ViewVC Help

View File | Revision Log | Show Annotations | Download File | Root Listing

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

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.22 by dl, Tue Aug 5 12:11:08 2003 UTC vs.
Revision 1.50 by dl, Wed Jun 2 23:45:46 2004 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2004 Sun Microsystems, Inc. All rights reserved.
5	>	* SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6	>	*/
7	>
8	>	package java.util;
9
10		/**
11	<	* An unbounded priority queue based on a priority heap.  This queue orders
12	<	* elements according to an order specified at construction time, which is
13	<	* specified in the same manner as {@link java.util.TreeSet} and
14	<	* {@link java.util.TreeMap}: elements are ordered
15	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
16	<	* according to a {@link java.util.Comparator}, depending on which
17	<	* constructor is used.
18	<	* <p>The <em>head</em> of this queue is the <em>least</em> element with
19	<	* respect to the specified ordering.
13	<	* If multiple elements are tied for least value, the
14	<	* head is one of those elements. A priority queue does not permit
15	<	* <tt>null</tt> elements.
11	>	* An unbounded priority {@linkplain Queue queue} based on a priority
12	>	* heap.  This queue orders elements according to an order specified
13	>	* at construction time, which is specified either according to their
14	>	* <i>natural order</i> (see {@link Comparable}), or according to a
15	>	* {@link java.util.Comparator}, depending on which constructor is
16	>	* used. A priority queue does not permit <tt>null</tt> elements.
17	>	* A priority queue relying on natural ordering also does not
18	>	* permit insertion of non-comparable objects (doing so may result
19	>	* in <tt>ClassCastException</tt>).
20		*
21	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and
22	<	* return the head of the queue.
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>The {@link #element()} and {@link #peek()} methods return, but do
29	<	* not delete, the head of the queue.
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>A priority queue has a <i>capacity</i>.  The capacity is the
36	<	* size of the array used internally to store the elements on the
37	<	* queue.
38	<	* It is always at least as large as the queue size.  As
39	<	* elements are added to a priority queue, its capacity grows
40	<	* automatically.  The details of the growth policy are not specified.
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.
38	>	* The
39	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
40	>	* guaranteed to traverse the elements of the PriorityQueue in any
41	>	* particular order. If you need ordered traversal, consider using
42	>	* <tt>Arrays.sort(pq.toArray())</tt>.
43		*
44	+	* <p> <strong>Note that this implementation is not synchronized.</strong>
45	+	* Multiple threads should not access a <tt>PriorityQueue</tt>
46	+	* instance concurrently if any of the threads modifies the list
47	+	* structurally. Instead, use the thread-safe {@link
48	+	* java.util.concurrent.PriorityBlockingQueue} class.
49	+	*
50	+	*
51		* <p>Implementation note: this implementation provides O(log(n)) time
52		* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
53		* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
#	Line 38 | Line 59
59		* <a href="{@docRoot}/../guide/collections/index.html">
60		* Java Collections Framework</a>.
61		* @since 1.5
62	+	* @version %I%, %G%
63		* @author Josh Bloch
64	+	* @param <E> the type of elements held in this collection
65		*/
66		public class PriorityQueue<E> extends AbstractQueue<E>
67	<	implements Queue<E>, java.io.Serializable {
67	>	implements java.io.Serializable {
68	>
69	>	private static final long serialVersionUID = -7720805057305804111L;
70
71		private static final int DEFAULT_INITIAL_CAPACITY = 11;
72
#	Line 80 | Line 105 | public class PriorityQueue<E> extends Ab
105		/**
106		* Creates a <tt>PriorityQueue</tt> with the default initial capacity
107		* (11) that orders its elements according to their natural
108	<	* ordering (using <tt>Comparable</tt>.)
108	>	* ordering (using <tt>Comparable</tt>).
109		*/
110		public PriorityQueue() {
111		this(DEFAULT_INITIAL_CAPACITY, null);
#	Line 89 | Line 114 | public class PriorityQueue<E> extends Ab
114		/**
115		* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
116		* that orders its elements according to their natural ordering
117	<	* (using <tt>Comparable</tt>.)
117	>	* (using <tt>Comparable</tt>).
118		*
119		* @param initialCapacity the initial capacity for this priority queue.
