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| 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 | import java.io.*; | ||
| 37 | |||
| 38 | /** | ||
| 39 | * Resizable-array implementation of the {@link Deque} interface. Array | ||
| 40 | * deques have no capacity restrictions; they grow as necessary to support | ||
| 41 | * usage. They are not thread-safe; in the absence of external | ||
| 42 | * synchronization, they do not support concurrent access by multiple threads. | ||
| 43 | * Null elements are prohibited. This class is likely to be faster than | ||
| 44 | * {@link Stack} when used as a stack, and faster than {@link LinkedList} | ||
| 45 | * when used as a queue. | ||
| 46 | * | ||
| 47 | * <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time. | ||
| 48 | * Exceptions include {@link #remove(Object) remove}, {@link | ||
| 49 | * #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence | ||
| 50 | * removeLastOccurrence}, {@link #contains contains}, {@link #iterator | ||
| 51 | * iterator.remove()}, and the bulk operations, all of which run in linear | ||
| 52 | * time. | ||
| 53 | * | ||
| 54 | * <p>The iterators returned by this class's <tt>iterator</tt> method are | ||
| 55 | * <i>fail-fast</i>: If the deque is modified at any time after the iterator | ||
| 56 | * is created, in any way except through the iterator's own <tt>remove</tt> | ||
| 57 | * method, the iterator will generally throw a {@link | ||
| 58 | * ConcurrentModificationException}. Thus, in the face of concurrent | ||
| 59 | * modification, the iterator fails quickly and cleanly, rather than risking | ||
| 60 | * arbitrary, non-deterministic behavior at an undetermined time in the | ||
| 61 | * future. | ||
| 62 | * | ||
| 63 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed | ||
| 64 | * as it is, generally speaking, impossible to make any hard guarantees in the | ||
| 65 | * presence of unsynchronized concurrent modification. Fail-fast iterators | ||
| 66 | * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. | ||
| 67 | * Therefore, it would be wrong to write a program that depended on this | ||
| 68 | * exception for its correctness: <i>the fail-fast behavior of iterators | ||
| 69 | * should be used only to detect bugs.</i> | ||
| 70 | * | ||
| 71 | * <p>This class and its iterator implement all of the | ||
| 72 | * <em>optional</em> methods of the {@link Collection} and {@link | ||
| 73 | * Iterator} interfaces. | ||
| 74 | * | ||
| 75 | * <p>This class is a member of the | ||
| 76 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 77 | * Java Collections Framework</a>. | ||
| 78 | * | ||
| 79 | * @author Josh Bloch and Doug Lea | ||
| 80 | * @since 1.6 | ||
| 81 | * @param <E> the type of elements held in this collection | ||
| 82 | */ | ||
| 83 | public class ArrayDeque<E> extends AbstractCollection<E> | ||
| 84 | implements Deque<E>, Cloneable, Serializable | ||
| 85 | { | ||
| 86 | /** | ||
| 87 | * The array in which the elements of the deque are stored. | ||
| 88 | * The capacity of the deque is the length of this array, which is | ||
| 89 | * always a power of two. The array is never allowed to become | ||
| 90 | * full, except transiently within an addX method where it is | ||
| 91 | * resized (see doubleCapacity) immediately upon becoming full, | ||
| 92 | * thus avoiding head and tail wrapping around to equal each | ||
| 93 | * other. We also guarantee that all array cells not holding | ||
| 94 | * deque elements are always null. | ||
| 95 | */ | ||
| 96 | private transient E[] elements; | ||
| 97 | |||
| 98 | /** | ||
| 99 | * The index of the element at the head of the deque (which is the | ||
| 100 | * element that would be removed by remove() or pop()); or an | ||
| 101 | * arbitrary number equal to tail if the deque is empty. | ||
| 102 | */ | ||
| 103 | private transient int head; | ||
| 104 | |||
| 105 | /** | ||
| 106 | * The index at which the next element would be added to the tail | ||
| 107 | * of the deque (via addLast(E), add(E), or push(E)). | ||
| 108 | */ | ||
| 109 | private transient int tail; | ||
| 110 | |||
| 111 | /** | ||
