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

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.1 by tim, Wed May 14 21:30:45 2003 UTC vs.
Revision 1.28 by dl, Wed Aug 13 14:11:59 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>Implementation note: this implementation provides O(log(n)) time
32	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
33	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
34	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
35	>	* constant time for the retrieval methods (<tt>peek</tt>,
36	>	* <tt>element</tt>, and <tt>size</tt>).
37	>	*
38	>	* <p>This class is a member of the
39	>	* <a href="{@docRoot}/../guide/collections/index.html">
40	>	* Java Collections Framework</a>.
41	>	* @since 1.5
42	>	* @author Josh Bloch
43	>	*/
44	>	public class PriorityQueue<E> extends AbstractQueue<E>
45	>	implements Queue<E>, java.io.Serializable {
46
47	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
47	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
48
49	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
49	>	/**
50	>	* Priority queue represented as a balanced binary heap: the two children
51	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
52	>	* ordered by comparator, or by the elements' natural ordering, if
53	>	* comparator is null:  For each node n in the heap and each descendant d
54	>	* of n, n <= d.
55	>	*
56	>	* The element with the lowest value is in queue[1], assuming the queue is
57	>	* nonempty.  (A one-based array is used in preference to the traditional
58	>	* zero-based array to simplify parent and child calculations.)
59	>	*
60	>	* queue.length must be >= 2, even if size == 0.
61	>	*/
62	>	private transient Object[] queue;
63
64	<	public boolean add(E x) {
65	<	return false;
64	>	/**
65	>	* The number of elements in the priority queue.
66	>	*/
67	>	private int size = 0;
68	>
69	>	/**
70	>	* The comparator, or null if priority queue uses elements'
71	>	* natural ordering.
72	>	*/
73	>	private final Comparator<? super E> comparator;
74	>
75	>	/**
76	>	* The number of times this priority queue has been
77	>	* <i>structurally modified</i>.  See AbstractList for gory details.
78	>	*/
79	>	private transient int modCount = 0;
80	>
81	>	/**
82	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
83	>	* (11) that orders its elements according to their natural
84	>	* ordering (using <tt>Comparable</tt>).
85	>	*/
86	>	public PriorityQueue() {
87	>	this(DEFAULT_INITIAL_CAPACITY, null);
88		}
89	<	public boolean offer(E x) {
90	<	return false;
89	>
90	>	/**
91	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
92	>	* that orders its elements according to their natural ordering
93	>	* (using <tt>Comparable</tt>).
94	>	*
95	>	* @param initialCapacity the initial capacity for this priority queue.
96	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
97	>	* than 1
98	>	*/
99	>	public PriorityQueue(int initialCapacity) {
100	>	this(initialCapacity, null);
101		}
102	<	public boolean remove(Object x) {
103	<	return false;
102	>
103	>	/**
104	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
105	>	* that orders its elements according to the specified comparator.
106	>	*
107	>	* @param initialCapacity the initial capacity for this priority queue.
108	>	* @param comparator the comparator used to order this priority queue.
109	>	* If <tt>null</tt> then the order depends on the elements' natural
110	>	* ordering.
111	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
112	>	* than 1
113	>	*/
114	>	public PriorityQueue(int initialCapacity,
115	>	Comparator<? super E> comparator) {
116	>	if (initialCapacity < 1)
117	>	throw new IllegalArgumentException();
118	>	this.queue = new Object[initialCapacity + 1];
119	>	this.comparator = comparator;
120		}
121
122	<	public E remove() {
123	<	return null;
122	>	/**
123	>	* Common code to initialize underlying queue array across
124	>	* constructors below.
125	>	*/
126	>	private void initializeArray(Collection<? extends E> c) {
127	>	int sz = c.size();
128	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
129	>	Integer.MAX_VALUE - 1);
130	>	if (initialCapacity < 1)
131	>	initialCapacity = 1;
132	>
133	>	this.queue = new Object[initialCapacity + 1];
134		}
135	<	public Iterator<E> iterator() {
136	<	return null;
135	>
136	>	/**
137	>	* Initially fill elements of the queue array under the
138	>	* knowledge that it is sorted or is another PQ, in which
139	>	* case we can just place the elements without fixups.
140	>	*/
141	>	private void fillFromSorted(Collection<? extends E> c) {
142	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
143	>	queue[++size] = i.next();
144		}
145
146	<	public E element() {
147	<	return null;
146	>
147	>	/**
148	>	* Initially fill elements of the queue array that is
149	>	* not to our knowledge sorted, so we must add them
150	>	* one by one.
