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 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.29 by dl, Sun Aug 24 23:31:53 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
2	<
3	<	import java.util.*;
1	>	package java.util;
2
3		/**
4	<	* An unbounded (resizable) priority queue based on a priority
5	<	* heap.The take operation returns the least element with respect to
6	<	* the given ordering. (If more than one element is tied for least
7	<	* value, one of them is arbitrarily chosen to be returned -- no
8	<	* guarantees are made for ordering across ties.) Ordering follows the
9	<	* java.util.Collection conventions: Either the elements must be
10	<	* Comparable, or a Comparator must be supplied. Comparison failures
11	<	* throw ClassCastExceptions during insertions and extractions.
12	<	**/
13	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
14	<	public PriorityQueue(int initialCapacity) {}
15	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
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.
12	>	* <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.
20	>	*
21	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
22	>	* not delete, the head of the queue.
23	>	*
24	>	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
25	>	* size of the array used internally to store the elements on the
26	>	* queue.
27	>	* It is always at least as large as the queue size.  As
28	>	* elements are added to a priority queue, its capacity grows
29	>	* automatically.  The details of the growth policy are not specified.
30	>	*
31	>	* <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
32	>	* guaranteed to traverse the elements of the PriorityQueue in any
33	>	* particular order. If you need ordered traversal, consider using
34	>	* <tt>Arrays.sort(pq.toArray())</tt>.
35	>	*
36	>	* <p> <strong>Note that this implementation is not synchronized.</strong>
37	>	* Multiple threads should not access a <tt>PriorityQueue</tt>
38	>	* instance concurrently if any of the threads modifies the list
39	>	* structurally. Instead, use the thread-safe {@link
40	>	* java.util.concurrent.BlockingPriorityQueue} class.
41	>	*
42	>	*
43	>	* <p>Implementation note: this implementation provides O(log(n)) time
44	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
45	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
46	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
47	>	* constant time for the retrieval methods (<tt>peek</tt>,
48	>	* <tt>element</tt>, and <tt>size</tt>).
49	>	*
50	>	* <p>This class is a member of the
51	>	* <a href="{@docRoot}/../guide/collections/index.html">
52	>	* Java Collections Framework</a>.
53	>	* @since 1.5
54	>	* @author Josh Bloch
55	>	*/
56	>	public class PriorityQueue<E> extends AbstractQueue<E>
57	>	implements Queue<E>, java.io.Serializable {
58
59	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
59	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
60
61	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
61	>	/**
62	>	* Priority queue represented as a balanced binary heap: the two children
63	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
64	>	* ordered by comparator, or by the elements' natural ordering, if
65	>	* comparator is null:  For each node n in the heap and each descendant d
66	>	* of n, n <= d.
67	>	*
68	>	* The element with the lowest value is in queue[1], assuming the queue is
69	>	* nonempty.  (A one-based array is used in preference to the traditional
70	>	* zero-based array to simplify parent and child calculations.)
71	>	*
72	>	* queue.length must be >= 2, even if size == 0.
73	>	*/
74	>	private transient Object[] queue;
75
76	<	public boolean add(E x) {
77	<	return false;
76	>	/**
77	>	* The number of elements in the priority queue.
78	>	*/
79	>	private int size = 0;
80	>
81	>	/**
82	>	* The comparator, or null if priority queue uses elements'
83	>	* natural ordering.
84	>	*/
85	>	private final Comparator<? super E> comparator;
86	>
87	>	/**
88	>	* The number of times this priority queue has been
89	>	* <i>structurally modified</i>.  See AbstractList for gory details.
90	>	*/
91	>	private transient int modCount = 0;
92	>
93	>	/**
94	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
95	>	* (11) that orders its elements according to their natural
96	>	* ordering (using <tt>Comparable</tt>).
97	>	*/
98	>	public PriorityQueue() {
99	>	this(DEFAULT_INITIAL_CAPACITY, null);
100		}
101	<	public boolean offer(E x) {
102	<	return false;
101	>
102	>	/**
103	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
104	>	* that orders its elements according to their natural ordering
105	>	* (using <tt>Comparable</tt>).
106	>	*
107	>	* @param initialCapacity the initial capacity for this priority queue.
