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1 : dl 1.38 /*
2 : jsr166 1.57 * %W% %E%
3 : dl 1.38 *
4 : jsr166 1.60 * Copyright 2006 Sun Microsystems, Inc. All rights reserved.
5 : dl 1.38 * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 :     */
7 :    
8 :     package java.util;
9 : tim 1.1
10 :     /**
11 : jsr166 1.63 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
12 :     * The elements of the priority queue are ordered according to their
13 :     * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
14 :     * provided at queue construction time, depending on which constructor is
15 :     * used. A priority queue does not permit {@code null} elements.
16 :     * A priority queue relying on natural ordering also does not permit
17 :     * insertion of non-comparable objects (doing so may result in
18 :     * {@code ClassCastException}).
19 : dl 1.40 *
20 : dl 1.41 * <p>The <em>head</em> of this queue is the <em>least</em> element
21 :     * with respect to the specified ordering. If multiple elements are
22 :     * tied for least value, the head is one of those elements -- ties are
23 : jsr166 1.63 * broken arbitrarily. The queue retrieval operations {@code poll},
24 :     * {@code remove}, {@code peek}, and {@code element} access the
25 : dl 1.42 * element at the head of the queue.
26 : tim 1.14 *
27 : dl 1.41 * <p>A priority queue is unbounded, but has an internal
28 :     * <i>capacity</i> governing the size of an array used to store the
29 : dl 1.40 * elements on the queue. It is always at least as large as the queue
30 :     * size. As elements are added to a priority queue, its capacity
31 :     * grows automatically. The details of the growth policy are not
32 :     * specified.
33 : tim 1.2 *
34 : dl 1.50 * <p>This class and its iterator implement all of the
35 :     * <em>optional</em> methods of the {@link Collection} and {@link
36 : dl 1.52 * Iterator} interfaces. The Iterator provided in method {@link
37 :     * #iterator()} is <em>not</em> guaranteed to traverse the elements of
38 :     * the priority queue in any particular order. If you need ordered
39 : jsr166 1.63 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
40 : dl 1.29 *
41 :     * <p> <strong>Note that this implementation is not synchronized.</strong>
42 : jsr166 1.63 * Multiple threads should not access a {@code PriorityQueue}
43 :     * instance concurrently if any of the threads modifies the queue.
44 :     * Instead, use the thread-safe {@link
45 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
46 : dl 1.29 *
47 : jsr166 1.63 * <p>Implementation note: this implementation provides
48 :     * O(log(n)) time for the enqueing and dequeing methods
49 :     * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
50 :     * linear time for the {@code remove(Object)} and {@code contains(Object)}
51 :     * methods; and constant time for the retrieval methods
52 :     * ({@code peek}, {@code element}, and {@code size}).
53 : tim 1.2 *
54 :     * <p>This class is a member of the
55 :     * <a href="{@docRoot}/../guide/collections/index.html">
56 :     * Java Collections Framework</a>.
57 : jsr166 1.63 *
58 : dl 1.7 * @since 1.5
59 : jsr166 1.62 * @version %I%, %G%
60 : jsr166 1.63 * @author Josh Bloch, Doug Lea
61 : dl 1.45 * @param <E> the type of elements held in this collection
62 : tim 1.2 */
63 :     public class PriorityQueue<E> extends AbstractQueue<E>
64 : dl 1.47 implements java.io.Serializable {
65 : dholmes 1.11
66 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
67 : dl 1.30
68 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
69 : tim 1.1
70 : tim 1.2 /**
71 : dl 1.55 * Priority queue represented as a balanced binary heap: the two
72 :     * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
73 :     * priority queue is ordered by comparator, or by the elements'
74 :     * natural ordering, if comparator is null: For each node n in the
75 :     * heap and each descendant d of n, n <= d. The element with the
76 :     * lowest value is in queue[0], assuming the queue is nonempty.
