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1 : dl 1.38 /*
2 : jsr166 1.67 * Copyright 2003-2006 Sun Microsystems, Inc. All Rights Reserved.
3 :     * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 : dl 1.38 *
5 : jsr166 1.67 * This code is free software; you can redistribute it and/or modify it
6 :     * under the terms of the GNU General Public License version 2 only, as
7 :     * published by the Free Software Foundation. Sun designates this
8 :     * particular file as subject to the "Classpath" exception as provided
9 :     * by Sun in the LICENSE file that accompanied this code.
10 :     *
11 :     * This code is distributed in the hope that it will be useful, but WITHOUT
12 :     * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 :     * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 :     * version 2 for more details (a copy is included in the LICENSE file that
15 :     * accompanied this code).
16 :     *
17 :     * You should have received a copy of the GNU General Public License version
18 :     * 2 along with this work; if not, write to the Free Software Foundation,
19 :     * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 :     *
21 :     * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa Clara,
22 :     * CA 95054 USA or visit www.sun.com if you need additional information or
23 :     * have any questions.
24 : dl 1.38 */
25 :    
26 :     package java.util;
27 : tim 1.1
28 :     /**
29 : jsr166 1.63 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
30 :     * The elements of the priority queue are ordered according to their
31 :     * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
32 :     * provided at queue construction time, depending on which constructor is
33 :     * used. A priority queue does not permit {@code null} elements.
34 :     * A priority queue relying on natural ordering also does not permit
35 :     * insertion of non-comparable objects (doing so may result in
36 :     * {@code ClassCastException}).
37 : dl 1.40 *
38 : dl 1.41 * <p>The <em>head</em> of this queue is the <em>least</em> element
39 :     * with respect to the specified ordering. If multiple elements are
40 :     * tied for least value, the head is one of those elements -- ties are
41 : jsr166 1.63 * broken arbitrarily. The queue retrieval operations {@code poll},
42 :     * {@code remove}, {@code peek}, and {@code element} access the
43 : dl 1.42 * element at the head of the queue.
44 : tim 1.14 *
45 : dl 1.41 * <p>A priority queue is unbounded, but has an internal
46 :     * <i>capacity</i> governing the size of an array used to store the
47 : dl 1.40 * elements on the queue. It is always at least as large as the queue
48 :     * size. As elements are added to a priority queue, its capacity
49 :     * grows automatically. The details of the growth policy are not
50 :     * specified.
51 : tim 1.2 *
52 : dl 1.50 * <p>This class and its iterator implement all of the
53 :     * <em>optional</em> methods of the {@link Collection} and {@link
54 : dl 1.52 * Iterator} interfaces. The Iterator provided in method {@link
55 :     * #iterator()} is <em>not</em> guaranteed to traverse the elements of
56 :     * the priority queue in any particular order. If you need ordered
57 : jsr166 1.63 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
58 : dl 1.29 *
59 :     * <p> <strong>Note that this implementation is not synchronized.</strong>
60 : jsr166 1.63 * Multiple threads should not access a {@code PriorityQueue}
61 :     * instance concurrently if any of the threads modifies the queue.
62 :     * Instead, use the thread-safe {@link
63 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
64 : dl 1.29 *
65 : jsr166 1.63 * <p>Implementation note: this implementation provides
66 :     * O(log(n)) time for the enqueing and dequeing methods
67 :     * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
68 :     * linear time for the {@code remove(Object)} and {@code contains(Object)}
69 :     * methods; and constant time for the retrieval methods
70 :     * ({@code peek}, {@code element}, and {@code size}).
71 : tim 1.2 *
72 :     * <p>This class is a member of the
73 : jsr166 1.65 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
74 : tim 1.2 * Java Collections Framework</a>.
