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 1.32 by dl, Mon Aug 25 23:47:01 2003 UTC vs.
Revision 1.44 by dl, Sat Oct 18 12:29:27 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
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 base class of all elements held in this collection
63		*/
64		public class PriorityQueue<E> extends AbstractQueue<E>
65		implements Queue<E>, java.io.Serializable {
#	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 271 | Line 279 | public class PriorityQueue<E> extends Ab
279		queue = newQueue;
280		}
281
274	–	// Queue Methods
275	–
276	–
282
283		/**
284	<	* Add the specified element to this priority queue.
284	>	* Inserts the specified element into this priority queue.
285		*
286		* @return <tt>true</tt>
287		* @throws ClassCastException if the specified element cannot be compared
#	Line 299 | Line 304 | public class PriorityQueue<E> extends Ab
304		return true;
305		}
306
307	<	public E poll() {
307	>	public E peek() {
308		if (size == 0)
309		return null;
305	–	return (E) remove(1);
306	–	}
307	–
308	–	public E peek() {
310		return (E) queue[1];
311		}
312
#	Line 316 | Line 317 | public class PriorityQueue<E> extends Ab
317		* @return <tt>true</tt> (as per the general contract of
318		* <tt>Collection.add</tt>).
319		*
320	<	* @throws NullPointerException {@inheritDoc}
320	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
321		* @throws ClassCastException if the specified element cannot be compared
322		* with elements currently in the priority queue according
323		* to the priority queue's ordering.
324		*/
325		public boolean add(E o) {
326	<	return super.add(o);
326	<	}
327	<
328	<
329	<	/**
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);
326	>	return offer(o);
327		}
328
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	–	*/
329		public boolean remove(Object o) {
330		if (o == null)
331		return false;
#	Line 366 | Line 333 | public class PriorityQueue<E> extends Ab
333		if (comparator == null) {
334		for (int i = 1; i <= size; i++) {
335		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
336	<	remove(i);
336	>	removeAt(i);
337		return true;
338		}
339		}
340		} else {
341		for (int i = 1; i <= size; i++) {
342		if (comparator.compare((E)queue[i], (E)o) == 0) {
343	<	remove(i);
343	>	removeAt(i);
344		return true;
345		}
346		}
#	Line 392 | Line 359 | public class PriorityQueue<E> extends Ab
359		}
360
361		private class Itr implements Iterator<E> {
362	+
363		/**
364		* Index (into queue array) of element to be returned by
365		* subsequent call to next.
#	Line 399 | Line 367 | public class PriorityQueue<E> extends Ab
367		private int cursor = 1;
368
369		/**
370	<	* Index of element returned by most recent call to next or
371	<	* previous.  Reset to 0 if this element is deleted by a call
372	<	* to remove.
370	>	* Index of element returned by most recent call to next,
371	>	* unless that element came from the forgetMeNot list.
372	>	* Reset to 0 if element is deleted by a call to remove.
373		*/
374		private int lastRet = 0;
375
#	Line 412 | Line 380 | public class PriorityQueue<E> extends Ab
380		*/
381		private int expectedModCount = modCount;
382
383	+	/**
384	+	* A list of elements that were moved from the unvisited portion of
385	+	* the heap into the visited portion as a result of "unlucky" element
386	+	* removals during the iteration.  (Unlucky element removals are those
387	+	* that require a fixup instead of a fixdown.)  We must visit all of
388	+	* the elements in this list to complete the iteration.  We do this
389	+	* after we've completed the "normal" iteration.
390	+	*
391	+	* We expect that most iterations, even those involving removals,
392	+	* will not use need to store elements in this field.
393	+	*/
394	+	private ArrayList<E> forgetMeNot = null;
395	+
396	+	/**
397	+	* Element returned by the most recent call to next iff that
398	+	* element was drawn from the forgetMeNot list.