151	>	*/
152	>	private void fillFromUnsorted(Collection<? extends E> c) {
153	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154	>	add(i.next());
155		}
156	+
157	+	/**
158	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
159	+	* specified collection.  The priority queue has an initial
160	+	* capacity of 110% of the size of the specified collection or 1
161	+	* if the collection is empty.  If the specified collection is an
162	+	* instance of a {@link java.util.SortedSet} or is another
163	+	* <tt>PriorityQueue</tt>, the priority queue will be sorted
164	+	* according to the same comparator, or according to its elements'
165	+	* natural order if the collection is sorted according to its
166	+	* elements' natural order.  Otherwise, the priority queue is
167	+	* ordered according to its elements' natural order.
168	+	*
169	+	* @param c the collection whose elements are to be placed
170	+	*        into this priority queue.
171	+	* @throws ClassCastException if elements of the specified collection
172	+	*         cannot be compared to one another according to the priority
173	+	*         queue's ordering.
174	+	* @throws NullPointerException if <tt>c</tt> or any element within it
175	+	* is <tt>null</tt>
176	+	*/
177	+	public PriorityQueue(Collection<? extends E> c) {
178	+	initializeArray(c);
179	+	if (c instanceof SortedSet) {
180	+	// @fixme double-cast workaround for compiler
181	+	SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
182	+	comparator = (Comparator<? super E>)s.comparator();
183	+	fillFromSorted(s);
184	+	} else if (c instanceof PriorityQueue) {
185	+	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
186	+	comparator = (Comparator<? super E>)s.comparator();
187	+	fillFromSorted(s);
188	+	} else {
189	+	comparator = null;
190	+	fillFromUnsorted(c);
191	+	}
192	+	}
193	+
194	+	/**
195	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
196	+	* specified collection.  The priority queue has an initial
197	+	* capacity of 110% of the size of the specified collection or 1
198	+	* if the collection is empty.  This priority queue will be sorted
199	+	* according to the same comparator as the given collection, or
200	+	* according to its elements' natural order if the collection is
201	+	* sorted according to its elements' natural order.
202	+	*
203	+	* @param c the collection whose elements are to be placed
204	+	*        into this priority queue.
205	+	* @throws ClassCastException if elements of the specified collection
206	+	*         cannot be compared to one another according to the priority
207	+	*         queue's ordering.
208	+	* @throws NullPointerException if <tt>c</tt> or any element within it
209	+	* is <tt>null</tt>
210	+	*/
211	+	public PriorityQueue(PriorityQueue<? extends E> c) {
212	+	initializeArray(c);
213	+	comparator = (Comparator<? super E>)c.comparator();
214	+	fillFromSorted(c);
215	+	}
216	+
217	+	/**
218	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
219	+	* specified collection.  The priority queue has an initial
220	+	* capacity of 110% of the size of the specified collection or 1
221	+	* if the collection is empty.  This priority queue will be sorted
222	+	* according to the same comparator as the given collection, or
223	+	* according to its elements' natural order if the collection is
224	+	* sorted according to its elements' natural order.
225	+	*
226	+	* @param c the collection whose elements are to be placed
227	+	*        into this priority queue.
228	+	* @throws ClassCastException if elements of the specified collection
229	+	*         cannot be compared to one another according to the priority
230	+	*         queue's ordering.
231	+	* @throws NullPointerException if <tt>c</tt> or any element within it
232	+	* is <tt>null</tt>
233	+	*/
234	+	public PriorityQueue(SortedSet<? extends E> c) {
235	+	initializeArray(c);
236	+	comparator = (Comparator<? super E>)c.comparator();
237	+	fillFromSorted(c);
238	+	}
239	+
240	+	/**
241	+	* Resize array, if necessary, to be able to hold given index
242	+	*/
243	+	private void grow(int index) {
244	+	int newlen = queue.length;
245	+	if (index < newlen) // don't need to grow
246	+	return;
247	+	if (index == Integer.MAX_VALUE)
248	+	throw new OutOfMemoryError();
249	+	while (newlen <= index) {
250	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
251	+	newlen = Integer.MAX_VALUE;
252	+	else
253	+	newlen <<= 2;
254	+	}
255	+	Object[] newQueue = new Object[newlen];
256	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
257	+	queue = newQueue;
258	+	}
259	+
260	+	// Queue Methods
261	+
262	+
263	+
264	+	/**
265	+	* Add the specified element to this priority queue.
266	+	*
267	+	* @return <tt>true</tt>
268	+	* @throws ClassCastException if the specified element cannot be compared
269	+	* with elements currently in the priority queue according
270	+	* to the priority queue's ordering.
