1 /*
2 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
3 *
4 * This code is free software; you can redistribute it and/or modify it
5 * under the terms of the GNU General Public License version 2 only, as
6 * published by the Free Software Foundation. Oracle designates this
7 * particular file as subject to the "Classpath" exception as provided
8 * by Oracle in the LICENSE file that accompanied this code.
9 *
10 * This code is distributed in the hope that it will be useful, but WITHOUT
11 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
13 * version 2 for more details (a copy is included in the LICENSE file that
14 * accompanied this code).
15 *
16 * You should have received a copy of the GNU General Public License version
17 * 2 along with this work; if not, write to the Free Software Foundation,
18 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
19 *
20 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
21 * or visit www.oracle.com if you need additional information or have any
22 * questions.
23 */
24
25 /*
26 * This file is available under and governed by the GNU General Public
27 * License version 2 only, as published by the Free Software Foundation.
28 * However, the following notice accompanied the original version of this
29 * file:
30 *
31 * Written by Josh Bloch of Google Inc. and released to the public domain,
32 * as explained at http://creativecommons.org/publicdomain/zero/1.0/.
33 */
34
35 package java.util;
36
37 import java.io.Serializable;
38 import java.util.function.Consumer;
39 import java.util.function.Predicate;
40 import java.util.function.UnaryOperator;
41 import jdk.internal.misc.SharedSecrets;
42
43 /**
44 * Resizable-array implementation of the {@link Deque} interface. Array
45 * deques have no capacity restrictions; they grow as necessary to support
46 * usage. They are not thread-safe; in the absence of external
47 * synchronization, they do not support concurrent access by multiple threads.
48 * Null elements are prohibited. This class is likely to be faster than
49 * {@link Stack} when used as a stack, and faster than {@link LinkedList}
50 * when used as a queue.
51 *
52 * <p>Most {@code ArrayDeque} operations run in amortized constant time.
53 * Exceptions include
54 * {@link #remove(Object) remove},
55 * {@link #removeFirstOccurrence removeFirstOccurrence},
56 * {@link #removeLastOccurrence removeLastOccurrence},
57 * {@link #contains contains},
58 * {@link #iterator iterator.remove()},
59 * and the bulk operations, all of which run in linear time.
60 *
61 * <p>The iterators returned by this class's {@link #iterator() iterator}
62 * method are <em>fail-fast</em>: If the deque is modified at any time after
63 * the iterator is created, in any way except through the iterator's own
64 * {@code remove} method, the iterator will generally throw a {@link
65 * ConcurrentModificationException}. Thus, in the face of concurrent
66 * modification, the iterator fails quickly and cleanly, rather than risking
67 * arbitrary, non-deterministic behavior at an undetermined time in the
68 * future.
69 *
70 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
71 * as it is, generally speaking, impossible to make any hard guarantees in the
72 * presence of unsynchronized concurrent modification. Fail-fast iterators
73 * throw {@code ConcurrentModificationException} on a best-effort basis.
74 * Therefore, it would be wrong to write a program that depended on this
75 * exception for its correctness: <i>the fail-fast behavior of iterators
76 * should be used only to detect bugs.</i>
77 *
78 * <p>This class and its iterator implement all of the
79 * <em>optional</em> methods of the {@link Collection} and {@link
80 * Iterator} interfaces.
81 *
82 * <p>This class is a member of the
83 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
84 * Java Collections Framework</a>.
85 *
86 * @author Josh Bloch and Doug Lea
87 * @param <E> the type of elements held in this deque
88 * @since 1.6
89 */
90 public class ArrayDeque<E> extends AbstractCollection<E>
91 implements Deque<E>, Cloneable, Serializable
92 {
93 /*
94 * VMs excel at optimizing simple array loops where indices are
95 * incrementing or decrementing over a valid slice, e.g.
96 *
97 * for (int i = start; i < end; i++) ... elements[i]
98 *
99 * Because in a circular array, elements are in general stored in
100 * two disjoint such slices, we help the VM by writing unusual
101 * nested loops for all traversals over the elements. Having only
102 * one hot inner loop body instead of two or three eases human
103 * maintenance and encourages VM loop inlining into the caller.
104 */
105
106 /**
107 * The array in which the elements of the deque are stored.
108 * All array cells not holding deque elements are always null.
109 * The array always has at least one null slot (at tail).
110 */
111 transient Object[] elements;
112
113 /**
114 * The index of the element at the head of the deque (which is the
115 * element that would be removed by remove() or pop()); or an
116 * arbitrary number 0 <= head < elements.length equal to tail if
117 * the deque is empty.
118 */
119 transient int head;
120
121 /**
122 * The index at which the next element would be added to the tail
123 * of the deque (via addLast(E), add(E), or push(E));
124 * elements[tail] is always null.
125 */
126 transient int tail;
127
128 /**
129 * The maximum size of array to allocate.
130 * Some VMs reserve some header words in an array.
131 * Attempts to allocate larger arrays may result in
132 * OutOfMemoryError: Requested array size exceeds VM limit
133 */
134 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
135
136 /**
137 * Increases the capacity of this deque by at least the given amount.
