1 /*
2 * Copyright (c) 2003, 2018, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 import java.util.function.Consumer;
29 import java.util.function.Predicate;
30 import jdk.internal.misc.SharedSecrets;
31
32 /**
33 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
34 * The elements of the priority queue are ordered according to their
35 * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
36 * provided at queue construction time, depending on which constructor is
37 * used. A priority queue does not permit {@code null} elements.
38 * A priority queue relying on natural ordering also does not permit
39 * insertion of non-comparable objects (doing so may result in
40 * {@code ClassCastException}).
41 *
42 * <p>The <em>head</em> of this queue is the <em>least</em> element
43 * with respect to the specified ordering. If multiple elements are
44 * tied for least value, the head is one of those elements -- ties are
45 * broken arbitrarily. The queue retrieval operations {@code poll},
46 * {@code remove}, {@code peek}, and {@code element} access the
47 * element at the head of the queue.
48 *
49 * <p>A priority queue is unbounded, but has an internal
50 * <i>capacity</i> governing the size of an array used to store the
51 * elements on the queue. It is always at least as large as the queue
52 * size. As elements are added to a priority queue, its capacity
53 * grows automatically. The details of the growth policy are not
54 * specified.
55 *
56 * <p>This class and its iterator implement all of the
57 * <em>optional</em> methods of the {@link Collection} and {@link
58 * Iterator} interfaces. The Iterator provided in method {@link
59 * #iterator()} and the Spliterator provided in method {@link #spliterator()}
60 * are <em>not</em> guaranteed to traverse the elements of
61 * the priority queue in any particular order. If you need ordered
62 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
63 *
64 * <p><strong>Note that this implementation is not synchronized.</strong>
65 * Multiple threads should not access a {@code PriorityQueue}
66 * instance concurrently if any of the threads modifies the queue.
67 * Instead, use the thread-safe {@link
68 * java.util.concurrent.PriorityBlockingQueue} class.
69 *
70 * <p>Implementation note: this implementation provides
71 * O(log(n)) time for the enqueuing and dequeuing methods
72 * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
73 * linear time for the {@code remove(Object)} and {@code contains(Object)}
74 * methods; and constant time for the retrieval methods
75 * ({@code peek}, {@code element}, and {@code size}).
76 *
77 * <p>This class is a member of the
78 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
79 * Java Collections Framework</a>.
80 *
81 * @since 1.5
82 * @author Josh Bloch, Doug Lea
83 * @param <E> the type of elements held in this queue
84 */
85 @SuppressWarnings("unchecked")
86 public class PriorityQueue<E> extends AbstractQueue<E>
87 implements java.io.Serializable {
88
89 private static final long serialVersionUID = -7720805057305804111L;
90
91 private static final int DEFAULT_INITIAL_CAPACITY = 11;
92
93 /**
94 * Priority queue represented as a balanced binary heap: the two
95 * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
96 * priority queue is ordered by comparator, or by the elements'
97 * natural ordering, if comparator is null: For each node n in the
98 * heap and each descendant d of n, n <= d. The element with the
99 * lowest value is in queue[0], assuming the queue is nonempty.
100 */
101 transient Object[] queue; // non-private to simplify nested class access
102
103 /**
104 * The number of elements in the priority queue.
105 */
106 int size;
107
108 /**
109 * The comparator, or null if priority queue uses elements'
110 * natural ordering.
111 */
112 private final Comparator<? super E> comparator;
113
114 /**
115 * The number of times this priority queue has been
116 * <i>structurally modified</i>. See AbstractList for gory details.
117 */
118 transient int modCount; // non-private to simplify nested class access
119
120 /**
121 * Creates a {@code PriorityQueue} with the default initial
122 * capacity (11) that orders its elements according to their
123 * {@linkplain Comparable natural ordering}.
