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.newLength(oldCapacity,
294 minCapacity - oldCapacity, /* minimum growth */
295 oldCapacity < 64 ? oldCapacity + 2 : oldCapacity >> 1
296 /* preferred growth */);
297 queue = Arrays.copyOf(queue, newCapacity);
298 }
299
300 /**
301 * Inserts the specified element into this priority queue.
302 *
303 * @return {@code true} (as specified by {@link Collection#add})
304 * @throws ClassCastException if the specified element cannot be
305 * compared with elements currently in this priority queue
306 * according to the priority queue's ordering
307 * @throws NullPointerException if the specified element is null
308 */
309 public boolean add(E e) {
310 return offer(e);
311 }
312
313 /**
314 * Inserts the specified element into this priority queue.
315 *
316 * @return {@code true} (as specified by {@link Queue#offer})
317 * @throws ClassCastException if the specified element cannot be
318 * compared with elements currently in this priority queue
319 * according to the priority queue's ordering
320 * @throws NullPointerException if the specified element is null
321 */
322 public boolean offer(E e) {
323 if (e == null)
324 throw new NullPointerException();
325 modCount++;
326 int i = size;
327 if (i >= queue.length)
328 grow(i + 1);
329 siftUp(i, e);
330 size = i + 1;
331 return true;
332 }
333
334 public E peek() {
335 return (E) queue[0];
336 }
337
338 private int indexOf(Object o) {
339 if (o != null) {
340 final Object[] es = queue;
341 for (int i = 0, n = size; i < n; i++)
342 if (o.equals(es[i]))
343 return i;
344 }
345 return -1;
346 }
347
348 /**
349 * Removes a single instance of the specified element from this queue,
350 * if it is present. More formally, removes an element {@code e} such
351 * that {@code o.equals(e)}, if this queue contains one or more such
352 * elements. Returns {@code true} if and only if this queue contained
353 * the specified element (or equivalently, if this queue changed as a
354 * result of the call).
355 *
356 * @param o element to be removed from this queue, if present
357 * @return {@code true} if this queue changed as a result of the call
358 */
359 public boolean remove(Object o) {
360 int i = indexOf(o);
361 if (i == -1)
362 return false;
363 else {
364 removeAt(i);
365 return true;
366 }
367 }
368
369 /**
370 * Identity-based version for use in Itr.remove.
371 *
372 * @param o element to be removed from this queue, if present
373 */
374 void removeEq(Object o) {
375 final Object[] es = queue;
376 for (int i = 0, n = size; i < n; i++) {
377 if (o == es[i]) {
378 removeAt(i);
379 break;
380 }
381 }
382 }
383
384 /**
385 * Returns {@code true} if this queue contains the specified element.
386 * More formally, returns {@code true} if and only if this queue contains
387 * at least one element {@code e} such that {@code o.equals(e)}.
388 *
389 * @param o object to be checked for containment in this queue
390 * @return {@code true} if this queue contains the specified element
391 */
392 public boolean contains(Object o) {
393 return indexOf(o) >= 0;
394 }
395
396 /**
397 * Returns an array containing all of the elements in this queue.
398 * The elements are in no particular order.
399 *
400 * <p>The returned array will be "safe" in that no references to it are
401 * maintained by this queue. (In other words, this method must allocate
402 * a new array). The caller is thus free to modify the returned array.
403 *
404 * <p>This method acts as bridge between array-based and collection-based
405 * APIs.
406 *
407 * @return an array containing all of the elements in this queue
408 */
409 public Object[] toArray() {
410 return Arrays.copyOf(queue, size);
411 }
412
413 /**
414 * Returns an array containing all of the elements in this queue; the
415 * runtime type of the returned array is that of the specified array.
416 * The returned array elements are in no particular order.
417 * If the queue fits in the specified array, it is returned therein.
418 * Otherwise, a new array is allocated with the runtime type of the
419 * specified array and the size of this queue.
420 *
421 * <p>If the queue fits in the specified array with room to spare
422 * (i.e., the array has more elements than the queue), the element in
423 * the array immediately following the end of the collection is set to
424 * {@code null}.
425 *
426 * <p>Like the {@link #toArray()} method, this method acts as bridge between
427 * array-based and collection-based APIs. Further, this method allows
428 * precise control over the runtime type of the output array, and may,
429 * under certain circumstances, be used to save allocation costs.
