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1 : dl 1.38 /*
2 :     * %W% %E%
3 :     *
4 :     * Copyright 2003 Sun Microsystems, Inc. All rights reserved.
5 :     * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
6 :     */
7 :    
8 :     package java.util;
9 : tim 1.1
10 :     /**
11 : dl 1.36 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
12 :     * This queue orders elements according to an order specified at construction
13 :     * time, which is specified in the same manner as {@link java.util.TreeSet}
14 :     * and {@link java.util.TreeMap}: elements are ordered either according to
15 :     * their <i>natural order</i> (see {@link Comparable}), or according to a
16 :     * {@link java.util.Comparator}, depending on which constructor is used.
17 : tim 1.19 * <p>The <em>head</em> of this queue is the <em>least</em> element with
18 : dl 1.36 * respect to the specified ordering. If multiple elements are tied for least
19 :     * value, the head is one of those elements. A priority queue does not permit
20 : dholmes 1.11 * <tt>null</tt> elements.
21 : tim 1.14 *
22 : dholmes 1.11 * <p>The {@link #remove()} and {@link #poll()} methods remove and
23 :     * return the head of the queue.
24 :     *
25 :     * <p>The {@link #element()} and {@link #peek()} methods return, but do
26 :     * not delete, the head of the queue.
27 : tim 1.2 *
28 : dl 1.7 * <p>A priority queue has a <i>capacity</i>. The capacity is the
29 :     * size of the array used internally to store the elements on the
30 : dholmes 1.20 * queue.
31 : dholmes 1.18 * It is always at least as large as the queue size. As
32 : dl 1.7 * elements are added to a priority queue, its capacity grows
33 :     * automatically. The details of the growth policy are not specified.
34 : tim 1.2 *
35 : dl 1.29 * <p>The Iterator provided in method {@link #iterator()} is <em>not</em>
36 :     * guaranteed to traverse the elements of the PriorityQueue in any
37 :     * particular order. If you need ordered traversal, consider using
38 :     * <tt>Arrays.sort(pq.toArray())</tt>.
39 :     *
40 :     * <p> <strong>Note that this implementation is not synchronized.</strong>
41 :     * Multiple threads should not access a <tt>PriorityQueue</tt>
42 :     * instance concurrently if any of the threads modifies the list
43 :     * structurally. Instead, use the thread-safe {@link
44 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
45 : dl 1.29 *
46 :     *
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 : dl 1.38 * @version %I%, %G%
59 : dl 1.7 * @author Josh Bloch
60 : tim 1.2 */
61 :     public class PriorityQueue<E> extends AbstractQueue<E>
62 : dl 1.22 implements Queue<E>, java.io.Serializable {
63 : dholmes 1.11
64 : dl 1.31 private static final long serialVersionUID = -7720805057305804111L;
65 : dl 1.30
66 : tim 1.2 private static final int DEFAULT_INITIAL_CAPACITY = 11;
67 : tim 1.1
68 : tim 1.2 /**
69 :     * Priority queue represented as a balanced binary heap: the two children
70 :     * of queue[n] are queue[2*n] and queue[2*n + 1]. The priority queue is
71 :     * ordered by comparator, or by the elements' natural ordering, if
72 : brian 1.6 * comparator is null: For each node n in the heap and each descendant d
73 :     * of n, n <= d.
74 : tim 1.2 *
75 : brian 1.6 * The element with the lowest value is in queue[1], assuming the queue is
76 :     * nonempty. (A one-based array is used in preference to the traditional
77 :     * zero-based array to simplify parent and child calculations.)
78 : tim 1.2 *
79 :     * queue.length must be >= 2, even if size == 0.
80 :     */
81 : tim 1.16 private transient Object[] queue;
82 : tim 1.1
83 : tim 1.2 /**
84 :     * The number of elements in the priority queue.
85 :     */
86 :     private int size = 0;
87 : tim 1.1
88 : tim 1.2 /**
89 :     * The comparator, or null if priority queue uses elements'
90 :     * natural ordering.
