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

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