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1 : dl 1.38 /*
2 : dl 1.52 * @(#)PriorityQueue.java 1.8 05/08/27
3 : dl 1.38 *
4 : dl 1.52 * Copyright 2005 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 : dl 1.52 import java.util.*; // for javadoc (till 6280605 is fixed)
10 : tim 1.1
11 :     /**
12 : dl 1.41 * An unbounded priority {@linkplain Queue queue} based on a priority
13 : dl 1.52 * heap. The elements of the priority queue are ordered according to
14 :     * their {@linkplain Comparable natural ordering}, or by a {@link
15 :     * Comparator} provided at queue construction time, depending on which
16 :     * constructor is used. A priority queue does not permit
17 :     * <tt>null</tt> elements. A priority queue relying on natural
18 :     * ordering also does not permit insertion of non-comparable objects
19 :     * (doing so may result in <tt>ClassCastException</tt>).
20 : dl 1.40 *
21 : dl 1.41 * <p>The <em>head</em> of this queue is the <em>least</em> element
22 :     * with respect to the specified ordering. If multiple elements are
23 :     * tied for least value, the head is one of those elements -- ties are
24 : dl 1.42 * broken arbitrarily. The queue retrieval operations <tt>poll</tt>,
25 :     * <tt>remove</tt>, <tt>peek</tt>, and <tt>element</tt> access the
26 :     * element at the head of the queue.
27 : tim 1.14 *
28 : dl 1.41 * <p>A priority queue is unbounded, but has an internal
29 :     * <i>capacity</i> governing the size of an array used to store the
30 : dl 1.40 * elements on the queue. It is always at least as large as the queue
31 :     * size. As elements are added to a priority queue, its capacity
32 :     * grows automatically. The details of the growth policy are not
33 :     * specified.
34 : tim 1.2 *
35 : dl 1.50 * <p>This class and its iterator implement all of the
36 :     * <em>optional</em> methods of the {@link Collection} and {@link
37 : dl 1.52 * Iterator} interfaces. The Iterator provided in method {@link
38 :     * #iterator()} is <em>not</em> guaranteed to traverse the elements of
39 :     * the priority queue in any particular order. If you need ordered
40 :     * traversal, consider using <tt>Arrays.sort(pq.toArray())</tt>.
41 : dl 1.29 *
42 :     * <p> <strong>Note that this implementation is not synchronized.</strong>
43 :     * Multiple threads should not access a <tt>PriorityQueue</tt>
44 :     * instance concurrently if any of the threads modifies the list
45 :     * structurally. Instead, use the thread-safe {@link
46 : dholmes 1.34 * java.util.concurrent.PriorityBlockingQueue} class.
47 : dl 1.29 *
48 : dholmes 1.11 * <p>Implementation note: this implementation provides O(log(n)) time
49 :     * for the insertion methods (<tt>offer</tt>, <tt>poll</tt>,
50 :     * <tt>remove()</tt> and <tt>add</tt>) methods; linear time for the
51 :     * <tt>remove(Object)</tt> and <tt>contains(Object)</tt> methods; and
52 :     * constant time for the retrieval methods (<tt>peek</tt>,
53 :     * <tt>element</tt>, and <tt>size</tt>).
54 : tim 1.2 *
55 :     * <p>This class is a member of the
56 :     * <a href="{@docRoot}/../guide/collections/index.html">
57 :     * Java Collections Framework</a>.
58 : dl 1.7 * @since 1.5
59 : dl 1.52 * @version 1.8, 08/27/05
60 : dl 1.7 * @author Josh Bloch
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 : dl 1.52 * Creates a <tt>PriorityQueue</tt> with the default initial
99 :     * 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 : dl 1.52 * Creates a <tt>PriorityQueue</tt> with the specified initial
108 :     * 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 : dholmes 1.23 * @throws IllegalArgumentException if <tt>initialCapacity</tt> 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 : dholmes 1.21 * Creates a <tt>PriorityQueue</tt> 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 :     * @param comparator the comparator that will be used to order
125 :     * this priority queue. If <tt>null</tt>, the <i>natural
126 :     * ordering</i> of the elements will be used.
