1 /*
2 * Copyright (c) 2003, 2019, 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 *
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20 *
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24 */
25
26 package java.util;
27
28 import java.util.function.Consumer;
29 import java.util.function.Predicate;
30 import jdk.internal.access.SharedSecrets;
31 import jdk.internal.util.ArraysSupport;
32
33 /**
34 * An unbounded priority {@linkplain Queue queue} based on a priority heap.
35 * The elements of the priority queue are ordered according to their
36 * {@linkplain Comparable natural ordering}, or by a {@link Comparator}
37 * provided at queue construction time, depending on which constructor is
38 * used. A priority queue does not permit {@code null} elements.
39 * A priority queue relying on natural ordering also does not permit
40 * insertion of non-comparable objects (doing so may result in
41 * {@code ClassCastException}).
42 *
43 * <p>The <em>head</em> of this queue is the <em>least</em> element
44 * with respect to the specified ordering. If multiple elements are
45 * tied for least value, the head is one of those elements -- ties are
46 * broken arbitrarily. The queue retrieval operations {@code poll},
47 * {@code remove}, {@code peek}, and {@code element} access the
48 * element at the head of the queue.
49 *
50 * <p>A priority queue is unbounded, but has an internal
51 * <i>capacity</i> governing the size of an array used to store the
52 * elements on the queue. It is always at least as large as the queue
53 * size. As elements are added to a priority queue, its capacity
54 * grows automatically. The details of the growth policy are not
55 * specified.
56 *
57 * <p>This class and its iterator implement all of the
58 * <em>optional</em> methods of the {@link Collection} and {@link
59 * Iterator} interfaces. The Iterator provided in method {@link
60 * #iterator()} and the Spliterator provided in method {@link #spliterator()}
61 * are <em>not</em> guaranteed to traverse the elements of
62 * the priority queue in any particular order. If you need ordered
63 * traversal, consider using {@code Arrays.sort(pq.toArray())}.
64 *
65 * <p><strong>Note that this implementation is not synchronized.</strong>
66 * Multiple threads should not access a {@code PriorityQueue}
67 * instance concurrently if any of the threads modifies the queue.
68 * Instead, use the thread-safe {@link
69 * java.util.concurrent.PriorityBlockingQueue} class.
70 *
71 * <p>Implementation note: this implementation provides
72 * O(log(n)) time for the enqueuing and dequeuing methods
73 * ({@code offer}, {@code poll}, {@code remove()} and {@code add});
74 * linear time for the {@code remove(Object)} and {@code contains(Object)}
75 * methods; and constant time for the retrieval methods
76 * ({@code peek}, {@code element}, and {@code size}).
77 *
78 * <p>This class is a member of the
79 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
80 * Java Collections Framework</a>.
81 *
82 * @since 1.5
83 * @author Josh Bloch, Doug Lea
84 * @param <E> the type of elements held in this queue
85 */
86 @SuppressWarnings("unchecked")
87 public class PriorityQueue<E> extends AbstractQueue<E>
88 implements java.io.Serializable {
89
90 private static final long serialVersionUID = -7720805057305804111L;
91
92 private static final int DEFAULT_INITIAL_CAPACITY = 11;
93
94 /**
95 * Priority queue represented as a balanced binary heap: the two
96 * children of queue[n] are queue[2*n+1] and queue[2*(n+1)]. The
97 * priority queue is ordered by comparator, or by the elements'
98 * natural ordering, if comparator is null: For each node n in the
99 * heap and each descendant d of n, n <= d. The element with the
100 * lowest value is in queue[0], assuming the queue is nonempty.
101 */
102 transient Object[] queue; // non-private to simplify nested class access
103
104 /**
105 * The number of elements in the priority queue.
106 */
107 int size;
108
109 /**
110 * The comparator, or null if priority queue uses elements'
111 * natural ordering.
