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| 1 | /* | ||
| 2 | * Copyright (c) 1997, 2011, Oracle and/or its affiliates. All rights reserved. | ||
| 3 | * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. | ||
| 4 | * | ||
| 5 | * This code is free software; you can redistribute it and/or modify it | ||
| 6 | * under the terms of the GNU General Public License version 2 only, as | ||
| 7 | * published by the Free Software Foundation. Oracle designates this | ||
| 8 | * particular file as subject to the "Classpath" exception as provided | ||
| 9 | * by Oracle in the LICENSE file that accompanied this code. | ||
| 10 | * | ||
| 11 | * This code is distributed in the hope that it will be useful, but WITHOUT | ||
| 12 | * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or | ||
| 13 | * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License | ||
| 14 | * version 2 for more details (a copy is included in the LICENSE file that | ||
| 15 | * accompanied this code). | ||
| 16 | * | ||
| 17 | * You should have received a copy of the GNU General Public License version | ||
| 18 | * 2 along with this work; if not, write to the Free Software Foundation, | ||
| 19 | * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. | ||
| 20 | * | ||
| 21 | * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA | ||
| 22 | * or visit www.oracle.com if you need additional information or have any | ||
| 23 | * questions. | ||
| 24 | */ | ||
| 25 | |||
| 26 | package java.util; | ||
| 27 | |||
| 28 | /** | ||
| 29 | * Doubly-linked list implementation of the {@code List} and {@code Deque} | ||
| 30 | * interfaces. Implements all optional list operations, and permits all | ||
| 31 | * elements (including {@code null}). | ||
| 32 | * | ||
| 33 | * <p>All of the operations perform as could be expected for a doubly-linked | ||
| 34 | * list. Operations that index into the list will traverse the list from | ||
| 35 | * the beginning or the end, whichever is closer to the specified index. | ||
| 36 | * | ||
| 37 | * <p><strong>Note that this implementation is not synchronized.</strong> | ||
| 38 | * If multiple threads access a linked list concurrently, and at least | ||
| 39 | * one of the threads modifies the list structurally, it <i>must</i> be | ||
| 40 | * synchronized externally. (A structural modification is any operation | ||
| 41 | * that adds or deletes one or more elements; merely setting the value of | ||
| 42 | * an element is not a structural modification.) This is typically | ||
| 43 | * accomplished by synchronizing on some object that naturally | ||
| 44 | * encapsulates the list. | ||
| 45 | * | ||
| 46 | * If no such object exists, the list should be "wrapped" using the | ||
| 47 | * {@link Collections#synchronizedList Collections.synchronizedList} | ||
| 48 | * method. This is best done at creation time, to prevent accidental | ||
| 49 | * unsynchronized access to the list:<pre> | ||
| 50 | * List list = Collections.synchronizedList(new LinkedList(...));</pre> | ||
| 51 | * | ||
| 52 | * <p>The iterators returned by this class's {@code iterator} and | ||
| 53 | * {@code listIterator} methods are <i>fail-fast</i>: if the list is | ||
| 54 | * structurally modified at any time after the iterator is created, in | ||
| 55 | * any way except through the Iterator's own {@code remove} or | ||
| 56 | * {@code add} methods, the iterator will throw a {@link | ||
| 57 | * ConcurrentModificationException}. Thus, in the face of concurrent | ||
| 58 | * modification, the iterator fails quickly and cleanly, rather than | ||
| 59 | * risking arbitrary, non-deterministic behavior at an undetermined | ||
| 60 | * time in the future. | ||
| 61 | * | ||
| 62 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed | ||
| 63 | * as it is, generally speaking, impossible to make any hard guarantees in the | ||
| 64 | * presence of unsynchronized concurrent modification. Fail-fast iterators | ||
| 65 | * throw {@code ConcurrentModificationException} on a best-effort basis. | ||
| 66 | * Therefore, it would be wrong to write a program that depended on this | ||
| 67 | * exception for its correctness: <i>the fail-fast behavior of iterators | ||
| 68 | * should be used only to detect bugs.</i> | ||
| 69 | * | ||
| 70 | * <p>This class is a member of the | ||
| 71 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> | ||
| 72 | * Java Collections Framework</a>. | ||
| 73 | * | ||
| 74 | * @author Josh Bloch | ||
| 75 | * @see List | ||
| 76 | * @see ArrayList | ||
| 77 | * @since 1.2 | ||
| 78 | * @param <E> the type of elements held in this collection | ||
| 79 | */ | ||
| 80 | |||
| 81 | public class LinkedList<E> | ||
| 82 | extends AbstractSequentialList<E> | ||
| 83 | implements List<E>, Deque<E>, Cloneable, java.io.Serializable | ||
| 84 | { | ||
| 85 | transient int size = 0; | ||
| 86 | |||
| 87 | /** | ||
| 88 | * Pointer to first node. | ||
| 89 | * Invariant: (first == null && last == null) || | ||
| 90 | * (first.prev == null && first.item != null) | ||
| 91 | */ | ||
| 92 | transient Node<E> first; | ||
| 93 | |||
| 94 | /** | ||
| 95 | * Pointer to last node. | ||
| 96 | * Invariant: (first == null && last == null) || | ||
| 97 | * (last.next == null && last.item != null) | ||
| 98 | */ | ||
| 99 | transient Node<E> last; | ||
| 100 | |||
| 101 | /** | ||
| 102 | * Constructs an empty list. | ||
| 103 | */ | ||
| 104 | public LinkedList() { | ||
