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 40 // BEGIN android-note 41 // removed link to collections framework docs 42 // END android-note 43 44 /** 45 * Resizable-array implementation of the {@link Deque} interface. Array 46 * deques have no capacity restrictions; they grow as necessary to support 47 * usage. They are not thread-safe; in the absence of external 48 * synchronization, they do not support concurrent access by multiple threads. 49 * Null elements are prohibited. This class is likely to be faster than 50 * {@link Stack} when used as a stack, and faster than {@link LinkedList} 51 * when used as a queue. 52 * 53 * <p>Most {@code ArrayDeque} operations run in amortized constant time. 54 * Exceptions include 55 * {@link #remove(Object) remove}, 56 * {@link #removeFirstOccurrence removeFirstOccurrence}, 57 * {@link #removeLastOccurrence removeLastOccurrence}, 58 * {@link #contains contains}, 59 * {@link #iterator iterator.remove()}, 60 * and the bulk operations, all of which run in linear time. 61 * 62 * <p>The iterators returned by this class's {@link #iterator() iterator} 63 * method are <em>fail-fast</em>: If the deque is modified at any time after 64 * the iterator is created, in any way except through the iterator's own 65 * {@code remove} method, the iterator will generally throw a {@link 66 * ConcurrentModificationException}. Thus, in the face of concurrent 67 * modification, the iterator fails quickly and cleanly, rather than risking 68 * arbitrary, non-deterministic behavior at an undetermined time in the 69 * future. 70 * 71 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed 72 * as it is, generally speaking, impossible to make any hard guarantees in the 73 * presence of unsynchronized concurrent modification. Fail-fast iterators 74 * throw {@code ConcurrentModificationException} on a best-effort basis. 75 * Therefore, it would be wrong to write a program that depended on this 76 * exception for its correctness: <i>the fail-fast behavior of iterators 77 * should be used only to detect bugs.</i> 78 * 79 * <p>This class and its iterator implement all of the 80 * <em>optional</em> methods of the {@link Collection} and {@link 81 * Iterator} interfaces. 82 * 83 * @author Josh Bloch and Doug Lea 84 * @since 1.6 85 * @param <E> the type of elements held in this deque 86 */ 87 public class ArrayDeque<E> extends AbstractCollection<E> 88 implements Deque<E>, Cloneable, Serializable 89 { 90 /** 91 * The array in which the elements of the deque are stored. 92 * The capacity of the deque is the length of this array, which is 93 * always a power of two. The array is never allowed to become 94 * full, except transiently within an addX method where it is 95 * resized (see doubleCapacity) immediately upon becoming full, 96 * thus avoiding head and tail wrapping around to equal each 97 * other. We also guarantee that all array cells not holding 98 * deque elements are always null. 99 */ 100 transient Object[] elements; // non-private to simplify nested class access 101 102 /** 103 * The index of the element at the head of the deque (which is the 104 * element that would be removed by remove() or pop()); or an 105 * arbitrary number equal to tail if the deque is empty. 106 */ 107 transient int head; 108 109 /** 110 * The index at which the next element would be added to the tail 111 * of the deque (via addLast(E), add(E), or push(E)). 112 */ 113 transient int tail; 114 115 /** 116 * The minimum capacity that we'll use for a newly created deque. 117 * Must be a power of 2. 118 */ 119 private static final int MIN_INITIAL_CAPACITY = 8; 120 121 // ****** Array allocation and resizing utilities ****** 122 123 /** 124 * Allocates empty array to hold the given number of elements. 125 * 126 * @param numElements the number of elements to hold 127 */ allocateElements(int numElements)128 private void allocateElements(int numElements) { 129 int initialCapacity = MIN_INITIAL_CAPACITY; 130 // Find the best power of two to hold elements. 