91 :     */
92 : tim 1.16 private final Comparator<? super E> comparator;
93 : tim 1.2
94 :     /**
95 :     * The number of times this priority queue has been
96 :     * <i>structurally modified</i>. See AbstractList for gory details.
97 :     */
98 : dl 1.5 private transient int modCount = 0;
99 : tim 1.2
100 :     /**
101 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the default initial capacity
102 : dl 1.7 * (11) that orders its elements according to their natural
103 : tim 1.24 * ordering (using <tt>Comparable</tt>).
104 : tim 1.2 */
105 :     public PriorityQueue() {
106 : dholmes 1.11 this(DEFAULT_INITIAL_CAPACITY, null);
107 : tim 1.1 }
108 : tim 1.2
109 :     /**
110 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
111 : dl 1.7 * that orders its elements according to their natural ordering
112 : tim 1.24 * (using <tt>Comparable</tt>).
113 : tim 1.2 *
114 :     * @param initialCapacity the initial capacity for this priority queue.
115 : dholmes 1.23 * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
116 :     * than 1
117 : tim 1.2 */
118 :     public PriorityQueue(int initialCapacity) {
119 :     this(initialCapacity, null);
120 : tim 1.1 }
121 : tim 1.2
122 :     /**
123 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> with the specified initial capacity
124 : tim 1.2 * that orders its elements according to the specified comparator.
125 :     *
126 :     * @param initialCapacity the initial capacity for this priority queue.
127 :     * @param comparator the comparator used to order this priority queue.
128 : dholmes 1.11 * If <tt>null</tt> then the order depends on the elements' natural
129 :     * ordering.
130 : dholmes 1.15 * @throws IllegalArgumentException if <tt>initialCapacity</tt> is less
131 :     * than 1
132 : tim 1.2 */
133 : dholmes 1.23 public PriorityQueue(int initialCapacity,
134 :     Comparator<? super E> comparator) {
135 : tim 1.2 if (initialCapacity < 1)
136 : dholmes 1.15 throw new IllegalArgumentException();
137 : tim 1.16 this.queue = new Object[initialCapacity + 1];
138 : tim 1.2 this.comparator = comparator;
139 : tim 1.1 }
140 :    
141 : tim 1.2 /**
142 : dl 1.22 * Common code to initialize underlying queue array across
143 :     * constructors below.
144 :     */
145 :     private void initializeArray(Collection<? extends E> c) {
146 :     int sz = c.size();
147 :     int initialCapacity = (int)Math.min((sz * 110L) / 100,
148 :     Integer.MAX_VALUE - 1);
149 :     if (initialCapacity < 1)
150 :     initialCapacity = 1;
151 :    
152 :     this.queue = new Object[initialCapacity + 1];
153 :     }
154 :    
155 :     /**
156 :     * Initially fill elements of the queue array under the
157 :     * knowledge that it is sorted or is another PQ, in which
158 : dl 1.36 * case we can just place the elements in the order presented.
159 : dl 1.22 */
160 :     private void fillFromSorted(Collection<? extends E> c) {
161 :     for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
162 :     queue[++size] = i.next();
163 :     }
164 :    
165 :     /**
166 : dl 1.36 * Initially fill elements of the queue array that is not to our knowledge
167 :     * sorted, so we must rearrange the elements to guarantee the heap
168 :     * invariant.
169 : dl 1.22 */
170 :     private void fillFromUnsorted(Collection<? extends E> c) {
171 :     for (Iterator<? extends E> i = c.iterator(); i.hasNext(); )
172 : dl 1.36 queue[++size] = i.next();
173 :     heapify();
174 : dl 1.22 }
175 :    
176 :     /**
177 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
178 :     * specified collection. The priority queue has an initial
179 :     * capacity of 110% of the size of the specified collection or 1
180 :     * if the collection is empty. If the specified collection is an
181 : tim 1.25 * instance of a {@link java.util.SortedSet} or is another
182 : dl 1.22 * <tt>PriorityQueue</tt>, the priority queue will be sorted
183 :     * according to the same comparator, or according to its elements'
184 :     * natural order if the collection is sorted according to its
185 :     * elements' natural order. Otherwise, the priority queue is
186 :     * ordered according to its elements' natural order.