112 */
113 private final Comparator<? super E> comparator;
114
115 /**
116 * The number of times this priority queue has been
117 * <i>structurally modified</i>. See AbstractList for gory details.
118 */
119 transient int modCount; // non-private to simplify nested class access
120
121 /**
122 * Creates a {@code PriorityQueue} with the default initial
123 * capacity (11) that orders its elements according to their
124 * {@linkplain Comparable natural ordering}.
125 */
126 public PriorityQueue() {
127 this(DEFAULT_INITIAL_CAPACITY, null);
128 }
129
130 /**
131 * Creates a {@code PriorityQueue} with the specified initial
132 * capacity that orders its elements according to their
133 * {@linkplain Comparable natural ordering}.
134 *
135 * @param initialCapacity the initial capacity for this priority queue
136 * @throws IllegalArgumentException if {@code initialCapacity} is less
137 * than 1
138 */
139 public PriorityQueue(int initialCapacity) {
140 this(initialCapacity, null);
141 }
142
143 /**
144 * Creates a {@code PriorityQueue} with the default initial capacity and
145 * whose elements are ordered according to the specified comparator.
146 *
147 * @param comparator the comparator that will be used to order this
148 * priority queue. If {@code null}, the {@linkplain Comparable
149 * natural ordering} of the elements will be used.
150 * @since 1.8
151 */
152 public PriorityQueue(Comparator<? super E> comparator) {
153 this(DEFAULT_INITIAL_CAPACITY, comparator);
154 }
155
156 /**
157 * Creates a {@code PriorityQueue} with the specified initial capacity
158 * that orders its elements according to the specified comparator.
159 *
160 * @param initialCapacity the initial capacity for this priority queue
161 * @param comparator the comparator that will be used to order this
162 * priority queue. If {@code null}, the {@linkplain Comparable
163 * natural ordering} of the elements will be used.
164 * @throws IllegalArgumentException if {@code initialCapacity} is
165 * less than 1
166 */
167 public PriorityQueue(int initialCapacity,
168 Comparator<? super E> comparator) {
169 // Note: This restriction of at least one is not actually needed,
170 // but continues for 1.5 compatibility
171 if (initialCapacity < 1)
172 throw new IllegalArgumentException();
173 this.queue = new Object[initialCapacity];
174 this.comparator = comparator;
175 }
176
177 /**
178 * Creates a {@code PriorityQueue} containing the elements in the
179 * specified collection. If the specified collection is an instance of
180 * a {@link SortedSet} or is another {@code PriorityQueue}, this
181 * priority queue will be ordered according to the same ordering.
182 * Otherwise, this priority queue will be ordered according to the
183 * {@linkplain Comparable natural ordering} of its elements.
184 *
185 * @param c the collection whose elements are to be placed
186 * into this priority queue
187 * @throws ClassCastException if elements of the specified collection
188 * cannot be compared to one another according to the priority
189 * queue's ordering
190 * @throws NullPointerException if the specified collection or any
191 * of its elements are null
192 */
193 public PriorityQueue(Collection<? extends E> c) {
194 if (c instanceof SortedSet<?>) {
195 SortedSet<? extends E> ss = (SortedSet<? extends E>) c;
196 this.comparator = (Comparator<? super E>) ss.comparator();
197 initElementsFromCollection(ss);
198 }
199 else if (c instanceof PriorityQueue<?>) {
200 PriorityQueue<? extends E> pq = (PriorityQueue<? extends E>) c;
201 this.comparator = (Comparator<? super E>) pq.comparator();
202 initFromPriorityQueue(pq);
203 }
204 else {
205 this.comparator = null;
206 initFromCollection(c);
207 }
208 }
209
210 /**
211 * Creates a {@code PriorityQueue} containing the elements in the
212 * specified priority queue. This priority queue will be
213 * ordered according to the same ordering as the given priority
214 * queue.