131 // Tests "<=" because arrays aren't kept full. 132 if (numElements >= initialCapacity) { 133 initialCapacity = numElements; 134 initialCapacity |= (initialCapacity >>> 1); 135 initialCapacity |= (initialCapacity >>> 2); 136 initialCapacity |= (initialCapacity >>> 4); 137 initialCapacity |= (initialCapacity >>> 8); 138 initialCapacity |= (initialCapacity >>> 16); 139 initialCapacity++; 140 141 if (initialCapacity < 0) // Too many elements, must back off 142 initialCapacity >>>= 1; // Good luck allocating 2^30 elements 143 } 144 elements = new Object[initialCapacity]; 145 } 146 147 /** 148 * Doubles the capacity of this deque. Call only when full, i.e., 149 * when head and tail have wrapped around to become equal. 150 */ doubleCapacity()151 private void doubleCapacity() { 152 assert head == tail; 153 int p = head; 154 int n = elements.length; 155 int r = n - p; // number of elements to the right of p 156 int newCapacity = n << 1; 157 if (newCapacity < 0) 158 throw new IllegalStateException("Sorry, deque too big"); 159 Object[] a = new Object[newCapacity]; 160 System.arraycopy(elements, p, a, 0, r); 161 System.arraycopy(elements, 0, a, r, p); 162 // Android-added: Clear old array instance that's about to become eligible for GC. 163 // This ensures that array elements can be eligible for garbage collection even 164 // before the array itself is recognized as being eligible; the latter might 165 // take a while in some GC implementations, if the array instance is longer lived 166 // (its liveness rarely checked) than some of its contents. 167 Arrays.fill(elements, null); 168 elements = a; 169 head = 0; 170 tail = n; 171 } 172 173 /** 174 * Constructs an empty array deque with an initial capacity 175 * sufficient to hold 16 elements. 176 */ ArrayDeque()177 public ArrayDeque() { 178 elements = new Object[16]; 179 } 180 181 /** 182 * Constructs an empty array deque with an initial capacity 183 * sufficient to hold the specified number of elements. 184 * 185 * @param numElements lower bound on initial capacity of the deque 186 */ ArrayDeque(int numElements)187 public ArrayDeque(int numElements) { 188 allocateElements(numElements); 189 } 190 191 /** 192 * Constructs a deque containing the elements of the specified 193 * collection, in the order they are returned by the collection's 194 * iterator. (The first element returned by the collection's 195 * iterator becomes the first element, or <i>front</i> of the 196 * deque.) 197 * 198 * @param c the collection whose elements are to be placed into the deque 199 * @throws NullPointerException if the specified collection is null 200 */ ArrayDeque(Collection<? extends E> c)201 public ArrayDeque(Collection<? extends E> c) { 202 allocateElements(c.size()); 203 addAll(c); 204 } 205 206 // The main insertion and extraction methods are addFirst, 207 // addLast, pollFirst, pollLast. The other methods are defined in 208 // terms of these. 209 210 /** 211 * Inserts the specified element at the front of this deque. 212 * 213 * @param e the element to add 214 * @throws NullPointerException if the specified element is null 215 */ addFirst(E e)216 public void addFirst(E e) { 217 if (e == null) 218 throw new NullPointerException(); 219 elements[head = (head - 1) & (elements.length - 1)] = e; 220 if (head == tail) 221 doubleCapacity(); 222 } 223 224 /** 225 * Inserts the specified element at the end of this deque. 226 * 227 * <p>This method is equivalent to {@link #add}. 228 * 229 * @param e the element to add 230 * @throws NullPointerException if the specified element is null 231 */ addLast(E e)232 public void addLast(E e) { 233 if (e == null) 234 throw new NullPointerException(); 235 elements[tail] = e; 236 if ( (tail = (tail + 1) & (elements.length - 1)) == head) 237 doubleCapacity(); 238 } 239 240 /** 241 * Inserts the specified element at the front of this deque. 