	>	private class Itr implements Iterator<E> {
424	>
425	>	/**
426	>	* Index (into queue array) of element to be returned by
427	>	* subsequent call to next.
428	>	*/
429	>	private int cursor = 1;
430	>
431	>	/**
432	>	* Index of element returned by most recent call to next,
433	>	* unless that element came from the forgetMeNot list.
434	>	* Reset to 0 if element is deleted by a call to remove.
435	>	*/
436	>	private int lastRet = 0;
437	>
438	>	/**
439	>	* The modCount value that the iterator believes that the backing
440	>	* List should have.  If this expectation is violated, the iterator
441	>	* has detected concurrent modification.
442	>	*/
443	>	private int expectedModCount = modCount;
444	>
445	>	/**
446	>	* A list of elements that were moved from the unvisited portion of
447	>	* the heap into the visited portion as a result of "unlucky" element
448	>	* removals during the iteration.  (Unlucky element removals are those
449	>	* that require a fixup instead of a fixdown.)  We must visit all of
450	>	* the elements in this list to complete the iteration.  We do this
451	>	* after we've completed the "normal" iteration.
452	>	*
453	>	* We expect that most iterations, even those involving removals,
454	>	* will not use need to store elements in this field.
455	>	*/
456	>	private ArrayList<E> forgetMeNot = null;
457	>
458	>	/**
459	>	* Element returned by the most recent call to next iff that
460	>	* element was drawn from the forgetMeNot list.
461	>	*/
462	>	private Object lastRetElt = null;
463	>
464	>	public boolean hasNext() {
465	>	return cursor <= size || forgetMeNot != null;
466	>	}
467	>
468	>	public E next() {
469	>	checkForComodification();
470	>	E result;
471	>	if (cursor <= size) {
472	>	result = (E) queue[cursor];
473	>	lastRet = cursor++;
474	>	}
475	>	else if (forgetMeNot == null)
476	>	throw new NoSuchElementException();
477	>	else {
478	>	int remaining = forgetMeNot.size();
479	>	result = forgetMeNot.remove(remaining - 1);
480	>	if (remaining == 1)
481	>	forgetMeNot = null;
482	>	lastRet = 0;
483	>	lastRetElt = result;
484	>	}
485	>	return result;
486	>	}
487	>
488	>	public void remove() {
489	>	checkForComodification();
490	>
491	>	if (lastRet != 0) {
492	>	E moved = PriorityQueue.this.removeAt(lastRet);
493	>	lastRet = 0;
494	>	if (moved == null) {
495	>	cursor--;
496	>	} else {
497	>	if (forgetMeNot == null)
498	>	forgetMeNot = new ArrayList<E>();
499	>	forgetMeNot.add(moved);
500	>	}
501	>	} else if (lastRetElt != null) {
502	>	PriorityQueue.this.remove(lastRetElt);
503	>	lastRetElt = null;
504	>	} else {
505	>	throw new IllegalStateException();
506	>	}
507	>
508	>	expectedModCount = modCount;
509	>	}
510	>
511	>	final void checkForComodification() {
512	>	if (modCount != expectedModCount)
513	>	throw new ConcurrentModificationException();
514	>	}
515	>	}
516	>
517	>	public int size() {
518	>	return size;
519	>	}
520	>
521	>	/**
522	>	* Removes all of the elements from this priority queue.
523	>	* The queue will be empty after this call returns.
524	>	*/
525	>	public void clear() {
526	>	modCount++;
527	>
528	>	// Null out element references to prevent memory leak
529	>	for (int i=1; i<=size; i++)
530	>	queue[i] = null;
531	>
532	>	size = 0;
533	>	}
534	>
535	>	public E poll() {
536	>	if (size == 0)
537	>	return null;
538	>	modCount++;
539	>
540	>	E result = (E) queue[1];
541	>	queue[1] = queue[size];
542	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
543	>	if (size > 1)
544	>	fixDown(1);
545	>
546	>	return result;
547	>	}
548	>
549	>	/**
550	>	* Removes and returns the ith element from queue.  (Recall that queue
551	>	* is one-based, so 1 <= i <= size.)
552	>	*
553	>	* Normally this method leaves the elements at positions from 1 up to i-1,
554	>	* inclusive, untouched.  Under these circumstances, it returns null.
555	>	* Occasionally, in order to maintain the heap invariant, it must move
556	>	* the last element of the list to some index in the range [2, i-1],
557	>	* and move the element previously at position (i/2) to position i.
558	>	* Under these circumstances, this method returns the element that was
559	>	* previously at the end of the list and is now at some position between
560	>	* 2 and i-1 inclusive.
