1 /*
2 * Copyright (c) 1997, 2012, 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
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20 *
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24 */
25
26 package java.util;
27
28 /**
29 * This class provides a skeletal implementation of the {@link List}
30 * interface to minimize the effort required to implement this interface
31 * backed by a "random access" data store (such as an array). For sequential
32 * access data (such as a linked list), {@link AbstractSequentialList} should
33 * be used in preference to this class.
34 *
35 * <p>To implement an unmodifiable list, the programmer needs only to extend
36 * this class and provide implementations for the {@link #get(int)} and
37 * {@link List#size() size()} methods.
38 *
39 * <p>To implement a modifiable list, the programmer must additionally
40 * override the {@link #set(int, Object) set(int, E)} method (which otherwise
41 * throws an {@code UnsupportedOperationException}). If the list is
42 * variable-size the programmer must additionally override the
43 * {@link #add(int, Object) add(int, E)} and {@link #remove(int)} methods.
44 *
45 * <p>The programmer should generally provide a void (no argument) and collection
46 * constructor, as per the recommendation in the {@link Collection} interface
47 * specification.
48 *
49 * <p>Unlike the other abstract collection implementations, the programmer does
50 * <i>not</i> have to provide an iterator implementation; the iterator and
51 * list iterator are implemented by this class, on top of the "random access"
52 * methods:
53 * {@link #get(int)},
54 * {@link #set(int, Object) set(int, E)},
55 * {@link #add(int, Object) add(int, E)} and
56 * {@link #remove(int)}.
57 *
58 * <p>The documentation for each non-abstract method in this class describes its
59 * implementation in detail. Each of these methods may be overridden if the
60 * collection being implemented admits a more efficient implementation.
61 *
62 * <p>This class is a member of the
63 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
64 * Java Collections Framework</a>.
65 *
66 * @author Josh Bloch
67 * @author Neal Gafter
68 * @since 1.2
69 */
70
71 public abstract class AbstractList<E> extends AbstractCollection<E> implements List<E> {
72 /**
73 * Sole constructor. (For invocation by subclass constructors, typically
74 * implicit.)
75 */
76 protected AbstractList() {
77 }
78
79 /**
80 * Appends the specified element to the end of this list (optional
81 * operation).
82 *
83 * <p>Lists that support this operation may place limitations on what
84 * elements may be added to this list. In particular, some
85 * lists will refuse to add null elements, and others will impose
86 * restrictions on the type of elements that may be added. List
87 * classes should clearly specify in their documentation any restrictions
88 * on what elements may be added.
89 *
90 * <p>This implementation calls {@code add(size(), e)}.
91 *
92 * <p>Note that this implementation throws an
93 * {@code UnsupportedOperationException} unless
94 * {@link #add(int, Object) add(int, E)} is overridden.
95 *
96 * @param e element to be appended to this list
97 * @return {@code true} (as specified by {@link Collection#add})
98 * @throws UnsupportedOperationException if the {@code add} operation
99 * is not supported by this list
100 * @throws ClassCastException if the class of the specified element
101 * prevents it from being added to this list
102 * @throws NullPointerException if the specified element is null and this
103 * list does not permit null elements
104 * @throws IllegalArgumentException if some property of this element
105 * prevents it from being added to this list
106 */
107 public boolean add(E e) {
108 add(size(), e);
109 return true;
110 }
111
112 /**
113 * {@inheritDoc}
114 *
115 * @throws IndexOutOfBoundsException {@inheritDoc}
116 */
117 abstract public E get(int index);
118
119 /**
120 * {@inheritDoc}
121 *
122 * <p>This implementation always throws an
123 * {@code UnsupportedOperationException}.
124 *
125 * @throws UnsupportedOperationException {@inheritDoc}
126 * @throws ClassCastException {@inheritDoc}
127 * @throws NullPointerException {@inheritDoc}
128 * @throws IllegalArgumentException {@inheritDoc}
129 * @throws IndexOutOfBoundsException {@inheritDoc}
130 */
131 public E set(int index, E element) {
132 throw new UnsupportedOperationException();
133 }
134
135 /**
136 * {@inheritDoc}
137 *
138 * <p>This implementation always throws an
139 * {@code UnsupportedOperationException}.