120	+	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
121	+	* than 1
122		*/
123		public PriorityQueue(int initialCapacity) {
124		this(initialCapacity, null);
#	Line 108 | Line 135 | public class PriorityQueue<E> extends Ab
135		* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
136		* than 1
137		*/
138	<	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
138	>	public PriorityQueue(int initialCapacity,
139	>	Comparator<? super E> comparator) {
140		if (initialCapacity < 1)
141		throw new IllegalArgumentException();
142		this.queue = new Object[initialCapacity + 1];
#	Line 132 | Line 160 | public class PriorityQueue<E> extends Ab
160		/**
161		* Initially fill elements of the queue array under the
162		* knowledge that it is sorted or is another PQ, in which
163	<	* case we can just place the elements without fixups.
163	>	* case we can just place the elements in the order presented.
164		*/
165		private void fillFromSorted(Collection<? extends E> c) {
166		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
167		queue[++size] = i.next();
168		}
169
142	–
170		/**
171	<	* Initially fill elements of the queue array that is
172	<	* not to our knowledge sorted, so we must add them
173	<	* one by one.
171	>	* Initially fill elements of the queue array that is not to our knowledge
172	>	* sorted, so we must rearrange the elements to guarantee the heap
173	>	* invariant.
174		*/
175		private void fillFromUnsorted(Collection<? extends E> c) {
176		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
177	<	add(i.next());
177	>	queue[++size] = i.next();
178	>	heapify();
179		}
180
181		/**
#	Line 155 | Line 183 | public class PriorityQueue<E> extends Ab
183		* specified collection.  The priority queue has an initial
184		* capacity of 110% of the size of the specified collection or 1
185		* if the collection is empty.  If the specified collection is an
186	<	* instance of a {@link SortedSet} or is another
186	>	* instance of a {@link java.util.SortedSet} or is another
187		* <tt>PriorityQueue</tt>, the priority queue will be sorted
188		* according to the same comparator, or according to its elements'
189		* natural order if the collection is sorted according to its
#	Line 172 | Line 200 | public class PriorityQueue<E> extends Ab
200		*/
201		public PriorityQueue(Collection<? extends E> c) {
202		initializeArray(c);
203	<	if (c instanceof SortedSet<? extends E>) {
204	<	SortedSet<? extends E> s = (SortedSet<? extends E>) c;
203	>	if (c instanceof SortedSet) {
204	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
205		comparator = (Comparator<? super E>)s.comparator();
206		fillFromSorted(s);
207	<	}
180	<	else if (c instanceof PriorityQueue<? extends E>) {
207	>	} else if (c instanceof PriorityQueue) {
208		PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
209		comparator = (Comparator<? super E>)s.comparator();
210		fillFromSorted(s);
211	<	}
185	<	else {
211	>	} else {
212		comparator = null;
213		fillFromUnsorted(c);
214		}
#	Line 254 | Line 280 | public class PriorityQueue<E> extends Ab
280		queue = newQueue;
281		}
282
257	–	// Queue Methods
283
284		/**
285	<	* Add the specified element to this priority queue.
285	>	* Inserts the specified element into this priority queue.
286		*
287		* @return <tt>true</tt>
288		* @throws ClassCastException if the specified element cannot be compared
#	Line 280 | Line 305 | public class PriorityQueue<E> extends Ab
305		return true;
306		}
307
308	<	public E poll() {
308	>	public E peek() {
309		if (size == 0)
310		return null;
286	–	return (E) remove(1);
287	–	}
288	–
289	–	public E peek() {
311		return (E) queue[1];
312		}
313
314	<	// Collection Methods
294	<
295	<	// these first two override just to get the throws docs
314	>	// Collection Methods - the first two override to update docs
315
316		/**
317	+	* Adds the specified element to this queue.
318	+	* @return <tt>true</tt> (as per the general contract of
319	+	* <tt>Collection.add</tt>).
320	+	*
321		* @throws NullPointerException if the specified element is <tt>null</tt>.
322		* @throws ClassCastException if the specified element cannot be compared
323		* with elements currently in the priority queue according
324		* to the priority queue's ordering.
325		*/
326		public boolean add(E o) {
327	<	return super.add(o);
327	>	return offer(o);
328		}
329
330		/**
331	<	* @throws ClassCastException if any element cannot be compared
332	<	* with elements currently in the priority queue according
310	<	* to the priority queue's ordering.
311	<	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
312	<	* is <tt>null</tt>
331	>	* Removes a single instance of the specified element from this
332	>	* queue, if it is present.
