1 /*
2 * Copyright (c) 1997, 2019, 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 import java.util.function.Consumer;
29 import java.util.function.Predicate;
30 import java.util.function.UnaryOperator;
31 import jdk.internal.access.SharedSecrets;
32 import jdk.internal.util.ArraysSupport;
33
34 /**
35 * Resizable-array implementation of the {@code List} interface. Implements
36 * all optional list operations, and permits all elements, including
37 * {@code null}. In addition to implementing the {@code List} interface,
38 * this class provides methods to manipulate the size of the array that is
39 * used internally to store the list. (This class is roughly equivalent to
40 * {@code Vector}, except that it is unsynchronized.)
41 *
42 * <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},
43 * {@code iterator}, and {@code listIterator} operations run in constant
44 * time. The {@code add} operation runs in <i>amortized constant time</i>,
45 * that is, adding n elements requires O(n) time. All of the other operations
46 * run in linear time (roughly speaking). The constant factor is low compared
47 * to that for the {@code LinkedList} implementation.
48 *
49 * <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is
50 * the size of the array used to store the elements in the list. It is always
51 * at least as large as the list size. As elements are added to an ArrayList,
52 * its capacity grows automatically. The details of the growth policy are not
53 * specified beyond the fact that adding an element has constant amortized
54 * time cost.
55 *
56 * <p>An application can increase the capacity of an {@code ArrayList} instance
57 * before adding a large number of elements using the {@code ensureCapacity}
58 * operation. This may reduce the amount of incremental reallocation.
59 *
60 * <p><strong>Note that this implementation is not synchronized.</strong>
61 * If multiple threads access an {@code ArrayList} instance concurrently,
62 * and at least one of the threads modifies the list structurally, it
63 * <i>must</i> be synchronized externally. (A structural modification is
64 * any operation that adds or deletes one or more elements, or explicitly
65 * resizes the backing array; merely setting the value of an element is not
66 * a structural modification.) This is typically accomplished by
67 * synchronizing on some object that naturally encapsulates the list.
68 *
69 * If no such object exists, the list should be "wrapped" using the
70 * {@link Collections#synchronizedList Collections.synchronizedList}
71 * method. This is best done at creation time, to prevent accidental
72 * unsynchronized access to the list:<pre>
73 * List list = Collections.synchronizedList(new ArrayList(...));</pre>
74 *
75 * <p id="fail-fast">
76 * The iterators returned by this class's {@link #iterator() iterator} and
77 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:
78 * if the list is structurally modified at any time after the iterator is
79 * created, in any way except through the iterator's own
80 * {@link ListIterator#remove() remove} or
81 * {@link ListIterator#add(Object) add} methods, the iterator will throw a
82 * {@link ConcurrentModificationException}. Thus, in the face of
83 * concurrent modification, the iterator fails quickly and cleanly, rather
84 * than risking arbitrary, non-deterministic behavior at an undetermined
85 * time in the future.
86 *
87 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
88 * as it is, generally speaking, impossible to make any hard guarantees in the
89 * presence of unsynchronized concurrent modification. Fail-fast iterators
90 * throw {@code ConcurrentModificationException} on a best-effort basis.
91 * Therefore, it would be wrong to write a program that depended on this
92 * exception for its correctness: <i>the fail-fast behavior of iterators
93 * should be used only to detect bugs.</i>
94 *
95 * <p>This class is a member of the
96 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
97 * Java Collections Framework</a>.
98 *
99 * @param <E> the type of elements in this list
100 *
101 * @author Josh Bloch
102 * @author Neal Gafter
103 * @see Collection
104 * @see List
105 * @see LinkedList
106 * @see Vector
107 * @since 1.2
108 */
109 public class ArrayList<E> extends AbstractList<E>
110 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
111 {
112 private static final long serialVersionUID = 8683452581122892189L;
113
114 /**
115 * Default initial capacity.
116 */
117 private static final int DEFAULT_CAPACITY = 10;
118
119 /**
120 * Shared empty array instance used for empty instances.
121 */
122 private static final Object[] EMPTY_ELEMENTDATA = {};
123
124 /**
125 * Shared empty array instance used for default sized empty instances. We
126 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
127 * first element is added.
