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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 1.2 by tim, Sun May 18 18:10:02 2003 UTC

#	Line 1 | Line 1
1	<	package java.util;
1	>	package java.util;
2
3	<	import java.util.*;
3	>	/*
4	>	* Todo
5	>	*
6	>	*   1) Make it serializable.
7	>	*/
8
9		/**
10	<	* An unbounded (resizable) priority queue based on a priority
11	<	* heap.The take operation returns the least element with respect to
12	<	* the given ordering. (If more than one element is tied for least
13	<	* value, one of them is arbitrarily chosen to be returned -- no
14	<	* guarantees are made for ordering across ties.) Ordering follows the
15	<	* java.util.Collection conventions: Either the elements must be
16	<	* Comparable, or a Comparator must be supplied. Comparison failures
17	<	* throw ClassCastExceptions during insertions and extractions.
18	<	**/
19	<	public class PriorityQueue<E> extends AbstractCollection<E> implements Queue<E> {
20	<	public PriorityQueue(int initialCapacity) {}
21	<	public PriorityQueue(int initialCapacity, Comparator comparator) {}
10	>	* An unbounded priority queue based on a priority heap.  This queue orders
11	>	* elements according to the order specified at creation time.  This order is
12	>	* specified as for {@link TreeSet} and {@link TreeMap}: Elements are ordered
13	>	* either according to their <i>natural order</i> (see {@link Comparable}), or
14	>	* according to a {@link Comparator}, depending on which constructor is used.
15	>	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
16	>	* minimal element with respect to the specified ordering.  If multiple
17	>	* these elements are tied for least value, no guarantees are made as to
18	>	* which of elements is returned.
19	>	*
20	>	* <p>Each priority queue has a <i>capacity</i>.  The capacity is the size of
21	>	* the array used to store the elements on the queue.  It is always at least
22	>	* as large as the queue size.  As elements are added to a priority list,
23	>	* its capacity grows automatically.  The details of the growth policy are not
24	>	* specified.
25	>	*
26	>	*<p>Implementation note: this implementation provides O(log(n)) time for
27	>	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
28	>	* methods; linear time for the <tt>remove(Object)</tt> and
29	>	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
30	>	* <tt>element</tt>, and <tt>size</tt> methods.
31	>	*
32	>	* <p>This class is a member of the
33	>	* <a href="{@docRoot}/../guide/collections/index.html">
34	>	* Java Collections Framework</a>.
35	>	*/
36	>	public class PriorityQueue<E> extends AbstractQueue<E>
37	>	implements Queue<E>
38	>	{
39	>	private static final int DEFAULT_INITIAL_CAPACITY = 11;
40
41	<	public PriorityQueue(int initialCapacity, Collection initialElements) {}
41	>	/**
42	>	* Priority queue represented as a balanced binary heap: the two children
43	>	* of queue[n] are queue[2*n] and queue[2*n + 1].  The priority queue is
44	>	* ordered by comparator, or by the elements' natural ordering, if
45	>	* comparator is null:  For each node n in the heap, and each descendant
46	>	* of n, d, n <= d.
47	>	*
48	>	* The element with the lowest value is in queue[1] (assuming the queue is
49	>	* nonempty). A one-based array is used in preference to the traditional
50	>	* zero-based array to simplify parent and child calculations.
51	>	*
52	>	* queue.length must be >= 2, even if size == 0.
53	>	*/
54	>	private E[] queue;
55
56	<	public PriorityQueue(int initialCapacity, Comparator comparator, Collection initialElements) {}
56	>	/**
57	>	* The number of elements in the priority queue.
58	>	*/
59	>	private int size = 0;
60
61	<	public boolean add(E x) {
62	<	return false;
63	<	}
64	<	public boolean offer(E x) {
65	<	return false;
66	<	}
67	<	public boolean remove(Object x) {
68	<	return false;
61	>	/**
62	>	* The comparator, or null if priority queue uses elements'
63	>	* natural ordering.