| 105 | } | ||
| 106 | |||
| 107 | /** | ||
| 108 | * Constructs a list containing the elements of the specified | ||
| 109 | * collection, in the order they are returned by the collection's | ||
| 110 | * iterator. | ||
| 111 | * | ||
| 112 | * @param c the collection whose elements are to be placed into this list | ||
| 113 | * @throws NullPointerException if the specified collection is null | ||
| 114 | */ | ||
| 115 | public LinkedList(Collection<? extends E> c) { | ||
| 116 | this(); | ||
| 117 | addAll(c); | ||
| 118 | } | ||
| 119 | |||
| 120 | /** | ||
| 121 | * Links e as first element. | ||
| 122 | */ | ||
| 123 | private void linkFirst(E e) { | ||
| 124 | final Node<E> f = first; | ||
| 125 | final Node<E> newNode = new Node<>(null, e, f); | ||
| 126 | first = newNode; | ||
| 127 | if (f == null) | ||
| 128 | last = newNode; | ||
| 129 | else | ||
| 130 | f.prev = newNode; | ||
| 131 | size++; | ||
| 132 | modCount++; | ||
| 133 | } | ||
| 134 | |||
| 135 | /** | ||
| 136 | * Links e as last element. | ||
| 137 | */ | ||
| 138 | void linkLast(E e) { | ||
| 139 | final Node<E> l = last; | ||
| 140 | final Node<E> newNode = new Node<>(l, e, null); | ||
| 141 | last = newNode; | ||
| 142 | if (l == null) | ||
| 143 | first = newNode; | ||
| 144 | else | ||
| 145 | l.next = newNode; | ||
| 146 | size++; | ||
| 147 | modCount++; | ||
| 148 | } | ||
| 149 | |||
| 150 | /** | ||
| 151 | * Inserts element e before non-null Node succ. | ||
| 152 | */ | ||
| 153 | void linkBefore(E e, Node<E> succ) { | ||
| 154 | // assert succ != null; | ||
| 155 | final Node<E> pred = succ.prev; | ||
| 156 | final Node<E> newNode = new Node<>(pred, e, succ); | ||
| 157 | succ.prev = newNode; | ||
| 158 | if (pred == null) | ||
| 159 | first = newNode; | ||
| 160 | else | ||
| 161 | pred.next = newNode; | ||
| 162 | size++; | ||
| 163 | modCount++; | ||
| 164 | } | ||
| 165 | |||
| 166 | /** | ||
| 167 | * Unlinks non-null first node f. | ||
| 168 | */ | ||
| 169 | private E unlinkFirst(Node<E> f) { | ||
| 170 | // assert f == first && f != null; | ||
| 171 | final E element = f.item; | ||
| 172 | final Node<E> next = f.next; | ||
| 173 | f.item = null; | ||
| 174 | f.next = null; // help GC | ||
| 175 | first = next; | ||
| 176 | if (next == null) | ||
| 177 | last = null; | ||
| 178 | else | ||
| 179 | next.prev = null; | ||
| 180 | size--; | ||
| 181 | modCount++; | ||
| 182 | return element; | ||
| 183 | } | ||
| 184 | |||
| 185 | /** | ||
| 186 | * Unlinks non-null last node l. | ||
| 187 | */ | ||
| 188 | private E unlinkLast(Node<E> l) { | ||
| 189 | // assert l == last && l != null; | ||
| 190 | final E element = l.item; | ||
| 191 | final Node<E> prev = l.prev; | ||
| 192 | l.item = null; | ||
| 193 | l.prev = null; // help GC | ||
| 194 | last = prev; | ||
| 195 | if (prev == null) | ||
| 196 | first = null; | ||
| 197 | else | ||
| 198 | prev.next = null; | ||
| 199 | size--; | ||
| 200 | modCount++; | ||
| 201 | return element; | ||
| 202 | } | ||
| 203 | |||
| 204 | /** | ||
| 205 | * Unlinks non-null node x. | ||
| 206 | */ | ||
| 207 | E unlink(Node<E> x) { | ||
| 208 | // assert x != null; | ||
| 209 | final E element = x.item; | ||
| 210 | final Node<E> next = x.next; | ||
| 211 | final Node<E> prev = x.prev; | ||
| 212 | |||
| 213 | if (prev == null) { | ||
| 214 | first = next; | ||
| 215 | } else { | ||
| 216 | prev.next = next; | ||
| 217 | x.prev = null; | ||
| 218 | } | ||
| 219 | |||
| 220 | if (next == null) { | ||
| 221 | last = prev; | ||
| 222 | } else { | ||
| 223 | next.prev = prev; | ||
| 224 | x.next = null; | ||
| 225 | } | ||
| 226 | |||
| 227 | x.item = null; | ||
| 228 | size--; | ||
| 229 | modCount++; | ||
| 230 | return element; | ||
| 231 | } | ||
| 232 | |||
| 233 | /** | ||
| 234 | * Returns the first element in this list. | ||
| 235 | * | ||
| 236 | * @return the first element in this list | ||
| 237 | * @throws NoSuchElementException if this list is empty | ||
| 238 | */ | ||
| 239 | public E getFirst() { | ||
| 240 | final Node<E> f = first; | ||
| 241 | if (f == null) | ||
| 242 | throw new NoSuchElementException(); | ||
| 243 | return f.item; | ||
| 244 | } | ||
| 245 | |||
| 246 | /** | ||
| 247 | * Returns the last element in this list. | ||
| 248 | * | ||
| 249 | * @return the last element in this list | ||
| 250 | * @throws NoSuchElementException if this list is empty | ||
| 251 | */ | ||
| 252 | public E getLast() { | ||
| 253 | final Node<E> l = last; | ||
| 254 | if (l == null) | ||
| 255 | throw new NoSuchElementException(); | ||
| 256 | return l.item; | ||
| 257 | } | ||
| 258 | |||
| 259 | /** | ||
| 260 | * Removes and returns the first element from this list. | ||
| 261 | * | ||
| 262 | * @return the first element from this list | ||
| 263 | * @throws NoSuchElementException if this list is empty | ||
| 264 | */ | ||
| 265 | public E removeFirst() { | ||
| 266 | final Node<E> f = first; | ||
| 267 | if (f == null) | ||
| 268 | throw new NoSuchElementException(); | ||
| 269 | return unlinkFirst(f); | ||
| 270 | } | ||
| 271 | |||
| 272 | /** | ||
| 273 | * Removes and returns the last element from this list. | ||
| 274 | * | ||
| 275 | * @return the last element from this list | ||
| 276 | * @throws NoSuchElementException if this list is empty | ||
| 277 | */ | ||
| 278 | public E removeLast() { | ||
| 279 | final Node<E> l = last; | ||
| 280 | if (l == null) | ||