77 : tim 1.2 */
78 : tim 1.16 private transient Object[] queue;
79 : tim 1.1
80 : tim 1.2 /**
81 :     * The number of elements in the priority queue.
82 :     */
83 :     private int size = 0;
84 : tim 1.1
85 : tim 1.2 /**
86 :     * The comparator, or null if priority queue uses elements'
87 :     * natural ordering.
88 :     */
89 : tim 1.16 private final Comparator<? super E> comparator;
90 : tim 1.2
91 :     /**
92 :     * The number of times this priority queue has been
93 :     * <i>structurally modified</i>. See AbstractList for gory details.
94 :     */
95 : dl 1.5 private transient int modCount = 0;
96 : tim 1.2
97 :     /**
98 : jsr166 1.63 * Creates a {@code PriorityQueue} with the default initial
99 : dl 1.52 * capacity (11) that orders its elements according to their
100 :     * {@linkplain Comparable natural ordering}.
101 : tim 1.2 */
102 :     public PriorityQueue() {
103 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
104 : tim 1.1 }
105 : tim 1.2
106 :     /**
107 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial
108 : dl 1.52 * capacity that orders its elements according to their
109 :     * {@linkplain Comparable natural ordering}.
110 : tim 1.2 *
111 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
112 : jsr166 1.63 * @throws IllegalArgumentException if {@code initialCapacity} is less
113 :     * than 1
114 : tim 1.2 */
115 :     public PriorityQueue(int initialCapacity) {
116 :     this(initialCapacity, null);
117 : tim 1.1 }
118 : tim 1.2
119 :     /**
120 : jsr166 1.63 * Creates a {@code PriorityQueue} with the specified initial capacity
121 : tim 1.2 * that orders its elements according to the specified comparator.
122 :     *
123 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
124 : jsr166 1.63 * @param comparator the comparator that will be used to order this
125 :     * priority queue. If {@code null}, the {@linkplain Comparable
126 :     * natural ordering} of the elements will be used.
127 :     * @throws IllegalArgumentException if {@code initialCapacity} is
128 : dl 1.52 * less than 1
129 : tim 1.2 */
130 : dl 1.52 public PriorityQueue(int initialCapacity,
131 : dholmes 1.23 Comparator<? super E> comparator) {
132 : dl 1.55 // Note: This restriction of at least one is not actually needed,
133 :     // but continues for 1.5 compatibility
134 : tim 1.2 if (initialCapacity < 1)
135 : dholmes 1.15 throw new IllegalArgumentException();
136 : dl 1.55 this.queue = new Object[initialCapacity];
137 : tim 1.2 this.comparator = comparator;
138 : tim 1.1 }
139 : jsr166 1.56
140 : dl 1.22 /**
141 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
142 :     * specified collection. If the specified collection is an instance of
143 :     * a {@link SortedSet} or is another {@code PriorityQueue}, this
144 :     * priority queue will be ordered according to the same ordering.
145 :     * Otherwise, this priority queue will be ordered according to the
146 :     * {@linkplain Comparable natural ordering} of its elements.
147 : tim 1.2 *
148 : dl 1.52 * @param c the collection whose elements are to be placed
149 :     * into this priority queue
150 : tim 1.2 * @throws ClassCastException if elements of the specified collection
151 :     * cannot be compared to one another according to the priority
152 : dl 1.52 * queue's ordering
153 :     * @throws NullPointerException if the specified collection or any
154 :     * of its elements are null
155 : tim 1.2 */
156 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
157 : dl 1.55 initFromCollection(c);
158 : jsr166 1.56 if (c instanceof SortedSet)
159 : dl 1.55 comparator = (Comparator<? super E>)
160 :     ((SortedSet<? extends E>)c).comparator();
161 : jsr166 1.56 else if (c instanceof PriorityQueue)
162 : dl 1.55 comparator = (Comparator<? super E>)
163 :     ((PriorityQueue<? extends E>)c).comparator();
164 :     else {
165 : tim 1.2 comparator = null;
166 : dl 1.55 heapify();
167 : tim 1.2 }
168 : dl 1.22 }
169 :    
170 :     /**
171 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
172 : dl 1.55 * specified priority queue. This priority queue will be
173 : dl 1.52 * ordered according to the same ordering as the given priority
174 :     * queue.