127 :     * @throws IllegalArgumentException if <tt>initialCapacity</tt> is
128 :     * 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 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
142 : dl 1.55 * specified collection. If the specified collection is an
143 : tim 1.25 * instance of a {@link java.util.SortedSet} or is another
144 : dl 1.52 * <tt>PriorityQueue</tt>, the priority queue will be ordered
145 :     * according to the same ordering. Otherwise, this priority queue
146 :     * will be ordered according to the 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 :     * Creates a <tt>PriorityQueue</tt> 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 :     * @throws ClassCastException if elements of <tt>c</tt> cannot be
179 :     * compared to one another according to <tt>c</tt>'s
180 :     * 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 :     * Creates a <tt>PriorityQueue</tt> containing the elements in the
191 : dl 1.55 * 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 :     * into this priority queue.
196 :     * @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 : dl 1.55 * Initialize queue array with elements from the given Collection.
209 :     * @param c the collection
210 : dl 1.22 */
211 : dl 1.55 private void initFromCollection(Collection<? extends E> c) {
212 :     Object[] a = c.toArray();
213 :     // If c.toArray incorrectly doesn't return Object[], copy it.
214 :     if (a.getClass() != Object[].class)
215 :     a = Arrays.copyOf(a, a.length, Object[].class);
216 :     queue = a;
217 :     size = a.length;
218 : jsr166 1.56 }
219 : dl 1.55
220 :     /**
221 :     * Increases the capacity of the array.
222 :     *
223 :     * @param minCapacity the desired minimum capacity
224 :     */
225 :     private void grow(int minCapacity) {
226 :     if (minCapacity < 0) // overflow
227 : dl 1.22 throw new OutOfMemoryError();
228 : dl 1.55 int oldCapacity = queue.length;
229 :     // Double size if small; else grow by 50%
230 :     int newCapacity = ((oldCapacity < 64)?
231 :     ((oldCapacity + 1) * 2):
232 :     ((oldCapacity * 3) / 2));
233 :     if (newCapacity < minCapacity)
234 :     newCapacity = minCapacity;
235 :     queue = Arrays.copyOf(queue, newCapacity);
236 : dl 1.22 }
237 : dl 1.36
238 : tim 1.2 /**
239 : dl 1.42 * Inserts the specified element into this priority queue.
240 : tim 1.2 *
241 : dl 1.52 * @return <tt>true</tt> (as specified by {@link Collection#add})
242 :     * @throws ClassCastException if the specified element cannot be
243 :     * compared with elements currently in this priority queue
244 :     * according to the priority queue's ordering
245 :     * @throws NullPointerException if the specified element is null
246 : tim 1.2 */
247 : dl 1.52 public boolean add(E e) {
248 :     return offer(e);
249 :     }
250 :    
251 :     /**
252 :     * Inserts the specified element into this priority queue.
253 :     *
254 :     * @return <tt>true</tt> (as specified by {@link Queue#offer})
255 :     * @throws ClassCastException if the specified element cannot be
256 :     * compared with elements currently in this priority queue
257 :     * according to the priority queue's ordering
258 :     * @throws NullPointerException if the specified element is null
259 :     */
260 :     public boolean offer(E e) {
261 :     if (e == null)
262 : dholmes 1.11 throw new NullPointerException();
263 :     modCount++;
264 : dl 1.55 int i = size;
265 :     if (i >= queue.length)
266 :     grow(i + 1);
267 :     size = i + 1;
268 :     if (i == 0)
269 :     queue[0] = e;
270 :     else
271 :     siftUp(i, e);
272 : dholmes 1.11 return true;
273 :     }
274 :    
275 : dl 1.40 public E peek() {
276 : tim 1.2 if (size == 0)
277 :     return null;
278 : dl 1.55 return (E) queue[0];
279 : tim 1.1 }
280 :    
281 : dl 1.52 private int indexOf(Object o) {
282 : dl 1.55 if (o != null) {
283 :     for (int i = 0; i < size; i++)
284 :     if (o.equals(queue[i]))
285 :     return i;
286 :     }
287 : dl 1.52 return -1;
288 :     }
289 :    
290 :     /**
291 :     * Removes a single instance of the specified element from this queue,
292 :     * if it is present. More formally, removes an element <tt>e</tt> such
293 :     * that <tt>o.equals(e)</tt>, if this queue contains one or more such
294 :     * elements. Returns true if this queue contained the specified element
295 :     * (or equivalently, if this queue changed as a result of the call).
