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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 1.22 by dl, Tue Aug 5 12:11:08 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 queue based on a priority heap.  This queue orders
5	>	* elements according to an order specified at construction time, which is
6	>	* specified in the same manner as {@link java.util.TreeSet} and
7	>	* {@link java.util.TreeMap}: elements are ordered
8	>	* either according to their <i>natural order</i> (see {@link Comparable}), or
9	>	* according to a {@link java.util.Comparator}, depending on which
10	>	* constructor is used.
11	>	* <p>The <em>head</em> of this queue is the <em>least</em> element with
12	>	* respect to the specified ordering.
13	>	* If multiple elements are tied for least value, the
14	>	* head is one of those elements. A priority queue does not permit
15	>	* <tt>null</tt> elements.
16	>	*
17	>	* <p>The {@link #remove()} and {@link #poll()} methods remove and
18	>	* return the head of the queue.
19	>	*
20	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
21	>	* not delete, the head of the queue.
22	>	*
23	>	* <p>A priority queue has a <i>capacity</i>.  The capacity is the
24	>	* size of the array used internally to store the elements on the
25	>	* queue.
26	>	* It is always at least as large as the queue size.  As
27	>	* elements are added to a priority queue, its capacity grows
28	>	* automatically.  The details of the growth policy are not specified.
29	>	*
30	>	* <p>Implementation note: this implementation provides O(log(n)) time
31	>	* for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
32	>	* <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
33	>	* <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
34	>	* constant time for the retrieval methods (<tt>peek</tt>,
35	>	* <tt>element</tt>, and <tt>size</tt>).
36	>	*
37	>	* <p>This class is a member of the
38	>	* <a href="{@docRoot}/../guide/collections/index.html">
39	>	* Java Collections Framework</a>.
40	>	* @since 1.5
41	>	* @author Josh Bloch
42	>	*/
43	>	public class PriorityQueue<E> extends AbstractQueue<E>
44	>	implements Queue<E>, java.io.Serializable {
45
46	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
46	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
47
48	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
48	>	/**
49	>	* Priority queue represented as a balanced binary heap: the two children
50	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
51	>	* ordered by comparator, or by the elements' natural ordering, if
52	>	* comparator is null:  For each node n in the heap and each descendant d
53	>	* of n, n <= d.
54	>	*
55	>	* The element with the lowest value is in queue[1], assuming the queue is
56	>	* nonempty.  (A one-based array is used in preference to the traditional
57	>	* zero-based array to simplify parent and child calculations.)
58	>	*
59	>	* queue.length must be >= 2, even if size == 0.
60	>	*/
61	>	private transient Object[] queue;
62
63	<	public boolean add(E x) {
64	<	return false;
63	>	/**
64	>	* The number of elements in the priority queue.
65	>	*/
66	>	private int size = 0;
67	>
68	>	/**
69	>	* The comparator, or null if priority queue uses elements'
70	>	* natural ordering.
71	>	*/
72	>	private final Comparator<? super E> comparator;
73	>
74	>	/**
75	>	* The number of times this priority queue has been
76	>	* <i>structurally modified</i>.  See AbstractList for gory details.
77	>	*/
78	>	private transient int modCount = 0;
79	>
80	>	/**
81	>	* Creates a <tt>PriorityQueue</tt> with the default initial capacity
82	>	* (11) that orders its elements according to their natural
83	>	* ordering (using <tt>Comparable</tt>.)
84	>	*/
85	>	public PriorityQueue() {
86	>	this(DEFAULT_INITIAL_CAPACITY, null);
87		}
88	<	public boolean offer(E x) {
89	<	return false;
88	>
89	>	/**
90	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
91	>	* that orders its elements according to their natural ordering
92	>	* (using <tt>Comparable</tt>.)
93	>	*
94	>	* @param initialCapacity the initial capacity for this priority queue.
95	>	*/
96	>	public PriorityQueue(int initialCapacity) {
97	>	this(initialCapacity, null);
98		}
99	<	public boolean remove(Object x) {
100	<	return false;
99	>
100	>	/**
101	>	* Creates a <tt>PriorityQueue</tt> with the specified initial capacity
102	>	* that orders its elements according to the specified comparator.
103	>	*
104	>	* @param initialCapacity the initial capacity for this priority queue.
105	>	* @param comparator the comparator used to order this priority queue.
106	>	* If <tt>null</tt> then the order depends on the elements' natural
107	>	* ordering.
108	>	* @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
109	>	* than 1
110	>	*/
111	>	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
112	>	if (initialCapacity < 1)
113	>	throw new IllegalArgumentException();
114	>	this.queue = new Object[initialCapacity + 1];
115	>	this.comparator = comparator;
116		}
117
118	<	public E remove() {
119	<	return null;
118	>	/**
119	>	* Common code to initialize underlying queue array across
120	>	* constructors below.
