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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.31 by dl, Mon Aug 25 19:27:54 2003 UTC vs.
Revision 1.38 by dl, Mon Sep 1 12:23:28 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	>	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
10	<	* according to a {@link java.util.Comparator}, depending on which
11	<	* constructor is used.
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.
19	<	* If multiple elements are tied for least value, the
15	<	* head is one of those elements. A priority queue does not permit
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
#	Line 37 | Line 41
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.BlockingPriorityQueue} class.
44	>	* java.util.concurrent.PriorityBlockingQueue} class.
45		*
46		*
47		* <p>Implementation note: this implementation provides O(log(n)) time
#	Line 51 | Line 55
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>
#	Line 150 | Line 155 | public class PriorityQueue<E> extends Ab
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 without fixups.
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
160	–
165		/**
166	<	* Initially fill elements of the queue array that is
167	<	* not to our knowledge sorted, so we must add them
168	<	* one by one.
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	<	add(i.next());
172	>	queue[++size] = i.next();
173	>	heapify();
174		}
175
176		/**
#	Line 271 | Line 276 | public class PriorityQueue<E> extends Ab
276		queue = newQueue;
277		}
278
274	–	// Queue Methods
275	–
279
280	+	// Queue Methods
281
282		/**
283		* Add the specified element to this priority queue.
#	Line 302 | Line 306 | public class PriorityQueue<E> extends Ab
306		public E poll() {
307		if (size == 0)
308		return null;
309	<	return (E) remove(1);
309	>	return remove();
310		}
311
312		public E peek() {
#	Line 345 | Line 349 | public class PriorityQueue<E> extends Ab
349		}
350
351
352	<	/**
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 :
#	Line 366 | Line 370 | public class PriorityQueue<E> extends Ab
370		if (comparator == null) {
371		for (int i = 1; i <= size; i++) {
372		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
373	<	remove(i);
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	<	remove(i);
380	>	removeAt(i);
381		return true;
382		}
383		}
#	Line 392 | Line 396 | public class PriorityQueue<E> extends Ab
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.
#	Line 399 | Line 404 | public class PriorityQueue<E> extends Ab
404		private int cursor = 1;
405
406		/**
407	<	* Index of element returned by most recent call to next or
408	<	* previous.  Reset to 0 if this element is deleted by a call
409	<	* to remove.
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
#	Line 412 | Line 417 | public class PriorityQueue<E> extends Ab
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;
440	>	return cursor <= size || forgetMeNot != null;
441		}
442
443		public E next() {
444		checkForComodification();
445	<	if (cursor > size)
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	<	E result = (E) queue[cursor];
453	<	lastRet = cursor++;
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() {
429	–	if (lastRet == 0)
430	–	throw new IllegalStateException();
464		checkForComodification();
465
466	<	PriorityQueue.this.remove(lastRet);
467	<	if (lastRet < cursor)
468	<	cursor--;
469	<	lastRet = 0;
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
#	Line 461 | Line 507 | public class PriorityQueue<E> extends Ab
507		}
508
509		/**
510	<	* Removes and returns the ith element from queue.  Recall
511	<	* that queue is one-based, so 1 <= i <= size.
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	>	/**
527	>	* Removes and returns the ith element from queue.  (Recall that queue
528	>	* is one-based, so 1 <= i <= size.)
529		*
530	<	* XXX: Could further special-case i==size, but is it worth it?
531	<	* XXX: Could special-case i==0, but is it worth it?
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 remove(int i) {
540	<	assert i <= size;
539	>	private E removeAt(int i) {
540	>	assert i > 0 && i <= size;
541		modCount++;
542
543	<	E result = (E) queue[i];
544	<	queue[i] = queue[size];
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)
546	>	if (i <= size) {
547		fixDown(i);
548	<	return result;
548	>	if (queue[i] == moved) {
549	>	fixUp(i);
550	>	if (queue[i] != moved)
551	>	return moved;
552	>	}
553	>	}
554	>	return null;
555		}
556
557		/**
#	Line 499 | Line 574 | public class PriorityQueue<E> extends Ab
574		}
575		} else {
576		while (k > 1) {
577	<	int j = 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;
#	Line 520 | Line 595 | public class PriorityQueue<E> extends Ab
595		private void fixDown(int k) {
596		int j;
597		if (comparator == null) {
598	<	while ((j = k << 1) <= size) {
599	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
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) {
610	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
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;
#	Line 540 | Line 618 | public class PriorityQueue<E> extends Ab
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>
#	Line 591 | Line 677 | public class PriorityQueue<E> extends Ab
677
678		// Read in all elements in the proper order.
679		for (int i=0; i<size; i++)
680	<	queue[i] = s.readObject();
680	>	queue[i] = (E) s.readObject();
681		}
682
683		}
598	–

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