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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 1.50 by dl, Wed Jun 2 23:45:46 2004 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	/*
2	>	* %W% %E%
3	>	*
4	>	* Copyright 2004 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 and its iterator implement all of the
36	>	* <em>optional</em> methods of the {@link Collection} and {@link
37	>	* Iterator} interfaces.
38	>	* The
39	>	* Iterator provided in method {@link #iterator()} is <em>not</em>
40		* guaranteed to traverse the elements of the PriorityQueue in any
41		* particular order. If you need ordered traversal, consider using
42		* <tt>Arrays.sort(pq.toArray())</tt>.
#	Line 51 | Line 59
59		* <a href="{@docRoot}/../guide/collections/index.html">
60		* Java Collections Framework</a>.
61		* @since 1.5
62	+	* @version %I%, %G%
63		* @author Josh Bloch
64	+	* @param <E> the type of elements held in this collection
65		*/
66		public class PriorityQueue<E> extends AbstractQueue<E>
67	<	implements Queue<E>, java.io.Serializable {
67	>	implements java.io.Serializable {
68
69		private static final long serialVersionUID = -7720805057305804111L;
70
#	Line 150 | Line 160 | public class PriorityQueue<E> extends Ab
160		/**
161		* Initially fill elements of the queue array under the
162		* knowledge that it is sorted or is another PQ, in which
163	<	* case we can just place the elements without fixups.
163	>	* case we can just place the elements in the order presented.
164		*/
165		private void fillFromSorted(Collection<? extends E> c) {
166		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
167		queue[++size] = i.next();
168		}
169
160	–
170		/**
171	<	* Initially fill elements of the queue array that is
172	<	* not to our knowledge sorted, so we must add them
173	<	* one by one.
171	>	* Initially fill elements of the queue array that is not to our knowledge
172	>	* sorted, so we must rearrange the elements to guarantee the heap
173	>	* invariant.
174		*/
175		private void fillFromUnsorted(Collection<? extends E> c) {
176		for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
177	<	add(i.next());
177	>	queue[++size] = i.next();
178	>	heapify();
179		}
180
181		/**
#	Line 191 | Line 201 | public class PriorityQueue<E> extends Ab
201		public PriorityQueue(Collection<? extends E> c) {
202		initializeArray(c);
203		if (c instanceof SortedSet) {
204	<	// @fixme double-cast workaround for compiler
195	<	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
204	>	SortedSet<? extends E> s = (SortedSet<? extends E>)c;
205		comparator = (Comparator<? super E>)s.comparator();
206		fillFromSorted(s);
207		} else if (c instanceof PriorityQueue) {
#	Line 271 | Line 280 | public class PriorityQueue<E> extends Ab
280		queue = newQueue;
281		}
282
274	–	// Queue Methods
275	–
276	–
283
284		/**
285	<	* Add the specified element to this priority queue.
285	>	* Inserts the specified element into this priority queue.
286		*
287		* @return <tt>true</tt>
288		* @throws ClassCastException if the specified element cannot be compared
#	Line 299 | Line 305 | public class PriorityQueue<E> extends Ab
305		return true;
306		}
307
308	<	public E poll() {
308	>	public E peek() {
309		if (size == 0)
310		return null;
305	–	return (E) remove(1);
306	–	}
307	–
308	–	public E peek() {
311		return (E) queue[1];
312		}
313
#	Line 316 | Line 318 | public class PriorityQueue<E> extends Ab
318		* @return <tt>true</tt> (as per the general contract of
319		* <tt>Collection.add</tt>).
320		*
321	<	* @throws NullPointerException {@inheritDoc}
321	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
322		* @throws ClassCastException if the specified element cannot be compared
323		* with elements currently in the priority queue according
324		* to the priority queue's ordering.
325		*/
326		public boolean add(E o) {
327	<	return super.add(o);
327	>	return offer(o);
328		}
329
328	–
330		/**
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	–	/**
331		* Removes a single instance of the specified element from this
332	<	* 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	<	*
332	>	* queue, if it is present.
