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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 1.5 by dl, Tue May 27 18:20:06 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 the order specified at creation time.  This order is
6	>	* specified as for {@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	>	* these elements are tied for least value, no guarantees are made as to
12	>	* which of elements is returned.
13	>	*
14	>	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
15	>	* the array used to store the elements on the queue.  It is always at least
16	>	* as large as the queue size.  As elements are added to a priority list,
17	>	* its capacity grows automatically.  The details of the growth policy are not
18	>	* specified.
19	>	*
20	>	*<p>Implementation note: this implementation provides O(log(n)) time for
21	>	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
22	>	* methods; linear time for the <tt>remove(Object)</tt> and
23	>	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
24	>	* <tt>element</tt>, and <tt>size</tt> methods.
25	>	*
26	>	* <p>This class is a member of the
27	>	* <a href="{@docRoot}/../guide/collections/index.html">
28	>	* Java Collections Framework</a>.
29	>	*/
30	>	public class PriorityQueue<E> extends AbstractQueue<E>
31	>	implements Queue<E>
32	>	{
33	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
34
35	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
35	>	/**
36	>	* Priority queue represented as a balanced binary heap: the two children
37	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
38	>	* ordered by comparator, or by the elements' natural ordering, if
39	>	* comparator is null:  For each node n in the heap, and each descendant
40	>	* of n, d, n <= d.
41	>	*
42	>	* The element with the lowest value is in queue[1] (assuming the queue is
43	>	* nonempty). A one-based array is used in preference to the traditional
44	>	* zero-based array to simplify parent and child calculations.
45	>	*
46	>	* queue.length must be >= 2, even if size == 0.
47	>	*/
48	>	private transient E[] queue;
49
50	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
50	>	/**
51	>	* The number of elements in the priority queue.
52	>	*/
53	>	private int size = 0;
54
55	<	public boolean add(E x) {
56	<	return false;
57	<	}
58	<	public boolean offer(E x) {
59	<	return false;
60	<	}
61	<	public boolean remove(Object x) {
62	<	return false;
55	>	/**
56	>	* The comparator, or null if priority queue uses elements'
57	>	* natural ordering.
58	>	*/
59	>	private final Comparator<E> comparator;
60	>
61	>	/**
62	>	* The number of times this priority queue has been
63	>	* <i>structurally modified</i>.  See AbstractList for gory details.
64	>	*/
65	>	private transient int modCount = 0;
66	>
67	>	/**
68	>	* Create a new priority queue with the default initial capacity (11)
69	>	* that orders its elements according to their natural ordering.
70	>	*/
71	>	public PriorityQueue() {
72	>	this(DEFAULT_INITIAL_CAPACITY);
73		}
74
75	<	public E remove() {
76	<	return null;
75	>	/**
76	>	* Create a new priority queue with the specified initial capacity
77	>	* that orders its elements according to their natural ordering.
78	>	*
79	>	* @param initialCapacity the initial capacity for this priority queue.
80	>	*/
81	>	public PriorityQueue(int initialCapacity) {
82	>	this(initialCapacity, null);
83		}
84	<	public Iterator<E> iterator() {
85	<	return null;
84	>
85	>	/**
86	>	* Create a new priority queue with the specified initial capacity (11)
87	>	* that orders its elements according to the specified comparator.
88	>	*
89	>	* @param initialCapacity the initial capacity for this priority queue.
90	>	* @param comparator the comparator used to order this priority queue.
91	>	*/
92	>	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
93	>	if (initialCapacity < 1)
94	>	initialCapacity = 1;
95	>	queue = new E[initialCapacity + 1];
96	>	this.comparator = comparator;
97		}
98
99	<	public E element() {
100	<	return null;
99	>	/**
100	>	* Create a new priority queue containing the elements in the specified
101	>	* collection.  The priority queue has an initial capacity of 110% of the
102	>	* size of the specified collection. If the specified collection
103	>	* implements the {@link Sorted} interface, the priority queue will be
104	>	* sorted according to the same comparator, or according to its elements'
105	>	* natural order if the collection is sorted according to its elements'
106	>	* natural order.  If the specified collection does not implement the
107	>	* <tt>Sorted</tt> interface, the priority queue is ordered according to
108	>	* its elements' natural order.