124 */
125 public PriorityQueue() {
126 this(DEFAULT_INITIAL_CAPACITY, null);
127 }
128
129 /**
130 * Creates a {@code PriorityQueue} with the specified initial
131 * capacity that orders its elements according to their
132 * {@linkplain Comparable natural ordering}.
133 *
134 * @param initialCapacity the initial capacity for this priority queue
135 * @throws IllegalArgumentException if {@code initialCapacity} is less
136 * than 1
137 */
138 public PriorityQueue(int initialCapacity) {
139 this(initialCapacity, null);
140 }
141
142 /**
143 * Creates a {@code PriorityQueue} with the default initial capacity and
144 * whose elements are ordered according to the specified comparator.
145 *
146 * @param comparator the comparator that will be used to order this
147 * priority queue. If {@code null}, the {@linkplain Comparable
148 * natural ordering} of the elements will be used.
149 * @since 1.8
150 */
151 public PriorityQueue(Comparator<? super E> comparator) {
152 this(DEFAULT_INITIAL_CAPACITY, comparator);
153 }
154
155 /**
156 * Creates a {@code PriorityQueue} with the specified initial capacity
157 * that orders its elements according to the specified comparator.
158 *
159 * @param initialCapacity the initial capacity for this priority queue
160 * @param comparator the comparator that will be used to order this
161 * priority queue. If {@code null}, the {@linkplain Comparable
162 * natural ordering} of the elements will be used.
163 * @throws IllegalArgumentException if {@code initialCapacity} is
164 * less than 1
165 */
166 public PriorityQueue(int initialCapacity,
167 Comparator<? super E> comparator) {
168 // Note: This restriction of at least one is not actually needed,
169 // but continues for 1.5 compatibility
170 if (initialCapacity < 1)
171 throw new IllegalArgumentException();
172 this.queue = new Object[initialCapacity];
173 this.comparator = comparator;
174 }
175
176 /**
177 * Creates a {@code PriorityQueue} containing the elements in the
178 * specified collection. If the specified collection is an instance of
179 * a {@link SortedSet} or is another {@code PriorityQueue}, this
180 * priority queue will be ordered according to the same ordering.
181 * Otherwise, this priority queue will be ordered according to the
182 * {@linkplain Comparable natural ordering} of its elements.
183 *
184 * @param c the collection whose elements are to be placed
185 * into this priority queue
186 * @throws ClassCastException if elements of the specified collection
187 * cannot be compared to one another according to the priority
188 * queue's ordering
189 * @throws NullPointerException if the specified collection or any
190 * of its elements are null
191 */
192 public PriorityQueue(Collection<? extends E> c) {
193 if (c instanceof SortedSet<?>) {
194 SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
195 this.comparator = (Comparator<? super E>) ss.comparator();
196 initElementsFromCollection(ss);
197 }
198 else if (c instanceof PriorityQueue<?>) {
199 PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
200 this.comparator = (Comparator<? super E>) pq.comparator();
201 initFromPriorityQueue(pq);
202 }
203 else {
204 this.comparator = null;
205 initFromCollection(c);
206 }
207 }
208
209 /**
210 * Creates a {@code PriorityQueue} containing the elements in the
211 * specified priority queue. This priority queue will be
212 * ordered according to the same ordering as the given priority
213 * queue.
214 *
215 * @param c the priority queue whose elements are to be placed
216 * into this priority queue
217 * @throws ClassCastException if elements of {@code c} cannot be
218 * compared to one another according to {@code c}'s
219 * ordering
220 * @throws NullPointerException if the specified priority queue or any
221 * of its elements are null
222 */
223 public PriorityQueue(PriorityQueue<? extends E> c) {
224 this.comparator = (Comparator<? super E>) c.comparator();
225 initFromPriorityQueue(c);
226 }
227
228 /**
229 * Creates a {@code PriorityQueue} containing the elements in the
230 * specified sorted set. This priority queue will be ordered
231 * according to the same ordering as the given sorted set.