138 *
139 * @param needed the required minimum extra capacity; must be positive
140 */
141 private void grow(int needed) {
142 // overflow-conscious code
143 final int oldCapacity = elements.length;
144 int newCapacity;
145 // Double capacity if small; else grow by 50%
146 int jump = (oldCapacity < 64) ? (oldCapacity + 2) : (oldCapacity >> 1);
147 if (jump < needed
148 || (newCapacity = (oldCapacity + jump)) - MAX_ARRAY_SIZE > 0)
149 newCapacity = newCapacity(needed, jump);
150 final Object[] es = elements = Arrays.copyOf(elements, newCapacity);
151 // Exceptionally, here tail == head needs to be disambiguated
152 if (tail < head || (tail == head && es[head] != null)) {
153 // wrap around; slide first leg forward to end of array
154 int newSpace = newCapacity - oldCapacity;
155 System.arraycopy(es, head,
156 es, head + newSpace,
157 oldCapacity - head);
158 for (int i = head, to = (head += newSpace); i < to; i++)
159 es[i] = null;
160 }
161 }
162
163 /** Capacity calculation for edge conditions, especially overflow. */
164 private int newCapacity(int needed, int jump) {
165 final int oldCapacity = elements.length, minCapacity;
166 if ((minCapacity = oldCapacity + needed) - MAX_ARRAY_SIZE > 0) {
167 if (minCapacity < 0)
168 throw new IllegalStateException("Sorry, deque too big");
169 return Integer.MAX_VALUE;
170 }
171 if (needed > jump)
172 return minCapacity;
173 return (oldCapacity + jump - MAX_ARRAY_SIZE < 0)
174 ? oldCapacity + jump
175 : MAX_ARRAY_SIZE;
176 }
177
178 /**
179 * Constructs an empty array deque with an initial capacity
180 * sufficient to hold 16 elements.
181 */
182 public ArrayDeque() {
183 // One extra slot for a null element at the tail
184 elements = new Object[16 + 1];
185 }
186
187 /**
188 * Constructs an empty array deque with an initial capacity
189 * sufficient to hold the specified number of elements.
190 *
191 * @param numElements lower bound on initial capacity of the deque
192 */
193 public ArrayDeque(int numElements) {
194 elements =
195 new Object[(numElements < 1) ? 1 :
196 (numElements == Integer.MAX_VALUE) ? Integer.MAX_VALUE :
197 numElements + 1];
198 }
199
200 /**
201 * Constructs a deque containing the elements of the specified
202 * collection, in the order they are returned by the collection's
203 * iterator. (The first element returned by the collection's
204 * iterator becomes the first element, or <i>front</i> of the
205 * deque.)
206 *
207 * @param c the collection whose elements are to be placed into the deque
208 * @throws NullPointerException if the specified collection is null
209 */
210 public ArrayDeque(Collection<? extends E> c) {
211 this(c.size());
212 copyElements(c);
213 }
214
215 /**
216 * Circularly increments i, mod modulus.
217 * Precondition and postcondition: 0 <= i < modulus.
218 */
219 static final int inc(int i, int modulus) {
220 if (++i >= modulus) i = 0;
221 return i;
222 }
223
224 /**
225 * Circularly decrements i, mod modulus.
226 * Precondition and postcondition: 0 <= i < modulus.
227 */
228 static final int dec(int i, int modulus) {
229 if (--i < 0) i = modulus - 1;
230 return i;
231 }
232
233 /**
234 * Circularly adds the given distance to index i, mod modulus.
235 * Precondition: 0 <= i < modulus, 0 <= distance <= modulus.
236 * @return index 0 <= i < modulus
237 */
238 static final int inc(int i, int distance, int modulus) {
239 if ((i += distance) - modulus >= 0) i -= modulus;
240 return i;
241 }
242
243 /**
244 * Subtracts j from i, mod modulus.
245 * Index i must be logically ahead of index j.
246 * Precondition: 0 <= i < modulus, 0 <= j < modulus.
247 * @return the "circular distance" from j to i; corner case i == j
248 * is disambiguated to "empty", returning 0.
249 */
250 static final int sub(int i, int j, int modulus) {
251 if ((i -= j) < 0) i += modulus;
252 return i;
253 }
254
255 /**
256 * Returns element at array index i.
257 * This is a slight abuse of generics, accepted by javac.
258 */
259 @SuppressWarnings("unchecked")
260 static final <E> E elementAt(Object[] es, int i) {
261 return (E) es[i];
262 }
263
264 /**
265 * A version of elementAt that checks for null elements.
266 * This check doesn't catch all possible comodifications,
267 * but does catch ones that corrupt traversal.
268 */
269 static final <E> E nonNullElementAt(Object[] es, int i) {
270 @SuppressWarnings("unchecked") E e = (E) es[i];
271 if (e == null)
272 throw new ConcurrentModificationException();
273 return e;
274 }
275
276 // The main insertion and extraction methods are addFirst,
277 // addLast, pollFirst, pollLast. The other methods are defined in
278 // terms of these.