| 112 | * The minimum capacity that we'll use for a newly created deque. | ||
| 113 | * Must be a power of 2. | ||
| 114 | */ | ||
| 115 | private static final int MIN_INITIAL_CAPACITY = 8; | ||
| 116 | |||
| 117 | // ****** Array allocation and resizing utilities ****** | ||
| 118 | |||
| 119 | /** | ||
| 120 | * Allocate empty array to hold the given number of elements. | ||
| 121 | * | ||
| 122 | * @param numElements the number of elements to hold | ||
| 123 | */ | ||
| 124 | private void allocateElements(int numElements) { | ||
| 125 | int initialCapacity = MIN_INITIAL_CAPACITY; | ||
| 126 | // Find the best power of two to hold elements. | ||
| 127 | // Tests "<=" because arrays aren't kept full. | ||
| 128 | if (numElements >= initialCapacity) { | ||
| 129 | initialCapacity = numElements; | ||
| 130 | initialCapacity |= (initialCapacity >>> 1); | ||
| 131 | initialCapacity |= (initialCapacity >>> 2); | ||
| 132 | initialCapacity |= (initialCapacity >>> 4); | ||
| 133 | initialCapacity |= (initialCapacity >>> 8); | ||
| 134 | initialCapacity |= (initialCapacity >>> 16); | ||
| 135 | initialCapacity++; | ||
| 136 | |||
| 137 | if (initialCapacity < 0) // Too many elements, must back off | ||
| 138 | initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements | ||
| 139 | } | ||
| 140 | elements = (E[]) new Object[initialCapacity]; | ||
| 141 | } | ||
| 142 | |||
| 143 | /** | ||
| 144 | * Double the capacity of this deque. Call only when full, i.e., | ||
| 145 | * when head and tail have wrapped around to become equal. | ||
| 146 | */ | ||
| 147 | private void doubleCapacity() { | ||
| 148 | assert head == tail; | ||
| 149 | int p = head; | ||
| 150 | int n = elements.length; | ||
| 151 | int r = n - p; // number of elements to the right of p | ||
| 152 | int newCapacity = n << 1; | ||
| 153 | if (newCapacity < 0) | ||
| 154 | throw new IllegalStateException("Sorry, deque too big"); | ||
| 155 | Object[] a = new Object[newCapacity]; | ||
| 156 | System.arraycopy(elements, p, a, 0, r); | ||
| 157 | System.arraycopy(elements, 0, a, r, p); | ||
| 158 | elements = (E[])a; | ||
| 159 | head = 0; | ||
| 160 | tail = n; | ||
| 161 | } | ||
| 162 | |||
| 163 | /** | ||
| 164 | * Copies the elements from our element array into the specified array, | ||
| 165 | * in order (from first to last element in the deque). It is assumed | ||
| 166 | * that the array is large enough to hold all elements in the deque. | ||
| 167 | * | ||
| 168 | * @return its argument | ||
| 169 | */ | ||
| 170 | private <T> T[] copyElements(T[] a) { | ||
| 171 | if (head < tail) { | ||
| 172 | System.arraycopy(elements, head, a, 0, size()); | ||
| 173 | } else if (head > tail) { | ||
| 174 | int headPortionLen = elements.length - head; | ||
| 175 | System.arraycopy(elements, head, a, 0, headPortionLen); | ||
| 176 | System.arraycopy(elements, 0, a, headPortionLen, tail); | ||
| 177 | } | ||
| 178 | return a; | ||
| 179 | } | ||
| 180 | |||
| 181 | /** | ||
| 182 | * Constructs an empty array deque with an initial capacity | ||
| 183 | * sufficient to hold 16 elements. | ||
| 184 | */ | ||
| 185 | public ArrayDeque() { | ||
| 186 | elements = (E[]) new Object[16]; | ||
| 187 | } | ||
| 188 | |||
| 189 | /** | ||
| 190 | * Constructs an empty array deque with an initial capacity | ||
| 191 | * sufficient to hold the specified number of elements. | ||
| 192 | * | ||
| 193 | * @param numElements lower bound on initial capacity of the deque | ||
| 194 | */ | ||
| 195 | public ArrayDeque(int numElements) { | ||
| 196 | allocateElements(numElements); | ||
| 197 | } | ||
| 198 | |||
| 199 | /** | ||
| 200 | * Constructs a deque containing the elements of the specified | ||
| 201 | * collection, in the order they are returned by the collection's | ||
| 202 | * iterator. (The first element returned by the collection's | ||
| 203 | * iterator becomes the first element, or <i>front</i> of the | ||
| 204 | * deque.) | ||
| 205 | * | ||
| 206 | * @param c the collection whose elements are to be placed into the deque | ||
| 207 | * @throws NullPointerException if the specified collection is null | ||
| 208 | */ | ||
