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Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.2 by tim, Sun May 18 18:10:02 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	–	/*
4	–	* Todo
5	–	*
6	–	*   1) Make it serializable.
7	–	*/
8	–
3		/**
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
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 Comparator}, depending on which constructor is used.
10	<	* The {@link #peek}, {@link #poll}, and {@link #remove} methods return the
11	<	* minimal element with respect to the specified ordering.  If multiple
12	<	* these elements are tied for least value, no guarantees are made as to
13	<	* which of elements is returned.
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>Each priority queue has a <i>capacity</i>.  The capacity is the size of
24	<	* the array used to store the elements on the queue.  It is always at least
25	<	* as large as the queue size.  As elements are added to a priority list,
26	<	* its capacity grows automatically.  The details of the growth policy are not
27	<	* specified.
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 for
31	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
32	<	* methods; linear time for the <tt>remove(Object)</tt> and
33	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
34	<	* <tt>element</tt>, and <tt>size</tt> methods.
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 Queue<E>
45	<	{
44	>	implements Sorted, Queue<E>, java.io.Serializable {
45	>
46		private static final int DEFAULT_INITIAL_CAPACITY = 11;
47
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
53	<	* of n, d, n <= d.
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.
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 E[] queue;
61	>	private transient Object[] queue;
62
63		/**
64		* The number of elements in the priority queue.
#	Line 62 | Line 69 | public class PriorityQueue<E> extends Ab
69		* The comparator, or null if priority queue uses elements'
70		* natural ordering.
71		*/
72	<	private final Comparator<E> comparator;
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 int modCount = 0;
78	>	private transient int modCount = 0;
79
80		/**
81	<	* Create a new priority queue with the default initial capacity (11)
82	<	* that orders its elements according to their natural ordering.
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);
86	>	this(DEFAULT_INITIAL_CAPACITY, null);
87		}
88
89		/**
90	<	* Create a new priority queue with the specified initial capacity
91	<	* that orders its elements according to their natural ordering.
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		*/
#	Line 89 | Line 98 | public class PriorityQueue<E> extends Ab
98		}
99
100		/**
101	<	* Create a new priority queue with the specified initial capacity (11)
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<E> comparator) {
111	>	public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
112		if (initialCapacity < 1)
113	<	initialCapacity = 1;
114	<	queue = new E[initialCapacity + 1];
113	>	throw new IllegalArgumentException();
114	>	this.queue = new Object[initialCapacity + 1];
115		this.comparator = comparator;
116		}
117
118		/**
119	<	* Create a new priority queue containing the elements in the specified
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. If the specified collection
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 the
127	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
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 initialElements the collection whose elements are to be placed
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 the specified collection or an
136	<	*         element of the specified collection is <tt>null</tt>.
135	>	* @throws NullPointerException if <tt>c</tt> or any element within it
136	>	* is <tt>null</tt>
137		*/
138	<	public PriorityQueue(Collection<E> initialElements) {
139	<	int sz = initialElements.size();
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;
130	–	queue = new E[initialCapacity + 1];
144
145	<	/* Commented out to compile with generics compiler
145	>	this.queue = new Object[initialCapacity + 1];
146
147	<	if (initialElements instanceof Sorted) {
148	<	comparator = ((Sorted)initialElements).comparator();
136	<	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
137	<	queue[++size] = i.next();
147	>	if (c instanceof Sorted) {
148	>	comparator = (Comparator<? super E>)((Sorted)c).comparator();
149		} else {
139	–	*/
140	–	{
150		comparator = null;
142	–	for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143	–	add(i.next());
151		}
152	+
153	+	for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
154	+	add(i.next());
155		}
156
157		// Queue Methods
158
159		/**
160	<	* 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.
160	>	* Add the specified element to this priority queue.
161		*
162	<	* @return the minimal element from this priority queue if it contains
163	<	*         one or more elements, otherwise <tt>null</tt>.
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		if (size == 0)
188		return null;
189	<	return remove(1);
189	>	return (E) remove(1);
190		}
191
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	–	*/
192		public E peek() {
193	<	return queue[1];
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	<	* 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
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.
192	<	* @throws NullPointerException if the specified element is null.
203	>	* with elements currently in the priority queue according
204	>	* to the priority queue's ordering.
205		*/
206	<	public boolean remove(Object element) {
207	<	if (element == null)
208	<	throw new NullPointerException();
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 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)queue[i]).compareTo(element) == 0) {
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(queue[i], (E) element) == 0) {
234	>	if (comparator.compare((E)queue[i], (E)o) == 0) {
235		remove(i);
236		return true;
237		}
#	Line 213 | Line 240 | public class PriorityQueue<E> extends Ab
240		return false;
241		}
242
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	–	*/
243		public Iterator<E> iterator() {
244		return new Itr();
245		}
#	Line 229 | Line 249 | public class PriorityQueue<E> extends Ab
249		* Index (into queue array) of element to be returned by
250		* subsequent call to next.
251		*/
252	<	int cursor = 1;
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	<	int lastRet = 0;
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	<	int expectedModCount = modCount;
266	>	private int expectedModCount = modCount;
267
268		public boolean hasNext() {
269		return cursor <= size;
#	Line 253 | Line 273 | public class PriorityQueue<E> extends Ab
273		checkForComodification();
274		if (cursor > size)
275		throw new NoSuchElementException();
276	<	E result = queue[cursor];
276	>	E result = (E) queue[cursor];
277		lastRet = cursor++;
278		return result;
279		}
#	Line 286 | Line 306 | public class PriorityQueue<E> extends Ab
306		}
307
308		/**
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	–	/**
309		* Remove all elements from the priority queue.
310		*/
311		public void clear() {
#	Line 336 | Line 329 | public class PriorityQueue<E> extends Ab
329		assert i <= size;
330		modCount++;
331
332	<	E result = queue[i];
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)
#	Line 357 | Line 350 | public class PriorityQueue<E> extends Ab
350		if (comparator == null) {
351		while (k > 1) {
352		int j = k >> 1;
353	<	if (((Comparable)queue[j]).compareTo(queue[k]) <= 0)
353	>	if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
354		break;
355	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
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(queue[j], queue[k]) <= 0)
361	>	if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
362		break;
363	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
363	>	Object tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
364		k = j;
365		}
366		}
#	Line 386 | Line 379 | public class PriorityQueue<E> extends Ab
379		int j;
380		if (comparator == null) {
381		while ((j = k << 1) <= size) {
382	<	if (j<size && ((Comparable)queue[j]).compareTo(queue[j+1]) > 0)
382	>	if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
383		j++; // j indexes smallest kid
384	<	if (((Comparable)queue[k]).compareTo(queue[j]) <= 0)
384	>	if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
385		break;
386	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
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(queue[j], queue[j+1]) > 0)
391	>	if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
392		j++; // j indexes smallest kid
393	<	if (comparator.compare(queue[k], queue[j]) <= 0)
393	>	if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
394		break;
395	<	E tmp = queue[j];  queue[j] = queue[k]; queue[k] = tmp;
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	<	* Returns the comparator associated with this priority queue, or
407	<	* <tt>null</tt> if it uses its elements' natural ordering.
406	>	* Save the state of the instance to a stream (that
407	>	* is, serialize it).
408		*
409	<	* @return the comparator associated with this priority queue, or
410	<	*         <tt>null</tt> if it uses its elements' natural ordering.
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	<	Comparator comparator() {
415	<	return comparator;
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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