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

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.32 by dl, Mon Aug 25 23:47:01 2003 UTC vs.
Revision 1.40 by dl, Fri Sep 12 15:38:26 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
17	<	* 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	>	*
18		* <p>The <em>head</em> of this queue is the <em>least</em> element with
19	<	* respect to the specified ordering.
20	<	* If multiple elements are tied for least value, the
21	<	* head is one of those elements. A priority queue does not permit
16	<	* <tt>null</tt> elements.
19	>	* respect to the specified ordering.  If multiple elements are tied for least
20	>	* value, the head is one of those elements. A priority queue does not permit
21	>	* <tt>null</tt> elements.
22		*
23		* <p>The {@link #remove()} and {@link #poll()} methods remove and
24		* return the head of the queue.
#	Line 21 | Line 26
26		* <p>The {@link #element()} and {@link #peek()} methods return, but do
27		* not delete, the head of the queue.
28		*
29	<	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
30	<	* size of the array used internally to store the elements on the
31	<	* queue.
32	<	* It is always at least as large as the queue size.  As
33	<	* elements are added to a priority queue, its capacity grows
34	<	* automatically.  The details of the growth policy are not specified.
29	>	* <p>A priority queue is unbounded, but has a <i>capacity</i>.  The
30	>	* capacity is the size of the array used internally to store the
31	>	* elements on the queue.  It is always at least as large as the queue
32	>	* size.  As elements are added to a priority queue, its capacity
33	>	* grows automatically.  The details of the growth policy are not
34	>	* specified.
35		*
36		* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
37		* guaranteed to traverse the elements of the PriorityQueue in any
#	Line 37 | Line 42
42		* Multiple threads should not access a <tt>PriorityQueue</tt>
43		* instance concurrently if any of the threads modifies the list
44		* structurally. Instead, use the thread-safe {@link
45	<	* java.util.concurrent.BlockingPriorityQueue} class.
45	>	* java.util.concurrent.PriorityBlockingQueue} class.
46		*
47		*
48		* <p>Implementation note: this implementation provides O(log(n)) time
#	Line 51 | Line 56
56		* <a href="{@docRoot}/../guide/collections/index.html">
57		* Java Collections Framework</a>.
58		* @since 1.5
59	+	* @version %I%, %G%
60		* @author Josh Bloch
61		*/
62		public class PriorityQueue<E> extends AbstractQueue<E>
#	Line 150 | Line 156 | public class PriorityQueue<E> extends Ab
156		/**
157		* Initially fill elements of the queue array under the
158		* knowledge that it is sorted or is another PQ, in which
159	<	* case we can just place the elements without fixups.
159	>	* case we can just place the elements in the order presented.
160		*/
161		private void fillFromSorted(Collection<? extends E> c) {
162		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
163		queue[++size] = i.next();
164		}
165
160	–
166		/**
167	<	* Initially fill elements of the queue array that is
168	<	* not to our knowledge sorted, so we must add them
169	<	* one by one.
167	>	* Initially fill elements of the queue array that is not to our knowledge
168	>	* sorted, so we must rearrange the elements to guarantee the heap
169	>	* invariant.
170		*/
171		private void fillFromUnsorted(Collection<? extends E> c) {
172		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
173	<	add(i.next());
173	>	queue[++size] = i.next();
174	>	heapify();
175		}
176
177		/**
#	Line 271 | Line 277 | public class PriorityQueue<E> extends Ab
277		queue = newQueue;
278		}
279
274	–	// Queue Methods
275	–
276	–
280
281		/**
282	<	* Add the specified element to this priority queue.
282	>	* Inserts the specified element to this priority queue.
283		*
284		* @return <tt>true</tt>
285		* @throws ClassCastException if the specified element cannot be compared
#	Line 299 | Line 302 | public class PriorityQueue<E> extends Ab
302		return true;
303		}
304
305	<	public E poll() {
305	>	public E peek() {
306		if (size == 0)
307		return null;
305	–	return (E) remove(1);
306	–	}
307	–
308	–	public E peek() {
308		return (E) queue[1];
309		}
310
#	Line 316 | Line 315 | public class PriorityQueue<E> extends Ab
315		* @return <tt>true</tt> (as per the general contract of
316		* <tt>Collection.add</tt>).
317		*
318	<	* @throws NullPointerException {@inheritDoc}
318	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
319		* @throws ClassCastException if the specified element cannot be compared
320		* with elements currently in the priority queue according
321		* to the priority queue's ordering.
