1 public class LinkedList 2 extends AbstractSequentialList 3 implements List, Deque, Cloneable, java.io.Serializable
4 {
5 transient int size = 0;
6
7 /**
8 * Pointer to first node.
9 * Invariant: (first == null && last == null) ||
10 * (first.prev == null && first.item != null)
11 */
12 transient Node first;
13
14 /**
15 * Pointer to last node.
16 * Invariant: (first == null && last == null) ||
17 * (last.next == null && last.item != null)
18 */
19 transient Node last;
20
21 /**
22 * Constructs an empty list.
23 */
24 public LinkedList() {
25 }
26
27 /**
28 * Constructs a list containing the elements of the specified
29 * collection, in the order they are returned by the collection‘s
30 * iterator.
31 *
32 * @param c the collection whose elements are to be placed into this list
33 * @throws NullPointerException if the specified collection is null
34 */
35 public LinkedList(Collection extends E> c) {
36 this();
37 addAll(c);
38 }
39
40 /**
41 * Links e as first element.
42 */
43 private void linkFirst(E e) {
44 final Node f = first;
45 final Node newNode = new Node(null, e, f);
46 first = newNode;
47 if (f == null)
48 last = newNode;
49 else
50 f.prev = newNode;
51 size++;
52 modCount++;
53 }
54
55 /**
56 * Links e as last element.
57 */
58 void linkLast(E e) {
59 final Node l = last;
60 final Node newNode = new Node(l, e, null);
61 last = newNode;
62 if (l == null)
63 first = newNode;
64 else
65 l.next = newNode;
66 size++;
67 modCount++;
68 }
69
70 /**
71 * Inserts element e before non-null Node succ.
72 */
73 void linkBefore(E e, Node succ) {
74 // assert succ != null;
75 final Node pred = succ.prev;
76 final Node newNode = new Node(pred, e, succ);
77 succ.prev = newNode;
78 if (pred == null)
79 first = newNode;
80 else
81 pred.next = newNode;
82 size++;
83 modCount++;
84 }
85
86 /**
87 * Unlinks non-null first node f.
88 */
89 private E unlinkFirst(Node f) {
90 // assert f == first && f != null;
91 final E element = f.item;
92 final Node next = f.next;
93 f.item = null;
94 f.next = null; // help GC
95 first = next;
96 if (next == null)
97 last = null;
98 else
99 next.prev = null;
100 size--;
101 modCount++;
102 return element;
103 }
104
105 /**
106 * Unlinks non-null last node l.
107 */
108 private E unlinkLast(Node l) {
109 // assert l == last && l != null;
110 final E element = l.item;
111 final Node prev = l.prev;
112 l.item = null;
113 l.prev = null; // help GC
114 last = prev;
115 if (prev == null)
116 first = null;
117 else
118 prev.next = null;
119 size--;
120 modCount++;
121 return element;
122 }
123
124 /**
125 * Unlinks non-null node x.
126 */
127 E unlink(Node x) {
128 // assert x != null;
129 final E element = x.item;
130 final Node next = x.next;
131 final Node prev = x.prev;
132
133 if (prev == null) {
134 first = next;
135 } else {
136 prev.next = next;
137 x.prev = null;
138 }
139
140 if (next == null) {
141 last = prev;
142 } else {
143 next.prev = prev;
144 x.next = null;
145 }
146
147 x.item = null;
148 size--;
149 modCount++;
150 return element;
151 }
152
153 /**
154 * Returns the first element in this list.
155 *
156 * @return the first element in this list
157 * @throws NoSuchElementException if this list is empty
158 */
159 public E getFirst() {
160 final Node f = first;
161 if (f == null)
162 throw new NoSuchElementException();
163 return f.item;
164 }
165
166 /**
167 * Returns the last element in this list.
168 *
169 * @return the last element in this list
170 * @throws NoSuchElementException if this list is empty
171 */
172 public E getLast() {
173 final Node l = last;
174 if (l == null)
175 throw new NoSuchElementException();
176 return l.item;
177 }
178
179 /**
180 * Removes and returns the first element from this list.
181 *
182 * @return the first element from this list
183 * @throws NoSuchElementException if this list is empty
184 */
185 public E removeFirst() {
186 final Node f = first;
187 if (f == null)
188 throw new NoSuchElementException();
189 return unlinkFirst(f);
190 }
191
192 /**
193 * Removes and returns the last element from this list.
194 *
195 * @return the last element from this list
196 * @throws NoSuchElementException if this list is empty
197 */
198 public E removeLast() {
199 final Node l = last;
200 if (l == null)
201 throw new NoSuchElementException();
202 return unlinkLast(l);
203 }
204
205 /**
206 * Inserts the specified element at the beginning of this list.
