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1 : tim 1.2 package java.util;
2 : tim 1.1
3 :     /**
4 : dholmes 1.20 * An unbounded priority queue based on a priority heap. This queue orders
5 : brian 1.6 * elements according to an order specified at construction time, which is
6 : tim 1.19 * specified in the same manner as {@link java.util.TreeSet} and
7 : dholmes 1.18 * {@link java.util.TreeMap}: elements are ordered
8 : tim 1.2 * either according to their <i>natural order</i> (see {@link Comparable}), or
9 : tim 1.19 * according to a {@link java.util.Comparator}, depending on which
10 : dholmes 1.18 * constructor is used.
11 : tim 1.19 * <p>The <em>head</em> of this queue is the <em>least</em> element with
12 :     * respect to the specified ordering.
13 : dholmes 1.18 * If multiple elements are tied for least value, the
14 : tim 1.14 * head is one of those elements. A priority queue does not permit
15 : dholmes 1.11 * <tt>null</tt> elements.
16 : tim 1.14 *
17 : dholmes 1.11 * <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 : tim 1.2 *
23 : dl 1.7 * <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 : dholmes 1.20 * queue.
26 : dholmes 1.18 * It is always at least as large as the queue size. As
27 : dl 1.7 * elements are added to a priority queue, its capacity grows
28 :     * automatically. The details of the growth policy are not specified.
29 : tim 1.2 *
30 : dholmes 1.11 * <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 : tim 1.2 *
37 :     * <p>This class is a member of the
38 :     * <a href="{@docRoot}/../guide/collections/index.html">
39 :     * Java Collections Framework</a>.
40 : dl 1.7 * @since 1.5
41 :     * @author Josh Bloch
42 : tim 1.2 */
43 :     public class PriorityQueue<E> extends AbstractQueue<E>
44 : dholmes 1.18 implements Sorted, Queue<E>, java.io.Serializable {
45 : dholmes 1.11
46 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
47 : tim 1.1
48 : tim 1.2 /**
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 : brian 1.6 * comparator is null: For each node n in the heap and each descendant d
53 :     * of n, n <= d.
54 : tim 1.2 *
55 : brian 1.6 * 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 : tim 1.2 *
59 :     * queue.length must be >= 2, even if size == 0.
60 :     */
61 : tim 1.16 private transient Object[] queue;
62 : tim 1.1
63 : tim 1.2 /**
64 :     * The number of elements in the priority queue.
65 :     */
66 :     private int size = 0;
67 : tim 1.1
68 : tim 1.2 /**
69 :     * The comparator, or null if priority queue uses elements'
70 :     * natural ordering.
71 :     */
72 : tim 1.16 private final Comparator<? super E> comparator;
73 : tim 1.2
74 :     /**
75 :     * The number of times this priority queue has been
76 :     * <i>structurally modified</i>. See AbstractList for gory details.
77 :     */
78 : dl 1.5 private transient int modCount = 0;
79 : tim 1.2
80 :     /**
81 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the default initial capacity
82 : dl 1.7 * (11) that orders its elements according to their natural
83 :     * ordering (using <tt>Comparable</tt>.)
84 : tim 1.2 */
85 :     public PriorityQueue() {
86 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
87 : tim 1.1 }
88 : tim 1.2
89 :     /**
90 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
91 : dl 1.7 * that orders its elements according to their natural ordering
92 :     * (using <tt>Comparable</tt>.)
93 : tim 1.2 *
94 :     * @param initialCapacity the initial capacity for this priority queue.
95 :     */
96 :     public PriorityQueue(int initialCapacity) {
97 :     this(initialCapacity, null);
98 : tim 1.1 }
99 : tim 1.2
100 :     /**
101 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
102 : tim 1.2 * 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 : dholmes 1.11 * If <tt>null</tt> then the order depends on the elements' natural
107 :     * ordering.
108 : dholmes 1.15 * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
109 :     * than 1
110 : tim 1.2 */
111 : tim 1.16 public PriorityQueue(int initialCapacity, Comparator<? super E> comparator) {
112 : tim 1.2 if (initialCapacity < 1)
113 : dholmes 1.15 throw new IllegalArgumentException();
114 : tim 1.16 this.queue = new Object[initialCapacity + 1];
115 : tim 1.2 this.comparator = comparator;
116 : tim 1.1 }
117 :    
118 : tim 1.2 /**
119 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> containing the elements in the
120 :     * specified collection.