| 281 | throw new NoSuchElementException(); | ||
| 282 | return unlinkLast(l); | ||
| 283 | } | ||
| 284 | |||
| 285 | /** | ||
| 286 | * Inserts the specified element at the beginning of this list. | ||
| 287 | * | ||
| 288 | * @param e the element to add | ||
| 289 | */ | ||
| 290 | public void addFirst(E e) { | ||
| 291 | linkFirst(e); | ||
| 292 | } | ||
| 293 | |||
| 294 | /** | ||
| 295 | * Appends the specified element to the end of this list. | ||
| 296 | * | ||
| 297 | * <p>This method is equivalent to {@link #add}. | ||
| 298 | * | ||
| 299 | * @param e the element to add | ||
| 300 | */ | ||
| 301 | public void addLast(E e) { | ||
| 302 | linkLast(e); | ||
| 303 | } | ||
| 304 | |||
| 305 | /** | ||
| 306 | * Returns {@code true} if this list contains the specified element. | ||
| 307 | * More formally, returns {@code true} if and only if this list contains | ||
| 308 | * at least one element {@code e} such that | ||
| 309 | * <tt>(o==null ? e==null : o.equals(e))</tt>. | ||
| 310 | * | ||
| 311 | * @param o element whose presence in this list is to be tested | ||
| 312 | * @return {@code true} if this list contains the specified element | ||
| 313 | */ | ||
| 314 | public boolean contains(Object o) { | ||
| 315 | return indexOf(o) != -1; | ||
| 316 | } | ||
| 317 | |||
| 318 | /** | ||
| 319 | * Returns the number of elements in this list. | ||
| 320 | * | ||
| 321 | * @return the number of elements in this list | ||
| 322 | */ | ||
| 323 | public int size() { | ||
| 324 | return size; | ||
| 325 | } | ||
| 326 | |||
| 327 | /** | ||
| 328 | * Appends the specified element to the end of this list. | ||
| 329 | * | ||
| 330 | * <p>This method is equivalent to {@link #addLast}. | ||
| 331 | * | ||
| 332 | * @param e element to be appended to this list | ||
| 333 | * @return {@code true} (as specified by {@link Collection#add}) | ||
| 334 | */ | ||
| 335 | public boolean add(E e) { | ||
| 336 | linkLast(e); | ||
| 337 | return true; | ||
| 338 | } | ||
| 339 | |||
| 340 | /** | ||
| 341 | * Removes the first occurrence of the specified element from this list, | ||
| 342 | * if it is present. If this list does not contain the element, it is | ||
| 343 | * unchanged. More formally, removes the element with the lowest index | ||
| 344 | * {@code i} such that | ||
| 345 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> | ||
| 346 | * (if such an element exists). Returns {@code true} if this list | ||
| 347 | * contained the specified element (or equivalently, if this list | ||
| 348 | * changed as a result of the call). | ||
| 349 | * | ||
| 350 | * @param o element to be removed from this list, if present | ||
| 351 | * @return {@code true} if this list contained the specified element | ||
| 352 | */ | ||
| 353 | public boolean remove(Object o) { | ||
| 354 | if (o == null) { | ||
| 355 | for (Node<E> x = first; x != null; x = x.next) { | ||
| 356 | if (x.item == null) { | ||
| 357 | unlink(x); | ||
| 358 | return true; | ||
| 359 | } | ||
| 360 | } | ||
| 361 | } else { | ||
| 362 | for (Node<E> x = first; x != null; x = x.next) { | ||
| 363 | if (o.equals(x.item)) { | ||
| 364 | unlink(x); | ||
| 365 | return true; | ||
| 366 | } | ||
| 367 | } | ||
| 368 | } | ||
| 369 | return false; | ||
| 370 | } | ||
| 371 | |||
| 372 | /** | ||
| 373 | * Appends all of the elements in the specified collection to the end of | ||
| 374 | * this list, in the order that they are returned by the specified | ||
| 375 | * collection's iterator. The behavior of this operation is undefined if | ||
| 376 | * the specified collection is modified while the operation is in | ||
| 377 | * progress. (Note that this will occur if the specified collection is | ||
| 378 | * this list, and it's nonempty.) | ||
| 379 | * | ||
| 380 | * @param c collection containing elements to be added to this list | ||
| 381 | * @return {@code true} if this list changed as a result of the call | ||
| 382 | * @throws NullPointerException if the specified collection is null | ||
| 383 | */ | ||
| 384 | public boolean addAll(Collection<? extends E> c) { | ||
| 385 | return addAll(size, c); | ||
| 386 | } | ||
| 387 | |||
| 388 | /** | ||
| 389 | * Inserts all of the elements in the specified collection into this | ||
| 390 | * list, starting at the specified position. Shifts the element | ||
| 391 | * currently at that position (if any) and any subsequent elements to | ||
| 392 | * the right (increases their indices). The new elements will appear | ||
| 393 | * in the list in the order that they are returned by the | ||
| 394 | * specified collection's iterator. | ||
| 395 | * | ||
| 396 | * @param index index at which to insert the first element | ||
| 397 | * from the specified collection | ||
| 398 | * @param c collection containing elements to be added to this list | ||
| 399 | * @return {@code true} if this list changed as a result of the call | ||
| 400 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 401 | * @throws NullPointerException if the specified collection is null | ||
| 402 | */ | ||
| 403 | public boolean addAll(int index, Collection<? extends E> c) { | ||
| 404 | checkPositionIndex(index); | ||
| 405 | |||
| 406 | Object[] a = c.toArray(); | ||
| 407 | int numNew = a.length; | ||
| 408 | if (numNew == 0) | ||
| 409 | return false; | ||
| 410 | |||
| 411 | Node<E> pred, succ; | ||
| 412 | if (index == size) { | ||
| 413 | succ = null; | ||