140 *
141 * @throws UnsupportedOperationException {@inheritDoc}
142 * @throws ClassCastException {@inheritDoc}
143 * @throws NullPointerException {@inheritDoc}
144 * @throws IllegalArgumentException {@inheritDoc}
145 * @throws IndexOutOfBoundsException {@inheritDoc}
146 */
147 public void add(int index, E element) {
148 throw new UnsupportedOperationException();
149 }
150
151 /**
152 * {@inheritDoc}
153 *
154 * <p>This implementation always throws an
155 * {@code UnsupportedOperationException}.
156 *
157 * @throws UnsupportedOperationException {@inheritDoc}
158 * @throws IndexOutOfBoundsException {@inheritDoc}
159 */
160 public E remove(int index) {
161 throw new UnsupportedOperationException();
162 }
163
164
165 // Search Operations
166
167 /**
168 * {@inheritDoc}
169 *
170 * <p>This implementation first gets a list iterator (with
171 * {@code listIterator()}). Then, it iterates over the list until the
172 * specified element is found or the end of the list is reached.
173 *
174 * @throws ClassCastException {@inheritDoc}
175 * @throws NullPointerException {@inheritDoc}
176 */
177 public int indexOf(Object o) {
178 ListIterator<E> it = listIterator();
179 if (o==null) {
180 while (it.hasNext())
181 if (it.next()==null)
182 return it.previousIndex();
183 } else {
184 while (it.hasNext())
185 if (o.equals(it.next()))
186 return it.previousIndex();
187 }
188 return -1;
189 }
190
191 /**
192 * {@inheritDoc}
193 *
194 * <p>This implementation first gets a list iterator that points to the end
195 * of the list (with {@code listIterator(size())}). Then, it iterates
196 * backwards over the list until the specified element is found, or the
197 * beginning of the list is reached.
198 *
199 * @throws ClassCastException {@inheritDoc}
200 * @throws NullPointerException {@inheritDoc}
201 */
202 public int lastIndexOf(Object o) {
203 ListIterator<E> it = listIterator(size());
204 if (o==null) {
205 while (it.hasPrevious())
206 if (it.previous()==null)
207 return it.nextIndex();
208 } else {
209 while (it.hasPrevious())
210 if (o.equals(it.previous()))
211 return it.nextIndex();
212 }
213 return -1;
214 }
215
216
217 // Bulk Operations
218
219 /**
220 * Removes all of the elements from this list (optional operation).
221 * The list will be empty after this call returns.
222 *
223 * <p>This implementation calls {@code removeRange(0, size())}.
224 *
225 * <p>Note that this implementation throws an
226 * {@code UnsupportedOperationException} unless {@code remove(int
227 * index)} or {@code removeRange(int fromIndex, int toIndex)} is
228 * overridden.
229 *
230 * @throws UnsupportedOperationException if the {@code clear} operation
231 * is not supported by this list
232 */
233 public void clear() {
234 removeRange(0, size());
235 }
236
237 /**
238 * {@inheritDoc}
239 *
240 * <p>This implementation gets an iterator over the specified collection
241 * and iterates over it, inserting the elements obtained from the
242 * iterator into this list at the appropriate position, one at a time,
243 * using {@code add(int, E)}.
244 * Many implementations will override this method for efficiency.
245 *
246 * <p>Note that this implementation throws an
247 * {@code UnsupportedOperationException} unless
248 * {@link #add(int, Object) add(int, E)} is overridden.
249 *
250 * @throws UnsupportedOperationException {@inheritDoc}
251 * @throws ClassCastException {@inheritDoc}
252 * @throws NullPointerException {@inheritDoc}
253 * @throws IllegalArgumentException {@inheritDoc}
254 * @throws IndexOutOfBoundsException {@inheritDoc}
255 */
256 public boolean addAll(int index, Collection<? extends E> c) {
257 rangeCheckForAdd(index);
258 boolean modified = false;
259 for (E e : c) {
260 add(index++, e);
261 modified = true;
262 }
263 return modified;
264 }
265
266
267 // Iterators
268
269 /**
270 * Returns an iterator over the elements in this list in proper sequence.