109	>	*
110	>	* @param initialElements the collection whose elements are to be placed
111	>	*        into this priority queue.
112	>	* @throws ClassCastException if elements of the specified collection
113	>	*         cannot be compared to one another according to the priority
114	>	*         queue's ordering.
115	>	* @throws NullPointerException if the specified collection or an
116	>	*         element of the specified collection is <tt>null</tt>.
117	>	*/
118	>	public PriorityQueue(Collection<E> initialElements) {
119	>	int sz = initialElements.size();
120	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
121	>	Integer.MAX_VALUE - 1);
122	>	if (initialCapacity < 1)
123	>	initialCapacity = 1;
124	>	queue = new E[initialCapacity + 1];
125	>
126	>	/* Commented out to compile with generics compiler
127	>
128	>	if (initialElements instanceof Sorted) {
129	>	comparator = ((Sorted)initialElements).comparator();
130	>	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
131	>	queue[++size] = i.next();
132	>	} else {
133	>	*/
134	>	{
135	>	comparator = null;
136	>	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	>	add(i.next());
138	>	}
139		}
140	+
141	+	// Queue Methods
142	+
143	+	/**
144	+	* Remove and return the minimal element from this priority queue if
145	+	* it contains one or more elements, otherwise <tt>null</tt>.  The term
146	+	* <i>minimal</i> is defined according to this priority queue's order.
147	+	*
148	+	* @return the minimal element from this priority queue if it contains
149	+	*         one or more elements, otherwise <tt>null</tt>.
150	+	*/
151		public E poll() {
152	<	return null;
152	>	if (size == 0)
153	>	return null;
154	>	return remove(1);
155		}
156	+
157	+	/**
158	+	* Return, but do not remove, the minimal element from the priority queue,
159	+	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
160	+	* defined according to this priority queue's order.  This method returns
161	+	* the same object reference that would be returned by by the
162	+	* <tt>poll</tt> method.  The two methods differ in that this method
163	+	* does not remove the element from the priority queue.
164	+	*
165	+	* @return the minimal element from this priority queue if it contains
166	+	*         one or more elements, otherwise <tt>null</tt>.
167	+	*/
168		public E peek() {
169	<	return null;
169	>	return queue[1];
170		}
171
172	<	public boolean isEmpty() {
172	>	// Collection Methods
173	>
174	>	/**
175	>	* Removes a single instance of the specified element from this priority
176	>	* queue, if it is present.  Returns true if this collection contained the
177	>	* specified element (or equivalently, if this collection changed as a
178	>	* result of the call).
179	>	*
180	>	* @param o element to be removed from this collection, if present.
181	>	* @return <tt>true</tt> if this collection changed as a result of the
182	>	*         call
183	>	* @throws ClassCastException if the specified element cannot be compared
184	>	*            with elements currently in the priority queue according
185	>	*            to the priority queue's ordering.
186	>	* @throws NullPointerException if the specified element is null.
187	>	*/
188	>	public boolean remove(Object element) {
189	>	if (element == null)
190	>	throw new NullPointerException();
191	>
192	>	if (comparator == null) {
193	>	for (int i = 1; i <= size; i++) {
194	>	if (((Comparable)queue[i]).compareTo(element) == 0) {
195	>	remove(i);
196	>	return true;
197	>	}
198	>	}
199	>	} else {
200	>	for (int i = 1; i <= size; i++) {
201	>	if (comparator.compare(queue[i], (E) element) == 0) {
202	>	remove(i);
203	>	return true;
204	>	}
205	>	}
206	>	}
207		return false;
208		}
209	+
210	+	/**
211	+	* Returns an iterator over the elements in this priority queue.  The
212	+	* first element returned by this iterator is the same element that
213	+	* would be returned by a call to <tt>peek</tt>.
