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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 1.19 by tim, Mon Aug 4 16:14:48 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	>	* A 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, and is limited to <tt>Integer.MAX_VALUE-1</tt>.
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 Sorted, 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;
65	<	}
66	<	public boolean offer(E x) {
67	<	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	>	* Create 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 remove(Object x) {
89	<	return false;
88	>
89	>	/**
90	>	* Create 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
100	<	public E remove() {
101	<	return null;
100	>	/**
101	>	* Create 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	<	public Iterator<E> iterator() {
118	<	return null;
117	>
118	>	/**
119	>	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
120	>	* collection.  The priority queue has an initial capacity of 110% of the
121	>	* size of the specified collection (bounded by
122	>	* <tt>Integer.MAX_VALUE-1</tt>); or 1 if the collection is empty.
123	>	* If the specified collection
124	>	* implements the {@link Sorted} interface, the priority queue will be
125	>	* sorted according to the same comparator, or according to its elements'
126	>	* natural order if the collection is sorted according to its elements'
127	>	* natural order.  If the specified collection does not implement
128	>	* <tt>Sorted</tt>, the priority queue is ordered according to
129	>	* its elements' natural order.
130	>	*
131	>	* @param c the collection whose elements are to be placed
132	>	*        into this priority queue.
133	>	* @throws ClassCastException if elements of the specified collection
134	>	*         cannot be compared to one another according to the priority
135	>	*         queue's ordering.
136	>	* @throws NullPointerException if <tt>c</tt> or any element within it
137	>	* is <tt>null</tt>
138	>	*/
139	>	public PriorityQueue(Collection<? extends E> c) {
140	>	int sz = c.size();
141	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
142	>	Integer.MAX_VALUE - 1);
143	>	if (initialCapacity < 1)
144	>	initialCapacity = 1;
145	>
146	>	this.queue = new Object[initialCapacity + 1];
147	>
148	>	// FIXME: if c is larger than Integer.MAX_VALUE we'll
149	>	// overflow the array
150	>
151	>	if (c instanceof Sorted) {
152	>	comparator = (Comparator<? super E>)((Sorted)c).comparator();
153	>	} else {
154	>	comparator = null;
155	>	}
156	>
157	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
158	>	add(i.next());
159		}
160
161	<	public E element() {
162	<	return null;
161	>	// Queue Methods
162	>
163	>	/**
164	>	* Add the specified element to this priority queue.
165	>	*
166	>	* @return <tt>true</tt>
167	>	* @throws ClassCastException if the specified element cannot be compared
168	>	* with elements currently in the priority queue according
169	>	* to the priority queue's ordering.
170	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
171	>	*/
172	>	public boolean offer(E o) {
173	>	if (o == null)
174	>	throw new NullPointerException();
175	>	modCount++;
176	>	++size;
177	>
178	>	// Grow backing store if necessary
179	>	// FIXME: watch for overflow
180	>	// FIXME: what if we're full?
181	>	while (size >= queue.length) {
182	>	Object[] newQueue = new Object[2 * queue.length];
183	>	System.arraycopy(queue, 0, newQueue, 0, queue.length);
184	>	queue = newQueue;
185	>	}
186	>
187	>	queue[size] = o;
188	>	fixUp(size);
189	>	return true;
190		}
191	+
192		public E poll() {
193	<	return null;
193	>	if (size == 0)
194	>	return null;
195	>	return (E) remove(1);
196		}
197	+
198		public E peek() {
199	<	return null;
199	>	return (E) queue[1];
200		}
201
202	<	public boolean isEmpty() {
202	>	// Collection Methods
203	>
204	>	// these first two override just to get the throws docs
205	>
206	>	/**
207	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
208	>	* @throws ClassCastException if the specified element cannot be compared
209	>	* with elements currently in the priority queue according
210	>	* to the priority queue's ordering.
211	>	*/
212	>	public boolean add(E o) {
213	>	return super.add(o);
214	>	}
215	>
216	>	/**
217	>	* @throws ClassCastException if any element cannot be compared
218	>	* with elements currently in the priority queue according
219	>	* to the priority queue's ordering.
220	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
221	>	* is <tt>null</tt>
222	>	*/
223	>	public boolean addAll(Collection<? extends E> c) {
224	>	return super.addAll(c);
225	>	}
226	>
227	>	public boolean remove(Object o) {
228	>	if (o == null)
229	>	return false;
230	>
231	>	if (comparator == null) {
232	>	for (int i = 1; i <= size; i++) {
233	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
234	>	remove(i);
235	>	return true;
236	>	}
237	>	}
238	>	} else {
239	>	for (int i = 1; i <= size; i++) {
240	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
241	>	remove(i);
242	>	return true;
243	>	}
244	>	}
245	>	}
246		return false;
247		}
248	+
249	+	public Iterator<E> iterator() {
250	+	return new Itr();
251	+	}
252	+
253	+	private class Itr implements Iterator<E> {
254	+	/**
255	+	* Index (into queue array) of element to be returned by
256	+	* subsequent call to next.
257	+	*/
258	+	private int cursor = 1;
259	+
260	+	/**
261	+	* Index of element returned by most recent call to next or
262	+	* previous.  Reset to 0 if this element is deleted by a call
263	+	* to remove.
264	+	*/
265	+	private int lastRet = 0;
266	+
267	+	/**
268	+	* The modCount value that the iterator believes that the backing
269	+	* List should have.  If this expectation is violated, the iterator
270	+	* has detected concurrent modification.