333		*/
314	–	public boolean addAll(Collection<? extends E> c) {
315	–	return super.addAll(c);
316	–	}
317	–
334		public boolean remove(Object o) {
335		if (o == null)
336		return false;
#	Line 322 | Line 338 | public class PriorityQueue<E> extends Ab
338		if (comparator == null) {
339		for (int i = 1; i <= size; i++) {
340		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
341	<	remove(i);
341	>	removeAt(i);
342		return true;
343		}
344		}
345		} else {
346		for (int i = 1; i <= size; i++) {
347		if (comparator.compare((E)queue[i], (E)o) == 0) {
348	<	remove(i);
348	>	removeAt(i);
349		return true;
350		}
351		}
#	Line 337 | Line 353 | public class PriorityQueue<E> extends Ab
353		return false;
354		}
355
356	+	/**
357	+	* Returns an iterator over the elements in this queue. The iterator
358	+	* does not return the elements in any particular order.
359	+	*
360	+	* @return an iterator over the elements in this queue.
361	+	*/
362		public Iterator<E> iterator() {
363		return new Itr();
364		}
365
366		private class Itr implements Iterator<E> {
367	+
368		/**
369		* Index (into queue array) of element to be returned by
370		* subsequent call to next.
#	Line 349 | Line 372 | public class PriorityQueue<E> extends Ab
372		private int cursor = 1;
373
374		/**
375	<	* Index of element returned by most recent call to next or
376	<	* previous.  Reset to 0 if this element is deleted by a call
377	<	* to remove.
375	>	* Index of element returned by most recent call to next,
376	>	* unless that element came from the forgetMeNot list.
377	>	* Reset to 0 if element is deleted by a call to remove.
378		*/
379		private int lastRet = 0;
380
#	Line 362 | Line 385 | public class PriorityQueue<E> extends Ab
385		*/
386		private int expectedModCount = modCount;
387
388	+	/**
389	+	* A list of elements that were moved from the unvisited portion of
390	+	* the heap into the visited portion as a result of "unlucky" element
391	+	* removals during the iteration.  (Unlucky element removals are those
392	+	* that require a fixup instead of a fixdown.)  We must visit all of
393	+	* the elements in this list to complete the iteration.  We do this
394	+	* after we've completed the "normal" iteration.
395	+	*
396	+	* We expect that most iterations, even those involving removals,
397	+	* will not use need to store elements in this field.
398	+	*/
399	+	private ArrayList<E> forgetMeNot = null;
400	+
401	+	/**
402	+	* Element returned by the most recent call to next iff that
403	+	* element was drawn from the forgetMeNot list.
404	+	*/
405	+	private Object lastRetElt = null;
406	+
407		public boolean hasNext() {
408	<	return cursor <= size;
408	>	return cursor <= size || forgetMeNot != null;
409		}
410
411		public E next() {
412		checkForComodification();
413	<	if (cursor > size)
413	>	E result;
414	>	if (cursor <= size) {
415	>	result = (E) queue[cursor];
416	>	lastRet = cursor++;
417	>	}
418	>	else if (forgetMeNot == null)
419		throw new NoSuchElementException();
420	<	E result = (E) queue[cursor];
421	<	lastRet = cursor++;
420	>	else {
421	>	int remaining = forgetMeNot.size();
422	>	result = forgetMeNot.remove(remaining - 1);
423	>	if (remaining == 1)
424	>	forgetMeNot = null;
425	>	lastRet = 0;
426	>	lastRetElt = result;
427	>	}
428		return result;
429		}
430
431		public void remove() {
379	–	if (lastRet == 0)
380	–	throw new IllegalStateException();
432		checkForComodification();
433
434	<	PriorityQueue.this.remove(lastRet);
435	<	if (lastRet < cursor)
436	<	cursor--;
437	<	lastRet = 0;
434	>	if (lastRet != 0) {
435	>	E moved = PriorityQueue.this.removeAt(lastRet);
436	>	lastRet = 0;
437	>	if (moved == null) {
438	>	cursor--;
439	>	} else {
440	>	if (forgetMeNot == null)
441	>	forgetMeNot = new ArrayList<E>();
442	>	forgetMeNot.add(moved);
443	>	}
444	>	} else if (lastRetElt != null) {
445	>	PriorityQueue.this.remove(lastRetElt);
446	>	lastRetElt = null;
447	>	} else {
448	>	throw new IllegalStateException();
449	>	}
450	>
451		expectedModCount = modCount;
452		}
453
#	Line 393 | Line 457 | public class PriorityQueue<E> extends Ab
457		}
458		}
459
396	–	/**
397	–	* Returns the number of elements in this priority queue.
398	–	*
399	–	* @return the number of elements in this priority queue.
400	–	*/
460		public int size() {
461		return size;
462		}
463
464		/**
465	<	* Remove all elements from the priority queue.
465	>	* Removes all elements from the priority queue.
466	>	* The queue will be empty after this call returns.