296 :     *
297 :     * @param o element to be removed from this queue, if present
298 :     * @return <tt>true</tt> if this queue changed as a result of the call
299 :     */
300 :     public boolean remove(Object o) {
301 :     int i = indexOf(o);
302 :     if (i == -1)
303 :     return false;
304 :     else {
305 :     removeAt(i);
306 :     return true;
307 :     }
308 :     }
309 : dholmes 1.11
310 : jsr166 1.56 /**
311 : dl 1.55 * Version of remove using reference equality, not equals.
312 :     * Needed by iterator.remove
313 : jsr166 1.56 *
314 : dl 1.55 * @param o element to be removed from this queue, if present
315 :     * @return <tt>true</tt> if removed.
316 :     */
317 :     boolean removeEq(Object o) {
318 :     for (int i = 0; i < size; i++) {
319 :     if (o == queue[i]) {
320 :     removeAt(i);
321 :     return true;
322 :     }
323 :     }
324 :     return false;
325 :     }
326 :    
327 : dholmes 1.11 /**
328 : dl 1.52 * Returns <tt>true</tt> if this queue contains the specified element.
329 :     * More formally, returns <tt>true</tt> if and only if this queue contains
330 :     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
331 : dholmes 1.23 *
332 : dl 1.52 * @param o object to be checked for containment in this queue
333 :     * @return <tt>true</tt> if this queue contains the specified element
334 : dholmes 1.11 */
335 : dl 1.52 public boolean contains(Object o) {
336 :     return indexOf(o) != -1;
337 : tim 1.14 }
338 : dholmes 1.11
339 : dl 1.49 /**
340 : dl 1.52 * Returns an array containing all of the elements in this queue,
341 :     * The elements are in no particular order.
342 :     *
343 :     * <p>The returned array will be "safe" in that no references to it are
344 :     * maintained by this list. (In other words, this method must allocate
345 :     * a new array). The caller is thus free to modify the returned array.
346 :     *
347 :     * @return an array containing all of the elements in this queue.
348 : dl 1.49 */
349 : dl 1.52 public Object[] toArray() {
350 : dl 1.55 return Arrays.copyOf(queue, size);
351 : dl 1.52 }
352 : tim 1.2
353 : dl 1.52 /**
354 :     * Returns an array containing all of the elements in this queue.
355 :     * The elements are in no particular order. The runtime type of
356 :     * the returned array is that of the specified array. If the queue
357 :     * fits in the specified array, it is returned therein.
358 :     * Otherwise, a new array is allocated with the runtime type of
359 :     * the specified array and the size of this queue.
360 :     *
361 :     * <p>If the queue fits in the specified array with room to spare
362 :     * (i.e., the array has more elements than the queue), the element in
363 :     * the array immediately following the end of the collection is set to
364 :     * <tt>null</tt>. (This is useful in determining the length of the
365 :     * queue <i>only</i> if the caller knows that the queue does not contain
366 :     * any null elements.)
367 :     *
368 :     * @param a the array into which the elements of the queue are to
369 :     * be stored, if it is big enough; otherwise, a new array of the
370 :     * same runtime type is allocated for this purpose.
371 :     * @return an array containing the elements of the queue
372 :     * @throws ArrayStoreException if the runtime type of the specified array
373 :     * is not a supertype of the runtime type of every element in
374 :     * this queue
375 :     * @throws NullPointerException if the specified array is null
376 :     */
377 :     public <T> T[] toArray(T[] a) {
378 :     if (a.length < size)
379 :     // Make a new array of a's runtime type, but my contents:
380 : dl 1.55 return (T[]) Arrays.copyOf(queue, size, a.getClass());
381 :     System.arraycopy(queue, 0, a, 0, size);
382 : dl 1.52 if (a.length > size)
383 :     a[size] = null;
384 :     return a;
385 : tim 1.1 }
386 : tim 1.2
387 : dholmes 1.23 /**
388 :     * Returns an iterator over the elements in this queue. The iterator
389 :     * does not return the elements in any particular order.
390 :     *
391 : dl 1.52 * @return an iterator over the elements in this queue
392 : dholmes 1.23 */
393 : tim 1.2 public Iterator<E> iterator() {
394 : dl 1.7 return new Itr();
395 : tim 1.2 }
396 :    
397 : dl 1.55 private final class Itr implements Iterator<E> {
398 : dl 1.7 /**
399 :     * Index (into queue array) of element to be returned by
400 : tim 1.2 * subsequent call to next.
