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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 1.27 by dl, Tue Aug 12 11:11:58 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	+	SortedSet<? extends E> s = (SortedSet<? extends E>) c;
181	+	comparator = (Comparator<? super E>)s.comparator();
182	+	fillFromSorted(s);
183	+	} else if (c instanceof PriorityQueue) {
184	+	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
185	+	comparator = (Comparator<? super E>)s.comparator();
186	+	fillFromSorted(s);
187	+	} else {
188	+	comparator = null;
189	+	fillFromUnsorted(c);
190	+	}
191	+	}
192	+
193	+	/**
194	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
195	+	* specified collection.  The priority queue has an initial
196	+	* capacity of 110% of the size of the specified collection or 1
197	+	* if the collection is empty.  This priority queue will be sorted
198	+	* according to the same comparator as the given collection, or
199	+	* according to its elements' natural order if the collection is
200	+	* sorted according to its elements' natural order.
201	+	*
202	+	* @param c the collection whose elements are to be placed
203	+	*        into this priority queue.
204	+	* @throws ClassCastException if elements of the specified collection
205	+	*         cannot be compared to one another according to the priority
206	+	*         queue's ordering.
207	+	* @throws NullPointerException if <tt>c</tt> or any element within it
208	+	* is <tt>null</tt>
209	+	*/
210	+	public PriorityQueue(PriorityQueue<? extends E> c) {
211	+	initializeArray(c);
212	+	comparator = (Comparator<? super E>)c.comparator();
213	+	fillFromSorted(c);
214	+	}
215	+
216	+	/**
217	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
218	+	* specified collection.  The priority queue has an initial
219	+	* capacity of 110% of the size of the specified collection or 1
220	+	* if the collection is empty.  This priority queue will be sorted
221	+	* according to the same comparator as the given collection, or
222	+	* according to its elements' natural order if the collection is
223	+	* sorted according to its elements' natural order.
224	+	*
225	+	* @param c the collection whose elements are to be placed
226	+	*        into this priority queue.
227	+	* @throws ClassCastException if elements of the specified collection
228	+	*         cannot be compared to one another according to the priority
229	+	*         queue's ordering.
230	+	* @throws NullPointerException if <tt>c</tt> or any element within it
231	+	* is <tt>null</tt>
232	+	*/
233	+	public PriorityQueue(SortedSet<? extends E> c) {
234	+	initializeArray(c);
235	+	comparator = (Comparator<? super E>)c.comparator();
236	+	fillFromSorted(c);
237	+	}
238	+
239	+	/**
240	+	* Resize array, if necessary, to be able to hold given index
241	+	*/
242	+	private void grow(int index) {
243	+	int newlen = queue.length;
244	+	if (index < newlen) // don't need to grow
245	+	return;
246	+	if (index == Integer.MAX_VALUE)
247	+	throw new OutOfMemoryError();
248	+	while (newlen <= index) {
249	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
250	+	newlen = Integer.MAX_VALUE;
251	+	else
252	+	newlen <<= 2;
253	+	}
254	+	Object[] newQueue = new Object[newlen];
255	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
256	+	queue = newQueue;
257	+	}
258	+
259	+	// Queue Methods
260	+
261	+
262	+
263	+	/**
264	+	* Add the specified element to this priority queue.
265	+	*
266	+	* @return <tt>true</tt>
267	+	* @throws ClassCastException if the specified element cannot be compared
268	+	* with elements currently in the priority queue according
269	+	* to the priority queue's ordering.
270	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
271	+	*/
272	+	public boolean offer(E o) {
273	+	if (o == null)
274	+	throw new NullPointerException();
275	+	modCount++;
276	+	++size;
277	+
278	+	// Grow backing store if necessary
279	+	if (size >= queue.length)
280	+	grow(size);
281	+
282	+	queue[size] = o;
283	+	fixUp(size);
284	+	return true;
285	+	}
286	+
287		public E poll() {
288	<	return null;
288	>	if (size == 0)
289	>	return null;
290	>	return (E) remove(1);
291		}
292	+
293		public E peek() {
294	<	return null;
294	>	return (E) queue[1];
295	>	}
296	>
297	>	// Collection Methods - the first two override to update docs
298	>
299	>	/**
300	>	* Adds the specified element to this queue.
301	>	* @return <tt>true</tt> (as per the general contract of
302	>	* <tt>Collection.add</tt>).