| 209 | public ArrayDeque(Collection<? extends E> c) { | ||
| 210 | allocateElements(c.size()); | ||
| 211 | addAll(c); | ||
| 212 | } | ||
| 213 | |||
| 214 | // The main insertion and extraction methods are addFirst, | ||
| 215 | // addLast, pollFirst, pollLast. The other methods are defined in | ||
| 216 | // terms of these. | ||
| 217 | |||
| 218 | /** | ||
| 219 | * Inserts the specified element at the front of this deque. | ||
| 220 | * | ||
| 221 | * @param e the element to add | ||
| 222 | * @throws NullPointerException if the specified element is null | ||
| 223 | */ | ||
| 224 | public void addFirst(E e) { | ||
| 225 | if (e == null) | ||
| 226 | throw new NullPointerException(); | ||
| 227 | elements[head = (head - 1) & (elements.length - 1)] = e; | ||
| 228 | if (head == tail) | ||
| 229 | doubleCapacity(); | ||
| 230 | } | ||
| 231 | |||
| 232 | /** | ||
| 233 | * Inserts the specified element at the end of this deque. | ||
| 234 | * | ||
| 235 | * <p>This method is equivalent to {@link #add}. | ||
| 236 | * | ||
| 237 | * @param e the element to add | ||
| 238 | * @throws NullPointerException if the specified element is null | ||
| 239 | */ | ||
| 240 | public void addLast(E e) { | ||
| 241 | if (e == null) | ||
| 242 | throw new NullPointerException(); | ||
| 243 | elements[tail] = e; | ||
| 244 | if ( (tail = (tail + 1) & (elements.length - 1)) == head) | ||
| 245 | doubleCapacity(); | ||
| 246 | } | ||
| 247 | |||
| 248 | /** | ||
| 249 | * Inserts the specified element at the front of this deque. | ||
| 250 | * | ||
| 251 | * @param e the element to add | ||
| 252 | * @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) | ||
| 253 | * @throws NullPointerException if the specified element is null | ||
| 254 | */ | ||
| 255 | public boolean offerFirst(E e) { | ||
| 256 | addFirst(e); | ||
| 257 | return true; | ||
| 258 | } | ||
| 259 | |||
| 260 | /** | ||
| 261 | * Inserts the specified element at the end of this deque. | ||
| 262 | * | ||
| 263 | * @param e the element to add | ||
| 264 | * @return <tt>true</tt> (as specified by {@link Deque#offerLast}) | ||
| 265 | * @throws NullPointerException if the specified element is null | ||
| 266 | */ | ||
| 267 | public boolean offerLast(E e) { | ||
| 268 | addLast(e); | ||
| 269 | return true; | ||
| 270 | } | ||
| 271 | |||
| 272 | /** | ||
| 273 | * @throws NoSuchElementException {@inheritDoc} | ||
| 274 | */ | ||
| 275 | public E removeFirst() { | ||
| 276 | E x = pollFirst(); | ||
| 277 | if (x == null) | ||
| 278 | throw new NoSuchElementException(); | ||
| 279 | return x; | ||
| 280 | } | ||
| 281 | |||
| 282 | /** | ||
| 283 | * @throws NoSuchElementException {@inheritDoc} | ||
| 284 | */ | ||
| 285 | public E removeLast() { | ||
| 286 | E x = pollLast(); | ||
| 287 | if (x == null) | ||
| 288 | throw new NoSuchElementException(); | ||
| 289 | return x; | ||
| 290 | } | ||
| 291 | |||
| 292 | public E pollFirst() { | ||
| 293 | int h = head; | ||
| 294 | E result = elements[h]; // Element is null if deque empty | ||
| 295 | if (result == null) | ||
| 296 | return null; | ||
| 297 | elements[h] = null; // Must null out slot | ||
| 298 | head = (h + 1) & (elements.length - 1); | ||
| 299 | return result; | ||
| 300 | } | ||
| 301 | |||
| 302 | public E pollLast() { | ||
| 303 | int t = (tail - 1) & (elements.length - 1); | ||
| 304 | E result = elements[t]; | ||
| 305 | if (result == null) | ||
| 306 | return null; | ||
| 307 | elements[t] = null; | ||
| 308 | tail = t; | ||
| 309 | return result; | ||
| 310 | } | ||
| 311 | |||
| 312 | /** | ||
| 313 | * @throws NoSuchElementException {@inheritDoc} | ||
| 314 | */ | ||
| 315 | public E getFirst() { | ||
| 316 | E x = elements[head]; | ||
| 317 | if (x == null) | ||
| 318 | throw new NoSuchElementException(); | ||
| 319 | return x; | ||
| 320 | } | ||
| 321 | |||
| 322 | /** | ||
| 323 | * @throws NoSuchElementException {@inheritDoc} | ||
| 324 | */ | ||
| 325 | public E getLast() { | ||
| 326 | E x = elements[(tail - 1) & (elements.length - 1)]; | ||
| 327 | if (x == null) | ||
| 328 | throw new NoSuchElementException(); | ||
| 329 | return x; | ||
| 330 | } | ||
| 331 | |||