| 414 | pred = last; | ||
| 415 | } else { | ||
| 416 | succ = node(index); | ||
| 417 | pred = succ.prev; | ||
| 418 | } | ||
| 419 | |||
| 420 | for (Object o : a) { | ||
| 421 | @SuppressWarnings("unchecked") E e = (E) o; | ||
| 422 | Node<E> newNode = new Node<>(pred, e, null); | ||
| 423 | if (pred == null) | ||
| 424 | first = newNode; | ||
| 425 | else | ||
| 426 | pred.next = newNode; | ||
| 427 | pred = newNode; | ||
| 428 | } | ||
| 429 | |||
| 430 | if (succ == null) { | ||
| 431 | last = pred; | ||
| 432 | } else { | ||
| 433 | pred.next = succ; | ||
| 434 | succ.prev = pred; | ||
| 435 | } | ||
| 436 | |||
| 437 | size += numNew; | ||
| 438 | modCount++; | ||
| 439 | return true; | ||
| 440 | } | ||
| 441 | |||
| 442 | /** | ||
| 443 | * Removes all of the elements from this list. | ||
| 444 | * The list will be empty after this call returns. | ||
| 445 | */ | ||
| 446 | public void clear() { | ||
| 447 | // Clearing all of the links between nodes is "unnecessary", but: | ||
| 448 | // - helps a generational GC if the discarded nodes inhabit | ||
| 449 | // more than one generation | ||
| 450 | // - is sure to free memory even if there is a reachable Iterator | ||
| 451 | for (Node<E> x = first; x != null; ) { | ||
| 452 | Node<E> next = x.next; | ||
| 453 | x.item = null; | ||
| 454 | x.next = null; | ||
| 455 | x.prev = null; | ||
| 456 | x = next; | ||
| 457 | } | ||
| 458 | first = last = null; | ||
| 459 | size = 0; | ||
| 460 | modCount++; | ||
| 461 | } | ||
| 462 | |||
| 463 | |||
| 464 | // Positional Access Operations | ||
| 465 | |||
| 466 | /** | ||
| 467 | * Returns the element at the specified position in this list. | ||
| 468 | * | ||
| 469 | * @param index index of the element to return | ||
| 470 | * @return the element at the specified position in this list | ||
| 471 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 472 | */ | ||
| 473 | public E get(int index) { | ||
| 474 | checkElementIndex(index); | ||
| 475 | return node(index).item; | ||
| 476 | } | ||
| 477 | |||
| 478 | /** | ||
| 479 | * Replaces the element at the specified position in this list with the | ||
| 480 | * specified element. | ||
| 481 | * | ||
| 482 | * @param index index of the element to replace | ||
| 483 | * @param element element to be stored at the specified position | ||
| 484 | * @return the element previously at the specified position | ||
| 485 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 486 | */ | ||
| 487 | public E set(int index, E element) { | ||
| 488 | checkElementIndex(index); | ||
| 489 | Node<E> x = node(index); | ||
| 490 | E oldVal = x.item; | ||
| 491 | x.item = element; | ||
| 492 | return oldVal; | ||
| 493 | } | ||
| 494 | |||
| 495 | /** | ||
| 496 | * Inserts the specified element at the specified position in this list. | ||
| 497 | * Shifts the element currently at that position (if any) and any | ||
| 498 | * subsequent elements to the right (adds one to their indices). | ||
| 499 | * | ||
| 500 | * @param index index at which the specified element is to be inserted | ||
| 501 | * @param element element to be inserted | ||
| 502 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 503 | */ | ||
| 504 | public void add(int index, E element) { | ||
| 505 | checkPositionIndex(index); | ||
| 506 | |||
| 507 | if (index == size) | ||
| 508 | linkLast(element); | ||
| 509 | else | ||
| 510 | linkBefore(element, node(index)); | ||
| 511 | } | ||
| 512 | |||
| 513 | /** | ||
| 514 | * Removes the element at the specified position in this list. Shifts any | ||
| 515 | * subsequent elements to the left (subtracts one from their indices). | ||
| 516 | * Returns the element that was removed from the list. | ||
| 517 | * | ||
| 518 | * @param index the index of the element to be removed | ||
| 519 | * @return the element previously at the specified position | ||
| 520 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 521 | */ | ||
| 522 | public E remove(int index) { | ||
| 523 | checkElementIndex(index); | ||
| 524 | return unlink(node(index)); | ||
| 525 | } | ||
| 526 | |||
| 527 | /** | ||
| 528 | * Tells if the argument is the index of an existing element. | ||
| 529 | */ | ||
| 530 | private boolean isElementIndex(int index) { | ||
| 531 | return index >= 0 && index < size; | ||
| 532 | } | ||
| 533 | |||
| 534 | /** | ||
| 535 | * Tells if the argument is the index of a valid position for an | ||
| 536 | * iterator or an add operation. | ||
| 537 | */ | ||
| 538 | private boolean isPositionIndex(int index) { | ||
| 539 | return index >= 0 && index <= size; | ||
| 540 | } | ||
| 541 | |||
| 542 | /** | ||
| 543 | * Constructs an IndexOutOfBoundsException detail message. | ||
| 544 | * Of the many possible refactorings of the error handling code, | ||
| 545 | * this "outlining" performs best with both server and client VMs. | ||
| 546 | */ | ||
| 547 | private String outOfBoundsMsg(int index) { | ||
| 548 | return "Index: "+index+", Size: "+size; | ||
| 549 | } | ||
| 550 | |||
| 551 | private void checkElementIndex(int index) { | ||
| 552 | if (!isElementIndex(index)) | ||
| 553 | throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); | ||
| 554 | } | ||
| 555 | |||
| 556 | private void checkPositionIndex(int index) { | ||
| 557 | if (!isPositionIndex(index)) | ||
| 558 | throw new IndexOutOfBoundsException(outOfBoundsMsg(index)); | ||
| 559 | } | ||
| 560 | |||
| 561 | /** | ||