187 : tim 1.2 *
188 : dholmes 1.15 * @param c the collection whose elements are to be placed
189 : tim 1.2 * into this priority queue.
190 :     * @throws ClassCastException if elements of the specified collection
191 :     * cannot be compared to one another according to the priority
192 :     * queue's ordering.
193 : dholmes 1.15 * @throws NullPointerException if <tt>c</tt> or any element within it
194 :     * is <tt>null</tt>
195 : tim 1.2 */
196 : tim 1.16 public PriorityQueue(Collection<? extends E> c) {
197 : dl 1.22 initializeArray(c);
198 : dl 1.27 if (c instanceof SortedSet) {
199 : dl 1.28 // @fixme double-cast workaround for compiler
200 :     SortedSet<? extends E> s = (SortedSet<? extends E>) (SortedSet)c;
201 : dl 1.22 comparator = (Comparator<? super E>)s.comparator();
202 :     fillFromSorted(s);
203 : dl 1.27 } else if (c instanceof PriorityQueue) {
204 : dl 1.22 PriorityQueue<? extends E> s = (PriorityQueue<? extends E>) c;
205 :     comparator = (Comparator<? super E>)s.comparator();
206 :     fillFromSorted(s);
207 : tim 1.26 } else {
208 : tim 1.2 comparator = null;
209 : dl 1.22 fillFromUnsorted(c);
210 : tim 1.2 }
211 : dl 1.22 }
212 :    
213 :     /**
214 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
215 :     * specified collection. The priority queue has an initial
216 :     * capacity of 110% of the size of the specified collection or 1
217 :     * if the collection is empty. This priority queue will be sorted
218 :     * according to the same comparator as the given collection, or
219 :     * according to its elements' natural order if the collection is
220 :     * sorted according to its elements' natural order.
221 :     *
222 :     * @param c the collection whose elements are to be placed
223 :     * into this priority queue.
224 :     * @throws ClassCastException if elements of the specified collection
225 :     * cannot be compared to one another according to the priority
226 :     * queue's ordering.
227 :     * @throws NullPointerException if <tt>c</tt> or any element within it
228 :     * is <tt>null</tt>
229 :     */
230 :     public PriorityQueue(PriorityQueue<? extends E> c) {
231 :     initializeArray(c);
232 :     comparator = (Comparator<? super E>)c.comparator();
233 :     fillFromSorted(c);
234 :     }
235 : dholmes 1.18
236 : dl 1.22 /**
237 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
238 :     * specified collection. The priority queue has an initial
239 :     * capacity of 110% of the size of the specified collection or 1
240 :     * if the collection is empty. This priority queue will be sorted
241 :     * according to the same comparator as the given collection, or
242 :     * according to its elements' natural order if the collection is
243 :     * sorted according to its elements' natural order.
244 :     *
245 :     * @param c the collection whose elements are to be placed
246 :     * into this priority queue.
247 :     * @throws ClassCastException if elements of the specified collection
248 :     * cannot be compared to one another according to the priority
249 :     * queue's ordering.
250 :     * @throws NullPointerException if <tt>c</tt> or any element within it
251 :     * is <tt>null</tt>
252 :     */
253 :     public PriorityQueue(SortedSet<? extends E> c) {
254 :     initializeArray(c);
255 :     comparator = (Comparator<? super E>)c.comparator();
256 :     fillFromSorted(c);
257 : tim 1.1 }
258 :    
259 : dl 1.22 /**
260 :     * Resize array, if necessary, to be able to hold given index
261 :     */
262 :     private void grow(int index) {
263 :     int newlen = queue.length;
264 :     if (index < newlen) // don't need to grow
265 :     return;
266 :     if (index == Integer.MAX_VALUE)
267 :     throw new OutOfMemoryError();
268 :     while (newlen <= index) {
269 :     if (newlen >= Integer.MAX_VALUE / 2) // avoid overflow
270 :     newlen = Integer.MAX_VALUE;
271 :     else
272 :     newlen <<= 2;
273 :     }
274 :     Object[] newQueue = new Object[newlen];
275 :     System.arraycopy(queue, 0, newQueue, 0, queue.length);
276 :     queue = newQueue;
277 :     }
278 :    
279 : dl 1.36
280 : tim 1.2 // Queue Methods
281 :    
282 :     /**
283 : dholmes 1.11 * Add the specified element to this priority queue.