242 * 243 * @param e the element to add 244 * @return {@code true} (as specified by {@link Deque#offerFirst}) 245 * @throws NullPointerException if the specified element is null 246 */ offerFirst(E e)247 public boolean offerFirst(E e) { 248 addFirst(e); 249 return true; 250 } 251 252 /** 253 * Inserts the specified element at the end of this deque. 254 * 255 * @param e the element to add 256 * @return {@code true} (as specified by {@link Deque#offerLast}) 257 * @throws NullPointerException if the specified element is null 258 */ offerLast(E e)259 public boolean offerLast(E e) { 260 addLast(e); 261 return true; 262 } 263 264 /** 265 * @throws NoSuchElementException {@inheritDoc} 266 */ removeFirst()267 public E removeFirst() { 268 E x = pollFirst(); 269 if (x == null) 270 throw new NoSuchElementException(); 271 return x; 272 } 273 274 /** 275 * @throws NoSuchElementException {@inheritDoc} 276 */ removeLast()277 public E removeLast() { 278 E x = pollLast(); 279 if (x == null) 280 throw new NoSuchElementException(); 281 return x; 282 } 283 pollFirst()284 public E pollFirst() { 285 final Object[] elements = this.elements; 286 final int h = head; 287 @SuppressWarnings("unchecked") 288 E result = (E) elements[h]; 289 // Element is null if deque empty 290 if (result != null) { 291 elements[h] = null; // Must null out slot 292 head = (h + 1) & (elements.length - 1); 293 } 294 return result; 295 } 296 pollLast()297 public E pollLast() { 298 final Object[] elements = this.elements; 299 final int t = (tail - 1) & (elements.length - 1); 300 @SuppressWarnings("unchecked") 301 E result = (E) elements[t]; 302 if (result != null) { 303 elements[t] = null; 304 tail = t; 305 } 306 return result; 307 } 308 309 /** 310 * @throws NoSuchElementException {@inheritDoc} 311 */ getFirst()312 public E getFirst() { 313 @SuppressWarnings("unchecked") 314 E result = (E) elements[head]; 315 if (result == null) 316 throw new NoSuchElementException(); 317 return result; 318 } 319 320 /** 321 * @throws NoSuchElementException {@inheritDoc} 322 */ getLast()323 public E getLast() { 324 @SuppressWarnings("unchecked") 325 E result = (E) elements[(tail - 1) & (elements.length - 1)]; 326 if (result == null) 327 throw new NoSuchElementException(); 328 return result; 329 } 330 331 @SuppressWarnings("unchecked") peekFirst()332 public E peekFirst() { 333 // elements[head] is null if deque empty 334 return (E) elements[head]; 335 } 336 337 @SuppressWarnings("unchecked") peekLast()338 public E peekLast() { 339 return (E) elements[(tail - 1) & (elements.length - 1)]; 340 } 341 342 /** 343 * Removes the first occurrence of the specified element in this 344 * deque (when traversing the deque from head to tail). 345 * If the deque does not contain the element, it is unchanged. 346 * More formally, removes the first element {@code e} such that 347 * {@code o.equals(e)} (if such an element exists). 348 * Returns {@code true} if this deque contained the specified element 349 * (or equivalently, if this deque changed as a result of the call). 350 * 351 * @param o element to be removed from this deque, if present 352 * @return {@code true} if the deque contained the specified element 353 */ removeFirstOccurrence(Object o)354 public boolean removeFirstOccurrence(Object o) { 355 if (o != null) { 356 int mask = elements.length - 1; 357 int i = head; 358 for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { 359 if (o.equals(x)) { 360 delete(i); 361 return true; 362 } 363 } 364 } 365 return false; 366 } 367 368 /** 369 * Removes the last occurrence of the specified element in this 370 * deque (when traversing the deque from head to tail). 371 * If the deque does not contain the element, it is unchanged. 372 * More formally, removes the last element {@code e} such that 373 * {@code o.equals(e)} (if such an element exists). 374 * Returns {@code true} if this deque contained the specified element 375 * (or equivalently, if this deque changed as a result of the call). 