| 562 | * Returns the (non-null) Node at the specified element index. | ||
| 563 | */ | ||
| 564 | Node<E> node(int index) { | ||
| 565 | // assert isElementIndex(index); | ||
| 566 | |||
| 567 | if (index < (size >> 1)) { | ||
| 568 | Node<E> x = first; | ||
| 569 | for (int i = 0; i < index; i++) | ||
| 570 | x = x.next; | ||
| 571 | return x; | ||
| 572 | } else { | ||
| 573 | Node<E> x = last; | ||
| 574 | for (int i = size - 1; i > index; i--) | ||
| 575 | x = x.prev; | ||
| 576 | return x; | ||
| 577 | } | ||
| 578 | } | ||
| 579 | |||
| 580 | // Search Operations | ||
| 581 | |||
| 582 | /** | ||
| 583 | * Returns the index of the first occurrence of the specified element | ||
| 584 | * in this list, or -1 if this list does not contain the element. | ||
| 585 | * More formally, returns the lowest index {@code i} such that | ||
| 586 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, | ||
| 587 | * or -1 if there is no such index. | ||
| 588 | * | ||
| 589 | * @param o element to search for | ||
| 590 | * @return the index of the first occurrence of the specified element in | ||
| 591 | * this list, or -1 if this list does not contain the element | ||
| 592 | */ | ||
| 593 | public int indexOf(Object o) { | ||
| 594 | int index = 0; | ||
| 595 | if (o == null) { | ||
| 596 | for (Node<E> x = first; x != null; x = x.next) { | ||
| 597 | if (x.item == null) | ||
| 598 | return index; | ||
| 599 | index++; | ||
| 600 | } | ||
| 601 | } else { | ||
| 602 | for (Node<E> x = first; x != null; x = x.next) { | ||
| 603 | if (o.equals(x.item)) | ||
| 604 | return index; | ||
| 605 | index++; | ||
| 606 | } | ||
| 607 | } | ||
| 608 | return -1; | ||
| 609 | } | ||
| 610 | |||
| 611 | /** | ||
| 612 | * Returns the index of the last occurrence of the specified element | ||
| 613 | * in this list, or -1 if this list does not contain the element. | ||
| 614 | * More formally, returns the highest index {@code i} such that | ||
| 615 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, | ||
| 616 | * or -1 if there is no such index. | ||
| 617 | * | ||
| 618 | * @param o element to search for | ||
| 619 | * @return the index of the last occurrence of the specified element in | ||
| 620 | * this list, or -1 if this list does not contain the element | ||
| 621 | */ | ||
| 622 | public int lastIndexOf(Object o) { | ||
| 623 | int index = size; | ||
| 624 | if (o == null) { | ||
| 625 | for (Node<E> x = last; x != null; x = x.prev) { | ||
| 626 | index--; | ||
| 627 | if (x.item == null) | ||
| 628 | return index; | ||
| 629 | } | ||
| 630 | } else { | ||
| 631 | for (Node<E> x = last; x != null; x = x.prev) { | ||
| 632 | index--; | ||
| 633 | if (o.equals(x.item)) | ||
| 634 | return index; | ||
| 635 | } | ||
| 636 | } | ||
| 637 | return -1; | ||
| 638 | } | ||
| 639 | |||
| 640 | // Queue operations. | ||
| 641 | |||
| 642 | /** | ||
| 643 | * Retrieves, but does not remove, the head (first element) of this list. | ||
| 644 | * | ||
| 645 | * @return the head of this list, or {@code null} if this list is empty | ||
| 646 | * @since 1.5 | ||
| 647 | */ | ||
| 648 | public E peek() { | ||
| 649 | final Node<E> f = first; | ||
| 650 | return (f == null) ? null : f.item; | ||
| 651 | } | ||
| 652 | |||
| 653 | /** | ||
| 654 | * Retrieves, but does not remove, the head (first element) of this list. | ||
| 655 | * | ||
| 656 | * @return the head of this list | ||
| 657 | * @throws NoSuchElementException if this list is empty | ||
| 658 | * @since 1.5 | ||
| 659 | */ | ||
| 660 | public E element() { | ||
| 661 | return getFirst(); | ||
| 662 | } | ||
| 663 | |||
| 664 | /** | ||
| 665 | * Retrieves and removes the head (first element) of this list. | ||
| 666 | * | ||
| 667 | * @return the head of this list, or {@code null} if this list is empty | ||
| 668 | * @since 1.5 | ||
| 669 | */ | ||
| 670 | public E poll() { | ||
| 671 | final Node<E> f = first; | ||
| 672 | return (f == null) ? null : unlinkFirst(f); | ||
| 673 | } | ||
| 674 | |||
| 675 | /** | ||
| 676 | * Retrieves and removes the head (first element) of this list. | ||
| 677 | * | ||
| 678 | * @return the head of this list | ||
| 679 | * @throws NoSuchElementException if this list is empty | ||
| 680 | * @since 1.5 | ||
| 681 | */ | ||
| 682 | public E remove() { | ||
| 683 | return removeFirst(); | ||
| 684 | } | ||
| 685 | |||
| 686 | /** | ||
| 687 | * Adds the specified element as the tail (last element) of this list. | ||
| 688 | * | ||
| 689 | * @param e the element to add | ||
| 690 | * @return {@code true} (as specified by {@link Queue#offer}) | ||
| 691 | * @since 1.5 | ||
| 692 | */ | ||
| 693 | public boolean offer(E e) { | ||
| 694 | return add(e); | ||
| 695 | } | ||
| 696 | |||
| 697 | // Deque operations | ||
| 698 | /** | ||
| 699 | * Inserts the specified element at the front of this list. | ||
| 700 | * | ||
| 701 | * @param e the element to insert | ||
| 702 | * @return {@code true} (as specified by {@link Deque#offerFirst}) | ||
| 703 | * @since 1.6 | ||
| 704 | */ | ||
| 705 | public boolean offerFirst(E e) { | ||
| 706 | addFirst(e); | ||
| 707 | return true; | ||
| 708 | } | ||
| 709 | |||
| 710 | /** | ||
| 711 | * Inserts the specified element at the end of this list. | ||
| 712 | * | ||
| 713 | * @param e the element to insert | ||
| 714 | * @return {@code true} (as specified by {@link Deque#offerLast}) | ||
| 715 | * @since 1.6 | ||
| 716 | */ | ||