175 :     *
176 :     * @param c the priority queue whose elements are to be placed
177 :     * into this priority queue
178 : jsr166 1.63 * @throws ClassCastException if elements of {@code c} cannot be
179 :     * compared to one another according to {@code c}'s
180 : dl 1.52 * ordering
181 :     * @throws NullPointerException if the specified priority queue or any
182 :     * of its elements are null
183 : dl 1.22 */
184 :     public PriorityQueue(PriorityQueue<? extends E> c) {
185 :     comparator = (Comparator<? super E>)c.comparator();
186 : dl 1.55 initFromCollection(c);
187 : dl 1.22 }
188 : dholmes 1.18
189 : dl 1.22 /**
190 : jsr166 1.63 * Creates a {@code PriorityQueue} containing the elements in the
191 :     * specified sorted set. This priority queue will be ordered
192 : dl 1.52 * according to the same ordering as the given sorted set.
193 :     *
194 :     * @param c the sorted set whose elements are to be placed
195 : jsr166 1.63 * into this priority queue
196 : dl 1.52 * @throws ClassCastException if elements of the specified sorted
197 :     * set cannot be compared to one another according to the
198 :     * sorted set's ordering
199 :     * @throws NullPointerException if the specified sorted set or any
200 :     * of its elements are null
201 : dl 1.22 */
202 :     public PriorityQueue(SortedSet<? extends E> c) {
203 :     comparator = (Comparator<? super E>)c.comparator();
204 : dl 1.55 initFromCollection(c);
205 : tim 1.1 }
206 :    
207 : dl 1.22 /**
208 : jsr166 1.63 * Initializes queue array with elements from the given Collection.
209 :     *
210 : dl 1.55 * @param c the collection
211 : dl 1.22 */
212 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
213 :     Object[] a = c.toArray();
214 :     // If c.toArray incorrectly doesn't return Object[], copy it.
215 :     if (a.getClass() != Object[].class)
216 :     a = Arrays.copyOf(a, a.length, Object[].class);
217 :     queue = a;
218 :     size = a.length;
219 : jsr166 1.56 }
220 : dl 1.55
221 :     /**
222 :     * Increases the capacity of the array.
223 :     *
224 :     * @param minCapacity the desired minimum capacity
225 :     */
226 :     private void grow(int minCapacity) {
227 :     if (minCapacity < 0) // overflow
228 : dl 1.22 throw new OutOfMemoryError();
229 : dl 1.55 int oldCapacity = queue.length;
230 :     // Double size if small; else grow by 50%
231 :     int newCapacity = ((oldCapacity < 64)?
232 :     ((oldCapacity + 1) * 2):
233 : dl 1.58 ((oldCapacity / 2) * 3));
234 :     if (newCapacity < 0) // overflow
235 :     newCapacity = Integer.MAX_VALUE;
236 : dl 1.55 if (newCapacity < minCapacity)
237 :     newCapacity = minCapacity;
238 :     queue = Arrays.copyOf(queue, newCapacity);
239 : dl 1.22 }
240 : dl 1.36
241 : tim 1.2 /**
242 : dl 1.42 * Inserts the specified element into this priority queue.
243 : tim 1.2 *
244 : jsr166 1.63 * @return {@code true} (as specified by {@link Collection#add})
245 : dl 1.52 * @throws ClassCastException if the specified element cannot be
246 :     * compared with elements currently in this priority queue
247 :     * according to the priority queue's ordering
248 :     * @throws NullPointerException if the specified element is null
249 : tim 1.2 */
250 : dl 1.52 public boolean add(E e) {
251 :     return offer(e);
252 :     }
253 :    
254 :     /**
255 :     * Inserts the specified element into this priority queue.