376 * 377 * @param o element to be removed from this deque, if present 378 * @return {@code true} if the deque contained the specified element 379 */ removeLastOccurrence(Object o)380 public boolean removeLastOccurrence(Object o) { 381 if (o != null) { 382 int mask = elements.length - 1; 383 int i = (tail - 1) & mask; 384 for (Object x; (x = elements[i]) != null; i = (i - 1) & mask) { 385 if (o.equals(x)) { 386 delete(i); 387 return true; 388 } 389 } 390 } 391 return false; 392 } 393 394 // *** Queue methods *** 395 396 /** 397 * Inserts the specified element at the end of this deque. 398 * 399 * <p>This method is equivalent to {@link #addLast}. 400 * 401 * @param e the element to add 402 * @return {@code true} (as specified by {@link Collection#add}) 403 * @throws NullPointerException if the specified element is null 404 */ add(E e)405 public boolean add(E e) { 406 addLast(e); 407 return true; 408 } 409 410 /** 411 * Inserts the specified element at the end of this deque. 412 * 413 * <p>This method is equivalent to {@link #offerLast}. 414 * 415 * @param e the element to add 416 * @return {@code true} (as specified by {@link Queue#offer}) 417 * @throws NullPointerException if the specified element is null 418 */ offer(E e)419 public boolean offer(E e) { 420 return offerLast(e); 421 } 422 423 /** 424 * Retrieves and removes the head of the queue represented by this deque. 425 * 426 * This method differs from {@link #poll poll} only in that it throws an 427 * exception if this deque is empty. 428 * 429 * <p>This method is equivalent to {@link #removeFirst}. 430 * 431 * @return the head of the queue represented by this deque 432 * @throws NoSuchElementException {@inheritDoc} 433 */ remove()434 public E remove() { 435 return removeFirst(); 436 } 437 438 /** 439 * Retrieves and removes the head of the queue represented by this deque 440 * (in other words, the first element of this deque), or returns 441 * {@code null} if this deque is empty. 442 * 443 * <p>This method is equivalent to {@link #pollFirst}. 444 * 445 * @return the head of the queue represented by this deque, or 446 * {@code null} if this deque is empty 447 */ poll()448 public E poll() { 449 return pollFirst(); 450 } 451 452 /** 453 * Retrieves, but does not remove, the head of the queue represented by 454 * this deque. This method differs from {@link #peek peek} only in 455 * that it throws an exception if this deque is empty. 456 * 457 * <p>This method is equivalent to {@link #getFirst}. 458 * 459 * @return the head of the queue represented by this deque 460 * @throws NoSuchElementException {@inheritDoc} 461 */ element()462 public E element() { 463 return getFirst(); 464 } 465 466 /** 467 * Retrieves, but does not remove, the head of the queue represented by 468 * this deque, or returns {@code null} if this deque is empty. 469 * 470 * <p>This method is equivalent to {@link #peekFirst}. 471 * 472 * @return the head of the queue represented by this deque, or 473 * {@code null} if this deque is empty 474 */ peek()475 public E peek() { 476 return peekFirst(); 477 } 478 479 // *** Stack methods *** 480 481 /** 482 * Pushes an element onto the stack represented by this deque. In other 483 * words, inserts the element at the front of this deque. 484 * 485 * <p>This method is equivalent to {@link #addFirst}. 486 * 487 * @param e the element to push 488 * @throws NullPointerException if the specified element is null 489 */ push(E e)490 public void push(E e) { 491 addFirst(e); 492 } 493 494 /** 495 * Pops an element from the stack represented by this deque. In other 496 * words, removes and returns the first element of this deque. 497 * 498 * <p>This method is equivalent to {@link #removeFirst()}. 