128 */
129 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
130
131 /**
132 * The array buffer into which the elements of the ArrayList are stored.
133 * The capacity of the ArrayList is the length of this array buffer. Any
134 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
135 * will be expanded to DEFAULT_CAPACITY when the first element is added.
136 */
137 transient Object[] elementData; // non-private to simplify nested class access
138
139 /**
140 * The size of the ArrayList (the number of elements it contains).
141 *
142 * @serial
143 */
144 private int size;
145
146 /**
147 * Constructs an empty list with the specified initial capacity.
148 *
149 * @param initialCapacity the initial capacity of the list
150 * @throws IllegalArgumentException if the specified initial capacity
151 * is negative
152 */
153 public ArrayList(int initialCapacity) {
154 if (initialCapacity > 0) {
155 this.elementData = new Object[initialCapacity];
156 } else if (initialCapacity == 0) {
157 this.elementData = EMPTY_ELEMENTDATA;
158 } else {
159 throw new IllegalArgumentException("Illegal Capacity: "+
160 initialCapacity);
161 }
162 }
163
164 /**
165 * Constructs an empty list with an initial capacity of ten.
166 */
167 public ArrayList() {
168 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
169 }
170
171 /**
172 * Constructs a list containing the elements of the specified
173 * collection, in the order they are returned by the collection's
174 * iterator.
175 *
176 * @param c the collection whose elements are to be placed into this list
177 * @throws NullPointerException if the specified collection is null
178 */
179 public ArrayList(Collection<? extends E> c) {
180 elementData = c.toArray();
181 if ((size = elementData.length) != 0) {
182 // defend against c.toArray (incorrectly) not returning Object[]
183 // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
184 if (elementData.getClass() != Object[].class)
185 elementData = Arrays.copyOf(elementData, size, Object[].class);
186 } else {
187 // replace with empty array.
188 this.elementData = EMPTY_ELEMENTDATA;
189 }
190 }
191
192 /**
193 * Trims the capacity of this {@code ArrayList} instance to be the
194 * list's current size. An application can use this operation to minimize
195 * the storage of an {@code ArrayList} instance.
196 */
197 public void trimToSize() {
198 modCount++;
199 if (size < elementData.length) {
200 elementData = (size == 0)
201 ? EMPTY_ELEMENTDATA
202 : Arrays.copyOf(elementData, size);
203 }
204 }
205
206 /**
207 * Increases the capacity of this {@code ArrayList} instance, if
208 * necessary, to ensure that it can hold at least the number of elements
209 * specified by the minimum capacity argument.
210 *
211 * @param minCapacity the desired minimum capacity
212 */
213 public void ensureCapacity(int minCapacity) {
214 if (minCapacity > elementData.length
215 && !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
216 && minCapacity <= DEFAULT_CAPACITY)) {
217 modCount++;
218 grow(minCapacity);
219 }
220 }
221
222 /**
223 * Increases the capacity to ensure that it can hold at least the
224 * number of elements specified by the minimum capacity argument.
225 *
226 * @param minCapacity the desired minimum capacity
227 * @throws OutOfMemoryError if minCapacity is less than zero
228 */
229 private Object[] grow(int minCapacity) {
230 int oldCapacity = elementData.length;
231 if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
232 int newCapacity = ArraysSupport.newCapacity(oldCapacity,
233 minCapacity - oldCapacity, oldCapacity >> 1);
234 return elementData = Arrays.copyOf(elementData, newCapacity);
235 } else {
236 return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];
237 }
238 }
239
240 private Object[] grow() {
241 return grow(size + 1);
242 }
243
244 /**
245 * Returns the number of elements in this list.
246 *
247 * @return the number of elements in this list
248 */
249 public int size() {
250 return size;
251 }
252
253 /**
254 * Returns {@code true} if this list contains no elements.
255 *
256 * @return {@code true} if this list contains no elements
257 */
258 public boolean isEmpty() {
259 return size == 0;
260 }
261
262 /**
263 * Returns {@code true} if this list contains the specified element.
264 * More formally, returns {@code true} if and only if this list contains
265 * at least one element {@code e} such that
266 * {@code Objects.equals(o, e)}.