| 332 | public E peekFirst() { | ||
| 333 | return elements[head]; // elements[head] is null if deque empty | ||
| 334 | } | ||
| 335 | |||
| 336 | public E peekLast() { | ||
| 337 | return elements[(tail - 1) & (elements.length - 1)]; | ||
| 338 | } | ||
| 339 | |||
| 340 | /** | ||
| 341 | * Removes the first occurrence of the specified element in this | ||
| 342 | * deque (when traversing the deque from head to tail). | ||
| 343 | * If the deque does not contain the element, it is unchanged. | ||
| 344 | * More formally, removes the first element <tt>e</tt> such that | ||
| 345 | * <tt>o.equals(e)</tt> (if such an element exists). | ||
| 346 | * Returns <tt>true</tt> if this deque contained the specified element | ||
| 347 | * (or equivalently, if this deque changed as a result of the call). | ||
| 348 | * | ||
| 349 | * @param o element to be removed from this deque, if present | ||
| 350 | * @return <tt>true</tt> if the deque contained the specified element | ||
| 351 | */ | ||
| 352 | public boolean removeFirstOccurrence(Object o) { | ||
| 353 | if (o == null) | ||
| 354 | return false; | ||
| 355 | int mask = elements.length - 1; | ||
| 356 | int i = head; | ||
| 357 | E x; | ||
| 358 | while ( (x = elements[i]) != null) { | ||
| 359 | if (o.equals(x)) { | ||
| 360 | delete(i); | ||
| 361 | return true; | ||
| 362 | } | ||
| 363 | i = (i + 1) & mask; | ||
| 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 <tt>e</tt> such that | ||
| 373 | * <tt>o.equals(e)</tt> (if such an element exists). | ||
| 374 | * Returns <tt>true</tt> 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 <tt>true</tt> if the deque contained the specified element | ||
| 379 | */ | ||
| 380 | public boolean removeLastOccurrence(Object o) { | ||
| 381 | if (o == null) | ||
| 382 | return false; | ||
| 383 | int mask = elements.length - 1; | ||
| 384 | int i = (tail - 1) & mask; | ||
| 385 | E x; | ||
| 386 | while ( (x = elements[i]) != null) { | ||
| 387 | if (o.equals(x)) { | ||
| 388 | delete(i); | ||
| 389 | return true; | ||
| 390 | } | ||
| 391 | i = (i - 1) & mask; | ||
| 392 | } | ||
| 393 | return false; | ||
| 394 | } | ||
| 395 | |||
| 396 | // *** Queue methods *** | ||
| 397 | |||
| 398 | /** | ||
| 399 | * Inserts the specified element at the end of this deque. | ||
| 400 | * | ||
| 401 | * <p>This method is equivalent to {@link #addLast}. | ||
| 402 | * | ||
| 403 | * @param e the element to add | ||
| 404 | * @return <tt>true</tt> (as specified by {@link Collection#add}) | ||
| 405 | * @throws NullPointerException if the specified element is null | ||
| 406 | */ | ||
| 407 | public boolean add(E e) { | ||
| 408 | addLast(e); | ||
| 409 | return true; | ||
| 410 | } | ||
| 411 | |||
| 412 | /** | ||
| 413 | * Inserts the specified element at the end of this deque. | ||
| 414 | * | ||
| 415 | * <p>This method is equivalent to {@link #offerLast}. | ||
| 416 | * | ||
| 417 | * @param e the element to add | ||
| 418 | * @return <tt>true</tt> (as specified by {@link Queue#offer}) | ||
| 419 | * @throws NullPointerException if the specified element is null | ||
| 420 | */ | ||
| 421 | public boolean offer(E e) { | ||
| 422 | return offerLast(e); | ||
| 423 | } | ||
| 424 | |||
| 425 | /** | ||
| 426 | * Retrieves and removes the head of the queue represented by this deque. | ||
| 427 | * | ||
| 428 | * This method differs from {@link #poll poll} only in that it throws an | ||
| 429 | * exception if this deque is empty. | ||
| 430 | * | ||
| 431 | * <p>This method is equivalent to {@link #removeFirst}. | ||
| 432 | * | ||
| 433 | * @return the head of the queue represented by this deque | ||
| 434 | * @throws NoSuchElementException {@inheritDoc} | ||
| 435 | */ | ||
| 436 | public E remove() { | ||
| 437 | return removeFirst(); | ||
| 438 | } | ||
| 439 | |||
| 440 | /** | ||
| 441 | * Retrieves and removes the head of the queue represented by this deque | ||
| 442 | * (in other words, the first element of this deque), or returns | ||
| 443 | * <tt>null</tt> if this deque is empty. | ||
| 444 | * | ||
| 445 | * <p>This method is equivalent to {@link #pollFirst}. | ||
| 446 | * | ||
