J. Duke | 319a3b9 | 2007-12-01 00:00:00 +0000 | [diff] [blame^] | 1 | /* |
| 2 | * Copyright 1997-2006 Sun Microsystems, Inc. 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. Sun designates this |
| 8 | * particular file as subject to the "Classpath" exception as provided |
| 9 | * by Sun 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 Sun Microsystems, Inc., 4150 Network Circle, Santa Clara, |
| 22 | * CA 95054 USA or visit www.sun.com if you need additional information or |
| 23 | * have any questions. |
| 24 | */ |
| 25 | |
| 26 | package java.util; |
| 27 | |
| 28 | /** |
| 29 | * Linked list implementation of the <tt>List</tt> interface. Implements all |
| 30 | * optional list operations, and permits all elements (including |
| 31 | * <tt>null</tt>). In addition to implementing the <tt>List</tt> interface, |
| 32 | * the <tt>LinkedList</tt> class provides uniformly named methods to |
| 33 | * <tt>get</tt>, <tt>remove</tt> and <tt>insert</tt> an element at the |
| 34 | * beginning and end of the list. These operations allow linked lists to be |
| 35 | * used as a stack, {@linkplain Queue queue}, or {@linkplain Deque |
| 36 | * double-ended queue}. <p> |
| 37 | * |
| 38 | * The class implements the <tt>Deque</tt> interface, providing |
| 39 | * first-in-first-out queue operations for <tt>add</tt>, |
| 40 | * <tt>poll</tt>, along with other stack and deque operations.<p> |
| 41 | * |
| 42 | * All of the operations perform as could be expected for a doubly-linked |
| 43 | * list. Operations that index into the list will traverse the list from |
| 44 | * the beginning or the end, whichever is closer to the specified index.<p> |
| 45 | * |
| 46 | * <p><strong>Note that this implementation is not synchronized.</strong> |
| 47 | * If multiple threads access a linked list concurrently, and at least |
| 48 | * one of the threads modifies the list structurally, it <i>must</i> be |
| 49 | * synchronized externally. (A structural modification is any operation |
| 50 | * that adds or deletes one or more elements; merely setting the value of |
| 51 | * an element is not a structural modification.) This is typically |
| 52 | * accomplished by synchronizing on some object that naturally |
| 53 | * encapsulates the list. |
| 54 | * |
| 55 | * If no such object exists, the list should be "wrapped" using the |
| 56 | * {@link Collections#synchronizedList Collections.synchronizedList} |
| 57 | * method. This is best done at creation time, to prevent accidental |
| 58 | * unsynchronized access to the list:<pre> |
| 59 | * List list = Collections.synchronizedList(new LinkedList(...));</pre> |
| 60 | * |
| 61 | * <p>The iterators returned by this class's <tt>iterator</tt> and |
| 62 | * <tt>listIterator</tt> methods are <i>fail-fast</i>: if the list is |
| 63 | * structurally modified at any time after the iterator is created, in |
| 64 | * any way except through the Iterator's own <tt>remove</tt> or |
| 65 | * <tt>add</tt> methods, the iterator will throw a {@link |
| 66 | * ConcurrentModificationException}. Thus, in the face of concurrent |
| 67 | * modification, the iterator fails quickly and cleanly, rather than |
| 68 | * risking arbitrary, non-deterministic behavior at an undetermined |
| 69 | * time in the future. |
| 70 | * |
| 71 | * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed |
| 72 | * as it is, generally speaking, impossible to make any hard guarantees in the |
| 73 | * presence of unsynchronized concurrent modification. Fail-fast iterators |
| 74 | * throw <tt>ConcurrentModificationException</tt> on a best-effort basis. |
| 75 | * Therefore, it would be wrong to write a program that depended on this |
| 76 | * exception for its correctness: <i>the fail-fast behavior of iterators |
| 77 | * should be used only to detect bugs.</i> |
| 78 | * |
| 79 | * <p>This class is a member of the |
| 80 | * <a href="{@docRoot}/../technotes/guides/collections/index.html"> |
| 81 | * Java Collections Framework</a>. |
| 82 | * |
| 83 | * @author Josh Bloch |
| 84 | * @see List |
| 85 | * @see ArrayList |
| 86 | * @see Vector |
| 87 | * @since 1.2 |
| 88 | * @param <E> the type of elements held in this collection |
| 89 | */ |
| 90 | |
| 91 | public class LinkedList<E> |
| 92 | extends AbstractSequentialList<E> |
| 93 | implements List<E>, Deque<E>, Cloneable, java.io.Serializable |
| 94 | { |
| 95 | private transient Entry<E> header = new Entry<E>(null, null, null); |