561	>	*/
562	>	private E removeAt(int i) {
563	>	assert i > 0 && i <= size;
564	>	modCount++;
565	>
566	>	E moved = (E) queue[size];
567	>	queue[i] = moved;
568	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
569	>	if (i <= size) {
570	>	fixDown(i);
571	>	if (queue[i] == moved) {
572	>	fixUp(i);
573	>	if (queue[i] != moved)
574	>	return moved;
575	>	}
576	>	}
577		return null;
578		}
579
580	+	/**
581	+	* Establishes the heap invariant (described above) assuming the heap
582	+	* satisfies the invariant except possibly for the leaf-node indexed by k
583	+	* (which may have a nextExecutionTime less than its parent's).
584	+	*
585	+	* This method functions by "promoting" queue[k] up the hierarchy
586	+	* (by swapping it with its parent) repeatedly until queue[k]
587	+	* is greater than or equal to its parent.
588	+	*/
589	+	private void fixUp(int k) {
590	+	if (comparator == null) {
591	+	while (k > 1) {
592	+	int j = k >> 1;
593	+	if (((Comparable<? super E>)queue[j]).compareTo((E)queue[k]) <= 0)
594	+	break;
595	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
596	+	k = j;
597	+	}
598	+	} else {
599	+	while (k > 1) {
600	+	int j = k >>> 1;
601	+	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
602	+	break;
603	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
604	+	k = j;
605	+	}
606	+	}
607	+	}
608	+
609	+	/**
610	+	* Establishes the heap invariant (described above) in the subtree
611	+	* rooted at k, which is assumed to satisfy the heap invariant except
612	+	* possibly for node k itself (which may be greater than its children).
613	+	*
614	+	* This method functions by "demoting" queue[k] down the hierarchy
615	+	* (by swapping it with its smaller child) repeatedly until queue[k]
616	+	* is less than or equal to its children.
617	+	*/
618	+	private void fixDown(int k) {
619	+	int j;
620	+	if (comparator == null) {
621	+	while ((j = k << 1) <= size && (j > 0)) {
622	+	if (j<size &&
623	+	((Comparable<? super E>)queue[j]).compareTo((E)queue[j+1]) > 0)
624	+	j++; // j indexes smallest kid
625	+
626	+	if (((Comparable<? super E>)queue[k]).compareTo((E)queue[j]) <= 0)
627	+	break;
628	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
629	+	k = j;
630	+	}
631	+	} else {
632	+	while ((j = k << 1) <= size && (j > 0)) {
633	+	if (j<size &&
634	+	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
635	+	j++; // j indexes smallest kid
636	+	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
637	+	break;
638	+	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
639	+	k = j;
640	+	}
641	+	}
642	+	}
643	+
644	+	/**
645	+	* Establishes the heap invariant (described above) in the entire tree,
646	+	* assuming nothing about the order of the elements prior to the call.
647	+	*/
648	+	private void heapify() {
649	+	for (int i = size/2; i >= 1; i--)
650	+	fixDown(i);
651	+	}
652	+
653	+	/**
654	+	* Returns the comparator used to order the elements in this
655	+	* queue, or <tt>null</tt> if this queue is sorted according to
656	+	* the {@linkplain Comparable natural ordering} of its elements.
657	+	*
658	+	* @return the comparator used to order this queue, or
659	+	*         <tt>null</tt> if this queue is sorted according to the
660	+	*         natural ordering of its elements.
661	+	*/
662	+	public Comparator<? super E> comparator() {
663	+	return comparator;
664	+	}
665	+
666	+	/**
667	+	* Save the state of the instance to a stream (that
668	+	* is, serialize it).
669	+	*
670	+	* @serialData The length of the array backing the instance is
671	+	* emitted (int), followed by all of its elements (each an
672	+	* <tt>Object</tt>) in the proper order.
673	+	* @param s the stream
674	+	*/
675	+	private void writeObject(java.io.ObjectOutputStream s)
676	+	throws java.io.IOException{
677	+	// Write out element count, and any hidden stuff
678	+	s.defaultWriteObject();
679	+
680	+	// Write out array length
681	+	s.writeInt(queue.length);
682	+
683	+	// Write out all elements in the proper order.
684	+	for (int i=1; i<=size; i++)
685	+	s.writeObject(queue[i]);
686	+	}
687	+
688	+	/**
689	+	* Reconstitute the <tt>PriorityQueue</tt> instance from a stream
690	+	* (that is, deserialize it).
691	+	* @param s the stream
692	+	*/
693	+	private void readObject(java.io.ObjectInputStream s)
694	+	throws java.io.IOException, ClassNotFoundException {
695	+	// Read in size, and any hidden stuff
696	+	s.defaultReadObject();
697	+
698	+	// Read in array length and allocate array
699	+	int arrayLength = s.readInt();
700	+	queue = new Object[arrayLength];
701	+
702	+	// Read in all elements in the proper order.
703	+	for (int i=1; i<=size; i++)
704	+	queue[i] = (E) s.readObject();
705	+	}
706	+
707		}

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