430 *
431 * <p>Suppose {@code x} is a queue known to contain only strings.
432 * The following code can be used to dump the queue into a newly
433 * allocated array of {@code String}:
434 *
435 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
436 *
437 * Note that {@code toArray(new Object[0])} is identical in function to
438 * {@code toArray()}.
439 *
440 * @param a the array into which the elements of the queue are to
441 * be stored, if it is big enough; otherwise, a new array of the
442 * same runtime type is allocated for this purpose.
443 * @return an array containing all of the elements in this queue
444 * @throws ArrayStoreException if the runtime type of the specified array
445 * is not a supertype of the runtime type of every element in
446 * this queue
447 * @throws NullPointerException if the specified array is null
448 */
449 public <T> T[] toArray(T[] a) {
450 final int size = this.size;
451 if (a.length < size)
452 // Make a new array of a's runtime type, but my contents:
453 return (T[]) Arrays.copyOf(queue, size, a.getClass());
454 System.arraycopy(queue, 0, a, 0, size);
455 if (a.length > size)
456 a[size] = null;
457 return a;
458 }
459
460 /**
461 * Returns an iterator over the elements in this queue. The iterator
462 * does not return the elements in any particular order.
463 *
464 * @return an iterator over the elements in this queue
465 */
466 public Iterator<E> iterator() {
467 return new Itr();
468 }
469
470 private final class Itr implements Iterator<E> {
471 /**
472 * Index (into queue array) of element to be returned by
473 * subsequent call to next.
474 */
475 private int cursor;
476
477 /**
478 * Index of element returned by most recent call to next,
479 * unless that element came from the forgetMeNot list.
480 * Set to -1 if element is deleted by a call to remove.
481 */
482 private int lastRet = -1;
483
484 /**
485 * A queue of elements that were moved from the unvisited portion of
486 * the heap into the visited portion as a result of "unlucky" element
487 * removals during the iteration. (Unlucky element removals are those
488 * that require a siftup instead of a siftdown.) We must visit all of
489 * the elements in this list to complete the iteration. We do this
490 * after we've completed the "normal" iteration.
491 *
492 * We expect that most iterations, even those involving removals,
493 * will not need to store elements in this field.
494 */
495 private ArrayDeque<E> forgetMeNot;
496
497 /**
498 * Element returned by the most recent call to next iff that
499 * element was drawn from the forgetMeNot list.
500 */
501 private E lastRetElt;
502
503 /**
504 * The modCount value that the iterator believes that the backing
505 * Queue should have. If this expectation is violated, the iterator
506 * has detected concurrent modification.
507 */
508 private int expectedModCount = modCount;
509
510 Itr() {} // prevent access constructor creation
511
512 public boolean hasNext() {
513 return cursor < size ||
514 (forgetMeNot != null && !forgetMeNot.isEmpty());
515 }
516
517 public E next() {
518 if (expectedModCount != modCount)
519 throw new ConcurrentModificationException();
520 if (cursor < size)
521 return (E) queue[lastRet = cursor++];
522 if (forgetMeNot != null) {
523 lastRet = -1;
524 lastRetElt = forgetMeNot.poll();
525 if (lastRetElt != null)
526 return lastRetElt;
527 }
528 throw new NoSuchElementException();
529 }
530
531 public void remove() {
532 if (expectedModCount != modCount)
533 throw new ConcurrentModificationException();
534 if (lastRet != -1) {
535 E moved = PriorityQueue.this.removeAt(lastRet);
536 lastRet = -1;
537 if (moved == null)
538 cursor--;
539 else {
540 if (forgetMeNot == null)
541 forgetMeNot = new ArrayDeque<>();
542 forgetMeNot.add(moved);
543 }
544 } else if (lastRetElt != null) {
545 PriorityQueue.this.removeEq(lastRetElt);
546 lastRetElt = null;
547 } else {
548 throw new IllegalStateException();
549 }
550 expectedModCount = modCount;
551 }
552 }
553
554 public int size() {
555 return size;
556 }
557
558 /**
559 * Removes all of the elements from this priority queue.
560 * The queue will be empty after this call returns.