399	+	*/
400	+	private Object lastRetElt = null;
401	+
402		public boolean hasNext() {
403	<	return cursor <= size;
403	>	return cursor <= size || forgetMeNot != null;
404		}
405
406		public E next() {
407		checkForComodification();
408	<	if (cursor > size)
408	>	E result;
409	>	if (cursor <= size) {
410	>	result = (E) queue[cursor];
411	>	lastRet = cursor++;
412	>	}
413	>	else if (forgetMeNot == null)
414		throw new NoSuchElementException();
415	<	E result = (E) queue[cursor];
416	<	lastRet = cursor++;
415	>	else {
416	>	int remaining = forgetMeNot.size();
417	>	result = forgetMeNot.remove(remaining - 1);
418	>	if (remaining == 1)
419	>	forgetMeNot = null;
420	>	lastRet = 0;
421	>	lastRetElt = result;
422	>	}
423		return result;
424		}
425
426		public void remove() {
429	–	if (lastRet == 0)
430	–	throw new IllegalStateException();
427		checkForComodification();
428
429	<	PriorityQueue.this.remove(lastRet);
430	<	cursor--;
431	<	lastRet = 0;
429	>	if (lastRet != 0) {
430	>	E moved = PriorityQueue.this.removeAt(lastRet);
431	>	lastRet = 0;
432	>	if (moved == null) {
433	>	cursor--;
434	>	} else {
435	>	if (forgetMeNot == null)
436	>	forgetMeNot = new ArrayList<E>();
437	>	forgetMeNot.add(moved);
438	>	}
439	>	} else if (lastRetElt != null) {
440	>	PriorityQueue.this.remove(lastRetElt);
441	>	lastRetElt = null;
442	>	} else {
443	>	throw new IllegalStateException();
444	>	}
445	>
446		expectedModCount = modCount;
447		}
448
#	Line 459 | Line 469 | public class PriorityQueue<E> extends Ab
469		size = 0;
470		}
471
472	+	public E poll() {
473	+	if (size == 0)
474	+	return null;
475	+	modCount++;
476	+
477	+	E result = (E) queue[1];
478	+	queue[1] = queue[size];
479	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
480	+	if (size > 1)
481	+	fixDown(1);
482	+
483	+	return result;
484	+	}
485	+
486		/**
487	<	* Removes and returns the ith element from queue.  Recall
488	<	* that queue is one-based, so 1 <= i <= size.
487	>	* Removes and returns the ith element from queue.  (Recall that queue
488	>	* is one-based, so 1 <= i <= size.)
489		*
490	+	* Normally this method leaves the elements at positions from 1 up to i-1,
491	+	* inclusive, untouched.  Under these circumstances, it returns null.
492	+	* Occasionally, in order to maintain the heap invariant, it must move
493	+	* the last element of the list to some index in the range [2, i-1],
494	+	* and move the element previously at position (i/2) to position i.
495	+	* Under these circumstances, this method returns the element that was
496	+	* previously at the end of the list and is now at some position between
497	+	* 2 and i-1 inclusive.
498		*/
499	<	private E remove(int i) {
500	<	assert i <= size;
499	>	private E removeAt(int i) {
500	>	assert i > 0 && i <= size;
501		modCount++;
502
503	<	E result = (E) queue[i];
504	<	queue[i] = queue[size];
503	>	E moved = (E) queue[size];
504	>	queue[i] = moved;
505		queue[size--] = null;  // Drop extra ref to prevent memory leak
506	<	if (i <= size)
506	>	if (i <= size) {
507		fixDown(i);
508	<	return result;
508	>	if (queue[i] == moved) {
509	>	fixUp(i);
510	>	if (queue[i] != moved)
511	>	return moved;
512	>	}
513	>	}
514	>	return null;
515		}
516
517		/**
#	Line 496 | Line 534 | public class PriorityQueue<E> extends Ab
534		}
535		} else {
536		while (k > 1) {
537	<	int j = k >> 1;
537	>	int j = k >>> 1;
538		if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
539		break;
540		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
#	Line 517 | Line 555 | public class PriorityQueue<E> extends Ab
555		private void fixDown(int k) {
556		int j;
557		if (comparator == null) {
558	<	while ((j = k << 1) <= size && j > 0) {
559	<	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
558	>	while ((j = k << 1) <= size && (j > 0)) {
559	>	if (j<size &&
560	>	((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
561		j++; // j indexes smallest kid
562	+
563		if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
564		break;
565		Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
566		k = j;
567		}
568		} else {
569	<	while ((j = k << 1) <= size && j > 0) {
570	<	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
569	>	while ((j = k << 1) <= size && (j > 0)) {
570	>	if (j<size &&
571	>	comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
572		j++; // j indexes smallest kid
573		if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
574		break;
#	Line 537 | Line 578 | public class PriorityQueue<E> extends Ab
578		}
579		}
580
581	+	/**
582	+	* Establishes the heap invariant (described above) in the entire tree,
583	+	* assuming nothing about the order of the elements prior to the call.
584	+	*/
585	+	private void heapify() {
586	+	for (int i = size/2; i >= 1; i--)
587	+	fixDown(i);
588	+	}
589
590		/**
591		* Returns the comparator used to order this collection, or <tt>null</tt>
#	Line 568 | Line 617 | public class PriorityQueue<E> extends Ab
617		s.writeInt(queue.length);
618
619		// Write out all elements in the proper order.
620	<	for (int i=0; i<size; i++)
620	>	for (int i=1; i<=size; i++)
621		s.writeObject(queue[i]);
622		}
623
#	Line 587 | Line 636 | public class PriorityQueue<E> extends Ab
636		queue = new Object[arrayLength];
637
638		// Read in all elements in the proper order.
639	<	for (int i=0; i<size; i++)
640	<	queue[i] = s.readObject();
639	>	for (int i=1; i<=size; i++)
640	>	queue[i] = (E) s.readObject();
641		}
642
643		}
595	–

Diff Legend

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