215 *
216 * @param c the priority queue whose elements are to be placed
217 * into this priority queue
218 * @throws ClassCastException if elements of {@code c} cannot be
219 * compared to one another according to {@code c}'s
220 * ordering
221 * @throws NullPointerException if the specified priority queue or any
222 * of its elements are null
223 */
224 public PriorityQueue(PriorityQueue<? extends E> c) {
225 this.comparator = (Comparator<? super E>) c.comparator();
226 initFromPriorityQueue(c);
227 }
228
229 /**
230 * Creates a {@code PriorityQueue} containing the elements in the
231 * specified sorted set. This priority queue will be ordered
232 * according to the same ordering as the given sorted set.
233 *
234 * @param c the sorted set whose elements are to be placed
235 * into this priority queue
236 * @throws ClassCastException if elements of the specified sorted
237 * set cannot be compared to one another according to the
238 * sorted set's ordering
239 * @throws NullPointerException if the specified sorted set or any
240 * of its elements are null
241 */
242 public PriorityQueue(SortedSet<? extends E> c) {
243 this.comparator = (Comparator<? super E>) c.comparator();
244 initElementsFromCollection(c);
245 }
246
247 /** Ensures that queue[0] exists, helping peek() and poll(). */
248 private static Object[] ensureNonEmpty(Object[] es) {
249 return (es.length > 0) ? es : new Object[1];
250 }
251
252 private void initFromPriorityQueue(PriorityQueue<? extends E> c) {
253 if (c.getClass() == PriorityQueue.class) {
254 this.queue = ensureNonEmpty(c.toArray());
255 this.size = c.size();
256 } else {
257 initFromCollection(c);
258 }
259 }
260
261 private void initElementsFromCollection(Collection<? extends E> c) {
262 Object[] es = c.toArray();
263 int len = es.length;
264 // If c.toArray incorrectly doesn't return Object[], copy it.
265 if (es.getClass() != Object[].class)
266 es = Arrays.copyOf(es, len, Object[].class);
267 if (len == 1 || this.comparator != null)
268 for (Object e : es)
269 if (e == null)
270 throw new NullPointerException();
271 this.queue = ensureNonEmpty(es);
272 this.size = len;
273 }
274
275 /**
276 * Initializes queue array with elements from the given Collection.
277 *
278 * @param c the collection
279 */
280 private void initFromCollection(Collection<? extends E> c) {
281 initElementsFromCollection(c);
282 heapify();
283 }
284
285 /**
286 * Increases the capacity of the array.
287 *
288 * @param minCapacity the desired minimum capacity
289 */
290 private void grow(int minCapacity) {
291 int oldCapacity = queue.length;
292 // Double size if small; else grow by 50%
293 int newCapacity = ArraysSupport.newCapacity(oldCapacity,
294 minCapacity - oldCapacity,
295 oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1);
296 queue = Arrays.copyOf(queue, newCapacity);
297 }
298
299 /**
300 * Inserts the specified element into this priority queue.
301 *
302 * @return {@code true} (as specified by {@link Collection#add})
303 * @throws ClassCastException if the specified element cannot be
304 * compared with elements currently in this priority queue
305 * according to the priority queue's ordering
306 * @throws NullPointerException if the specified element is null
307 */
308 public boolean add(E e) {
309 return offer(e);
310 }
311
312 /**
313 * Inserts the specified element into this priority queue.
314 *
315 * @return {@code true} (as specified by {@link Queue#offer})
316 * @throws ClassCastException if the specified element cannot be
317 * compared with elements currently in this priority queue
318 * according to the priority queue's ordering
319 * @throws NullPointerException if the specified element is null
320 */
321 public boolean offer(E e) {
322 if (e == null)
323 throw new NullPointerException();
324 modCount++;
325 int i = size;
326 if (i >= queue.length)
327 grow(i + 1);
328 siftUp(i, e);
329 size = i + 1;
330 return true;
331 }
332
333 public E peek() {
334 return (E) queue[0];
335 }
336
337 private int indexOf(Object o) {
338 if (o != null) {
339 final Object[] es = queue;
340 for (int i = 0, n = size; i < n; i++)
341 if (o.equals(es[i]))
342 return i;
343 }
344 return -1;
345 }
346
347 /**
348 * Removes a single instance of the specified element from this queue,
349 * if it is present. More formally, removes an element {@code e} such
350 * that {@code o.equals(e)}, if this queue contains one or more such
351 * elements. Returns {@code true} if and only if this queue contained
352 * the specified element (or equivalently, if this queue changed as a
353 * result of the call).
