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