267 *
268 * @param o element whose presence in this list is to be tested
269 * @return {@code true} if this list contains the specified element
270 */
271 public boolean contains(Object o) {
272 return indexOf(o) >= 0;
273 }
274
275 /**
276 * Returns the index of the first occurrence of the specified element
277 * in this list, or -1 if this list does not contain the element.
278 * More formally, returns the lowest index {@code i} such that
279 * {@code Objects.equals(o, get(i))},
280 * or -1 if there is no such index.
281 */
282 public int indexOf(Object o) {
283 return indexOfRange(o, 0, size);
284 }
285
286 int indexOfRange(Object o, int start, int end) {
287 Object[] es = elementData;
288 if (o == null) {
289 for (int i = start; i < end; i++) {
290 if (es[i] == null) {
291 return i;
292 }
293 }
294 } else {
295 for (int i = start; i < end; i++) {
296 if (o.equals(es[i])) {
297 return i;
298 }
299 }
300 }
301 return -1;
302 }
303
304 /**
305 * Returns the index of the last occurrence of the specified element
306 * in this list, or -1 if this list does not contain the element.
307 * More formally, returns the highest index {@code i} such that
308 * {@code Objects.equals(o, get(i))},
309 * or -1 if there is no such index.
310 */
311 public int lastIndexOf(Object o) {
312 return lastIndexOfRange(o, 0, size);
313 }
314
315 int lastIndexOfRange(Object o, int start, int end) {
316 Object[] es = elementData;
317 if (o == null) {
318 for (int i = end - 1; i >= start; i--) {
319 if (es[i] == null) {
320 return i;
321 }
322 }
323 } else {
324 for (int i = end - 1; i >= start; i--) {
325 if (o.equals(es[i])) {
326 return i;
327 }
328 }
329 }
330 return -1;
331 }
332
333 /**
334 * Returns a shallow copy of this {@code ArrayList} instance. (The
335 * elements themselves are not copied.)
336 *
337 * @return a clone of this {@code ArrayList} instance
338 */
339 public Object clone() {
340 try {
341 ArrayList<?> v = (ArrayList<?>) super.clone();
342 v.elementData = Arrays.copyOf(elementData, size);
343 v.modCount = 0;
344 return v;
345 } catch (CloneNotSupportedException e) {
346 // this shouldn't happen, since we are Cloneable
347 throw new InternalError(e);
348 }
349 }
350
351 /**
352 * Returns an array containing all of the elements in this list
353 * in proper sequence (from first to last element).
354 *
355 * <p>The returned array will be "safe" in that no references to it are
356 * maintained by this list. (In other words, this method must allocate
357 * a new array). The caller is thus free to modify the returned array.
358 *
359 * <p>This method acts as bridge between array-based and collection-based
360 * APIs.
361 *
362 * @return an array containing all of the elements in this list in
363 * proper sequence
364 */
365 public Object[] toArray() {
366 return Arrays.copyOf(elementData, size);
367 }
368
369 /**
370 * Returns an array containing all of the elements in this list in proper
371 * sequence (from first to last element); the runtime type of the returned
372 * array is that of the specified array. If the list fits in the
373 * specified array, it is returned therein. Otherwise, a new array is
374 * allocated with the runtime type of the specified array and the size of
375 * this list.
376 *
377 * <p>If the list fits in the specified array with room to spare
378 * (i.e., the array has more elements than the list), the element in
379 * the array immediately following the end of the collection is set to
380 * {@code null}. (This is useful in determining the length of the
381 * list <i>only</i> if the caller knows that the list does not contain
382 * any null elements.)
383 *
384 * @param a the array into which the elements of the list are to
385 * be stored, if it is big enough; otherwise, a new array of the
386 * same runtime type is allocated for this purpose.
387 * @return an array containing the elements of the list
388 * @throws ArrayStoreException if the runtime type of the specified array
389 * is not a supertype of the runtime type of every element in
390 * this list
391 * @throws NullPointerException if the specified array is null
392 */
393 @SuppressWarnings("unchecked")
394 public <T> T[] toArray(T[] a) {
395 if (a.length < size)
396 // Make a new array of a's runtime type, but my contents:
397 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
398 System.arraycopy(elementData, 0, a, 0, size);
399 if (a.length > size)
400 a[size] = null;
401 return a;
402 }
403
404 // Positional Access Operations
405
406 @SuppressWarnings("unchecked")
407 E elementData(int index) {
408 return (E) elementData[index];
409 }
410
411 @SuppressWarnings("unchecked")
412 static <E> E elementAt(Object[] es, int index) {
413 return (E) es[index];
414 }
415
416 /**
417 * Returns the element at the specified position in this list.