207 *
208 * @param e the element to add
209 */
210 public void addFirst(E e) {
211 linkFirst(e);
212 }
213
214 /**
215 * Appends the specified element to the end of this list.
216 *
217 * This method is equivalent to {
@link #add}.
218 *
219 * @param e the element to add
220 */
221 public void addLast(E e) {
222 linkLast(e);
223 }
224
225 /**
226 * Returns {@code true} if this list contains the specified element.
227 * More formally, returns {@code true} if and only if this list contains
228 * at least one element {@code e} such that
229 * (o==null ? e==null : o.equals(e)).
230 *
231 * @param o element whose presence in this list is to be tested
232 * @return {@code true} if this list contains the specified element
233 */
234 public boolean contains(Object o) {
235 return indexOf(o) != -1;
236 }
237
238 /**
239 * Returns the number of elements in this list.
240 *
241 * @return the number of elements in this list
242 */
243 public int size() {
244 return size;
245 }
246
247 /**
248 * Appends the specified element to the end of this list.
249 *
250 * This method is equivalent to {
@link #addLast}.
251 *
252 * @param e element to be appended to this list
253 * @return {@code true} (as specified by {@link Collection#add})
254 */
255 public boolean add(E e) {
256 linkLast(e);
257 return true;
258 }
259
260 /**
261 * Removes the first occurrence of the specified element from this list,
262 * if it is present. If this list does not contain the element, it is
263 * unchanged. More formally, removes the element with the lowest index
264 * {@code i} such that
265 * (o==null ? get(i)==null : o.equals(get(i)))
266 * (if such an element exists). Returns {@code true} if this list
267 * contained the specified element (or equivalently, if this list
268 * changed as a result of the call).
269 *
270 * @param o element to be removed from this list, if present
271 * @return {@code true} if this list contained the specified element
272 */
273 public boolean remove(Object o) {
274 if (o == null) {
275 for (Node x = first; x != null; x = x.next) {
276 if (x.item == null) {
277 unlink(x);
278 return true;
279 }
280 }
281 } else {
282 for (Node x = first; x != null; x = x.next) {
283 if (o.equals(x.item)) {
284 unlink(x);
285 return true;
286 }
287 }
288 }
289 return false;
290 }
291
292 /**
293 * Appends all of the elements in the specified collection to the end of
294 * this list, in the order that they are returned by the specified
295 * collection‘s iterator. The behavior of this operation is undefined if
296 * the specified collection is modified while the operation is in
297 * progress. (Note that this will occur if the specified collection is
298 * this list, and it‘s nonempty.)
299 *
300 * @param c collection containing elements to be added to this list
301 * @return {@code true} if this list changed as a result of the call
302 * @throws NullPointerException if the specified collection is null
303 */
304 public boolean addAll(Collection extends E> c) {
305 return addAll(size, c);
306 }
307
308 /**
309 * Inserts all of the elements in the specified collection into this
310 * list, starting at the specified position. Shifts the element
311 * currently at that position (if any) and any subsequent elements to
312 * the right (increases their indices). The new elements will appear
313 * in the list in the order that they are returned by the
314 * specified collection‘s iterator.
315 *
316 * @param index index at which to insert the first element
317 * from the specified collection
318 * @param c collection containing elements to be added to this list
319 * @return {@code true} if this list changed as a result of the call
320 * @throws IndexOutOfBoundsException {@inheritDoc}
321 * @throws NullPointerException if the specified collection is null
322 */
323 public boolean addAll(int index, Collection extends E> c) {
324 checkPositionIndex(index);
325
326 Object[] a = c.toArray();
327 int numNew = a.length;
328 if (numNew == 0)
329 return false;
330
331 Node pred, succ;
332 if (index == size) {
333 succ = null;
334 pred = last;
335 } else {
336 succ = node(index);
337 pred = succ.prev;
338 }
339
340 for (Object o : a) {
341 @SuppressWarnings("unchecked") E e = (E) o;
342 Node newNode = new Node(pred, e, null);
343 if (pred == null)
344 first = newNode;
345 else
346 pred.next = newNode;
347 pred = newNode;
348 }
349
350 if (succ == null) {
351 last = pred;
352 } else {
353 pred.next = succ;
354 succ.prev = pred;
355 }
356
357 size += numNew;
358 modCount++;
359 return true;
360 }
361
362 /**
363 * Removes all of the elements from this list.
364 * The list will be empty after this call returns.