121 :     * The priority queue has an initial capacity of 110% of the
122 : dholmes 1.20 * size of the specified collection or 1 if the collection is empty.
123 : dholmes 1.15 * If the specified collection
124 : tim 1.2 * 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 : brian 1.6 * natural order. If the specified collection does not implement
128 :     * <tt>Sorted</tt>, the priority queue is ordered according to
129 : tim 1.2 * its elements' natural order.
130 :     *
131 : dholmes 1.15 * @param c the collection whose elements are to be placed
132 : tim 1.2 * 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 : dholmes 1.15 * @throws NullPointerException if <tt>c</tt> or any element within it
137 :     * is <tt>null</tt>
138 : tim 1.2 */
139 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
140 : dholmes 1.15 int sz = c.size();
141 : tim 1.2 int initialCapacity = (int)Math.min((sz * 110L) / 100,
142 :     Integer.MAX_VALUE - 1);
143 :     if (initialCapacity < 1)
144 :     initialCapacity = 1;
145 : dholmes 1.15
146 : tim 1.16 this.queue = new Object[initialCapacity + 1];
147 : tim 1.2
148 : dholmes 1.15 if (c instanceof Sorted) {
149 : tim 1.19 comparator = (Comparator<? super E>)((Sorted)c).comparator();
150 : tim 1.2 } else {
151 :     comparator = null;
152 :     }
153 : dholmes 1.18
154 :     for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
155 :     add(i.next());
156 : tim 1.1 }
157 :    
158 : tim 1.2 // Queue Methods
159 :    
160 :     /**
161 : dholmes 1.11 * Add the specified element to this priority queue.
162 : tim 1.2 *
163 : dholmes 1.11 * @return <tt>true</tt>
164 :     * @throws ClassCastException if the specified element cannot be compared
165 :     * with elements currently in the priority queue according
166 :     * to the priority queue's ordering.
167 : dholmes 1.18 * @throws NullPointerException if the specified element is <tt>null</tt>.
168 : tim 1.2 */
169 : dholmes 1.18 public boolean offer(E o) {
170 :     if (o == null)
171 : dholmes 1.11 throw new NullPointerException();
172 :     modCount++;
173 :     ++size;
174 :    
175 :     // Grow backing store if necessary
176 :     while (size >= queue.length) {
177 : tim 1.16 Object[] newQueue = new Object[2 * queue.length];
178 : dholmes 1.11 System.arraycopy(queue, 0, newQueue, 0, queue.length);
179 :     queue = newQueue;
180 :     }
181 :    
182 : dholmes 1.18 queue[size] = o;
183 : dholmes 1.11 fixUp(size);
184 :     return true;
185 :     }
186 :    
187 : tim 1.1 public E poll() {
188 : tim 1.2 if (size == 0)
189 :     return null;
190 : tim 1.16 return (E) remove(1);
191 : tim 1.1 }
192 : tim 1.2
193 : tim 1.1 public E peek() {
194 : tim 1.16 return (E) queue[1];
195 : tim 1.1 }
196 :    
197 : tim 1.2 // Collection Methods
198 :    
199 : dholmes 1.11 // these first two override just to get the throws docs
200 :    
201 :     /**
202 :     * @throws NullPointerException if the specified element is <tt>null</tt>.
203 : dholmes 1.15 * @throws ClassCastException if the specified element cannot be compared
204 :     * with elements currently in the priority queue according
205 :     * to the priority queue's ordering.
206 : dholmes 1.11 */
207 : dholmes 1.18 public boolean add(E o) {
208 :     return super.add(o);
209 : dholmes 1.11 }
210 :    
211 : tim 1.14 /**
212 : dholmes 1.15 * @throws ClassCastException if any element cannot be compared
213 :     * with elements currently in the priority queue according
214 :     * to the priority queue's ordering.