467		*/
468		public void clear() {
469		modCount++;
#	Line 415 | Line 475 | public class PriorityQueue<E> extends Ab
475		size = 0;
476		}
477
478	+	public E poll() {
479	+	if (size == 0)
480	+	return null;
481	+	modCount++;
482	+
483	+	E result = (E) queue[1];
484	+	queue[1] = queue[size];
485	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
486	+	if (size > 1)
487	+	fixDown(1);
488	+
489	+	return result;
490	+	}
491	+
492		/**
493	<	* Removes and returns the ith element from queue.  Recall
494	<	* that queue is one-based, so 1 <= i <= size.
493	>	* Removes and returns the ith element from queue.  (Recall that queue
494	>	* is one-based, so 1 <= i <= size.)
495		*
496	<	* XXX: Could further special-case i==size, but is it worth it?
497	<	* XXX: Could special-case i==0, but is it worth it?
496	>	* Normally this method leaves the elements at positions from 1 up to i-1,
497	>	* inclusive, untouched.  Under these circumstances, it returns null.
498	>	* Occasionally, in order to maintain the heap invariant, it must move
499	>	* the last element of the list to some index in the range [2, i-1],
500	>	* and move the element previously at position (i/2) to position i.
501	>	* Under these circumstances, this method returns the element that was
502	>	* previously at the end of the list and is now at some position between
503	>	* 2 and i-1 inclusive.
504		*/
505	<	private E remove(int i) {
506	<	assert i <= size;
505	>	private E removeAt(int i) {
506	>	assert i > 0 && i <= size;
507		modCount++;
508
509	<	E result = (E) queue[i];
510	<	queue[i] = queue[size];
509	>	E moved = (E) queue[size];
510	>	queue[i] = moved;
511		queue[size--] = null;  // Drop extra ref to prevent memory leak
512	<	if (i <= size)
512	>	if (i <= size) {
513		fixDown(i);
514	<	return result;
514	>	if (queue[i] == moved) {
515	>	fixUp(i);
516	>	if (queue[i] != moved)
517	>	return moved;
518	>	}
519	>	}
520	>	return null;
521		}
522
523		/**
#	Line 454 | Line 540 | public class PriorityQueue<E> extends Ab
540		}
541		} else {
542		while (k > 1) {
543	<	int j = k >> 1;
543	>	int j = k >>> 1;
544		if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
545		break;
546		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
#	Line 475 | Line 561 | public class PriorityQueue<E> extends Ab
561		private void fixDown(int k) {
562		int j;
563		if (comparator == null) {
564	<	while ((j = k << 1) <= size) {
565	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
564	>	while ((j = k << 1) <= size && (j > 0)) {
565	>	if (j<size &&
566	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
567		j++; // j indexes smallest kid
568	+
569		if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
570		break;
571		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
572		k = j;
573		}
574		} else {
575	<	while ((j = k << 1) <= size) {
576	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
575	>	while ((j = k << 1) <= size && (j > 0)) {
576	>	if (j<size &&
577	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
578		j++; // j indexes smallest kid
579		if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
580		break;
#	Line 495 | Line 584 | public class PriorityQueue<E> extends Ab
584		}
585		}
586
587	+	/**
588	+	* Establishes the heap invariant (described above) in the entire tree,
589	+	* assuming nothing about the order of the elements prior to the call.
590	+	*/
591	+	private void heapify() {
592	+	for (int i = size/2; i >= 1; i--)
593	+	fixDown(i);
594	+	}
595	+
596	+	/**
597	+	* Returns the comparator used to order this collection, or <tt>null</tt>
598	+	* if this collection is sorted according to its elements natural ordering
599	+	* (using <tt>Comparable</tt>).
600	+	*
601	+	* @return the comparator used to order this collection, or <tt>null</tt>
602	+	* if this collection is sorted according to its elements natural ordering.
603	+	*/
604		public Comparator<? super E> comparator() {
605		return comparator;
606		}
#	Line 517 | Line 623 | public class PriorityQueue<E> extends Ab
623		s.writeInt(queue.length);
624
625		// Write out all elements in the proper order.
626	<	for (int i=0; i<size; i++)
626	>	for (int i=1; i<=size; i++)
627		s.writeObject(queue[i]);
628		}
629
#	Line 536 | Line 642 | public class PriorityQueue<E> extends Ab
642		queue = new Object[arrayLength];
643
644		// Read in all elements in the proper order.
645	<	for (int i=0; i<size; i++)
646	<	queue[i] = s.readObject();
645	>	for (int i=1; i<=size; i++)
646	>	queue[i] = (E) s.readObject();
647		}
648
649		}
544	–

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines