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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 1.7 by dl, Tue Jun 24 14:34:30 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	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
36
37	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
37	>	/**
38	>	* Priority queue represented as a balanced binary heap: the two children
39	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
40	>	* ordered by comparator, or by the elements' natural ordering, if
41	>	* comparator is null:  For each node n in the heap and each descendant d
42	>	* of n, n <= d.
43	>	*
44	>	* The element with the lowest value is in queue[1], assuming the queue is
45	>	* nonempty.  (A one-based array is used in preference to the traditional
46	>	* zero-based array to simplify parent and child calculations.)
47	>	*
48	>	* queue.length must be >= 2, even if size == 0.
49	>	*/
50	>	private transient E[] queue;
51
52	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
52	>	/**
53	>	* The number of elements in the priority queue.
54	>	*/
55	>	private int size = 0;
56
57	<	public boolean add(E x) {
58	<	return false;
59	<	}
60	<	public boolean offer(E x) {
61	<	return false;
62	<	}
63	<	public boolean remove(Object x) {
64	<	return false;
57	>	/**
58	>	* The comparator, or null if priority queue uses elements'
59	>	* natural ordering.
60	>	*/
61	>	private final Comparator<E> comparator;
62	>
63	>	/**
64	>	* The number of times this priority queue has been
65	>	* <i>structurally modified</i>.  See AbstractList for gory details.
66	>	*/
67	>	private transient int modCount = 0;
68	>
69	>	/**
70	>	* Create a new priority queue with the default initial capacity
71	>	* (11) that orders its elements according to their natural
72	>	* ordering (using <tt>Comparable</tt>.)
73	>	*/
74	>	public PriorityQueue() {
75	>	this(DEFAULT_INITIAL_CAPACITY);
76		}
77
78	<	public E remove() {
79	<	return null;
78	>	/**
79	>	* Create a new priority queue with the specified initial capacity
80	>	* that orders its elements according to their natural ordering
81	>	* (using <tt>Comparable</tt>.)
82	>	*
83	>	* @param initialCapacity the initial capacity for this priority queue.
84	>	*/
85	>	public PriorityQueue(int initialCapacity) {
86	>	this(initialCapacity, null);
87		}
88	<	public Iterator<E> iterator() {
89	<	return null;
88	>
89	>	/**
90	>	* Create a new priority queue with the specified initial capacity (11)
91	>	* that orders its elements according to the specified comparator.
92	>	*
93	>	* @param initialCapacity the initial capacity for this priority queue.
94	>	* @param comparator the comparator used to order this priority queue.
95	>	*/
96	>	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
97	>	if (initialCapacity < 1)
98	>	initialCapacity = 1;
99	>	queue = new E[initialCapacity + 1];
100	>	this.comparator = comparator;
101		}
102
103	<	public E element() {
104	<	return null;
103	>	/**
104	>	* Create a new priority queue containing the elements in the specified
105	>	* collection.  The priority queue has an initial capacity of 110% of the
106	>	* size of the specified collection. If the specified collection
107	>	* implements the {@link Sorted} interface, the priority queue will be
108	>	* sorted according to the same comparator, or according to its elements'
109	>	* natural order if the collection is sorted according to its elements'
110	>	* natural order.  If the specified collection does not implement
111	>	* <tt>Sorted</tt>, the priority queue is ordered according to
112	>	* its elements' natural order.
113	>	*
114	>	* @param initialElements the collection whose elements are to be placed
115	>	*        into this priority queue.
116	>	* @throws ClassCastException if elements of the specified collection
117	>	*         cannot be compared to one another according to the priority
118	>	*         queue's ordering.
119	>	* @throws NullPointerException if the specified collection or an
120	>	*         element of the specified collection is <tt>null</tt>.
121	>	*/
122	>	public PriorityQueue(Collection<E> initialElements) {
123	>	int sz = initialElements.size();
124	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
125	>	Integer.MAX_VALUE - 1);
126	>	if (initialCapacity < 1)
127	>	initialCapacity = 1;
128	>	queue = new E[initialCapacity + 1];
129	>
130	>	/* Commented out to compile with generics compiler
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	>	*/
138	>	{
139	>	comparator = null;
140	>	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
141	>	add(i.next());
142	>	}
143		}
144	+
145	+	// Queue Methods
146	+
147	+	/**
148	+	* Remove and return the minimal element from this priority queue
149	+	* if it contains one or more elements, otherwise return
150	+	* <tt>null</tt>.  The term <i>minimal</i> is defined according to
151	+	* this priority queue's order.
152	+	*
153	+	* @return the minimal element from this priority queue if it contains
154	+	*         one or more elements, otherwise <tt>null</tt>.
155	+	*/
156		public E poll() {
157	<	return null;
157	>	if (size == 0)
158	>	return null;
159	>	return remove(1);
160		}
161	+
162	+	/**
163	+	* Return, but do not remove, the minimal element from the
164	+	* priority queue, or return <tt>null</tt> if the queue is empty.