108	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
109	>	* than 1
110	>	*/
111	>	public PriorityQueue(int initialCapacity) {
112	>	this(initialCapacity, null);
113		}
114	<	public boolean remove(Object x) {
115	<	return false;
114	>
115	>	/**
116	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
117	>	* that orders its elements according to the specified comparator.
118	>	*
119	>	* @param initialCapacity the initial capacity for this priority queue.
120	>	* @param comparator the comparator used to order this priority queue.
121	>	* If <tt>null</tt> then the order depends on the elements' natural
122	>	* ordering.
123	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
124	>	* than 1
125	>	*/
126	>	public PriorityQueue(int initialCapacity,
127	>	Comparator<? super E> comparator) {
128	>	if (initialCapacity < 1)
129	>	throw new IllegalArgumentException();
130	>	this.queue = new Object[initialCapacity + 1];
131	>	this.comparator = comparator;
132		}
133
134	<	public E remove() {
135	<	return null;
134	>	/**
135	>	* Common code to initialize underlying queue array across
136	>	* constructors below.
137	>	*/
138	>	private void initializeArray(Collection<? extends E> c) {
139	>	int sz = c.size();
140	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
141	>	Integer.MAX_VALUE - 1);
142	>	if (initialCapacity < 1)
143	>	initialCapacity = 1;
144	>
145	>	this.queue = new Object[initialCapacity + 1];
146		}
147	<	public Iterator<E> iterator() {
148	<	return null;
147	>
148	>	/**
149	>	* Initially fill elements of the queue array under the
150	>	* knowledge that it is sorted or is another PQ, in which
151	>	* case we can just place the elements without fixups.
152	>	*/
153	>	private void fillFromSorted(Collection<? extends E> c) {
154	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
155	>	queue[++size] = i.next();
156		}
157
158	<	public E element() {
159	<	return null;
158	>
159	>	/**
160	>	* Initially fill elements of the queue array that is
161	>	* not to our knowledge sorted, so we must add them
162	>	* one by one.
163	>	*/
164	>	private void fillFromUnsorted(Collection<? extends E> c) {
165	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
166	>	add(i.next());
167		}
168	+
169	+	/**
170	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
171	+	* specified collection.  The priority queue has an initial
172	+	* capacity of 110% of the size of the specified collection or 1
173	+	* if the collection is empty.  If the specified collection is an
174	+	* instance of a {@link java.util.SortedSet} or is another
175	+	* <tt>PriorityQueue</tt>, the priority queue will be sorted
176	+	* according to the same comparator, or according to its elements'
177	+	* natural order if the collection is sorted according to its
178	+	* elements' natural order.  Otherwise, the priority queue is
179	+	* ordered according to its elements' natural order.
180	+	*
181	+	* @param c the collection whose elements are to be placed
182	+	*        into this priority queue.
183	+	* @throws ClassCastException if elements of the specified collection
184	+	*         cannot be compared to one another according to the priority
185	+	*         queue's ordering.
186	+	* @throws NullPointerException if <tt>c</tt> or any element within it
187	+	* is <tt>null</tt>
188	+	*/
189	+	public PriorityQueue(Collection<? extends E> c) {
190	+	initializeArray(c);
191	+	if (c instanceof SortedSet) {
192	+	// @fixme double-cast workaround for compiler
193	+	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
194	+	comparator = (Comparator<? super E>)s.comparator();
195	+	fillFromSorted(s);
196	+	} else if (c instanceof PriorityQueue) {
197	+	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
198	+	comparator = (Comparator<? super E>)s.comparator();
199	+	fillFromSorted(s);
200	+	} else {
201	+	comparator = null;
202	+	fillFromUnsorted(c);
203	+	}
204	+	}
205	+
206	+	/**
207	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
208	+	* specified collection.  The priority queue has an initial
209	+	* capacity of 110% of the size of the specified collection or 1
210	+	* if the collection is empty.  This priority queue will be sorted
211	+	* according to the same comparator as the given collection, or
212	+	* according to its elements' natural order if the collection is
213	+	* sorted according to its elements' natural order.
214	+	*
215	+	* @param c the collection whose elements are to be placed
216	+	*        into this priority queue.