232 *
233 * @param c the sorted set whose elements are to be placed
234 * into this priority queue
235 * @throws ClassCastException if elements of the specified sorted
236 * set cannot be compared to one another according to the
237 * sorted set's ordering
238 * @throws NullPointerException if the specified sorted set or any
239 * of its elements are null
240 */
241 public PriorityQueue(SortedSet<? extends E> c) {
242 this.comparator = (Comparator<? super E>) c.comparator();
243 initElementsFromCollection(c);
244 }
245
246 /** Ensures that queue[0] exists, helping peek() and poll(). */
247 private static Object[] ensureNonEmpty(Object[] es) {
248 return (es.length > 0) ? es : new Object[1];
249 }
250
251 private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
252 if (c.getClass() == PriorityQueue.class) {
253 this.queue = ensureNonEmpty(c.toArray());
254 this.size = c.size();
255 } else {
256 initFromCollection(c);
257 }
258 }
259
260 private void initElementsFromCollection(Collection<? extends E> c) {
261 Object[] es = c.toArray();
262 int len = es.length;
263 // If c.toArray incorrectly doesn't return Object[], copy it.
264 if (es.getClass() != Object[].class)
265 es = Arrays.copyOf(es, len, Object[].class);
266 if (len == 1 || this.comparator != null)
267 for (Object e : es)
268 if (e == null)
269 throw new NullPointerException();
270 this.queue = ensureNonEmpty(es);
271 this.size = len;
272 }
273
274 /**
275 * Initializes queue array with elements from the given Collection.
276 *
277 * @param c the collection
278 */
279 private void initFromCollection(Collection<? extends E> c) {
280 initElementsFromCollection(c);
281 heapify();
282 }
283
284 /**
285 * The maximum size of array to allocate.
286 * Some VMs reserve some header words in an array.
287 * Attempts to allocate larger arrays may result in
288 * OutOfMemoryError: Requested array size exceeds VM limit
289 */
290 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
291
292 /**
293 * Increases the capacity of the array.
294 *
295 * @param minCapacity the desired minimum capacity
296 */
297 private void grow(int minCapacity) {
298 int oldCapacity = queue.length;
299 // Double size if small; else grow by 50%
300 int newCapacity = oldCapacity + ((oldCapacity < 64) ?
301 (oldCapacity + 2) :
302 (oldCapacity >> 1));
303 // overflow-conscious code
304 if (newCapacity - MAX_ARRAY_SIZE > 0)
305 newCapacity = hugeCapacity(minCapacity);
306 queue = Arrays.copyOf(queue, newCapacity);
307 }
308
309 private static int hugeCapacity(int minCapacity) {
310 if (minCapacity < 0) // overflow
311 throw new OutOfMemoryError();
312 return (minCapacity > MAX_ARRAY_SIZE) ?
313 Integer.MAX_VALUE :
314 MAX_ARRAY_SIZE;
315 }
316
317 /**
318 * Inserts the specified element into this priority queue.
319 *
320 * @return {@code true} (as specified by {@link Collection#add})
321 * @throws ClassCastException if the specified element cannot be
322 * compared with elements currently in this priority queue
323 * according to the priority queue's ordering
324 * @throws NullPointerException if the specified element is null
325 */
326 public boolean add(E e) {
327 return offer(e);
328 }
329
330 /**
331 * Inserts the specified element into this priority queue.
332 *
333 * @return {@code true} (as specified by {@link Queue#offer})
334 * @throws ClassCastException if the specified element cannot be
335 * compared with elements currently in this priority queue
336 * according to the priority queue's ordering
337 * @throws NullPointerException if the specified element is null
338 */
339 public boolean offer(E e) {
340 if (e == null)
341 throw new NullPointerException();
342 modCount++;
343 int i = size;
344 if (i >= queue.length)
345 grow(i + 1);
346 siftUp(i, e);
347 size = i + 1;
348 return true;
349 }
350
351 public E peek() {
352 return (E) queue[0];
353 }
354
355 private int indexOf(Object o) {
356 if (o != null) {
357 final Object[] es = queue;
358 for (int i = 0, n = size; i < n; i++)
359 if (o.equals(es[i]))
360 return i;
361 }
362 return -1;
363 }
364
365 /**
366 * Removes a single instance of the specified element from this queue,
367 * if it is present. More formally, removes an element {@code e} such
368 * that {@code o.equals(e)}, if this queue contains one or more such
369 * elements. Returns {@code true} if and only if this queue contained
370 * the specified element (or equivalently, if this queue changed as a
371 * result of the call).
