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1 : dl 1.38 /*
2 : jsr166 1.71 * Copyright (c) 2003, 2006, Oracle and/or its affiliates. All rights reserved.
3 : jsr166 1.67 * 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 : jsr166 1.71 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 :     * or visit www.oracle.com if you need additional information or have any
23 :     * 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 : jsr166 1.70 @SuppressWarnings("unchecked")
174 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
175 : jsr166 1.70 if (c instanceof SortedSet<?>) {
176 :     SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
177 :     this.comparator = (Comparator<? super E>) ss.comparator();
178 :     initElementsFromCollection(ss);
179 :     }
180 :     else if (c instanceof PriorityQueue<?>) {
181 :     PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
182 :     this.comparator = (Comparator<? super E>) pq.comparator();
183 :     initFromPriorityQueue(pq);
184 :     }
185 : dl 1.55 else {
186 : jsr166 1.70 this.comparator = null;
187 :     initFromCollection(c);
188 : tim 1.2 }
189 : dl 1.22 }
190 :    
191 :     /**
192 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
193 : dl 1.55 * specified priority queue. This priority queue will be
194 : dl 1.52 * ordered according to the same ordering as the given priority
195 :     * queue.
196 :     *
197 :     * @param c the priority queue whose elements are to be placed
198 :     * into this priority queue
199 : jsr166 1.63 * @throws ClassCastException if elements of {@code c} cannot be
200 :     * compared to one another according to {@code c}'s
201 : dl 1.52 * ordering
202 :     * @throws NullPointerException if the specified priority queue or any
203 :     * of its elements are null
204 : dl 1.22 */
205 : jsr166 1.70 @SuppressWarnings("unchecked")
206 : dl 1.22 public PriorityQueue(PriorityQueue<? extends E> c) {
207 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
208 :     initFromPriorityQueue(c);
209 : dl 1.22 }
210 : dholmes 1.18
211 : dl 1.22 /**
212 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
213 :     * specified sorted set. This priority queue will be ordered
214 : dl 1.52 * according to the same ordering as the given sorted set.
215 :     *
216 :     * @param c the sorted set whose elements are to be placed
217 : jsr166 1.63 * into this priority queue
218 : dl 1.52 * @throws ClassCastException if elements of the specified sorted
219 :     * set cannot be compared to one another according to the
220 :     * sorted set's ordering
221 :     * @throws NullPointerException if the specified sorted set or any
222 :     * of its elements are null
223 : dl 1.22 */
224 : jsr166 1.70 @SuppressWarnings("unchecked")
225 : dl 1.22 public PriorityQueue(SortedSet<? extends E> c) {
226 : jsr166 1.70 this.comparator = (Comparator<? super E>) c.comparator();
227 :     initElementsFromCollection(c);
228 :     }
229 :    
230 :     private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
231 :     if (c.getClass() == PriorityQueue.class) {
232 :     this.queue = c.toArray();
233 :     this.size = c.size();
234 :     } else {
235 :     initFromCollection(c);
236 :     }
237 :     }
238 :    
239 :     private void initElementsFromCollection(Collection<? extends E> c) {
240 :     Object[] a = c.toArray();
241 :     // If c.toArray incorrectly doesn't return Object[], copy it.
242 :     if (a.getClass() != Object[].class)
243 :     a = Arrays.copyOf(a, a.length, Object[].class);
244 :     int len = a.length;
245 :     if (len == 1 || this.comparator != null)
246 :     for (int i = 0; i < len; i++)
247 :     if (a[i] == null)
248 :     throw new NullPointerException();
249 :     this.queue = a;
250 :     this.size = a.length;
251 : tim 1.1 }
252 :    
253 : dl 1.22 /**
254 : jsr166 1.63 * Initializes queue array with elements from the given Collection.
255 :     *
256 : dl 1.55 * @param c the collection
257 : dl 1.22 */
258 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
259 : jsr166 1.70 initElementsFromCollection(c);
260 :     heapify();
261 : jsr166 1.56 }
262 : dl 1.55
263 :     /**
264 : jsr166 1.70 * The maximum size of array to allocate.
265 :     * Some VMs reserve some header words in an array.