418 *
419 * @param index index of the element to return
420 * @return the element at the specified position in this list
421 * @throws IndexOutOfBoundsException {@inheritDoc}
422 */
423 public E get(int index) {
424 Objects.checkIndex(index, size);
425 return elementData(index);
426 }
427
428 /**
429 * Replaces the element at the specified position in this list with
430 * the specified element.
431 *
432 * @param index index of the element to replace
433 * @param element element to be stored at the specified position
434 * @return the element previously at the specified position
435 * @throws IndexOutOfBoundsException {@inheritDoc}
436 */
437 public E set(int index, E element) {
438 Objects.checkIndex(index, size);
439 E oldValue = elementData(index);
440 elementData[index] = element;
441 return oldValue;
442 }
443
444 /**
445 * This helper method split out from add(E) to keep method
446 * bytecode size under 35 (the -XX:MaxInlineSize default value),
447 * which helps when add(E) is called in a C1-compiled loop.
448 */
449 private void add(E e, Object[] elementData, int s) {
450 if (s == elementData.length)
451 elementData = grow();
452 elementData[s] = e;
453 size = s + 1;
454 }
455
456 /**
457 * Appends the specified element to the end of this list.
458 *
459 * @param e element to be appended to this list
460 * @return {@code true} (as specified by {@link Collection#add})
461 */
462 public boolean add(E e) {
463 modCount++;
464 add(e, elementData, size);
465 return true;
466 }
467
468 /**
469 * Inserts the specified element at the specified position in this
470 * list. Shifts the element currently at that position (if any) and
471 * any subsequent elements to the right (adds one to their indices).
472 *
473 * @param index index at which the specified element is to be inserted
474 * @param element element to be inserted
475 * @throws IndexOutOfBoundsException {@inheritDoc}
476 */
477 public void add(int index, E element) {
478 rangeCheckForAdd(index);
479 modCount++;
480 final int s;
481 Object[] elementData;
482 if ((s = size) == (elementData = this.elementData).length)
483 elementData = grow();
484 System.arraycopy(elementData, index,
485 elementData, index + 1,
486 s - index);
487 elementData[index] = element;
488 size = s + 1;
489 }
490
491 /**
492 * Removes the element at the specified position in this list.
493 * Shifts any subsequent elements to the left (subtracts one from their
494 * indices).
495 *
496 * @param index the index of the element to be removed
497 * @return the element that was removed from the list
498 * @throws IndexOutOfBoundsException {@inheritDoc}
499 */
500 public E remove(int index) {
501 Objects.checkIndex(index, size);
502 final Object[] es = elementData;
503
504 @SuppressWarnings("unchecked") E oldValue = (E) es[index];
505 fastRemove(es, index);
506
507 return oldValue;
508 }
509
510 /**
511 * {@inheritDoc}
512 */
513 public boolean equals(Object o) {
514 if (o == this) {
515 return true;
516 }
517
518 if (!(o instanceof List)) {
519 return false;
520 }
521
522 final int expectedModCount = modCount;
523 // ArrayList can be subclassed and given arbitrary behavior, but we can
524 // still deal with the common case where o is ArrayList precisely
525 boolean equal = (o.getClass() == ArrayList.class)
526 ? equalsArrayList((ArrayList<?>) o)
527 : equalsRange((List<?>) o, 0, size);
528
529 checkForComodification(expectedModCount);
530 return equal;
531 }
532
533 boolean equalsRange(List<?> other, int from, int to) {
534 final Object[] es = elementData;
535 if (to > es.length) {
536 throw new ConcurrentModificationException();
537 }
538 var oit = other.iterator();
539 for (; from < to; from++) {
540 if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {
541 return false;
542 }
543 }
544 return !oit.hasNext();
545 }
546
547 private boolean equalsArrayList(ArrayList<?> other) {
548 final int otherModCount = other.modCount;
549 final int s = size;
550 boolean equal;
551 if (equal = (s == other.size)) {
552 final Object[] otherEs = other.elementData;
553 final Object[] es = elementData;
554 if (s > es.length || s > otherEs.length) {