214	+	*
215	+	* @return an <tt>Iterator</tt> over the elements in this priority queue.
216	+	*/
217	+	public Iterator<E> iterator() {
218	+	return new Itr();
219	+	}
220	+
221	+	private class Itr implements Iterator<E> {
222	+	/**
223	+	* Index (into queue array) of element to be returned by
224	+	* subsequent call to next.
225	+	*/
226	+	int cursor = 1;
227	+
228	+	/**
229	+	* Index of element returned by most recent call to next or
230	+	* previous.  Reset to 0 if this element is deleted by a call
231	+	* to remove.
232	+	*/
233	+	int lastRet = 0;
234	+
235	+	/**
236	+	* The modCount value that the iterator believes that the backing
237	+	* List should have.  If this expectation is violated, the iterator
238	+	* has detected concurrent modification.
239	+	*/
240	+	int expectedModCount = modCount;
241	+
242	+	public boolean hasNext() {
243	+	return cursor <= size;
244	+	}
245	+
246	+	public E next() {
247	+	checkForComodification();
248	+	if (cursor > size)
249	+	throw new NoSuchElementException();
250	+	E result = queue[cursor];
251	+	lastRet = cursor++;
252	+	return result;
253	+	}
254	+
255	+	public void remove() {
256	+	if (lastRet == 0)
257	+	throw new IllegalStateException();
258	+	checkForComodification();
259	+
260	+	PriorityQueue.this.remove(lastRet);
261	+	if (lastRet < cursor)
262	+	cursor--;
263	+	lastRet = 0;
264	+	expectedModCount = modCount;
265	+	}
266	+
267	+	final void checkForComodification() {
268	+	if (modCount != expectedModCount)
269	+	throw new ConcurrentModificationException();
270	+	}
271	+	}
272	+
273	+	/**
274	+	* Returns the number of elements in this priority queue.
275	+	*
276	+	* @return the number of elements in this priority queue.
277	+	*/
278		public int size() {
279	<	return 0;
279	>	return size;
280	>	}
281	>
282	>	/**
283	>	* Add the specified element to this priority queue.
284	>	*
285	>	* @param element the element to add.
286	>	* @return true
287	>	* @throws ClassCastException if the specified element cannot be compared
288	>	*            with elements currently in the priority queue according
289	>	*            to the priority queue's ordering.
290	>	* @throws NullPointerException if the specified element is null.
291	>	*/
292	>	public boolean offer(E element) {
293	>	if (element == null)
294	>	throw new NullPointerException();
295	>	modCount++;
296	>
297	>	// Grow backing store if necessary
298	>	if (++size == queue.length) {
299	>	E[] newQueue = new E[2 * queue.length];
300	>	System.arraycopy(queue, 0, newQueue, 0, size);
301	>	queue = newQueue;
302	>	}
303	>
304	>	queue[size] = element;
305	>	fixUp(size);
306	>	return true;
307	>	}
308	>
309	>	/**
310	>	* Remove all elements from the priority queue.
311	>	*/
312	>	public void clear() {
313	>	modCount++;
314	>
315	>	// Null out element references to prevent memory leak
316	>	for (int i=1; i<=size; i++)
317	>	queue[i] = null;
318	>
319	>	size = 0;
320	>	}
321	>
322	>	/**
323	>	* Removes and returns the ith element from queue.  Recall
324	>	* that queue is one-based, so 1 <= i <= size.
325	>	*
326	>	* XXX: Could further special-case i==size, but is it worth it?
327	>	* XXX: Could special-case i==0, but is it worth it?