284 : tim 1.2 *
285 : dholmes 1.11 * @return <tt>true</tt>
286 :     * @throws ClassCastException if the specified element cannot be compared
287 :     * with elements currently in the priority queue according
288 :     * to the priority queue's ordering.
289 : dholmes 1.18 * @throws NullPointerException if the specified element is <tt>null</tt>.
290 : tim 1.2 */
291 : dholmes 1.18 public boolean offer(E o) {
292 :     if (o == null)
293 : dholmes 1.11 throw new NullPointerException();
294 :     modCount++;
295 :     ++size;
296 :    
297 :     // Grow backing store if necessary
298 : dl 1.22 if (size >= queue.length)
299 :     grow(size);
300 : dholmes 1.11
301 : dholmes 1.18 queue[size] = o;
302 : dholmes 1.11 fixUp(size);
303 :     return true;
304 :     }
305 :    
306 : tim 1.1 public E poll() {
307 : tim 1.2 if (size == 0)
308 :     return null;
309 : dl 1.36 return remove();
310 : tim 1.1 }
311 : tim 1.2
312 : tim 1.1 public E peek() {
313 : tim 1.16 return (E) queue[1];
314 : tim 1.1 }
315 :    
316 : dholmes 1.23 // Collection Methods - the first two override to update docs
317 : dholmes 1.11
318 :     /**
319 : dholmes 1.23 * Adds the specified element to this queue.
320 :     * @return <tt>true</tt> (as per the general contract of
321 :     * <tt>Collection.add</tt>).
322 :     *
323 :     * @throws NullPointerException {@inheritDoc}
324 : dholmes 1.15 * @throws ClassCastException if the specified element cannot be compared
325 :     * with elements currently in the priority queue according
326 :     * to the priority queue's ordering.
327 : dholmes 1.11 */
328 : dholmes 1.18 public boolean add(E o) {
329 :     return super.add(o);
330 : dholmes 1.11 }
331 :    
332 : dholmes 1.23
333 : tim 1.14 /**
334 : dholmes 1.23 * Adds all of the elements in the specified collection to this queue.
335 :     * The behavior of this operation is undefined if
336 :     * the specified collection is modified while the operation is in
337 :     * progress. (This implies that the behavior of this call is undefined if
338 :     * the specified collection is this queue, and this queue is nonempty.)
339 :     * <p>
340 :     * This implementation iterates over the specified collection, and adds
341 :     * each object returned by the iterator to this collection, in turn.
342 :     * @throws NullPointerException {@inheritDoc}
343 : dholmes 1.15 * @throws ClassCastException if any element cannot be compared
344 :     * with elements currently in the priority queue according
345 :     * to the priority queue's ordering.
346 : tim 1.14 */
347 :     public boolean addAll(Collection<? extends E> c) {
348 :     return super.addAll(c);
349 :     }
350 : dholmes 1.11
351 : dholmes 1.23
352 : dl 1.36 /**
353 : dholmes 1.23 * Removes a single instance of the specified element from this
354 :     * queue, if it is present. More formally,
355 :     * removes an element <tt>e</tt> such that <tt>(o==null ? e==null :
356 :     * o.equals(e))</tt>, if the queue contains one or more such
357 :     * elements. Returns <tt>true</tt> if the queue contained the
358 :     * specified element (or equivalently, if the queue changed as a
359 :     * result of the call).