271	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
272	+	*/
273	+	public boolean offer(E o) {
274	+	if (o == null)
275	+	throw new NullPointerException();
276	+	modCount++;
277	+	++size;
278	+
279	+	// Grow backing store if necessary
280	+	if (size >= queue.length)
281	+	grow(size);
282	+
283	+	queue[size] = o;
284	+	fixUp(size);
285	+	return true;
286	+	}
287	+
288		public E poll() {
289	<	return null;
289	>	if (size == 0)
290	>	return null;
291	>	return (E) remove(1);
292		}
293	+
294		public E peek() {
295	<	return null;
295	>	return (E) queue[1];
296	>	}
297	>
298	>	// Collection Methods - the first two override to update docs
299	>
300	>	/**
301	>	* Adds the specified element to this queue.
302	>	* @return <tt>true</tt> (as per the general contract of
303	>	* <tt>Collection.add</tt>).
304	>	*
305	>	* @throws NullPointerException {@inheritDoc}
306	>	* @throws ClassCastException if the specified element cannot be compared
307	>	* with elements currently in the priority queue according
308	>	* to the priority queue's ordering.
309	>	*/
310	>	public boolean add(E o) {
311	>	return super.add(o);
312	>	}
313	>
314	>
315	>	/**
316	>	* Adds all of the elements in the specified collection to this queue.
317	>	* The behavior of this operation is undefined if
318	>	* the specified collection is modified while the operation is in
319	>	* progress.  (This implies that the behavior of this call is undefined if
320	>	* the specified collection is this queue, and this queue is nonempty.)
321	>	* <p>
322	>	* This implementation iterates over the specified collection, and adds
323	>	* each object returned by the iterator to this collection, in turn.
324	>	* @throws NullPointerException {@inheritDoc}
325	>	* @throws ClassCastException if any element cannot be compared
326	>	* with elements currently in the priority queue according
327	>	* to the priority queue's ordering.
328	>	*/
329	>	public boolean addAll(Collection<? extends E> c) {
330	>	return super.addAll(c);
331		}
332
333	<	public boolean isEmpty() {
333	>
334	>	/**
335	>	* Removes a single instance of the specified element from this
336	>	* queue, if it is present.  More formally,
337	>	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
338	>	* o.equals(e))</tt>, if the queue contains one or more such
339	>	* elements.  Returns <tt>true</tt> if the queue contained the
340	>	* specified element (or equivalently, if the queue changed as a
341	>	* result of the call).
342	>	*
343	>	* <p>This implementation iterates over the queue looking for the
344	>	* specified element.  If it finds the element, it removes the element
345	>	* from the queue using the iterator's remove method.<p>
346	>	*
347	>	*/
348	>	public boolean remove(Object o) {
349	>	if (o == null)
350	>	return false;
351	>
352	>	if (comparator == null) {
353	>	for (int i = 1; i <= size; i++) {
354	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
355	>	remove(i);
356	>	return true;
357	>	}
358	>	}
359	>	} else {
360	>	for (int i = 1; i <= size; i++) {
361	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
362	>	remove(i);
363	>	return true;
364	>	}
365	>	}
366	>	}
367		return false;
368		}
369	+
370	+	/**
371	+	* Returns an iterator over the elements in this queue. The iterator
372	+	* does not return the elements in any particular order.
373	+	*
374	+	* @return an iterator over the elements in this queue.
375	+	*/
376	+	public Iterator<E> iterator() {
377	+	return new Itr();
378	+	}
379	+
380	+	private class Itr implements Iterator<E> {
381	+	/**
382	+	* Index (into queue array) of element to be returned by
383	+	* subsequent call to next.
384	+	*/
385	+	private int cursor = 1;
386	+
387	+	/**
388	+	* Index of element returned by most recent call to next or
389	+	* previous.  Reset to 0 if this element is deleted by a call
390	+	* to remove.
391	+	*/
392	+	private int lastRet = 0;
393	+
394	+	/**
395	+	* The modCount value that the iterator believes that the backing
396	+	* List should have.  If this expectation is violated, the iterator
397	+	* has detected concurrent modification.
398	+	*/
399	+	private int expectedModCount = modCount;
400	+
401	+	public boolean hasNext() {
402	+	return cursor <= size;
403	+	}
404	+
405	+	public E next() {
406	+	checkForComodification();
407	+	if (cursor > size)
408	+	throw new NoSuchElementException();
409	+	E result = (E) queue[cursor];
410	+	lastRet = cursor++;
411	+	return result;
412	+	}
413	+
414	+	public void remove() {
415	+	if (lastRet == 0)
416	+	throw new IllegalStateException();
417	+	checkForComodification();
418	+
419	+	PriorityQueue.this.remove(lastRet);
420	+	if (lastRet < cursor)
421	+	cursor--;
422	+	lastRet = 0;
423	+	expectedModCount = modCount;
424	+	}
425	+
426	+	final void checkForComodification() {
427	+	if (modCount != expectedModCount)
428	+	throw new ConcurrentModificationException();
429	+	}
430	+	}
431	+
432		public int size() {
433	<	return 0;
433	>	return size;
434	>	}
435	>
436	>	/**
437	>	* Remove all elements from the priority queue.