555 throw new ConcurrentModificationException();
556 }
557 for (int i = 0; i < s; i++) {
558 if (!Objects.equals(es[i], otherEs[i])) {
559 equal = false;
560 break;
561 }
562 }
563 }
564 other.checkForComodification(otherModCount);
565 return equal;
566 }
567
568 private void checkForComodification(final int expectedModCount) {
569 if (modCount != expectedModCount) {
570 throw new ConcurrentModificationException();
571 }
572 }
573
574 /**
575 * {@inheritDoc}
576 */
577 public int hashCode() {
578 int expectedModCount = modCount;
579 int hash = hashCodeRange(0, size);
580 checkForComodification(expectedModCount);
581 return hash;
582 }
583
584 int hashCodeRange(int from, int to) {
585 final Object[] es = elementData;
586 if (to > es.length) {
587 throw new ConcurrentModificationException();
588 }
589 int hashCode = 1;
590 for (int i = from; i < to; i++) {
591 Object e = es[i];
592 hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
593 }
594 return hashCode;
595 }
596
597 /**
598 * Removes the first occurrence of the specified element from this list,
599 * if it is present. If the list does not contain the element, it is
600 * unchanged. More formally, removes the element with the lowest index
601 * {@code i} such that
602 * {@code Objects.equals(o, get(i))}
603 * (if such an element exists). Returns {@code true} if this list
604 * contained the specified element (or equivalently, if this list
605 * changed as a result of the call).
606 *
607 * @param o element to be removed from this list, if present
608 * @return {@code true} if this list contained the specified element
609 */
610 public boolean remove(Object o) {
611 final Object[] es = elementData;
612 final int size = this.size;
613 int i = 0;
614 found: {
615 if (o == null) {
616 for (; i < size; i++)
617 if (es[i] == null)
618 break found;
619 } else {
620 for (; i < size; i++)
621 if (o.equals(es[i]))
622 break found;
623 }
624 return false;
625 }
626 fastRemove(es, i);
627 return true;
628 }
629
630 /**
631 * Private remove method that skips bounds checking and does not
632 * return the value removed.
633 */
634 private void fastRemove(Object[] es, int i) {
635 modCount++;
636 final int newSize;
637 if ((newSize = size - 1) > i)
638 System.arraycopy(es, i + 1, es, i, newSize - i);
639 es[size = newSize] = null;
640 }
641
642 /**
643 * Removes all of the elements from this list. The list will
644 * be empty after this call returns.
645 */
646 public void clear() {
647 modCount++;
648 final Object[] es = elementData;
649 for (int to = size, i = size = 0; i < to; i++)
650 es[i] = null;
651 }
652
653 /**
654 * Appends all of the elements in the specified collection to the end of
655 * this list, in the order that they are returned by the
656 * specified collection's Iterator. The behavior of this operation is
657 * undefined if the specified collection is modified while the operation
658 * is in progress. (This implies that the behavior of this call is
659 * undefined if the specified collection is this list, and this
660 * list is nonempty.)
661 *
662 * @param c collection containing elements to be added to this list
663 * @return {@code true} if this list changed as a result of the call
664 * @throws NullPointerException if the specified collection is null
665 */
666 public boolean addAll(Collection<? extends E> c) {
667 Object[] a = c.toArray();
668 modCount++;
669 int numNew = a.length;
670 if (numNew == 0)
671 return false;
672 Object[] elementData;
673 final int s;
674 if (numNew > (elementData = this.elementData).length - (s = size))
675 elementData = grow(s + numNew);
676 System.arraycopy(a, 0, elementData, s, numNew);
677 size = s + numNew;
678 return true;
679 }
680
681 /**
682 * Inserts all of the elements in the specified collection into this
683 * list, starting at the specified position. Shifts the element
684 * currently at that position (if any) and any subsequent elements to
685 * the right (increases their indices). The new elements will appear
686 * in the list in the order that they are returned by the
687 * specified collection's iterator.