279
280 /**
281 * Inserts the specified element at the front of this deque.
282 *
283 * @param e the element to add
284 * @throws NullPointerException if the specified element is null
285 */
286 public void addFirst(E e) {
287 if (e == null)
288 throw new NullPointerException();
289 final Object[] es = elements;
290 es[head = dec(head, es.length)] = e;
291 if (head == tail)
292 grow(1);
293 }
294
295 /**
296 * Inserts the specified element at the end of this deque.
297 *
298 * <p>This method is equivalent to {@link #add}.
299 *
300 * @param e the element to add
301 * @throws NullPointerException if the specified element is null
302 */
303 public void addLast(E e) {
304 if (e == null)
305 throw new NullPointerException();
306 final Object[] es = elements;
307 es[tail] = e;
308 if (head == (tail = inc(tail, es.length)))
309 grow(1);
310 }
311
312 /**
313 * Adds all of the elements in the specified collection at the end
314 * of this deque, as if by calling {@link #addLast} on each one,
315 * in the order that they are returned by the collection's iterator.
316 *
317 * @param c the elements to be inserted into this deque
318 * @return {@code true} if this deque changed as a result of the call
319 * @throws NullPointerException if the specified collection or any
320 * of its elements are null
321 */
322 public boolean addAll(Collection<? extends E> c) {
323 final int s, needed;
324 if ((needed = (s = size()) + c.size() + 1 - elements.length) > 0)
325 grow(needed);
326 copyElements(c);
327 return size() > s;
328 }
329
330 private void copyElements(Collection<? extends E> c) {
331 c.forEach(this::addLast);
332 }
333
334 /**
335 * Inserts the specified element at the front of this deque.
336 *
337 * @param e the element to add
338 * @return {@code true} (as specified by {@link Deque#offerFirst})
339 * @throws NullPointerException if the specified element is null
340 */
341 public boolean offerFirst(E e) {
342 addFirst(e);
343 return true;
344 }
345
346 /**
347 * Inserts the specified element at the end of this deque.
348 *
349 * @param e the element to add
350 * @return {@code true} (as specified by {@link Deque#offerLast})
351 * @throws NullPointerException if the specified element is null
352 */
353 public boolean offerLast(E e) {
354 addLast(e);
355 return true;
356 }
357
358 /**
359 * @throws NoSuchElementException {@inheritDoc}
360 */
361 public E removeFirst() {
362 E e = pollFirst();
363 if (e == null)
364 throw new NoSuchElementException();
365 return e;
366 }
367
368 /**
369 * @throws NoSuchElementException {@inheritDoc}
370 */
371 public E removeLast() {
372 E e = pollLast();
373 if (e == null)
374 throw new NoSuchElementException();
375 return e;
376 }
377
378 public E pollFirst() {
379 final Object[] es;
380 final int h;
381 E e = elementAt(es = elements, h = head);
382 if (e != null) {
383 es[h] = null;
384 head = inc(h, es.length);
385 }
386 return e;
387 }
388
389 public E pollLast() {
390 final Object[] es;
391 final int t;
392 E e = elementAt(es = elements, t = dec(tail, es.length));
393 if (e != null)
394 es[tail = t] = null;
395 return e;
396 }
397
398 /**
399 * @throws NoSuchElementException {@inheritDoc}
400 */
401 public E getFirst() {
402 E e = elementAt(elements, head);
403 if (e == null)
404 throw new NoSuchElementException();
405 return e;
406 }
407
408 /**
409 * @throws NoSuchElementException {@inheritDoc}
410 */
411 public E getLast() {
412 final Object[] es = elements;
413 E e = elementAt(es, dec(tail, es.length));
414 if (e == null)
415 throw new NoSuchElementException();
416 return e;
417 }
418
419 public E peekFirst() {
420 return elementAt(elements, head);
421 }
422
423 public E peekLast() {
424 final Object[] es;
425 return elementAt(es = elements, dec(tail, es.length));
426 }
427
428 /**
429 * Removes the first occurrence of the specified element in this
430 * deque (when traversing the deque from head to tail).
431 * If the deque does not contain the element, it is unchanged.
432 * More formally, removes the first element {@code e} such that
433 * {@code o.equals(e)} (if such an element exists).
434 * Returns {@code true} if this deque contained the specified element
435 * (or equivalently, if this deque changed as a result of the call).
436 *
437 * @param o element to be removed from this deque, if present
438 * @return {@code true} if the deque contained the specified element
439 */
440 public boolean removeFirstOccurrence(Object o) {
441 if (o != null) {
442 final Object[] es = elements;
443 for (int i = head, end = tail, to = (i <= end) ? end : es.length;
444 ; i = 0, to = end) {
445 for (; i < to; i++)
446 if (o.equals(es[i])) {
447 delete(i);
448 return true;
449 }
450 if (to == end) break;
451 }
452 }
453 return false;
454 }
455
456 /**
457 * Removes the last occurrence of the specified element in this
458 * deque (when traversing the deque from head to tail).