256 :     *
257 : jsr166 1.63 * @return {@code true} (as specified by {@link Queue#offer})
258 : dl 1.52 * @throws ClassCastException if the specified element cannot be
259 :     * compared with elements currently in this priority queue
260 :     * according to the priority queue's ordering
261 :     * @throws NullPointerException if the specified element is null
262 :     */
263 :     public boolean offer(E e) {
264 :     if (e == null)
265 : dholmes 1.11 throw new NullPointerException();
266 :     modCount++;
267 : dl 1.55 int i = size;
268 :     if (i >= queue.length)
269 :     grow(i + 1);
270 :     size = i + 1;
271 :     if (i == 0)
272 :     queue[0] = e;
273 :     else
274 :     siftUp(i, e);
275 : dholmes 1.11 return true;
276 :     }
277 :    
278 : dl 1.40 public E peek() {
279 : tim 1.2 if (size == 0)
280 :     return null;
281 : dl 1.55 return (E) queue[0];
282 : tim 1.1 }
283 :    
284 : dl 1.52 private int indexOf(Object o) {
285 : dl 1.55 if (o != null) {
286 :     for (int i = 0; i < size; i++)
287 :     if (o.equals(queue[i]))
288 :     return i;
289 :     }
290 : dl 1.52 return -1;
291 :     }
292 :    
293 :     /**
294 :     * Removes a single instance of the specified element from this queue,
295 : jsr166 1.63 * if it is present. More formally, removes an element {@code e} such
296 :     * that {@code o.equals(e)}, if this queue contains one or more such
297 :     * elements. Returns {@code true} if and only if this queue contained
298 :     * the specified element (or equivalently, if this queue changed as a
299 :     * result of the call).
300 : dl 1.52 *
301 :     * @param o element to be removed from this queue, if present
302 : jsr166 1.63 * @return {@code true} if this queue changed as a result of the call
303 : dl 1.52 */
304 :     public boolean remove(Object o) {
305 :     int i = indexOf(o);
306 :     if (i == -1)
307 :     return false;
308 :     else {
309 :     removeAt(i);
310 :     return true;
311 :     }
312 :     }
313 : dholmes 1.11
314 : jsr166 1.56 /**
315 : dl 1.55 * Version of remove using reference equality, not equals.
316 : jsr166 1.59 * Needed by iterator.remove.
317 : jsr166 1.56 *
318 : dl 1.55 * @param o element to be removed from this queue, if present
319 : jsr166 1.63 * @return {@code true} if removed
320 : dl 1.55 */
321 :     boolean removeEq(Object o) {
322 :     for (int i = 0; i < size; i++) {
323 :     if (o == queue[i]) {
324 :     removeAt(i);
325 :     return true;
326 :     }
327 :     }
328 :     return false;
329 :     }
330 :    
331 : dholmes 1.11 /**
332 : jsr166 1.63 * Returns {@code true} if this queue contains the specified element.
333 :     * More formally, returns {@code true} if and only if this queue contains
334 :     * at least one element {@code e} such that {@code o.equals(e)}.
335 : dholmes 1.23 *
336 : dl 1.52 * @param o object to be checked for containment in this queue
337 : jsr166 1.63 * @return {@code true} if this queue contains the specified element
338 : dholmes 1.11 */
339 : dl 1.52 public boolean contains(Object o) {
340 :     return indexOf(o) != -1;
341 : tim 1.14 }
342 : dholmes 1.11
343 : dl 1.49 /**
344 : jsr166 1.63 * Returns an array containing all of the elements in this queue.
345 : dl 1.52 * The elements are in no particular order.