561 */
562 public void clear() {
563 modCount++;
564 final Object[] es = queue;
565 for (int i = 0, n = size; i < n; i++)
566 es[i] = null;
567 size = 0;
568 }
569
570 public E poll() {
571 final Object[] es;
572 final E result;
573
574 if ((result = (E) ((es = queue)[0])) != null) {
575 modCount++;
576 final int n;
577 final E x = (E) es[(n = --size)];
578 es[n] = null;
579 if (n > 0) {
580 final Comparator<? super E> cmp;
581 if ((cmp = comparator) == null)
582 siftDownComparable(0, x, es, n);
583 else
584 siftDownUsingComparator(0, x, es, n, cmp);
585 }
586 }
587 return result;
588 }
589
590 /**
591 * Removes the ith element from queue.
592 *
593 * Normally this method leaves the elements at up to i-1,
594 * inclusive, untouched. Under these circumstances, it returns
595 * null. Occasionally, in order to maintain the heap invariant,
596 * it must swap a later element of the list with one earlier than
597 * i. Under these circumstances, this method returns the element
598 * that was previously at the end of the list and is now at some
599 * position before i. This fact is used by iterator.remove so as to
600 * avoid missing traversing elements.
601 */
602 E removeAt(int i) {
603 // assert i >= 0 && i < size;
604 final Object[] es = queue;
605 modCount++;
606 int s = --size;
607 if (s == i) // removed last element
608 es[i] = null;
609 else {
610 E moved = (E) es[s];
611 es[s] = null;
612 siftDown(i, moved);
613 if (es[i] == moved) {
614 siftUp(i, moved);
615 if (es[i] != moved)
616 return moved;
617 }
618 }
619 return null;
620 }
621
622 /**
623 * Inserts item x at position k, maintaining heap invariant by
624 * promoting x up the tree until it is greater than or equal to
625 * its parent, or is the root.
626 *
627 * To simplify and speed up coercions and comparisons, the
628 * Comparable and Comparator versions are separated into different
629 * methods that are otherwise identical. (Similarly for siftDown.)
630 *
631 * @param k the position to fill
632 * @param x the item to insert
633 */
634 private void siftUp(int k, E x) {
635 if (comparator != null)
636 siftUpUsingComparator(k, x, queue, comparator);
637 else
638 siftUpComparable(k, x, queue);
639 }
640
641 private static <T> void siftUpComparable(int k, T x, Object[] es) {
642 Comparable<? super T> key = (Comparable<? super T>) x;
643 while (k > 0) {
644 int parent = (k - 1) >>> 1;
645 Object e = es[parent];
646 if (key.compareTo((T) e) >= 0)
647 break;
648 es[k] = e;
649 k = parent;
650 }
651 es[k] = key;
652 }
653
654 private static <T> void siftUpUsingComparator(
655 int k, T x, Object[] es, Comparator<? super T> cmp) {
656 while (k > 0) {
657 int parent = (k - 1) >>> 1;
658 Object e = es[parent];
659 if (cmp.compare(x, (T) e) >= 0)
660 break;
661 es[k] = e;
662 k = parent;
663 }
664 es[k] = x;
665 }
666
667 /**
668 * Inserts item x at position k, maintaining heap invariant by
669 * demoting x down the tree repeatedly until it is less than or
670 * equal to its children or is a leaf.
671 *
672 * @param k the position to fill
673 * @param x the item to insert
674 */
675 private void siftDown(int k, E x) {
676 if (comparator != null)
677 siftDownUsingComparator(k, x, queue, size, comparator);
678 else
679 siftDownComparable(k, x, queue, size);
680 }
681
682 private static <T> void siftDownComparable(int k, T x, Object[] es, int n) {
683 // assert n > 0;
684 Comparable<? super T> key = (Comparable<? super T>)x;
685 int half = n >>> 1; // loop while a non-leaf
686 while (k < half) {
687 int child = (k << 1) + 1; // assume left child is least
688 Object c = es[child];
689 int right = child + 1;
690 if (right < n &&
691 ((Comparable<? super T>) c).compareTo((T) es[right]) > 0)
692 c = es[child = right];
693 if (key.compareTo((T) c) <= 0)
694 break;
695 es[k] = c;
696 k = child;
697 }
698 es[k] = key;
699 }
700
701 private static <T> void siftDownUsingComparator(
702 int k, T x, Object[] es, int n, Comparator<? super T> cmp) {
703 // assert n > 0;
704 int half = n >>> 1;
705 while (k < half) {
706 int child = (k << 1) + 1;
707 Object c = es[child];
708 int right = child + 1;
709 if (right < n && cmp.compare((T) c, (T) es[right]) > 0)
710 c = es[child = right];
711 if (cmp.compare(x, (T) c) <= 0)
712 break;
713 es[k] = c;
714 k = child;
715 }
716 es[k] = x;
717 }
718
719 /**
720 * Establishes the heap invariant (described above) in the entire tree,
721 * assuming nothing about the order of the elements prior to the call.