64	>	*/
65	>	private final Comparator<E> comparator;
66	>
67	>	/**
68	>	* The number of times this priority queue has been
69	>	* <i>structurally modified</i>.  See AbstractList for gory details.
70	>	*/
71	>	private int modCount = 0;
72	>
73	>	/**
74	>	* Create a new priority queue with the default initial capacity (11)
75	>	* that orders its elements according to their natural ordering.
76	>	*/
77	>	public PriorityQueue() {
78	>	this(DEFAULT_INITIAL_CAPACITY);
79		}
80
81	<	public E remove() {
82	<	return null;
81	>	/**
82	>	* Create a new priority queue with the specified initial capacity
83	>	* that orders its elements according to their natural ordering.
84	>	*
85	>	* @param initialCapacity the initial capacity for this priority queue.
86	>	*/
87	>	public PriorityQueue(int initialCapacity) {
88	>	this(initialCapacity, null);
89		}
90	<	public Iterator<E> iterator() {
91	<	return null;
90	>
91	>	/**
92	>	* Create a new priority queue with the specified initial capacity (11)
93	>	* that orders its elements according to the specified comparator.
94	>	*
95	>	* @param initialCapacity the initial capacity for this priority queue.
96	>	* @param comparator the comparator used to order this priority queue.
97	>	*/
98	>	public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
99	>	if (initialCapacity < 1)
100	>	initialCapacity = 1;
101	>	queue = new E[initialCapacity + 1];
102	>	this.comparator = comparator;
103		}
104
105	<	public E element() {
106	<	return null;
105	>	/**
106	>	* Create a new priority queue containing the elements in the specified
107	>	* collection.  The priority queue has an initial capacity of 110% of the
108	>	* size of the specified collection. If the specified collection
109	>	* implements the {@link Sorted} interface, the priority queue will be
110	>	* sorted according to the same comparator, or according to its elements'
111	>	* natural order if the collection is sorted according to its elements'
112	>	* natural order.  If the specified collection does not implement the
113	>	* <tt>Sorted</tt> interface, the priority queue is ordered according to
114	>	* its elements' natural order.
115	>	*
116	>	* @param initialElements the collection whose elements are to be placed
117	>	*        into this priority queue.
118	>	* @throws ClassCastException if elements of the specified collection
119	>	*         cannot be compared to one another according to the priority
120	>	*         queue's ordering.
121	>	* @throws NullPointerException if the specified collection or an
122	>	*         element of the specified collection is <tt>null</tt>.
123	>	*/
124	>	public PriorityQueue(Collection<E> initialElements) {
125	>	int sz = initialElements.size();
126	>	int initialCapacity = (int)Math.min((sz * 110L) / 100,
127	>	Integer.MAX_VALUE - 1);
128	>	if (initialCapacity < 1)
129	>	initialCapacity = 1;
130	>	queue = new E[initialCapacity + 1];
131	>
132	>	/* Commented out to compile with generics compiler
133	>
134	>	if (initialElements instanceof Sorted) {
135	>	comparator = ((Sorted)initialElements).comparator();
136	>	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	>	queue[++size] = i.next();
138	>	} else {
139	>	*/
140	>	{
141	>	comparator = null;
142	>	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	>	add(i.next());
144	>	}
145		}
146	+
147	+	// Queue Methods
148	+
149	+	/**
150	+	* Remove and return the minimal element from this priority queue if
151	+	* it contains one or more elements, otherwise <tt>null</tt>.  The term
152	+	* <i>minimal</i> is defined according to this priority queue's order.
153	+	*
154	+	* @return the minimal element from this priority queue if it contains
155	+	*         one or more elements, otherwise <tt>null</tt>.
156	+	*/
157		public E poll() {
158	<	return null;
158	>	if (size == 0)
159	>	return null;
160	>	return remove(1);
161		}
162	+
163	+	/**
164	+	* Return, but do not remove, the minimal element from the priority queue,
165	+	* or <tt>null</tt> if the queue is empty.  The term <i>minimal</i> is
166	+	* defined according to this priority queue's order.  This method returns
167	+	* the same object reference that would be returned by by the
168	+	* <tt>poll</tt> method.  The two methods differ in that this method
169	+	* does not remove the element 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 o element to be removed from this collection, if present.