372 *
373 * @param o element to be removed from this queue, if present
374 * @return {@code true} if this queue changed as a result of the call
375 */
376 public boolean remove(Object o) {
377 int i = indexOf(o);
378 if (i == -1)
379 return false;
380 else {
381 removeAt(i);
382 return true;
383 }
384 }
385
386 /**
387 * Identity-based version for use in Itr.remove.
388 *
389 * @param o element to be removed from this queue, if present
390 */
391 void removeEq(Object o) {
392 final Object[] es = queue;
393 for (int i = 0, n = size; i < n; i++) {
394 if (o == es[i]) {
395 removeAt(i);
396 break;
397 }
398 }
399 }
400
401 /**
402 * Returns {@code true} if this queue contains the specified element.
403 * More formally, returns {@code true} if and only if this queue contains
404 * at least one element {@code e} such that {@code o.equals(e)}.
405 *
406 * @param o object to be checked for containment in this queue
407 * @return {@code true} if this queue contains the specified element
408 */
409 public boolean contains(Object o) {
410 return indexOf(o) >= 0;
411 }
412
413 /**
414 * Returns an array containing all of the elements in this queue.
415 * The elements are in no particular order.
416 *
417 * <p>The returned array will be "safe" in that no references to it are
418 * maintained by this queue. (In other words, this method must allocate
419 * a new array). The caller is thus free to modify the returned array.
420 *
421 * <p>This method acts as bridge between array-based and collection-based
422 * APIs.
423 *
424 * @return an array containing all of the elements in this queue
425 */
426 public Object[] toArray() {
427 return Arrays.copyOf(queue, size);
428 }
429
430 /**
431 * Returns an array containing all of the elements in this queue; the
432 * runtime type of the returned array is that of the specified array.
433 * The returned array elements are in no particular order.
434 * If the queue fits in the specified array, it is returned therein.
435 * Otherwise, a new array is allocated with the runtime type of the
436 * specified array and the size of this queue.
437 *
438 * <p>If the queue fits in the specified array with room to spare
439 * (i.e., the array has more elements than the queue), the element in
440 * the array immediately following the end of the collection is set to
441 * {@code null}.
442 *
443 * <p>Like the {@link #toArray()} method, this method acts as bridge between
444 * array-based and collection-based APIs. Further, this method allows
445 * precise control over the runtime type of the output array, and may,
446 * under certain circumstances, be used to save allocation costs.
447 *
448 * <p>Suppose {@code x} is a queue known to contain only strings.
449 * The following code can be used to dump the queue into a newly
450 * allocated array of {@code String}:
451 *
452 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
453 *
454 * Note that {@code toArray(new Object[0])} is identical in function to
455 * {@code toArray()}.
456 *
457 * @param a the array into which the elements of the queue are to
458 * be stored, if it is big enough; otherwise, a new array of the
459 * same runtime type is allocated for this purpose.
460 * @return an array containing all of the elements in this queue
461 * @throws ArrayStoreException if the runtime type of the specified array
462 * is not a supertype of the runtime type of every element in
463 * this queue
464 * @throws NullPointerException if the specified array is null
465 */
466 public <T> T[] toArray(T[] a) {
467 final int size = this.size;
468 if (a.length < size)
469 // Make a new array of a's runtime type, but my contents:
470 return (T[]) Arrays.copyOf(queue, size, a.getClass());
471 System.arraycopy(queue, 0, a, 0, size);
472 if (a.length > size)
473 a[size] = null;
474 return a;
475 }
476
477 /**
478 * Returns an iterator over the elements in this queue. The iterator
479 * does not return the elements in any particular order.