| 447 | * @return the head of the queue represented by this deque, or | ||
| 448 | * <tt>null</tt> if this deque is empty | ||
| 449 | */ | ||
| 450 | public E poll() { | ||
| 451 | return pollFirst(); | ||
| 452 | } | ||
| 453 | |||
| 454 | /** | ||
| 455 | * Retrieves, but does not remove, the head of the queue represented by | ||
| 456 | * this deque. This method differs from {@link #peek peek} only in | ||
| 457 | * that it throws an exception if this deque is empty. | ||
| 458 | * | ||
| 459 | * <p>This method is equivalent to {@link #getFirst}. | ||
| 460 | * | ||
| 461 | * @return the head of the queue represented by this deque | ||
| 462 | * @throws NoSuchElementException {@inheritDoc} | ||
| 463 | */ | ||
| 464 | public E element() { | ||
| 465 | return getFirst(); | ||
| 466 | } | ||
| 467 | |||
| 468 | /** | ||
| 469 | * Retrieves, but does not remove, the head of the queue represented by | ||
| 470 | * this deque, or returns <tt>null</tt> if this deque is empty. | ||
| 471 | * | ||
| 472 | * <p>This method is equivalent to {@link #peekFirst}. | ||
| 473 | * | ||
| 474 | * @return the head of the queue represented by this deque, or | ||
| 475 | * <tt>null</tt> if this deque is empty | ||
| 476 | */ | ||
| 477 | public E peek() { | ||
| 478 | return peekFirst(); | ||
| 479 | } | ||
| 480 | |||
| 481 | // *** Stack methods *** | ||
| 482 | |||
| 483 | /** | ||
| 484 | * Pushes an element onto the stack represented by this deque. In other | ||
| 485 | * words, inserts the element at the front of this deque. | ||
| 486 | * | ||
| 487 | * <p>This method is equivalent to {@link #addFirst}. | ||
| 488 | * | ||
| 489 | * @param e the element to push | ||
| 490 | * @throws NullPointerException if the specified element is null | ||
| 491 | */ | ||
| 492 | public void push(E e) { | ||
| 493 | addFirst(e); | ||
| 494 | } | ||
| 495 | |||
| 496 | /** | ||
| 497 | * Pops an element from the stack represented by this deque. In other | ||
| 498 | * words, removes and returns the first element of this deque. | ||
| 499 | * | ||
| 500 | * <p>This method is equivalent to {@link #removeFirst()}. | ||
| 501 | * | ||
| 502 | * @return the element at the front of this deque (which is the top | ||
| 503 | * of the stack represented by this deque) | ||
| 504 | * @throws NoSuchElementException {@inheritDoc} | ||
| 505 | */ | ||
| 506 | public E pop() { | ||
| 507 | return removeFirst(); | ||
| 508 | } | ||
| 509 | |||
| 510 | private void checkInvariants() { | ||
| 511 | assert elements[tail] == null; | ||
| 512 | assert head == tail ? elements[head] == null : | ||
| 513 | (elements[head] != null && | ||
| 514 | elements[(tail - 1) & (elements.length - 1)] != null); | ||
| 515 | assert elements[(head - 1) & (elements.length - 1)] == null; | ||
| 516 | } | ||
| 517 | |||
| 518 | /** | ||
| 519 | * Removes the element at the specified position in the elements array, | ||
| 520 | * adjusting head and tail as necessary. This can result in motion of | ||
| 521 | * elements backwards or forwards in the array. | ||
| 522 | * | ||
| 523 | * <p>This method is called delete rather than remove to emphasize | ||
| 524 | * that its semantics differ from those of {@link List#remove(int)}. | ||
| 525 | * | ||
| 526 | * @return true if elements moved backwards | ||
| 527 | */ | ||
| 528 | private boolean delete(int i) { | ||
| 529 | checkInvariants(); | ||
| 530 | final E[] elements = this.elements; | ||
| 531 | final int mask = elements.length - 1; | ||
| 532 | final int h = head; | ||
| 533 | final int t = tail; | ||
| 534 | final int front = (i - h) & mask; | ||
| 535 | final int back = (t - i) & mask; | ||
| 536 | |||
| 537 | // Invariant: head <= i < tail mod circularity | ||
| 538 | if (front >= ((t - h) & mask)) | ||
| 539 | throw new ConcurrentModificationException(); | ||
| 540 | |||
| 541 | // Optimize for least element motion | ||
| 542 | if (front < back) { | ||
| 543 | if (h <= i) { | ||
| 544 | System.arraycopy(elements, h, elements, h + 1, front); | ||
| 545 | } else { // Wrap around | ||
| 546 | System.arraycopy(elements, 0, elements, 1, i); | ||
| 547 | elements[0] = elements[mask]; | ||