75 : jsr166 1.63 *
76 : dl 1.7 * @since 1.5
77 : jsr166 1.63 * @author Josh Bloch, Doug Lea
78 : dl 1.45 * @param <E> the type of elements held in this collection
79 : tim 1.2 */
80 :     public class PriorityQueue<E> extends AbstractQueue<E>
81 : dl 1.47 implements java.io.Serializable {
82 : dholmes 1.11
83 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
84 : dl 1.30
85 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
86 : tim 1.1
87 : tim 1.2 /**
88 : dl 1.55 * Priority queue represented as a balanced binary heap: the two
89 :     * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
90 :     * priority queue is ordered by comparator, or by the elements'
91 :     * natural ordering, if comparator is null: For each node n in the
92 :     * heap and each descendant d of n, n <= d. The element with the
93 :     * lowest value is in queue[0], assuming the queue is nonempty.
94 : tim 1.2 */
95 : tim 1.16 private transient Object[] queue;
96 : tim 1.1
97 : tim 1.2 /**
98 :     * The number of elements in the priority queue.
99 :     */
100 :     private int size = 0;
101 : tim 1.1
102 : tim 1.2 /**
103 :     * The comparator, or null if priority queue uses elements'
104 :     * natural ordering.
105 :     */
106 : tim 1.16 private final Comparator<? super E> comparator;
107 : tim 1.2
108 :     /**
109 :     * The number of times this priority queue has been
110 :     * <i>structurally modified</i>. See AbstractList for gory details.
111 :     */
112 : dl 1.5 private transient int modCount = 0;
113 : tim 1.2
114 :     /**
115 : jsr166 1.63 * Creates a {@code PriorityQueue} with the default initial
116 : dl 1.52 * capacity (11) that orders its elements according to their
117 :     * {@linkplain Comparable natural ordering}.
118 : tim 1.2 */
119 :     public PriorityQueue() {
120 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
121 : tim 1.1 }
122 : tim 1.2
123 :     /**
124 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial
125 : dl 1.52 * capacity that orders its elements according to their
126 :     * {@linkplain Comparable natural ordering}.
127 : tim 1.2 *
128 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
129 : jsr166 1.63 * @throws IllegalArgumentException if {@code initialCapacity} is less
130 :     * than 1
131 : tim 1.2 */
132 :     public PriorityQueue(int initialCapacity) {
133 :     this(initialCapacity, null);
134 : tim 1.1 }
135 : tim 1.2
136 :     /**
137 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial capacity
138 : tim 1.2 * that orders its elements according to the specified comparator.
139 :     *
140 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
141 : jsr166 1.63 * @param comparator the comparator that will be used to order this
142 :     * priority queue. If {@code null}, the {@linkplain Comparable
143 :     * natural ordering} of the elements will be used.
144 :     * @throws IllegalArgumentException if {@code initialCapacity} is
145 : dl 1.52 * less than 1
146 : tim 1.2 */
147 : dl 1.52 public PriorityQueue(int initialCapacity,
148 : dholmes 1.23 Comparator<? super E> comparator) {
149 : dl 1.55 // Note: This restriction of at least one is not actually needed,
150 :     // but continues for 1.5 compatibility
151 : tim 1.2 if (initialCapacity < 1)
152 : dholmes 1.15 throw new IllegalArgumentException();
153 : dl 1.55 this.queue = new Object[initialCapacity];
154 : tim 1.2 this.comparator = comparator;
155 : tim 1.1 }
156 : jsr166 1.56
157 : dl 1.22 /**
158 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
159 :     * specified collection. If the specified collection is an instance of
160 :     * a {@link SortedSet} or is another {@code PriorityQueue}, this
161 :     * priority queue will be ordered according to the same ordering.
162 :     * Otherwise, this priority queue will be ordered according to the
163 :     * {@linkplain Comparable natural ordering} of its elements.
