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root/jsr166/jsr166/src/main/java/util/PriorityQueue.java

Comparing jsr166/src/main/java/util/PriorityQueue.java (file contents):
Revision 1.2 by tim, Sun May 18 18:10:02 2003 UTC vs.
Revision 1.12 by dl, Mon Jul 28 09:40:07 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 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 {@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.
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>Each priority queue has a <i>capacity</i>.  The capacity is the size of
19	<	* 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.
18	>	* <p>The {@link #element()} and {@link #peek()} methods return, but do
19	>	* not delete, the head of the queue.
20		*
21	<	*<p>Implementation note: this implementation provides O(log(n)) time for
22	<	* the <tt>offer</tt>, <tt>poll</tt>, <tt>remove()</tt> and <tt>add</tt>
23	<	* methods; linear time for the <tt>remove(Object)</tt> and
24	<	* <tt>contains</tt> methods; and constant time for the <tt>peek</tt>,
25	<	* <tt>element</tt>, and <tt>size</tt> methods.
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>
42	<	{
41	>	implements Queue<E>, Sorted, java.io.Serializable {
42	>
43		private static final int DEFAULT_INITIAL_CAPACITY = 11;
44
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
50	<	* of n, d, n <= d.
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.
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 E[] queue;
58	>	private transient E[] queue;
59
60		/**
61		* The number of elements in the priority queue.
#	Line 68 | Line 72 | public class PriorityQueue<E> extends Ab
72		* The number of times this priority queue has been
73		* <i>structurally modified</i>.  See AbstractList for gory details.
74		*/
75	<	private int modCount = 0;
75	>	private transient int modCount = 0;
76
77		/**
78	<	* Create a new priority queue with the default initial capacity (11)
79	<	* that orders its elements according to their natural ordering.
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);
83	>	this(DEFAULT_INITIAL_CAPACITY, null);
84		}
85
86		/**
87	<	* Create a new priority queue with the specified initial capacity
88	<	* that orders its elements according to their natural ordering.
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		*/
#	Line 89 | Line 95 | public class PriorityQueue<E> extends Ab
95		}
96
97		/**
98	<	* Create a new priority queue with the specified initial capacity (11)
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		*/
106		public PriorityQueue(int initialCapacity, Comparator<E> comparator) {
107		if (initialCapacity < 1)
108		initialCapacity = 1;
109	<	queue = new E[initialCapacity + 1];
109	>	queue = (E[]) new Object[initialCapacity + 1];
110		this.comparator = comparator;
111		}
112
113		/**
114	<	* Create a new priority queue containing the elements in the specified
114	>	* Create a <tt>PriorityQueue</tt> containing the elements in the specified
115		* collection.  The priority queue has an initial capacity of 110% of the
116		* size of the specified collection. If the specified collection
117		* implements the {@link Sorted} interface, the priority queue will be
118		* sorted according to the same comparator, or according to its elements'
119		* natural order if the collection is sorted according to its elements'
120	<	* natural order.  If the specified collection does not implement the
121	<	* <tt>Sorted</tt> interface, the priority queue is ordered according to
120	>	* natural order.  If the specified collection does not implement
121	>	* <tt>Sorted</tt>, the priority queue is ordered according to
122		* its elements' natural order.
123		*
124		* @param initialElements the collection whose elements are to be placed
#	Line 127 | Line 135 | public class PriorityQueue<E> extends Ab
135		Integer.MAX_VALUE - 1);
136		if (initialCapacity < 1)
137		initialCapacity = 1;
138	<	queue = new E[initialCapacity + 1];
131	<
132	<	/* Commented out to compile with generics compiler
138	>	queue = (E[]) new Object[initialCapacity + 1];
139
140		if (initialElements instanceof Sorted) {
141		comparator = ((Sorted)initialElements).comparator();
142		for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
143		queue[++size] = i.next();
144		} else {
139	–	*/
140	–	{
145		comparator = null;
146		for (Iterator<E> i = initialElements.iterator(); i.hasNext(); )
147		add(i.next());
#	Line 147 | Line 151 | public class PriorityQueue<E> extends Ab
151		// Queue Methods
152
153		/**
154	<	* 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.
154	>	* Add the specified element to this priority queue.
155		*
156	<	* @return the minimal element from this priority queue if it contains
157	<	*         one or more elements, otherwise <tt>null</tt>.
156	>	* @param element the element to add.