271 *
272 * <p>This implementation returns a straightforward implementation of the
273 * iterator interface, relying on the backing list's {@code size()},
274 * {@code get(int)}, and {@code remove(int)} methods.
275 *
276 * <p>Note that the iterator returned by this method will throw an
277 * {@link UnsupportedOperationException} in response to its
278 * {@code remove} method unless the list's {@code remove(int)} method is
279 * overridden.
280 *
281 * <p>This implementation can be made to throw runtime exceptions in the
282 * face of concurrent modification, as described in the specification
283 * for the (protected) {@link #modCount} field.
284 *
285 * @return an iterator over the elements in this list in proper sequence
286 */
287 public Iterator<E> iterator() {
288 return new Itr();
289 }
290
291 /**
292 * {@inheritDoc}
293 *
294 * <p>This implementation returns {@code listIterator(0)}.
295 *
296 * @see #listIterator(int)
297 */
298 public ListIterator<E> listIterator() {
299 return listIterator(0);
300 }
301
302 /**
303 * {@inheritDoc}
304 *
305 * <p>This implementation returns a straightforward implementation of the
306 * {@code ListIterator} interface that extends the implementation of the
307 * {@code Iterator} interface returned by the {@code iterator()} method.
308 * The {@code ListIterator} implementation relies on the backing list's
309 * {@code get(int)}, {@code set(int, E)}, {@code add(int, E)}
310 * and {@code remove(int)} methods.
311 *
312 * <p>Note that the list iterator returned by this implementation will
313 * throw an {@link UnsupportedOperationException} in response to its
314 * {@code remove}, {@code set} and {@code add} methods unless the
315 * list's {@code remove(int)}, {@code set(int, E)}, and
316 * {@code add(int, E)} methods are overridden.
317 *
318 * <p>This implementation can be made to throw runtime exceptions in the
319 * face of concurrent modification, as described in the specification for
320 * the (protected) {@link #modCount} field.
321 *
322 * @throws IndexOutOfBoundsException {@inheritDoc}
323 */
324 public ListIterator<E> listIterator(final int index) {
325 rangeCheckForAdd(index);
326
327 return new ListItr(index);
328 }
329
330 private class Itr implements Iterator<E> {
331 /**
332 * Index of element to be returned by subsequent call to next.
333 */
334 int cursor = 0;
335
336 /**
337 * Index of element returned by most recent call to next or
338 * previous. Reset to -1 if this element is deleted by a call
339 * to remove.
340 */
341 int lastRet = -1;
342
343 /**
344 * The modCount value that the iterator believes that the backing
345 * List should have. If this expectation is violated, the iterator
346 * has detected concurrent modification.
347 */
348 int expectedModCount = modCount;
349
350 public boolean hasNext() {
351 return cursor != size();
352 }
353
354 public E next() {
355 checkForComodification();
356 try {
357 int i = cursor;
358 E next = get(i);
359 lastRet = i;
360 cursor = i + 1;
361 return next;
362 } catch (IndexOutOfBoundsException e) {
363 checkForComodification();
364 throw new NoSuchElementException();
365 }
366 }
367
368 public void remove() {
369 if (lastRet < 0)
370 throw new IllegalStateException();
371 checkForComodification();
372
373 try {
374 AbstractList.this.remove(lastRet);
375 if (lastRet < cursor)
376 cursor--;
377 lastRet = -1;
378 expectedModCount = modCount;
379 } catch (IndexOutOfBoundsException e) {
380 throw new ConcurrentModificationException();
381 }
382 }
383
384 final void checkForComodification() {
385 if (modCount != expectedModCount)
386 throw new ConcurrentModificationException();
387 }
388 }
389
390 private class ListItr extends Itr implements ListIterator<E> {
391 ListItr(int index) {
392 cursor = index;
393 }
394
395 public boolean hasPrevious() {
396 return cursor != 0;
397 }
398
399 public E previous() {
400 checkForComodification();
401 try {
402 int i = cursor - 1;
403 E previous = get(i);
404 lastRet = cursor = i;
405 return previous;
406 } catch (IndexOutOfBoundsException e) {
