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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 1.20 by dholmes, Tue Aug 5 06:18:17 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 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.
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 or 1 if the collection is empty.
122	>	* If the specified collection
123	>	* implements the {@link Sorted} interface, the priority queue will be
124	>	* sorted according to the same comparator, or according to its elements'
125	>	* natural order if the collection is sorted according to its elements'
126	>	* natural order.  If the specified collection does not implement
127	>	* <tt>Sorted</tt>, the priority queue is ordered according to
128	>	* its elements' natural order.
129	>	*
130	>	* @param c the collection whose elements are to be placed
131	>	*        into this priority queue.
132	>	* @throws ClassCastException if elements of the specified collection
133	>	*         cannot be compared to one another according to the priority
134	>	*         queue's ordering.
135	>	* @throws NullPointerException if <tt>c</tt> or any element within it
136	>	* is <tt>null</tt>
137	>	*/
138	>	public PriorityQueue(Collection<? extends E> c) {
139	>	int sz = c.size();
140	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
141	>	Integer.MAX_VALUE - 1);
142	>	if (initialCapacity < 1)
143	>	initialCapacity = 1;
144	>
145	>	this.queue = new Object[initialCapacity + 1];
146	>
147	>	if (c instanceof Sorted) {
148	>	comparator = (Comparator<? super E>)((Sorted)c).comparator();
149	>	} else {
150	>	comparator = null;
151	>	}
152	>
153	>	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154	>	add(i.next());
155		}
156
157	<	public E element() {
158	<	return null;
157	>	// Queue Methods
158	>
159	>	/**
160	>	* Add the specified element to this priority queue.
161	>	*
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 <tt>null</tt>.
167	>	*/
168	>	public boolean offer(E o) {
169	>	if (o == 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] = o;
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 o) {
207	>	return super.add(o);
208	>	}
209	>
210	>	/**
211	>	* @throws ClassCastException if any element cannot be compared
212	>	* with elements currently in the priority queue according
213	>	* to the priority queue's ordering.
214	>	* @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
215	>	* is <tt>null</tt>
216	>	*/
217	>	public boolean addAll(Collection<? extends E> c) {
218	>	return super.addAll(c);
219		}
220
221	<	public boolean isEmpty() {
221	>	public boolean remove(Object o) {
222	>	if (o == null)
223	>	return false;
224	>
225	>	if (comparator == null) {
226	>	for (int i = 1; i <= size; i++) {
227	>	if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
228	>	remove(i);
229	>	return true;
230	>	}
231	>	}
232	>	} else {
233	>	for (int i = 1; i <= size; i++) {
234	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
235	>	remove(i);
236	>	return true;
237	>	}
238	>	}
239	>	}
240		return false;
241		}
242	+
243	+	public Iterator<E> iterator() {
244	+	return new Itr();
245	+	}
246	+
247	+	private class Itr implements Iterator<E> {
248	+	/**
249	+	* Index (into queue array) of element to be returned by
250	+	* subsequent call to next.
251	+	*/
252	+	private int cursor = 1;
253	+
254	+	/**
255	+	* Index of element returned by most recent call to next or
256	+	* previous.  Reset to 0 if this element is deleted by a call
257	+	* to remove.
258	+	*/
259	+	private int lastRet = 0;
260	+
261	+	/**
262	+	* The modCount value that the iterator believes that the backing
263	+	* List should have.  If this expectation is violated, the iterator
264	+	* has detected concurrent modification.
265	+	*/
266	+	private int expectedModCount = modCount;
267	+
268	+	public boolean hasNext() {
269	+	return cursor <= size;
270	+	}
271	+
272	+	public E next() {
273	+	checkForComodification();
274	+	if (cursor > size)
275	+	throw new NoSuchElementException();
276	+	E result = (E) queue[cursor];
277	+	lastRet = cursor++;
278	+	return result;
279	+	}
280	+
281	+	public void remove() {
282	+	if (lastRet == 0)
283	+	throw new IllegalStateException();
284	+	checkForComodification();
285	+
286	+	PriorityQueue.this.remove(lastRet);
287	+	if (lastRet < cursor)
288	+	cursor--;
289	+	lastRet = 0;
290	+	expectedModCount = modCount;
291	+	}
292	+
293	+	final void checkForComodification() {
294	+	if (modCount != expectedModCount)
295	+	throw new ConcurrentModificationException();
296	+	}
297	+	}
298	+
299	+	/**
300	+	* Returns the number of elements in this priority queue.
301	+	*
302	+	* @return the number of elements in this priority queue.