499 * 500 * @return the element at the front of this deque (which is the top 501 * of the stack represented by this deque) 502 * @throws NoSuchElementException {@inheritDoc} 503 */ pop()504 public E pop() { 505 return removeFirst(); 506 } 507 checkInvariants()508 private void checkInvariants() { 509 assert elements[tail] == null; 510 assert head == tail ? elements[head] == null : 511 (elements[head] != null && 512 elements[(tail - 1) & (elements.length - 1)] != null); 513 assert elements[(head - 1) & (elements.length - 1)] == null; 514 } 515 516 /** 517 * Removes the element at the specified position in the elements array, 518 * adjusting head and tail as necessary. This can result in motion of 519 * elements backwards or forwards in the array. 520 * 521 * <p>This method is called delete rather than remove to emphasize 522 * that its semantics differ from those of {@link List#remove(int)}. 523 * 524 * @return true if elements moved backwards 525 */ delete(int i)526 boolean delete(int i) { 527 checkInvariants(); 528 final Object[] elements = this.elements; 529 final int mask = elements.length - 1; 530 final int h = head; 531 final int t = tail; 532 final int front = (i - h) & mask; 533 final int back = (t - i) & mask; 534 535 // Invariant: head <= i < tail mod circularity 536 if (front >= ((t - h) & mask)) 537 throw new ConcurrentModificationException(); 538 539 // Optimize for least element motion 540 if (front < back) { 541 if (h <= i) { 542 System.arraycopy(elements, h, elements, h + 1, front); 543 } else { // Wrap around 544 System.arraycopy(elements, 0, elements, 1, i); 545 elements[0] = elements[mask]; 546 System.arraycopy(elements, h, elements, h + 1, mask - h); 547 } 548 elements[h] = null; 549 head = (h + 1) & mask; 550 return false; 551 } else { 552 if (i < t) { // Copy the null tail as well 553 System.arraycopy(elements, i + 1, elements, i, back); 554 tail = t - 1; 555 } else { // Wrap around 556 System.arraycopy(elements, i + 1, elements, i, mask - i); 557 elements[mask] = elements[0]; 558 System.arraycopy(elements, 1, elements, 0, t); 559 tail = (t - 1) & mask; 560 } 561 return true; 562 } 563 } 564 565 // *** Collection Methods *** 566 567 /** 568 * Returns the number of elements in this deque. 569 * 570 * @return the number of elements in this deque 571 */ size()572 public int size() { 573 return (tail - head) & (elements.length - 1); 574 } 575 576 /** 577 * Returns {@code true} if this deque contains no elements. 578 * 579 * @return {@code true} if this deque contains no elements 580 */ isEmpty()581 public boolean isEmpty() { 582 return head == tail; 583 } 584 585 /** 586 * Returns an iterator over the elements in this deque. The elements 587 * will be ordered from first (head) to last (tail). This is the same 588 * order that elements would be dequeued (via successive calls to 589 * {@link #remove} or popped (via successive calls to {@link #pop}). 590 * 591 * @return an iterator over the elements in this deque 592 */ iterator()593 public Iterator<E> iterator() { 594 return new DeqIterator(); 595 } 596 descendingIterator()597 public Iterator<E> descendingIterator() { 598 return new DescendingIterator(); 599 } 600 601 private class DeqIterator implements Iterator<E> { 602 /** 603 * Index of element to be returned by subsequent call to next. 604 */ 605 private int cursor = head; 606 607 /** 608 * Tail recorded at construction (also in remove), to stop 609 * iterator and also to check for comodification. 610 */ 611 private int fence = tail; 612 613 /** 614 * Index of element returned by most recent call to next. 615 * Reset to -1 if element is deleted by a call to remove. 