157	>	* @return <tt>true</tt>
158	>	* @throws ClassCastException if the specified element cannot be compared
159	>	* with elements currently in the priority queue according
160	>	* to the priority queue's ordering.
161	>	* @throws NullPointerException if the specified element is null.
162		*/
163	+	public boolean offer(E element) {
164	+	if (element == null)
165	+	throw new NullPointerException();
166	+	modCount++;
167	+	++size;
168	+
169	+	// Grow backing store if necessary
170	+	while (size >= queue.length) {
171	+	E[] newQueue = (E[]) new Object[2 * queue.length];
172	+	System.arraycopy(queue, 0, newQueue, 0, queue.length);
173	+	queue = newQueue;
174	+	}
175	+
176	+	queue[size] = element;
177	+	fixUp(size);
178	+	return true;
179	+	}
180	+
181		public E poll() {
182		if (size == 0)
183		return null;
184		return remove(1);
185		}
186
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	–	*/
187		public E peek() {
188		return queue[1];
189		}
190
191		// Collection Methods
192
193	+	// these first two override just to get the throws docs
194	+
195		/**
196	<	* 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.
196	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
197		*/
198	<	public boolean remove(Object element) {
199	<	if (element == null)
198	>	public boolean add(E element) {
199	>	return super.add(element);
200	>	}
201	>
202	>	//    /**
203	>	//     * @throws NullPointerException if any element is <tt>null</tt>.
204	>	//     */
205	>	//    public boolean addAll(Collection c) {
206	>	//        return super.addAll(c);
207	>	//    }
208	>
209	>	/**
210	>	* @throws NullPointerException if the specified element is <tt>null</tt>.
211	>	*/
212	>	public boolean remove(Object o) {
213	>	if (o == null)
214		throw new NullPointerException();
215
216		if (comparator == null) {
217		for (int i = 1; i <= size; i++) {
218	<	if (((Comparable)queue[i]).compareTo(element) == 0) {
218	>	if (((Comparable)queue[i]).compareTo(o) == 0) {
219		remove(i);
220		return true;
221		}
222		}
223		} else {
224		for (int i = 1; i <= size; i++) {
225	<	if (comparator.compare(queue[i], (E) element) == 0) {
225	>	if (comparator.compare(queue[i], (E)o) == 0) {
226		remove(i);
227		return true;
228		}
#	Line 215 | Line 233 | public class PriorityQueue<E> extends Ab
233
234		/**
235		* Returns an iterator over the elements in this priority queue.  The
236	<	* first element returned by this iterator is the same element that
237	<	* would be returned by a call to <tt>peek</tt>.
236	>	* elements of the priority queue will be returned by this iterator in the
237	>	* order specified by the queue, which is to say the order they would be
238	>	* returned by repeated calls to <tt>poll</tt>.
239		*
240		* @return an <tt>Iterator</tt> over the elements in this priority queue.
241		*/
#	Line 229 | Line 248 | public class PriorityQueue<E> extends Ab
248		* Index (into queue array) of element to be returned by
249		* subsequent call to next.
250		*/
251	<	int cursor = 1;
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	<	int lastRet = 0;
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	<	int expectedModCount = modCount;
265	>	private int expectedModCount = modCount;
266
267		public boolean hasNext() {
268		return cursor <= size;
#	Line 286 | Line 305 | public class PriorityQueue<E> extends Ab
305		}
306
307		/**
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	–	/**
308		* Remove all elements from the priority queue.
309		*/
310		public void clear() {
#	Line 405 | Line 397 | public class PriorityQueue<E> extends Ab
397		}
398		}
399
400	+	public Comparator comparator() {
401	+	return comparator;
402	+	}
403	+
404		/**
405	<	* Returns the comparator associated with this priority queue, or
406	<	* <tt>null</tt> if it uses its elements' natural ordering.
405	>	* Save the state of the instance to a stream (that
406	>	* is, serialize it).
407		*
408	<	* @return the comparator associated with this priority queue, or
409	<	*         <tt>null</tt> if it uses its elements' natural ordering.
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	<	Comparator comparator() {
414	<	return comparator;
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	+	/**
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 = (E[]) new Object[arrayLength];
439	+
440	+	// Read in all elements in the proper order.
441	+	for (int i=0; i<size; i++)
442	+	queue[i] = (E)s.readObject();
443	+	}
444	+
445		}
446	+

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