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

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