407 checkForComodification();
408 throw new NoSuchElementException();
409 }
410 }
411
412 public int nextIndex() {
413 return cursor;
414 }
415
416 public int previousIndex() {
417 return cursor-1;
418 }
419
420 public void set(E e) {
421 if (lastRet < 0)
422 throw new IllegalStateException();
423 checkForComodification();
424
425 try {
426 AbstractList.this.set(lastRet, e);
427 expectedModCount = modCount;
428 } catch (IndexOutOfBoundsException ex) {
429 throw new ConcurrentModificationException();
430 }
431 }
432
433 public void add(E e) {
434 checkForComodification();
435
436 try {
437 int i = cursor;
438 AbstractList.this.add(i, e);
439 lastRet = -1;
440 cursor = i + 1;
441 expectedModCount = modCount;
442 } catch (IndexOutOfBoundsException ex) {
443 throw new ConcurrentModificationException();
444 }
445 }
446 }
447
448 /**
449 * {@inheritDoc}
450 *
451 * <p>This implementation returns a list that subclasses
452 * {@code AbstractList}. The subclass stores, in private fields, the
453 * offset of the subList within the backing list, the size of the subList
454 * (which can change over its lifetime), and the expected
455 * {@code modCount} value of the backing list. There are two variants
456 * of the subclass, one of which implements {@code RandomAccess}.
457 * If this list implements {@code RandomAccess} the returned list will
458 * be an instance of the subclass that implements {@code RandomAccess}.
459 *
460 * <p>The subclass's {@code set(int, E)}, {@code get(int)},
461 * {@code add(int, E)}, {@code remove(int)}, {@code addAll(int,
462 * Collection)} and {@code removeRange(int, int)} methods all
463 * delegate to the corresponding methods on the backing abstract list,
464 * after bounds-checking the index and adjusting for the offset. The
465 * {@code addAll(Collection c)} method merely returns {@code addAll(size,
466 * c)}.
467 *
468 * <p>The {@code listIterator(int)} method returns a "wrapper object"
469 * over a list iterator on the backing list, which is created with the
470 * corresponding method on the backing list. The {@code iterator} method
471 * merely returns {@code listIterator()}, and the {@code size} method
472 * merely returns the subclass's {@code size} field.
473 *
474 * <p>All methods first check to see if the actual {@code modCount} of
475 * the backing list is equal to its expected value, and throw a
476 * {@code ConcurrentModificationException} if it is not.
477 *
478 * @throws IndexOutOfBoundsException if an endpoint index value is out of range
479 * {@code (fromIndex < 0 || toIndex > size)}
480 * @throws IllegalArgumentException if the endpoint indices are out of order
481 * {@code (fromIndex > toIndex)}
482 */
483 public List<E> subList(int fromIndex, int toIndex) {
484 return (this instanceof RandomAccess ?
485 new RandomAccessSubList<>(this, fromIndex, toIndex) :
486 new SubList<>(this, fromIndex, toIndex));
487 }
488
489 // Comparison and hashing
490
491 /**
492 * Compares the specified object with this list for equality. Returns
493 * {@code true} if and only if the specified object is also a list, both
494 * lists have the same size, and all corresponding pairs of elements in
495 * the two lists are <i>equal</i>. (Two elements {@code e1} and
496 * {@code e2} are <i>equal</i> if {@code (e1==null ? e2==null :
497 * e1.equals(e2))}.) In other words, two lists are defined to be
498 * equal if they contain the same elements in the same order.<p>
499 *
500 * This implementation first checks if the specified object is this
501 * list. If so, it returns {@code true}; if not, it checks if the
502 * specified object is a list. If not, it returns {@code false}; if so,
503 * it iterates over both lists, comparing corresponding pairs of elements.
504 * If any comparison returns {@code false}, this method returns
505 * {@code false}. If either iterator runs out of elements before the
506 * other it returns {@code false} (as the lists are of unequal length);
507 * otherwise it returns {@code true} when the iterations complete.