354 *
355 * @param o element to be removed from this queue, if present
356 * @return {@code true} if this queue changed as a result of the call
357 */
358 public boolean remove(Object o) {
359 int i = indexOf(o);
360 if (i == -1)
361 return false;
362 else {
363 removeAt(i);
364 return true;
365 }
366 }
367
368 /**
369 * Identity-based version for use in Itr.remove.
370 *
371 * @param o element to be removed from this queue, if present
372 */
373 void removeEq(Object o) {
374 final Object[] es = queue;
375 for (int i = 0, n = size; i < n; i++) {
376 if (o == es[i]) {
377 removeAt(i);
378 break;
379 }
380 }
381 }
382
383 /**
384 * Returns {@code true} if this queue contains the specified element.
385 * More formally, returns {@code true} if and only if this queue contains
386 * at least one element {@code e} such that {@code o.equals(e)}.
387 *
388 * @param o object to be checked for containment in this queue
389 * @return {@code true} if this queue contains the specified element
390 */
391 public boolean contains(Object o) {
392 return indexOf(o) >= 0;
393 }
394
395 /**
396 * Returns an array containing all of the elements in this queue.
397 * The elements are in no particular order.
398 *
399 * <p>The returned array will be "safe" in that no references to it are
400 * maintained by this queue. (In other words, this method must allocate
401 * a new array). The caller is thus free to modify the returned array.
402 *
403 * <p>This method acts as bridge between array-based and collection-based
404 * APIs.
405 *
406 * @return an array containing all of the elements in this queue
407 */
408 public Object[] toArray() {
409 return Arrays.copyOf(queue, size);
410 }
411
412 /**
413 * Returns an array containing all of the elements in this queue; the
414 * runtime type of the returned array is that of the specified array.
415 * The returned array elements are in no particular order.
416 * If the queue fits in the specified array, it is returned therein.
417 * Otherwise, a new array is allocated with the runtime type of the
418 * specified array and the size of this queue.
419 *
420 * <p>If the queue fits in the specified array with room to spare
421 * (i.e., the array has more elements than the queue), the element in
422 * the array immediately following the end of the collection is set to
423 * {@code null}.
424 *
425 * <p>Like the {@link #toArray()} method, this method acts as bridge between
426 * array-based and collection-based APIs. Further, this method allows
427 * precise control over the runtime type of the output array, and may,
428 * under certain circumstances, be used to save allocation costs.
429 *
430 * <p>Suppose {@code x} is a queue known to contain only strings.
431 * The following code can be used to dump the queue into a newly
432 * allocated array of {@code String}:
433 *
434 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
435 *
436 * Note that {@code toArray(new Object[0])} is identical in function to
437 * {@code toArray()}.
438 *
439 * @param a the array into which the elements of the queue are to
440 * be stored, if it is big enough; otherwise, a new array of the
441 * same runtime type is allocated for this purpose.
442 * @return an array containing all of the elements in this queue
443 * @throws ArrayStoreException if the runtime type of the specified array
444 * is not a supertype of the runtime type of every element in
445 * this queue
446 * @throws NullPointerException if the specified array is null
447 */
448 public <T> T[] toArray(T[] a) {
449 final int size = this.size;
450 if (a.length < size)
451 // Make a new array of a's runtime type, but my contents:
452 return (T[]) Arrays.copyOf(queue, size, a.getClass());
453 System.arraycopy(queue, 0, a, 0, size);
454 if (a.length > size)
455 a[size] = null;
456 return a;
457 }
458
459 /**
460 * Returns an iterator over the elements in this queue. The iterator
461 * does not return the elements in any particular order.