688 *
689 * @param index index at which to insert the first element from the
690 * specified collection
691 * @param c collection containing elements to be added to this list
692 * @return {@code true} if this list changed as a result of the call
693 * @throws IndexOutOfBoundsException {@inheritDoc}
694 * @throws NullPointerException if the specified collection is null
695 */
696 public boolean addAll(int index, Collection<? extends E> c) {
697 rangeCheckForAdd(index);
698
699 Object[] a = c.toArray();
700 modCount++;
701 int numNew = a.length;
702 if (numNew == 0)
703 return false;
704 Object[] elementData;
705 final int s;
706 if (numNew > (elementData = this.elementData).length - (s = size))
707 elementData = grow(s + numNew);
708
709 int numMoved = s - index;
710 if (numMoved > 0)
711 System.arraycopy(elementData, index,
712 elementData, index + numNew,
713 numMoved);
714 System.arraycopy(a, 0, elementData, index, numNew);
715 size = s + numNew;
716 return true;
717 }
718
719 /**
720 * Removes from this list all of the elements whose index is between
721 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
722 * Shifts any succeeding elements to the left (reduces their index).
723 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
724 * (If {@code toIndex==fromIndex}, this operation has no effect.)
725 *
726 * @throws IndexOutOfBoundsException if {@code fromIndex} or
727 * {@code toIndex} is out of range
728 * ({@code fromIndex < 0 ||
729 * toIndex > size() ||
730 * toIndex < fromIndex})
731 */
732 protected void removeRange(int fromIndex, int toIndex) {
733 if (fromIndex > toIndex) {
734 throw new IndexOutOfBoundsException(
735 outOfBoundsMsg(fromIndex, toIndex));
736 }
737 modCount++;
738 shiftTailOverGap(elementData, fromIndex, toIndex);
739 }
740
741 /** Erases the gap from lo to hi, by sliding down following elements. */
742 private void shiftTailOverGap(Object[] es, int lo, int hi) {
743 System.arraycopy(es, hi, es, lo, size - hi);
744 for (int to = size, i = (size -= hi - lo); i < to; i++)
745 es[i] = null;
746 }
747
748 /**
749 * A version of rangeCheck used by add and addAll.
750 */
751 private void rangeCheckForAdd(int index) {
752 if (index > size || index < 0)
753 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
754 }
755
756 /**
757 * Constructs an IndexOutOfBoundsException detail message.
758 * Of the many possible refactorings of the error handling code,
759 * this "outlining" performs best with both server and client VMs.
760 */
761 private String outOfBoundsMsg(int index) {
762 return "Index: "+index+", Size: "+size;
763 }
764
765 /**
766 * A version used in checking (fromIndex > toIndex) condition
767 */
768 private static String outOfBoundsMsg(int fromIndex, int toIndex) {
769 return "From Index: " + fromIndex + " > To Index: " + toIndex;
770 }
771
772 /**
773 * Removes from this list all of its elements that are contained in the
774 * specified collection.
775 *
776 * @param c collection containing elements to be removed from this list
777 * @return {@code true} if this list changed as a result of the call
778 * @throws ClassCastException if the class of an element of this list
779 * is incompatible with the specified collection
780 * (<a href="Collection.html#optional-restrictions">optional</a>)
781 * @throws NullPointerException if this list contains a null element and the
782 * specified collection does not permit null elements
783 * (<a href="Collection.html#optional-restrictions">optional</a>),
784 * or if the specified collection is null
785 * @see Collection#contains(Object)
786 */
787 public boolean removeAll(Collection<?> c) {
788 return batchRemove(c, false, 0, size);
789 }
790
791 /**
792 * Retains only the elements in this list that are contained in the
793 * specified collection. In other words, removes from this list all
794 * of its elements that are not contained in the specified collection.