508 *
509 * @param o the object to be compared for equality with this list
510 * @return {@code true} if the specified object is equal to this list
511 */
512 public boolean equals(Object o) {
513 if (o == this)
514 return true;
515 if (!(o instanceof List))
516 return false;
517
518 ListIterator<E> e1 = listIterator();
519 ListIterator<?> e2 = ((List<?>) o).listIterator();
520 while (e1.hasNext() && e2.hasNext()) {
521 E o1 = e1.next();
522 Object o2 = e2.next();
523 if (!(o1==null ? o2==null : o1.equals(o2)))
524 return false;
525 }
526 return !(e1.hasNext() || e2.hasNext());
527 }
528
529 /**
530 * Returns the hash code value for this list.
531 *
532 * <p>This implementation uses exactly the code that is used to define the
533 * list hash function in the documentation for the {@link List#hashCode}
534 * method.
535 *
536 * @return the hash code value for this list
537 */
538 public int hashCode() {
539 int hashCode = 1;
540 for (E e : this)
541 hashCode = 31*hashCode + (e==null ? 0 : e.hashCode());
542 return hashCode;
543 }
544
545 /**
546 * Removes from this list all of the elements whose index is between
547 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
548 * Shifts any succeeding elements to the left (reduces their index).
549 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
550 * (If {@code toIndex==fromIndex}, this operation has no effect.)
551 *
552 * <p>This method is called by the {@code clear} operation on this list
553 * and its subLists. Overriding this method to take advantage of
554 * the internals of the list implementation can <i>substantially</i>
555 * improve the performance of the {@code clear} operation on this list
556 * and its subLists.
557 *
558 * <p>This implementation gets a list iterator positioned before
559 * {@code fromIndex}, and repeatedly calls {@code ListIterator.next}
560 * followed by {@code ListIterator.remove} until the entire range has
561 * been removed. <b>Note: if {@code ListIterator.remove} requires linear
562 * time, this implementation requires quadratic time.</b>
563 *
564 * @param fromIndex index of first element to be removed
565 * @param toIndex index after last element to be removed
566 */
567 protected void removeRange(int fromIndex, int toIndex) {
568 ListIterator<E> it = listIterator(fromIndex);
569 for (int i=0, n=toIndex-fromIndex; i<n; i++) {
570 it.next();
571 it.remove();
572 }
573 }
574
575 /**
576 * The number of times this list has been <i>structurally modified</i>.
577 * Structural modifications are those that change the size of the
578 * list, or otherwise perturb it in such a fashion that iterations in
579 * progress may yield incorrect results.
580 *
581 * <p>This field is used by the iterator and list iterator implementation
582 * returned by the {@code iterator} and {@code listIterator} methods.
583 * If the value of this field changes unexpectedly, the iterator (or list
584 * iterator) will throw a {@code ConcurrentModificationException} in
585 * response to the {@code next}, {@code remove}, {@code previous},
586 * {@code set} or {@code add} operations. This provides
587 * <i>fail-fast</i> behavior, rather than non-deterministic behavior in
588 * the face of concurrent modification during iteration.
589 *
590 * <p><b>Use of this field by subclasses is optional.</b> If a subclass
591 * wishes to provide fail-fast iterators (and list iterators), then it
592 * merely has to increment this field in its {@code add(int, E)} and
593 * {@code remove(int)} methods (and any other methods that it overrides
594 * that result in structural modifications to the list). A single call to
595 * {@code add(int, E)} or {@code remove(int)} must add no more than
596 * one to this field, or the iterators (and list iterators) will throw
597 * bogus {@code ConcurrentModificationExceptions}. If an implementation
598 * does not wish to provide fail-fast iterators, this field may be
599 * ignored.