303	>	*
304	>	* @throws NullPointerException {@inheritDoc}
305	>	* @throws ClassCastException if the specified element cannot be compared
306	>	* with elements currently in the priority queue according
307	>	* to the priority queue's ordering.
308	>	*/
309	>	public boolean add(E o) {
310	>	return super.add(o);
311	>	}
312	>
313	>
314	>	/**
315	>	* Adds all of the elements in the specified collection to this queue.
316	>	* The behavior of this operation is undefined if
317	>	* the specified collection is modified while the operation is in
318	>	* progress.  (This implies that the behavior of this call is undefined if
319	>	* the specified collection is this queue, and this queue is nonempty.)
320	>	* <p>
321	>	* This implementation iterates over the specified collection, and adds
322	>	* each object returned by the iterator to this collection, in turn.
323	>	* @throws NullPointerException {@inheritDoc}
324	>	* @throws ClassCastException if any element cannot be compared
325	>	* with elements currently in the priority queue according
326	>	* to the priority queue's ordering.
327	>	*/
328	>	public boolean addAll(Collection<? extends E> c) {
329	>	return super.addAll(c);
330		}
331
332	<	public boolean isEmpty() {
332	>
333	>	/**
334	>	* Removes a single instance of the specified element from this
335	>	* queue, if it is present.  More formally,
336	>	* removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
337	>	* o.equals(e))</tt>, if the queue contains one or more such
338	>	* elements.  Returns <tt>true</tt> if the queue contained the
339	>	* specified element (or equivalently, if the queue changed as a
340	>	* result of the call).
341	>	*
342	>	* <p>This implementation iterates over the queue looking for the
343	>	* specified element.  If it finds the element, it removes the element
344	>	* from the queue using the iterator's remove method.<p>
345	>	*
346	>	*/
347	>	public boolean remove(Object o) {
348	>	if (o == null)
349	>	return false;
350	>
351	>	if (comparator == null) {
352	>	for (int i = 1; i <= size; i++) {
353	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
354	>	remove(i);
355	>	return true;
356	>	}
357	>	}
358	>	} else {
359	>	for (int i = 1; i <= size; i++) {
360	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
361	>	remove(i);
362	>	return true;
363	>	}
364	>	}
365	>	}
366		return false;
367		}
368	+
369	+	/**
370	+	* Returns an iterator over the elements in this queue. The iterator
371	+	* does not return the elements in any particular order.
372	+	*
373	+	* @return an iterator over the elements in this queue.
374	+	*/
375	+	public Iterator<E> iterator() {
376	+	return new Itr();
377	+	}
378	+
379	+	private class Itr implements Iterator<E> {
380	+	/**
381	+	* Index (into queue array) of element to be returned by
382	+	* subsequent call to next.
383	+	*/
384	+	private int cursor = 1;
385	+
386	+	/**
387	+	* Index of element returned by most recent call to next or
388	+	* previous.  Reset to 0 if this element is deleted by a call
389	+	* to remove.
390	+	*/
391	+	private int lastRet = 0;
392	+
393	+	/**
394	+	* The modCount value that the iterator believes that the backing
395	+	* List should have.  If this expectation is violated, the iterator
396	+	* has detected concurrent modification.
397	+	*/
398	+	private int expectedModCount = modCount;
399	+
400	+	public boolean hasNext() {
401	+	return cursor <= size;
402	+	}
403	+
404	+	public E next() {
405	+	checkForComodification();
406	+	if (cursor > size)
407	+	throw new NoSuchElementException();
408	+	E result = (E) queue[cursor];
409	+	lastRet = cursor++;
410	+	return result;
411	+	}
412	+
413	+	public void remove() {
414	+	if (lastRet == 0)
415	+	throw new IllegalStateException();
416	+	checkForComodification();
417	+
418	+	PriorityQueue.this.remove(lastRet);
419	+	if (lastRet < cursor)
420	+	cursor--;
421	+	lastRet = 0;
422	+	expectedModCount = modCount;
423	+	}
424	+
425	+	final void checkForComodification() {
426	+	if (modCount != expectedModCount)
427	+	throw new ConcurrentModificationException();
428	+	}
429	+	}
430	+
431		public int size() {
432	<	return 0;
432	>	return size;
433	>	}
434	>
435	>	/**
436	>	* Remove all elements from the priority queue.
437	>	*/
438	>	public void clear() {
439	>	modCount++;
440	>
441	>	// Null out element references to prevent memory leak
442	>	for (int i=1; i<=size; i++)
443	>	queue[i] = null;
444	>
445	>	size = 0;
446		}
447	<	public Object[] toArray() {
448	<	return null;
447	>
448	>	/**
449	>	* Removes and returns the ith element from queue.  Recall
450	>	* that queue is one-based, so 1 <= i <= size.
