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