600 */
601 protected transient int modCount = 0;
602
603 private void rangeCheckForAdd(int index) {
604 if (index < 0 || index > size())
605 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
606 }
607
608 private String outOfBoundsMsg(int index) {
609 return "Index: "+index+", Size: "+size();
610 }
611 }
612
613 class SubList<E> extends AbstractList<E> {
614 private final AbstractList<E> l;
615 private final int offset;
616 private int size;
617
618 SubList(AbstractList<E> list, int fromIndex, int toIndex) {
619 if (fromIndex < 0)
620 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
621 if (toIndex > list.size())
622 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
623 if (fromIndex > toIndex)
624 throw new IllegalArgumentException("fromIndex(" + fromIndex +
625 ") > toIndex(" + toIndex + ")");
626 l = list;
627 offset = fromIndex;
628 size = toIndex - fromIndex;
629 this.modCount = l.modCount;
630 }
631
632 public E set(int index, E element) {
633 rangeCheck(index);
634 checkForComodification();
635 return l.set(index+offset, element);
636 }
637
638 public E get(int index) {
639 rangeCheck(index);
640 checkForComodification();
641 return l.get(index+offset);
642 }
643
644 public int size() {
645 checkForComodification();
646 return size;
647 }
648
649 public void add(int index, E element) {
650 rangeCheckForAdd(index);
651 checkForComodification();
652 l.add(index+offset, element);
653 this.modCount = l.modCount;
654 size++;
655 }
656
657 public E remove(int index) {
658 rangeCheck(index);
659 checkForComodification();
660 E result = l.remove(index+offset);
661 this.modCount = l.modCount;
662 size--;
663 return result;
664 }
665
666 protected void removeRange(int fromIndex, int toIndex) {
667 checkForComodification();
668 l.removeRange(fromIndex+offset, toIndex+offset);
669 this.modCount = l.modCount;
670 size -= (toIndex-fromIndex);
671 }
672
673 public boolean addAll(Collection<? extends E> c) {
674 return addAll(size, c);
675 }
676
677 public boolean addAll(int index, Collection<? extends E> c) {
678 rangeCheckForAdd(index);
679 int cSize = c.size();
680 if (cSize==0)
681 return false;
682
683 checkForComodification();
684 l.addAll(offset+index, c);
685 this.modCount = l.modCount;
686 size += cSize;
687 return true;
688 }
689
690 public Iterator<E> iterator() {
691 return listIterator();
692 }
693
694 public ListIterator<E> listIterator(final int index) {
695 checkForComodification();
696 rangeCheckForAdd(index);
697
698 return new ListIterator<E>() {
699 private final ListIterator<E> i = l.listIterator(index+offset);
700
701 public boolean hasNext() {
702 return nextIndex() < size;
703 }
704
705 public E next() {
706 if (hasNext())
707 return i.next();
708 else
709 throw new NoSuchElementException();
710 }
711
712 public boolean hasPrevious() {
713 return previousIndex() >= 0;
714 }
715
716 public E previous() {
717 if (hasPrevious())
718 return i.previous();
719 else
720 throw new NoSuchElementException();
721 }
722
723 public int nextIndex() {
724 return i.nextIndex() - offset;
725 }
726
727 public int previousIndex() {
728 return i.previousIndex() - offset;
729 }
730
731 public void remove() {
732 i.remove();
733 SubList.this.modCount = l.modCount;
734 size--;
735 }
736
737 public void set(E e) {
738 i.set(e);
739 }
740
741 public void add(E e) {
742 i.add(e);
743 SubList.this.modCount = l.modCount;
744 size++;
745 }
746 };
747 }
748
749 public List<E> subList(int fromIndex, int toIndex) {
750 return new SubList<>(this, fromIndex, toIndex);
751 }
752
753 private void rangeCheck(int index) {
754 if (index < 0 || index >= size)
755 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
756 }
757
758 private void rangeCheckForAdd(int index) {
759 if (index < 0 || index > size)
760 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
761 }
762
763 private String outOfBoundsMsg(int index) {
764 return "Index: "+index+", Size: "+size;
765 }
766
767 private void checkForComodification() {
768 if (this.modCount != l.modCount)
769 throw new ConcurrentModificationException();
770 }
771 }
772
773 class RandomAccessSubList<E> extends SubList<E> implements RandomAccess {
774 RandomAccessSubList(AbstractList<E> list, int fromIndex, int toIndex) {
775 super(list, fromIndex, toIndex);
776 }
777
778 public List<E> subList(int fromIndex, int toIndex) {
779 return new RandomAccessSubList<>(this, fromIndex, toIndex);
780 }
781 }