217	+	* @throws ClassCastException if elements of the specified collection
218	+	*         cannot be compared to one another according to the priority
219	+	*         queue's ordering.
220	+	* @throws NullPointerException if <tt>c</tt> or any element within it
221	+	* is <tt>null</tt>
222	+	*/
223	+	public PriorityQueue(PriorityQueue<? extends E> c) {
224	+	initializeArray(c);
225	+	comparator = (Comparator<? super E>)c.comparator();
226	+	fillFromSorted(c);
227	+	}
228	+
229	+	/**
230	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
231	+	* specified collection.  The priority queue has an initial
232	+	* capacity of 110% of the size of the specified collection or 1
233	+	* if the collection is empty.  This priority queue will be sorted
234	+	* according to the same comparator as the given collection, or
235	+	* according to its elements' natural order if the collection is
236	+	* sorted according to its elements' natural order.
237	+	*
238	+	* @param c the collection whose elements are to be placed
239	+	*        into this priority queue.
240	+	* @throws ClassCastException if elements of the specified collection
241	+	*         cannot be compared to one another according to the priority
242	+	*         queue's ordering.
243	+	* @throws NullPointerException if <tt>c</tt> or any element within it
244	+	* is <tt>null</tt>
245	+	*/
246	+	public PriorityQueue(SortedSet<? extends E> c) {
247	+	initializeArray(c);
248	+	comparator = (Comparator<? super E>)c.comparator();
249	+	fillFromSorted(c);
250	+	}
251	+
252	+	/**
253	+	* Resize array, if necessary, to be able to hold given index
254	+	*/
255	+	private void grow(int index) {
256	+	int newlen = queue.length;
257	+	if (index < newlen) // don't need to grow
258	+	return;
259	+	if (index == Integer.MAX_VALUE)
260	+	throw new OutOfMemoryError();
261	+	while (newlen <= index) {
262	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
263	+	newlen = Integer.MAX_VALUE;
264	+	else
265	+	newlen <<= 2;
266	+	}
267	+	Object[] newQueue = new Object[newlen];
268	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
269	+	queue = newQueue;
270	+	}
271	+
272	+	// Queue Methods
273	+
274	+
275	+
276	+	/**
277	+	* Add the specified element to this priority queue.
278	+	*
279	+	* @return <tt>true</tt>
280	+	* @throws ClassCastException if the specified element cannot be compared
281	+	* with elements currently in the priority queue according
282	+	* to the priority queue's ordering.
283	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
284	+	*/
285	+	public boolean offer(E o) {
286	+	if (o == null)
287	+	throw new NullPointerException();
288	+	modCount++;
289	+	++size;
290	+
291	+	// Grow backing store if necessary
292	+	if (size >= queue.length)
293	+	grow(size);
294	+
295	+	queue[size] = o;
296	+	fixUp(size);
297	+	return true;
298	+	}
299	+
300		public E poll() {
301	<	return null;
301	>	if (size == 0)
302	>	return null;
303	>	return (E) remove(1);
304		}
305	+
306		public E peek() {
307	<	return null;
307	>	return (E) queue[1];
308	>	}
309	>
310	>	// Collection Methods - the first two override to update docs
311	>
312	>	/**
313	>	* Adds the specified element to this queue.
314	>	* @return <tt>true</tt> (as per the general contract of
315	>	* <tt>Collection.add</tt>).
316	>	*
317	>	* @throws NullPointerException {@inheritDoc}
318	>	* @throws ClassCastException if the specified element cannot be compared
319	>	* with elements currently in the priority queue according
320	>	* to the priority queue's ordering.
321	>	*/
322	>	public boolean add(E o) {
323	>	return super.add(o);
324	>	}
325	>
326	>
327	>	/**
328	>	* Adds all of the elements in the specified collection to this queue.
329	>	* The behavior of this operation is undefined if
330	>	* the specified collection is modified while the operation is in
331	>	* progress.  (This implies that the behavior of this call is undefined if
332	>	* the specified collection is this queue, and this queue is nonempty.)
333	>	* <p>
334	>	* This implementation iterates over the specified collection, and adds
335	>	* each object returned by the iterator to this collection, in turn.