360 :     *
361 :     * <p>This implementation iterates over the queue looking for the
362 :     * specified element. If it finds the element, it removes the element
363 :     * from the queue using the iterator's remove method.<p>
364 :     *
365 :     */
366 : dl 1.12 public boolean remove(Object o) {
367 : dholmes 1.11 if (o == null)
368 : dholmes 1.15 return false;
369 : tim 1.2
370 :     if (comparator == null) {
371 :     for (int i = 1; i <= size; i++) {
372 : tim 1.16 if (((Comparable<E>)queue[i]).compareTo((E)o) == 0) {
373 : dl 1.36 removeAt(i);
374 : tim 1.2 return true;
375 :     }
376 :     }
377 :     } else {
378 :     for (int i = 1; i <= size; i++) {
379 : tim 1.16 if (comparator.compare((E)queue[i], (E)o) == 0) {
380 : dl 1.36 removeAt(i);
381 : tim 1.2 return true;
382 :     }
383 :     }
384 :     }
385 : tim 1.1 return false;
386 :     }
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 :     * @return an iterator over the elements in this queue.
393 :     */
394 : tim 1.2 public Iterator<E> iterator() {
395 : dl 1.7 return new Itr();
396 : tim 1.2 }
397 :    
398 :     private class Itr implements Iterator<E> {
399 : dl 1.35
400 : dl 1.7 /**
401 :     * Index (into queue array) of element to be returned by
402 : tim 1.2 * subsequent call to next.
403 : dl 1.7 */
404 :     private int cursor = 1;
405 : tim 1.2
406 : dl 1.7 /**
407 : dl 1.36 * Index of element returned by most recent call to next,
408 :     * unless that element came from the forgetMeNot list.
409 :     * Reset to 0 if element is deleted by a call to remove.
410 : dl 1.7 */
411 :     private int lastRet = 0;
412 :    
413 :     /**
414 :     * The modCount value that the iterator believes that the backing
415 :     * List should have. If this expectation is violated, the iterator
416 :     * has detected concurrent modification.
417 :     */
418 :     private int expectedModCount = modCount;
419 : tim 1.2
420 : dl 1.36 /**
421 :     * A list of elements that were moved from the unvisited portion of
422 :     * the heap into the visited portion as a result of "unlucky" element
423 :     * removals during the iteration. (Unlucky element removals are those
424 :     * that require a fixup instead of a fixdown.) We must visit all of
425 :     * the elements in this list to complete the iteration. We do this
426 :     * after we've completed the "normal" iteration.
427 :     *
428 :     * We expect that most iterations, even those involving removals,
429 :     * will not use need to store elements in this field.
430 :     */
431 :     private ArrayList<E> forgetMeNot = null;
432 :    
433 :     /**
434 :     * Element returned by the most recent call to next iff that
435 :     * element was drawn from the forgetMeNot list.
436 :     */
437 :     private Object lastRetElt = null;
438 : dl 1.35
439 : dl 1.7 public boolean hasNext() {
440 : dl 1.36 return cursor <= size || forgetMeNot != null;
441 : dl 1.7 }
442 :    
443 :     public E next() {
444 : tim 1.2 checkForComodification();
445 : dl 1.36 E result;
446 :     if (cursor <= size) {
447 :     result = (E) queue[cursor];
448 :     lastRet = cursor++;
449 :     }
450 :     else if (forgetMeNot == null)
451 : dl 1.7 throw new NoSuchElementException();
452 : dl 1.36 else {
453 :     int remaining = forgetMeNot.size();
454 :     result = forgetMeNot.remove(remaining - 1);
455 :     if (remaining == 1)
456 :     forgetMeNot = null;
457 :     lastRet = 0;
458 :     lastRetElt = result;
459 :     }
460 : tim 1.2 return result;
461 : dl 1.7 }
462 : tim 1.2
463 : dl 1.7 public void remove() {
464 : tim 1.2 checkForComodification();
465 :    
466 : dl 1.36 if (lastRet != 0) {
467 :     E moved = PriorityQueue.this.removeAt(lastRet);
468 :     lastRet = 0;
469 :     if (moved == null) {
470 :     cursor--;
471 :     } else {
472 :     if (forgetMeNot == null)
473 : dl 1.37 forgetMeNot = new ArrayList<E>();
474 : dl 1.36 forgetMeNot.add(moved);
475 :     }
476 :     } else if (lastRetElt != null) {
477 :     PriorityQueue.this.remove(lastRetElt);
478 :     lastRetElt = null;
479 :     } else {
480 :     throw new IllegalStateException();
481 : dl 1.35 }
482 :    
483 : tim 1.2 expectedModCount = modCount;
484 : dl 1.7 }
485 : tim 1.2
486 : dl 1.7 final void checkForComodification() {
487 :     if (modCount != expectedModCount)
488 :     throw new ConcurrentModificationException();
489 :     }
490 : tim 1.2 }
491 :    
492 : tim 1.1 public int size() {
493 : tim 1.2 return size;
494 : tim 1.1 }
495 : tim 1.2
496 :     /**
497 :     * Remove all elements from the priority queue.