| 96 | private transient int size = 0; |
| 97 | |
| 98 | /** |
| 99 | * Constructs an empty list. |
| 100 | */ |
| 101 | public LinkedList() { |
| 102 | header.next = header.previous = header; |
| 103 | } |
| 104 | |
| 105 | /** |
| 106 | * Constructs a list containing the elements of the specified |
| 107 | * collection, in the order they are returned by the collection's |
| 108 | * iterator. |
| 109 | * |
| 110 | * @param c the collection whose elements are to be placed into this list |
| 111 | * @throws NullPointerException if the specified collection is null |
| 112 | */ |
| 113 | public LinkedList(Collection<? extends E> c) { |
| 114 | this(); |
| 115 | addAll(c); |
| 116 | } |
| 117 | |
| 118 | /** |
| 119 | * Returns the first element in this list. |
| 120 | * |
| 121 | * @return the first element in this list |
| 122 | * @throws NoSuchElementException if this list is empty |
| 123 | */ |
| 124 | public E getFirst() { |
| 125 | if (size==0) |
| 126 | throw new NoSuchElementException(); |
| 127 | |
| 128 | return header.next.element; |
| 129 | } |
| 130 | |
| 131 | /** |
| 132 | * Returns the last element in this list. |
| 133 | * |
| 134 | * @return the last element in this list |
| 135 | * @throws NoSuchElementException if this list is empty |
| 136 | */ |
| 137 | public E getLast() { |
| 138 | if (size==0) |
| 139 | throw new NoSuchElementException(); |
| 140 | |
| 141 | return header.previous.element; |
| 142 | } |
| 143 | |
| 144 | /** |
| 145 | * Removes and returns the first element from this list. |
| 146 | * |
| 147 | * @return the first element from this list |
| 148 | * @throws NoSuchElementException if this list is empty |
| 149 | */ |
| 150 | public E removeFirst() { |
| 151 | return remove(header.next); |
| 152 | } |
| 153 | |
| 154 | /** |
| 155 | * Removes and returns the last element from this list. |
| 156 | * |
| 157 | * @return the last element from this list |
| 158 | * @throws NoSuchElementException if this list is empty |
| 159 | */ |
| 160 | public E removeLast() { |
| 161 | return remove(header.previous); |
| 162 | } |
| 163 | |
| 164 | /** |
| 165 | * Inserts the specified element at the beginning of this list. |
| 166 | * |
| 167 | * @param e the element to add |
| 168 | */ |
| 169 | public void addFirst(E e) { |
| 170 | addBefore(e, header.next); |
| 171 | } |
| 172 | |
| 173 | /** |
| 174 | * Appends the specified element to the end of this list. |
| 175 | * |
| 176 | * <p>This method is equivalent to {@link #add}. |
| 177 | * |
| 178 | * @param e the element to add |
| 179 | */ |
| 180 | public void addLast(E e) { |
| 181 | addBefore(e, header); |
| 182 | } |
| 183 | |
| 184 | /** |
| 185 | * Returns <tt>true</tt> if this list contains the specified element. |
| 186 | * More formally, returns <tt>true</tt> if and only if this list contains |
| 187 | * at least one element <tt>e</tt> such that |
| 188 | * <tt>(o==null ? e==null : o.equals(e))</tt>. |
| 189 | * |
| 190 | * @param o element whose presence in this list is to be tested |
| 191 | * @return <tt>true</tt> if this list contains the specified element |
| 192 | */ |
| 193 | public boolean contains(Object o) { |
| 194 | return indexOf(o) != -1; |
| 195 | } |
| 196 | |
| 197 | /** |
| 198 | * Returns the number of elements in this list. |
| 199 | * |
| 200 | * @return the number of elements in this list |
| 201 | */ |
| 202 | public int size() { |
| 203 | return size; |
| 204 | } |
| 205 | |
| 206 | /** |
| 207 | * Appends the specified element to the end of this list. |
| 208 | * |
| 209 | * <p>This method is equivalent to {@link #addLast}. |
| 210 | * |
| 211 | * @param e element to be appended to this list |
| 212 | * @return <tt>true</tt> (as specified by {@link Collection#add}) |
| 213 | */ |
| 214 | public boolean add(E e) { |
| 215 | addBefore(e, header); |
| 216 | return true; |
| 217 | } |
| 218 | |
| 219 | /** |
| 220 | * Removes the first occurrence of the specified element from this list, |
| 221 | * if it is present. If this list does not contain the element, it is |
| 222 | * unchanged. More formally, removes the element with the lowest index |
| 223 | * <tt>i</tt> such that |
| 224 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt> |
| 225 | * (if such an element exists). Returns <tt>true</tt> if this list |
| 226 | * contained the specified element (or equivalently, if this list |
| 227 | * changed as a result of the call). |
| 228 | * |