401 : dl 1.7 */
402 : dl 1.55 private int cursor = 0;
403 : tim 1.2
404 : dl 1.7 /**
405 : dl 1.36 * Index of element returned by most recent call to next,
406 :     * unless that element came from the forgetMeNot list.
407 : dl 1.55 * Set to -1 if element is deleted by a call to remove.
408 : dl 1.7 */
409 : dl 1.55 private int lastRet = -1;
410 : dl 1.7
411 :     /**
412 : dl 1.55 * A queue of elements that were moved from the unvisited portion of
413 : dl 1.36 * the heap into the visited portion as a result of "unlucky" element
414 :     * removals during the iteration. (Unlucky element removals are those
415 : dl 1.55 * that require a siftup instead of a siftdown.) We must visit all of
416 : dl 1.36 * the elements in this list to complete the iteration. We do this
417 :     * after we've completed the "normal" iteration.
418 :     *
419 :     * We expect that most iterations, even those involving removals,
420 :     * will not use need to store elements in this field.
421 :     */
422 : dl 1.55 private ArrayDeque<E> forgetMeNot = null;
423 : dl 1.36
424 :     /**
425 :     * Element returned by the most recent call to next iff that
426 :     * element was drawn from the forgetMeNot list.
427 :     */
428 : dl 1.55 private E lastRetElt = null;
429 :    
430 :     /**
431 :     * The modCount value that the iterator believes that the backing
432 :     * List should have. If this expectation is violated, the iterator
433 :     * has detected concurrent modification.
434 :     */
435 :     private int expectedModCount = modCount;
436 : dl 1.35
437 : dl 1.7 public boolean hasNext() {
438 : jsr166 1.56 return cursor < size ||
439 : dl 1.55 (forgetMeNot != null && !forgetMeNot.isEmpty());
440 : dl 1.7 }
441 :    
442 :     public E next() {
443 : dl 1.55 if (expectedModCount != modCount)
444 :     throw new ConcurrentModificationException();
445 : jsr166 1.56 if (cursor < size)
446 : dl 1.55 return (E) queue[lastRet = cursor++];
447 :     if (forgetMeNot != null) {
448 :     lastRet = -1;
449 :     lastRetElt = forgetMeNot.poll();
450 : jsr166 1.56 if (lastRetElt != null)
451 : dl 1.55 return lastRetElt;
452 : dl 1.36 }
453 : dl 1.55 throw new NoSuchElementException();
454 : dl 1.7 }
455 : tim 1.2
456 : dl 1.7 public void remove() {
457 : dl 1.55 if (expectedModCount != modCount)
458 :     throw new ConcurrentModificationException();
459 :     if (lastRet == -1 && lastRetElt == null)
460 :     throw new IllegalStateException();
461 :     if (lastRet != -1) {
462 : dl 1.36 E moved = PriorityQueue.this.removeAt(lastRet);
463 : dl 1.55 lastRet = -1;
464 : jsr166 1.56 if (moved == null)
465 : dl 1.36 cursor--;
466 : dl 1.55 else {
467 : dl 1.36 if (forgetMeNot == null)
468 : dl 1.55 forgetMeNot = new ArrayDeque<E>();
469 : dl 1.36 forgetMeNot.add(moved);
470 : jsr166 1.56 }
471 : dl 1.55 } else {
472 :     PriorityQueue.this.removeEq(lastRetElt);
473 : dl 1.36 lastRetElt = null;
474 : jsr166 1.56 }
475 : tim 1.2 expectedModCount = modCount;
476 : dl 1.7 }
477 : tim 1.2
478 :     }
479 :    
480 : tim 1.1 public int size() {
481 : tim 1.2 return size;
482 : tim 1.1 }
483 : tim 1.2
484 :     /**
485 : dl 1.52 * Removes all of the elements from this priority queue.
486 : dl 1.49 * The queue will be empty after this call returns.
