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

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.35 by dl, Wed Aug 27 10:27:07 2003 UTC vs.
Revision 1.46 by dl, Mon Dec 29 19:05:19 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 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 {
#	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	–
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);
345	–	}
346	–
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	–	*/
328		public boolean remove(Object o) {
329		if (o == null)
330		return false;
#	Line 366 | Line 332 | public class PriorityQueue<E> extends Ab
332		if (comparator == null) {
333		for (int i = 1; i <= size; i++) {
334		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
335	<	remove(i);
335	>	removeAt(i);
336		return true;
337		}
338		}
339		} else {
340		for (int i = 1; i <= size; i++) {
341		if (comparator.compare((E)queue[i], (E)o) == 0) {
342	<	remove(i);
342	>	removeAt(i);
343		return true;
344		}
345		}
#	Line 400 | Line 366 | public class PriorityQueue<E> extends Ab
366		private int cursor = 1;
367
368		/**
369	<	* Index of element returned by most recent call to next or
370	<	* previous.  Reset to 0 if this element is deleted by a call
371	<	* to remove.
369	>	* Index of element returned by most recent call to next,
370	>	* unless that element came from the forgetMeNot list.
371	>	* Reset to 0 if element is deleted by a call to remove.
372		*/
373		private int lastRet = 0;
374
#	Line 413 | Line 379 | public class PriorityQueue<E> extends Ab
379		*/
380		private int expectedModCount = modCount;
381
382	<	// Workarounds until version that better handles remove() installed.
383	<	// These are used to copy-on-write the array upon first remove
384	<	private Object[] q = queue;
385	<	private int qsize = size;
382	>	/**
383	>	* A list of elements that were moved from the unvisited portion of
384	>	* the heap into the visited portion as a result of "unlucky" element
385	>	* removals during the iteration.  (Unlucky element removals are those
386	>	* that require a fixup instead of a fixdown.)  We must visit all of
387	>	* the elements in this list to complete the iteration.  We do this
388	>	* after we've completed the "normal" iteration.
389	>	*
390	>	* We expect that most iterations, even those involving removals,
391	>	* will not use need to store elements in this field.
392	>	*/
393	>	private ArrayList<E> forgetMeNot = null;
394	>
395	>	/**
396	>	* Element returned by the most recent call to next iff that
397	>	* element was drawn from the forgetMeNot list.
398	>	*/
399	>	private Object lastRetElt = null;
400
401		public boolean hasNext() {
402	<	return cursor <= qsize;
402	>	return cursor <= size || forgetMeNot != null;
403		}
404
405		public E next() {
406		checkForComodification();
407	<	if (cursor > qsize)
407	>	E result;
408	>	if (cursor <= size) {
409	>	result = (E) queue[cursor];
410	>	lastRet = cursor++;
411	>	}
412	>	else if (forgetMeNot == null)
413		throw new NoSuchElementException();
414	<	E result = (E) q[cursor];
415	<	lastRet = cursor++;
414	>	else {
415	>	int remaining = forgetMeNot.size();
416	>	result = forgetMeNot.remove(remaining - 1);
417	>	if (remaining == 1)
418	>	forgetMeNot = null;
419	>	lastRet = 0;
420	>	lastRetElt = result;
421	>	}
422		return result;
423		}
424
425		public void remove() {
435	–	if (lastRet == 0)
436	–	throw new IllegalStateException();
426		checkForComodification();
427
428	<	// Copy on first remove
429	<	if (q == queue) {
430	<	q = new Object[queue.length];
431	<	System.arraycopy(queue, 0, q, 0, queue.length);
428	>	if (lastRet != 0) {
429	>	E moved = PriorityQueue.this.removeAt(lastRet);
430	>	lastRet = 0;
431	>	if (moved == null) {
432	>	cursor--;
433	>	} else {
434	>	if (forgetMeNot == null)
435	>	forgetMeNot = new ArrayList<E>();
436	>	forgetMeNot.add(moved);
437	>	}
438	>	} else if (lastRetElt != null) {
439	>	PriorityQueue.this.remove(lastRetElt);
440	>	lastRetElt = null;
441	>	} else {
442	>	throw new IllegalStateException();
443		}
444	–	PriorityQueue.this.remove(q[lastRet]);
444
446	–	lastRet = 0;
445		expectedModCount = modCount;
446		}
447
#	Line 470 | Line 468 | public class PriorityQueue<E> extends Ab
468		size = 0;
469		}
470
471	+	public E poll() {
472	+	if (size == 0)
473	+	return null;
474	+	modCount++;
475	+
476	+	E result = (E) queue[1];
477	+	queue[1] = queue[size];
478	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
479	+	if (size > 1)
480	+	fixDown(1);
481	+
482	+	return result;
483	+	}
484	+
485		/**
486	<	* Removes and returns the ith element from queue.  Recall
487	<	* that queue is one-based, so 1 <= i <= size.
486	>	* Removes and returns the ith element from queue.  (Recall that queue
487	>	* is one-based, so 1 <= i <= size.)
488		*
489	+	* Normally this method leaves the elements at positions from 1 up to i-1,
490	+	* inclusive, untouched.  Under these circumstances, it returns null.
491	+	* Occasionally, in order to maintain the heap invariant, it must move
492	+	* the last element of the list to some index in the range [2, i-1],
493	+	* and move the element previously at position (i/2) to position i.
494	+	* Under these circumstances, this method returns the element that was
495	+	* previously at the end of the list and is now at some position between
496	+	* 2 and i-1 inclusive.
497		*/
498	<	private E remove(int i) {
499	<	assert i <= size;
498	>	private E removeAt(int i) {
499	>	assert i > 0 && i <= size;
500		modCount++;
501
502	<	E result = (E) queue[i];
503	<	queue[i] = queue[size];
502	>	E moved = (E) queue[size];
503	>	queue[i] = moved;
504		queue[size--] = null;  // Drop extra ref to prevent memory leak
505		if (i <= size) {
506		fixDown(i);
507	<	fixUp(i);
507	>	if (queue[i] == moved) {
508	>	fixUp(i);
509	>	if (queue[i] != moved)
510	>	return moved;
511	>	}
512		}
513	<
490	<	return result;
513	>	return null;
514		}
515
516		/**
#	Line 552 | Line 575 | public class PriorityQueue<E> extends Ab
575		k = j;
576		}
577		}
555	–
578		}
579
580	+	/**
581	+	* Establishes the heap invariant (described above) in the entire tree,
582	+	* assuming nothing about the order of the elements prior to the call.
583	+	*/
584	+	private void heapify() {
585	+	for (int i = size/2; i >= 1; i--)
586	+	fixDown(i);
587	+	}
588
589		/**
590		* Returns the comparator used to order this collection, or <tt>null</tt>
#	Line 586 | Line 616 | public class PriorityQueue<E> extends Ab
616		s.writeInt(queue.length);
617
618		// Write out all elements in the proper order.
619	<	for (int i=0; i<size; i++)
619	>	for (int i=1; i<=size; i++)
620		s.writeObject(queue[i]);
621		}
622
#	Line 605 | Line 635 | public class PriorityQueue<E> extends Ab
635		queue = new Object[arrayLength];
636
637		// Read in all elements in the proper order.
638	<	for (int i=0; i<size; i++)
639	<	queue[i] = s.readObject();
638	>	for (int i=1; i<=size; i++)
639	>	queue[i] = (E) s.readObject();
640		}
641
642		}
613	–

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