| 229 | * @param o element to be removed from this list, if present |
| 230 | * @return <tt>true</tt> if this list contained the specified element |
| 231 | */ |
| 232 | public boolean remove(Object o) { |
| 233 | if (o==null) { |
| 234 | for (Entry<E> e = header.next; e != header; e = e.next) { |
| 235 | if (e.element==null) { |
| 236 | remove(e); |
| 237 | return true; |
| 238 | } |
| 239 | } |
| 240 | } else { |
| 241 | for (Entry<E> e = header.next; e != header; e = e.next) { |
| 242 | if (o.equals(e.element)) { |
| 243 | remove(e); |
| 244 | return true; |
| 245 | } |
| 246 | } |
| 247 | } |
| 248 | return false; |
| 249 | } |
| 250 | |
| 251 | /** |
| 252 | * Appends all of the elements in the specified collection to the end of |
| 253 | * this list, in the order that they are returned by the specified |
| 254 | * collection's iterator. The behavior of this operation is undefined if |
| 255 | * the specified collection is modified while the operation is in |
| 256 | * progress. (Note that this will occur if the specified collection is |
| 257 | * this list, and it's nonempty.) |
| 258 | * |
| 259 | * @param c collection containing elements to be added to this list |
| 260 | * @return <tt>true</tt> if this list changed as a result of the call |
| 261 | * @throws NullPointerException if the specified collection is null |
| 262 | */ |
| 263 | public boolean addAll(Collection<? extends E> c) { |
| 264 | return addAll(size, c); |
| 265 | } |
| 266 | |
| 267 | /** |
| 268 | * Inserts all of the elements in the specified collection into this |
| 269 | * list, starting at the specified position. Shifts the element |
| 270 | * currently at that position (if any) and any subsequent elements to |
| 271 | * the right (increases their indices). The new elements will appear |
| 272 | * in the list in the order that they are returned by the |
| 273 | * specified collection's iterator. |
| 274 | * |
| 275 | * @param index index at which to insert the first element |
| 276 | * from the specified collection |
| 277 | * @param c collection containing elements to be added to this list |
| 278 | * @return <tt>true</tt> if this list changed as a result of the call |
| 279 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 280 | * @throws NullPointerException if the specified collection is null |
| 281 | */ |
| 282 | public boolean addAll(int index, Collection<? extends E> c) { |
| 283 | if (index < 0 || index > size) |
| 284 | throw new IndexOutOfBoundsException("Index: "+index+ |
| 285 | ", Size: "+size); |
| 286 | Object[] a = c.toArray(); |
| 287 | int numNew = a.length; |
| 288 | if (numNew==0) |
| 289 | return false; |
| 290 | modCount++; |
| 291 | |
| 292 | Entry<E> successor = (index==size ? header : entry(index)); |
| 293 | Entry<E> predecessor = successor.previous; |
| 294 | for (int i=0; i<numNew; i++) { |
| 295 | Entry<E> e = new Entry<E>((E)a[i], successor, predecessor); |
| 296 | predecessor.next = e; |
| 297 | predecessor = e; |
| 298 | } |
| 299 | successor.previous = predecessor; |
| 300 | |
| 301 | size += numNew; |
| 302 | return true; |
| 303 | } |
| 304 | |
| 305 | /** |
| 306 | * Removes all of the elements from this list. |
| 307 | */ |
| 308 | public void clear() { |
| 309 | Entry<E> e = header.next; |
| 310 | while (e != header) { |
| 311 | Entry<E> next = e.next; |
| 312 | e.next = e.previous = null; |
| 313 | e.element = null; |
| 314 | e = next; |
| 315 | } |
| 316 | header.next = header.previous = header; |
| 317 | size = 0; |
| 318 | modCount++; |
| 319 | } |
| 320 | |
| 321 | |
| 322 | // Positional Access Operations |
| 323 | |
| 324 | /** |
| 325 | * Returns the element at the specified position in this list. |
| 326 | * |
| 327 | * @param index index of the element to return |
| 328 | * @return the element at the specified position in this list |
| 329 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 330 | */ |
| 331 | public E get(int index) { |
| 332 | return entry(index).element; |
| 333 | } |
| 334 | |
| 335 | /** |
| 336 | * Replaces the element at the specified position in this list with the |
| 337 | * specified element. |
| 338 | * |
| 339 | * @param index index of the element to replace |
| 340 | * @param element element to be stored at the specified position |
| 341 | * @return the element previously at the specified position |
| 342 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 343 | */ |
| 344 | public E set(int index, E element) { |