165	+	* The term <i>minimal</i> is defined according to this priority
166	+	* queue's order.  This method returns the same object reference
167	+	* that would be returned by by the <tt>poll</tt> method.  The two
168	+	* methods differ in that this method does not remove the element
169	+	* from the priority queue.
170	+	*
171	+	* @return the minimal element from this priority queue if it contains
172	+	*         one or more elements, otherwise <tt>null</tt>.
173	+	*/
174		public E peek() {
175	<	return null;
175	>	return queue[1];
176		}
177
178	<	public boolean isEmpty() {
178	>	// Collection Methods
179	>
180	>	/**
181	>	* Removes a single instance of the specified element from this priority
182	>	* queue, if it is present.  Returns true if this collection contained the
183	>	* specified element (or equivalently, if this collection changed as a
184	>	* result of the call).
185	>	*
186	>	* @param element the element to be removed from this collection,
187	>	* if present.
188	>	* @return <tt>true</tt> if this collection changed as a result of the
189	>	*         call
190	>	* @throws ClassCastException if the specified element cannot be compared
191	>	*            with elements currently in the priority queue according
192	>	*            to the priority queue's ordering.
193	>	* @throws NullPointerException if the specified element is null.
194	>	*/
195	>	public boolean remove(Object element) {
196	>	if (element == null)
197	>	throw new NullPointerException();
198	>
199	>	if (comparator == null) {
200	>	for (int i = 1; i <= size; i++) {
201	>	if (((Comparable)queue[i]).compareTo(element) == 0) {
202	>	remove(i);
203	>	return true;
204	>	}
205	>	}
206	>	} else {
207	>	for (int i = 1; i <= size; i++) {
208	>	if (comparator.compare(queue[i], (E) element) == 0) {
209	>	remove(i);
210	>	return true;
211	>	}
212	>	}
213	>	}
214		return false;
215		}
216	+
217	+	/**
218	+	* Returns an iterator over the elements in this priority queue.  The
219	+	* elements of the priority queue will be returned by this iterator in the
220	+	* order specified by the queue, which is to say the order they would be
221	+	* returned by repeated calls to <tt>poll</tt>.
222	+	*
223	+	* @return an <tt>Iterator</tt> over the elements in this priority queue.
224	+	*/
225	+	public Iterator<E> iterator() {
226	+	return new Itr();
227	+	}
228	+
229	+	private class Itr implements Iterator<E> {
230	+	/**
231	+	* Index (into queue array) of element to be returned by
232	+	* subsequent call to next.
233	+	*/
234	+	private int cursor = 1;
235	+
236	+	/**
237	+	* Index of element returned by most recent call to next or
238	+	* previous.  Reset to 0 if this element is deleted by a call
239	+	* to remove.
240	+	*/
241	+	private int lastRet = 0;
242	+
243	+	/**
244	+	* The modCount value that the iterator believes that the backing
245	+	* List should have.  If this expectation is violated, the iterator
246	+	* has detected concurrent modification.
247	+	*/
248	+	private int expectedModCount = modCount;
249	+
250	+	public boolean hasNext() {
251	+	return cursor <= size;
252	+	}
253	+
254	+	public E next() {
255	+	checkForComodification();
256	+	if (cursor > size)
257	+	throw new NoSuchElementException();
258	+	E result = queue[cursor];
259	+	lastRet = cursor++;
260	+	return result;
261	+	}
262	+
263	+	public void remove() {
264	+	if (lastRet == 0)
265	+	throw new IllegalStateException();
266	+	checkForComodification();
267	+
268	+	PriorityQueue.this.remove(lastRet);
269	+	if (lastRet < cursor)
270	+	cursor--;
271	+	lastRet = 0;
272	+	expectedModCount = modCount;
273	+	}
274	+
275	+	final void checkForComodification() {
276	+	if (modCount != expectedModCount)
277	+	throw new ConcurrentModificationException();
278	+	}
279	+	}
280	+
281	+	/**
282	+	* Returns the number of elements in this priority queue.
283	+	*
284	+	* @return the number of elements in this priority queue.
285	+	*/
286		public int size() {
287	<	return 0;
287	>	return size;
288	>	}
289	>
290	>	/**
291	>	* Add the specified element to this priority queue.
292	>	*
293	>	* @param element the element to add.
294	>	* @return true
295	>	* @throws ClassCastException if the specified element cannot be compared
296	>	*            with elements currently in the priority queue according
297	>	*            to the priority queue's ordering.
298	>	* @throws NullPointerException if the specified element is null.
299	>	*/
300	>	public boolean offer(E element) {
301	>	if (element == null)
302	>	throw new NullPointerException();
303	>	modCount++;
304	>
305	>	// Grow backing store if necessary
306	>	if (++size == queue.length) {
307	>	E[] newQueue = new E[2 * queue.length];
308	>	System.arraycopy(queue, 0, newQueue, 0, size);
309	>	queue = newQueue;
310	>	}
311	>
312	>	queue[size] = element;
313	>	fixUp(size);
314	>	return true;
315	>	}
316	>
317	>	/**
318	>	* Remove all elements from the priority queue.
