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

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.25 by tim, Wed Aug 6 18:42:49 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		/**
4	<	* An unbounded priority {@linkplain Queue queue} based on a priority heap.
5	<	* This queue orders
6	<	* elements according to an order specified at construction time, which is
7	<	* specified in the same manner as {@link java.util.TreeSet} and
8	<	* {@link java.util.TreeMap}: elements are ordered
9	<	* 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.
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.
12	<	* If multiple elements are tied for least value, the
15	<	* head is one of those elements. A priority queue does not permit
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
#	Line 28 | Line 25
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
#	Line 44 | Line 53
53		public class PriorityQueue<E> extends AbstractQueue<E>
54		implements Queue<E>, java.io.Serializable {
55
56	+	private static final long serialVersionUID = -7720805057305804111L;
57	+
58		private static final int DEFAULT_INITIAL_CAPACITY = 11;
59
60		/**
#	Line 136 | Line 147 | public class PriorityQueue<E> extends Ab
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 without fixups.
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
146	–
157		/**
158	<	* Initially fill elements of the queue array that is
159	<	* not to our knowledge sorted, so we must add them
160	<	* one by one.
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	<	add(i.next());
164	>	queue[++size] = i.next();
165	>	heapify();
166		}
167
168		/**
#	Line 176 | Line 187 | public class PriorityQueue<E> extends Ab
187		*/
188		public PriorityQueue(Collection<? extends E> c) {
189		initializeArray(c);
190	<	if (c instanceof SortedSet<? extends E>) {
191	<	SortedSet<? extends E> s = (SortedSet<? extends E>) 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	<	}
184	<	else if (c instanceof PriorityQueue<? extends E>) {
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	<	}
189	<	else {
199	>	} else {
200		comparator = null;
201		fillFromUnsorted(c);
202		}
#	Line 258 | Line 268 | public class PriorityQueue<E> extends Ab
268		queue = newQueue;
269		}
270
261	–	// Queue Methods
262	–
271
272	+	// Queue Methods
273
274		/**
275		* Add the specified element to this priority queue.
#	Line 289 | Line 298 | public class PriorityQueue<E> extends Ab
298		public E poll() {
299		if (size == 0)
300		return null;
301	<	return (E) remove(1);
301	>	return remove();
302		}
303
304		public E peek() {
#	Line 332 | Line 341 | public class PriorityQueue<E> extends Ab
341		}
342
343
344	<	/**
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 :
#	Line 353 | Line 362 | public class PriorityQueue<E> extends Ab
362		if (comparator == null) {
363		for (int i = 1; i <= size; i++) {
364		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
365	<	remove(i);
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	<	remove(i);
372	>	removeAt(i);
373		return true;
374		}
375		}
#	Line 379 | Line 388 | public class PriorityQueue<E> extends Ab
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.
#	Line 386 | Line 396 | public class PriorityQueue<E> extends Ab
396		private int cursor = 1;
397
398		/**
399	<	* Index of element returned by most recent call to next or
400	<	* previous.  Reset to 0 if this element is deleted by a call
401	<	* to remove.
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
#	Line 399 | Line 409 | public class PriorityQueue<E> extends Ab
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;
432	>	return cursor <= size || forgetMeNot != null;
433		}
434
435		public E next() {
436		checkForComodification();
437	<	if (cursor > size)
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	<	E result = (E) queue[cursor];
445	<	lastRet = cursor++;
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() {
416	–	if (lastRet == 0)
417	–	throw new IllegalStateException();
456		checkForComodification();
457
458	<	PriorityQueue.this.remove(lastRet);
459	<	if (lastRet < cursor)
460	<	cursor--;
461	<	lastRet = 0;
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
#	Line 448 | Line 499 | public class PriorityQueue<E> extends Ab
499		}
500
501		/**
502	<	* Removes and returns the ith element from queue.  Recall
503	<	* that queue is one-based, so 1 <= i <= size.
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	>	/**
519	>	* Removes and returns the ith element from queue.  (Recall that queue
520	>	* is one-based, so 1 <= i <= size.)
521		*
522	<	* XXX: Could further special-case i==size, but is it worth it?
523	<	* XXX: Could special-case i==0, but is it worth it?
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 remove(int i) {
532	<	assert i <= size;
531	>	private E removeAt(int i) {
532	>	assert i > 0 && i <= size;
533		modCount++;
534
535	<	E result = (E) queue[i];
536	<	queue[i] = queue[size];
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)
538	>	if (i <= size) {
539		fixDown(i);
540	<	return result;
540	>	if (queue[i] == moved) {
541	>	fixUp(i);
542	>	if (queue[i] != moved)
543	>	return moved;
544	>	}
545	>	}
546	>	return null;
547		}
548
549		/**
#	Line 486 | Line 566 | public class PriorityQueue<E> extends Ab
566		}
567		} else {
568		while (k > 1) {
569	<	int j = 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;
#	Line 507 | Line 587 | public class PriorityQueue<E> extends Ab
587		private void fixDown(int k) {
588		int j;
589		if (comparator == null) {
590	<	while ((j = k << 1) <= size) {
591	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
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) {
602	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
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;
#	Line 527 | Line 610 | public class PriorityQueue<E> extends Ab
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>
#	Line 582 | Line 673 | public class PriorityQueue<E> extends Ab
673		}
674
675		}
585	–

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