616 */ 617 private int lastRet = -1; 618 hasNext()619 public boolean hasNext() { 620 return cursor != fence; 621 } 622 next()623 public E next() { 624 if (cursor == fence) 625 throw new NoSuchElementException(); 626 @SuppressWarnings("unchecked") 627 E result = (E) elements[cursor]; 628 // This check doesn't catch all possible comodifications, 629 // but does catch the ones that corrupt traversal 630 if (tail != fence || result == null) 631 throw new ConcurrentModificationException(); 632 lastRet = cursor; 633 cursor = (cursor + 1) & (elements.length - 1); 634 return result; 635 } 636 remove()637 public void remove() { 638 if (lastRet < 0) 639 throw new IllegalStateException(); 640 if (delete(lastRet)) { // if left-shifted, undo increment in next() 641 cursor = (cursor - 1) & (elements.length - 1); 642 fence = tail; 643 } 644 lastRet = -1; 645 } 646 647 @Override forEachRemaining(Consumer<? super E> action)648 public void forEachRemaining(Consumer<? super E> action) { 649 Objects.requireNonNull(action); 650 Object[] a = elements; 651 int m = a.length - 1, f = fence, i = cursor; 652 cursor = f; 653 while (i != f) { 654 @SuppressWarnings("unchecked") E e = (E)a[i]; 655 i = (i + 1) & m; 656 // Android-note: This uses a different heuristic for detecting 657 // concurrent modification exceptions than next(). As such, this is a less 658 // precise test. 659 if (e == null) 660 throw new ConcurrentModificationException(); 661 action.accept(e); 662 } 663 } 664 } 665 666 /** 667 * This class is nearly a mirror-image of DeqIterator, using tail 668 * instead of head for initial cursor, and head instead of tail 669 * for fence. 670 */ 671 private class DescendingIterator implements Iterator<E> { 672 private int cursor = tail; 673 private int fence = head; 674 private int lastRet = -1; 675 hasNext()676 public boolean hasNext() { 677 return cursor != fence; 678 } 679 next()680 public E next() { 681 if (cursor == fence) 682 throw new NoSuchElementException(); 683 cursor = (cursor - 1) & (elements.length - 1); 684 @SuppressWarnings("unchecked") 685 E result = (E) elements[cursor]; 686 if (head != fence || result == null) 687 throw new ConcurrentModificationException(); 688 lastRet = cursor; 689 return result; 690 } 691 remove()692 public void remove() { 693 if (lastRet < 0) 694 throw new IllegalStateException(); 695 if (!delete(lastRet)) { 696 cursor = (cursor + 1) & (elements.length - 1); 697 fence = head; 698 } 699 lastRet = -1; 700 } 701 } 702 703 /** 704 * Returns {@code true} if this deque contains the specified element. 705 * More formally, returns {@code true} if and only if this deque contains 706 * at least one element {@code e} such that {@code o.equals(e)}. 707 * 708 * @param o object to be checked for containment in this deque 709 * @return {@code true} if this deque contains the specified element 710 */ contains(Object o)711 public boolean contains(Object o) { 712 if (o != null) { 713 int mask = elements.length - 1; 714 int i = head; 715 for (Object x; (x = elements[i]) != null; i = (i + 1) & mask) { 716 if (o.equals(x)) 717 return true; 718 } 719 } 720 return false; 721 } 722 723 /** 724 * Removes a single instance of the specified element from this deque. 725 * If the deque does not contain the element, it is unchanged. 726 * More formally, removes the first element {@code e} such that 727 * {@code o.equals(e)} (if such an element exists). 728 * Returns {@code true} if this deque contained the specified element 729 * (or equivalently, if this deque changed as a result of the call). 730 * 731 * <p>This method is equivalent to {@link #removeFirstOccurrence(Object)}. 732 * 733 * @param o element to be removed from this deque, if present 734 * @return {@code true} if this deque contained the specified element 735 */ remove(Object o)736 public boolean remove(Object o) { 737 return removeFirstOccurrence(o); 738 } 739 740 /** 741 * Removes all of the elements from this deque. 742 * The deque will be empty after this call returns. 743 */ clear()744 public void clear() { 745 int h = head; 746 int t = tail; 747 if (h != t) { // clear all cells 748 head = tail = 0; 749 int i = h; 750 int mask = elements.length - 1; 751 do { 752 elements[i] = null; 753 i = (i + 1) & mask; 754 } while (i != t); 755 } 756 } 757 758 /** 759 * Returns an array containing all of the elements in this deque 760 * in proper sequence (from first to last element). 761 * 762 * <p>The returned array will be "safe" in that no references to it are 763 * maintained by this deque. (In other words, this method must allocate 764 * a new array). The caller is thus free to modify the returned array. 