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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 : dl 1.41 * An unbounded priority {@linkplain Queue queue} based on a priority
12 : dl 1.52 * heap. The elements of the priority queue are ordered according to
13 :     * their {@linkplain Comparable natural ordering}, or by a {@link
14 :     * Comparator} provided at queue construction time, depending on which
15 :     * constructor is used. A priority queue does not permit
16 :     * <tt>null</tt> elements. A priority queue relying on natural
17 :     * ordering also does not permit insertion of non-comparable objects
18 :     * (doing so may result in <tt>ClassCastException</tt>).
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 : dl 1.42 * broken arbitrarily. The queue retrieval operations <tt>poll</tt>,
24 :     * <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the
25 :     * 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 :     * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
40 : dl 1.29 *
41 :     * <p> <strong>Note that this implementation is not synchronized.</strong>
42 :     * Multiple threads should not access a <tt>PriorityQueue</tt>
43 :     * instance concurrently if any of the threads modifies the list
44 :     * structurally. Instead, use the thread-safe {@link
45 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
46 : dl 1.29 *
47 : dholmes 1.11 * <p>Implementation note: this implementation provides O(log(n)) time
48 :     * for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
49 :     * <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
50 :     * <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
51 :     * constant time for the retrieval methods (<tt>peek</tt>,
52 :     * <tt>element</tt>, and <tt>size</tt>).
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 : dl 1.7 * @since 1.5
58 : jsr166 1.62 * @version %I%, %G%
59 : dl 1.7 * @author Josh Bloch
60 : dl 1.45 * @param <E> the type of elements held in this collection
61 : tim 1.2 */
62 :     public class PriorityQueue<E> extends AbstractQueue<E>
63 : dl 1.47 implements java.io.Serializable {
64 : dholmes 1.11
65 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
66 : dl 1.30
67 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
68 : tim 1.1
69 : tim 1.2 /**
70 : dl 1.55 * Priority queue represented as a balanced binary heap: the two
71 :     * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
72 :     * priority queue is ordered by comparator, or by the elements'
73 :     * natural ordering, if comparator is null: For each node n in the
74 :     * heap and each descendant d of n, n <= d. The element with the
75 :     * lowest value is in queue[0], assuming the queue is nonempty.
76 : tim 1.2 */
77 : tim 1.16 private transient Object[] queue;
78 : tim 1.1
79 : tim 1.2 /**
80 :     * The number of elements in the priority queue.
81 :     */
82 :     private int size = 0;
83 : tim 1.1
84 : tim 1.2 /**
85 :     * The comparator, or null if priority queue uses elements'
86 :     * natural ordering.
87 :     */
88 : tim 1.16 private final Comparator<? super E> comparator;
89 : tim 1.2
90 :     /**
91 :     * The number of times this priority queue has been
92 :     * <i>structurally modified</i>. See AbstractList for gory details.
93 :     */
94 : dl 1.5 private transient int modCount = 0;
95 : tim 1.2
96 :     /**
97 : dl 1.52 * Creates a <tt>PriorityQueue</tt> with the default initial
98 :     * capacity (11) that orders its elements according to their
99 :     * {@linkplain Comparable natural ordering}.
100 : tim 1.2 */
101 :     public PriorityQueue() {
102 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
103 : tim 1.1 }
104 : tim 1.2
105 :     /**
106 : dl 1.52 * Creates a <tt>PriorityQueue</tt> with the specified initial
107 :     * capacity that orders its elements according to their
108 :     * {@linkplain Comparable natural ordering}.
109 : tim 1.2 *
110 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
111 : dholmes 1.23 * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
112 :     * than 1
113 : tim 1.2 */
114 :     public PriorityQueue(int initialCapacity) {
115 :     this(initialCapacity, null);
116 : tim 1.1 }
117 : tim 1.2
118 :     /**
119 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
120 : tim 1.2 * that orders its elements according to the specified comparator.