459 * If the deque does not contain the element, it is unchanged.
460 * More formally, removes the last element {@code e} such that
461 * {@code o.equals(e)} (if such an element exists).
462 * Returns {@code true} if this deque contained the specified element
463 * (or equivalently, if this deque changed as a result of the call).
464 *
465 * @param o element to be removed from this deque, if present
466 * @return {@code true} if the deque contained the specified element
467 */
468 public boolean removeLastOccurrence(Object o) {
469 if (o != null) {
470 final Object[] es = elements;
471 for (int i = tail, end = head, to = (i >= end) ? end : 0;
472 ; i = es.length, to = end) {
473 for (i--; i > to - 1; i--)
474 if (o.equals(es[i])) {
475 delete(i);
476 return true;
477 }
478 if (to == end) break;
479 }
480 }
481 return false;
482 }
483
484 // *** Queue methods ***
485
486 /**
487 * Inserts the specified element at the end of this deque.
488 *
489 * <p>This method is equivalent to {@link #addLast}.
490 *
491 * @param e the element to add
492 * @return {@code true} (as specified by {@link Collection#add})
493 * @throws NullPointerException if the specified element is null
494 */
495 public boolean add(E e) {
496 addLast(e);
497 return true;
498 }
499
500 /**
501 * Inserts the specified element at the end of this deque.
502 *
503 * <p>This method is equivalent to {@link #offerLast}.
504 *
505 * @param e the element to add
506 * @return {@code true} (as specified by {@link Queue#offer})
507 * @throws NullPointerException if the specified element is null
508 */
509 public boolean offer(E e) {
510 return offerLast(e);
511 }
512
513 /**
514 * Retrieves and removes the head of the queue represented by this deque.
515 *
516 * This method differs from {@link #poll() poll()} only in that it
517 * throws an exception if this deque is empty.
518 *
519 * <p>This method is equivalent to {@link #removeFirst}.
520 *
521 * @return the head of the queue represented by this deque
522 * @throws NoSuchElementException {@inheritDoc}
523 */
524 public E remove() {
525 return removeFirst();
526 }
527
528 /**
529 * Retrieves and removes the head of the queue represented by this deque
530 * (in other words, the first element of this deque), or returns
531 * {@code null} if this deque is empty.
532 *
533 * <p>This method is equivalent to {@link #pollFirst}.
534 *
535 * @return the head of the queue represented by this deque, or
536 * {@code null} if this deque is empty
537 */
538 public E poll() {
539 return pollFirst();
540 }
541
542 /**
543 * Retrieves, but does not remove, the head of the queue represented by
544 * this deque. This method differs from {@link #peek peek} only in
545 * that it throws an exception if this deque is empty.
546 *
547 * <p>This method is equivalent to {@link #getFirst}.
548 *
549 * @return the head of the queue represented by this deque
550 * @throws NoSuchElementException {@inheritDoc}
551 */
552 public E element() {
553 return getFirst();
554 }
555
556 /**
557 * Retrieves, but does not remove, the head of the queue represented by
558 * this deque, or returns {@code null} if this deque is empty.
559 *
560 * <p>This method is equivalent to {@link #peekFirst}.
561 *
562 * @return the head of the queue represented by this deque, or
563 * {@code null} if this deque is empty
564 */
565 public E peek() {
566 return peekFirst();
567 }
568
569 // *** Stack methods ***
570
571 /**
572 * Pushes an element onto the stack represented by this deque. In other
573 * words, inserts the element at the front of this deque.
574 *
575 * <p>This method is equivalent to {@link #addFirst}.
576 *
577 * @param e the element to push
578 * @throws NullPointerException if the specified element is null
579 */
580 public void push(E e) {
581 addFirst(e);
582 }
583
584 /**
585 * Pops an element from the stack represented by this deque. In other
586 * words, removes and returns the first element of this deque.
587 *
588 * <p>This method is equivalent to {@link #removeFirst()}.
589 *
590 * @return the element at the front of this deque (which is the top
591 * of the stack represented by this deque)
592 * @throws NoSuchElementException {@inheritDoc}
593 */
594 public E pop() {
595 return removeFirst();
596 }
597
598 /**
599 * Removes the element at the specified position in the elements array.
600 * This can result in forward or backwards motion of array elements.
601 * We optimize for least element motion.
602 *
603 * <p>This method is called delete rather than remove to emphasize
604 * that its semantics differ from those of {@link List#remove(int)}.