765 * 766 * <p>This method acts as bridge between array-based and collection-based 767 * APIs. 768 * 769 * @return an array containing all of the elements in this deque 770 */ toArray()771 public Object[] toArray() { 772 final int head = this.head; 773 final int tail = this.tail; 774 boolean wrap = (tail < head); 775 int end = wrap ? tail + elements.length : tail; 776 Object[] a = Arrays.copyOfRange(elements, head, end); 777 if (wrap) 778 System.arraycopy(elements, 0, a, elements.length - head, tail); 779 return a; 780 } 781 782 /** 783 * Returns an array containing all of the elements in this deque in 784 * proper sequence (from first to last element); the runtime type of the 785 * returned array is that of the specified array. If the deque fits in 786 * the specified array, it is returned therein. Otherwise, a new array 787 * is allocated with the runtime type of the specified array and the 788 * size of this deque. 789 * 790 * <p>If this deque fits in the specified array with room to spare 791 * (i.e., the array has more elements than this deque), the element in 792 * the array immediately following the end of the deque is set to 793 * {@code null}. 794 * 795 * <p>Like the {@link #toArray()} method, this method acts as bridge between 796 * array-based and collection-based APIs. Further, this method allows 797 * precise control over the runtime type of the output array, and may, 798 * under certain circumstances, be used to save allocation costs. 799 * 800 * <p>Suppose {@code x} is a deque known to contain only strings. 801 * The following code can be used to dump the deque into a newly 802 * allocated array of {@code String}: 803 * 804 * <pre> {@code String[] y = x.toArray(new String[0]);}</pre> 805 * 806 * Note that {@code toArray(new Object[0])} is identical in function to 807 * {@code toArray()}. 808 * 809 * @param a the array into which the elements of the deque are to 810 * be stored, if it is big enough; otherwise, a new array of the 811 * same runtime type is allocated for this purpose 812 * @return an array containing all of the elements in this deque 813 * @throws ArrayStoreException if the runtime type of the specified array 814 * is not a supertype of the runtime type of every element in 815 * this deque 816 * @throws NullPointerException if the specified array is null 817 */ 818 @SuppressWarnings("unchecked") toArray(T[] a)819 public <T> T[] toArray(T[] a) { 820 final int head = this.head; 821 final int tail = this.tail; 822 boolean wrap = (tail < head); 823 int size = (tail - head) + (wrap ? elements.length : 0); 824 int firstLeg = size - (wrap ? tail : 0); 825 int len = a.length; 826 if (size > len) { 827 a = (T[]) Arrays.copyOfRange(elements, head, head + size, 828 a.getClass()); 829 } else { 830 System.arraycopy(elements, head, a, 0, firstLeg); 831 if (size < len) 832 a[size] = null; 833 } 834 if (wrap) 835 System.arraycopy(elements, 0, a, firstLeg, tail); 836 return a; 837 } 838 839 // *** Object methods *** 840 841 /** 842 * Returns a copy of this deque. 843 * 844 * @return a copy of this deque 845 */ clone()846 public ArrayDeque<E> clone() { 847 try { 848 @SuppressWarnings("unchecked") 849 ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); 850 result.elements = Arrays.copyOf(elements, elements.length); 851 return result; 852 } catch (CloneNotSupportedException e) { 853 throw new AssertionError(); 854 } 855 } 856 857 private static final long serialVersionUID = 2340985798034038923L; 858 859 /** 860 * Saves this deque to a stream (that is, serializes it). 861 * 862 * @param s the stream 863 * @throws java.io.IOException if an I/O error occurs 864 * @serialData The current size ({@code int}) of the deque, 865 * followed by all of its elements (each an object reference) in 866 * first-to-last order. 