795 *
796 * @param c collection containing elements to be retained in this list
797 * @return {@code true} if this list changed as a result of the call
798 * @throws ClassCastException if the class of an element of this list
799 * is incompatible with the specified collection
800 * (<a href="Collection.html#optional-restrictions">optional</a>)
801 * @throws NullPointerException if this list contains a null element and the
802 * specified collection does not permit null elements
803 * (<a href="Collection.html#optional-restrictions">optional</a>),
804 * or if the specified collection is null
805 * @see Collection#contains(Object)
806 */
807 public boolean retainAll(Collection<?> c) {
808 return batchRemove(c, true, 0, size);
809 }
810
811 boolean batchRemove(Collection<?> c, boolean complement,
812 final int from, final int end) {
813 Objects.requireNonNull(c);
814 final Object[] es = elementData;
815 int r;
816 // Optimize for initial run of survivors
817 for (r = from;; r++) {
818 if (r == end)
819 return false;
820 if (c.contains(es[r]) != complement)
821 break;
822 }
823 int w = r++;
824 try {
825 for (Object e; r < end; r++)
826 if (c.contains(e = es[r]) == complement)
827 es[w++] = e;
828 } catch (Throwable ex) {
829 // Preserve behavioral compatibility with AbstractCollection,
830 // even if c.contains() throws.
831 System.arraycopy(es, r, es, w, end - r);
832 w += end - r;
833 throw ex;
834 } finally {
835 modCount += end - w;
836 shiftTailOverGap(es, w, end);
837 }
838 return true;
839 }
840
841 /**
842 * Saves the state of the {@code ArrayList} instance to a stream
843 * (that is, serializes it).
844 *
845 * @param s the stream
846 * @throws java.io.IOException if an I/O error occurs
847 * @serialData The length of the array backing the {@code ArrayList}
848 * instance is emitted (int), followed by all of its elements
849 * (each an {@code Object}) in the proper order.
850 */
851 private void writeObject(java.io.ObjectOutputStream s)
852 throws java.io.IOException {
853 // Write out element count, and any hidden stuff
854 int expectedModCount = modCount;
855 s.defaultWriteObject();
856
857 // Write out size as capacity for behavioral compatibility with clone()
858 s.writeInt(size);
859
860 // Write out all elements in the proper order.
861 for (int i=0; i<size; i++) {
862 s.writeObject(elementData[i]);
863 }
864
865 if (modCount != expectedModCount) {
866 throw new ConcurrentModificationException();
867 }
868 }
869
870 /**
871 * Reconstitutes the {@code ArrayList} instance from a stream (that is,
872 * deserializes it).
873 * @param s the stream
874 * @throws ClassNotFoundException if the class of a serialized object
875 * could not be found
876 * @throws java.io.IOException if an I/O error occurs
877 */
878 private void readObject(java.io.ObjectInputStream s)
879 throws java.io.IOException, ClassNotFoundException {
880
881 // Read in size, and any hidden stuff
882 s.defaultReadObject();
883
884 // Read in capacity
885 s.readInt(); // ignored
886
887 if (size > 0) {
888 // like clone(), allocate array based upon size not capacity
889 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
890 Object[] elements = new Object[size];
891
892 // Read in all elements in the proper order.
893 for (int i = 0; i < size; i++) {
894 elements[i] = s.readObject();
895 }
896
897 elementData = elements;
898 } else if (size == 0) {
899 elementData = EMPTY_ELEMENTDATA;
900 } else {
901 throw new java.io.InvalidObjectException("Invalid size: " + size);
902 }
903 }
904
905 /**
906 * Returns a list iterator over the elements in this list (in proper
907 * sequence), starting at the specified position in the list.
908 * The specified index indicates the first element that would be
909 * returned by an initial call to {@link ListIterator#next next}.
910 * An initial call to {@link ListIterator#previous previous} would
911 * return the element with the specified index minus one.
912 *
913 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
914 *
915 * @throws IndexOutOfBoundsException {@inheritDoc}
916 */
917 public ListIterator<E> listIterator(int index) {
918 rangeCheckForAdd(index);
919 return new ListItr(index);
920 }
921
922 /**
923 * Returns a list iterator over the elements in this list (in proper
924 * sequence).
925 *
926 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
927 *
928 * @see #listIterator(int)
929 */
930 public ListIterator<E> listIterator() {
931 return new ListItr(0);
932 }
933
934 /**
935 * Returns an iterator over the elements in this list in proper sequence.