462 *
463 * @return an iterator over the elements in this queue
464 */
465 public Iterator<E> iterator() {
466 return new Itr();
467 }
468
469 private final class Itr implements Iterator<E> {
470 /**
471 * Index (into queue array) of element to be returned by
472 * subsequent call to next.
473 */
474 private int cursor;
475
476 /**
477 * Index of element returned by most recent call to next,
478 * unless that element came from the forgetMeNot list.
479 * Set to -1 if element is deleted by a call to remove.
480 */
481 private int lastRet = -1;
482
483 /**
484 * A queue of elements that were moved from the unvisited portion of
485 * the heap into the visited portion as a result of "unlucky" element
486 * removals during the iteration. (Unlucky element removals are those
487 * that require a siftup instead of a siftdown.) We must visit all of
488 * the elements in this list to complete the iteration. We do this
489 * after we've completed the "normal" iteration.
490 *
491 * We expect that most iterations, even those involving removals,
492 * will not need to store elements in this field.
493 */
494 private ArrayDeque<E> forgetMeNot;
495
496 /**
497 * Element returned by the most recent call to next iff that
498 * element was drawn from the forgetMeNot list.
499 */
500 private E lastRetElt;
501
502 /**
503 * The modCount value that the iterator believes that the backing
504 * Queue should have. If this expectation is violated, the iterator
505 * has detected concurrent modification.
506 */
507 private int expectedModCount = modCount;
508
509 Itr() {} // prevent access constructor creation
510
511 public boolean hasNext() {
512 return cursor < size ||
513 (forgetMeNot != null && !forgetMeNot.isEmpty());
514 }
515
516 public E next() {
517 if (expectedModCount != modCount)
518 throw new ConcurrentModificationException();
519 if (cursor < size)
520 return (E) queue[lastRet = cursor++];
521 if (forgetMeNot != null) {
522 lastRet = -1;
523 lastRetElt = forgetMeNot.poll();
524 if (lastRetElt != null)
525 return lastRetElt;
526 }
527 throw new NoSuchElementException();
528 }
529
530 public void remove() {
531 if (expectedModCount != modCount)
532 throw new ConcurrentModificationException();
533 if (lastRet != -1) {
534 E moved = PriorityQueue.this.removeAt(lastRet);
535 lastRet = -1;
536 if (moved == null)
537 cursor--;
538 else {
539 if (forgetMeNot == null)
540 forgetMeNot = new ArrayDeque<>();
541 forgetMeNot.add(moved);
542 }
543 } else if (lastRetElt != null) {
544 PriorityQueue.this.removeEq(lastRetElt);
545 lastRetElt = null;
546 } else {
547 throw new IllegalStateException();
548 }
549 expectedModCount = modCount;
550 }
551 }
552
553 public int size() {
554 return size;
555 }
556
557 /**
558 * Removes all of the elements from this priority queue.
559 * The queue will be empty after this call returns.
560 */
561 public void clear() {
562 modCount++;
563 final Object[] es = queue;
564 for (int i = 0, n = size; i < n; i++)
565 es[i] = null;
566 size = 0;
567 }
568
569 public E poll() {
570 final Object[] es;
571 final E result;
572
573 if ((result = (E) ((es = queue)[0])) != null) {
574 modCount++;
575 final int n;
576 final E x = (E) es[(n = --size)];
577 es[n] = null;
578 if (n > 0) {
579 final Comparator<? super E> cmp;
580 if ((cmp = comparator) == null)
581 siftDownComparable(0, x, es, n);
582 else
583 siftDownUsingComparator(0, x, es, n, cmp);
584 }
585 }
586 return result;
587 }
588
589 /**
590 * Removes the ith element from queue.
