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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.30 by dl, Mon Aug 25 18:33:03 2003 UTC vs.
Revision 1.49 by dl, Thu May 27 11:05:44 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 {@linkplain Queue queue} based on a priority heap.
12	<	* This queue orders
13	<	* elements according to an order specified at construction time, which is
14	<	* specified in the same manner as {@link java.util.TreeSet} and
15	<	* {@link java.util.TreeMap}: elements are ordered
16	<	* either according to their <i>natural order</i> (see {@link Comparable}), or
17	<	* according to a {@link java.util.Comparator}, depending on which
18	<	* constructor is used.
19	<	* <p>The <em>head</em> of this queue is the <em>least</em> element with
13	<	* respect to the specified ordering.
14	<	* If multiple elements are tied for least value, the
15	<	* head is one of those elements. A priority queue does not permit
16	<	* <tt>null</tt> elements.
17	<	*
18	<	* <p>The {@link #remove()} and {@link #poll()} methods remove and
19	<	* return the head of the queue.
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 #element()} and {@link #peek()} methods return, but do
22	<	* not delete, 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>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.
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>The Iterator provided in method {@link #iterator()} is <em>not</em>
35	>	* <p>This class implements all of the <em>optional</em> methods of
36	>	* the {@link Collection} and {@link Iterator} interfaces.  The
37	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
38		* guaranteed to traverse the elements of the PriorityQueue in any
39		* particular order. If you need ordered traversal, consider using
40		* <tt>Arrays.sort(pq.toArray())</tt>.
#	Line 37 | Line 43
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.BlockingPriorityQueue} class.
46	>	* java.util.concurrent.PriorityBlockingQueue} class.
47		*
48		*
49		* <p>Implementation note: this implementation provides O(log(n)) time
#	Line 51 | Line 57
57		* <a href="{@docRoot}/../guide/collections/index.html">
58		* Java Collections Framework</a>.
59		* @since 1.5
60	+	* @version %I%, %G%
61		* @author Josh Bloch
62	+	* @param <E> the type of elements held in this collection
63		*/
64		public class PriorityQueue<E> extends AbstractQueue<E>
65	<	implements Queue<E>, java.io.Serializable {
65	>	implements java.io.Serializable {
66
67	<	static final long serialVersionUID = -7720805057305804111L;
67	>	private static final long serialVersionUID = -7720805057305804111L;
68
69		private static final int DEFAULT_INITIAL_CAPACITY = 11;
70
#	Line 150 | Line 158 | public class PriorityQueue<E> extends Ab
158		/**
159		* Initially fill elements of the queue array under the
160		* knowledge that it is sorted or is another PQ, in which
161	<	* case we can just place the elements without fixups.
161	>	* case we can just place the elements in the order presented.
162		*/
163		private void fillFromSorted(Collection<? extends E> c) {
164		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
165		queue[++size] = i.next();
166		}
167
160	–
168		/**
169	<	* Initially fill elements of the queue array that is
170	<	* not to our knowledge sorted, so we must add them
171	<	* one by one.
169	>	* Initially fill elements of the queue array that is not to our knowledge
170	>	* sorted, so we must rearrange the elements to guarantee the heap
171	>	* invariant.
172		*/
173		private void fillFromUnsorted(Collection<? extends E> c) {
174		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
175	<	add(i.next());
175	>	queue[++size] = i.next();
176	>	heapify();
177		}
178
179		/**
#	Line 191 | Line 199 | public class PriorityQueue<E> extends Ab
199		public PriorityQueue(Collection<? extends E> c) {
200		initializeArray(c);
201		if (c instanceof SortedSet) {
202	<	// @fixme double-cast workaround for compiler
195	<	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
202	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
203		comparator = (Comparator<? super E>)s.comparator();
204		fillFromSorted(s);
205		} else if (c instanceof PriorityQueue) {
#	Line 271 | Line 278 | public class PriorityQueue<E> extends Ab
278		queue = newQueue;
279		}
280
274	–	// Queue Methods
275	–
276	–
281
282		/**
283	<	* Add the specified element to this priority queue.
283	>	* Inserts the specified element into this priority queue.
284		*
285		* @return <tt>true</tt>
286		* @throws ClassCastException if the specified element cannot be compared
#	Line 299 | Line 303 | public class PriorityQueue<E> extends Ab
303		return true;
304		}
305
306	<	public E poll() {
306	>	public E peek() {
307		if (size == 0)
308		return null;
305	–	return (E) remove(1);
306	–	}
307	–
308	–	public E peek() {
309		return (E) queue[1];
310		}
311
#	Line 316 | Line 316 | public class PriorityQueue<E> extends Ab
316		* @return <tt>true</tt> (as per the general contract of
317		* <tt>Collection.add</tt>).
318		*
319	<	* @throws NullPointerException {@inheritDoc}
319	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
320		* @throws ClassCastException if the specified element cannot be compared
321		* with elements currently in the priority queue according
322		* to the priority queue's ordering.