303	+	*/
304		public int size() {
305	<	return 0;
305	>	return size;
306		}
307	<	public Object[] toArray() {
308	<	return null;
307	>
308	>	/**
309	>	* Remove all elements from the priority queue.
310	>	*/
311	>	public void clear() {
312	>	modCount++;
313	>
314	>	// Null out element references to prevent memory leak
315	>	for (int i=1; i<=size; i++)
316	>	queue[i] = null;
317	>
318	>	size = 0;
319		}
320
321	<	public <T> T[] toArray(T[] array) {
322	<	return null;
321	>	/**
322	>	* Removes and returns the ith element from queue.  Recall
323	>	* that queue is one-based, so 1 <= i <= size.
324	>	*
325	>	* XXX: Could further special-case i==size, but is it worth it?
326	>	* XXX: Could special-case i==0, but is it worth it?
327	>	*/
328	>	private E remove(int i) {
329	>	assert i <= size;
330	>	modCount++;
331	>
332	>	E result = (E) queue[i];
333	>	queue[i] = queue[size];
334	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
335	>	if (i <= size)
336	>	fixDown(i);
337	>	return result;
338	>	}
339	>
340	>	/**
341	>	* Establishes the heap invariant (described above) assuming the heap
342	>	* satisfies the invariant except possibly for the leaf-node indexed by k
343	>	* (which may have a nextExecutionTime less than its parent's).
344	>	*
345	>	* This method functions by "promoting" queue[k] up the hierarchy
346	>	* (by swapping it with its parent) repeatedly until queue[k]
347	>	* is greater than or equal to its parent.
348	>	*/
349	>	private void fixUp(int k) {
350	>	if (comparator == null) {
351	>	while (k > 1) {
352	>	int j = k >> 1;
353	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
354	>	break;
355	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
356	>	k = j;
357	>	}
358	>	} else {
359	>	while (k > 1) {
360	>	int j = k >> 1;
361	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
362	>	break;
363	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
364	>	k = j;
365	>	}
366	>	}
367	>	}
368	>
369	>	/**
370	>	* Establishes the heap invariant (described above) in the subtree
371	>	* rooted at k, which is assumed to satisfy the heap invariant except
372	>	* possibly for node k itself (which may be greater than its children).
373	>	*
374	>	* This method functions by "demoting" queue[k] down the hierarchy
375	>	* (by swapping it with its smaller child) repeatedly until queue[k]
376	>	* is less than or equal to its children.
377	>	*/
378	>	private void fixDown(int k) {
379	>	int j;
380	>	if (comparator == null) {
381	>	while ((j = k << 1) <= size) {
382	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
383	>	j++; // j indexes smallest kid
384	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
385	>	break;
386	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
387	>	k = j;
388	>	}
389	>	} else {
390	>	while ((j = k << 1) <= size) {
391	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
392	>	j++; // j indexes smallest kid
393	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
394	>	break;
395	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
396	>	k = j;
397	>	}
398	>	}
399	>	}
400	>
401	>	public Comparator<? super E> comparator() {
402	>	return comparator;
403	>	}
404	>
405	>	/**
406	>	* Save the state of the instance to a stream (that
407	>	* is, serialize it).
408	>	*
409	>	* @serialData The length of the array backing the instance is
410	>	* emitted (int), followed by all of its elements (each an
411	>	* <tt>Object</tt>) in the proper order.
412	>	* @param s the stream
413	>	*/
414	>	private synchronized void writeObject(java.io.ObjectOutputStream s)
415	>	throws java.io.IOException{
416	>	// Write out element count, and any hidden stuff
417	>	s.defaultWriteObject();
418	>
419	>	// Write out array length
420	>	s.writeInt(queue.length);
421	>
422	>	// Write out all elements in the proper order.
423	>	for (int i=0; i<size; i++)
424	>	s.writeObject(queue[i]);
425	>	}
426	>
427	>	/**
428	>	* Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
429	>	* deserialize it).
430	>	* @param s the stream
431	>	*/
432	>	private synchronized void readObject(java.io.ObjectInputStream s)
433	>	throws java.io.IOException, ClassNotFoundException {
434	>	// Read in size, and any hidden stuff
435	>	s.defaultReadObject();
436	>
437	>	// Read in array length and allocate array
438	>	int arrayLength = s.readInt();
439	>	queue = new Object[arrayLength];
440	>
441	>	// Read in all elements in the proper order.
442	>	for (int i=0; i<size; i++)
443	>	queue[i] = s.readObject();
444		}
445
446		}
447	+

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