164 : tim 1.2 *
165 : dl 1.52 * @param c the collection whose elements are to be placed
166 :     * into this priority queue
167 : tim 1.2 * @throws ClassCastException if elements of the specified collection
168 :     * cannot be compared to one another according to the priority
169 : dl 1.52 * queue's ordering
170 :     * @throws NullPointerException if the specified collection or any
171 :     * of its elements are null
172 : tim 1.2 */
173 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
174 : dl 1.55 initFromCollection(c);
175 : jsr166 1.56 if (c instanceof SortedSet)
176 : dl 1.55 comparator = (Comparator<? super E>)
177 :     ((SortedSet<? extends E>)c).comparator();
178 : jsr166 1.56 else if (c instanceof PriorityQueue)
179 : dl 1.55 comparator = (Comparator<? super E>)
180 :     ((PriorityQueue<? extends E>)c).comparator();
181 :     else {
182 : tim 1.2 comparator = null;
183 : dl 1.55 heapify();
184 : tim 1.2 }
185 : dl 1.22 }
186 :    
187 :     /**
188 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
189 : dl 1.55 * specified priority queue. This priority queue will be
190 : dl 1.52 * ordered according to the same ordering as the given priority
191 :     * queue.
192 :     *
193 :     * @param c the priority queue whose elements are to be placed
194 :     * into this priority queue
195 : jsr166 1.63 * @throws ClassCastException if elements of {@code c} cannot be
196 :     * compared to one another according to {@code c}'s
197 : dl 1.52 * ordering
198 :     * @throws NullPointerException if the specified priority queue or any
199 :     * of its elements are null
200 : dl 1.22 */
201 :     public PriorityQueue(PriorityQueue<? extends E> c) {
202 :     comparator = (Comparator<? super E>)c.comparator();
203 : dl 1.55 initFromCollection(c);
204 : dl 1.22 }
205 : dholmes 1.18
206 : dl 1.22 /**
207 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
208 :     * specified sorted set. This priority queue will be ordered
209 : dl 1.52 * according to the same ordering as the given sorted set.
210 :     *
211 :     * @param c the sorted set whose elements are to be placed
212 : jsr166 1.63 * into this priority queue
213 : dl 1.52 * @throws ClassCastException if elements of the specified sorted
214 :     * set cannot be compared to one another according to the
215 :     * sorted set's ordering
216 :     * @throws NullPointerException if the specified sorted set or any
217 :     * of its elements are null
218 : dl 1.22 */
219 :     public PriorityQueue(SortedSet<? extends E> c) {
220 :     comparator = (Comparator<? super E>)c.comparator();
221 : dl 1.55 initFromCollection(c);
222 : tim 1.1 }
223 :    
224 : dl 1.22 /**
225 : jsr166 1.63 * Initializes queue array with elements from the given Collection.
226 :     *
227 : dl 1.55 * @param c the collection
228 : dl 1.22 */
229 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
230 :     Object[] a = c.toArray();
231 :     // If c.toArray incorrectly doesn't return Object[], copy it.
232 :     if (a.getClass() != Object[].class)
233 :     a = Arrays.copyOf(a, a.length, Object[].class);
234 :     queue = a;
235 :     size = a.length;
236 : jsr166 1.56 }
237 : dl 1.55
238 :     /**
239 :     * Increases the capacity of the array.
240 :     *
241 :     * @param minCapacity the desired minimum capacity
242 :     */
243 :     private void grow(int minCapacity) {
244 :     if (minCapacity < 0) // overflow
245 : dl 1.22 throw new OutOfMemoryError();
246 : jsr166 1.68 int oldCapacity = queue.length;
247 : dl 1.55 // Double size if small; else grow by 50%
248 :     int newCapacity = ((oldCapacity < 64)?
249 :     ((oldCapacity + 1) * 2):
250 : dl 1.58 ((oldCapacity / 2) * 3));
251 :     if (newCapacity < 0) // overflow
252 :     newCapacity = Integer.MAX_VALUE;
253 : dl 1.55 if (newCapacity < minCapacity)
254 :     newCapacity = minCapacity;
255 :     queue = Arrays.copyOf(queue, newCapacity);
256 : dl 1.22 }
257 : dl 1.36
258 : tim 1.2 /**
259 : dl 1.42 * Inserts the specified element into this priority queue.