121 :     *
122 : dl 1.52 * @param initialCapacity the initial capacity for this priority queue
123 :     * @param comparator the comparator that will be used to order
124 :     * this priority queue. If <tt>null</tt>, the <i>natural
125 :     * ordering</i> of the elements will be used.
126 :     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is
127 :     * less than 1
128 : tim 1.2 */
129 : dl 1.52 public PriorityQueue(int initialCapacity,
130 : dholmes 1.23 Comparator<? super E> comparator) {
131 : dl 1.55 // Note: This restriction of at least one is not actually needed,
132 :     // but continues for 1.5 compatibility
133 : tim 1.2 if (initialCapacity < 1)
134 : dholmes 1.15 throw new IllegalArgumentException();
135 : dl 1.55 this.queue = new Object[initialCapacity];
136 : tim 1.2 this.comparator = comparator;
137 : tim 1.1 }
138 : jsr166 1.56
139 : dl 1.22 /**
140 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
141 : dl 1.55 * specified collection. If the specified collection is an
142 : tim 1.25 * instance of a {@link java.util.SortedSet} or is another
143 : dl 1.52 * <tt>PriorityQueue</tt>, the priority queue will be ordered
144 :     * according to the same ordering. Otherwise, this priority queue
145 :     * will be ordered according to the natural ordering of its elements.
146 : tim 1.2 *
147 : dl 1.52 * @param c the collection whose elements are to be placed
148 :     * into this priority queue
149 : tim 1.2 * @throws ClassCastException if elements of the specified collection
150 :     * cannot be compared to one another according to the priority
151 : dl 1.52 * queue's ordering
152 :     * @throws NullPointerException if the specified collection or any
153 :     * of its elements are null
154 : tim 1.2 */
155 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
156 : dl 1.55 initFromCollection(c);
157 : jsr166 1.56 if (c instanceof SortedSet)
158 : dl 1.55 comparator = (Comparator<? super E>)
159 :     ((SortedSet<? extends E>)c).comparator();
160 : jsr166 1.56 else if (c instanceof PriorityQueue)
161 : dl 1.55 comparator = (Comparator<? super E>)
162 :     ((PriorityQueue<? extends E>)c).comparator();
163 :     else {
164 : tim 1.2 comparator = null;
165 : dl 1.55 heapify();
166 : tim 1.2 }
167 : dl 1.22 }
168 :    
169 :     /**
170 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
171 : dl 1.55 * specified priority queue. This priority queue will be
172 : dl 1.52 * ordered according to the same ordering as the given priority
173 :     * queue.
174 :     *
175 :     * @param c the priority queue whose elements are to be placed
176 :     * into this priority queue
177 :     * @throws ClassCastException if elements of <tt>c</tt> cannot be
178 :     * compared to one another according to <tt>c</tt>'s
179 :     * ordering
180 :     * @throws NullPointerException if the specified priority queue or any
181 :     * of its elements are null
182 : dl 1.22 */
183 :     public PriorityQueue(PriorityQueue<? extends E> c) {
184 :     comparator = (Comparator<? super E>)c.comparator();
185 : dl 1.55 initFromCollection(c);
186 : dl 1.22 }
187 : dholmes 1.18
188 : dl 1.22 /**
189 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
190 : dl 1.55 * specified sorted set. This priority queue will be ordered
191 : dl 1.52 * according to the same ordering as the given sorted set.
192 :     *
193 :     * @param c the sorted set whose elements are to be placed
194 :     * into this priority queue.
195 :     * @throws ClassCastException if elements of the specified sorted
196 :     * set cannot be compared to one another according to the
197 :     * sorted set's ordering
198 :     * @throws NullPointerException if the specified sorted set or any
199 :     * of its elements are null
200 : dl 1.22 */
201 :     public PriorityQueue(SortedSet<? extends E> c) {
202 :     comparator = (Comparator<? super E>)c.comparator();
203 : dl 1.55 initFromCollection(c);
204 : tim 1.1 }
205 :    
206 : dl 1.22 /**
207 : dl 1.55 * Initialize queue array with elements from the given Collection.