333		*/
334		public boolean remove(Object o) {
335		if (o == null)
#	Line 366 | Line 338 | public class PriorityQueue<E> extends Ab
338		if (comparator == null) {
339		for (int i = 1; i <= size; i++) {
340		if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
341	<	remove(i);
341	>	removeAt(i);
342		return true;
343		}
344		}
345		} else {
346		for (int i = 1; i <= size; i++) {
347		if (comparator.compare((E)queue[i], (E)o) == 0) {
348	<	remove(i);
348	>	removeAt(i);
349		return true;
350		}
351		}
#	Line 400 | Line 372 | public class PriorityQueue<E> extends Ab
372		private int cursor = 1;
373
374		/**
375	<	* Index of element returned by most recent call to next or
376	<	* previous.  Reset to 0 if this element is deleted by a call
377	<	* to remove.
375	>	* Index of element returned by most recent call to next,
376	>	* unless that element came from the forgetMeNot list.
377	>	* Reset to 0 if element is deleted by a call to remove.
378		*/
379		private int lastRet = 0;
380
#	Line 413 | Line 385 | public class PriorityQueue<E> extends Ab
385		*/
386		private int expectedModCount = modCount;
387
388	<	// Workarounds until version that better handles remove() installed.
389	<	// These are used to copy-on-write the array upon first remove
390	<	private Object[] q = queue;
391	<	private int qsize = size;
388	>	/**
389	>	* A list of elements that were moved from the unvisited portion of
390	>	* the heap into the visited portion as a result of "unlucky" element
391	>	* removals during the iteration.  (Unlucky element removals are those
392	>	* that require a fixup instead of a fixdown.)  We must visit all of
393	>	* the elements in this list to complete the iteration.  We do this
394	>	* after we've completed the "normal" iteration.
395	>	*
396	>	* We expect that most iterations, even those involving removals,
397	>	* will not use need to store elements in this field.
398	>	*/
399	>	private ArrayList<E> forgetMeNot = null;
400	>
401	>	/**
402	>	* Element returned by the most recent call to next iff that
403	>	* element was drawn from the forgetMeNot list.
404	>	*/
405	>	private Object lastRetElt = null;
406
407		public boolean hasNext() {
408	<	return cursor <= qsize;
408	>	return cursor <= size || forgetMeNot != null;
409		}
410
411		public E next() {
412		checkForComodification();
413	<	if (cursor > qsize)
413	>	E result;
414	>	if (cursor <= size) {
415	>	result = (E) queue[cursor];
416	>	lastRet = cursor++;
417	>	}
418	>	else if (forgetMeNot == null)
419		throw new NoSuchElementException();
420	<	E result = (E) q[cursor];
421	<	lastRet = cursor++;
420	>	else {
421	>	int remaining = forgetMeNot.size();
422	>	result = forgetMeNot.remove(remaining - 1);
423	>	if (remaining == 1)
424	>	forgetMeNot = null;
425	>	lastRet = 0;
426	>	lastRetElt = result;
427	>	}
428		return result;
429		}
430
431		public void remove() {
435	–	if (lastRet == 0)
436	–	throw new IllegalStateException();
432		checkForComodification();
433
434	<	// Copy on first remove
435	<	if (q == queue) {
436	<	q = new Object[queue.length];
437	<	System.arraycopy(queue, 0, q, 0, queue.length);
434	>	if (lastRet != 0) {
435	>	E moved = PriorityQueue.this.removeAt(lastRet);
436	>	lastRet = 0;
437	>	if (moved == null) {
438	>	cursor--;
439	>	} else {
440	>	if (forgetMeNot == null)
441	>	forgetMeNot = new ArrayList<E>();
442	>	forgetMeNot.add(moved);
443	>	}
444	>	} else if (lastRetElt != null) {
445	>	PriorityQueue.this.remove(lastRetElt);
446	>	lastRetElt = null;
447	>	} else {
448	>	throw new IllegalStateException();
449		}
444	–	PriorityQueue.this.remove(q[lastRet]);
450
446	–	lastRet = 0;
451		expectedModCount = modCount;
452		}
453
#	Line 458 | Line 462 | public class PriorityQueue<E> extends Ab
462		}
463
464		/**
465	<	* Remove all elements from the priority queue.