215 : dholmes 1.18 * @throws NullPointerException if <tt>c</tt> or any element in <tt>c</tt>
216 :     * is <tt>null</tt>
217 : tim 1.14 */
218 :     public boolean addAll(Collection<? extends E> c) {
219 :     return super.addAll(c);
220 :     }
221 : dholmes 1.11
222 : dl 1.12 public boolean remove(Object o) {
223 : dholmes 1.11 if (o == null)
224 : dholmes 1.15 return false;
225 : tim 1.2
226 :     if (comparator == null) {
227 :     for (int i = 1; i <= size; i++) {
228 : tim 1.16 if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
229 : tim 1.2 remove(i);
230 :     return true;
231 :     }
232 :     }
233 :     } else {
234 :     for (int i = 1; i <= size; i++) {
235 : tim 1.16 if (comparator.compare((E)queue[i], (E)o) == 0) {
236 : tim 1.2 remove(i);
237 :     return true;
238 :     }
239 :     }
240 :     }
241 : tim 1.1 return false;
242 :     }
243 : tim 1.2
244 :     public Iterator<E> iterator() {
245 : dl 1.7 return new Itr();
246 : tim 1.2 }
247 :    
248 :     private class Itr implements Iterator<E> {
249 : dl 1.7 /**
250 :     * Index (into queue array) of element to be returned by
251 : tim 1.2 * subsequent call to next.
252 : dl 1.7 */
253 :     private int cursor = 1;
254 : tim 1.2
255 : dl 1.7 /**
256 :     * Index of element returned by most recent call to next or
257 :     * previous. Reset to 0 if this element is deleted by a call
258 :     * to remove.
259 :     */
260 :     private int lastRet = 0;
261 :    
262 :     /**
263 :     * The modCount value that the iterator believes that the backing
264 :     * List should have. If this expectation is violated, the iterator
265 :     * has detected concurrent modification.
266 :     */
267 :     private int expectedModCount = modCount;
268 : tim 1.2
269 : dl 1.7 public boolean hasNext() {
270 :     return cursor <= size;
271 :     }
272 :    
273 :     public E next() {
274 : tim 1.2 checkForComodification();
275 :     if (cursor > size)
276 : dl 1.7 throw new NoSuchElementException();
277 : tim 1.16 E result = (E) queue[cursor];
278 : tim 1.2 lastRet = cursor++;
279 :     return result;
280 : dl 1.7 }
281 : tim 1.2
282 : dl 1.7 public void remove() {
283 :     if (lastRet == 0)
284 :     throw new IllegalStateException();
285 : tim 1.2 checkForComodification();
286 :    
287 :     PriorityQueue.this.remove(lastRet);
288 :     if (lastRet < cursor)
289 :     cursor--;
290 :     lastRet = 0;
291 :     expectedModCount = modCount;
292 : dl 1.7 }
293 : tim 1.2
294 : dl 1.7 final void checkForComodification() {
295 :     if (modCount != expectedModCount)
296 :     throw new ConcurrentModificationException();
297 :     }
298 : tim 1.2 }
299 :    
300 :     /**
301 :     * Returns the number of elements in this priority queue.
302 : tim 1.10 *
303 : tim 1.2 * @return the number of elements in this priority queue.
304 :     */
305 : tim 1.1 public int size() {
306 : tim 1.2 return size;
307 : tim 1.1 }
308 : tim 1.2
309 :     /**
310 :     * Remove all elements from the priority queue.
311 :     */
312 :     public void clear() {
313 :     modCount++;
314 :    
315 :     // Null out element references to prevent memory leak
316 :     for (int i=1; i<=size; i++)
317 :     queue[i] = null;
318 :    
319 :     size = 0;
320 :     }
321 :    
322 :     /**
323 :     * Removes and returns the ith element from queue. Recall
324 :     * that queue is one-based, so 1 <= i <= size.
325 :     *
326 :     * XXX: Could further special-case i==size, but is it worth it?
327 :     * XXX: Could special-case i==0, but is it worth it?