480 *
481 * @return an iterator over the elements in this queue
482 */
483 public Iterator<E> iterator() {
484 return new Itr();
485 }
486
487 private final class Itr implements Iterator<E> {
488 /**
489 * Index (into queue array) of element to be returned by
490 * subsequent call to next.
491 */
492 private int cursor;
493
494 /**
495 * Index of element returned by most recent call to next,
496 * unless that element came from the forgetMeNot list.
497 * Set to -1 if element is deleted by a call to remove.
498 */
499 private int lastRet = -1;
500
501 /**
502 * A queue of elements that were moved from the unvisited portion of
503 * the heap into the visited portion as a result of "unlucky" element
504 * removals during the iteration. (Unlucky element removals are those
505 * that require a siftup instead of a siftdown.) We must visit all of
506 * the elements in this list to complete the iteration. We do this
507 * after we've completed the "normal" iteration.
508 *
509 * We expect that most iterations, even those involving removals,
510 * will not need to store elements in this field.
511 */
512 private ArrayDeque<E> forgetMeNot;
513
514 /**
515 * Element returned by the most recent call to next iff that
516 * element was drawn from the forgetMeNot list.
517 */
518 private E lastRetElt;
519
520 /**
521 * The modCount value that the iterator believes that the backing
522 * Queue should have. If this expectation is violated, the iterator
523 * has detected concurrent modification.
524 */
525 private int expectedModCount = modCount;
526
527 Itr() {} // prevent access constructor creation
528
529 public boolean hasNext() {
530 return cursor < size ||
531 (forgetMeNot != null && !forgetMeNot.isEmpty());
532 }
533
534 public E next() {
535 if (expectedModCount != modCount)
536 throw new ConcurrentModificationException();
537 if (cursor < size)
538 return (E) queue[lastRet = cursor++];
539 if (forgetMeNot != null) {
540 lastRet = -1;
541 lastRetElt = forgetMeNot.poll();
542 if (lastRetElt != null)
543 return lastRetElt;
544 }
545 throw new NoSuchElementException();
546 }
547
548 public void remove() {
549 if (expectedModCount != modCount)
550 throw new ConcurrentModificationException();
551 if (lastRet != -1) {
552 E moved = PriorityQueue.this.removeAt(lastRet);
553 lastRet = -1;
554 if (moved == null)
555 cursor--;
556 else {
557 if (forgetMeNot == null)
558 forgetMeNot = new ArrayDeque<>();
559 forgetMeNot.add(moved);
560 }
561 } else if (lastRetElt != null) {
562 PriorityQueue.this.removeEq(lastRetElt);
563 lastRetElt = null;
564 } else {
565 throw new IllegalStateException();
566 }
567 expectedModCount = modCount;
568 }
569 }
570
571 public int size() {
572 return size;
573 }
574
575 /**
576 * Removes all of the elements from this priority queue.
577 * The queue will be empty after this call returns.
578 */
579 public void clear() {
580 modCount++;
581 final Object[] es = queue;
582 for (int i = 0, n = size; i < n; i++)
583 es[i] = null;
584 size = 0;
585 }
586
587 public E poll() {
588 final Object[] es;
589 final E result;
590
591 if ((result = (E) ((es = queue)[0])) != null) {
592 modCount++;
593 final int n;
594 final E x = (E) es[(n = --size)];
595 es[n] = null;
596 if (n > 0) {
597 final Comparator<? super E> cmp;
598 if ((cmp = comparator) == null)
599 siftDownComparable(0, x, es, n);
600 else
601 siftDownUsingComparator(0, x, es, n, cmp);
602 }
603 }
604 return result;
605 }
606
607 /**
608 * Removes the ith element from queue.