121	>	*/
122	>	private void initializeArray(Collection<? extends E> c) {
123	>	int sz = c.size();
124	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
125	>	Integer.MAX_VALUE - 1);
126	>	if (initialCapacity < 1)
127	>	initialCapacity = 1;
128	>
129	>	this.queue = new Object[initialCapacity + 1];
130		}
131	<	public Iterator<E> iterator() {
132	<	return null;
131	>
132	>	/**
133	>	* Initially fill elements of the queue array under the
134	>	* knowledge that it is sorted or is another PQ, in which
135	>	* case we can just place the elements without fixups.
136	>	*/
137	>	private void fillFromSorted(Collection<? extends E> c) {
138	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
139	>	queue[++size] = i.next();
140	>	}
141	>
142	>
143	>	/**
144	>	* Initially fill elements of the queue array that is
145	>	* not to our knowledge sorted, so we must add them
146	>	* one by one.
147	>	*/
148	>	private void fillFromUnsorted(Collection<? extends E> c) {
149	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
150	>	add(i.next());
151	>	}
152	>
153	>	/**
154	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
155	>	* specified collection.  The priority queue has an initial
156	>	* capacity of 110% of the size of the specified collection or 1
157	>	* if the collection is empty.  If the specified collection is an
158	>	* instance of a {@link SortedSet} or is another
159	>	* <tt>PriorityQueue</tt>, the priority queue will be sorted
160	>	* according to the same comparator, or according to its elements'
161	>	* natural order if the collection is sorted according to its
162	>	* elements' natural order.  Otherwise, the priority queue is
163	>	* ordered according to its elements' natural order.
164	>	*
165	>	* @param c the collection whose elements are to be placed
166	>	*        into this priority queue.
167	>	* @throws ClassCastException if elements of the specified collection
168	>	*         cannot be compared to one another according to the priority
169	>	*         queue's ordering.
170	>	* @throws NullPointerException if <tt>c</tt> or any element within it
171	>	* is <tt>null</tt>
172	>	*/
173	>	public PriorityQueue(Collection<? extends E> c) {
174	>	initializeArray(c);
175	>	if (c instanceof SortedSet<? extends E>) {
176	>	SortedSet<? extends E> s = (SortedSet<? extends E>) c;
177	>	comparator = (Comparator<? super E>)s.comparator();
178	>	fillFromSorted(s);
179	>	}
180	>	else if (c instanceof PriorityQueue<? extends E>) {
181	>	PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
182	>	comparator = (Comparator<? super E>)s.comparator();
183	>	fillFromSorted(s);
184	>	}
185	>	else {
186	>	comparator = null;
187	>	fillFromUnsorted(c);
188	>	}
189		}
190
191	<	public E element() {
192	<	return null;
191	>	/**
192	>	* Creates a <tt>PriorityQueue</tt> containing the elements in the
193	>	* specified collection.  The priority queue has an initial
194	>	* capacity of 110% of the size of the specified collection or 1
195	>	* if the collection is empty.  This priority queue will be sorted
196	>	* according to the same comparator as the given collection, or
197	>	* according to its elements' natural order if the collection is
198	>	* sorted according to its elements' natural order.
199	>	*
200	>	* @param c the collection whose elements are to be placed
201	>	*        into this priority queue.
202	>	* @throws ClassCastException if elements of the specified collection
203	>	*         cannot be compared to one another according to the priority
204	>	*         queue's ordering.
205	>	* @throws NullPointerException if <tt>c</tt> or any element within it
206	>	* is <tt>null</tt>
207	>	*/
208	>	public PriorityQueue(PriorityQueue<? extends E> c) {
209	>	initializeArray(c);
210	>	comparator = (Comparator<? super E>)c.comparator();
211	>	fillFromSorted(c);
212		}
213	+
214	+	/**
215	+	* Creates a <tt>PriorityQueue</tt> containing the elements in the
216	+	* specified collection.  The priority queue has an initial
217	+	* capacity of 110% of the size of the specified collection or 1
218	+	* if the collection is empty.  This priority queue will be sorted
219	+	* according to the same comparator as the given collection, or
220	+	* according to its elements' natural order if the collection is
221	+	* sorted according to its elements' natural order.
222	+	*
223	+	* @param c the collection whose elements are to be placed
224	+	*        into this priority queue.
225	+	* @throws ClassCastException if elements of the specified collection
226	+	*         cannot be compared to one another according to the priority
227	+	*         queue's ordering.