#	Line 335 | Line 334 | public class PriorityQueue<E> extends Ab
334		* <p>
335		* This implementation iterates over the specified collection, and adds
336		* each object returned by the iterator to this collection, in turn.
337	<	* @throws NullPointerException {@inheritDoc}
337	>	* @param c collection whose elements are to be added to this queue
338	>	* @return <tt>true</tt> if this queue changed as a result of the
339	>	*         call.
340	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
341	>	* is <tt>null</tt>
342		* @throws ClassCastException if any element cannot be compared
343		* with elements currently in the priority queue according
344		* to the priority queue's ordering.
#	Line 344 | Line 347 | public class PriorityQueue<E> extends Ab
347		return super.addAll(c);
348		}
349
347	–
348	–	/**
349	–	* Removes a single instance of the specified element from this
350	–	* 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	–	*
361	–	*/
350		public boolean remove(Object o) {
351		if (o == null)
352		return false;
#	Line 366 | Line 354 | public class PriorityQueue<E> extends Ab
354		if (comparator == null) {
355		for (int i = 1; i <= size; i++) {
356		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
357	<	remove(i);
357	>	removeAt(i);
358		return true;
359		}
360		}
361		} else {
362		for (int i = 1; i <= size; i++) {
363		if (comparator.compare((E)queue[i], (E)o) == 0) {
364	<	remove(i);
364	>	removeAt(i);
365		return true;
366		}
367		}
#	Line 392 | Line 380 | public class PriorityQueue<E> extends Ab
380		}
381
382		private class Itr implements Iterator<E> {
383	+
384		/**
385		* Index (into queue array) of element to be returned by
386		* subsequent call to next.
#	Line 399 | Line 388 | public class PriorityQueue<E> extends Ab
388		private int cursor = 1;
389
390		/**
391	<	* Index of element returned by most recent call to next or
392	<	* previous.  Reset to 0 if this element is deleted by a call
393	<	* to remove.
391	>	* Index of element returned by most recent call to next,
392	>	* unless that element came from the forgetMeNot list.
393	>	* Reset to 0 if element is deleted by a call to remove.
394		*/
395		private int lastRet = 0;
396
#	Line 412 | Line 401 | public class PriorityQueue<E> extends Ab
401		*/
402		private int expectedModCount = modCount;
403
404	+	/**
405	+	* A list of elements that were moved from the unvisited portion of
406	+	* the heap into the visited portion as a result of "unlucky" element
407	+	* removals during the iteration.  (Unlucky element removals are those
408	+	* that require a fixup instead of a fixdown.)  We must visit all of
409	+	* the elements in this list to complete the iteration.  We do this
410	+	* after we've completed the "normal" iteration.
411	+	*
412	+	* We expect that most iterations, even those involving removals,
413	+	* will not use need to store elements in this field.
414	+	*/
415	+	private ArrayList<E> forgetMeNot = null;
416	+
417	+	/**
418	+	* Element returned by the most recent call to next iff that
419	+	* element was drawn from the forgetMeNot list.
420	+	*/
421	+	private Object lastRetElt = null;
422	+
423		public boolean hasNext() {
424	<	return cursor <= size;
424	>	return cursor <= size || forgetMeNot != null;
425		}
426
427		public E next() {
428		checkForComodification();
429	<	if (cursor > size)
429	>	E result;
430	>	if (cursor <= size) {
431	>	result = (E) queue[cursor];
432	>	lastRet = cursor++;
433	>	}
434	>	else if (forgetMeNot == null)
435		throw new NoSuchElementException();
436	<	E result = (E) queue[cursor];
437	<	lastRet = cursor++;
436	>	else {
437	>	int remaining = forgetMeNot.size();
438	>	result = forgetMeNot.remove(remaining - 1);
439	>	if (remaining == 1)
440	>	forgetMeNot = null;
441	>	lastRet = 0;
442	>	lastRetElt = result;
443	>	}
444		return result;
445		}
446
447		public void remove() {
429	–	if (lastRet == 0)
430	–	throw new IllegalStateException();
448		checkForComodification();
449
450	<	PriorityQueue.this.remove(lastRet);
451	<	cursor--;
452	<	lastRet = 0;
450	>	if (lastRet != 0) {
451	>	E moved = PriorityQueue.this.removeAt(lastRet);
452	>	lastRet = 0;
453	>	if (moved == null) {
454	>	cursor--;
455	>	} else {
456	>	if (forgetMeNot == null)
457	>	forgetMeNot = new ArrayList<E>();
458	>	forgetMeNot.add(moved);
459	>	}
460	>	} else if (lastRetElt != null) {
461	>	PriorityQueue.this.remove(lastRetElt);
462	>	lastRetElt = null;
463	>	} else {
464	>	throw new IllegalStateException();
465	>	}
466	>
467		expectedModCount = modCount;
468		}
469
#	Line 459 | Line 490 | public class PriorityQueue<E> extends Ab
490		size = 0;
491		}
492
493	+	public E poll() {
494	+	if (size == 0)
495	+	return null;
496	+	modCount++;
497	+
498	+	E result = (E) queue[1];
499	+	queue[1] = queue[size];
500	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
501	+	if (size > 1)
502	+	fixDown(1);
503	+
504	+	return result;
505	+	}
506	+
507		/**
508	<	* Removes and returns the ith element from queue.  Recall
509	<	* that queue is one-based, so 1 <= i <= size.