260 : tim 1.2 *
261 : jsr166 1.63 * @return {@code true} (as specified by {@link Collection#add})
262 : dl 1.52 * @throws ClassCastException if the specified element cannot be
263 :     * compared with elements currently in this priority queue
264 :     * according to the priority queue's ordering
265 :     * @throws NullPointerException if the specified element is null
266 : tim 1.2 */
267 : dl 1.52 public boolean add(E e) {
268 :     return offer(e);
269 :     }
270 :    
271 :     /**
272 :     * Inserts the specified element into this priority queue.
273 :     *
274 : jsr166 1.63 * @return {@code true} (as specified by {@link Queue#offer})
275 : dl 1.52 * @throws ClassCastException if the specified element cannot be
276 :     * compared with elements currently in this priority queue
277 :     * according to the priority queue's ordering
278 :     * @throws NullPointerException if the specified element is null
279 :     */
280 :     public boolean offer(E e) {
281 :     if (e == null)
282 : dholmes 1.11 throw new NullPointerException();
283 :     modCount++;
284 : dl 1.55 int i = size;
285 :     if (i >= queue.length)
286 :     grow(i + 1);
287 :     size = i + 1;
288 :     if (i == 0)
289 :     queue[0] = e;
290 :     else
291 :     siftUp(i, e);
292 : dholmes 1.11 return true;
293 :     }
294 :    
295 : dl 1.40 public E peek() {
296 : tim 1.2 if (size == 0)
297 :     return null;
298 : dl 1.55 return (E) queue[0];
299 : tim 1.1 }
300 :    
301 : dl 1.52 private int indexOf(Object o) {
302 : jsr166 1.68 if (o != null) {
303 : dl 1.55 for (int i = 0; i < size; i++)
304 :     if (o.equals(queue[i]))
305 :     return i;
306 :     }
307 : dl 1.52 return -1;
308 :     }
309 :    
310 :     /**
311 :     * Removes a single instance of the specified element from this queue,
312 : jsr166 1.63 * if it is present. More formally, removes an element {@code e} such
313 :     * that {@code o.equals(e)}, if this queue contains one or more such
314 :     * elements. Returns {@code true} if and only if this queue contained
315 :     * the specified element (or equivalently, if this queue changed as a
316 :     * result of the call).
317 : dl 1.52 *
318 :     * @param o element to be removed from this queue, if present
319 : jsr166 1.63 * @return {@code true} if this queue changed as a result of the call
320 : dl 1.52 */
321 :     public boolean remove(Object o) {
322 : jsr166 1.68 int i = indexOf(o);
323 :     if (i == -1)
324 :     return false;
325 :     else {
326 :     removeAt(i);
327 :     return true;
328 :     }
329 : dl 1.52 }
330 : dholmes 1.11
331 : jsr166 1.56 /**
332 : dl 1.55 * Version of remove using reference equality, not equals.
333 : jsr166 1.59 * Needed by iterator.remove.
334 : jsr166 1.56 *
335 : dl 1.55 * @param o element to be removed from this queue, if present
336 : jsr166 1.63 * @return {@code true} if removed
337 : dl 1.55 */
338 :     boolean removeEq(Object o) {
339 : jsr166 1.68 for (int i = 0; i < size; i++) {
340 :     if (o == queue[i]) {
341 : dl 1.55 removeAt(i);
342 :     return true;
343 :     }
344 :     }
345 :     return false;
346 :     }
347 :    
348 : dholmes 1.11 /**
349 : jsr166 1.63 * Returns {@code true} if this queue contains the specified element.
350 :     * More formally, returns {@code true} if and only if this queue contains
351 :     * at least one element {@code e} such that {@code o.equals(e)}.
352 : dholmes 1.23 *
353 : dl 1.52 * @param o object to be checked for containment in this queue
354 : jsr166 1.63 * @return {@code true} if this queue contains the specified element
355 : dholmes 1.11 */
356 : dl 1.52 public boolean contains(Object o) {
357 : jsr166 1.68 return indexOf(o) != -1;
358 : tim 1.14 }
359 : dholmes 1.11
360 : dl 1.49 /**
361 : jsr166 1.63 * Returns an array containing all of the elements in this queue.