609 *
610 * Normally this method leaves the elements at up to i-1,
611 * inclusive, untouched. Under these circumstances, it returns
612 * null. Occasionally, in order to maintain the heap invariant,
613 * it must swap a later element of the list with one earlier than
614 * i. Under these circumstances, this method returns the element
615 * that was previously at the end of the list and is now at some
616 * position before i. This fact is used by iterator.remove so as to
617 * avoid missing traversing elements.
618 */
619 E removeAt(int i) {
620 // assert i >= 0 && i < size;
621 final Object[] es = queue;
622 modCount++;
623 int s = --size;
624 if (s == i) // removed last element
625 es[i] = null;
626 else {
627 E moved = (E) es[s];
628 es[s] = null;
629 siftDown(i, moved);
630 if (es[i] == moved) {
631 siftUp(i, moved);
632 if (es[i] != moved)
633 return moved;
634 }
635 }
636 return null;
637 }
638
639 /**
640 * Inserts item x at position k, maintaining heap invariant by
641 * promoting x up the tree until it is greater than or equal to
642 * its parent, or is the root.
643 *
644 * To simplify and speed up coercions and comparisons, the
645 * Comparable and Comparator versions are separated into different
646 * methods that are otherwise identical. (Similarly for siftDown.)
647 *
648 * @param k the position to fill
649 * @param x the item to insert
650 */
651 private void siftUp(int k, E x) {
652 if (comparator != null)
653 siftUpUsingComparator(k, x, queue, comparator);
654 else
655 siftUpComparable(k, x, queue);
656 }
657
658 private static <T> void siftUpComparable(int k, T x, Object[] es) {
659 Comparable<? super T> key = (Comparable<? super T>) x;
660 while (k > 0) {
661 int parent = (k - 1) >>> 1;
662 Object e = es[parent];
663 if (key.compareTo((T) e) >= 0)
664 break;
665 es[k] = e;
666 k = parent;
667 }
668 es[k] = key;
669 }
670
671 private static <T> void siftUpUsingComparator(
672 int k, T x, Object[] es, Comparator<? super T> cmp) {
673 while (k > 0) {
674 int parent = (k - 1) >>> 1;
675 Object e = es[parent];
676 if (cmp.compare(x, (T) e) >= 0)
677 break;
678 es[k] = e;
679 k = parent;
680 }
681 es[k] = x;
682 }
683
684 /**
685 * Inserts item x at position k, maintaining heap invariant by
686 * demoting x down the tree repeatedly until it is less than or
687 * equal to its children or is a leaf.
688 *
689 * @param k the position to fill
690 * @param x the item to insert
691 */
692 private void siftDown(int k, E x) {
693 if (comparator != null)
694 siftDownUsingComparator(k, x, queue, size, comparator);
695 else
696 siftDownComparable(k, x, queue, size);
697 }
698
699 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
700 // assert n > 0;
701 Comparable<? super T> key = (Comparable<? super T>)x;
702 int half = n >>> 1; // loop while a non-leaf
703 while (k < half) {
704 int child = (k << 1) + 1; // assume left child is least
705 Object c = es[child];
706 int right = child + 1;
707 if (right < n &&
708 ((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
709 c = es[child = right];
710 if (key.compareTo((T) c) <= 0)
711 break;
712 es[k] = c;
713 k = child;
714 }
715 es[k] = key;
716 }
717
718 private static <T> void siftDownUsingComparator(
719 int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
720 // assert n > 0;
721 int half = n >>> 1;
722 while (k < half) {
723 int child = (k << 1) + 1;
724 Object c = es[child];
725 int right = child + 1;
726 if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
727 c = es[child = right];
728 if (cmp.compare(x, (T) c) <= 0)
729 break;
730 es[k] = c;
731 k = child;
732 }
733 es[k] = x;
734 }
735
736 /**
737 * Establishes the heap invariant (described above) in the entire tree,
738 * assuming nothing about the order of the elements prior to the call.