228	+	* @throws NullPointerException if <tt>c</tt> or any element within it
229	+	* is <tt>null</tt>
230	+	*/
231	+	public PriorityQueue(SortedSet<? extends E> c) {
232	+	initializeArray(c);
233	+	comparator = (Comparator<? super E>)c.comparator();
234	+	fillFromSorted(c);
235	+	}
236	+
237	+	/**
238	+	* Resize array, if necessary, to be able to hold given index
239	+	*/
240	+	private void grow(int index) {
241	+	int newlen = queue.length;
242	+	if (index < newlen) // don't need to grow
243	+	return;
244	+	if (index == Integer.MAX_VALUE)
245	+	throw new OutOfMemoryError();
246	+	while (newlen <= index) {
247	+	if (newlen >= Integer.MAX_VALUE / 2)  // avoid overflow
248	+	newlen = Integer.MAX_VALUE;
249	+	else
250	+	newlen <<= 2;
251	+	}
252	+	Object[] newQueue = new Object[newlen];
253	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
254	+	queue = newQueue;
255	+	}
256	+
257	+	// Queue Methods
258	+
259	+	/**
260	+	* Add the specified element to this priority queue.
261	+	*
262	+	* @return <tt>true</tt>
263	+	* @throws ClassCastException if the specified element cannot be compared
264	+	* with elements currently in the priority queue according
265	+	* to the priority queue's ordering.
266	+	* @throws NullPointerException if the specified element is <tt>null</tt>.
267	+	*/
268	+	public boolean offer(E o) {
269	+	if (o == null)
270	+	throw new NullPointerException();
271	+	modCount++;
272	+	++size;
273	+
274	+	// Grow backing store if necessary
275	+	if (size >= queue.length)
276	+	grow(size);
277	+
278	+	queue[size] = o;
279	+	fixUp(size);
280	+	return true;
281	+	}
282	+
283		public E poll() {
284	<	return null;
284	>	if (size == 0)
285	>	return null;
286	>	return (E) remove(1);
287		}
288	+
289		public E peek() {
290	<	return null;
290	>	return (E) queue[1];
291	>	}
292	>
293	>	// Collection Methods
294	>
295	>	// these first two override just to get the throws docs
296	>
297	>	/**
298	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
299	>	* @throws ClassCastException if the specified element cannot be compared
300	>	* with elements currently in the priority queue according
301	>	* to the priority queue's ordering.
302	>	*/
303	>	public boolean add(E o) {
304	>	return super.add(o);
305	>	}
306	>
307	>	/**
308	>	* @throws ClassCastException if any element cannot be compared
309	>	* with elements currently in the priority queue according
310	>	* to the priority queue's ordering.
311	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
312	>	* is <tt>null</tt>
313	>	*/
314	>	public boolean addAll(Collection<? extends E> c) {
315	>	return super.addAll(c);
316		}
317
318	<	public boolean isEmpty() {
318	>	public boolean remove(Object o) {
319	>	if (o == null)
320	>	return false;
321	>
322	>	if (comparator == null) {
323	>	for (int i = 1; i <= size; i++) {
324	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
325	>	remove(i);
326	>	return true;
327	>	}
328	>	}
329	>	} else {
330	>	for (int i = 1; i <= size; i++) {
331	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
332	>	remove(i);
333	>	return true;
334	>	}
335	>	}
336	>	}
337		return false;
338		}
339	+
340	+	public Iterator<E> iterator() {
341	+	return new Itr();
342	+	}
343	+
344	+	private class Itr implements Iterator<E> {
345	+	/**
346	+	* Index (into queue array) of element to be returned by
347	+	* subsequent call to next.
348	+	*/
349	+	private int cursor = 1;
350	+
351	+	/**
352	+	* Index of element returned by most recent call to next or
353	+	* previous.  Reset to 0 if this element is deleted by a call
354	+	* to remove.
355	+	*/
356	+	private int lastRet = 0;
357	+
358	+	/**
359	+	* The modCount value that the iterator believes that the backing
360	+	* List should have.  If this expectation is violated, the iterator
361	+	* has detected concurrent modification.
362	+	*/
363	+	private int expectedModCount = modCount;
364	+
365	+	public boolean hasNext() {
366	+	return cursor <= size;
367	+	}
368	+
369	+	public E next() {
370	+	checkForComodification();
371	+	if (cursor > size)
372	+	throw new NoSuchElementException();
373	+	E result = (E) queue[cursor];
374	+	lastRet = cursor++;
375	+	return result;
376	+	}
377	+
378	+	public void remove() {
379	+	if (lastRet == 0)
380	+	throw new IllegalStateException();
381	+	checkForComodification();
382	+
383	+	PriorityQueue.this.remove(lastRet);
384	+	if (lastRet < cursor)
385	+	cursor--;
386	+	lastRet = 0;
387	+	expectedModCount = modCount;
388	+	}
389	+
390	+	final void checkForComodification() {
391	+	if (modCount != expectedModCount)
392	+	throw new ConcurrentModificationException();
393	+	}
394	+	}
395	+
396	+	/**
397	+	* Returns the number of elements in this priority queue.