| 717 | public boolean offerLast(E e) { | ||
| 718 | addLast(e); | ||
| 719 | return true; | ||
| 720 | } | ||
| 721 | |||
| 722 | /** | ||
| 723 | * Retrieves, but does not remove, the first element of this list, | ||
| 724 | * or returns {@code null} if this list is empty. | ||
| 725 | * | ||
| 726 | * @return the first element of this list, or {@code null} | ||
| 727 | * if this list is empty | ||
| 728 | * @since 1.6 | ||
| 729 | */ | ||
| 730 | public E peekFirst() { | ||
| 731 | final Node<E> f = first; | ||
| 732 | return (f == null) ? null : f.item; | ||
| 733 | } | ||
| 734 | |||
| 735 | /** | ||
| 736 | * Retrieves, but does not remove, the last element of this list, | ||
| 737 | * or returns {@code null} if this list is empty. | ||
| 738 | * | ||
| 739 | * @return the last element of this list, or {@code null} | ||
| 740 | * if this list is empty | ||
| 741 | * @since 1.6 | ||
| 742 | */ | ||
| 743 | public E peekLast() { | ||
| 744 | final Node<E> l = last; | ||
| 745 | return (l == null) ? null : l.item; | ||
| 746 | } | ||
| 747 | |||
| 748 | /** | ||
| 749 | * Retrieves and removes the first element of this list, | ||
| 750 | * or returns {@code null} if this list is empty. | ||
| 751 | * | ||
| 752 | * @return the first element of this list, or {@code null} if | ||
| 753 | * this list is empty | ||
| 754 | * @since 1.6 | ||
| 755 | */ | ||
| 756 | public E pollFirst() { | ||
| 757 | final Node<E> f = first; | ||
| 758 | return (f == null) ? null : unlinkFirst(f); | ||
| 759 | } | ||
| 760 | |||
| 761 | /** | ||
| 762 | * Retrieves and removes the last element of this list, | ||
| 763 | * or returns {@code null} if this list is empty. | ||
| 764 | * | ||
| 765 | * @return the last element of this list, or {@code null} if | ||
| 766 | * this list is empty | ||
| 767 | * @since 1.6 | ||
| 768 | */ | ||
| 769 | public E pollLast() { | ||
| 770 | final Node<E> l = last; | ||
| 771 | return (l == null) ? null : unlinkLast(l); | ||
| 772 | } | ||
| 773 | |||
| 774 | /** | ||
| 775 | * Pushes an element onto the stack represented by this list. In other | ||
| 776 | * words, inserts the element at the front of this list. | ||
| 777 | * | ||
| 778 | * <p>This method is equivalent to {@link #addFirst}. | ||
| 779 | * | ||
| 780 | * @param e the element to push | ||
| 781 | * @since 1.6 | ||
| 782 | */ | ||
| 783 | public void push(E e) { | ||
| 784 | addFirst(e); | ||
| 785 | } | ||
| 786 | |||
| 787 | /** | ||
| 788 | * Pops an element from the stack represented by this list. In other | ||
| 789 | * words, removes and returns the first element of this list. | ||
| 790 | * | ||
| 791 | * <p>This method is equivalent to {@link #removeFirst()}. | ||
| 792 | * | ||
| 793 | * @return the element at the front of this list (which is the top | ||
| 794 | * of the stack represented by this list) | ||
| 795 | * @throws NoSuchElementException if this list is empty | ||
| 796 | * @since 1.6 | ||
| 797 | */ | ||
| 798 | public E pop() { | ||
| 799 | return removeFirst(); | ||
| 800 | } | ||
| 801 | |||
| 802 | /** | ||
| 803 | * Removes the first occurrence of the specified element in this | ||
| 804 | * list (when traversing the list from head to tail). If the list | ||
| 805 | * does not contain the element, it is unchanged. | ||
| 806 | * | ||
| 807 | * @param o element to be removed from this list, if present | ||
| 808 | * @return {@code true} if the list contained the specified element | ||
| 809 | * @since 1.6 | ||
| 810 | */ | ||
| 811 | public boolean removeFirstOccurrence(Object o) { | ||
| 812 | return remove(o); | ||
| 813 | } | ||
| 814 | |||
| 815 | /** | ||
| 816 | * Removes the last occurrence of the specified element in this | ||
| 817 | * list (when traversing the list from head to tail). If the list | ||
| 818 | * does not contain the element, it is unchanged. | ||
| 819 | * | ||
| 820 | * @param o element to be removed from this list, if present | ||
| 821 | * @return {@code true} if the list contained the specified element | ||
| 822 | * @since 1.6 | ||
| 823 | */ | ||
| 824 | public boolean removeLastOccurrence(Object o) { | ||
| 825 | if (o == null) { | ||
| 826 | for (Node<E> x = last; x != null; x = x.prev) { | ||
| 827 | if (x.item == null) { | ||
| 828 | unlink(x); | ||
| 829 | return true; | ||
| 830 | } | ||
| 831 | } | ||
| 832 | } else { | ||
| 833 | for (Node<E> x = last; x != null; x = x.prev) { | ||
| 834 | if (o.equals(x.item)) { | ||
| 835 | unlink(x); | ||
| 836 | return true; | ||
| 837 | } | ||
| 838 | } | ||
| 839 | } | ||
| 840 | return false; | ||
| 841 | } | ||
| 842 | |||
| 843 | /** | ||
| 844 | * Returns a list-iterator of the elements in this list (in proper | ||
| 845 | * sequence), starting at the specified position in the list. | ||
| 846 | * Obeys the general contract of {@code List.listIterator(int)}.<p> | ||
| 847 | * | ||
| 848 | * The list-iterator is <i>fail-fast</i>: if the list is structurally | ||
| 849 | * modified at any time after the Iterator is created, in any way except | ||
| 850 | * through the list-iterator's own {@code remove} or {@code add} | ||
| 851 | * methods, the list-iterator will throw a | ||
| 852 | * {@code ConcurrentModificationException}. Thus, in the face of | ||
| 853 | * concurrent modification, the iterator fails quickly and cleanly, rather | ||
| 854 | * than risking arbitrary, non-deterministic behavior at an undetermined | ||
| 855 | * time in the future. | ||