605 *
606 * @return true if elements near tail moved backwards
607 */
608 boolean delete(int i) {
609 final Object[] es = elements;
610 final int capacity = es.length;
611 final int h, t;
612 // number of elements before to-be-deleted elt
613 final int front = sub(i, h = head, capacity);
614 // number of elements after to-be-deleted elt
615 final int back = sub(t = tail, i, capacity) - 1;
616 if (front < back) {
617 // move front elements forwards
618 if (h <= i) {
619 System.arraycopy(es, h, es, h + 1, front);
620 } else { // Wrap around
621 System.arraycopy(es, 0, es, 1, i);
622 es[0] = es[capacity - 1];
623 System.arraycopy(es, h, es, h + 1, front - (i + 1));
624 }
625 es[h] = null;
626 head = inc(h, capacity);
627 return false;
628 } else {
629 // move back elements backwards
630 tail = dec(t, capacity);
631 if (i <= tail) {
632 System.arraycopy(es, i + 1, es, i, back);
633 } else { // Wrap around
634 System.arraycopy(es, i + 1, es, i, capacity - (i + 1));
635 es[capacity - 1] = es[0];
636 System.arraycopy(es, 1, es, 0, t - 1);
637 }
638 es[tail] = null;
639 return true;
640 }
641 }
642
643 // *** Collection Methods ***
644
645 /**
646 * Returns the number of elements in this deque.
647 *
648 * @return the number of elements in this deque
649 */
650 public int size() {
651 return sub(tail, head, elements.length);
652 }
653
654 /**
655 * Returns {@code true} if this deque contains no elements.
656 *
657 * @return {@code true} if this deque contains no elements
658 */
659 public boolean isEmpty() {
660 return head == tail;
661 }
662
663 /**
664 * Returns an iterator over the elements in this deque. The elements
665 * will be ordered from first (head) to last (tail). This is the same
666 * order that elements would be dequeued (via successive calls to
667 * {@link #remove} or popped (via successive calls to {@link #pop}).
668 *
669 * @return an iterator over the elements in this deque
670 */
671 public Iterator<E> iterator() {
672 return new DeqIterator();
673 }
674
675 public Iterator<E> descendingIterator() {
676 return new DescendingIterator();
677 }
678
679 private class DeqIterator implements Iterator<E> {
680 /** Index of element to be returned by subsequent call to next. */
681 int cursor;
682
683 /** Number of elements yet to be returned. */
684 int remaining = size();
685
686 /**
687 * Index of element returned by most recent call to next.
688 * Reset to -1 if element is deleted by a call to remove.
689 */
690 int lastRet = -1;
691
692 DeqIterator() { cursor = head; }
693
694 public final boolean hasNext() {
695 return remaining > 0;
696 }
697
698 public E next() {
699 if (remaining <= 0)
700 throw new NoSuchElementException();
701 final Object[] es = elements;
702 E e = nonNullElementAt(es, cursor);
703 cursor = inc(lastRet = cursor, es.length);
704 remaining--;
705 return e;
706 }
707
708 void postDelete(boolean leftShifted) {
709 if (leftShifted)
710 cursor = dec(cursor, elements.length);
711 }
712
713 public final void remove() {
714 if (lastRet < 0)
715 throw new IllegalStateException();
716 postDelete(delete(lastRet));
717 lastRet = -1;
718 }
719
720 public void forEachRemaining(Consumer<? super E> action) {
721 Objects.requireNonNull(action);
722 int r;
723 if ((r = remaining) <= 0)
724 return;
725 remaining = 0;
726 final Object[] es = elements;
727 if (es[cursor] == null || sub(tail, cursor, es.length) != r)
728 throw new ConcurrentModificationException();
729 for (int i = cursor, end = tail, to = (i <= end) ? end : es.length;
730 ; i = 0, to = end) {
731 for (; i < to; i++)
732 action.accept(elementAt(es, i));
733 if (to == end) {
734 if (end != tail)
735 throw new ConcurrentModificationException();
736 lastRet = dec(end, es.length);
737 break;
738 }
739 }
740 }
741 }
742
743 private class DescendingIterator extends DeqIterator {
744 DescendingIterator() { cursor = dec(tail, elements.length); }
745
746 public final E next() {
747 if (remaining <= 0)
748 throw new NoSuchElementException();
749 final Object[] es = elements;
750 E e = nonNullElementAt(es, cursor);
751 cursor = dec(lastRet = cursor, es.length);
752 remaining--;
753 return e;
754 }
755
756 void postDelete(boolean leftShifted) {
757 if (!leftShifted)
758 cursor = inc(cursor, elements.length);
759 }
760
761 public final void forEachRemaining(Consumer<? super E> action) {
762 Objects.requireNonNull(action);
763 int r;
764 if ((r = remaining) <= 0)
765 return;
766 remaining = 0;
767 final Object[] es = elements;
768 if (es[cursor] == null || sub(cursor, head, es.length) + 1 != r)
769 throw new ConcurrentModificationException();
770 for (int i = cursor, end = head, to = (i >= end) ? end : 0;
771 ; i = es.length - 1, to = end) {
772 // hotspot generates faster code than for: i >= to !
773 for (; i > to - 1; i--)
774 action.accept(elementAt(es, i));
775 if (to == end) {
776 if (end != head)
777 throw new ConcurrentModificationException();
778 lastRet = end;
779 break;
780 }
781 }
782 }
783 }
784
785 /**
786 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
787 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
788 * deque.
789 *
790 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
791 * {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and
792 * {@link Spliterator#NONNULL}. Overriding implementations should document
793 * the reporting of additional characteristic values.