323		*/
324		public boolean add(E o) {
325	<	return super.add(o);
325	>	return offer(o);
326		}
327
328	–
328		/**
330	–	* Adds all of the elements in the specified collection to this queue.
331	–	* The behavior of this operation is undefined if
332	–	* the specified collection is modified while the operation is in
333	–	* progress.  (This implies that the behavior of this call is undefined if
334	–	* the specified collection is this queue, and this queue is nonempty.)
335	–	* <p>
336	–	* This implementation iterates over the specified collection, and adds
337	–	* each object returned by the iterator to this collection, in turn.
338	–	* @throws NullPointerException {@inheritDoc}
339	–	* @throws ClassCastException if any element cannot be compared
340	–	* with elements currently in the priority queue according
341	–	* to the priority queue's ordering.
342	–	*/
343	–	public boolean addAll(Collection<? extends E> c) {
344	–	return super.addAll(c);
345	–	}
346	–
347	–
348	–	/**
329		* Removes a single instance of the specified element from this
330	<	* queue, if it is present.  More formally,
351	<	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
352	<	* o.equals(e))</tt>, if the queue contains one or more such
353	<	* elements.  Returns <tt>true</tt> if the queue contained the
354	<	* specified element (or equivalently, if the queue changed as a
355	<	* result of the call).
356	<	*
357	<	* <p>This implementation iterates over the queue looking for the
358	<	* specified element.  If it finds the element, it removes the element
359	<	* from the queue using the iterator's remove method.<p>
360	<	*
330	>	* collection, if it is present.
331		*/
332		public boolean remove(Object o) {
333		if (o == null)
#	Line 366 | Line 336 | public class PriorityQueue<E> extends Ab
336		if (comparator == null) {
337		for (int i = 1; i <= size; i++) {
338		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
339	<	remove(i);
339	>	removeAt(i);
340		return true;
341		}
342		}
343		} else {
344		for (int i = 1; i <= size; i++) {
345		if (comparator.compare((E)queue[i], (E)o) == 0) {
346	<	remove(i);
346	>	removeAt(i);
347		return true;
348		}
349		}
#	Line 392 | Line 362 | public class PriorityQueue<E> extends Ab
362		}
363
364		private class Itr implements Iterator<E> {
365	+
366		/**
367		* Index (into queue array) of element to be returned by
368		* subsequent call to next.
#	Line 399 | Line 370 | public class PriorityQueue<E> extends Ab
370		private int cursor = 1;
371
372		/**
373	<	* Index of element returned by most recent call to next or
374	<	* previous.  Reset to 0 if this element is deleted by a call
375	<	* to remove.
373	>	* Index of element returned by most recent call to next,
374	>	* unless that element came from the forgetMeNot list.
375	>	* Reset to 0 if element is deleted by a call to remove.
376		*/
377		private int lastRet = 0;
378
#	Line 412 | Line 383 | public class PriorityQueue<E> extends Ab
383		*/
384		private int expectedModCount = modCount;
385
386	+	/**
387	+	* A list of elements that were moved from the unvisited portion of
388	+	* the heap into the visited portion as a result of "unlucky" element
389	+	* removals during the iteration.  (Unlucky element removals are those
390	+	* that require a fixup instead of a fixdown.)  We must visit all of
391	+	* the elements in this list to complete the iteration.  We do this
392	+	* after we've completed the "normal" iteration.
393	+	*
394	+	* We expect that most iterations, even those involving removals,
395	+	* will not use need to store elements in this field.
396	+	*/
397	+	private ArrayList<E> forgetMeNot = null;
398	+
399	+	/**
400	+	* Element returned by the most recent call to next iff that
401	+	* element was drawn from the forgetMeNot list.
402	+	*/
403	+	private Object lastRetElt = null;
404	+
405		public boolean hasNext() {
406	<	return cursor <= size;
406	>	return cursor <= size || forgetMeNot != null;
407		}
408
409		public E next() {
410		checkForComodification();
411	<	if (cursor > size)
411	>	E result;
412	>	if (cursor <= size) {
413	>	result = (E) queue[cursor];
414	>	lastRet = cursor++;
415	>	}
416	>	else if (forgetMeNot == null)
417		throw new NoSuchElementException();
418	<	E result = (E) queue[cursor];
419	<	lastRet = cursor++;
418	>	else {
419	>	int remaining = forgetMeNot.size();
420	>	result = forgetMeNot.remove(remaining - 1);
421	>	if (remaining == 1)
422	>	forgetMeNot = null;
423	>	lastRet = 0;
424	>	lastRetElt = result;
425	>	}
426		return result;
427		}
428
429		public void remove() {
429	–	if (lastRet == 0)
430	–	throw new IllegalStateException();
430		checkForComodification();
431
432	<	PriorityQueue.this.remove(lastRet);
433	<	if (lastRet < cursor)
434	<	cursor--;
435	<	lastRet = 0;
432	>	if (lastRet != 0) {
433	>	E moved = PriorityQueue.this.removeAt(lastRet);
434	>	lastRet = 0;
435	>	if (moved == null) {
436	>	cursor--;
437	>	} else {
438	>	if (forgetMeNot == null)
439	>	forgetMeNot = new ArrayList<E>();
440	>	forgetMeNot.add(moved);
441	>	}
442	>	} else if (lastRetElt != null) {
443	>	PriorityQueue.this.remove(lastRetElt);
444	>	lastRetElt = null;
445	>	} else {
446	>	throw new IllegalStateException();
447	>	}
448	>
449		expectedModCount = modCount;
450		}
451
#	Line 448 | Line 460 | public class PriorityQueue<E> extends Ab
460		}
461
462		/**
463	<	* Remove all elements from the priority queue.