| 856 | * | ||
| 857 | * @param index index of the first element to be returned from the | ||
| 858 | * list-iterator (by a call to {@code next}) | ||
| 859 | * @return a ListIterator of the elements in this list (in proper | ||
| 860 | * sequence), starting at the specified position in the list | ||
| 861 | * @throws IndexOutOfBoundsException {@inheritDoc} | ||
| 862 | * @see List#listIterator(int) | ||
| 863 | */ | ||
| 864 | public ListIterator<E> listIterator(int index) { | ||
| 865 | checkPositionIndex(index); | ||
| 866 | return new ListItr(index); | ||
| 867 | } | ||
| 868 | |||
| 869 | private class ListItr implements ListIterator<E> { | ||
| 870 | private Node<E> lastReturned = null; | ||
| 871 | private Node<E> next; | ||
| 872 | private int nextIndex; | ||
| 873 | private int expectedModCount = modCount; | ||
| 874 | |||
| 875 | ListItr(int index) { | ||
| 876 | // assert isPositionIndex(index); | ||
| 877 | next = (index == size) ? null : node(index); | ||
| 878 | nextIndex = index; | ||
| 879 | } | ||
| 880 | |||
| 881 | public boolean hasNext() { | ||
| 882 | return nextIndex < size; | ||
| 883 | } | ||
| 884 | |||
| 885 | public E next() { | ||
| 886 | checkForComodification(); | ||
| 887 | if (!hasNext()) | ||
| 888 | throw new NoSuchElementException(); | ||
| 889 | |||
| 890 | lastReturned = next; | ||
| 891 | next = next.next; | ||
| 892 | nextIndex++; | ||
| 893 | return lastReturned.item; | ||
| 894 | } | ||
| 895 | |||
| 896 | public boolean hasPrevious() { | ||
| 897 | return nextIndex > 0; | ||
| 898 | } | ||
| 899 | |||
| 900 | public E previous() { | ||
| 901 | checkForComodification(); | ||
| 902 | if (!hasPrevious()) | ||
| 903 | throw new NoSuchElementException(); | ||
| 904 | |||
| 905 | lastReturned = next = (next == null) ? last : next.prev; | ||
| 906 | nextIndex--; | ||
| 907 | return lastReturned.item; | ||
| 908 | } | ||
| 909 | |||
| 910 | public int nextIndex() { | ||
| 911 | return nextIndex; | ||
| 912 | } | ||
| 913 | |||
| 914 | public int previousIndex() { | ||
| 915 | return nextIndex - 1; | ||
| 916 | } | ||
| 917 | |||
| 918 | public void remove() { | ||
| 919 | checkForComodification(); | ||
| 920 | if (lastReturned == null) | ||
| 921 | throw new IllegalStateException(); | ||
| 922 | |||
| 923 | Node<E> lastNext = lastReturned.next; | ||
| 924 | unlink(lastReturned); | ||
| 925 | if (next == lastReturned) | ||
| 926 | next = lastNext; | ||
| 927 | else | ||
| 928 | nextIndex--; | ||
| 929 | lastReturned = null; | ||
| 930 | expectedModCount++; | ||
| 931 | } | ||
| 932 | |||
| 933 | public void set(E e) { | ||
| 934 | if (lastReturned == null) | ||
| 935 | throw new IllegalStateException(); | ||
| 936 | checkForComodification(); | ||
| 937 | lastReturned.item = e; | ||
| 938 | } | ||
| 939 | |||
| 940 | public void add(E e) { | ||
| 941 | checkForComodification(); | ||
| 942 | lastReturned = null; | ||
| 943 | if (next == null) | ||
| 944 | linkLast(e); | ||
| 945 | else | ||
| 946 | linkBefore(e, next); | ||
| 947 | nextIndex++; | ||
| 948 | expectedModCount++; | ||
| 949 | } | ||
| 950 | |||
| 951 | final void checkForComodification() { | ||
| 952 | if (modCount != expectedModCount) | ||
| 953 | throw new ConcurrentModificationException(); | ||
| 954 | } | ||
| 955 | } | ||
| 956 | |||
| 957 | private static class Node<E> { | ||
| 958 | E item; | ||
| 959 | Node<E> next; | ||
| 960 | Node<E> prev; | ||
| 961 | |||
| 962 | Node(Node<E> prev, E element, Node<E> next) { | ||
| 963 | this.item = element; | ||
| 964 | this.next = next; | ||
| 965 | this.prev = prev; | ||
| 966 | } | ||
| 967 | } | ||
| 968 | |||
| 969 | /** | ||
| 970 | * @since 1.6 | ||
| 971 | */ | ||
| 972 | public Iterator<E> descendingIterator() { | ||
| 973 | return new DescendingIterator(); | ||
| 974 | } | ||
| 975 | |||
| 976 | /** | ||
| 977 | * Adapter to provide descending iterators via ListItr.previous | ||
| 978 | */ | ||
| 979 | private class DescendingIterator implements Iterator<E> { | ||
| 980 | private final ListItr itr = new ListItr(size()); | ||
| 981 | public boolean hasNext() { | ||
| 982 | return itr.hasPrevious(); | ||
| 983 | } | ||
| 984 | public E next() { | ||
| 985 | return itr.previous(); | ||
| 986 | } | ||
| 987 | public void remove() { | ||
| 988 | itr.remove(); | ||
| 989 | } | ||
| 990 | } | ||
| 991 | |||
| 992 | @SuppressWarnings("unchecked") | ||
| 993 | private LinkedList<E> superClone() { | ||
| 994 | try { | ||
| 995 | return (LinkedList<E>) super.clone(); | ||
| 996 | } catch (CloneNotSupportedException e) { | ||
| 997 | throw new InternalError(); | ||
| 998 | } | ||
| 999 | } | ||
| 1000 | |||
| 1001 | /** | ||
| 1002 | * Returns a shallow copy of this {@code LinkedList}. (The elements | ||
| 1003 | * themselves are not cloned.) | ||
| 1004 | * | ||
| 1005 | * @return a shallow copy of this {@code LinkedList} instance | ||
| 1006 | */ | ||
| 1007 | public Object clone() { | ||
| 1008 | LinkedList<E> clone = superClone(); | ||
| 1009 | |||
| 1010 | // Put clone into "virgin" state | ||
| 1011 | clone.first = clone.last = null; | ||
| 1012 | clone.size = 0; | ||
| 1013 | clone.modCount = 0; | ||
| 1014 | |||
| 1015 | // Initialize clone with our elements | ||
| 1016 | for (Node<E> x = first; x != null; x = x.next) | ||
| 1017 | clone.add(x.item); | ||
| 1018 | |||
| 1019 | return clone; | ||
| 1020 | } | ||
| 1021 | |||
| 1022 | /** | ||