208 :     * @param c the collection
209 : dl 1.22 */
210 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
211 :     Object[] a = c.toArray();
212 :     // If c.toArray incorrectly doesn't return Object[], copy it.
213 :     if (a.getClass() != Object[].class)
214 :     a = Arrays.copyOf(a, a.length, Object[].class);
215 :     queue = a;
216 :     size = a.length;
217 : jsr166 1.56 }
218 : dl 1.55
219 :     /**
220 :     * Increases the capacity of the array.
221 :     *
222 :     * @param minCapacity the desired minimum capacity
223 :     */
224 :     private void grow(int minCapacity) {
225 :     if (minCapacity < 0) // overflow
226 : dl 1.22 throw new OutOfMemoryError();
227 : dl 1.55 int oldCapacity = queue.length;
228 :     // Double size if small; else grow by 50%
229 :     int newCapacity = ((oldCapacity < 64)?
230 :     ((oldCapacity + 1) * 2):
231 : dl 1.58 ((oldCapacity / 2) * 3));
232 :     if (newCapacity < 0) // overflow
233 :     newCapacity = Integer.MAX_VALUE;
234 : dl 1.55 if (newCapacity < minCapacity)
235 :     newCapacity = minCapacity;
236 :     queue = Arrays.copyOf(queue, newCapacity);
237 : dl 1.22 }
238 : dl 1.36
239 : tim 1.2 /**
240 : dl 1.42 * Inserts the specified element into this priority queue.
241 : tim 1.2 *
242 : dl 1.52 * @return <tt>true</tt> (as specified by {@link Collection#add})
243 :     * @throws ClassCastException if the specified element cannot be
244 :     * compared with elements currently in this priority queue
245 :     * according to the priority queue's ordering
246 :     * @throws NullPointerException if the specified element is null
247 : tim 1.2 */
248 : dl 1.52 public boolean add(E e) {
249 :     return offer(e);
250 :     }
251 :    
252 :     /**
253 :     * Inserts the specified element into this priority queue.
254 :     *
255 :     * @return <tt>true</tt> (as specified by {@link Queue#offer})
256 :     * @throws ClassCastException if the specified element cannot be
257 :     * compared with elements currently in this priority queue
258 :     * according to the priority queue's ordering
259 :     * @throws NullPointerException if the specified element is null
260 :     */
261 :     public boolean offer(E e) {
262 :     if (e == null)
263 : dholmes 1.11 throw new NullPointerException();
264 :     modCount++;
265 : dl 1.55 int i = size;
266 :     if (i >= queue.length)
267 :     grow(i + 1);
268 :     size = i + 1;
269 :     if (i == 0)
270 :     queue[0] = e;
271 :     else
272 :     siftUp(i, e);
273 : dholmes 1.11 return true;
274 :     }
275 :    
276 : dl 1.40 public E peek() {
277 : tim 1.2 if (size == 0)
278 :     return null;
279 : dl 1.55 return (E) queue[0];
280 : tim 1.1 }
281 :    
282 : dl 1.52 private int indexOf(Object o) {
283 : dl 1.55 if (o != null) {
284 :     for (int i = 0; i < size; i++)
285 :     if (o.equals(queue[i]))
286 :     return i;
287 :     }
288 : dl 1.52 return -1;
289 :     }
290 :    
291 :     /**
292 :     * Removes a single instance of the specified element from this queue,
293 :     * if it is present. More formally, removes an element <tt>e</tt> such
294 :     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
295 :     * elements. Returns true if this queue contained the specified element
296 :     * (or equivalently, if this queue changed as a result of the call).
297 :     *
298 :     * @param o element to be removed from this queue, if present
299 :     * @return <tt>true</tt> if this queue changed as a result of the call
300 :     */
301 :     public boolean remove(Object o) {
302 :     int i = indexOf(o);
303 :     if (i == -1)
304 :     return false;
305 :     else {
306 :     removeAt(i);
307 :     return true;
308 :     }
309 :     }
310 : dholmes 1.11
311 : jsr166 1.56 /**
312 : dl 1.55 * Version of remove using reference equality, not equals.