187	>	* @return <tt>true</tt> if this collection changed as a result of the
188	>	*         call
189	>	* @throws ClassCastException if the specified element cannot be compared
190	>	*            with elements currently in the priority queue according
191	>	*            to the priority queue's ordering.
192	>	* @throws NullPointerException if the specified element is null.
193	>	*/
194	>	public boolean remove(Object element) {
195	>	if (element == null)
196	>	throw new NullPointerException();
197	>
198	>	if (comparator == null) {
199	>	for (int i = 1; i <= size; i++) {
200	>	if (((Comparable)queue[i]).compareTo(element) == 0) {
201	>	remove(i);
202	>	return true;
203	>	}
204	>	}
205	>	} else {
206	>	for (int i = 1; i <= size; i++) {
207	>	if (comparator.compare(queue[i], (E) element) == 0) {
208	>	remove(i);
209	>	return true;
210	>	}
211	>	}
212	>	}
213		return false;
214		}
215	+
216	+	/**
217	+	* Returns an iterator over the elements in this priority queue.  The
218	+	* first element returned by this iterator is the same element that
219	+	* would be returned by a call to <tt>peek</tt>.
220	+	*
221	+	* @return an <tt>Iterator</tt> over the elements in this priority queue.
222	+	*/
223	+	public Iterator<E> iterator() {
224	+	return new Itr();
225	+	}
226	+
227	+	private class Itr implements Iterator<E> {
228	+	/**
229	+	* Index (into queue array) of element to be returned by
230	+	* subsequent call to next.
231	+	*/
232	+	int cursor = 1;
233	+
234	+	/**
235	+	* Index of element returned by most recent call to next or
236	+	* previous.  Reset to 0 if this element is deleted by a call
237	+	* to remove.
238	+	*/
239	+	int lastRet = 0;
240	+
241	+	/**
242	+	* The modCount value that the iterator believes that the backing
243	+	* List should have.  If this expectation is violated, the iterator
244	+	* has detected concurrent modification.
245	+	*/
246	+	int expectedModCount = modCount;
247	+
248	+	public boolean hasNext() {
249	+	return cursor <= size;
250	+	}
251	+
252	+	public E next() {
253	+	checkForComodification();
254	+	if (cursor > size)
255	+	throw new NoSuchElementException();
256	+	E result = queue[cursor];
257	+	lastRet = cursor++;
258	+	return result;
259	+	}
260	+
261	+	public void remove() {
262	+	if (lastRet == 0)
263	+	throw new IllegalStateException();
264	+	checkForComodification();
265	+
266	+	PriorityQueue.this.remove(lastRet);
267	+	if (lastRet < cursor)
268	+	cursor--;
269	+	lastRet = 0;
270	+	expectedModCount = modCount;
271	+	}
272	+
273	+	final void checkForComodification() {
274	+	if (modCount != expectedModCount)
275	+	throw new ConcurrentModificationException();
276	+	}
277	+	}
278	+
279	+	/**
280	+	* Returns the number of elements in this priority queue.
281	+	*
282	+	* @return the number of elements in this priority queue.
283	+	*/
284		public int size() {
285	<	return 0;
285	>	return size;
286		}
287	<	public Object[] toArray() {
288	<	return null;
287	>
288	>	/**
289	>	* Add the specified element to this priority queue.
290	>	*
291	>	* @param element the element to add.
292	>	* @return true
293	>	* @throws ClassCastException if the specified element cannot be compared
294	>	*            with elements currently in the priority queue according
295	>	*            to the priority queue's ordering.
296	>	* @throws NullPointerException if the specified element is null.