266 :     * Attempts to allocate larger arrays may result in
267 :     * OutOfMemoryError: Requested array size exceeds VM limit
268 :     */
269 :     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
270 :    
271 :     /**
272 : dl 1.55 * Increases the capacity of the array.
273 :     *
274 :     * @param minCapacity the desired minimum capacity
275 :     */
276 :     private void grow(int minCapacity) {
277 : jsr166 1.68 int oldCapacity = queue.length;
278 : dl 1.55 // Double size if small; else grow by 50%
279 : jsr166 1.70 int newCapacity = oldCapacity + ((oldCapacity < 64) ?
280 :     (oldCapacity + 2) :
281 :     (oldCapacity >> 1));
282 :     // overflow-conscious code
283 :     if (newCapacity - MAX_ARRAY_SIZE > 0)
284 :     newCapacity = hugeCapacity(minCapacity);
285 : dl 1.55 queue = Arrays.copyOf(queue, newCapacity);
286 : dl 1.22 }
287 : dl 1.36
288 : jsr166 1.70 private static int hugeCapacity(int minCapacity) {
289 :     if (minCapacity < 0) // overflow
290 :     throw new OutOfMemoryError();
291 :     return (minCapacity > MAX_ARRAY_SIZE) ?
292 :     Integer.MAX_VALUE :
293 :     MAX_ARRAY_SIZE;
294 :     }
295 :    
296 : tim 1.2 /**
297 : dl 1.42 * Inserts the specified element into this priority queue.
298 : tim 1.2 *
299 : jsr166 1.63 * @return {@code true} (as specified by {@link Collection#add})
300 : dl 1.52 * @throws ClassCastException if the specified element cannot be
301 :     * compared with elements currently in this priority queue
302 :     * according to the priority queue's ordering
303 :     * @throws NullPointerException if the specified element is null
304 : tim 1.2 */
305 : dl 1.52 public boolean add(E e) {
306 :     return offer(e);
307 :     }
308 :    
309 :     /**
310 :     * Inserts the specified element into this priority queue.
311 :     *
312 : jsr166 1.63 * @return {@code true} (as specified by {@link Queue#offer})
313 : dl 1.52 * @throws ClassCastException if the specified element cannot be
314 :     * compared with elements currently in this priority queue
315 :     * according to the priority queue's ordering
316 :     * @throws NullPointerException if the specified element is null
317 :     */
318 :     public boolean offer(E e) {
319 :     if (e == null)
320 : dholmes 1.11 throw new NullPointerException();
321 :     modCount++;
322 : dl 1.55 int i = size;
323 :     if (i >= queue.length)
324 :     grow(i + 1);
325 :     size = i + 1;
326 :     if (i == 0)
327 :     queue[0] = e;
328 :     else
329 :     siftUp(i, e);
330 : dholmes 1.11 return true;
331 :     }
332 :    
333 : dl 1.40 public E peek() {
334 : tim 1.2 if (size == 0)
335 :     return null;
336 : dl 1.55 return (E) queue[0];
337 : tim 1.1 }
338 :    
339 : dl 1.52 private int indexOf(Object o) {
340 : jsr166 1.68 if (o != null) {
341 : dl 1.55 for (int i = 0; i < size; i++)
342 :     if (o.equals(queue[i]))
343 :     return i;
344 :     }
345 : dl 1.52 return -1;
346 :     }
347 :    
348 :     /**
349 :     * Removes a single instance of the specified element from this queue,
350 : jsr166 1.63 * if it is present. More formally, removes an element {@code e} such
351 :     * that {@code o.equals(e)}, if this queue contains one or more such
352 :     * elements. Returns {@code true} if and only if this queue contained
353 :     * the specified element (or equivalently, if this queue changed as a
354 :     * result of the call).
355 : dl 1.52 *
356 :     * @param o element to be removed from this queue, if present
357 : jsr166 1.63 * @return {@code true} if this queue changed as a result of the call
358 : dl 1.52 */
359 :     public boolean remove(Object o) {
360 : jsr166 1.68 int i = indexOf(o);
361 :     if (i == -1)
362 :     return false;
363 :     else {
364 :     removeAt(i);
365 :     return true;
366 :     }
367 : dl 1.52 }
368 : dholmes 1.11
369 : jsr166 1.56 /**
370 : dl 1.55 * Version of remove using reference equality, not equals.