465	>	* Removes all elements from the priority queue.
466	>	* The queue will be empty after this call returns.
467		*/
468		public void clear() {
469		modCount++;
#	Line 470 | Line 475 | public class PriorityQueue<E> extends Ab
475		size = 0;
476		}
477
478	+	public E poll() {
479	+	if (size == 0)
480	+	return null;
481	+	modCount++;
482	+
483	+	E result = (E) queue[1];
484	+	queue[1] = queue[size];
485	+	queue[size--] = null;  // Drop extra ref to prevent memory leak
486	+	if (size > 1)
487	+	fixDown(1);
488	+
489	+	return result;
490	+	}
491	+
492		/**
493	<	* Removes and returns the ith element from queue.  Recall
494	<	* that queue is one-based, so 1 <= i <= size.
493	>	* Removes and returns the ith element from queue.  (Recall that queue
494	>	* is one-based, so 1 <= i <= size.)
495		*
496	+	* Normally this method leaves the elements at positions from 1 up to i-1,
497	+	* inclusive, untouched.  Under these circumstances, it returns null.
498	+	* Occasionally, in order to maintain the heap invariant, it must move
499	+	* the last element of the list to some index in the range [2, i-1],
500	+	* and move the element previously at position (i/2) to position i.
501	+	* Under these circumstances, this method returns the element that was
502	+	* previously at the end of the list and is now at some position between
503	+	* 2 and i-1 inclusive.
504		*/
505	<	private E remove(int i) {
506	<	assert i <= size;
505	>	private E removeAt(int i) {
506	>	assert i > 0 && i <= size;
507		modCount++;
508
509	<	E result = (E) queue[i];
510	<	queue[i] = queue[size];
509	>	E moved = (E) queue[size];
510	>	queue[i] = moved;
511		queue[size--] = null;  // Drop extra ref to prevent memory leak
512		if (i <= size) {
513		fixDown(i);
514	<	fixUp(i);
514	>	if (queue[i] == moved) {
515	>	fixUp(i);
516	>	if (queue[i] != moved)
517	>	return moved;
518	>	}
519		}
520	<
490	<	return result;
520	>	return null;
521		}
522
523		/**
#	Line 552 | Line 582 | public class PriorityQueue<E> extends Ab
582		k = j;
583		}
584		}
555	–
585		}
586
587	+	/**
588	+	* Establishes the heap invariant (described above) in the entire tree,
589	+	* assuming nothing about the order of the elements prior to the call.
590	+	*/
591	+	private void heapify() {
592	+	for (int i = size/2; i >= 1; i--)
593	+	fixDown(i);
594	+	}
595
596		/**
597		* Returns the comparator used to order this collection, or <tt>null</tt>
#	Line 586 | Line 623 | public class PriorityQueue<E> extends Ab
623		s.writeInt(queue.length);
624
625		// Write out all elements in the proper order.
626	<	for (int i=0; i<size; i++)
626	>	for (int i=1; i<=size; i++)
627		s.writeObject(queue[i]);
628		}
629
#	Line 605 | Line 642 | public class PriorityQueue<E> extends Ab
642		queue = new Object[arrayLength];
643
644		// Read in all elements in the proper order.
645	<	for (int i=0; i<size; i++)
646	<	queue[i] = s.readObject();
645	>	for (int i=1; i<=size; i++)
646	>	queue[i] = (E) s.readObject();
647		}
648
649		}
613	–

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