438	>	*/
439	>	public void clear() {
440	>	modCount++;
441	>
442	>	// Null out element references to prevent memory leak
443	>	for (int i=1; i<=size; i++)
444	>	queue[i] = null;
445	>
446	>	size = 0;
447		}
448	<	public Object[] toArray() {
449	<	return null;
448	>
449	>	/**
450	>	* Removes and returns the ith element from queue.  Recall
451	>	* that queue is one-based, so 1 <= i <= size.
452	>	*
453	>	* XXX: Could further special-case i==size, but is it worth it?
454	>	* XXX: Could special-case i==0, but is it worth it?
455	>	*/
456	>	private E remove(int i) {
457	>	assert i <= size;
458	>	modCount++;
459	>
460	>	E result = (E) queue[i];
461	>	queue[i] = queue[size];
462	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
463	>	if (i <= size)
464	>	fixDown(i);
465	>	return result;
466	>	}
467	>
468	>	/**
469	>	* Establishes the heap invariant (described above) assuming the heap
470	>	* satisfies the invariant except possibly for the leaf-node indexed by k
471	>	* (which may have a nextExecutionTime less than its parent's).
472	>	*
473	>	* This method functions by "promoting" queue[k] up the hierarchy
474	>	* (by swapping it with its parent) repeatedly until queue[k]
475	>	* is greater than or equal to its parent.
476	>	*/
477	>	private void fixUp(int k) {
478	>	if (comparator == null) {
479	>	while (k > 1) {
480	>	int j = k >> 1;
481	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
482	>	break;
483	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
484	>	k = j;
485	>	}
486	>	} else {
487	>	while (k > 1) {
488	>	int j = k >> 1;
489	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
490	>	break;
491	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
492	>	k = j;
493	>	}
494	>	}
495		}
496
497	<	public <T> T[] toArray(T[] array) {
498	<	return null;
497	>	/**
498	>	* Establishes the heap invariant (described above) in the subtree
499	>	* rooted at k, which is assumed to satisfy the heap invariant except
500	>	* possibly for node k itself (which may be greater than its children).
501	>	*
502	>	* This method functions by "demoting" queue[k] down the hierarchy
503	>	* (by swapping it with its smaller child) repeatedly until queue[k]
504	>	* is less than or equal to its children.
505	>	*/
506	>	private void fixDown(int k) {
507	>	int j;
508	>	if (comparator == null) {
509	>	while ((j = k << 1) <= size) {
510	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
511	>	j++; // j indexes smallest kid
512	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
513	>	break;
514	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
515	>	k = j;
516	>	}
517	>	} else {
518	>	while ((j = k << 1) <= size) {
519	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
520	>	j++; // j indexes smallest kid
521	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
522	>	break;
523	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
524	>	k = j;
525	>	}
526	>	}
527	>	}
528	>
529	>
530	>	/**
531	>	* Returns the comparator used to order this collection, or <tt>null</tt>
532	>	* if this collection is sorted according to its elements natural ordering
533	>	* (using <tt>Comparable</tt>).
534	>	*
535	>	* @return the comparator used to order this collection, or <tt>null</tt>
536	>	* if this collection is sorted according to its elements natural ordering.
537	>	*/
538	>	public Comparator<? super E> comparator() {
539	>	return comparator;
540	>	}
541	>
542	>	/**
543	>	* Save the state of the instance to a stream (that
544	>	* is, serialize it).
545	>	*
546	>	* @serialData The length of the array backing the instance is
547	>	* emitted (int), followed by all of its elements (each an
548	>	* <tt>Object</tt>) in the proper order.
549	>	* @param s the stream
550	>	*/
551	>	private void writeObject(java.io.ObjectOutputStream s)
552	>	throws java.io.IOException{
553	>	// Write out element count, and any hidden stuff
554	>	s.defaultWriteObject();
555	>
556	>	// Write out array length
557	>	s.writeInt(queue.length);
558	>
559	>	// Write out all elements in the proper order.
560	>	for (int i=0; i<size; i++)
561	>	s.writeObject(queue[i]);
562	>	}
563	>
564	>	/**
565	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
566	>	* deserialize it).
567	>	* @param s the stream
568	>	*/
569	>	private void readObject(java.io.ObjectInputStream s)
570	>	throws java.io.IOException, ClassNotFoundException {
571	>	// Read in size, and any hidden stuff
572	>	s.defaultReadObject();
573	>
574	>	// Read in array length and allocate array
575	>	int arrayLength = s.readInt();
576	>	queue = new Object[arrayLength];
577	>
578	>	// Read in all elements in the proper order.
579	>	for (int i=0; i<size; i++)
580	>	queue[i] = s.readObject();
581		}
582
583		}
584	+

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