346 :     *
347 :     * <p>The returned array will be "safe" in that no references to it are
348 : jsr166 1.63 * maintained by this queue. (In other words, this method must allocate
349 : dl 1.52 * a new array). The caller is thus free to modify the returned array.
350 :     *
351 : jsr166 1.63 * <p>This method acts as bridge between array-based and collection-based
352 :     * APIs.
353 :     *
354 : jsr166 1.59 * @return an array containing all of the elements in this queue
355 : dl 1.49 */
356 : dl 1.52 public Object[] toArray() {
357 : dl 1.55 return Arrays.copyOf(queue, size);
358 : dl 1.52 }
359 : tim 1.2
360 : dl 1.52 /**
361 : jsr166 1.63 * Returns an array containing all of the elements in this queue; the
362 :     * runtime type of the returned array is that of the specified array.
363 :     * The returned array elements are in no particular order.
364 :     * If the queue fits in the specified array, it is returned therein.
365 :     * Otherwise, a new array is allocated with the runtime type of the
366 :     * specified array and the size of this queue.
367 : dl 1.52 *
368 :     * <p>If the queue fits in the specified array with room to spare
369 :     * (i.e., the array has more elements than the queue), the element in
370 :     * the array immediately following the end of the collection is set to
371 : jsr166 1.63 * {@code null}.
372 :     *
373 :     * <p>Like the {@link #toArray()} method, this method acts as bridge between
374 :     * array-based and collection-based APIs. Further, this method allows
375 :     * precise control over the runtime type of the output array, and may,
376 :     * under certain circumstances, be used to save allocation costs.
377 :     *
378 :     * <p>Suppose <tt>x</tt> is a queue known to contain only strings.
379 :     * The following code can be used to dump the queue into a newly
380 :     * allocated array of <tt>String</tt>:
381 :     *
382 :     * <pre>
383 :     * String[] y = x.toArray(new String[0]);</pre>
384 :     *
385 :     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
386 :     * <tt>toArray()</tt>.
387 : dl 1.52 *
388 :     * @param a the array into which the elements of the queue are to
389 :     * be stored, if it is big enough; otherwise, a new array of the
390 :     * same runtime type is allocated for this purpose.
391 : jsr166 1.63 * @return an array containing all of the elements in this queue
392 : dl 1.52 * @throws ArrayStoreException if the runtime type of the specified array
393 :     * is not a supertype of the runtime type of every element in
394 :     * this queue
395 :     * @throws NullPointerException if the specified array is null
396 :     */
397 :     public <T> T[] toArray(T[] a) {
398 :     if (a.length < size)
399 :     // Make a new array of a's runtime type, but my contents:
400 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
401 :     System.arraycopy(queue, 0, a, 0, size);
402 : dl 1.52 if (a.length > size)
403 :     a[size] = null;
404 :     return a;
405 : tim 1.1 }
406 : tim 1.2
407 : dholmes 1.23 /**
408 :     * Returns an iterator over the elements in this queue. The iterator
409 :     * does not return the elements in any particular order.
410 :     *
411 : dl 1.52 * @return an iterator over the elements in this queue
412 : dholmes 1.23 */
413 : tim 1.2 public Iterator<E> iterator() {
414 : dl 1.7 return new Itr();
415 : tim 1.2 }
416 :    
417 : dl 1.55 private final class Itr implements Iterator<E> {
418 : dl 1.7 /**
419 :     * Index (into queue array) of element to be returned by
420 : tim 1.2 * subsequent call to next.
421 : dl 1.7 */
422 : dl 1.55 private int cursor = 0;
423 : tim 1.2
424 : dl 1.7 /**
425 : dl 1.36 * Index of element returned by most recent call to next,
426 :     * unless that element came from the forgetMeNot list.
427 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
428 : dl 1.7 */
429 : dl 1.55 private int lastRet = -1;
430 : dl 1.7
431 :     /**
432 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
433 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
434 :     * removals during the iteration. (Unlucky element removals are those
435 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
436 : dl 1.36 * the elements in this list to complete the iteration. We do this
437 :     * after we've completed the "normal" iteration.