487 : tim 1.2 */
488 :     public void clear() {
489 :     modCount++;
490 : dl 1.55 for (int i = 0; i < size; i++)
491 : tim 1.2 queue[i] = null;
492 :     size = 0;
493 :     }
494 :    
495 : dl 1.40 public E poll() {
496 : dl 1.36 if (size == 0)
497 : dl 1.40 return null;
498 : dl 1.55 int s = --size;
499 : dl 1.36 modCount++;
500 : dl 1.55 E result = (E)queue[0];
501 :     E x = (E)queue[s];
502 :     queue[s] = null;
503 :     if (s != 0)
504 :     siftDown(0, x);
505 : dl 1.36 return result;
506 :     }
507 :    
508 :     /**
509 : dl 1.55 * Removes the ith element from queue.
510 : tim 1.2 *
511 : dl 1.55 * Normally this method leaves the elements at up to i-1,
512 :     * inclusive, untouched. Under these circumstances, it returns
513 :     * null. Occasionally, in order to maintain the heap invariant,
514 :     * it must swap a later element of the list with one earlier than
515 :     * i. Under these circumstances, this method returns the element
516 :     * that was previously at the end of the list and is now at some
517 :     * position before i. This fact is used by iterator.remove so as to
518 :     * avoid missing traverseing elements.
519 : tim 1.2 */
520 : dl 1.52 private E removeAt(int i) {
521 : dl 1.55 assert i >= 0 && i < size;
522 : tim 1.2 modCount++;
523 : dl 1.55 int s = --size;
524 :     if (s == i) // removed last element
525 :     queue[i] = null;
526 :     else {
527 :     E moved = (E) queue[s];
528 : jsr166 1.56 queue[s] = null;
529 : dl 1.55 siftDown(i, moved);
530 : dl 1.36 if (queue[i] == moved) {
531 : dl 1.55 siftUp(i, moved);
532 : dl 1.36 if (queue[i] != moved)
533 :     return moved;
534 :     }
535 : dl 1.35 }
536 : dl 1.36 return null;
537 : tim 1.1 }
538 :    
539 : tim 1.2 /**
540 : dl 1.55 * Inserts item x at position k, maintaining heap invariant by
541 :     * promoting x up the tree until it is greater than or equal to
542 :     * its parent, or is the root.
543 :     *
544 :     * To simplify and speed up coercions and comparisons. the
545 :     * Comparable and Comparator versions are separated into different
546 :     * methods that are otherwise identical. (Similarly for siftDown.)
547 : jsr166 1.56 *
548 : dl 1.55 * @param k the position to fill
549 :     * @param x the item to insert
550 :     */
551 :     private void siftUp(int k, E x) {
552 : jsr166 1.56 if (comparator != null)
553 : dl 1.55 siftUpUsingComparator(k, x);
554 :     else
555 :     siftUpComparable(k, x);
556 :     }
557 :    
558 :     private void siftUpComparable(int k, E x) {
559 :     Comparable<? super E> key = (Comparable<? super E>) x;
560 :     while (k > 0) {
561 :     int parent = (k - 1) >>> 1;
562 :     Object e = queue[parent];
563 : jsr166 1.56 if (key.compareTo((E)e) >= 0)
564 : dl 1.55 break;
565 :     queue[k] = e;
566 :     k = parent;
567 :     }
568 :     queue[k] = key;
569 :     }
570 :    
571 :     private void siftUpUsingComparator(int k, E x) {
572 :     while (k > 0) {
573 :     int parent = (k - 1) >>> 1;
574 :     Object e = queue[parent];
575 : jsr166 1.56 if (comparator.compare(x, (E)e) >= 0)
576 : dl 1.55 break;
577 :     queue[k] = e;
578 :     k = parent;
579 :     }
580 :     queue[k] = x;
581 :     }
582 :    
583 :     /**
584 :     * Inserts item x at position k, maintaining heap invariant by
585 :     * demoting x down the tree repeatedly until it is less than or
586 :     * equal to its children or is a leaf.