313 : jsr166 1.59 * Needed by iterator.remove.
314 : jsr166 1.56 *
315 : dl 1.55 * @param o element to be removed from this queue, if present
316 : jsr166 1.59 * @return <tt>true</tt> if removed
317 : dl 1.55 */
318 :     boolean removeEq(Object o) {
319 :     for (int i = 0; i < size; i++) {
320 :     if (o == queue[i]) {
321 :     removeAt(i);
322 :     return true;
323 :     }
324 :     }
325 :     return false;
326 :     }
327 :    
328 : dholmes 1.11 /**
329 : dl 1.52 * Returns <tt>true</tt> if this queue contains the specified element.
330 :     * More formally, returns <tt>true</tt> if and only if this queue contains
331 :     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
332 : dholmes 1.23 *
333 : dl 1.52 * @param o object to be checked for containment in this queue
334 :     * @return <tt>true</tt> if this queue contains the specified element
335 : dholmes 1.11 */
336 : dl 1.52 public boolean contains(Object o) {
337 :     return indexOf(o) != -1;
338 : tim 1.14 }
339 : dholmes 1.11
340 : dl 1.49 /**
341 : dl 1.52 * Returns an array containing all of the elements in this queue,
342 :     * The elements are in no particular order.
343 :     *
344 :     * <p>The returned array will be "safe" in that no references to it are
345 :     * maintained by this list. (In other words, this method must allocate
346 :     * a new array). The caller is thus free to modify the returned array.
347 :     *
348 : jsr166 1.59 * @return an array containing all of the elements in this queue
349 : dl 1.49 */
350 : dl 1.52 public Object[] toArray() {
351 : dl 1.55 return Arrays.copyOf(queue, size);
352 : dl 1.52 }
353 : tim 1.2
354 : dl 1.52 /**
355 :     * Returns an array containing all of the elements in this queue.
356 :     * The elements are in no particular order. The runtime type of
357 :     * the returned array is that of the specified array. If the queue
358 :     * fits in the specified array, it is returned therein.
359 :     * Otherwise, a new array is allocated with the runtime type of
360 :     * the specified array and the size of this queue.
361 :     *
362 :     * <p>If the queue fits in the specified array with room to spare
363 :     * (i.e., the array has more elements than the queue), the element in
364 :     * the array immediately following the end of the collection is set to
365 :     * <tt>null</tt>. (This is useful in determining the length of the
366 :     * queue <i>only</i> if the caller knows that the queue does not contain
367 :     * any null elements.)
368 :     *
369 :     * @param a the array into which the elements of the queue are to
370 :     * be stored, if it is big enough; otherwise, a new array of the
371 :     * same runtime type is allocated for this purpose.
372 :     * @return an array containing the elements of the queue
373 :     * @throws ArrayStoreException if the runtime type of the specified array
374 :     * is not a supertype of the runtime type of every element in
375 :     * this queue
376 :     * @throws NullPointerException if the specified array is null
377 :     */
378 :     public <T> T[] toArray(T[] a) {
379 :     if (a.length < size)
380 :     // Make a new array of a's runtime type, but my contents:
381 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
382 :     System.arraycopy(queue, 0, a, 0, size);
383 : dl 1.52 if (a.length > size)
384 :     a[size] = null;
385 :     return a;
386 : tim 1.1 }
387 : tim 1.2
388 : dholmes 1.23 /**
389 :     * Returns an iterator over the elements in this queue. The iterator
390 :     * does not return the elements in any particular order.
391 :     *
392 : dl 1.52 * @return an iterator over the elements in this queue
393 : dholmes 1.23 */
394 : tim 1.2 public Iterator<E> iterator() {
395 : dl 1.7 return new Itr();
396 : tim 1.2 }
397 :    
398 : dl 1.55 private final class Itr implements Iterator<E> {
399 : dl 1.7 /**
400 :     * Index (into queue array) of element to be returned by
401 : tim 1.2 * subsequent call to next.