319	>	*/
320	>	public void clear() {
321	>	modCount++;
322	>
323	>	// Null out element references to prevent memory leak
324	>	for (int i=1; i<=size; i++)
325	>	queue[i] = null;
326	>
327	>	size = 0;
328	>	}
329	>
330	>	/**
331	>	* Removes and returns the ith element from queue.  Recall
332	>	* that queue is one-based, so 1 <= i <= size.
333	>	*
334	>	* XXX: Could further special-case i==size, but is it worth it?
335	>	* XXX: Could special-case i==0, but is it worth it?
336	>	*/
337	>	private E remove(int i) {
338	>	assert i <= size;
339	>	modCount++;
340	>
341	>	E result = queue[i];
342	>	queue[i] = queue[size];
343	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
344	>	if (i <= size)
345	>	fixDown(i);
346	>	return result;
347	>	}
348	>
349	>	/**
350	>	* Establishes the heap invariant (described above) assuming the heap
351	>	* satisfies the invariant except possibly for the leaf-node indexed by k
352	>	* (which may have a nextExecutionTime less than its parent's).
353	>	*
354	>	* This method functions by "promoting" queue[k] up the hierarchy
355	>	* (by swapping it with its parent) repeatedly until queue[k]
356	>	* is greater than or equal to its parent.
357	>	*/
358	>	private void fixUp(int k) {
359	>	if (comparator == null) {
360	>	while (k > 1) {
361	>	int j = k >> 1;
362	>	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
363	>	break;
364	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
365	>	k = j;
366	>	}
367	>	} else {
368	>	while (k > 1) {
369	>	int j = k >> 1;
370	>	if (comparator.compare(queue[j], queue[k]) <= 0)
371	>	break;
372	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
373	>	k = j;
374	>	}
375	>	}
376		}
377	<	public Object[] toArray() {
378	<	return null;
377	>
378	>	/**
379	>	* Establishes the heap invariant (described above) in the subtree
380	>	* rooted at k, which is assumed to satisfy the heap invariant except
381	>	* possibly for node k itself (which may be greater than its children).
382	>	*
383	>	* This method functions by "demoting" queue[k] down the hierarchy
384	>	* (by swapping it with its smaller child) repeatedly until queue[k]
385	>	* is less than or equal to its children.
386	>	*/
387	>	private void fixDown(int k) {
388	>	int j;
389	>	if (comparator == null) {
390	>	while ((j = k << 1) <= size) {
391	>	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
392	>	j++; // j indexes smallest kid
393	>	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
394	>	break;
395	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
396	>	k = j;
397	>	}
398	>	} else {
399	>	while ((j = k << 1) <= size) {
400	>	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
401	>	j++; // j indexes smallest kid
402	>	if (comparator.compare(queue[k], queue[j]) <= 0)
403	>	break;
404	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
405	>	k = j;
406	>	}
407	>	}
408	>	}
409	>
410	>	/**
411	>	* Returns the comparator associated with this priority queue, or
412	>	* <tt>null</tt> if it uses its elements' natural ordering.
413	>	*
414	>	* @return the comparator associated with this priority queue, or
415	>	*         <tt>null</tt> if it uses its elements' natural ordering.
416	>	*/
417	>	Comparator comparator() {
418	>	return comparator;
419		}
420
421	<	public <T> T[] toArray(T[] array) {
422	<	return null;
421	>	/**
422	>	* Save the state of the instance to a stream (that
423	>	* is, serialize it).
424	>	*
425	>	* @serialData The length of the array backing the instance is
426	>	* emitted (int), followed by all of its elements (each an
427	>	* <tt>Object</tt>) in the proper order.
428	>	* @param s the stream
429	>	*/
430	>	private synchronized void writeObject(java.io.ObjectOutputStream s)
431	>	throws java.io.IOException{
432	>	// Write out element count, and any hidden stuff
433	>	s.defaultWriteObject();
434	>
435	>	// Write out array length
436	>	s.writeInt(queue.length);
437	>
438	>	// Write out all elements in the proper order.
439	>	for (int i=0; i<size; i++)
440	>	s.writeObject(queue[i]);
441	>	}
442	>
443	>	/**
444	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
445	>	* deserialize it).
446	>	* @param s the stream
447	>	*/
448	>	private synchronized void readObject(java.io.ObjectInputStream s)
449	>	throws java.io.IOException, ClassNotFoundException {
450	>	// Read in size, and any hidden stuff
451	>	s.defaultReadObject();
452	>
453	>	// Read in array length and allocate array
454	>	int arrayLength = s.readInt();
455	>	queue = new E[arrayLength];
456	>
457	>	// Read in all elements in the proper order.
458	>	for (int i=0; i<size; i++)
459	>	queue[i] = (E)s.readObject();
460		}
461
462		}

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