498 :     */
499 :     public void clear() {
500 :     modCount++;
501 :    
502 :     // Null out element references to prevent memory leak
503 :     for (int i=1; i<=size; i++)
504 :     queue[i] = null;
505 :    
506 :     size = 0;
507 :     }
508 :    
509 :     /**
510 : dl 1.36 * Removes and returns the first element from queue.
511 :     */
512 :     public E remove() {
513 :     if (size == 0)
514 :     throw new NoSuchElementException();
515 :     modCount++;
516 :    
517 :     E result = (E) queue[1];
518 :     queue[1] = queue[size];
519 :     queue[size--] = null; // Drop extra ref to prevent memory leak
520 :     if (size > 1)
521 :     fixDown(1);
522 :    
523 :     return result;
524 :     }
525 :    
526 :     /**
527 :     * Removes and returns the ith element from queue. (Recall that queue
528 :     * is one-based, so 1 <= i <= size.)
529 : tim 1.2 *
530 : dl 1.36 * Normally this method leaves the elements at positions from 1 up to i-1,
531 :     * inclusive, untouched. Under these circumstances, it returns null.
532 :     * Occasionally, in order to maintain the heap invariant, it must move
533 :     * the last element of the list to some index in the range [2, i-1],
534 :     * and move the element previously at position (i/2) to position i.
535 :     * Under these circumstances, this method returns the element that was
536 :     * previously at the end of the list and is now at some position between
537 :     * 2 and i-1 inclusive.
538 : tim 1.2 */
539 : dl 1.36 private E removeAt(int i) {
540 :     assert i > 0 && i <= size;
541 : tim 1.2 modCount++;
542 :    
543 : dl 1.36 E moved = (E) queue[size];
544 :     queue[i] = moved;
545 : tim 1.2 queue[size--] = null; // Drop extra ref to prevent memory leak
546 : dl 1.35 if (i <= size) {
547 : tim 1.2 fixDown(i);
548 : dl 1.36 if (queue[i] == moved) {
549 :     fixUp(i);
550 :     if (queue[i] != moved)
551 :     return moved;
552 :     }
553 : dl 1.35 }
554 : dl 1.36 return null;
555 : tim 1.1 }
556 :    
557 : tim 1.2 /**
558 :     * Establishes the heap invariant (described above) assuming the heap
559 :     * satisfies the invariant except possibly for the leaf-node indexed by k
560 :     * (which may have a nextExecutionTime less than its parent's).
561 :     *
562 :     * This method functions by "promoting" queue[k] up the hierarchy
563 :     * (by swapping it with its parent) repeatedly until queue[k]
564 :     * is greater than or equal to its parent.
565 :     */
566 :     private void fixUp(int k) {
567 :     if (comparator == null) {
568 :     while (k > 1) {
569 :     int j = k >> 1;
570 : tim 1.16 if (((Comparable<E>)queue[j]).compareTo((E)queue[k]) <= 0)
571 : tim 1.2 break;
572 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
573 : tim 1.2 k = j;
574 :     }
575 :     } else {
576 :     while (k > 1) {
577 : dl 1.35 int j = k >>> 1;
578 : tim 1.16 if (comparator.compare((E)queue[j], (E)queue[k]) <= 0)
579 : tim 1.2 break;
580 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
581 : tim 1.2 k = j;
582 :     }
583 :     }
584 :     }
585 :    
586 :     /**
587 :     * Establishes the heap invariant (described above) in the subtree
588 :     * rooted at k, which is assumed to satisfy the heap invariant except
589 :     * possibly for node k itself (which may be greater than its children).