371 : jsr166 1.59 * Needed by iterator.remove.
372 : jsr166 1.56 *
373 : dl 1.55 * @param o element to be removed from this queue, if present
374 : jsr166 1.63 * @return {@code true} if removed
375 : dl 1.55 */
376 :     boolean removeEq(Object o) {
377 : jsr166 1.68 for (int i = 0; i < size; i++) {
378 :     if (o == queue[i]) {
379 : dl 1.55 removeAt(i);
380 :     return true;
381 :     }
382 :     }
383 :     return false;
384 :     }
385 :    
386 : dholmes 1.11 /**
387 : jsr166 1.63 * Returns {@code true} if this queue contains the specified element.
388 :     * More formally, returns {@code true} if and only if this queue contains
389 :     * at least one element {@code e} such that {@code o.equals(e)}.
390 : dholmes 1.23 *
391 : dl 1.52 * @param o object to be checked for containment in this queue
392 : jsr166 1.63 * @return {@code true} if this queue contains the specified element
393 : dholmes 1.11 */
394 : dl 1.52 public boolean contains(Object o) {
395 : jsr166 1.68 return indexOf(o) != -1;
396 : tim 1.14 }
397 : dholmes 1.11
398 : dl 1.49 /**
399 : jsr166 1.63 * Returns an array containing all of the elements in this queue.
400 : dl 1.52 * The elements are in no particular order.
401 :     *
402 :     * <p>The returned array will be "safe" in that no references to it are
403 : jsr166 1.63 * maintained by this queue. (In other words, this method must allocate
404 : dl 1.52 * a new array). The caller is thus free to modify the returned array.
405 :     *
406 : jsr166 1.63 * <p>This method acts as bridge between array-based and collection-based
407 :     * APIs.
408 :     *
409 : jsr166 1.59 * @return an array containing all of the elements in this queue
410 : dl 1.49 */
411 : dl 1.52 public Object[] toArray() {
412 : dl 1.55 return Arrays.copyOf(queue, size);
413 : dl 1.52 }
414 : tim 1.2
415 : dl 1.52 /**
416 : jsr166 1.63 * Returns an array containing all of the elements in this queue; the
417 :     * runtime type of the returned array is that of the specified array.
418 :     * The returned array elements are in no particular order.
419 :     * If the queue fits in the specified array, it is returned therein.
420 :     * Otherwise, a new array is allocated with the runtime type of the
421 :     * specified array and the size of this queue.
422 : dl 1.52 *
423 :     * <p>If the queue fits in the specified array with room to spare
424 :     * (i.e., the array has more elements than the queue), the element in
425 :     * the array immediately following the end of the collection is set to
426 : jsr166 1.63 * {@code null}.
427 :     *
428 :     * <p>Like the {@link #toArray()} method, this method acts as bridge between
429 :     * array-based and collection-based APIs. Further, this method allows
430 :     * precise control over the runtime type of the output array, and may,
431 :     * under certain circumstances, be used to save allocation costs.
432 :     *
433 :     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
434 :     * The following code can be used to dump the queue into a newly
435 :     * allocated array of <tt>String</tt>:
436 :     *
437 : jsr166 1.72 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
438 : jsr166 1.63 *
439 :     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
440 :     * <tt>toArray()</tt>.
441 : dl 1.52 *
442 :     * @param a the array into which the elements of the queue are to
443 :     * be stored, if it is big enough; otherwise, a new array of the
444 :     * same runtime type is allocated for this purpose.
445 : jsr166 1.63 * @return an array containing all of the elements in this queue
446 : dl 1.52 * @throws ArrayStoreException if the runtime type of the specified array
447 :     * is not a supertype of the runtime type of every element in
448 :     * this queue
449 :     * @throws NullPointerException if the specified array is null
450 :     */
451 :     public <T> T[] toArray(T[] a) {
452 :     if (a.length < size)
453 :     // Make a new array of a's runtime type, but my contents:
454 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
455 : jsr166 1.68 System.arraycopy(queue, 0, a, 0, size);
456 : dl 1.52 if (a.length > size)
457 :     a[size] = null;
458 :     return a;
459 : tim 1.1 }
460 : tim 1.2
461 : dholmes 1.23 /**
462 :     * Returns an iterator over the elements in this queue. The iterator
463 :     * does not return the elements in any particular order.