328	>	*/
329	>	private E remove(int i) {
330	>	assert i <= size;
331	>	modCount++;
332	>
333	>	E result = queue[i];
334	>	queue[i] = queue[size];
335	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
336	>	if (i <= size)
337	>	fixDown(i);
338	>	return result;
339	>	}
340	>
341	>	/**
342	>	* Establishes the heap invariant (described above) assuming the heap
343	>	* satisfies the invariant except possibly for the leaf-node indexed by k
344	>	* (which may have a nextExecutionTime less than its parent's).
345	>	*
346	>	* This method functions by "promoting" queue[k] up the hierarchy
347	>	* (by swapping it with its parent) repeatedly until queue[k]
348	>	* is greater than or equal to its parent.
349	>	*/
350	>	private void fixUp(int k) {
351	>	if (comparator == null) {
352	>	while (k > 1) {
353	>	int j = k >> 1;
354	>	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
355	>	break;
356	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
357	>	k = j;
358	>	}
359	>	} else {
360	>	while (k > 1) {
361	>	int j = k >> 1;
362	>	if (comparator.compare(queue[j], queue[k]) <= 0)
363	>	break;
364	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
365	>	k = j;
366	>	}
367	>	}
368		}
369	<	public Object[] toArray() {
370	<	return null;
369	>
370	>	/**
371	>	* Establishes the heap invariant (described above) in the subtree
372	>	* rooted at k, which is assumed to satisfy the heap invariant except
373	>	* possibly for node k itself (which may be greater than its children).
374	>	*
375	>	* This method functions by "demoting" queue[k] down the hierarchy
376	>	* (by swapping it with its smaller child) repeatedly until queue[k]
377	>	* is less than or equal to its children.
378	>	*/
379	>	private void fixDown(int k) {
380	>	int j;
381	>	if (comparator == null) {
382	>	while ((j = k << 1) <= size) {
383	>	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
384	>	j++; // j indexes smallest kid
385	>	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
386	>	break;
387	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
388	>	k = j;
389	>	}
390	>	} else {
391	>	while ((j = k << 1) <= size) {
392	>	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
393	>	j++; // j indexes smallest kid
394	>	if (comparator.compare(queue[k], queue[j]) <= 0)
395	>	break;
396	>	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
397	>	k = j;
398	>	}
399	>	}
400	>	}
401	>
402	>	/**
403	>	* Returns the comparator associated with this priority queue, or
404	>	* <tt>null</tt> if it uses its elements' natural ordering.
405	>	*
406	>	* @return the comparator associated with this priority queue, or
407	>	*         <tt>null</tt> if it uses its elements' natural ordering.
408	>	*/
409	>	Comparator comparator() {
410	>	return comparator;
411		}
412
413	<	public <T> T[] toArray(T[] array) {
414	<	return null;
413	>	/**
414	>	* Save the state of the instance to a stream (that
415	>	* is, serialize it).
416	>	*
417	>	* @serialData The length of the array backing the instance is
418	>	* emitted (int), followed by all of its elements (each an
419	>	* <tt>Object</tt>) in the proper order.
420	>	*/
421	>	private synchronized void writeObject(java.io.ObjectOutputStream s)
422	>	throws java.io.IOException{
423	>	// Write out element count, and any hidden stuff
424	>	s.defaultWriteObject();
425	>
426	>	// Write out array length
427	>	s.writeInt(queue.length);
428	>
429	>	// Write out all elements in the proper order.
430	>	for (int i=0; i<size; i++)
431	>	s.writeObject(queue[i]);
432	>	}
433	>
434	>	/**
435	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
436	>	* deserialize it).
437	>	*/
438	>	private synchronized void readObject(java.io.ObjectInputStream s)
439	>	throws java.io.IOException, ClassNotFoundException {
440	>	// Read in size, and any hidden stuff
441	>	s.defaultReadObject();
442	>
443	>	// Read in array length and allocate array
444	>	int arrayLength = s.readInt();
445	>	queue = new E[arrayLength];
446	>
447	>	// Read in all elements in the proper order.
448	>	for (int i=0; i<size; i++)
449	>	queue[i] = (E)s.readObject();
450		}
451
452		}

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