591 *
592 * Normally this method leaves the elements at up to i-1,
593 * inclusive, untouched. Under these circumstances, it returns
594 * null. Occasionally, in order to maintain the heap invariant,
595 * it must swap a later element of the list with one earlier than
596 * i. Under these circumstances, this method returns the element
597 * that was previously at the end of the list and is now at some
598 * position before i. This fact is used by iterator.remove so as to
599 * avoid missing traversing elements.
600 */
601 E removeAt(int i) {
602 // assert i >= 0 && i < size;
603 final Object[] es = queue;
604 modCount++;
605 int s = --size;
606 if (s == i) // removed last element
607 es[i] = null;
608 else {
609 E moved = (E) es[s];
610 es[s] = null;
611 siftDown(i, moved);
612 if (es[i] == moved) {
613 siftUp(i, moved);
614 if (es[i] != moved)
615 return moved;
616 }
617 }
618 return null;
619 }
620
621 /**
622 * Inserts item x at position k, maintaining heap invariant by
623 * promoting x up the tree until it is greater than or equal to
624 * its parent, or is the root.
625 *
626 * To simplify and speed up coercions and comparisons, the
627 * Comparable and Comparator versions are separated into different
628 * methods that are otherwise identical. (Similarly for siftDown.)
629 *
630 * @param k the position to fill
631 * @param x the item to insert
632 */
633 private void siftUp(int k, E x) {
634 if (comparator != null)
635 siftUpUsingComparator(k, x, queue, comparator);
636 else
637 siftUpComparable(k, x, queue);
638 }
639
640 private static <T> void siftUpComparable(int k, T x, Object[] es) {
641 Comparable<? super T> key = (Comparable<? super T>) x;
642 while (k > 0) {
643 int parent = (k - 1) >>> 1;
644 Object e = es[parent];
645 if (key.compareTo((T) e) >= 0)
646 break;
647 es[k] = e;
648 k = parent;
649 }
650 es[k] = key;
651 }
652
653 private static <T> void siftUpUsingComparator(
654 int k, T x, Object[] es, Comparator<? super T> cmp) {
655 while (k > 0) {
656 int parent = (k - 1) >>> 1;
657 Object e = es[parent];
658 if (cmp.compare(x, (T) e) >= 0)
659 break;
660 es[k] = e;
661 k = parent;
662 }
663 es[k] = x;
664 }
665
666 /**
667 * Inserts item x at position k, maintaining heap invariant by
668 * demoting x down the tree repeatedly until it is less than or
669 * equal to its children or is a leaf.
670 *
671 * @param k the position to fill
672 * @param x the item to insert
673 */
674 private void siftDown(int k, E x) {
675 if (comparator != null)
676 siftDownUsingComparator(k, x, queue, size, comparator);
677 else
678 siftDownComparable(k, x, queue, size);
679 }
680
681 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
682 // assert n > 0;
683 Comparable<? super T> key = (Comparable<? super T>)x;
684 int half = n >>> 1; // loop while a non-leaf
685 while (k < half) {
686 int child = (k << 1) + 1; // assume left child is least
687 Object c = es[child];
688 int right = child + 1;
689 if (right < n &&
690 ((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
691 c = es[child = right];
692 if (key.compareTo((T) c) <= 0)
693 break;
694 es[k] = c;
695 k = child;
696 }
697 es[k] = key;
698 }
699
700 private static <T> void siftDownUsingComparator(
701 int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
702 // assert n > 0;
703 int half = n >>> 1;
704 while (k < half) {
705 int child = (k << 1) + 1;
706 Object c = es[child];
707 int right = child + 1;
708 if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
709 c = es[child = right];
710 if (cmp.compare(x, (T) c) <= 0)
711 break;
712 es[k] = c;
713 k = child;
714 }
715 es[k] = x;
716 }
717
718 /**
719 * Establishes the heap invariant (described above) in the entire tree,
720 * assuming nothing about the order of the elements prior to the call.