| 345 | Entry<E> e = entry(index); |
| 346 | E oldVal = e.element; |
| 347 | e.element = element; |
| 348 | return oldVal; |
| 349 | } |
| 350 | |
| 351 | /** |
| 352 | * Inserts the specified element at the specified position in this list. |
| 353 | * Shifts the element currently at that position (if any) and any |
| 354 | * subsequent elements to the right (adds one to their indices). |
| 355 | * |
| 356 | * @param index index at which the specified element is to be inserted |
| 357 | * @param element element to be inserted |
| 358 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 359 | */ |
| 360 | public void add(int index, E element) { |
| 361 | addBefore(element, (index==size ? header : entry(index))); |
| 362 | } |
| 363 | |
| 364 | /** |
| 365 | * Removes the element at the specified position in this list. Shifts any |
| 366 | * subsequent elements to the left (subtracts one from their indices). |
| 367 | * Returns the element that was removed from the list. |
| 368 | * |
| 369 | * @param index the index of the element to be removed |
| 370 | * @return the element previously at the specified position |
| 371 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 372 | */ |
| 373 | public E remove(int index) { |
| 374 | return remove(entry(index)); |
| 375 | } |
| 376 | |
| 377 | /** |
| 378 | * Returns the indexed entry. |
| 379 | */ |
| 380 | private Entry<E> entry(int index) { |
| 381 | if (index < 0 || index >= size) |
| 382 | throw new IndexOutOfBoundsException("Index: "+index+ |
| 383 | ", Size: "+size); |
| 384 | Entry<E> e = header; |
| 385 | if (index < (size >> 1)) { |
| 386 | for (int i = 0; i <= index; i++) |
| 387 | e = e.next; |
| 388 | } else { |
| 389 | for (int i = size; i > index; i--) |
| 390 | e = e.previous; |
| 391 | } |
| 392 | return e; |
| 393 | } |
| 394 | |
| 395 | |
| 396 | // Search Operations |
| 397 | |
| 398 | /** |
| 399 | * Returns the index of the first occurrence of the specified element |
| 400 | * in this list, or -1 if this list does not contain the element. |
| 401 | * More formally, returns the lowest index <tt>i</tt> such that |
| 402 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
| 403 | * or -1 if there is no such index. |
| 404 | * |
| 405 | * @param o element to search for |
| 406 | * @return the index of the first occurrence of the specified element in |
| 407 | * this list, or -1 if this list does not contain the element |
| 408 | */ |
| 409 | public int indexOf(Object o) { |
| 410 | int index = 0; |
| 411 | if (o==null) { |
| 412 | for (Entry e = header.next; e != header; e = e.next) { |
| 413 | if (e.element==null) |
| 414 | return index; |
| 415 | index++; |
| 416 | } |
| 417 | } else { |
| 418 | for (Entry e = header.next; e != header; e = e.next) { |
| 419 | if (o.equals(e.element)) |
| 420 | return index; |
| 421 | index++; |
| 422 | } |
| 423 | } |
| 424 | return -1; |
| 425 | } |
| 426 | |
| 427 | /** |
| 428 | * Returns the index of the last occurrence of the specified element |
| 429 | * in this list, or -1 if this list does not contain the element. |
| 430 | * More formally, returns the highest index <tt>i</tt> such that |
| 431 | * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>, |
| 432 | * or -1 if there is no such index. |
| 433 | * |
| 434 | * @param o element to search for |
| 435 | * @return the index of the last occurrence of the specified element in |
| 436 | * this list, or -1 if this list does not contain the element |
| 437 | */ |
| 438 | public int lastIndexOf(Object o) { |
| 439 | int index = size; |
| 440 | if (o==null) { |
| 441 | for (Entry e = header.previous; e != header; e = e.previous) { |
| 442 | index--; |
| 443 | if (e.element==null) |
| 444 | return index; |
| 445 | } |
| 446 | } else { |
| 447 | for (Entry e = header.previous; e != header; e = e.previous) { |
| 448 | index--; |
| 449 | if (o.equals(e.element)) |
| 450 | return index; |
| 451 | } |
| 452 | } |
| 453 | return -1; |
| 454 | } |
| 455 | |
| 456 | // Queue operations. |
| 457 | |
| 458 | /** |
| 459 | * Retrieves, but does not remove, the head (first element) of this list. |
| 460 | * @return the head of this list, or <tt>null</tt> if this list is empty |
| 461 | * @since 1.5 |
| 462 | */ |
| 463 | public E peek() { |
| 464 | if (size==0) |
| 465 | return null; |
| 466 | return getFirst(); |
| 467 | } |
| 468 | |
| 469 | /** |
| 470 | * Retrieves, but does not remove, the head (first element) of this list. |