362 : dl 1.52 * The elements are in no particular order.
363 :     *
364 :     * <p>The returned array will be "safe" in that no references to it are
365 : jsr166 1.63 * maintained by this queue. (In other words, this method must allocate
366 : dl 1.52 * a new array). The caller is thus free to modify the returned array.
367 :     *
368 : jsr166 1.63 * <p>This method acts as bridge between array-based and collection-based
369 :     * APIs.
370 :     *
371 : jsr166 1.59 * @return an array containing all of the elements in this queue
372 : dl 1.49 */
373 : dl 1.52 public Object[] toArray() {
374 : dl 1.55 return Arrays.copyOf(queue, size);
375 : dl 1.52 }
376 : tim 1.2
377 : dl 1.52 /**
378 : jsr166 1.63 * Returns an array containing all of the elements in this queue; the
379 :     * runtime type of the returned array is that of the specified array.
380 :     * The returned array elements are in no particular order.
381 :     * If the queue fits in the specified array, it is returned therein.
382 :     * Otherwise, a new array is allocated with the runtime type of the
383 :     * specified array and the size of this queue.
384 : dl 1.52 *
385 :     * <p>If the queue fits in the specified array with room to spare
386 :     * (i.e., the array has more elements than the queue), the element in
387 :     * the array immediately following the end of the collection is set to
388 : jsr166 1.63 * {@code null}.
389 :     *
390 :     * <p>Like the {@link #toArray()} method, this method acts as bridge between
391 :     * array-based and collection-based APIs. Further, this method allows
392 :     * precise control over the runtime type of the output array, and may,
393 :     * under certain circumstances, be used to save allocation costs.
394 :     *
395 :     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
396 :     * The following code can be used to dump the queue into a newly
397 :     * allocated array of <tt>String</tt>:
398 :     *
399 :     * <pre>
400 :     * String[] y = x.toArray(new String[0]);</pre>
401 :     *
402 :     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
403 :     * <tt>toArray()</tt>.
404 : dl 1.52 *
405 :     * @param a the array into which the elements of the queue are to
406 :     * be stored, if it is big enough; otherwise, a new array of the
407 :     * same runtime type is allocated for this purpose.
408 : jsr166 1.63 * @return an array containing all of the elements in this queue
409 : dl 1.52 * @throws ArrayStoreException if the runtime type of the specified array
410 :     * is not a supertype of the runtime type of every element in
411 :     * this queue
412 :     * @throws NullPointerException if the specified array is null
413 :     */
414 :     public <T> T[] toArray(T[] a) {
415 :     if (a.length < size)
416 :     // Make a new array of a's runtime type, but my contents:
417 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
418 : jsr166 1.68 System.arraycopy(queue, 0, a, 0, size);
419 : dl 1.52 if (a.length > size)
420 :     a[size] = null;
421 :     return a;
422 : tim 1.1 }
423 : tim 1.2
424 : dholmes 1.23 /**
425 :     * Returns an iterator over the elements in this queue. The iterator
426 :     * does not return the elements in any particular order.
427 :     *
428 : dl 1.52 * @return an iterator over the elements in this queue
429 : dholmes 1.23 */
430 : tim 1.2 public Iterator<E> iterator() {
431 : dl 1.7 return new Itr();
432 : tim 1.2 }
433 :    
434 : dl 1.55 private final class Itr implements Iterator<E> {
435 : dl 1.7 /**
436 :     * Index (into queue array) of element to be returned by
437 : tim 1.2 * subsequent call to next.
438 : dl 1.7 */
439 : dl 1.55 private int cursor = 0;
440 : tim 1.2
441 : dl 1.7 /**
442 : dl 1.36 * Index of element returned by most recent call to next,
443 :     * unless that element came from the forgetMeNot list.