271	+	*/
272	+	private int expectedModCount = modCount;
273	+
274	+	public boolean hasNext() {
275	+	return cursor <= size;
276	+	}
277	+
278	+	public E next() {
279	+	checkForComodification();
280	+	if (cursor > size)
281	+	throw new NoSuchElementException();
282	+	E result = (E) queue[cursor];
283	+	lastRet = cursor++;
284	+	return result;
285	+	}
286	+
287	+	public void remove() {
288	+	if (lastRet == 0)
289	+	throw new IllegalStateException();
290	+	checkForComodification();
291	+
292	+	PriorityQueue.this.remove(lastRet);
293	+	if (lastRet < cursor)
294	+	cursor--;
295	+	lastRet = 0;
296	+	expectedModCount = modCount;
297	+	}
298	+
299	+	final void checkForComodification() {
300	+	if (modCount != expectedModCount)
301	+	throw new ConcurrentModificationException();
302	+	}
303	+	}
304	+
305	+	/**
306	+	* Returns the number of elements in this priority queue.
307	+	*
308	+	* @return the number of elements in this priority queue.
309	+	*/
310		public int size() {
311	<	return 0;
311	>	return size;
312		}
313	<	public Object[] toArray() {
314	<	return null;
313	>
314	>	/**
315	>	* Remove all elements from the priority queue.
316	>	*/
317	>	public void clear() {
318	>	modCount++;
319	>
320	>	// Null out element references to prevent memory leak
321	>	for (int i=1; i<=size; i++)
322	>	queue[i] = null;
323	>
324	>	size = 0;
325		}
326
327	<	public <T> T[] toArray(T[] array) {
328	<	return null;
327	>	/**
328	>	* Removes and returns the ith element from queue.  Recall
329	>	* that queue is one-based, so 1 <= i <= size.
330	>	*
331	>	* XXX: Could further special-case i==size, but is it worth it?
332	>	* XXX: Could special-case i==0, but is it worth it?
333	>	*/
334	>	private E remove(int i) {
335	>	assert i <= size;
336	>	modCount++;
337	>
338	>	E result = (E) queue[i];
339	>	queue[i] = queue[size];
340	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
341	>	if (i <= size)
342	>	fixDown(i);
343	>	return result;
344	>	}
345	>
346	>	/**
347	>	* Establishes the heap invariant (described above) assuming the heap
348	>	* satisfies the invariant except possibly for the leaf-node indexed by k
349	>	* (which may have a nextExecutionTime less than its parent's).
350	>	*
351	>	* This method functions by "promoting" queue[k] up the hierarchy
352	>	* (by swapping it with its parent) repeatedly until queue[k]
353	>	* is greater than or equal to its parent.
354	>	*/
355	>	private void fixUp(int k) {
356	>	if (comparator == null) {
357	>	while (k > 1) {
358	>	int j = k >> 1;
359	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
360	>	break;
361	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
362	>	k = j;
363	>	}
364	>	} else {
365	>	while (k > 1) {
366	>	int j = k >> 1;
367	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
368	>	break;
369	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
370	>	k = j;
371	>	}
372	>	}
373	>	}
374	>
375	>	/**
376	>	* Establishes the heap invariant (described above) in the subtree
377	>	* rooted at k, which is assumed to satisfy the heap invariant except
378	>	* possibly for node k itself (which may be greater than its children).
379	>	*
380	>	* This method functions by "demoting" queue[k] down the hierarchy
381	>	* (by swapping it with its smaller child) repeatedly until queue[k]
382	>	* is less than or equal to its children.
383	>	*/
384	>	private void fixDown(int k) {
385	>	int j;
386	>	if (comparator == null) {
387	>	while ((j = k << 1) <= size) {
388	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
389	>	j++; // j indexes smallest kid
390	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
391	>	break;
392	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
393	>	k = j;
394	>	}
395	>	} else {
396	>	while ((j = k << 1) <= size) {
397	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
398	>	j++; // j indexes smallest kid
399	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
400	>	break;
401	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
402	>	k = j;
403	>	}
404	>	}
405	>	}
406	>
407	>	public Comparator<? super E> comparator() {
408	>	return comparator;
409	>	}
410	>
411	>	/**
412	>	* Save the state of the instance to a stream (that
413	>	* is, serialize it).
414	>	*
415	>	* @serialData The length of the array backing the instance is
416	>	* emitted (int), followed by all of its elements (each an
417	>	* <tt>Object</tt>) in the proper order.
418	>	* @param s the stream
419	>	*/
420	>	private synchronized void writeObject(java.io.ObjectOutputStream s)
421	>	throws java.io.IOException{
422	>	// Write out element count, and any hidden stuff
423	>	s.defaultWriteObject();
424	>
425	>	// Write out array length
426	>	s.writeInt(queue.length);
427	>
428	>	// Write out all elements in the proper order.
429	>	for (int i=0; i<size; i++)
430	>	s.writeObject(queue[i]);
431	>	}
432	>
433	>	/**
434	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
435	>	* deserialize it).
436	>	* @param s the stream
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 Object[arrayLength];
446	>
447	>	// Read in all elements in the proper order.
448	>	for (int i=0; i<size; i++)
449	>	queue[i] = s.readObject();
450		}
451
452		}
453	+

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