464 :     *
465 : dl 1.52 * @return an iterator over the elements in this queue
466 : dholmes 1.23 */
467 : tim 1.2 public Iterator<E> iterator() {
468 : dl 1.7 return new Itr();
469 : tim 1.2 }
470 :    
471 : dl 1.55 private final class Itr implements Iterator<E> {
472 : dl 1.7 /**
473 :     * Index (into queue array) of element to be returned by
474 : tim 1.2 * subsequent call to next.
475 : dl 1.7 */
476 : dl 1.55 private int cursor = 0;
477 : tim 1.2
478 : dl 1.7 /**
479 : dl 1.36 * Index of element returned by most recent call to next,
480 :     * unless that element came from the forgetMeNot list.
481 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
482 : dl 1.7 */
483 : dl 1.55 private int lastRet = -1;
484 : dl 1.7
485 :     /**
486 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
487 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
488 :     * removals during the iteration. (Unlucky element removals are those
489 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
490 : dl 1.36 * the elements in this list to complete the iteration. We do this
491 :     * after we've completed the "normal" iteration.
492 :     *
493 :     * We expect that most iterations, even those involving removals,
494 : jsr166 1.63 * will not need to store elements in this field.
495 : dl 1.36 */
496 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
497 : dl 1.36
498 :     /**
499 :     * Element returned by the most recent call to next iff that
500 :     * element was drawn from the forgetMeNot list.
501 :     */
502 : dl 1.55 private E lastRetElt = null;
503 :    
504 :     /**
505 :     * The modCount value that the iterator believes that the backing
506 : jsr166 1.63 * Queue should have. If this expectation is violated, the iterator
507 : dl 1.55 * has detected concurrent modification.
508 :     */
509 :     private int expectedModCount = modCount;
510 : dl 1.35
511 : dl 1.7 public boolean hasNext() {
512 : jsr166 1.56 return cursor < size ||
513 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
514 : dl 1.7 }
515 :    
516 :     public E next() {
517 : dl 1.55 if (expectedModCount != modCount)
518 :     throw new ConcurrentModificationException();
519 : jsr166 1.56 if (cursor < size)
520 : dl 1.55 return (E) queue[lastRet = cursor++];
521 :     if (forgetMeNot != null) {
522 :     lastRet = -1;
523 :     lastRetElt = forgetMeNot.poll();
524 : jsr166 1.56 if (lastRetElt != null)
525 : dl 1.55 return lastRetElt;
526 : dl 1.36 }
527 : dl 1.55 throw new NoSuchElementException();
528 : dl 1.7 }
529 : tim 1.2
530 : dl 1.7 public void remove() {
531 : dl 1.55 if (expectedModCount != modCount)
532 :     throw new ConcurrentModificationException();
533 :     if (lastRet != -1) {
534 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
535 : dl 1.55 lastRet = -1;
536 : jsr166 1.56 if (moved == null)
537 : dl 1.36 cursor--;
538 : dl 1.55 else {
539 : dl 1.36 if (forgetMeNot == null)
540 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
541 : dl 1.36 forgetMeNot.add(moved);
542 : jsr166 1.56 }
543 : jsr166 1.63 } else if (lastRetElt != null) {
544 : dl 1.55 PriorityQueue.this.removeEq(lastRetElt);
545 : dl 1.36 lastRetElt = null;
546 : jsr166 1.63 } else {
547 :     throw new IllegalStateException();
548 : jsr166 1.68 }
549 : tim 1.2 expectedModCount = modCount;
550 : dl 1.7 }
551 : tim 1.2 }
552 :    
553 : tim 1.1 public int size() {
554 : tim 1.2 return size;
555 : tim 1.1 }
556 : tim 1.2
557 :     /**
558 : dl 1.52 * Removes all of the elements from this priority queue.
559 : dl 1.49 * The queue will be empty after this call returns.