722 * This classic algorithm due to Floyd (1964) is known to be O(size).
723 */
724 private void heapify() {
725 final Object[] es = queue;
726 int n = size, i = (n >>> 1) - 1;
727 final Comparator<? super E> cmp;
728 if ((cmp = comparator) == null)
729 for (; i >= 0; i--)
730 siftDownComparable(i, (E) es[i], es, n);
731 else
732 for (; i >= 0; i--)
733 siftDownUsingComparator(i, (E) es[i], es, n, cmp);
734 }
735
736 /**
737 * Returns the comparator used to order the elements in this
738 * queue, or {@code null} if this queue is sorted according to
739 * the {@linkplain Comparable natural ordering} of its elements.
740 *
741 * @return the comparator used to order this queue, or
742 * {@code null} if this queue is sorted according to the
743 * natural ordering of its elements
744 */
745 public Comparator<? super E> comparator() {
746 return comparator;
747 }
748
749 /**
750 * Saves this queue to a stream (that is, serializes it).
751 *
752 * @param s the stream
753 * @throws java.io.IOException if an I/O error occurs
754 * @serialData The length of the array backing the instance is
755 * emitted (int), followed by all of its elements
756 * (each an {@code Object}) in the proper order.
757 */
758 private void writeObject(java.io.ObjectOutputStream s)
759 throws java.io.IOException {
760 // Write out element count, and any hidden stuff
761 s.defaultWriteObject();
762
763 // Write out array length, for compatibility with 1.5 version
764 s.writeInt(Math.max(2, size + 1));
765
766 // Write out all elements in the "proper order".
767 final Object[] es = queue;
768 for (int i = 0, n = size; i < n; i++)
769 s.writeObject(es[i]);
770 }
771
772 /**
773 * Reconstitutes the {@code PriorityQueue} instance from a stream
774 * (that is, deserializes it).
775 *
776 * @param s the stream
777 * @throws ClassNotFoundException if the class of a serialized object
778 * could not be found
779 * @throws java.io.IOException if an I/O error occurs
780 */
781 private void readObject(java.io.ObjectInputStream s)
782 throws java.io.IOException, ClassNotFoundException {
783 // Read in size, and any hidden stuff
784 s.defaultReadObject();
785
786 // Read in (and discard) array length
787 s.readInt();
788
789 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
790 final Object[] es = queue = new Object[Math.max(size, 1)];
791
792 // Read in all elements.
793 for (int i = 0, n = size; i < n; i++)
794 es[i] = s.readObject();
795
796 // Elements are guaranteed to be in "proper order", but the
797 // spec has never explained what that might be.
798 heapify();
799 }
800
801 /**
802 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
803 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
804 * queue. The spliterator does not traverse elements in any particular order
805 * (the {@link Spliterator#ORDERED ORDERED} characteristic is not reported).
806 *
807 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
808 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#NONNULL}.
809 * Overriding implementations should document the reporting of additional
810 * characteristic values.