| 548 | System.arraycopy(elements, h, elements, h + 1, mask - h); | ||
| 549 | } | ||
| 550 | elements[h] = null; | ||
| 551 | head = (h + 1) & mask; | ||
| 552 | return false; | ||
| 553 | } else { | ||
| 554 | if (i < t) { // Copy the null tail as well | ||
| 555 | System.arraycopy(elements, i + 1, elements, i, back); | ||
| 556 | tail = t - 1; | ||
| 557 | } else { // Wrap around | ||
| 558 | System.arraycopy(elements, i + 1, elements, i, mask - i); | ||
| 559 | elements[mask] = elements[0]; | ||
| 560 | System.arraycopy(elements, 1, elements, 0, t); | ||
| 561 | tail = (t - 1) & mask; | ||
| 562 | } | ||
| 563 | return true; | ||
| 564 | } | ||
| 565 | } | ||
| 566 | |||
| 567 | // *** Collection Methods *** | ||
| 568 | |||
| 569 | /** | ||
| 570 | * Returns the number of elements in this deque. | ||
| 571 | * | ||
| 572 | * @return the number of elements in this deque | ||
| 573 | */ | ||
| 574 | public int size() { | ||
| 575 | return (tail - head) & (elements.length - 1); | ||
| 576 | } | ||
| 577 | |||
| 578 | /** | ||
| 579 | * Returns <tt>true</tt> if this deque contains no elements. | ||
| 580 | * | ||
| 581 | * @return <tt>true</tt> if this deque contains no elements | ||
| 582 | */ | ||
| 583 | public boolean isEmpty() { | ||
| 584 | return head == tail; | ||
| 585 | } | ||
| 586 | |||
| 587 | /** | ||
| 588 | * Returns an iterator over the elements in this deque. The elements | ||
| 589 | * will be ordered from first (head) to last (tail). This is the same | ||
| 590 | * order that elements would be dequeued (via successive calls to | ||
| 591 | * {@link #remove} or popped (via successive calls to {@link #pop}). | ||
| 592 | * | ||
| 593 | * @return an iterator over the elements in this deque | ||
| 594 | */ | ||
| 595 | public Iterator<E> iterator() { | ||
| 596 | return new DeqIterator(); | ||
| 597 | } | ||
| 598 | |||
| 599 | public Iterator<E> descendingIterator() { | ||
| 600 | return new DescendingIterator(); | ||
| 601 | } | ||
| 602 | |||
| 603 | private class DeqIterator implements Iterator<E> { | ||
| 604 | /** | ||
| 605 | * Index of element to be returned by subsequent call to next. | ||
| 606 | */ | ||
| 607 | private int cursor = head; | ||
| 608 | |||
| 609 | /** | ||
| 610 | * Tail recorded at construction (also in remove), to stop | ||
| 611 | * iterator and also to check for comodification. | ||
| 612 | */ | ||
| 613 | private int fence = tail; | ||
| 614 | |||
| 615 | /** | ||
| 616 | * Index of element returned by most recent call to next. | ||
| 617 | * Reset to -1 if element is deleted by a call to remove. | ||
| 618 | */ | ||
| 619 | private int lastRet = -1; | ||
| 620 | |||
| 621 | public boolean hasNext() { | ||
| 622 | return cursor != fence; | ||
| 623 | } | ||
| 624 | |||
| 625 | public E next() { | ||
| 626 | if (cursor == fence) | ||
| 627 | throw new NoSuchElementException(); | ||
| 628 | E result = elements[cursor]; | ||
| 629 | // This check doesn't catch all possible comodifications, | ||
| 630 | // but does catch the ones that corrupt traversal | ||
| 631 | if (tail != fence || result == null) | ||
| 632 | throw new ConcurrentModificationException(); | ||
| 633 | lastRet = cursor; | ||
| 634 | cursor = (cursor + 1) & (elements.length - 1); | ||
| 635 | return result; | ||
| 636 | } | ||
| 637 | |||
| 638 | public void remove() { | ||
| 639 | if (lastRet < 0) | ||
| 640 | throw new IllegalStateException(); | ||
| 641 | if (delete(lastRet)) { // if left-shifted, undo increment in next() | ||
| 642 | cursor = (cursor - 1) & (elements.length - 1); | ||
| 643 | fence = tail; | ||
| 644 | } | ||
| 645 | lastRet = -1; | ||
| 646 | } | ||
| 647 | } | ||
| 648 | |||
| 649 | private class DescendingIterator implements Iterator<E> { | ||
| 650 | /* | ||
| 651 | * This class is nearly a mirror-image of DeqIterator, using | ||
| 652 | * tail instead of head for initial cursor, and head instead of | ||
| 653 | * tail for fence. | ||
| 654 | */ | ||
| 655 | private int cursor = tail; | ||
| 656 | private int fence = head; | ||
| 657 | private int lastRet = -1; | ||
| 658 | |||
| 659 | public boolean hasNext() { | ||
| 660 | return cursor != fence; | ||
| 661 | } | ||
| 662 | |||