402 : dl 1.7 */
403 : dl 1.55 private int cursor = 0;
404 : tim 1.2
405 : dl 1.7 /**
406 : dl 1.36 * Index of element returned by most recent call to next,
407 :     * unless that element came from the forgetMeNot list.
408 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
409 : dl 1.7 */
410 : dl 1.55 private int lastRet = -1;
411 : dl 1.7
412 :     /**
413 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
414 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
415 :     * removals during the iteration. (Unlucky element removals are those
416 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
417 : dl 1.36 * the elements in this list to complete the iteration. We do this
418 :     * after we've completed the "normal" iteration.
419 :     *
420 :     * We expect that most iterations, even those involving removals,
421 :     * will not use need to store elements in this field.
422 :     */
423 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
424 : dl 1.36
425 :     /**
426 :     * Element returned by the most recent call to next iff that
427 :     * element was drawn from the forgetMeNot list.
428 :     */
429 : dl 1.55 private E lastRetElt = null;
430 :    
431 :     /**
432 :     * The modCount value that the iterator believes that the backing
433 :     * List should have. If this expectation is violated, the iterator
434 :     * has detected concurrent modification.
435 :     */
436 :     private int expectedModCount = modCount;
437 : dl 1.35
438 : dl 1.7 public boolean hasNext() {
439 : jsr166 1.56 return cursor < size ||
440 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
441 : dl 1.7 }
442 :    
443 :     public E next() {
444 : dl 1.55 if (expectedModCount != modCount)
445 :     throw new ConcurrentModificationException();
446 : jsr166 1.56 if (cursor < size)
447 : dl 1.55 return (E) queue[lastRet = cursor++];
448 :     if (forgetMeNot != null) {
449 :     lastRet = -1;
450 :     lastRetElt = forgetMeNot.poll();
451 : jsr166 1.56 if (lastRetElt != null)
452 : dl 1.55 return lastRetElt;
453 : dl 1.36 }
454 : dl 1.55 throw new NoSuchElementException();
455 : dl 1.7 }
456 : tim 1.2
457 : dl 1.7 public void remove() {
458 : dl 1.55 if (expectedModCount != modCount)
459 :     throw new ConcurrentModificationException();
460 :     if (lastRet == -1 && lastRetElt == null)
461 :     throw new IllegalStateException();
462 :     if (lastRet != -1) {
463 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
464 : dl 1.55 lastRet = -1;
465 : jsr166 1.56 if (moved == null)
466 : dl 1.36 cursor--;
467 : dl 1.55 else {
468 : dl 1.36 if (forgetMeNot == null)
469 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
470 : dl 1.36 forgetMeNot.add(moved);
471 : jsr166 1.56 }
472 : dl 1.55 } else {
473 :     PriorityQueue.this.removeEq(lastRetElt);
474 : dl 1.36 lastRetElt = null;
475 : jsr166 1.56 }
476 : tim 1.2 expectedModCount = modCount;
477 : dl 1.7 }
478 : tim 1.2
479 :     }
480 :    
481 : tim 1.1 public int size() {
482 : tim 1.2 return size;
483 : tim 1.1 }
484 : tim 1.2
485 :     /**
486 : dl 1.52 * Removes all of the elements from this priority queue.
487 : dl 1.49 * The queue will be empty after this call returns.
488 : tim 1.2 */
489 :     public void clear() {
490 :     modCount++;
491 : dl 1.55 for (int i = 0; i < size; i++)
492 : tim 1.2 queue[i] = null;
493 :     size = 0;
494 :     }
495 :    
496 : dl 1.40 public E poll() {
497 : dl 1.36 if (size == 0)
498 : dl 1.40 return null;
499 : dl 1.55 int s = --size;
500 : dl 1.36 modCount++;
501 : dl 1.55 E result = (E)queue[0];
502 :     E x = (E)queue[s];
503 :     queue[s] = null;
504 :     if (s != 0)
505 :     siftDown(0, x);
506 : dl 1.36 return result;
507 :     }
508 :    
509 :     /**
510 : dl 1.55 * Removes the ith element from queue.