| 471 | * @return the head of this list |
| 472 | * @throws NoSuchElementException if this list is empty |
| 473 | * @since 1.5 |
| 474 | */ |
| 475 | public E element() { |
| 476 | return getFirst(); |
| 477 | } |
| 478 | |
| 479 | /** |
| 480 | * Retrieves and removes the head (first element) of this list |
| 481 | * @return the head of this list, or <tt>null</tt> if this list is empty |
| 482 | * @since 1.5 |
| 483 | */ |
| 484 | public E poll() { |
| 485 | if (size==0) |
| 486 | return null; |
| 487 | return removeFirst(); |
| 488 | } |
| 489 | |
| 490 | /** |
| 491 | * Retrieves and removes the head (first element) of this list. |
| 492 | * |
| 493 | * @return the head of this list |
| 494 | * @throws NoSuchElementException if this list is empty |
| 495 | * @since 1.5 |
| 496 | */ |
| 497 | public E remove() { |
| 498 | return removeFirst(); |
| 499 | } |
| 500 | |
| 501 | /** |
| 502 | * Adds the specified element as the tail (last element) of this list. |
| 503 | * |
| 504 | * @param e the element to add |
| 505 | * @return <tt>true</tt> (as specified by {@link Queue#offer}) |
| 506 | * @since 1.5 |
| 507 | */ |
| 508 | public boolean offer(E e) { |
| 509 | return add(e); |
| 510 | } |
| 511 | |
| 512 | // Deque operations |
| 513 | /** |
| 514 | * Inserts the specified element at the front of this list. |
| 515 | * |
| 516 | * @param e the element to insert |
| 517 | * @return <tt>true</tt> (as specified by {@link Deque#offerFirst}) |
| 518 | * @since 1.6 |
| 519 | */ |
| 520 | public boolean offerFirst(E e) { |
| 521 | addFirst(e); |
| 522 | return true; |
| 523 | } |
| 524 | |
| 525 | /** |
| 526 | * Inserts the specified element at the end of this list. |
| 527 | * |
| 528 | * @param e the element to insert |
| 529 | * @return <tt>true</tt> (as specified by {@link Deque#offerLast}) |
| 530 | * @since 1.6 |
| 531 | */ |
| 532 | public boolean offerLast(E e) { |
| 533 | addLast(e); |
| 534 | return true; |
| 535 | } |
| 536 | |
| 537 | /** |
| 538 | * Retrieves, but does not remove, the first element of this list, |
| 539 | * or returns <tt>null</tt> if this list is empty. |
| 540 | * |
| 541 | * @return the first element of this list, or <tt>null</tt> |
| 542 | * if this list is empty |
| 543 | * @since 1.6 |
| 544 | */ |
| 545 | public E peekFirst() { |
| 546 | if (size==0) |
| 547 | return null; |
| 548 | return getFirst(); |
| 549 | } |
| 550 | |
| 551 | /** |
| 552 | * Retrieves, but does not remove, the last element of this list, |
| 553 | * or returns <tt>null</tt> if this list is empty. |
| 554 | * |
| 555 | * @return the last element of this list, or <tt>null</tt> |
| 556 | * if this list is empty |
| 557 | * @since 1.6 |
| 558 | */ |
| 559 | public E peekLast() { |
| 560 | if (size==0) |
| 561 | return null; |
| 562 | return getLast(); |
| 563 | } |
| 564 | |
| 565 | /** |
| 566 | * Retrieves and removes the first element of this list, |
| 567 | * or returns <tt>null</tt> if this list is empty. |
| 568 | * |
| 569 | * @return the first element of this list, or <tt>null</tt> if |
| 570 | * this list is empty |
| 571 | * @since 1.6 |
| 572 | */ |
| 573 | public E pollFirst() { |
| 574 | if (size==0) |
| 575 | return null; |
| 576 | return removeFirst(); |
| 577 | } |
| 578 | |
| 579 | /** |
| 580 | * Retrieves and removes the last element of this list, |
| 581 | * or returns <tt>null</tt> if this list is empty. |
| 582 | * |
| 583 | * @return the last element of this list, or <tt>null</tt> if |
| 584 | * this list is empty |
| 585 | * @since 1.6 |
| 586 | */ |
| 587 | public E pollLast() { |
| 588 | if (size==0) |
| 589 | return null; |
| 590 | return removeLast(); |
| 591 | } |
| 592 | |
| 593 | /** |
| 594 | * Pushes an element onto the stack represented by this list. In other |
| 595 | * words, inserts the element at the front of this list. |
| 596 | * |
| 597 | * <p>This method is equivalent to {@link #addFirst}. |
| 598 | * |
| 599 | * @param e the element to push |
| 600 | * @since 1.6 |
| 601 | */ |
| 602 | public void push(E e) { |
| 603 | addFirst(e); |
| 604 | } |
| 605 | |
| 606 | /** |
| 607 | * Pops an element from the stack represented by this list. In other |
| 608 | * words, removes and returns the first element of this list. |
| 609 | * |
| 610 | * <p>This method is equivalent to {@link #removeFirst()}. |
| 611 | * |
| 612 | * @return the element at the front of this list (which is the top |
| 613 | * of the stack represented by this list) |