739 * This classic algorithm due to Floyd (1964) is known to be O(size).
740 */
741 private void heapify() {
742 final Object[] es = queue;
743 int n = size, i = (n >>> 1) - 1;
744 final Comparator<? super E> cmp;
745 if ((cmp = comparator) == null)
746 for (; i >= 0; i--)
747 siftDownComparable(i, (E) es[i], es, n);
748 else
749 for (; i >= 0; i--)
750 siftDownUsingComparator(i, (E) es[i], es, n, cmp);
751 }
752
753 /**
754 * Returns the comparator used to order the elements in this
755 * queue, or {@code null} if this queue is sorted according to
756 * the {@linkplain Comparable natural ordering} of its elements.
757 *
758 * @return the comparator used to order this queue, or
759 * {@code null} if this queue is sorted according to the
760 * natural ordering of its elements
761 */
762 public Comparator<? super E> comparator() {
763 return comparator;
764 }
765
766 /**
767 * Saves this queue to a stream (that is, serializes it).
768 *
769 * @param s the stream
770 * @throws java.io.IOException if an I/O error occurs
771 * @serialData The length of the array backing the instance is
772 * emitted (int), followed by all of its elements
773 * (each an {@code Object}) in the proper order.
774 */
775 private void writeObject(java.io.ObjectOutputStream s)
776 throws java.io.IOException {
777 // Write out element count, and any hidden stuff
778 s.defaultWriteObject();
779
780 // Write out array length, for compatibility with 1.5 version
781 s.writeInt(Math.max(2, size + 1));
782
783 // Write out all elements in the "proper order".
784 final Object[] es = queue;
785 for (int i = 0, n = size; i < n; i++)
786 s.writeObject(es[i]);
787 }
788
789 /**
790 * Reconstitutes the {@code PriorityQueue} instance from a stream
791 * (that is, deserializes it).
792 *
793 * @param s the stream
794 * @throws ClassNotFoundException if the class of a serialized object
795 * could not be found
796 * @throws java.io.IOException if an I/O error occurs
797 */
798 private void readObject(java.io.ObjectInputStream s)
799 throws java.io.IOException, ClassNotFoundException {
800 // Read in size, and any hidden stuff
801 s.defaultReadObject();
802
803 // Read in (and discard) array length
804 s.readInt();
805
806 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
807 final Object[] es = queue = new Object[Math.max(size, 1)];
808
809 // Read in all elements.
810 for (int i = 0, n = size; i < n; i++)
811 es[i] = s.readObject();
812
813 // Elements are guaranteed to be in "proper order", but the
814 // spec has never explained what that might be.
815 heapify();
816 }
817
818 /**
819 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
820 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
821 * queue. The spliterator does not traverse elements in any particular order
822 * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
823 *
824 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
825 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
826 * Overriding implementations should document the reporting of additional
827 * characteristic values.