508	>	* Removes and returns the ith element from queue.  (Recall that queue
509	>	* is one-based, so 1 <= i <= size.)
510		*
511	+	* Normally this method leaves the elements at positions from 1 up to i-1,
512	+	* inclusive, untouched.  Under these circumstances, it returns null.
513	+	* Occasionally, in order to maintain the heap invariant, it must move
514	+	* the last element of the list to some index in the range [2, i-1],
515	+	* and move the element previously at position (i/2) to position i.
516	+	* Under these circumstances, this method returns the element that was
517	+	* previously at the end of the list and is now at some position between
518	+	* 2 and i-1 inclusive.
519		*/
520	<	private E remove(int i) {
521	<	assert i <= size;
520	>	private E removeAt(int i) {
521	>	assert i > 0 && i <= size;
522		modCount++;
523
524	<	E result = (E) queue[i];
525	<	queue[i] = queue[size];
524	>	E moved = (E) queue[size];
525	>	queue[i] = moved;
526		queue[size--] = null;  // Drop extra ref to prevent memory leak
527	<	if (i <= size)
527	>	if (i <= size) {
528		fixDown(i);
529	<	return result;
529	>	if (queue[i] == moved) {
530	>	fixUp(i);
531	>	if (queue[i] != moved)
532	>	return moved;
533	>	}
534	>	}
535	>	return null;
536		}
537
538		/**
#	Line 496 | Line 555 | public class PriorityQueue<E> extends Ab
555		}
556		} else {
557		while (k > 1) {
558	<	int j = k >> 1;
558	>	int j = k >>> 1;
559		if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
560		break;
561		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
#	Line 517 | Line 576 | public class PriorityQueue<E> extends Ab
576		private void fixDown(int k) {
577		int j;
578		if (comparator == null) {
579	<	while ((j = k << 1) <= size && j > 0) {
580	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
579	>	while ((j = k << 1) <= size && (j > 0)) {
580	>	if (j<size &&
581	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
582		j++; // j indexes smallest kid
583	+
584		if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
585		break;
586		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
587		k = j;
588		}
589		} else {
590	<	while ((j = k << 1) <= size && j > 0) {
591	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
590	>	while ((j = k << 1) <= size && (j > 0)) {
591	>	if (j<size &&
592	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
593		j++; // j indexes smallest kid
594		if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
595		break;
#	Line 537 | Line 599 | public class PriorityQueue<E> extends Ab
599		}
600		}
601
602	+	/**
603	+	* Establishes the heap invariant (described above) in the entire tree,
604	+	* assuming nothing about the order of the elements prior to the call.
605	+	*/
606	+	private void heapify() {
607	+	for (int i = size/2; i >= 1; i--)
608	+	fixDown(i);
609	+	}
610
611		/**
612		* Returns the comparator used to order this collection, or <tt>null</tt>
#	Line 568 | Line 638 | public class PriorityQueue<E> extends Ab
638		s.writeInt(queue.length);
639
640		// Write out all elements in the proper order.
641	<	for (int i=0; i<size; i++)
641	>	for (int i=1; i<=size; i++)
642		s.writeObject(queue[i]);
643		}
644
#	Line 587 | Line 657 | public class PriorityQueue<E> extends Ab
657		queue = new Object[arrayLength];
658
659		// Read in all elements in the proper order.
660	<	for (int i=0; i<size; i++)
661	<	queue[i] = s.readObject();
660	>	for (int i=1; i<=size; i++)
661	>	queue[i] = (E) s.readObject();
662		}
663
664		}
595	–

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