297	>	*/
298	>	public boolean offer(E element) {
299	>	if (element == null)
300	>	throw new NullPointerException();
301	>	modCount++;
302	>
303	>	// Grow backing store if necessary
304	>	if (++size == queue.length) {
305	>	E[] newQueue = new E[2 * queue.length];
306	>	System.arraycopy(queue, 0, newQueue, 0, size);
307	>	queue = newQueue;
308	>	}
309	>
310	>	queue[size] = element;
311	>	fixUp(size);
312	>	return true;
313		}
314
315	<	public <T> T[] toArray(T[] array) {
316	<	return null;
315	>	/**
316	>	* Remove all elements from the priority queue.
317	>	*/
318	>	public void clear() {
319	>	modCount++;
320	>
321	>	// Null out element references to prevent memory leak
322	>	for (int i=1; i<=size; i++)
323	>	queue[i] = null;
324	>
325	>	size = 0;
326	>	}
327	>
328	>	/**
329	>	* Removes and returns the ith element from queue.  Recall
330	>	* that queue is one-based, so 1 <= i <= size.
331	>	*
332	>	* XXX: Could further special-case i==size, but is it worth it?
333	>	* XXX: Could special-case i==0, but is it worth it?
334	>	*/
335	>	private E remove(int i) {
336	>	assert i <= size;
337	>	modCount++;
338	>
339	>	E result = queue[i];
340	>	queue[i] = queue[size];
341	>	queue[size--] = null;  // Drop extra ref to prevent memory leak
342	>	if (i <= size)
343	>	fixDown(i);
344	>	return result;
345		}
346
347	+	/**
348	+	* Establishes the heap invariant (described above) assuming the heap
349	+	* satisfies the invariant except possibly for the leaf-node indexed by k
350	+	* (which may have a nextExecutionTime less than its parent's).
351	+	*
352	+	* This method functions by "promoting" queue[k] up the hierarchy
353	+	* (by swapping it with its parent) repeatedly until queue[k]
354	+	* is greater than or equal to its parent.
355	+	*/
356	+	private void fixUp(int k) {
357	+	if (comparator == null) {
358	+	while (k > 1) {
359	+	int j = k >> 1;
360	+	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
361	+	break;
362	+	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
363	+	k = j;
364	+	}
365	+	} else {
366	+	while (k > 1) {
367	+	int j = k >> 1;
368	+	if (comparator.compare(queue[j], queue[k]) <= 0)
369	+	break;
370	+	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
371	+	k = j;
372	+	}
373	+	}
374	+	}
375	+
376	+	/**
377	+	* Establishes the heap invariant (described above) in the subtree
378	+	* rooted at k, which is assumed to satisfy the heap invariant except
379	+	* possibly for node k itself (which may be greater than its children).
380	+	*
381	+	* This method functions by "demoting" queue[k] down the hierarchy
382	+	* (by swapping it with its smaller child) repeatedly until queue[k]
383	+	* is less than or equal to its children.
384	+	*/
385	+	private void fixDown(int k) {
386	+	int j;
387	+	if (comparator == null) {
388	+	while ((j = k << 1) <= size) {
389	+	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
390	+	j++; // j indexes smallest kid
391	+	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
392	+	break;
393	+	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
394	+	k = j;
395	+	}
396	+	} else {
397	+	while ((j = k << 1) <= size) {
398	+	if (j < size && comparator.compare(queue[j], queue[j+1]) > 0)
399	+	j++; // j indexes smallest kid
400	+	if (comparator.compare(queue[k], queue[j]) <= 0)
401	+	break;
402	+	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
403	+	k = j;
404	+	}
405	+	}
406	+	}
407	+
408	+	/**
409	+	* Returns the comparator associated with this priority queue, or
410	+	* <tt>null</tt> if it uses its elements' natural ordering.
411	+	*
412	+	* @return the comparator associated with this priority queue, or
413	+	*         <tt>null</tt> if it uses its elements' natural ordering.
414	+	*/
415	+	Comparator comparator() {
416	+	return comparator;
417	+	}
418		}

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