| 614 | * @throws NoSuchElementException if this list is empty |
| 615 | * @since 1.6 |
| 616 | */ |
| 617 | public E pop() { |
| 618 | return removeFirst(); |
| 619 | } |
| 620 | |
| 621 | /** |
| 622 | * Removes the first occurrence of the specified element in this |
| 623 | * list (when traversing the list from head to tail). If the list |
| 624 | * does not contain the element, it is unchanged. |
| 625 | * |
| 626 | * @param o element to be removed from this list, if present |
| 627 | * @return <tt>true</tt> if the list contained the specified element |
| 628 | * @since 1.6 |
| 629 | */ |
| 630 | public boolean removeFirstOccurrence(Object o) { |
| 631 | return remove(o); |
| 632 | } |
| 633 | |
| 634 | /** |
| 635 | * Removes the last occurrence of the specified element in this |
| 636 | * list (when traversing the list from head to tail). If the list |
| 637 | * does not contain the element, it is unchanged. |
| 638 | * |
| 639 | * @param o element to be removed from this list, if present |
| 640 | * @return <tt>true</tt> if the list contained the specified element |
| 641 | * @since 1.6 |
| 642 | */ |
| 643 | public boolean removeLastOccurrence(Object o) { |
| 644 | if (o==null) { |
| 645 | for (Entry<E> e = header.previous; e != header; e = e.previous) { |
| 646 | if (e.element==null) { |
| 647 | remove(e); |
| 648 | return true; |
| 649 | } |
| 650 | } |
| 651 | } else { |
| 652 | for (Entry<E> e = header.previous; e != header; e = e.previous) { |
| 653 | if (o.equals(e.element)) { |
| 654 | remove(e); |
| 655 | return true; |
| 656 | } |
| 657 | } |
| 658 | } |
| 659 | return false; |
| 660 | } |
| 661 | |
| 662 | /** |
| 663 | * Returns a list-iterator of the elements in this list (in proper |
| 664 | * sequence), starting at the specified position in the list. |
| 665 | * Obeys the general contract of <tt>List.listIterator(int)</tt>.<p> |
| 666 | * |
| 667 | * The list-iterator is <i>fail-fast</i>: if the list is structurally |
| 668 | * modified at any time after the Iterator is created, in any way except |
| 669 | * through the list-iterator's own <tt>remove</tt> or <tt>add</tt> |
| 670 | * methods, the list-iterator will throw a |
| 671 | * <tt>ConcurrentModificationException</tt>. Thus, in the face of |
| 672 | * concurrent modification, the iterator fails quickly and cleanly, rather |
| 673 | * than risking arbitrary, non-deterministic behavior at an undetermined |
| 674 | * time in the future. |
| 675 | * |
| 676 | * @param index index of the first element to be returned from the |
| 677 | * list-iterator (by a call to <tt>next</tt>) |
| 678 | * @return a ListIterator of the elements in this list (in proper |
| 679 | * sequence), starting at the specified position in the list |
| 680 | * @throws IndexOutOfBoundsException {@inheritDoc} |
| 681 | * @see List#listIterator(int) |
| 682 | */ |
| 683 | public ListIterator<E> listIterator(int index) { |
| 684 | return new ListItr(index); |
| 685 | } |
| 686 | |
| 687 | private class ListItr implements ListIterator<E> { |
| 688 | private Entry<E> lastReturned = header; |
| 689 | private Entry<E> next; |
| 690 | private int nextIndex; |
| 691 | private int expectedModCount = modCount; |
| 692 | |
| 693 | ListItr(int index) { |
| 694 | if (index < 0 || index > size) |
| 695 | throw new IndexOutOfBoundsException("Index: "+index+ |
| 696 | ", Size: "+size); |
| 697 | if (index < (size >> 1)) { |
| 698 | next = header.next; |
| 699 | for (nextIndex=0; nextIndex<index; nextIndex++) |
| 700 | next = next.next; |
| 701 | } else { |
| 702 | next = header; |
| 703 | for (nextIndex=size; nextIndex>index; nextIndex--) |
| 704 | next = next.previous; |
| 705 | } |
| 706 | } |
| 707 | |
| 708 | public boolean hasNext() { |
| 709 | return nextIndex != size; |
| 710 | } |
| 711 | |
| 712 | public E next() { |
| 713 | checkForComodification(); |
| 714 | if (nextIndex == size) |
| 715 | throw new NoSuchElementException(); |
| 716 | |
| 717 | lastReturned = next; |
| 718 | next = next.next; |
| 719 | nextIndex++; |
| 720 | return lastReturned.element; |
| 721 | } |
| 722 | |
| 723 | public boolean hasPrevious() { |
| 724 | return nextIndex != 0; |
| 725 | } |
| 726 | |
| 727 | public E previous() { |
| 728 | if (nextIndex == 0) |
| 729 | throw new NoSuchElementException(); |
| 730 | |
| 731 | lastReturned = next = next.previous; |
| 732 | nextIndex--; |
| 733 | checkForComodification(); |
| 734 | return lastReturned.element; |
| 735 | } |