828 *
829 * @return a {@code Spliterator} over the elements in this queue
830 * @since 1.8
831 */
832 public final Spliterator<E> spliterator() {
833 return new PriorityQueueSpliterator(0, -1, 0);
834 }
835
836 final class PriorityQueueSpliterator implements Spliterator<E> {
837 private int index; // current index, modified on advance/split
838 private int fence; // -1 until first use
839 private int expectedModCount; // initialized when fence set
840
841 /** Creates new spliterator covering the given range. */
842 PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
843 this.index = origin;
844 this.fence = fence;
845 this.expectedModCount = expectedModCount;
846 }
847
848 private int getFence() { // initialize fence to size on first use
849 int hi;
850 if ((hi = fence) < 0) {
851 expectedModCount = modCount;
852 hi = fence = size;
853 }
854 return hi;
855 }
856
857 public PriorityQueueSpliterator trySplit() {
858 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
859 return (lo >= mid) ? null :
860 new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
861 }
862
863 public void forEachRemaining(Consumer<? super E> action) {
864 if (action == null)
865 throw new NullPointerException();
866 if (fence < 0) { fence = size; expectedModCount = modCount; }
867 final Object[] es = queue;
868 int i, hi; E e;
869 for (i = index, index = hi = fence; i < hi; i++) {
870 if ((e = (E) es[i]) == null)
871 break; // must be CME
872 action.accept(e);
873 }
874 if (modCount != expectedModCount)
875 throw new ConcurrentModificationException();
876 }
877
878 public boolean tryAdvance(Consumer<? super E> action) {
879 if (action == null)
880 throw new NullPointerException();
881 if (fence < 0) { fence = size; expectedModCount = modCount; }
882 int i;
883 if ((i = index) < fence) {
884 index = i + 1;
885 E e;
886 if ((e = (E) queue[i]) == null
887 || modCount != expectedModCount)
888 throw new ConcurrentModificationException();
889 action.accept(e);
890 return true;
891 }
892 return false;
893 }
894
895 public long estimateSize() {
896 return getFence() - index;
897 }
898
899 public int characteristics() {
900 return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
901 }
902 }
903
904 /**
905 * @throws NullPointerException {@inheritDoc}
906 */
907 public boolean removeIf(Predicate<? super E> filter) {
908 Objects.requireNonNull(filter);
909 return bulkRemove(filter);
910 }
911
912 /**
913 * @throws NullPointerException {@inheritDoc}
914 */
915 public boolean removeAll(Collection<?> c) {
916 Objects.requireNonNull(c);
917 return bulkRemove(e -> c.contains(e));
918 }
919
920 /**
921 * @throws NullPointerException {@inheritDoc}
922 */
923 public boolean retainAll(Collection<?> c) {
924 Objects.requireNonNull(c);
925 return bulkRemove(e -> !c.contains(e));
926 }
927
928 // A tiny bit set implementation
929
930 private static long[] nBits(int n) {
931 return new long[((n - 1) >> 6) + 1];
932 }
933 private static void setBit(long[] bits, int i) {
934 bits[i >> 6] |= 1L << i;
935 }
936 private static boolean isClear(long[] bits, int i) {
937 return (bits[i >> 6] & (1L << i)) == 0;
938 }
939
940 /** Implementation of bulk remove methods. */
941 private boolean bulkRemove(Predicate<? super E> filter) {
942 final int expectedModCount = ++modCount;
943 final Object[] es = queue;
944 final int end = size;
945 int i;
946 // Optimize for initial run of survivors
947 for (i = 0; i < end && !filter.test((E) es[i]); i++)
948 ;
949 if (i >= end) {
950 if (modCount != expectedModCount)
951 throw new ConcurrentModificationException();
952 return false;
953 }
954 // Tolerate predicates that reentrantly access the collection for
955 // read (but writers still get CME), so traverse once to find
956 // elements to delete, a second pass to physically expunge.
957 final int beg = i;
958 final long[] deathRow = nBits(end - beg);
959 deathRow[0] = 1L; // set bit 0
960 for (i = beg + 1; i < end; i++)
961 if (filter.test((E) es[i]))
962 setBit(deathRow, i - beg);
963 if (modCount != expectedModCount)
964 throw new ConcurrentModificationException();
965 int w = beg;
966 for (i = beg; i < end; i++)
967 if (isClear(deathRow, i - beg))
968 es[w++] = es[i];
969 for (i = size = w; i < end; i++)
970 es[i] = null;
971 heapify();
972 return true;
973 }
974
975 /**
976 * @throws NullPointerException {@inheritDoc}
977 */
978 public void forEach(Consumer<? super E> action) {
979 Objects.requireNonNull(action);
980 final int expectedModCount = modCount;
981 final Object[] es = queue;
982 for (int i = 0, n = size; i < n; i++)
983 action.accept((E) es[i]);
984 if (expectedModCount != modCount)
985 throw new ConcurrentModificationException();
986 }
987 }