328 :     */
329 :     private E remove(int i) {
330 :     assert i <= size;
331 :     modCount++;
332 :    
333 : tim 1.16 E result = (E) queue[i];
334 : tim 1.2 queue[i] = queue[size];
335 :     queue[size--] = null; // Drop extra ref to prevent memory leak
336 :     if (i <= size)
337 :     fixDown(i);
338 :     return result;
339 : tim 1.1 }
340 :    
341 : tim 1.2 /**
342 :     * Establishes the heap invariant (described above) assuming the heap
343 :     * satisfies the invariant except possibly for the leaf-node indexed by k
344 :     * (which may have a nextExecutionTime less than its parent's).
345 :     *
346 :     * This method functions by "promoting" queue[k] up the hierarchy
347 :     * (by swapping it with its parent) repeatedly until queue[k]
348 :     * is greater than or equal to its parent.
349 :     */
350 :     private void fixUp(int k) {
351 :     if (comparator == null) {
352 :     while (k > 1) {
353 :     int j = k >> 1;
354 : tim 1.16 if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
355 : tim 1.2 break;
356 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
357 : tim 1.2 k = j;
358 :     }
359 :     } else {
360 :     while (k > 1) {
361 :     int j = k >> 1;
362 : tim 1.16 if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
363 : tim 1.2 break;
364 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
365 : tim 1.2 k = j;
366 :     }
367 :     }
368 :     }
369 :    
370 :     /**
371 :     * Establishes the heap invariant (described above) in the subtree
372 :     * rooted at k, which is assumed to satisfy the heap invariant except
373 :     * possibly for node k itself (which may be greater than its children).
374 :     *
375 :     * This method functions by "demoting" queue[k] down the hierarchy
376 :     * (by swapping it with its smaller child) repeatedly until queue[k]
377 :     * is less than or equal to its children.
378 :     */
379 :     private void fixDown(int k) {
380 :     int j;
381 :     if (comparator == null) {
382 :     while ((j = k << 1) <= size) {
383 : tim 1.16 if (j<size && ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
384 : tim 1.2 j++; // j indexes smallest kid
385 : tim 1.16 if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
386 : tim 1.2 break;
387 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
388 : tim 1.2 k = j;
389 :     }
390 :     } else {
391 :     while ((j = k << 1) <= size) {
392 : tim 1.16 if (j < size && comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
393 : tim 1.2 j++; // j indexes smallest kid
394 : tim 1.16 if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
395 : tim 1.2 break;
396 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
397 : tim 1.2 k = j;
398 :     }
399 :     }
400 :     }
401 :    
402 : tim 1.16 public Comparator<? super E> comparator() {
403 : tim 1.2 return comparator;
404 :     }
405 : dl 1.5
406 :     /**
407 :     * Save the state of the instance to a stream (that
408 :     * is, serialize it).
409 :     *
410 :     * @serialData The length of the array backing the instance is
411 :     * emitted (int), followed by all of its elements (each an
412 :     * <tt>Object</tt>) in the proper order.
413 : dl 1.7 * @param s the stream
414 : dl 1.5 */
415 :     private synchronized void writeObject(java.io.ObjectOutputStream s)
416 :     throws java.io.IOException{
417 : dl 1.7 // Write out element count, and any hidden stuff
418 :     s.defaultWriteObject();
419 : dl 1.5
420 :     // Write out array length
421 :     s.writeInt(queue.length);
422 :    
423 : dl 1.7 // Write out all elements in the proper order.
424 :     for (int i=0; i<size; i++)
425 : dl 1.5 s.writeObject(queue[i]);
426 :     }
427 :    
428 :     /**
429 :     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
430 :     * deserialize it).
431 : dl 1.7 * @param s the stream
432 : dl 1.5 */
433 :     private synchronized void readObject(java.io.ObjectInputStream s)
434 :     throws java.io.IOException, ClassNotFoundException {
435 : dl 1.7 // Read in size, and any hidden stuff
436 :     s.defaultReadObject();
437 : dl 1.5
438 :     // Read in array length and allocate array
439 :     int arrayLength = s.readInt();
440 : tim 1.16 queue = new Object[arrayLength];
441 : dl 1.5
442 : dl 1.7 // Read in all elements in the proper order.
443 :     for (int i=0; i<size; i++)
444 : tim 1.16 queue[i] = s.readObject();
445 : dl 1.5 }
446 :    
447 : tim 1.1 }
448 : dholmes 1.11

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