444 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
445 : dl 1.7 */
446 : dl 1.55 private int lastRet = -1;
447 : dl 1.7
448 :     /**
449 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
450 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
451 :     * removals during the iteration. (Unlucky element removals are those
452 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
453 : dl 1.36 * the elements in this list to complete the iteration. We do this
454 :     * after we've completed the "normal" iteration.
455 :     *
456 :     * We expect that most iterations, even those involving removals,
457 : jsr166 1.63 * will not need to store elements in this field.
458 : dl 1.36 */
459 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
460 : dl 1.36
461 :     /**
462 :     * Element returned by the most recent call to next iff that
463 :     * element was drawn from the forgetMeNot list.
464 :     */
465 : dl 1.55 private E lastRetElt = null;
466 :    
467 :     /**
468 :     * The modCount value that the iterator believes that the backing
469 : jsr166 1.63 * Queue should have. If this expectation is violated, the iterator
470 : dl 1.55 * has detected concurrent modification.
471 :     */
472 :     private int expectedModCount = modCount;
473 : dl 1.35
474 : dl 1.7 public boolean hasNext() {
475 : jsr166 1.56 return cursor < size ||
476 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
477 : dl 1.7 }
478 :    
479 :     public E next() {
480 : dl 1.55 if (expectedModCount != modCount)
481 :     throw new ConcurrentModificationException();
482 : jsr166 1.56 if (cursor < size)
483 : dl 1.55 return (E) queue[lastRet = cursor++];
484 :     if (forgetMeNot != null) {
485 :     lastRet = -1;
486 :     lastRetElt = forgetMeNot.poll();
487 : jsr166 1.56 if (lastRetElt != null)
488 : dl 1.55 return lastRetElt;
489 : dl 1.36 }
490 : dl 1.55 throw new NoSuchElementException();
491 : dl 1.7 }
492 : tim 1.2
493 : dl 1.7 public void remove() {
494 : dl 1.55 if (expectedModCount != modCount)
495 :     throw new ConcurrentModificationException();
496 :     if (lastRet != -1) {
497 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
498 : dl 1.55 lastRet = -1;
499 : jsr166 1.56 if (moved == null)
500 : dl 1.36 cursor--;
501 : dl 1.55 else {
502 : dl 1.36 if (forgetMeNot == null)
503 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
504 : dl 1.36 forgetMeNot.add(moved);
505 : jsr166 1.56 }
506 : jsr166 1.63 } else if (lastRetElt != null) {
507 : dl 1.55 PriorityQueue.this.removeEq(lastRetElt);
508 : dl 1.36 lastRetElt = null;
509 : jsr166 1.63 } else {
510 :     throw new IllegalStateException();
511 : jsr166 1.68 }
512 : tim 1.2 expectedModCount = modCount;
513 : dl 1.7 }
514 : tim 1.2 }
515 :    
516 : tim 1.1 public int size() {
517 : tim 1.2 return size;
518 : tim 1.1 }
519 : tim 1.2
520 :     /**
521 : dl 1.52 * Removes all of the elements from this priority queue.
522 : dl 1.49 * The queue will be empty after this call returns.
523 : tim 1.2 */
524 :     public void clear() {
525 :     modCount++;
526 : dl 1.55 for (int i = 0; i < size; i++)
527 : tim 1.2 queue[i] = null;
528 :     size = 0;
529 :     }
530 :    
531 : dl 1.40 public E poll() {
532 : dl 1.36 if (size == 0)
533 : dl 1.40 return null;
534 : dl 1.55 int s = --size;
535 : dl 1.36 modCount++;
536 : jsr166 1.63 E result = (E) queue[0];
537 :     E x = (E) queue[s];
538 : dl 1.55 queue[s] = null;
539 :     if (s != 0)
540 :     siftDown(0, x);
541 : dl 1.36 return result;
542 :     }
543 :    
544 :     /**
545 : dl 1.55 * Removes the ith element from queue.