590 :     *
591 :     * This method functions by "demoting" queue[k] down the hierarchy
592 :     * (by swapping it with its smaller child) repeatedly until queue[k]
593 :     * is less than or equal to its children.
594 :     */
595 :     private void fixDown(int k) {
596 :     int j;
597 :     if (comparator == null) {
598 : dl 1.33 while ((j = k << 1) <= size && (j > 0)) {
599 : dl 1.35 if (j<size &&
600 :     ((Comparable<E>)queue[j]).compareTo((E)queue[j+1]) > 0)
601 : tim 1.2 j++; // j indexes smallest kid
602 : dl 1.35
603 : tim 1.16 if (((Comparable<E>)queue[k]).compareTo((E)queue[j]) <= 0)
604 : tim 1.2 break;
605 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
606 : tim 1.2 k = j;
607 :     }
608 :     } else {
609 : dl 1.33 while ((j = k << 1) <= size && (j > 0)) {
610 : dl 1.35 if (j<size &&
611 :     comparator.compare((E)queue[j], (E)queue[j+1]) > 0)
612 : tim 1.2 j++; // j indexes smallest kid
613 : tim 1.16 if (comparator.compare((E)queue[k], (E)queue[j]) <= 0)
614 : tim 1.2 break;
615 : tim 1.16 Object tmp = queue[j]; queue[j] = queue[k]; queue[k] = tmp;
616 : tim 1.2 k = j;
617 :     }
618 :     }
619 : dl 1.36 }
620 : dl 1.35
621 : dl 1.36 /**
622 :     * Establishes the heap invariant (described above) in the entire tree,
623 :     * assuming nothing about the order of the elements prior to the call.
624 :     */
625 :     private void heapify() {
626 :     for (int i = size/2; i >= 1; i--)
627 :     fixDown(i);
628 : tim 1.2 }
629 :    
630 : dholmes 1.23 /**
631 :     * Returns the comparator used to order this collection, or <tt>null</tt>
632 :     * if this collection is sorted according to its elements natural ordering
633 : tim 1.24 * (using <tt>Comparable</tt>).
634 : dholmes 1.23 *
635 :     * @return the comparator used to order this collection, or <tt>null</tt>
636 :     * if this collection is sorted according to its elements natural ordering.
637 :     */
638 : tim 1.16 public Comparator<? super E> comparator() {
639 : tim 1.2 return comparator;
640 :     }
641 : dl 1.5
642 :     /**
643 :     * Save the state of the instance to a stream (that
644 :     * is, serialize it).
645 :     *
646 :     * @serialData The length of the array backing the instance is
647 :     * emitted (int), followed by all of its elements (each an
648 :     * <tt>Object</tt>) in the proper order.
649 : dl 1.7 * @param s the stream
650 : dl 1.5 */
651 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
652 : dl 1.5 throws java.io.IOException{
653 : dl 1.7 // Write out element count, and any hidden stuff
654 :     s.defaultWriteObject();
655 : dl 1.5
656 :     // Write out array length
657 :     s.writeInt(queue.length);
658 :    
659 : dl 1.7 // Write out all elements in the proper order.
660 :     for (int i=0; i<size; i++)
661 : dl 1.5 s.writeObject(queue[i]);
662 :     }
663 :    
664 :     /**
665 :     * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
666 :     * deserialize it).
667 : dl 1.7 * @param s the stream
668 : dl 1.5 */
669 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
670 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
671 : dl 1.7 // Read in size, and any hidden stuff
672 :     s.defaultReadObject();
673 : dl 1.5
674 :     // Read in array length and allocate array
675 :     int arrayLength = s.readInt();
676 : tim 1.16 queue = new Object[arrayLength];
677 : dl 1.5
678 : dl 1.7 // Read in all elements in the proper order.
679 :     for (int i=0; i<size; i++)
680 : dl 1.37 queue[i] = (E) s.readObject();
681 : dl 1.5 }
682 :    
683 : tim 1.1 }

Doug Lea
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