867 */ writeObject(java.io.ObjectOutputStream s)868 private void writeObject(java.io.ObjectOutputStream s) 869 throws java.io.IOException { 870 s.defaultWriteObject(); 871 872 // Write out size 873 s.writeInt(size()); 874 875 // Write out elements in order. 876 int mask = elements.length - 1; 877 for (int i = head; i != tail; i = (i + 1) & mask) 878 s.writeObject(elements[i]); 879 } 880 881 /** 882 * Reconstitutes this deque from a stream (that is, deserializes it). 883 * @param s the stream 884 * @throws ClassNotFoundException if the class of a serialized object 885 * could not be found 886 * @throws java.io.IOException if an I/O error occurs 887 */ readObject(java.io.ObjectInputStream s)888 private void readObject(java.io.ObjectInputStream s) 889 throws java.io.IOException, ClassNotFoundException { 890 s.defaultReadObject(); 891 892 // Read in size and allocate array 893 int size = s.readInt(); 894 allocateElements(size); 895 head = 0; 896 tail = size; 897 898 // Read in all elements in the proper order. 899 for (int i = 0; i < size; i++) 900 elements[i] = s.readObject(); 901 } 902 903 /** 904 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em> 905 * and <em>fail-fast</em> {@link Spliterator} over the elements in this 906 * deque. 907 * 908 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED}, 909 * {@link Spliterator#SUBSIZED}, {@link Spliterator#ORDERED}, and 910 * {@link Spliterator#NONNULL}. Overriding implementations should document 911 * the reporting of additional characteristic values. 912 * 913 * @return a {@code Spliterator} over the elements in this deque 914 * @since 1.8 915 */ spliterator()916 public Spliterator<E> spliterator() { 917 return new DeqSpliterator<>(this, -1, -1); 918 } 919 920 static final class DeqSpliterator<E> implements Spliterator<E> { 921 private final ArrayDeque<E> deq; 922 private int fence; // -1 until first use 923 private int index; // current index, modified on traverse/split 924 925 /** Creates new spliterator covering the given array and range. */ DeqSpliterator(ArrayDeque<E> deq, int origin, int fence)926 DeqSpliterator(ArrayDeque<E> deq, int origin, int fence) { 927 this.deq = deq; 928 this.index = origin; 929 this.fence = fence; 930 } 931 getFence()932 private int getFence() { // force initialization 933 int t; 934 if ((t = fence) < 0) { 935 t = fence = deq.tail; 936 index = deq.head; 937 } 938 return t; 939 } 940 trySplit()941 public DeqSpliterator<E> trySplit() { 942 int t = getFence(), h = index, n = deq.elements.length; 943 if (h != t && ((h + 1) & (n - 1)) != t) { 944 if (h > t) 945 t += n; 946 int m = ((h + t) >>> 1) & (n - 1); 947 return new DeqSpliterator<E>(deq, h, index = m); 948 } 949 return null; 950 } 951 forEachRemaining(Consumer<? super E> consumer)952 public void forEachRemaining(Consumer<? super E> consumer) { 953 if (consumer == null) 954 throw new NullPointerException(); 955 Object[] a = deq.elements; 956 int m = a.length - 1, f = getFence(), i = index; 957 index = f; 958 while (i != f) { 959 @SuppressWarnings("unchecked") E e = (E)a[i]; 960 i = (i + 1) & m; 961 if (e == null) 962 throw new ConcurrentModificationException(); 963 consumer.accept(e); 964 } 965 } 966 tryAdvance(Consumer<? super E> consumer)967 public boolean tryAdvance(Consumer<? super E> consumer) { 968 if (consumer == null) 969 throw new NullPointerException(); 970 Object[] a = deq.elements; 971 int m = a.length - 1, f = getFence(), i = index; 972 if (i != f) { 973 @SuppressWarnings("unchecked") E e = (E)a[i]; 974 index = (i + 1) & m; 975 if (e == null) 976 throw new ConcurrentModificationException(); 977 consumer.accept(e); 978 return true; 979 } 980 return false; 981 } 982 estimateSize()983 public long estimateSize() { 984 int n = getFence() - index; 985 if (n < 0) 986 n += deq.elements.length; 987 return (long) n; 988 } 989 990 @Override characteristics()991 public int characteristics() { 992 return Spliterator.ORDERED | Spliterator.SIZED | 993 Spliterator.NONNULL | Spliterator.SUBSIZED; 994 } 995 } 996 997 } 998