438 :     *
439 :     * We expect that most iterations, even those involving removals,
440 : jsr166 1.63 * will not need to store elements in this field.
441 : dl 1.36 */
442 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
443 : dl 1.36
444 :     /**
445 :     * Element returned by the most recent call to next iff that
446 :     * element was drawn from the forgetMeNot list.
447 :     */
448 : dl 1.55 private E lastRetElt = null;
449 :    
450 :     /**
451 :     * The modCount value that the iterator believes that the backing
452 : jsr166 1.63 * Queue should have. If this expectation is violated, the iterator
453 : dl 1.55 * has detected concurrent modification.
454 :     */
455 :     private int expectedModCount = modCount;
456 : dl 1.35
457 : dl 1.7 public boolean hasNext() {
458 : jsr166 1.56 return cursor < size ||
459 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
460 : dl 1.7 }
461 :    
462 :     public E next() {
463 : dl 1.55 if (expectedModCount != modCount)
464 :     throw new ConcurrentModificationException();
465 : jsr166 1.56 if (cursor < size)
466 : dl 1.55 return (E) queue[lastRet = cursor++];
467 :     if (forgetMeNot != null) {
468 :     lastRet = -1;
469 :     lastRetElt = forgetMeNot.poll();
470 : jsr166 1.56 if (lastRetElt != null)
471 : dl 1.55 return lastRetElt;
472 : dl 1.36 }
473 : dl 1.55 throw new NoSuchElementException();
474 : dl 1.7 }
475 : tim 1.2
476 : dl 1.7 public void remove() {
477 : dl 1.55 if (expectedModCount != modCount)
478 :     throw new ConcurrentModificationException();
479 :     if (lastRet != -1) {
480 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
481 : dl 1.55 lastRet = -1;
482 : jsr166 1.56 if (moved == null)
483 : dl 1.36 cursor--;
484 : dl 1.55 else {
485 : dl 1.36 if (forgetMeNot == null)
486 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
487 : dl 1.36 forgetMeNot.add(moved);
488 : jsr166 1.56 }
489 : jsr166 1.63 } else if (lastRetElt != null) {
490 : dl 1.55 PriorityQueue.this.removeEq(lastRetElt);
491 : dl 1.36 lastRetElt = null;
492 : jsr166 1.63 } else {
493 :     throw new IllegalStateException();
494 :     }
495 : tim 1.2 expectedModCount = modCount;
496 : dl 1.7 }
497 : tim 1.2 }
498 :    
499 : tim 1.1 public int size() {
500 : tim 1.2 return size;
501 : tim 1.1 }
502 : tim 1.2
503 :     /**
504 : dl 1.52 * Removes all of the elements from this priority queue.
505 : dl 1.49 * The queue will be empty after this call returns.
506 : tim 1.2 */
507 :     public void clear() {
508 :     modCount++;
509 : dl 1.55 for (int i = 0; i < size; i++)
510 : tim 1.2 queue[i] = null;
511 :     size = 0;
512 :     }
513 :    
514 : dl 1.40 public E poll() {
515 : dl 1.36 if (size == 0)
516 : dl 1.40 return null;
517 : dl 1.55 int s = --size;
518 : dl 1.36 modCount++;
519 : jsr166 1.63 E result = (E) queue[0];
520 :     E x = (E) queue[s];
521 : dl 1.55 queue[s] = null;
522 :     if (s != 0)
523 :     siftDown(0, x);
524 : dl 1.36 return result;
525 :     }
526 :    
527 :     /**
528 : dl 1.55 * Removes the ith element from queue.