721 * This classic algorithm due to Floyd (1964) is known to be O(size).
722 */
723 private void heapify() {
724 final Object[] es = queue;
725 int n = size, i = (n >>> 1) - 1;
726 final Comparator<? super E> cmp;
727 if ((cmp = comparator) == null)
728 for (; i >= 0; i--)
729 siftDownComparable(i, (E) es[i], es, n);
730 else
731 for (; i >= 0; i--)
732 siftDownUsingComparator(i, (E) es[i], es, n, cmp);
733 }
734
735 /**
736 * Returns the comparator used to order the elements in this
737 * queue, or {@code null} if this queue is sorted according to
738 * the {@linkplain Comparable natural ordering} of its elements.
739 *
740 * @return the comparator used to order this queue, or
741 * {@code null} if this queue is sorted according to the
742 * natural ordering of its elements
743 */
744 public Comparator<? super E> comparator() {
745 return comparator;
746 }
747
748 /**
749 * Saves this queue to a stream (that is, serializes it).
750 *
751 * @param s the stream
752 * @throws java.io.IOException if an I/O error occurs
753 * @serialData The length of the array backing the instance is
754 * emitted (int), followed by all of its elements
755 * (each an {@code Object}) in the proper order.
756 */
757 private void writeObject(java.io.ObjectOutputStream s)
758 throws java.io.IOException {
759 // Write out element count, and any hidden stuff
760 s.defaultWriteObject();
761
762 // Write out array length, for compatibility with 1.5 version
763 s.writeInt(Math.max(2, size + 1));
764
765 // Write out all elements in the "proper order".
766 final Object[] es = queue;
767 for (int i = 0, n = size; i < n; i++)
768 s.writeObject(es[i]);
769 }
770
771 /**
772 * Reconstitutes the {@code PriorityQueue} instance from a stream
773 * (that is, deserializes it).
774 *
775 * @param s the stream
776 * @throws ClassNotFoundException if the class of a serialized object
777 * could not be found
778 * @throws java.io.IOException if an I/O error occurs
779 */
780 private void readObject(java.io.ObjectInputStream s)
781 throws java.io.IOException, ClassNotFoundException {
782 // Read in size, and any hidden stuff
783 s.defaultReadObject();
784
785 // Read in (and discard) array length
786 s.readInt();
787
788 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
789 final Object[] es = queue = new Object[Math.max(size, 1)];
790
791 // Read in all elements.
792 for (int i = 0, n = size; i < n; i++)
793 es[i] = s.readObject();
794
795 // Elements are guaranteed to be in "proper order", but the
796 // spec has never explained what that might be.
797 heapify();
798 }
799
800 /**
801 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
802 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
803 * queue. The spliterator does not traverse elements in any particular order
804 * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
805 *
806 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
807 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
808 * Overriding implementations should document the reporting of additional
809 * characteristic values.