546 : tim 1.2 *
547 : dl 1.55 * Normally this method leaves the elements at up to i-1,
548 :     * inclusive, untouched. Under these circumstances, it returns
549 :     * null. Occasionally, in order to maintain the heap invariant,
550 :     * it must swap a later element of the list with one earlier than
551 :     * i. Under these circumstances, this method returns the element
552 :     * that was previously at the end of the list and is now at some
553 :     * position before i. This fact is used by iterator.remove so as to
554 : jsr166 1.63 * avoid missing traversing elements.
555 : tim 1.2 */
556 : dl 1.52 private E removeAt(int i) {
557 : dl 1.55 assert i >= 0 && i < size;
558 : tim 1.2 modCount++;
559 : dl 1.55 int s = --size;
560 :     if (s == i) // removed last element
561 :     queue[i] = null;
562 :     else {
563 :     E moved = (E) queue[s];
564 : jsr166 1.56 queue[s] = null;
565 : dl 1.55 siftDown(i, moved);
566 : dl 1.36 if (queue[i] == moved) {
567 : dl 1.55 siftUp(i, moved);
568 : dl 1.36 if (queue[i] != moved)
569 :     return moved;
570 :     }
571 : dl 1.35 }
572 : dl 1.36 return null;
573 : tim 1.1 }
574 :    
575 : tim 1.2 /**
576 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
577 :     * promoting x up the tree until it is greater than or equal to
578 :     * its parent, or is the root.
579 :     *
580 :     * To simplify and speed up coercions and comparisons. the
581 :     * Comparable and Comparator versions are separated into different
582 :     * methods that are otherwise identical. (Similarly for siftDown.)
583 : jsr166 1.56 *
584 : dl 1.55 * @param k the position to fill
585 :     * @param x the item to insert
586 :     */
587 :     private void siftUp(int k, E x) {
588 : jsr166 1.56 if (comparator != null)
589 : dl 1.55 siftUpUsingComparator(k, x);
590 :     else
591 :     siftUpComparable(k, x);
592 :     }
593 :    
594 :     private void siftUpComparable(int k, E x) {
595 :     Comparable<? super E> key = (Comparable<? super E>) x;
596 :     while (k > 0) {
597 :     int parent = (k - 1) >>> 1;
598 :     Object e = queue[parent];
599 : jsr166 1.63 if (key.compareTo((E) e) >= 0)
600 : dl 1.55 break;
601 :     queue[k] = e;
602 :     k = parent;
603 :     }
604 :     queue[k] = key;
605 :     }
606 :    
607 :     private void siftUpUsingComparator(int k, E x) {
608 :     while (k > 0) {
609 :     int parent = (k - 1) >>> 1;
610 :     Object e = queue[parent];
611 : jsr166 1.63 if (comparator.compare(x, (E) e) >= 0)
612 : dl 1.55 break;
613 :     queue[k] = e;
614 :     k = parent;
615 :     }
616 :     queue[k] = x;
617 :     }
618 :    
619 :     /**
620 :     * Inserts item x at position k, maintaining heap invariant by
621 :     * demoting x down the tree repeatedly until it is less than or
622 :     * equal to its children or is a leaf.