398	+	*
399	+	* @return the number of elements in this priority queue.
400	+	*/
401		public int size() {
402	<	return 0;
402	>	return size;
403		}
404	<	public Object[] toArray() {
405	<	return null;
404	>
405	>	/**
406	>	* Remove all elements from the priority queue.
407	>	*/
408	>	public void clear() {
409	>	modCount++;
410	>
411	>	// Null out element references to prevent memory leak
412	>	for (int i=1; i<=size; i++)
413	>	queue[i] = null;
414	>
415	>	size = 0;
416		}
417
418	<	public <T> T[] toArray(T[] array) {
419	<	return null;
418	>	/**
419	>	* Removes and returns the ith element from queue.  Recall
420	>	* that queue is one-based, so 1 <= i <= size.
421	>	*
422	>	* XXX: Could further special-case i==size, but is it worth it?
423	>	* XXX: Could special-case i==0, but is it worth it?
424	>	*/
425	>	private E remove(int i) {
426	>	assert i <= size;
427	>	modCount++;
428	>
429	>	E result = (E) queue[i];
430	>	queue[i] = queue[size];
431	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
432	>	if (i <= size)
433	>	fixDown(i);
434	>	return result;
435	>	}
436	>
437	>	/**
438	>	* Establishes the heap invariant (described above) assuming the heap
439	>	* satisfies the invariant except possibly for the leaf-node indexed by k
440	>	* (which may have a nextExecutionTime less than its parent's).
441	>	*
442	>	* This method functions by "promoting" queue[k] up the hierarchy
443	>	* (by swapping it with its parent) repeatedly until queue[k]
444	>	* is greater than or equal to its parent.
445	>	*/
446	>	private void fixUp(int k) {
447	>	if (comparator == null) {
448	>	while (k > 1) {
449	>	int j = k >> 1;
450	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
451	>	break;
452	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
453	>	k = j;
454	>	}
455	>	} else {
456	>	while (k > 1) {
457	>	int j = k >> 1;
458	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
459	>	break;
460	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
461	>	k = j;
462	>	}
463	>	}
464	>	}
465	>
466	>	/**
467	>	* Establishes the heap invariant (described above) in the subtree
468	>	* rooted at k, which is assumed to satisfy the heap invariant except
469	>	* possibly for node k itself (which may be greater than its children).
470	>	*
471	>	* This method functions by "demoting" queue[k] down the hierarchy
472	>	* (by swapping it with its smaller child) repeatedly until queue[k]
473	>	* is less than or equal to its children.
474	>	*/
475	>	private void fixDown(int k) {
476	>	int j;
477	>	if (comparator == null) {
478	>	while ((j = k << 1) <= size) {
479	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
480	>	j++; // j indexes smallest kid
481	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
482	>	break;
483	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
484	>	k = j;
485	>	}
486	>	} else {
487	>	while ((j = k << 1) <= size) {
488	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
489	>	j++; // j indexes smallest kid
490	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
491	>	break;
492	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
493	>	k = j;
494	>	}
495	>	}
496	>	}
497	>
498	>	public Comparator<? super E> comparator() {
499	>	return comparator;
500	>	}
501	>
502	>	/**
503	>	* Save the state of the instance to a stream (that
504	>	* is, serialize it).
505	>	*
506	>	* @serialData The length of the array backing the instance is
507	>	* emitted (int), followed by all of its elements (each an
508	>	* <tt>Object</tt>) in the proper order.
509	>	* @param s the stream
510	>	*/
511	>	private void writeObject(java.io.ObjectOutputStream s)
512	>	throws java.io.IOException{
513	>	// Write out element count, and any hidden stuff
514	>	s.defaultWriteObject();
515	>
516	>	// Write out array length
517	>	s.writeInt(queue.length);
518	>
519	>	// Write out all elements in the proper order.
520	>	for (int i=0; i<size; i++)
521	>	s.writeObject(queue[i]);
522	>	}
523	>
524	>	/**
525	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
526	>	* deserialize it).
527	>	* @param s the stream
528	>	*/
529	>	private void readObject(java.io.ObjectInputStream s)
530	>	throws java.io.IOException, ClassNotFoundException {
531	>	// Read in size, and any hidden stuff
532	>	s.defaultReadObject();
533	>
534	>	// Read in array length and allocate array
535	>	int arrayLength = s.readInt();
536	>	queue = new Object[arrayLength];
537	>
538	>	// Read in all elements in the proper order.
539	>	for (int i=0; i<size; i++)
540	>	queue[i] = s.readObject();
541		}
542
543		}
544	+

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