| 663 | public E next() { | ||
| 664 | if (cursor == fence) | ||
| 665 | throw new NoSuchElementException(); | ||
| 666 | cursor = (cursor - 1) & (elements.length - 1); | ||
| 667 | E result = elements[cursor]; | ||
| 668 | if (head != fence || result == null) | ||
| 669 | throw new ConcurrentModificationException(); | ||
| 670 | lastRet = cursor; | ||
| 671 | return result; | ||
| 672 | } | ||
| 673 | |||
| 674 | public void remove() { | ||
| 675 | if (lastRet < 0) | ||
| 676 | throw new IllegalStateException(); | ||
| 677 | if (!delete(lastRet)) { | ||
| 678 | cursor = (cursor + 1) & (elements.length - 1); | ||
| 679 | fence = head; | ||
| 680 | } | ||
| 681 | lastRet = -1; | ||
| 682 | } | ||
| 683 | } | ||
| 684 | |||
| 685 | /** | ||
| 686 | * Returns <tt>true</tt> if this deque contains the specified element. | ||
| 687 | * More formally, returns <tt>true</tt> if and only if this deque contains | ||
| 688 | * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>. | ||
| 689 | * | ||
| 690 | * @param o object to be checked for containment in this deque | ||
| 691 | * @return <tt>true</tt> if this deque contains the specified element | ||
| 692 | */ | ||
| 693 | public boolean contains(Object o) { | ||
| 694 | if (o == null) | ||
| 695 | return false; | ||
| 696 | int mask = elements.length - 1; | ||
| 697 | int i = head; | ||
| 698 | E x; | ||
| 699 | while ( (x = elements[i]) != null) { | ||
| 700 | if (o.equals(x)) | ||
| 701 | return true; | ||
| 702 | i = (i + 1) & mask; | ||
| 703 | } | ||
| 704 | return false; | ||
| 705 | } | ||
| 706 | |||
| 707 | /** | ||
| 708 | * Removes a single instance of the specified element from this deque. | ||
| 709 | * If the deque does not contain the element, it is unchanged. | ||
| 710 | * More formally, removes the first element <tt>e</tt> such that | ||
| 711 | * <tt>o.equals(e)</tt> (if such an element exists). | ||
| 712 | * Returns <tt>true</tt> if this deque contained the specified element | ||
| 713 | * (or equivalently, if this deque changed as a result of the call). | ||
| 714 | * | ||
| 715 | * <p>This method is equivalent to {@link #removeFirstOccurrence}. | ||
| 716 | * | ||
| 717 | * @param o element to be removed from this deque, if present | ||
| 718 | * @return <tt>true</tt> if this deque contained the specified element | ||
| 719 | */ | ||
| 720 | public boolean remove(Object o) { | ||
| 721 | return removeFirstOccurrence(o); | ||
| 722 | } | ||
| 723 | |||
| 724 | /** | ||
| 725 | * Removes all of the elements from this deque. | ||
| 726 | * The deque will be empty after this call returns. | ||
| 727 | */ | ||
| 728 | public void clear() { | ||
| 729 | int h = head; | ||
| 730 | int t = tail; | ||
| 731 | if (h != t) { // clear all cells | ||
| 732 | head = tail = 0; | ||
| 733 | int i = h; | ||
| 734 | int mask = elements.length - 1; | ||
| 735 | do { | ||
| 736 | elements[i] = null; | ||
| 737 | i = (i + 1) & mask; | ||
| 738 | } while (i != t); | ||
| 739 | } | ||
| 740 | } | ||
| 741 | |||
| 742 | /** | ||
| 743 | * Returns an array containing all of the elements in this deque | ||
| 744 | * in proper sequence (from first to last element). | ||
| 745 | * | ||
| 746 | * <p>The returned array will be "safe" in that no references to it are | ||
| 747 | * maintained by this deque. (In other words, this method must allocate | ||
| 748 | * a new array). The caller is thus free to modify the returned array. | ||
| 749 | * | ||
| 750 | * <p>This method acts as bridge between array-based and collection-based | ||
| 751 | * APIs. | ||
| 752 | * | ||
| 753 | * @return an array containing all of the elements in this deque | ||
| 754 | */ | ||
| 755 | public Object[] toArray() { | ||
| 756 | return copyElements(new Object[size()]); | ||
| 757 | } | ||
| 758 | |||
| 759 | /** | ||
| 760 | * Returns an array containing all of the elements in this deque in | ||
| 761 | * proper sequence (from first to last element); the runtime type of the | ||
| 762 | * returned array is that of the specified array. If the deque fits in | ||
| 763 | * the specified array, it is returned therein. Otherwise, a new array | ||