587 :     *
588 :     * @param k the position to fill
589 :     * @param x the item to insert
590 :     */
591 :     private void siftDown(int k, E x) {
592 : jsr166 1.56 if (comparator != null)
593 : dl 1.55 siftDownUsingComparator(k, x);
594 :     else
595 :     siftDownComparable(k, x);
596 :     }
597 :    
598 :     private void siftDownComparable(int k, E x) {
599 :     Comparable<? super E> key = (Comparable<? super E>)x;
600 :     int half = size >>> 1; // loop while a non-leaf
601 :     while (k < half) {
602 :     int child = (k << 1) + 1; // assume left child is least
603 :     Object c = queue[child];
604 :     int right = child + 1;
605 :     if (right < size &&
606 :     ((Comparable<? super E>)c).compareTo((E)queue[right]) > 0)
607 :     c = queue[child = right];
608 :     if (key.compareTo((E)c) <= 0)
609 :     break;
610 :     queue[k] = c;
611 :     k = child;
612 :     }
613 :     queue[k] = key;
614 :     }
615 :    
616 :     private void siftDownUsingComparator(int k, E x) {
617 :     int half = size >>> 1;
618 :     while (k < half) {
619 :     int child = (k << 1) + 1;
620 :     Object c = queue[child];
621 :     int right = child + 1;
622 :     if (right < size &&
623 :     comparator.compare((E)c, (E)queue[right]) > 0)
624 : jsr166 1.56 c = queue[child = right];
625 :     if (comparator.compare(x, (E)c) <= 0)
626 : dl 1.55 break;
627 :     queue[k] = c;
628 :     k = child;
629 : tim 1.2 }
630 : dl 1.55 queue[k] = x;
631 : dl 1.36 }
632 : dl 1.35
633 : dl 1.36 /**
634 :     * Establishes the heap invariant (described above) in the entire tree,
635 :     * assuming nothing about the order of the elements prior to the call.
636 :     */
637 :     private void heapify() {
638 : jsr166 1.56 for (int i = (size >>> 1) - 1; i >= 0; i--)
639 : dl 1.55 siftDown(i, (E)queue[i]);
640 : tim 1.2 }
641 :    
642 : dholmes 1.23 /**
643 : dl 1.52 * Returns the comparator used to order the elements in this
644 :     * queue, or <tt>null</tt> if this queue is sorted according to
645 :     * the {@linkplain Comparable natural ordering} of its elements.
646 :     *
647 :     * @return the comparator used to order this queue, or
648 :     * <tt>null</tt> if this queue is sorted according to the
649 :     * natural ordering of its elements.
650 : dholmes 1.23 */
651 : tim 1.16 public Comparator<? super E> comparator() {
652 : tim 1.2 return comparator;
653 :     }
654 : dl 1.5
655 :     /**
656 :     * Save the state of the instance to a stream (that
657 :     * is, serialize it).
658 :     *
659 :     * @serialData The length of the array backing the instance is
660 :     * emitted (int), followed by all of its elements (each an
661 :     * <tt>Object</tt>) in the proper order.
662 : dl 1.7 * @param s the stream
663 : dl 1.5 */
664 : dl 1.22 private void writeObject(java.io.ObjectOutputStream s)
665 : dl 1.5 throws java.io.IOException{
666 : dl 1.7 // Write out element count, and any hidden stuff
667 :     s.defaultWriteObject();
668 : dl 1.5
669 :     // Write out array length
670 : dl 1.55 // For compatibility with 1.5 version, must be at least 2.
671 :     s.writeInt(Math.max(2, queue.length));
672 : dl 1.5
673 : dl 1.7 // Write out all elements in the proper order.
674 : dl 1.55 for (int i=0; i<size; i++)
675 : dl 1.5 s.writeObject(queue[i]);
676 :     }
677 :    
678 :     /**
679 : dl 1.52 * Reconstitute the <tt>PriorityQueue</tt> instance from a stream
680 :     * (that is, deserialize it).
681 : dl 1.7 * @param s the stream
682 : dl 1.5 */
683 : dl 1.22 private void readObject(java.io.ObjectInputStream s)
684 : dl 1.5 throws java.io.IOException, ClassNotFoundException {
685 : dl 1.7 // Read in size, and any hidden stuff
686 :     s.defaultReadObject();
687 : dl 1.5
688 :     // Read in array length and allocate array
689 :     int arrayLength = s.readInt();
690 : tim 1.16 queue = new Object[arrayLength];
691 : dl 1.5
692 : dl 1.7 // Read in all elements in the proper order.
693 : dl 1.55 for (int i=0; i<size; i++)
694 : dl 1.37 queue[i] = (E) s.readObject();
695 : dl 1.5 }
696 :    
697 : tim 1.1 }

Doug Lea
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