794 *
795 * @return a {@code Spliterator} over the elements in this deque
796 * @since 1.8
797 */
798 public Spliterator<E> spliterator() {
799 return new DeqSpliterator();
800 }
801
802 final class DeqSpliterator implements Spliterator<E> {
803 private int fence; // -1 until first use
804 private int cursor; // current index, modified on traverse/split
805
806 /** Constructs late-binding spliterator over all elements. */
807 DeqSpliterator() {
808 this.fence = -1;
809 }
810
811 /** Constructs spliterator over the given range. */
812 DeqSpliterator(int origin, int fence) {
813 // assert 0 <= origin && origin < elements.length;
814 // assert 0 <= fence && fence < elements.length;
815 this.cursor = origin;
816 this.fence = fence;
817 }
818
819 /** Ensures late-binding initialization; then returns fence. */
820 private int getFence() { // force initialization
821 int t;
822 if ((t = fence) < 0) {
823 t = fence = tail;
824 cursor = head;
825 }
826 return t;
827 }
828
829 public DeqSpliterator trySplit() {
830 final Object[] es = elements;
831 final int i, n;
832 return ((n = sub(getFence(), i = cursor, es.length) >> 1) <= 0)
833 ? null
834 : new DeqSpliterator(i, cursor = inc(i, n, es.length));
835 }
836
837 public void forEachRemaining(Consumer<? super E> action) {
838 if (action == null)
839 throw new NullPointerException();
840 final int end = getFence(), cursor = this.cursor;
841 final Object[] es = elements;
842 if (cursor != end) {
843 this.cursor = end;
844 // null check at both ends of range is sufficient
845 if (es[cursor] == null || es[dec(end, es.length)] == null)
846 throw new ConcurrentModificationException();
847 for (int i = cursor, to = (i <= end) ? end : es.length;
848 ; i = 0, to = end) {
849 for (; i < to; i++)
850 action.accept(elementAt(es, i));
851 if (to == end) break;
852 }
853 }
854 }
855
856 public boolean tryAdvance(Consumer<? super E> action) {
857 Objects.requireNonNull(action);
858 final Object[] es = elements;
859 if (fence < 0) { fence = tail; cursor = head; } // late-binding
860 final int i;
861 if ((i = cursor) == fence)
862 return false;
863 E e = nonNullElementAt(es, i);
864 cursor = inc(i, es.length);
865 action.accept(e);
866 return true;
867 }
868
869 public long estimateSize() {
870 return sub(getFence(), cursor, elements.length);
871 }
872
873 public int characteristics() {
874 return Spliterator.NONNULL
875 | Spliterator.ORDERED
876 | Spliterator.SIZED
877 | Spliterator.SUBSIZED;
878 }
879 }
880
881 /**
882 * @throws NullPointerException {@inheritDoc}
883 */
884 public void forEach(Consumer<? super E> action) {
885 Objects.requireNonNull(action);
886 final Object[] es = elements;
887 for (int i = head, end = tail, to = (i <= end) ? end : es.length;
888 ; i = 0, to = end) {
889 for (; i < to; i++)
890 action.accept(elementAt(es, i));
891 if (to == end) {
892 if (end != tail) throw new ConcurrentModificationException();
893 break;
894 }
895 }
896 }
897
898 /**
899 * @throws NullPointerException {@inheritDoc}
900 */
901 public boolean removeIf(Predicate<? super E> filter) {
902 Objects.requireNonNull(filter);
903 return bulkRemove(filter);
904 }
905
906 /**
907 * @throws NullPointerException {@inheritDoc}
908 */
909 public boolean removeAll(Collection<?> c) {
910 Objects.requireNonNull(c);
911 return bulkRemove(e -> c.contains(e));
912 }
913
914 /**
915 * @throws NullPointerException {@inheritDoc}
916 */
917 public boolean retainAll(Collection<?> c) {
918 Objects.requireNonNull(c);
919 return bulkRemove(e -> !c.contains(e));
920 }
921
922 /** Implementation of bulk remove methods. */
923 private boolean bulkRemove(Predicate<? super E> filter) {
924 final Object[] es = elements;
925 // Optimize for initial run of survivors
926 for (int i = head, end = tail, to = (i <= end) ? end : es.length;
927 ; i = 0, to = end) {
928 for (; i < to; i++)
929 if (filter.test(elementAt(es, i)))
930 return bulkRemoveModified(filter, i);
931 if (to == end) {
932 if (end != tail) throw new ConcurrentModificationException();
933 break;
934 }
935 }
936 return false;
937 }
938
939 // A tiny bit set implementation
940
941 private static long[] nBits(int n) {
942 return new long[((n - 1) >> 6) + 1];
943 }
944 private static void setBit(long[] bits, int i) {
945 bits[i >> 6] |= 1L << i;
946 }
947 private static boolean isClear(long[] bits, int i) {
948 return (bits[i >> 6] & (1L << i)) == 0;
949 }
950
951 /**
952 * Helper for bulkRemove, in case of at least one deletion.
953 * Tolerate predicates that reentrantly access the collection for
954 * read (but writers still get CME), so traverse once to find
955 * elements to delete, a second pass to physically expunge.