| 736 | |
| 737 | public int nextIndex() { |
| 738 | return nextIndex; |
| 739 | } |
| 740 | |
| 741 | public int previousIndex() { |
| 742 | return nextIndex-1; |
| 743 | } |
| 744 | |
| 745 | public void remove() { |
| 746 | checkForComodification(); |
| 747 | Entry<E> lastNext = lastReturned.next; |
| 748 | try { |
| 749 | LinkedList.this.remove(lastReturned); |
| 750 | } catch (NoSuchElementException e) { |
| 751 | throw new IllegalStateException(); |
| 752 | } |
| 753 | if (next==lastReturned) |
| 754 | next = lastNext; |
| 755 | else |
| 756 | nextIndex--; |
| 757 | lastReturned = header; |
| 758 | expectedModCount++; |
| 759 | } |
| 760 | |
| 761 | public void set(E e) { |
| 762 | if (lastReturned == header) |
| 763 | throw new IllegalStateException(); |
| 764 | checkForComodification(); |
| 765 | lastReturned.element = e; |
| 766 | } |
| 767 | |
| 768 | public void add(E e) { |
| 769 | checkForComodification(); |
| 770 | lastReturned = header; |
| 771 | addBefore(e, next); |
| 772 | nextIndex++; |
| 773 | expectedModCount++; |
| 774 | } |
| 775 | |
| 776 | final void checkForComodification() { |
| 777 | if (modCount != expectedModCount) |
| 778 | throw new ConcurrentModificationException(); |
| 779 | } |
| 780 | } |
| 781 | |
| 782 | private static class Entry<E> { |
| 783 | E element; |
| 784 | Entry<E> next; |
| 785 | Entry<E> previous; |
| 786 | |
| 787 | Entry(E element, Entry<E> next, Entry<E> previous) { |
| 788 | this.element = element; |
| 789 | this.next = next; |
| 790 | this.previous = previous; |
| 791 | } |
| 792 | } |
| 793 | |
| 794 | private Entry<E> addBefore(E e, Entry<E> entry) { |
| 795 | Entry<E> newEntry = new Entry<E>(e, entry, entry.previous); |
| 796 | newEntry.previous.next = newEntry; |
| 797 | newEntry.next.previous = newEntry; |
| 798 | size++; |
| 799 | modCount++; |
| 800 | return newEntry; |
| 801 | } |
| 802 | |
| 803 | private E remove(Entry<E> e) { |
| 804 | if (e == header) |
| 805 | throw new NoSuchElementException(); |
| 806 | |
| 807 | E result = e.element; |
| 808 | e.previous.next = e.next; |
| 809 | e.next.previous = e.previous; |
| 810 | e.next = e.previous = null; |
| 811 | e.element = null; |
| 812 | size--; |
| 813 | modCount++; |
| 814 | return result; |
| 815 | } |
| 816 | |
| 817 | /** |
| 818 | * @since 1.6 |
| 819 | */ |
| 820 | public Iterator<E> descendingIterator() { |
| 821 | return new DescendingIterator(); |
| 822 | } |
| 823 | |
| 824 | /** Adapter to provide descending iterators via ListItr.previous */ |
| 825 | private class DescendingIterator implements Iterator { |
| 826 | final ListItr itr = new ListItr(size()); |
| 827 | public boolean hasNext() { |
| 828 | return itr.hasPrevious(); |
| 829 | } |
| 830 | public E next() { |
| 831 | return itr.previous(); |
| 832 | } |
| 833 | public void remove() { |
| 834 | itr.remove(); |
| 835 | } |
| 836 | } |
| 837 | |
| 838 | /** |
| 839 | * Returns a shallow copy of this <tt>LinkedList</tt>. (The elements |
| 840 | * themselves are not cloned.) |
| 841 | * |
| 842 | * @return a shallow copy of this <tt>LinkedList</tt> instance |
| 843 | */ |
| 844 | public Object clone() { |
| 845 | LinkedList<E> clone = null; |
| 846 | try { |
| 847 | clone = (LinkedList<E>) super.clone(); |
| 848 | } catch (CloneNotSupportedException e) { |
| 849 | throw new InternalError(); |
| 850 | } |
| 851 | |
| 852 | // Put clone into "virgin" state |
| 853 | clone.header = new Entry<E>(null, null, null); |
| 854 | clone.header.next = clone.header.previous = clone.header; |
| 855 | clone.size = 0; |
| 856 | clone.modCount = 0; |
| 857 | |
| 858 | // Initialize clone with our elements |
| 859 | for (Entry<E> e = header.next; e != header; e = e.next) |
| 860 | clone.add(e.element); |
| 861 | |
| 862 | return clone; |
| 863 | } |
| 864 | |
| 865 | /** |
| 866 | * Returns an array containing all of the elements in this list |
| 867 | * in proper sequence (from first to last element). |
| 868 | * |
| 869 | * <p>The returned array will be "safe" in that no references to it are |
| 870 | * maintained by this list. (In other words, this method must allocate |
| 871 | * a new array). The caller is thus free to modify the returned array. |
| 872 | * |
| 873 | * <p>This method acts as bridge between array-based and collection-based |
| 874 | * APIs. |
| 875 | * |
| 876 | * @return an array containing all of the elements in this list |
| 877 | * in proper sequence |
| 878 | */ |