463	>	* Removes all elements from the priority queue.
464	>	* The queue will be empty after this call returns.
465		*/
466		public void clear() {
467		modCount++;
#	Line 460 | Line 473 | public class PriorityQueue<E> extends Ab
473		size = 0;
474		}
475
476	+	public E poll() {
477	+	if (size == 0)
478	+	return null;
479	+	modCount++;
480	+
481	+	E result = (E) queue[1];
482	+	queue[1] = queue[size];
483	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
484	+	if (size > 1)
485	+	fixDown(1);
486	+
487	+	return result;
488	+	}
489	+
490		/**
491	<	* Removes and returns the ith element from queue.  Recall
492	<	* that queue is one-based, so 1 <= i <= size.
491	>	* Removes and returns the ith element from queue.  (Recall that queue
492	>	* is one-based, so 1 <= i <= size.)
493		*
494	<	* XXX: Could further special-case i==size, but is it worth it?
495	<	* XXX: Could special-case i==0, but is it worth it?
494	>	* Normally this method leaves the elements at positions from 1 up to i-1,
495	>	* inclusive, untouched.  Under these circumstances, it returns null.
496	>	* Occasionally, in order to maintain the heap invariant, it must move
497	>	* the last element of the list to some index in the range [2, i-1],
498	>	* and move the element previously at position (i/2) to position i.
499	>	* Under these circumstances, this method returns the element that was
500	>	* previously at the end of the list and is now at some position between
501	>	* 2 and i-1 inclusive.
502		*/
503	<	private E remove(int i) {
504	<	assert i <= size;
503	>	private E removeAt(int i) {
504	>	assert i > 0 && i <= size;
505		modCount++;
506
507	<	E result = (E) queue[i];
508	<	queue[i] = queue[size];
507	>	E moved = (E) queue[size];
508	>	queue[i] = moved;
509		queue[size--] = null;  // Drop extra ref to prevent memory leak
510	<	if (i <= size)
510	>	if (i <= size) {
511		fixDown(i);
512	<	return result;
512	>	if (queue[i] == moved) {
513	>	fixUp(i);
514	>	if (queue[i] != moved)
515	>	return moved;
516	>	}
517	>	}
518	>	return null;
519		}
520
521		/**
#	Line 499 | Line 538 | public class PriorityQueue<E> extends Ab
538		}
539		} else {
540		while (k > 1) {
541	<	int j = k >> 1;
541	>	int j = k >>> 1;
542		if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
543		break;
544		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
#	Line 520 | Line 559 | public class PriorityQueue<E> extends Ab
559		private void fixDown(int k) {
560		int j;
561		if (comparator == null) {
562	<	while ((j = k << 1) <= size) {
563	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
562	>	while ((j = k << 1) <= size && (j > 0)) {
563	>	if (j<size &&
564	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
565		j++; // j indexes smallest kid
566	+
567		if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
568		break;
569		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
570		k = j;
571		}
572		} else {
573	<	while ((j = k << 1) <= size) {
574	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
573	>	while ((j = k << 1) <= size && (j > 0)) {
574	>	if (j<size &&
575	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
576		j++; // j indexes smallest kid
577		if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
578		break;
#	Line 540 | Line 582 | public class PriorityQueue<E> extends Ab
582		}
583		}
584
585	+	/**
586	+	* Establishes the heap invariant (described above) in the entire tree,
587	+	* assuming nothing about the order of the elements prior to the call.
588	+	*/
589	+	private void heapify() {
590	+	for (int i = size/2; i >= 1; i--)
591	+	fixDown(i);
592	+	}
593
594		/**
595		* Returns the comparator used to order this collection, or <tt>null</tt>
#	Line 571 | Line 621 | public class PriorityQueue<E> extends Ab
621		s.writeInt(queue.length);
622
623		// Write out all elements in the proper order.
624	<	for (int i=0; i<size; i++)
624	>	for (int i=1; i<=size; i++)
625		s.writeObject(queue[i]);
626		}
627
#	Line 590 | Line 640 | public class PriorityQueue<E> extends Ab
640		queue = new Object[arrayLength];
641
642		// Read in all elements in the proper order.
643	<	for (int i=0; i<size; i++)
644	<	queue[i] = s.readObject();
643	>	for (int i=1; i<=size; i++)
644	>	queue[i] = (E) s.readObject();
645		}
646
647		}
598	–

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