511 : tim 1.2 *
512 : dl 1.55 * Normally this method leaves the elements at up to i-1,
513 :     * inclusive, untouched. Under these circumstances, it returns
514 :     * null. Occasionally, in order to maintain the heap invariant,
515 :     * it must swap a later element of the list with one earlier than
516 :     * i. Under these circumstances, this method returns the element
517 :     * that was previously at the end of the list and is now at some
518 :     * position before i. This fact is used by iterator.remove so as to
519 :     * avoid missing traverseing elements.
520 : tim 1.2 */
521 : dl 1.52 private E removeAt(int i) {
522 : dl 1.55 assert i >= 0 && i < size;
523 : tim 1.2 modCount++;
524 : dl 1.55 int s = --size;
525 :     if (s == i) // removed last element
526 :     queue[i] = null;
527 :     else {
528 :     E moved = (E) queue[s];
529 : jsr166 1.56 queue[s] = null;
530 : dl 1.55 siftDown(i, moved);
531 : dl 1.36 if (queue[i] == moved) {
532 : dl 1.55 siftUp(i, moved);
533 : dl 1.36 if (queue[i] != moved)
534 :     return moved;
535 :     }
536 : dl 1.35 }
537 : dl 1.36 return null;
538 : tim 1.1 }
539 :    
540 : tim 1.2 /**
541 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
542 :     * promoting x up the tree until it is greater than or equal to
543 :     * its parent, or is the root.
544 :     *
545 :     * To simplify and speed up coercions and comparisons. the
546 :     * Comparable and Comparator versions are separated into different
547 :     * methods that are otherwise identical. (Similarly for siftDown.)
548 : jsr166 1.56 *
549 : dl 1.55 * @param k the position to fill
550 :     * @param x the item to insert
551 :     */
552 :     private void siftUp(int k, E x) {
553 : jsr166 1.56 if (comparator != null)
554 : dl 1.55 siftUpUsingComparator(k, x);
555 :     else
556 :     siftUpComparable(k, x);
557 :     }
558 :    
559 :     private void siftUpComparable(int k, E x) {
560 :     Comparable<? super E> key = (Comparable<? super E>) x;
561 :     while (k > 0) {
562 :     int parent = (k - 1) >>> 1;
563 :     Object e = queue[parent];
564 : jsr166 1.56 if (key.compareTo((E)e) >= 0)
565 : dl 1.55 break;
566 :     queue[k] = e;
567 :     k = parent;
568 :     }
569 :     queue[k] = key;
570 :     }
571 :    
572 :     private void siftUpUsingComparator(int k, E x) {
573 :     while (k > 0) {
574 :     int parent = (k - 1) >>> 1;
575 :     Object e = queue[parent];
576 : jsr166 1.56 if (comparator.compare(x, (E)e) >= 0)
577 : dl 1.55 break;
578 :     queue[k] = e;
579 :     k = parent;
580 :     }
581 :     queue[k] = x;
582 :     }
583 :    
584 :     /**
585 :     * Inserts item x at position k, maintaining heap invariant by
586 :     * demoting x down the tree repeatedly until it is less than or
587 :     * equal to its children or is a leaf.