| 1023 | * Returns an array containing all of the elements in this list | ||
| 1024 | * in proper sequence (from first to last element). | ||
| 1025 | * | ||
| 1026 | * <p>The returned array will be "safe" in that no references to it are | ||
| 1027 | * maintained by this list. (In other words, this method must allocate | ||
| 1028 | * a new array). The caller is thus free to modify the returned array. | ||
| 1029 | * | ||
| 1030 | * <p>This method acts as bridge between array-based and collection-based | ||
| 1031 | * APIs. | ||
| 1032 | * | ||
| 1033 | * @return an array containing all of the elements in this list | ||
| 1034 | * in proper sequence | ||
| 1035 | */ | ||
| 1036 | public Object[] toArray() { | ||
| 1037 | Object[] result = new Object[size]; | ||
| 1038 | int i = 0; | ||
| 1039 | for (Node<E> x = first; x != null; x = x.next) | ||
| 1040 | result[i++] = x.item; | ||
| 1041 | return result; | ||
| 1042 | } | ||
| 1043 | |||
| 1044 | /** | ||
| 1045 | * Returns an array containing all of the elements in this list in | ||
| 1046 | * proper sequence (from first to last element); the runtime type of | ||
| 1047 | * the returned array is that of the specified array. If the list fits | ||
| 1048 | * in the specified array, it is returned therein. Otherwise, a new | ||
| 1049 | * array is allocated with the runtime type of the specified array and | ||
| 1050 | * the size of this list. | ||
| 1051 | * | ||
| 1052 | * <p>If the list fits in the specified array with room to spare (i.e., | ||
| 1053 | * the array has more elements than the list), the element in the array | ||
| 1054 | * immediately following the end of the list is set to {@code null}. | ||
| 1055 | * (This is useful in determining the length of the list <i>only</i> if | ||
| 1056 | * the caller knows that the list does not contain any null elements.) | ||
| 1057 | * | ||
| 1058 | * <p>Like the {@link #toArray()} method, this method acts as bridge between | ||
| 1059 | * array-based and collection-based APIs. Further, this method allows | ||
| 1060 | * precise control over the runtime type of the output array, and may, | ||
| 1061 | * under certain circumstances, be used to save allocation costs. | ||
| 1062 | * | ||
| 1063 | * <p>Suppose {@code x} is a list known to contain only strings. | ||
| 1064 | * The following code can be used to dump the list into a newly | ||
| 1065 | * allocated array of {@code String}: | ||
| 1066 | * | ||
| 1067 | * <pre> | ||
| 1068 | * String[] y = x.toArray(new String[0]);</pre> | ||
| 1069 | * | ||
| 1070 | * Note that {@code toArray(new Object[0])} is identical in function to | ||
| 1071 | * {@code toArray()}. | ||
| 1072 | * | ||
| 1073 | * @param a the array into which the elements of the list are to | ||
| 1074 | * be stored, if it is big enough; otherwise, a new array of the | ||
| 1075 | * same runtime type is allocated for this purpose. | ||
| 1076 | * @return an array containing the elements of the list | ||
| 1077 | * @throws ArrayStoreException if the runtime type of the specified array | ||
| 1078 | * is not a supertype of the runtime type of every element in | ||
| 1079 | * this list | ||
| 1080 | * @throws NullPointerException if the specified array is null | ||
| 1081 | */ | ||
| 1082 | @SuppressWarnings("unchecked") | ||
| 1083 | public <T> T[] toArray(T[] a) { | ||
| 1084 | if (a.length < size) | ||
| 1085 | a = (T[])java.lang.reflect.Array.newInstance( | ||
| 1086 | a.getClass().getComponentType(), size); | ||
| 1087 | int i = 0; | ||
| 1088 | Object[] result = a; | ||
| 1089 | for (Node<E> x = first; x != null; x = x.next) | ||
| 1090 | result[i++] = x.item; | ||
| 1091 | |||
| 1092 | if (a.length > size) | ||
| 1093 | a[size] = null; | ||
| 1094 | |||
| 1095 | return a; | ||
| 1096 | } | ||
| 1097 | |||
| 1098 | private static final long serialVersionUID = 876323262645176354L; | ||
| 1099 | |||
| 1100 | /** | ||
| 1101 | * Saves the state of this {@code LinkedList} instance to a stream | ||
| 1102 | * (that is, serializes it). | ||
| 1103 | * | ||
| 1104 | * @serialData The size of the list (the number of elements it | ||
| 1105 | * contains) is emitted (int), followed by all of its | ||
| 1106 | * elements (each an Object) in the proper order. | ||
| 1107 | */ | ||
| 1108 | private void writeObject(java.io.ObjectOutputStream s) | ||
| 1109 | throws java.io.IOException { | ||
| 1110 | // Write out any hidden serialization magic | ||
| 1111 | s.defaultWriteObject(); | ||
| 1112 | |||
| 1113 | // Write out size | ||
| 1114 | s.writeInt(size); | ||
| 1115 | |||
| 1116 | // Write out all elements in the proper order. | ||
| 1117 | for (Node<E> x = first; x != null; x = x.next) | ||
| 1118 | s.writeObject(x.item); | ||
| 1119 | } | ||
| 1120 | |||
| 1121 | /** | ||
| 1122 | * Reconstitutes this {@code LinkedList} instance from a stream | ||
| 1123 | * (that is, deserializes it). | ||
| 1124 | */ | ||
| 1125 | @SuppressWarnings("unchecked") | ||
| 1126 | private void readObject(java.io.ObjectInputStream s) | ||
| 1127 | throws java.io.IOException, ClassNotFoundException { | ||
| 1128 | // Read in any hidden serialization magic | ||
| 1129 | s.defaultReadObject(); | ||
| 1130 | |||
| 1131 | // Read in size | ||
| 1132 | int size = s.readInt(); | ||
| 1133 | |||
| 1134 | // Read in all elements in the proper order. | ||
| 1135 | for (int i = 0; i < size; i++) | ||
| 1136 | linkLast((E)s.readObject()); | ||
| 1137 | } | ||
| 1138 | } | ||