623 :     *
624 :     * @param k the position to fill
625 :     * @param x the item to insert
626 :     */
627 :     private void siftDown(int k, E x) {
628 : jsr166 1.56 if (comparator != null)
629 : dl 1.55 siftDownUsingComparator(k, x);
630 :     else
631 :     siftDownComparable(k, x);
632 :     }
633 :    
634 :     private void siftDownComparable(int k, E x) {
635 :     Comparable<? super E> key = (Comparable<? super E>)x;
636 :     int half = size >>> 1; // loop while a non-leaf
637 :     while (k < half) {
638 :     int child = (k << 1) + 1; // assume left child is least
639 :     Object c = queue[child];
640 :     int right = child + 1;
641 :     if (right < size &&
642 : jsr166 1.63 ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
643 : dl 1.55 c = queue[child = right];
644 : jsr166 1.63 if (key.compareTo((E) c) <= 0)
645 : dl 1.55 break;
646 :     queue[k] = c;
647 :     k = child;
648 :     }
649 :     queue[k] = key;
650 :     }
651 :    
652 :     private void siftDownUsingComparator(int k, E x) {
653 :     int half = size >>> 1;
654 :     while (k < half) {
655 :     int child = (k << 1) + 1;
656 :     Object c = queue[child];
657 :     int right = child + 1;
658 :     if (right < size &&
659 : jsr166 1.63 comparator.compare((E) c, (E) queue[right]) > 0)
660 : jsr166 1.56 c = queue[child = right];
661 : jsr166 1.63 if (comparator.compare(x, (E) c) <= 0)
662 : dl 1.55 break;
663 :     queue[k] = c;
664 :     k = child;
665 : tim 1.2 }
666 : dl 1.55 queue[k] = x;
667 : dl 1.36 }
668 : dl 1.35
669 : dl 1.36 /**
670 :     * Establishes the heap invariant (described above) in the entire tree,
671 :     * assuming nothing about the order of the elements prior to the call.
672 :     */
673 :     private void heapify() {
674 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
675 : jsr166 1.63 siftDown(i, (E) queue[i]);
676 : tim 1.2 }
677 :    
678 : dholmes 1.23 /**
679 : dl 1.52 * Returns the comparator used to order the elements in this
680 : jsr166 1.63 * queue, or {@code null} if this queue is sorted according to
681 : dl 1.52 * the {@linkplain Comparable natural ordering} of its elements.
682 :     *
683 :     * @return the comparator used to order this queue, or
684 : jsr166 1.63 * {@code null} if this queue is sorted according to the
685 :     * natural ordering of its elements
686 : dholmes 1.23 */
687 : tim 1.16 public Comparator<? super E> comparator() {
688 : tim 1.2 return comparator;
689 :     }
690 : dl 1.5
691 :     /**
692 : jsr166 1.63 * Saves the state of the instance to a stream (that
693 :     * is, serializes it).
694 : dl 1.5 *
695 :     * @serialData The length of the array backing the instance is
696 : jsr166 1.63 * emitted (int), followed by all of its elements
697 :     * (each an {@code Object}) in the proper order.
698 : dl 1.7 * @param s the stream
699 : dl 1.5 */
700 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
701 : dl 1.5 throws java.io.IOException{
702 : dl 1.7 // Write out element count, and any hidden stuff
703 :     s.defaultWriteObject();
704 : dl 1.5
705 : jsr166 1.63 // Write out array length, for compatibility with 1.5 version
706 :     s.writeInt(Math.max(2, size + 1));
707 : dl 1.5
708 : jsr166 1.64 // Write out all elements in the "proper order".
709 : jsr166 1.63 for (int i = 0; i < size; i++)
710 : dl 1.5 s.writeObject(queue[i]);
711 :     }
712 :    
713 :     /**
714 : jsr166 1.63 * Reconstitutes the {@code PriorityQueue} instance from a stream
715 :     * (that is, deserializes it).
716 :     *
717 : dl 1.7 * @param s the stream
718 : dl 1.5 */
719 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
720 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
721 : dl 1.7 // Read in size, and any hidden stuff
722 :     s.defaultReadObject();
723 : dl 1.5
724 : jsr166 1.63 // Read in (and discard) array length
725 :     s.readInt();
726 :    
727 : jsr166 1.68 queue = new Object[size];
728 : dl 1.5
729 : jsr166 1.64 // Read in all elements.
730 : jsr166 1.63 for (int i = 0; i < size; i++)
731 :     queue[i] = s.readObject();
732 : jsr166 1.64
733 : jsr166 1.68 // Elements are guaranteed to be in "proper order", but the
734 :     // spec has never explained what that might be.
735 :     heapify();
736 : dl 1.5 }
737 : tim 1.1 }

Doug Lea
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