560 : tim 1.2 */
561 :     public void clear() {
562 :     modCount++;
563 : dl 1.55 for (int i = 0; i < size; i++)
564 : tim 1.2 queue[i] = null;
565 :     size = 0;
566 :     }
567 :    
568 : dl 1.40 public E poll() {
569 : dl 1.36 if (size == 0)
570 : dl 1.40 return null;
571 : dl 1.55 int s = --size;
572 : dl 1.36 modCount++;
573 : jsr166 1.63 E result = (E) queue[0];
574 :     E x = (E) queue[s];
575 : dl 1.55 queue[s] = null;
576 :     if (s != 0)
577 :     siftDown(0, x);
578 : dl 1.36 return result;
579 :     }
580 :    
581 :     /**
582 : dl 1.55 * Removes the ith element from queue.
583 : tim 1.2 *
584 : dl 1.55 * Normally this method leaves the elements at up to i-1,
585 :     * inclusive, untouched. Under these circumstances, it returns
586 :     * null. Occasionally, in order to maintain the heap invariant,
587 :     * it must swap a later element of the list with one earlier than
588 :     * i. Under these circumstances, this method returns the element
589 :     * that was previously at the end of the list and is now at some
590 :     * position before i. This fact is used by iterator.remove so as to
591 : jsr166 1.63 * avoid missing traversing elements.
592 : tim 1.2 */
593 : dl 1.52 private E removeAt(int i) {
594 : dl 1.55 assert i >= 0 && i < size;
595 : tim 1.2 modCount++;
596 : dl 1.55 int s = --size;
597 :     if (s == i) // removed last element
598 :     queue[i] = null;
599 :     else {
600 :     E moved = (E) queue[s];
601 : jsr166 1.56 queue[s] = null;
602 : dl 1.55 siftDown(i, moved);
603 : dl 1.36 if (queue[i] == moved) {
604 : dl 1.55 siftUp(i, moved);
605 : dl 1.36 if (queue[i] != moved)
606 :     return moved;
607 :     }
608 : dl 1.35 }
609 : dl 1.36 return null;
610 : tim 1.1 }
611 :    
612 : tim 1.2 /**
613 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
614 :     * promoting x up the tree until it is greater than or equal to
615 :     * its parent, or is the root.
616 :     *
617 :     * To simplify and speed up coercions and comparisons. the
618 :     * Comparable and Comparator versions are separated into different
619 :     * methods that are otherwise identical. (Similarly for siftDown.)
620 : jsr166 1.56 *
621 : dl 1.55 * @param k the position to fill
622 :     * @param x the item to insert
623 :     */
624 :     private void siftUp(int k, E x) {
625 : jsr166 1.56 if (comparator != null)
626 : dl 1.55 siftUpUsingComparator(k, x);
627 :     else
628 :     siftUpComparable(k, x);
629 :     }
630 :    
631 :     private void siftUpComparable(int k, E x) {
632 :     Comparable<? super E> key = (Comparable<? super E>) x;
633 :     while (k > 0) {
634 :     int parent = (k - 1) >>> 1;
635 :     Object e = queue[parent];
636 : jsr166 1.63 if (key.compareTo((E) e) >= 0)
637 : dl 1.55 break;
638 :     queue[k] = e;
639 :     k = parent;
640 :     }
641 :     queue[k] = key;
642 :     }
643 :    
644 :     private void siftUpUsingComparator(int k, E x) {
645 :     while (k > 0) {
646 :     int parent = (k - 1) >>> 1;
647 :     Object e = queue[parent];
648 : jsr166 1.63 if (comparator.compare(x, (E) e) >= 0)
649 : dl 1.55 break;
650 :     queue[k] = e;
651 :     k = parent;
652 :     }
653 :     queue[k] = x;
654 :     }
655 :    
656 :     /**
657 :     * Inserts item x at position k, maintaining heap invariant by
658 :     * demoting x down the tree repeatedly until it is less than or
659 :     * equal to its children or is a leaf.