811 *
812 * @return a {@code Spliterator} over the elements in this queue
813 * @since 1.8
814 */
815 public final Spliterator<E> spliterator() {
816 return new PriorityQueueSpliterator(0, -1, 0);
817 }
818
819 final class PriorityQueueSpliterator implements Spliterator<E> {
820 private int index; // current index, modified on advance/split
821 private int fence; // -1 until first use
822 private int expectedModCount; // initialized when fence set
823
824 /** Creates new spliterator covering the given range. */
825 PriorityQueueSpliterator(int origin, int fence, int expectedModCount) {
826 this.index = origin;
827 this.fence = fence;
828 this.expectedModCount = expectedModCount;
829 }
830
831 private int getFence() { // initialize fence to size on first use
832 int hi;
833 if ((hi = fence) < 0) {
834 expectedModCount = modCount;
835 hi = fence = size;
836 }
837 return hi;
838 }
839
840 public PriorityQueueSpliterator trySplit() {
841 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
842 return (lo >= mid) ? null :
843 new PriorityQueueSpliterator(lo, index = mid, expectedModCount);
844 }
845
846 public void forEachRemaining(Consumer<? super E> action) {
847 if (action == null)
848 throw new NullPointerException();
849 if (fence < 0) { fence = size; expectedModCount = modCount; }
850 final Object[] es = queue;
851 int i, hi; E e;
852 for (i = index, index = hi = fence; i < hi; i++) {
853 if ((e = (E) es[i]) == null)
854 break; // must be CME
855 action.accept(e);
856 }
857 if (modCount != expectedModCount)
858 throw new ConcurrentModificationException();
859 }
860
861 public boolean tryAdvance(Consumer<? super E> action) {
862 if (action == null)
863 throw new NullPointerException();
864 if (fence < 0) { fence = size; expectedModCount = modCount; }
865 int i;
866 if ((i = index) < fence) {
867 index = i + 1;
868 E e;
869 if ((e = (E) queue[i]) == null
870 || modCount != expectedModCount)
871 throw new ConcurrentModificationException();
872 action.accept(e);
873 return true;
874 }
875 return false;
876 }
877
878 public long estimateSize() {
879 return getFence() - index;
880 }
881
882 public int characteristics() {
883 return Spliterator.SIZED | Spliterator.SUBSIZED | Spliterator.NONNULL;
884 }
885 }
886
887 /**
888 * @throws NullPointerException {@inheritDoc}
889 */
890 public boolean removeIf(Predicate<? super E> filter) {
891 Objects.requireNonNull(filter);
892 return bulkRemove(filter);
893 }
894
895 /**
896 * @throws NullPointerException {@inheritDoc}
897 */
898 public boolean removeAll(Collection<?> c) {
899 Objects.requireNonNull(c);
900 return bulkRemove(e -> c.contains(e));
901 }
902
903 /**
904 * @throws NullPointerException {@inheritDoc}
905 */
906 public boolean retainAll(Collection<?> c) {
907 Objects.requireNonNull(c);
908 return bulkRemove(e -> !c.contains(e));
909 }
910
911 // A tiny bit set implementation
912
913 private static long[] nBits(int n) {
914 return new long[((n - 1) >> 6) + 1];
915 }
916 private static void setBit(long[] bits, int i) {
917 bits[i >> 6] |= 1L << i;
918 }
919 private static boolean isClear(long[] bits, int i) {
920 return (bits[i >> 6] & (1L << i)) == 0;
921 }
922
923 /** Implementation of bulk remove methods. */
924 private boolean bulkRemove(Predicate<? super E> filter) {
925 final int expectedModCount = ++modCount;
926 final Object[] es = queue;
927 final int end = size;
928 int i;
929 // Optimize for initial run of survivors
930 for (i = 0; i < end && !filter.test((E) es[i]); i++)
931 ;
932 if (i >= end) {
933 if (modCount != expectedModCount)
934 throw new ConcurrentModificationException();
935 return false;
936 }
937 // Tolerate predicates that reentrantly access the collection for
938 // read (but writers still get CME), so traverse once to find
939 // elements to delete, a second pass to physically expunge.
940 final int beg = i;
941 final long[] deathRow = nBits(end - beg);
942 deathRow[0] = 1L; // set bit 0
943 for (i = beg + 1; i < end; i++)
944 if (filter.test((E) es[i]))
945 setBit(deathRow, i - beg);
946 if (modCount != expectedModCount)
947 throw new ConcurrentModificationException();
948 int w = beg;
949 for (i = beg; i < end; i++)
950 if (isClear(deathRow, i - beg))
951 es[w++] = es[i];
952 for (i = size = w; i < end; i++)
953 es[i] = null;
954 heapify();
955 return true;
956 }
957
958 /**
959 * @throws NullPointerException {@inheritDoc}
960 */
961 public void forEach(Consumer<? super E> action) {
962 Objects.requireNonNull(action);
963 final int expectedModCount = modCount;
964 final Object[] es = queue;
965 for (int i = 0, n = size; i < n; i++)
966 action.accept((E) es[i]);
967 if (expectedModCount != modCount)
968 throw new ConcurrentModificationException();
969 }
970 }