| 879 | public Object[] toArray() { |
| 880 | Object[] result = new Object[size]; |
| 881 | int i = 0; |
| 882 | for (Entry<E> e = header.next; e != header; e = e.next) |
| 883 | result[i++] = e.element; |
| 884 | return result; |
| 885 | } |
| 886 | |
| 887 | /** |
| 888 | * Returns an array containing all of the elements in this list in |
| 889 | * proper sequence (from first to last element); the runtime type of |
| 890 | * the returned array is that of the specified array. If the list fits |
| 891 | * in the specified array, it is returned therein. Otherwise, a new |
| 892 | * array is allocated with the runtime type of the specified array and |
| 893 | * the size of this list. |
| 894 | * |
| 895 | * <p>If the list fits in the specified array with room to spare (i.e., |
| 896 | * the array has more elements than the list), the element in the array |
| 897 | * immediately following the end of the list is set to <tt>null</tt>. |
| 898 | * (This is useful in determining the length of the list <i>only</i> if |
| 899 | * the caller knows that the list does not contain any null elements.) |
| 900 | * |
| 901 | * <p>Like the {@link #toArray()} method, this method acts as bridge between |
| 902 | * array-based and collection-based APIs. Further, this method allows |
| 903 | * precise control over the runtime type of the output array, and may, |
| 904 | * under certain circumstances, be used to save allocation costs. |
| 905 | * |
| 906 | * <p>Suppose <tt>x</tt> is a list known to contain only strings. |
| 907 | * The following code can be used to dump the list into a newly |
| 908 | * allocated array of <tt>String</tt>: |
| 909 | * |
| 910 | * <pre> |
| 911 | * String[] y = x.toArray(new String[0]);</pre> |
| 912 | * |
| 913 | * Note that <tt>toArray(new Object[0])</tt> is identical in function to |
| 914 | * <tt>toArray()</tt>. |
| 915 | * |
| 916 | * @param a the array into which the elements of the list are to |
| 917 | * be stored, if it is big enough; otherwise, a new array of the |
| 918 | * same runtime type is allocated for this purpose. |
| 919 | * @return an array containing the elements of the list |
| 920 | * @throws ArrayStoreException if the runtime type of the specified array |
| 921 | * is not a supertype of the runtime type of every element in |
| 922 | * this list |
| 923 | * @throws NullPointerException if the specified array is null |
| 924 | */ |
| 925 | public <T> T[] toArray(T[] a) { |
| 926 | if (a.length < size) |
| 927 | a = (T[])java.lang.reflect.Array.newInstance( |
| 928 | a.getClass().getComponentType(), size); |
| 929 | int i = 0; |
| 930 | Object[] result = a; |
| 931 | for (Entry<E> e = header.next; e != header; e = e.next) |
| 932 | result[i++] = e.element; |
| 933 | |
| 934 | if (a.length > size) |
| 935 | a[size] = null; |
| 936 | |
| 937 | return a; |
| 938 | } |
| 939 | |
| 940 | private static final long serialVersionUID = 876323262645176354L; |
| 941 | |
| 942 | /** |
| 943 | * Save the state of this <tt>LinkedList</tt> instance to a stream (that |
| 944 | * is, serialize it). |
| 945 | * |
| 946 | * @serialData The size of the list (the number of elements it |
| 947 | * contains) is emitted (int), followed by all of its |
| 948 | * elements (each an Object) in the proper order. |
| 949 | */ |
| 950 | private void writeObject(java.io.ObjectOutputStream s) |
| 951 | throws java.io.IOException { |
| 952 | // Write out any hidden serialization magic |
| 953 | s.defaultWriteObject(); |
| 954 | |
| 955 | // Write out size |
| 956 | s.writeInt(size); |
| 957 | |
| 958 | // Write out all elements in the proper order. |
| 959 | for (Entry e = header.next; e != header; e = e.next) |
| 960 | s.writeObject(e.element); |
| 961 | } |
| 962 | |
| 963 | /** |
| 964 | * Reconstitute this <tt>LinkedList</tt> instance from a stream (that is |
| 965 | * deserialize it). |
| 966 | */ |
| 967 | private void readObject(java.io.ObjectInputStream s) |
| 968 | throws java.io.IOException, ClassNotFoundException { |
| 969 | // Read in any hidden serialization magic |
| 970 | s.defaultReadObject(); |
| 971 | |
| 972 | // Read in size |
| 973 | int size = s.readInt(); |
| 974 | |
| 975 | // Initialize header |
| 976 | header = new Entry<E>(null, null, null); |
| 977 | header.next = header.previous = header; |
| 978 | |
| 979 | // Read in all elements in the proper order. |
| 980 | for (int i=0; i<size; i++) |
| 981 | addBefore((E)s.readObject(), header); |
| 982 | } |
| 983 | } |