336	>	* @throws NullPointerException {@inheritDoc}
337	>	* @throws ClassCastException if any element cannot be compared
338	>	* with elements currently in the priority queue according
339	>	* to the priority queue's ordering.
340	>	*/
341	>	public boolean addAll(Collection<? extends E> c) {
342	>	return super.addAll(c);
343		}
344
345	<	public boolean isEmpty() {
345	>
346	>	/**
347	>	* Removes a single instance of the specified element from this
348	>	* queue, if it is present.  More formally,
349	>	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
350	>	* o.equals(e))</tt>, if the queue contains one or more such
351	>	* elements.  Returns <tt>true</tt> if the queue contained the
352	>	* specified element (or equivalently, if the queue changed as a
353	>	* result of the call).
354	>	*
355	>	* <p>This implementation iterates over the queue looking for the
356	>	* specified element.  If it finds the element, it removes the element
357	>	* from the queue using the iterator's remove method.<p>
358	>	*
359	>	*/
360	>	public boolean remove(Object o) {
361	>	if (o == null)
362	>	return false;
363	>
364	>	if (comparator == null) {
365	>	for (int i = 1; i <= size; i++) {
366	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
367	>	remove(i);
368	>	return true;
369	>	}
370	>	}
371	>	} else {
372	>	for (int i = 1; i <= size; i++) {
373	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
374	>	remove(i);
375	>	return true;
376	>	}
377	>	}
378	>	}
379		return false;
380		}
381	+
382	+	/**
383	+	* Returns an iterator over the elements in this queue. The iterator
384	+	* does not return the elements in any particular order.
385	+	*
386	+	* @return an iterator over the elements in this queue.
387	+	*/
388	+	public Iterator<E> iterator() {
389	+	return new Itr();
390	+	}
391	+
392	+	private class Itr implements Iterator<E> {
393	+	/**
394	+	* Index (into queue array) of element to be returned by
395	+	* subsequent call to next.
396	+	*/
397	+	private int cursor = 1;
398	+
399	+	/**
400	+	* Index of element returned by most recent call to next or
401	+	* previous.  Reset to 0 if this element is deleted by a call
402	+	* to remove.
403	+	*/
404	+	private int lastRet = 0;
405	+
406	+	/**
407	+	* The modCount value that the iterator believes that the backing
408	+	* List should have.  If this expectation is violated, the iterator
409	+	* has detected concurrent modification.
410	+	*/
411	+	private int expectedModCount = modCount;
412	+
413	+	public boolean hasNext() {
414	+	return cursor <= size;
415	+	}
416	+
417	+	public E next() {
418	+	checkForComodification();
419	+	if (cursor > size)
420	+	throw new NoSuchElementException();
421	+	E result = (E) queue[cursor];
422	+	lastRet = cursor++;
423	+	return result;
424	+	}
425	+
426	+	public void remove() {
427	+	if (lastRet == 0)
428	+	throw new IllegalStateException();
429	+	checkForComodification();
430	+
431	+	PriorityQueue.this.remove(lastRet);
432	+	if (lastRet < cursor)
433	+	cursor--;
434	+	lastRet = 0;
435	+	expectedModCount = modCount;
436	+	}
437	+
438	+	final void checkForComodification() {
439	+	if (modCount != expectedModCount)
440	+	throw new ConcurrentModificationException();
441	+	}
442	+	}
443	+
444		public int size() {
445	<	return 0;
445	>	return size;
446	>	}
447	>
448	>	/**
449	>	* Remove all elements from the priority queue.
450	>	*/
451	>	public void clear() {
452	>	modCount++;
453	>
454	>	// Null out element references to prevent memory leak
455	>	for (int i=1; i<=size; i++)
456	>	queue[i] = null;
457	>
458	>	size = 0;
459		}
460	<	public Object[] toArray() {
461	<	return null;
460	>
461	>	/**
462	>	* Removes and returns the ith element from queue.  Recall
463	>	* that queue is one-based, so 1 <= i <= size.
464	>	*
465	>	* XXX: Could further special-case i==size, but is it worth it?
466	>	* XXX: Could special-case i==0, but is it worth it?