956 *
957 * @param beg valid index of first element to be deleted
958 */
959 private boolean bulkRemoveModified(
960 Predicate<? super E> filter, final int beg) {
961 final Object[] es = elements;
962 final int capacity = es.length;
963 final int end = tail;
964 final long[] deathRow = nBits(sub(end, beg, capacity));
965 deathRow[0] = 1L; // set bit 0
966 for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
967 ; i = 0, to = end, k -= capacity) {
968 for (; i < to; i++)
969 if (filter.test(elementAt(es, i)))
970 setBit(deathRow, i - k);
971 if (to == end) break;
972 }
973 // a two-finger traversal, with hare i reading, tortoise w writing
974 int w = beg;
975 for (int i = beg + 1, to = (i <= end) ? end : es.length, k = beg;
976 ; w = 0) { // w rejoins i on second leg
977 // In this loop, i and w are on the same leg, with i > w
978 for (; i < to; i++)
979 if (isClear(deathRow, i - k))
980 es[w++] = es[i];
981 if (to == end) break;
982 // In this loop, w is on the first leg, i on the second
983 for (i = 0, to = end, k -= capacity; i < to && w < capacity; i++)
984 if (isClear(deathRow, i - k))
985 es[w++] = es[i];
986 if (i >= to) {
987 if (w == capacity) w = 0; // "corner" case
988 break;
989 }
990 }
991 if (end != tail) throw new ConcurrentModificationException();
992 circularClear(es, tail = w, end);
993 return true;
994 }
995
996 /**
997 * Returns {@code true} if this deque contains the specified element.
998 * More formally, returns {@code true} if and only if this deque contains
999 * at least one element {@code e} such that {@code o.equals(e)}.
1000 *
1001 * @param o object to be checked for containment in this deque
1002 * @return {@code true} if this deque contains the specified element
1003 */
1004 public boolean contains(Object o) {
1005 if (o != null) {
1006 final Object[] es = elements;
1007 for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1008 ; i = 0, to = end) {
1009 for (; i < to; i++)
1010 if (o.equals(es[i]))
1011 return true;
1012 if (to == end) break;
1013 }
1014 }
1015 return false;
1016 }
1017
1018 /**
1019 * Removes a single instance of the specified element from this deque.
1020 * If the deque does not contain the element, it is unchanged.
1021 * More formally, removes the first element {@code e} such that
1022 * {@code o.equals(e)} (if such an element exists).
1023 * Returns {@code true} if this deque contained the specified element
1024 * (or equivalently, if this deque changed as a result of the call).
1025 *
1026 * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}.
1027 *
1028 * @param o element to be removed from this deque, if present
1029 * @return {@code true} if this deque contained the specified element
1030 */
1031 public boolean remove(Object o) {
1032 return removeFirstOccurrence(o);
1033 }
1034
1035 /**
1036 * Removes all of the elements from this deque.
1037 * The deque will be empty after this call returns.
1038 */
1039 public void clear() {
1040 circularClear(elements, head, tail);
1041 head = tail = 0;
1042 }
1043
1044 /**
1045 * Nulls out slots starting at array index i, upto index end.
1046 * Condition i == end means "empty" - nothing to do.
1047 */
1048 private static void circularClear(Object[] es, int i, int end) {
1049 // assert 0 <= i && i < es.length;
1050 // assert 0 <= end && end < es.length;
1051 for (int to = (i <= end) ? end : es.length;
1052 ; i = 0, to = end) {
1053 for (; i < to; i++) es[i] = null;
1054 if (to == end) break;
1055 }
1056 }
1057
1058 /**
1059 * Returns an array containing all of the elements in this deque
1060 * in proper sequence (from first to last element).
1061 *
1062 * <p>The returned array will be "safe" in that no references to it are
1063 * maintained by this deque. (In other words, this method must allocate
1064 * a new array). The caller is thus free to modify the returned array.
1065 *
1066 * <p>This method acts as bridge between array-based and collection-based
1067 * APIs.
1068 *
1069 * @return an array containing all of the elements in this deque
1070 */
1071 public Object[] toArray() {
1072 return toArray(Object[].class);
1073 }
1074
1075 private <T> T[] toArray(Class<T[]> klazz) {
1076 final Object[] es = elements;
1077 final T[] a;
1078 final int head = this.head, tail = this.tail, end;
1079 if ((end = tail + ((head <= tail) ? 0 : es.length)) >= 0) {
1080 // Uses null extension feature of copyOfRange
1081 a = Arrays.copyOfRange(es, head, end, klazz);
1082 } else {
1083 // integer overflow!
1084 a = Arrays.copyOfRange(es, 0, end - head, klazz);
1085 System.arraycopy(es, head, a, 0, es.length - head);
1086 }
1087 if (end != tail)
1088 System.arraycopy(es, 0, a, es.length - head, tail);
1089 return a;
1090 }
1091
1092 /**
1093 * Returns an array containing all of the elements in this deque in
1094 * proper sequence (from first to last element); the runtime type of the
1095 * returned array is that of the specified array. If the deque fits in
1096 * the specified array, it is returned therein. Otherwise, a new array
1097 * is allocated with the runtime type of the specified array and the
1098 * size of this deque.