810 *
811 * @return a {@code Spliterator} over the elements in this queue
812 * @since 1.8
813 */
814 public final Spliterator<E> spliterator() {
815 return new PriorityQueueSpliterator(0, -1, 0);
816 }
817
818 final class PriorityQueueSpliterator implements Spliterator<E> {
819 private int index; // current index, modified on advance/split
820 private int fence; // -1 until first use
821 private int expectedModCount; // initialized when fence set
822
823 /** Creates new spliterator covering the given range. */
824 PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
825 this.index = origin;
826 this.fence = fence;
827 this.expectedModCount = expectedModCount;
828 }
829
830 private int getFence() { // initialize fence to size on first use
831 int hi;
832 if ((hi = fence) < 0) {
833 expectedModCount = modCount;
834 hi = fence = size;
835 }
836 return hi;
837 }
838
839 public PriorityQueueSpliterator trySplit() {
840 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
841 return (lo >= mid) ? null :
842 new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
843 }
844
845 public void forEachRemaining(Consumer<? super E> action) {
846 if (action == null)
847 throw new NullPointerException();
848 if (fence < 0) { fence = size; expectedModCount = modCount; }
849 final Object[] es = queue;
850 int i, hi; E e;
851 for (i = index, index = hi = fence; i < hi; i++) {
852 if ((e = (E) es[i]) == null)
853 break; // must be CME
854 action.accept(e);
855 }
856 if (modCount != expectedModCount)
857 throw new ConcurrentModificationException();
858 }
859
860 public boolean tryAdvance(Consumer<? super E> action) {
861 if (action == null)
862 throw new NullPointerException();
863 if (fence < 0) { fence = size; expectedModCount = modCount; }
864 int i;
865 if ((i = index) < fence) {
866 index = i + 1;
867 E e;
868 if ((e = (E) queue[i]) == null
869 || modCount != expectedModCount)
870 throw new ConcurrentModificationException();
871 action.accept(e);
872 return true;
873 }
874 return false;
875 }
876
877 public long estimateSize() {
878 return getFence() - index;
879 }
880
881 public int characteristics() {
882 return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
883 }
884 }
885
886 /**
887 * @throws NullPointerException {@inheritDoc}
888 */
889 public boolean removeIf(Predicate<? super E> filter) {
890 Objects.requireNonNull(filter);
891 return bulkRemove(filter);
892 }
893
894 /**
895 * @throws NullPointerException {@inheritDoc}
896 */
897 public boolean removeAll(Collection<?> c) {
898 Objects.requireNonNull(c);
899 return bulkRemove(e -> c.contains(e));
900 }
901
902 /**
903 * @throws NullPointerException {@inheritDoc}
904 */
905 public boolean retainAll(Collection<?> c) {
906 Objects.requireNonNull(c);
907 return bulkRemove(e -> !c.contains(e));
908 }
909
910 // A tiny bit set implementation
911
912 private static long[] nBits(int n) {
913 return new long[((n - 1) >> 6) + 1];
914 }
915 private static void setBit(long[] bits, int i) {
916 bits[i >> 6] |= 1L << i;
917 }
918 private static boolean isClear(long[] bits, int i) {
919 return (bits[i >> 6] & (1L << i)) == 0;
920 }
921
922 /** Implementation of bulk remove methods. */
923 private boolean bulkRemove(Predicate<? super E> filter) {
924 final int expectedModCount = ++modCount;
925 final Object[] es = queue;
926 final int end = size;
927 int i;
928 // Optimize for initial run of survivors
929 for (i = 0; i < end && !filter.test((E) es[i]); i++)
930 ;
931 if (i >= end) {
932 if (modCount != expectedModCount)
933 throw new ConcurrentModificationException();
934 return false;
935 }
936 // Tolerate predicates that reentrantly access the collection for
937 // read (but writers still get CME), so traverse once to find
938 // elements to delete, a second pass to physically expunge.
939 final int beg = i;
940 final long[] deathRow = nBits(end - beg);
941 deathRow[0] = 1L; // set bit 0
942 for (i = beg + 1; i < end; i++)
943 if (filter.test((E) es[i]))
944 setBit(deathRow, i - beg);
945 if (modCount != expectedModCount)
946 throw new ConcurrentModificationException();
947 int w = beg;
948 for (i = beg; i < end; i++)
949 if (isClear(deathRow, i - beg))
950 es[w++] = es[i];
951 for (i = size = w; i < end; i++)
952 es[i] = null;
953 heapify();
954 return true;
955 }
956
957 /**
958 * @throws NullPointerException {@inheritDoc}
959 */
960 public void forEach(Consumer<? super E> action) {
961 Objects.requireNonNull(action);
962 final int expectedModCount = modCount;
963 final Object[] es = queue;
964 for (int i = 0, n = size; i < n; i++)
965 action.accept((E) es[i]);
966 if (expectedModCount != modCount)
967 throw new ConcurrentModificationException();
968 }
969 }