| 764 | * is allocated with the runtime type of the specified array and the | ||
| 765 | * size of this deque. | ||
| 766 | * | ||
| 767 | * <p>If this deque fits in the specified array with room to spare | ||
| 768 | * (i.e., the array has more elements than this deque), the element in | ||
| 769 | * the array immediately following the end of the deque is set to | ||
| 770 | * <tt>null</tt>. | ||
| 771 | * | ||
| 772 | * <p>Like the {@link #toArray()} method, this method acts as bridge between | ||
| 773 | * array-based and collection-based APIs. Further, this method allows | ||
| 774 | * precise control over the runtime type of the output array, and may, | ||
| 775 | * under certain circumstances, be used to save allocation costs. | ||
| 776 | * | ||
| 777 | * <p>Suppose <tt>x</tt> is a deque known to contain only strings. | ||
| 778 | * The following code can be used to dump the deque into a newly | ||
| 779 | * allocated array of <tt>String</tt>: | ||
| 780 | * | ||
| 781 | * <pre> | ||
| 782 | * String[] y = x.toArray(new String[0]);</pre> | ||
| 783 | * | ||
| 784 | * Note that <tt>toArray(new Object[0])</tt> is identical in function to | ||
| 785 | * <tt>toArray()</tt>. | ||
| 786 | * | ||
| 787 | * @param a the array into which the elements of the deque are to | ||
| 788 | * be stored, if it is big enough; otherwise, a new array of the | ||
| 789 | * same runtime type is allocated for this purpose | ||
| 790 | * @return an array containing all of the elements in this deque | ||
| 791 | * @throws ArrayStoreException if the runtime type of the specified array | ||
| 792 | * is not a supertype of the runtime type of every element in | ||
| 793 | * this deque | ||
| 794 | * @throws NullPointerException if the specified array is null | ||
| 795 | */ | ||
| 796 | public <T> T[] toArray(T[] a) { | ||
| 797 | int size = size(); | ||
| 798 | if (a.length < size) | ||
| 799 | a = (T[])java.lang.reflect.Array.newInstance( | ||
| 800 | a.getClass().getComponentType(), size); | ||
| 801 | copyElements(a); | ||
| 802 | if (a.length > size) | ||
| 803 | a[size] = null; | ||
| 804 | return a; | ||
| 805 | } | ||
| 806 | |||
| 807 | // *** Object methods *** | ||
| 808 | |||
| 809 | /** | ||
| 810 | * Returns a copy of this deque. | ||
| 811 | * | ||
| 812 | * @return a copy of this deque | ||
| 813 | */ | ||
| 814 | public ArrayDeque<E> clone() { | ||
| 815 | try { | ||
| 816 | ArrayDeque<E> result = (ArrayDeque<E>) super.clone(); | ||
| 817 | result.elements = Arrays.copyOf(elements, elements.length); | ||
| 818 | return result; | ||
| 819 | |||
| 820 | } catch (CloneNotSupportedException e) { | ||
| 821 | throw new AssertionError(); | ||
| 822 | } | ||
| 823 | } | ||
| 824 | |||
| 825 | /** | ||
| 826 | * Appease the serialization gods. | ||
| 827 | */ | ||
| 828 | private static final long serialVersionUID = 2340985798034038923L; | ||
| 829 | |||
| 830 | /** | ||
| 831 | * Serialize this deque. | ||
| 832 | * | ||
| 833 | * @serialData The current size (<tt>int</tt>) of the deque, | ||
| 834 | * followed by all of its elements (each an object reference) in | ||
| 835 | * first-to-last order. | ||
| 836 | */ | ||
| 837 | private void writeObject(ObjectOutputStream s) throws IOException { | ||
| 838 | s.defaultWriteObject(); | ||
| 839 | |||
| 840 | // Write out size | ||
| 841 | s.writeInt(size()); | ||
| 842 | |||
| 843 | // Write out elements in order. | ||
| 844 | int mask = elements.length - 1; | ||
| 845 | for (int i = head; i != tail; i = (i + 1) & mask) | ||
| 846 | s.writeObject(elements[i]); | ||
| 847 | } | ||
| 848 | |||
| 849 | /** | ||
| 850 | * Deserialize this deque. | ||
| 851 | */ | ||
| 852 | private void readObject(ObjectInputStream s) | ||
| 853 | throws IOException, ClassNotFoundException { | ||
| 854 | s.defaultReadObject(); | ||
| 855 | |||
| 856 | // Read in size and allocate array | ||
| 857 | int size = s.readInt(); | ||
| 858 | allocateElements(size); | ||
| 859 | head = 0; | ||
| 860 | tail = size; | ||
| 861 | |||
| 862 | // Read in all elements in the proper order. | ||
| 863 | for (int i = 0; i < size; i++) | ||
| 864 | elements[i] = (E)s.readObject(); | ||
| 865 | } | ||
| 866 | } | ||