660 :     *
661 :     * @param k the position to fill
662 :     * @param x the item to insert
663 :     */
664 :     private void siftDown(int k, E x) {
665 : jsr166 1.56 if (comparator != null)
666 : dl 1.55 siftDownUsingComparator(k, x);
667 :     else
668 :     siftDownComparable(k, x);
669 :     }
670 :    
671 :     private void siftDownComparable(int k, E x) {
672 :     Comparable<? super E> key = (Comparable<? super E>)x;
673 :     int half = size >>> 1; // loop while a non-leaf
674 :     while (k < half) {
675 :     int child = (k << 1) + 1; // assume left child is least
676 :     Object c = queue[child];
677 :     int right = child + 1;
678 :     if (right < size &&
679 : jsr166 1.63 ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
680 : dl 1.55 c = queue[child = right];
681 : jsr166 1.63 if (key.compareTo((E) c) <= 0)
682 : dl 1.55 break;
683 :     queue[k] = c;
684 :     k = child;
685 :     }
686 :     queue[k] = key;
687 :     }
688 :    
689 :     private void siftDownUsingComparator(int k, E x) {
690 :     int half = size >>> 1;
691 :     while (k < half) {
692 :     int child = (k << 1) + 1;
693 :     Object c = queue[child];
694 :     int right = child + 1;
695 :     if (right < size &&
696 : jsr166 1.63 comparator.compare((E) c, (E) queue[right]) > 0)
697 : jsr166 1.56 c = queue[child = right];
698 : jsr166 1.63 if (comparator.compare(x, (E) c) <= 0)
699 : dl 1.55 break;
700 :     queue[k] = c;
701 :     k = child;
702 : tim 1.2 }
703 : dl 1.55 queue[k] = x;
704 : dl 1.36 }
705 : dl 1.35
706 : dl 1.36 /**
707 :     * Establishes the heap invariant (described above) in the entire tree,
708 :     * assuming nothing about the order of the elements prior to the call.
709 :     */
710 :     private void heapify() {
711 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
712 : jsr166 1.63 siftDown(i, (E) queue[i]);
713 : tim 1.2 }
714 :    
715 : dholmes 1.23 /**
716 : dl 1.52 * Returns the comparator used to order the elements in this
717 : jsr166 1.63 * queue, or {@code null} if this queue is sorted according to
718 : dl 1.52 * the {@linkplain Comparable natural ordering} of its elements.
719 :     *
720 :     * @return the comparator used to order this queue, or
721 : jsr166 1.63 * {@code null} if this queue is sorted according to the
722 :     * natural ordering of its elements
723 : dholmes 1.23 */
724 : tim 1.16 public Comparator<? super E> comparator() {
725 : tim 1.2 return comparator;
726 :     }
727 : dl 1.5
728 :     /**
729 : jsr166 1.63 * Saves the state of the instance to a stream (that
730 :     * is, serializes it).
731 : dl 1.5 *
732 :     * @serialData The length of the array backing the instance is
733 : jsr166 1.63 * emitted (int), followed by all of its elements
734 :     * (each an {@code Object}) in the proper order.
735 : dl 1.7 * @param s the stream
736 : dl 1.5 */
737 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
738 : dl 1.5 throws java.io.IOException{
739 : dl 1.7 // Write out element count, and any hidden stuff
740 :     s.defaultWriteObject();
741 : dl 1.5
742 : jsr166 1.63 // Write out array length, for compatibility with 1.5 version
743 :     s.writeInt(Math.max(2, size + 1));
744 : dl 1.5
745 : jsr166 1.64 // Write out all elements in the "proper order".
746 : jsr166 1.63 for (int i = 0; i < size; i++)
747 : dl 1.5 s.writeObject(queue[i]);
748 :     }
749 :    
750 :     /**
751 : jsr166 1.63 * Reconstitutes the {@code PriorityQueue} instance from a stream
752 :     * (that is, deserializes it).
753 :     *
754 : dl 1.7 * @param s the stream
755 : dl 1.5 */
756 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
757 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
758 : dl 1.7 // Read in size, and any hidden stuff
759 :     s.defaultReadObject();
760 : dl 1.5
761 : jsr166 1.63 // Read in (and discard) array length
762 :     s.readInt();
763 :    
764 : jsr166 1.68 queue = new Object[size];
765 : dl 1.5
766 : jsr166 1.64 // Read in all elements.
767 : jsr166 1.63 for (int i = 0; i < size; i++)
768 :     queue[i] = s.readObject();
769 : jsr166 1.64
770 : jsr166 1.68 // Elements are guaranteed to be in "proper order", but the
771 :     // spec has never explained what that might be.
772 :     heapify();
773 : dl 1.5 }
774 : tim 1.1 }

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