1099 *
1100 * <p>If this deque fits in the specified array with room to spare
1101 * (i.e., the array has more elements than this deque), the element in
1102 * the array immediately following the end of the deque is set to
1103 * {@code null}.
1104 *
1105 * <p>Like the {@link #toArray()} method, this method acts as bridge between
1106 * array-based and collection-based APIs. Further, this method allows
1107 * precise control over the runtime type of the output array, and may,
1108 * under certain circumstances, be used to save allocation costs.
1109 *
1110 * <p>Suppose {@code x} is a deque known to contain only strings.
1111 * The following code can be used to dump the deque into a newly
1112 * allocated array of {@code String}:
1113 *
1114 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre>
1115 *
1116 * Note that {@code toArray(new Object[0])} is identical in function to
1117 * {@code toArray()}.
1118 *
1119 * @param a the array into which the elements of the deque are to
1120 * be stored, if it is big enough; otherwise, a new array of the
1121 * same runtime type is allocated for this purpose
1122 * @return an array containing all of the elements in this deque
1123 * @throws ArrayStoreException if the runtime type of the specified array
1124 * is not a supertype of the runtime type of every element in
1125 * this deque
1126 * @throws NullPointerException if the specified array is null
1127 */
1128 @SuppressWarnings("unchecked")
1129 public <T> T[] toArray(T[] a) {
1130 final int size;
1131 if ((size = size()) > a.length)
1132 return toArray((Class<T[]>) a.getClass());
1133 final Object[] es = elements;
1134 for (int i = head, j = 0, len = Math.min(size, es.length - i);
1135 ; i = 0, len = tail) {
1136 System.arraycopy(es, i, a, j, len);
1137 if ((j += len) == size) break;
1138 }
1139 if (size < a.length)
1140 a[size] = null;
1141 return a;
1142 }
1143
1144 // *** Object methods ***
1145
1146 /**
1147 * Returns a copy of this deque.
1148 *
1149 * @return a copy of this deque
1150 */
1151 public ArrayDeque<E> clone() {
1152 try {
1153 @SuppressWarnings("unchecked")
1154 ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
1155 result.elements = Arrays.copyOf(elements, elements.length);
1156 return result;
1157 } catch (CloneNotSupportedException e) {
1158 throw new AssertionError();
1159 }
1160 }
1161
1162 private static final long serialVersionUID = 2340985798034038923L;
1163
1164 /**
1165 * Saves this deque to a stream (that is, serializes it).
1166 *
1167 * @param s the stream
1168 * @throws java.io.IOException if an I/O error occurs
1169 * @serialData The current size ({@code int}) of the deque,
1170 * followed by all of its elements (each an object reference) in
1171 * first-to-last order.
1172 */
1173 private void writeObject(java.io.ObjectOutputStream s)
1174 throws java.io.IOException {
1175 s.defaultWriteObject();
1176
1177 // Write out size
1178 s.writeInt(size());
1179
1180 // Write out elements in order.
1181 final Object[] es = elements;
1182 for (int i = head, end = tail, to = (i <= end) ? end : es.length;
1183 ; i = 0, to = end) {
1184 for (; i < to; i++)
1185 s.writeObject(es[i]);
1186 if (to == end) break;
1187 }
1188 }
1189
1190 /**
1191 * Reconstitutes this deque from a stream (that is, deserializes it).
1192 * @param s the stream
1193 * @throws ClassNotFoundException if the class of a serialized object
1194 * could not be found
1195 * @throws java.io.IOException if an I/O error occurs
1196 */
1197 private void readObject(java.io.ObjectInputStream s)
1198 throws java.io.IOException, ClassNotFoundException {
1199 s.defaultReadObject();
1200
1201 // Read in size and allocate array
1202 int size = s.readInt();
1203 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size + 1);
1204 elements = new Object[size + 1];
1205 this.tail = size;
1206
1207 // Read in all elements in the proper order.
1208 for (int i = 0; i < size; i++)
1209 elements[i] = s.readObject();
1210 }
1211
1212 /** debugging */
1213 void checkInvariants() {
1214 // Use head and tail fields with empty slot at tail strategy.
1215 // head == tail disambiguates to "empty".
1216 try {
1217 int capacity = elements.length;
1218 // assert 0 <= head && head < capacity;
1219 // assert 0 <= tail && tail < capacity;
1220 // assert capacity > 0;
1221 // assert size() < capacity;
1222 // assert head == tail || elements[head] != null;
1223 // assert elements[tail] == null;
1224 // assert head == tail || elements[dec(tail, capacity)] != null;
1225 } catch (Throwable t) {
1226 System.err.printf("head=%d tail=%d capacity=%d%n",
1227 head, tail, elements.length);
1228 System.err.printf("elements=%s%n",
1229 Arrays.toString(elements));
1230 throw t;
1231 }
1232 }
1233
1234 }