365 */
366 public void clear() {
367 // Clearing all of the links between nodes is "unnecessary", but:
368 // - helps a generational GC if the discarded nodes inhabit
369 // more than one generation
370 // - is sure to free memory even if there is a reachable Iterator
371 for (Node x = first; x != null; ) {
372 Node next = x.next;
373 x.item = null;
374 x.next = null;
375 x.prev = null;
376 x = next;
377 }
378 first = last = null;
379 size = 0;
380 modCount++;
381 }
382
383
384 // Positional Access Operations
385
386 /**
387 * Returns the element at the specified position in this list.
388 *
389 * @param index index of the element to return
390 * @return the element at the specified position in this list
391 * @throws IndexOutOfBoundsException {@inheritDoc}
392 */
393 public E get(int index) {
394 checkElementIndex(index);
395 return node(index).item;
396 }
397
398 /**
399 * Replaces the element at the specified position in this list with the
400 * specified element.
401 *
402 * @param index index of the element to replace
403 * @param element element to be stored at the specified position
404 * @return the element previously at the specified position
405 * @throws IndexOutOfBoundsException {@inheritDoc}
406 */
407 public E set(int index, E element) {
408 checkElementIndex(index);
409 Node x = node(index);
410 E oldVal = x.item;
411 x.item = element;
412 return oldVal;
413 }
414
415 /**
416 * Inserts the specified element at the specified position in this list.
417 * Shifts the element currently at that position (if any) and any
418 * subsequent elements to the right (adds one to their indices).
419 *
420 * @param index index at which the specified element is to be inserted
421 * @param element element to be inserted
422 * @throws IndexOutOfBoundsException {@inheritDoc}
423 */
424 public void add(int index, E element) {
425 checkPositionIndex(index);
426
427 if (index == size)
428 linkLast(element);
429 else
430 linkBefore(element, node(index));
431 }
432
433 /**
434 * Removes the element at the specified position in this list. Shifts any
435 * subsequent elements to the left (subtracts one from their indices).
436 * Returns the element that was removed from the list.
437 *
438 * @param index the index of the element to be removed
439 * @return the element previously at the specified position
440 * @throws IndexOutOfBoundsException {@inheritDoc}
441 */
442 public E remove(int index) {
443 checkElementIndex(index);
444 return unlink(node(index));
445 }
446
447 /**
448 * Tells if the argument is the index of an existing element.
449 */
450 private boolean isElementIndex(int index) {
451 return index >= 0 && index size;
452 }
453
454 /**
455 * Tells if the argument is the index of a valid position for an
456 * iterator or an add operation.
457 */
458 private boolean isPositionIndex(int index) {
459 return index >= 0 && index size;
460 }
461
462 /**
463 * Constructs an IndexOutOfBoundsException detail message.
464 * Of the many possible refactorings of the error handling code,
465 * this "outlining" performs best with both server and client VMs.
466 */
467 private String outOfBoundsMsg(int index) {
468 return "Index: "+index+", Size: "+size;
469 }
470
471 private void checkElementIndex(int index) {
472 if (!isElementIndex(index))
473 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
474 }
475
476 private void checkPositionIndex(int index) {
477 if (!isPositionIndex(index))
478 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
479 }
480
481 /**
482 * Returns the (non-null) Node at the specified element index.
483 */
484 Node node(int index) {
485 // assert isElementIndex(index);
486
487 if (index > 1)) {
488 Node x = first;
489 for (int i = 0; i )
490 x = x.next;
491 return x;
492 } else {
493 Node x = last;
494 for (int i = size - 1; i > index; i--)
495 x = x.prev;
496 return x;
497 }
498 }
499
500 // Search Operations
501
502 /**
503 * Returns the index of the first occurrence of the specified element
504 * in this list, or -1 if this list does not contain the element.
505 * More formally, returns the lowest index {@code i} such that
506 * (o==null ? get(i)==null : o.equals(get(i))),
507 * or -1 if there is no such index.
508 *
509 * @param o element to search for
510 * @return the index of the first occurrence of the specified element in
511 * this list, or -1 if this list does not contain the element
512 */
513 public int indexOf(Object o) {
514 int index = 0;
515 if (o == null) {
516 for (Node x = first; x != null; x = x.next) {
517 if (x.item == null)
518 return index;
519 index++;
520 }
521 } else {
522 for (Node x = first; x != null; x = x.next) {
523 if (o.equals(x.item))
524 return index;
525 index++;
526 }
527 }
528 return -1;
529 }
530
531 /**
532 * Returns the index of the last occurrence of the specified element
&l