529 : tim 1.2 *
530 : dl 1.55 * Normally this method leaves the elements at up to i-1,
531 :     * inclusive, untouched. Under these circumstances, it returns
532 :     * null. Occasionally, in order to maintain the heap invariant,
533 :     * it must swap a later element of the list with one earlier than
534 :     * i. Under these circumstances, this method returns the element
535 :     * that was previously at the end of the list and is now at some
536 :     * position before i. This fact is used by iterator.remove so as to
537 : jsr166 1.63 * avoid missing traversing elements.
538 : tim 1.2 */
539 : dl 1.52 private E removeAt(int i) {
540 : dl 1.55 assert i >= 0 && i < size;
541 : tim 1.2 modCount++;
542 : dl 1.55 int s = --size;
543 :     if (s == i) // removed last element
544 :     queue[i] = null;
545 :     else {
546 :     E moved = (E) queue[s];
547 : jsr166 1.56 queue[s] = null;
548 : dl 1.55 siftDown(i, moved);
549 : dl 1.36 if (queue[i] == moved) {
550 : dl 1.55 siftUp(i, moved);
551 : dl 1.36 if (queue[i] != moved)
552 :     return moved;
553 :     }
554 : dl 1.35 }
555 : dl 1.36 return null;
556 : tim 1.1 }
557 :    
558 : tim 1.2 /**
559 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
560 :     * promoting x up the tree until it is greater than or equal to
561 :     * its parent, or is the root.
562 :     *
563 :     * To simplify and speed up coercions and comparisons. the
564 :     * Comparable and Comparator versions are separated into different
565 :     * methods that are otherwise identical. (Similarly for siftDown.)
566 : jsr166 1.56 *
567 : dl 1.55 * @param k the position to fill
568 :     * @param x the item to insert
569 :     */
570 :     private void siftUp(int k, E x) {
571 : jsr166 1.56 if (comparator != null)
572 : dl 1.55 siftUpUsingComparator(k, x);
573 :     else
574 :     siftUpComparable(k, x);
575 :     }
576 :    
577 :     private void siftUpComparable(int k, E x) {
578 :     Comparable<? super E> key = (Comparable<? super E>) x;
579 :     while (k > 0) {
580 :     int parent = (k - 1) >>> 1;
581 :     Object e = queue[parent];
582 : jsr166 1.63 if (key.compareTo((E) e) >= 0)
583 : dl 1.55 break;
584 :     queue[k] = e;
585 :     k = parent;
586 :     }
587 :     queue[k] = key;
588 :     }
589 :    
590 :     private void siftUpUsingComparator(int k, E x) {
591 :     while (k > 0) {
592 :     int parent = (k - 1) >>> 1;
593 :     Object e = queue[parent];
594 : jsr166 1.63 if (comparator.compare(x, (E) e) >= 0)
595 : dl 1.55 break;
596 :     queue[k] = e;
597 :     k = parent;
598 :     }
599 :     queue[k] = x;
600 :     }
601 :    
602 :     /**
603 :     * Inserts item x at position k, maintaining heap invariant by
604 :     * demoting x down the tree repeatedly until it is less than or
605 :     * equal to its children or is a leaf.