451	>	*
452	>	* XXX: Could further special-case i==size, but is it worth it?
453	>	* XXX: Could special-case i==0, but is it worth it?
454	>	*/
455	>	private E remove(int i) {
456	>	assert i <= size;
457	>	modCount++;
458	>
459	>	E result = (E) queue[i];
460	>	queue[i] = queue[size];
461	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
462	>	if (i <= size)
463	>	fixDown(i);
464	>	return result;
465	>	}
466	>
467	>	/**
468	>	* Establishes the heap invariant (described above) assuming the heap
469	>	* satisfies the invariant except possibly for the leaf-node indexed by k
470	>	* (which may have a nextExecutionTime less than its parent's).
471	>	*
472	>	* This method functions by "promoting" queue[k] up the hierarchy
473	>	* (by swapping it with its parent) repeatedly until queue[k]
474	>	* is greater than or equal to its parent.
475	>	*/
476	>	private void fixUp(int k) {
477	>	if (comparator == null) {
478	>	while (k > 1) {
479	>	int j = k >> 1;
480	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
481	>	break;
482	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
483	>	k = j;
484	>	}
485	>	} else {
486	>	while (k > 1) {
487	>	int j = k >> 1;
488	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
489	>	break;
490	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
491	>	k = j;
492	>	}
493	>	}
494		}
495
496	<	public <T> T[] toArray(T[] array) {
497	<	return null;
496	>	/**
497	>	* Establishes the heap invariant (described above) in the subtree
498	>	* rooted at k, which is assumed to satisfy the heap invariant except
499	>	* possibly for node k itself (which may be greater than its children).
500	>	*
501	>	* This method functions by "demoting" queue[k] down the hierarchy
502	>	* (by swapping it with its smaller child) repeatedly until queue[k]
503	>	* is less than or equal to its children.
504	>	*/
505	>	private void fixDown(int k) {
506	>	int j;
507	>	if (comparator == null) {
508	>	while ((j = k << 1) <= size) {
509	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
510	>	j++; // j indexes smallest kid
511	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
512	>	break;
513	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
514	>	k = j;
515	>	}
516	>	} else {
517	>	while ((j = k << 1) <= size) {
518	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
519	>	j++; // j indexes smallest kid
520	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
521	>	break;
522	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
523	>	k = j;
524	>	}
525	>	}
526	>	}
527	>
528	>
529	>	/**
530	>	* Returns the comparator used to order this collection, or <tt>null</tt>
531	>	* if this collection is sorted according to its elements natural ordering
532	>	* (using <tt>Comparable</tt>).
533	>	*
534	>	* @return the comparator used to order this collection, or <tt>null</tt>
535	>	* if this collection is sorted according to its elements natural ordering.
536	>	*/
537	>	public Comparator<? super E> comparator() {
538	>	return comparator;
539	>	}
540	>
541	>	/**
542	>	* Save the state of the instance to a stream (that
543	>	* is, serialize it).
544	>	*
545	>	* @serialData The length of the array backing the instance is
546	>	* emitted (int), followed by all of its elements (each an
547	>	* <tt>Object</tt>) in the proper order.
548	>	* @param s the stream
549	>	*/
550	>	private void writeObject(java.io.ObjectOutputStream s)
551	>	throws java.io.IOException{
552	>	// Write out element count, and any hidden stuff
553	>	s.defaultWriteObject();
554	>
555	>	// Write out array length
556	>	s.writeInt(queue.length);
557	>
558	>	// Write out all elements in the proper order.
559	>	for (int i=0; i<size; i++)
560	>	s.writeObject(queue[i]);
561	>	}
562	>
563	>	/**
564	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
565	>	* deserialize it).
566	>	* @param s the stream
567	>	*/
568	>	private void readObject(java.io.ObjectInputStream s)
569	>	throws java.io.IOException, ClassNotFoundException {
570	>	// Read in size, and any hidden stuff
571	>	s.defaultReadObject();
572	>
573	>	// Read in array length and allocate array
574	>	int arrayLength = s.readInt();
575	>	queue = new Object[arrayLength];
576	>
577	>	// Read in all elements in the proper order.
578	>	for (int i=0; i<size; i++)
579	>	queue[i] = s.readObject();
580		}
581
582		}
583	+

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