588 :     *
589 :     * @param k the position to fill
590 :     * @param x the item to insert
591 :     */
592 :     private void siftDown(int k, E x) {
593 : jsr166 1.56 if (comparator != null)
594 : dl 1.55 siftDownUsingComparator(k, x);
595 :     else
596 :     siftDownComparable(k, x);
597 :     }
598 :    
599 :     private void siftDownComparable(int k, E x) {
600 :     Comparable<? super E> key = (Comparable<? super E>)x;
601 :     int half = size >>> 1; // loop while a non-leaf
602 :     while (k < half) {
603 :     int child = (k << 1) + 1; // assume left child is least
604 :     Object c = queue[child];
605 :     int right = child + 1;
606 :     if (right < size &&
607 :     ((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
608 :     c = queue[child = right];
609 :     if (key.compareTo((E)c) <= 0)
610 :     break;
611 :     queue[k] = c;
612 :     k = child;
613 :     }
614 :     queue[k] = key;
615 :     }
616 :    
617 :     private void siftDownUsingComparator(int k, E x) {
618 :     int half = size >>> 1;
619 :     while (k < half) {
620 :     int child = (k << 1) + 1;
621 :     Object c = queue[child];
622 :     int right = child + 1;
623 :     if (right < size &&
624 :     comparator.compare((E)c, (E)queue[right]) > 0)
625 : jsr166 1.56 c = queue[child = right];
626 :     if (comparator.compare(x, (E)c) <= 0)
627 : dl 1.55 break;
628 :     queue[k] = c;
629 :     k = child;
630 : tim 1.2 }
631 : dl 1.55 queue[k] = x;
632 : dl 1.36 }
633 : dl 1.35
634 : dl 1.36 /**
635 :     * Establishes the heap invariant (described above) in the entire tree,
636 :     * assuming nothing about the order of the elements prior to the call.
637 :     */
638 :     private void heapify() {
639 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
640 : dl 1.55 siftDown(i, (E)queue[i]);
641 : tim 1.2 }
642 :    
643 : dholmes 1.23 /**
644 : dl 1.52 * Returns the comparator used to order the elements in this
645 :     * queue, or <tt>null</tt> if this queue is sorted according to
646 :     * the {@linkplain Comparable natural ordering} of its elements.
647 :     *
648 :     * @return the comparator used to order this queue, or
649 :     * <tt>null</tt> if this queue is sorted according to the
650 :     * natural ordering of its elements.
651 : dholmes 1.23 */
652 : tim 1.16 public Comparator<? super E> comparator() {
653 : tim 1.2 return comparator;
654 :     }
655 : dl 1.5
656 :     /**
657 :     * Save the state of the instance to a stream (that
658 :     * is, serialize it).
659 :     *
660 :     * @serialData The length of the array backing the instance is
661 :     * emitted (int), followed by all of its elements (each an
662 :     * <tt>Object</tt>) in the proper order.
663 : dl 1.7 * @param s the stream
664 : dl 1.5 */
665 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
666 : dl 1.5 throws java.io.IOException{
667 : dl 1.7 // Write out element count, and any hidden stuff
668 :     s.defaultWriteObject();
669 : dl 1.5
670 :     // Write out array length
671 : dl 1.55 // For compatibility with 1.5 version, must be at least 2.
672 :     s.writeInt(Math.max(2, queue.length));
673 : dl 1.5
674 : dl 1.7 // Write out all elements in the proper order.
675 : dl 1.55 for (int i=0; i<size; i++)
676 : dl 1.5 s.writeObject(queue[i]);
677 :     }
678 :    
679 :     /**
680 : dl 1.52 * Reconstitute the <tt>PriorityQueue</tt> instance from a stream
681 :     * (that is, deserialize it).
682 : dl 1.7 * @param s the stream
683 : dl 1.5 */
684 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
685 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
686 : dl 1.7 // Read in size, and any hidden stuff
687 :     s.defaultReadObject();
688 : dl 1.5
689 :     // Read in array length and allocate array
690 :     int arrayLength = s.readInt();
691 : tim 1.16 queue = new Object[arrayLength];
692 : dl 1.5
693 : dl 1.7 // Read in all elements in the proper order.
694 : dl 1.55 for (int i=0; i<size; i++)
695 : dl 1.37 queue[i] = (E) s.readObject();
696 : dl 1.5 }
697 :    
698 : tim 1.1 }

Doug Lea
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