467	>	*/
468	>	private E remove(int i) {
469	>	assert i <= size;
470	>	modCount++;
471	>
472	>	E result = (E) queue[i];
473	>	queue[i] = queue[size];
474	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
475	>	if (i <= size)
476	>	fixDown(i);
477	>	return result;
478	>	}
479	>
480	>	/**
481	>	* Establishes the heap invariant (described above) assuming the heap
482	>	* satisfies the invariant except possibly for the leaf-node indexed by k
483	>	* (which may have a nextExecutionTime less than its parent's).
484	>	*
485	>	* This method functions by "promoting" queue[k] up the hierarchy
486	>	* (by swapping it with its parent) repeatedly until queue[k]
487	>	* is greater than or equal to its parent.
488	>	*/
489	>	private void fixUp(int k) {
490	>	if (comparator == null) {
491	>	while (k > 1) {
492	>	int j = k >> 1;
493	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
494	>	break;
495	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
496	>	k = j;
497	>	}
498	>	} else {
499	>	while (k > 1) {
500	>	int j = k >> 1;
501	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
502	>	break;
503	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
504	>	k = j;
505	>	}
506	>	}
507		}
508
509	<	public <T> T[] toArray(T[] array) {
510	<	return null;
509	>	/**
510	>	* Establishes the heap invariant (described above) in the subtree
511	>	* rooted at k, which is assumed to satisfy the heap invariant except
512	>	* possibly for node k itself (which may be greater than its children).
513	>	*
514	>	* This method functions by "demoting" queue[k] down the hierarchy
515	>	* (by swapping it with its smaller child) repeatedly until queue[k]
516	>	* is less than or equal to its children.
517	>	*/
518	>	private void fixDown(int k) {
519	>	int j;
520	>	if (comparator == null) {
521	>	while ((j = k << 1) <= size) {
522	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
523	>	j++; // j indexes smallest kid
524	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
525	>	break;
526	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
527	>	k = j;
528	>	}
529	>	} else {
530	>	while ((j = k << 1) <= size) {
531	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
532	>	j++; // j indexes smallest kid
533	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
534	>	break;
535	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
536	>	k = j;
537	>	}
538	>	}
539	>	}
540	>
541	>
542	>	/**
543	>	* Returns the comparator used to order this collection, or <tt>null</tt>
544	>	* if this collection is sorted according to its elements natural ordering
545	>	* (using <tt>Comparable</tt>).
546	>	*
547	>	* @return the comparator used to order this collection, or <tt>null</tt>
548	>	* if this collection is sorted according to its elements natural ordering.
549	>	*/
550	>	public Comparator<? super E> comparator() {
551	>	return comparator;
552	>	}
553	>
554	>	/**
555	>	* Save the state of the instance to a stream (that
556	>	* is, serialize it).
557	>	*
558	>	* @serialData The length of the array backing the instance is
559	>	* emitted (int), followed by all of its elements (each an
560	>	* <tt>Object</tt>) in the proper order.
561	>	* @param s the stream
562	>	*/
563	>	private void writeObject(java.io.ObjectOutputStream s)
564	>	throws java.io.IOException{
565	>	// Write out element count, and any hidden stuff
566	>	s.defaultWriteObject();
567	>
568	>	// Write out array length
569	>	s.writeInt(queue.length);
570	>
571	>	// Write out all elements in the proper order.
572	>	for (int i=0; i<size; i++)
573	>	s.writeObject(queue[i]);
574	>	}
575	>
576	>	/**
577	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
578	>	* deserialize it).
579	>	* @param s the stream
580	>	*/
581	>	private void readObject(java.io.ObjectInputStream s)
582	>	throws java.io.IOException, ClassNotFoundException {
583	>	// Read in size, and any hidden stuff
584	>	s.defaultReadObject();
585	>
586	>	// Read in array length and allocate array
587	>	int arrayLength = s.readInt();
588	>	queue = new Object[arrayLength];
589	>
590	>	// Read in all elements in the proper order.
591	>	for (int i=0; i<size; i++)
592	>	queue[i] = s.readObject();
593		}
594
595		}
596	+

Diff Legend

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