606 :     *
607 :     * @param k the position to fill
608 :     * @param x the item to insert
609 :     */
610 :     private void siftDown(int k, E x) {
611 : jsr166 1.56 if (comparator != null)
612 : dl 1.55 siftDownUsingComparator(k, x);
613 :     else
614 :     siftDownComparable(k, x);
615 :     }
616 :    
617 :     private void siftDownComparable(int k, E x) {
618 :     Comparable<? super E> key = (Comparable<? super E>)x;
619 :     int half = size >>> 1; // loop while a non-leaf
620 :     while (k < half) {
621 :     int child = (k << 1) + 1; // assume left child is least
622 :     Object c = queue[child];
623 :     int right = child + 1;
624 :     if (right < size &&
625 : jsr166 1.63 ((Comparable<? super E>) c).compareTo((E) queue[right]) > 0)
626 : dl 1.55 c = queue[child = right];
627 : jsr166 1.63 if (key.compareTo((E) c) <= 0)
628 : dl 1.55 break;
629 :     queue[k] = c;
630 :     k = child;
631 :     }
632 :     queue[k] = key;
633 :     }
634 :    
635 :     private void siftDownUsingComparator(int k, E x) {
636 :     int half = size >>> 1;
637 :     while (k < half) {
638 :     int child = (k << 1) + 1;
639 :     Object c = queue[child];
640 :     int right = child + 1;
641 :     if (right < size &&
642 : jsr166 1.63 comparator.compare((E) c, (E) queue[right]) > 0)
643 : jsr166 1.56 c = queue[child = right];
644 : jsr166 1.63 if (comparator.compare(x, (E) c) <= 0)
645 : dl 1.55 break;
646 :     queue[k] = c;
647 :     k = child;
648 : tim 1.2 }
649 : dl 1.55 queue[k] = x;
650 : dl 1.36 }
651 : dl 1.35
652 : dl 1.36 /**
653 :     * Establishes the heap invariant (described above) in the entire tree,
654 :     * assuming nothing about the order of the elements prior to the call.
655 :     */
656 :     private void heapify() {
657 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
658 : jsr166 1.63 siftDown(i, (E) queue[i]);
659 : tim 1.2 }
660 :    
661 : dholmes 1.23 /**
662 : dl 1.52 * Returns the comparator used to order the elements in this
663 : jsr166 1.63 * queue, or {@code null} if this queue is sorted according to
664 : dl 1.52 * the {@linkplain Comparable natural ordering} of its elements.
665 :     *
666 :     * @return the comparator used to order this queue, or
667 : jsr166 1.63 * {@code null} if this queue is sorted according to the
668 :     * natural ordering of its elements
669 : dholmes 1.23 */
670 : tim 1.16 public Comparator<? super E> comparator() {
671 : tim 1.2 return comparator;
672 :     }
673 : dl 1.5
674 :     /**
675 : jsr166 1.63 * Saves the state of the instance to a stream (that
676 :     * is, serializes it).
677 : dl 1.5 *
678 :     * @serialData The length of the array backing the instance is
679 : jsr166 1.63 * emitted (int), followed by all of its elements
680 :     * (each an {@code Object}) in the proper order.
681 : dl 1.7 * @param s the stream
682 : dl 1.5 */
683 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
684 : dl 1.5 throws java.io.IOException{
685 : dl 1.7 // Write out element count, and any hidden stuff
686 :     s.defaultWriteObject();
687 : dl 1.5
688 : jsr166 1.63 // Write out array length, for compatibility with 1.5 version
689 :     s.writeInt(Math.max(2, size + 1));
690 : dl 1.5
691 : jsr166 1.64 // Write out all elements in the "proper order".
692 : jsr166 1.63 for (int i = 0; i < size; i++)
693 : dl 1.5 s.writeObject(queue[i]);
694 :     }
695 :    
696 :     /**
697 : jsr166 1.63 * Reconstitutes the {@code PriorityQueue} instance from a stream
698 :     * (that is, deserializes it).
699 :     *
700 : dl 1.7 * @param s the stream
701 : dl 1.5 */
702 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
703 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
704 : dl 1.7 // Read in size, and any hidden stuff
705 :     s.defaultReadObject();
706 : dl 1.5
707 : jsr166 1.63 // Read in (and discard) array length
708 :     s.readInt();
709 :    
710 :     queue = new Object[size];
711 : dl 1.5
712 : jsr166 1.64 // Read in all elements.
713 : jsr166 1.63 for (int i = 0; i < size; i++)
714 :     queue[i] = s.readObject();
715 : jsr166 1.64
716 :     // Elements are guaranteed to be in "proper order", but the
717 :     // spec has never explained what that might be.
718 :     heapify();
719 : dl 1.5 }
720 : tim 1.1 }

Doug Lea
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