936 *
937 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
938 *
939 * @return an iterator over the elements in this list in proper sequence
940 */
941 public Iterator<E> iterator() {
942 return new Itr();
943 }
944
945 /**
946 * An optimized version of AbstractList.Itr
947 */
948 private class Itr implements Iterator<E> {
949 int cursor; // index of next element to return
950 int lastRet = -1; // index of last element returned; -1 if no such
951 int expectedModCount = modCount;
952
953 // prevent creating a synthetic constructor
954 Itr() {}
955
956 public boolean hasNext() {
957 return cursor != size;
958 }
959
960 @SuppressWarnings("unchecked")
961 public E next() {
962 checkForComodification();
963 int i = cursor;
964 if (i >= size)
965 throw new NoSuchElementException();
966 Object[] elementData = ArrayList.this.elementData;
967 if (i >= elementData.length)
968 throw new ConcurrentModificationException();
969 cursor = i + 1;
970 return (E) elementData[lastRet = i];
971 }
972
973 public void remove() {
974 if (lastRet < 0)
975 throw new IllegalStateException();
976 checkForComodification();
977
978 try {
979 ArrayList.this.remove(lastRet);
980 cursor = lastRet;
981 lastRet = -1;
982 expectedModCount = modCount;
983 } catch (IndexOutOfBoundsException ex) {
984 throw new ConcurrentModificationException();
985 }
986 }
987
988 @Override
989 public void forEachRemaining(Consumer<? super E> action) {
990 Objects.requireNonNull(action);
991 final int size = ArrayList.this.size;
992 int i = cursor;
993 if (i < size) {
994 final Object[] es = elementData;
995 if (i >= es.length)
996 throw new ConcurrentModificationException();
997 for (; i < size && modCount == expectedModCount; i++)
998 action.accept(elementAt(es, i));
999 // update once at end to reduce heap write traffic
1000 cursor = i;
1001 lastRet = i - 1;
1002 checkForComodification();
1003 }
1004 }
1005
1006 final void checkForComodification() {
1007 if (modCount != expectedModCount)
1008 throw new ConcurrentModificationException();
1009 }
1010 }
1011
1012 /**
1013 * An optimized version of AbstractList.ListItr
1014 */
1015 private class ListItr extends Itr implements ListIterator<E> {
1016 ListItr(int index) {
1017 super();
1018 cursor = index;
1019 }
1020
1021 public boolean hasPrevious() {
1022 return cursor != 0;
1023 }
1024
1025 public int nextIndex() {
1026 return cursor;
1027 }
1028
1029 public int previousIndex() {
1030 return cursor - 1;
1031 }
1032
1033 @SuppressWarnings("unchecked")
1034 public E previous() {
1035 checkForComodification();
1036 int i = cursor - 1;
1037 if (i < 0)
1038 throw new NoSuchElementException();
1039 Object[] elementData = ArrayList.this.elementData;
1040 if (i >= elementData.length)
1041 throw new ConcurrentModificationException();
1042 cursor = i;
1043 return (E) elementData[lastRet = i];
1044 }
1045
1046 public void set(E e) {
1047 if (lastRet < 0)
1048 throw new IllegalStateException();
1049 checkForComodification();
1050
1051 try {
1052 ArrayList.this.set(lastRet, e);
1053 } catch (IndexOutOfBoundsException ex) {
1054 throw new ConcurrentModificationException();
1055 }
1056 }
1057
1058 public void add(E e) {
1059 checkForComodification();
1060
1061 try {
1062 int i = cursor;
1063 ArrayList.this.add(i, e);
1064 cursor = i + 1;
1065 lastRet = -1;
1066 expectedModCount = modCount;
1067 } catch (IndexOutOfBoundsException ex) {
1068 throw new ConcurrentModificationException();
1069 }
1070 }
1071 }
1072
1073 /**
1074 * Returns a view of the portion of this list between the specified
1075 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
1076 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
1077 * empty.) The returned list is backed by this list, so non-structural
1078 * changes in the returned list are reflected in this list, and vice-versa.
1079 * The returned list supports all of the optional list operations.
1080 *
1081 * <p>This method eliminates the need for explicit range operations (of
1082 * the sort that commonly exist for arrays). Any operation that expects
1083 * a list can be used as a range operation by passing a subList view
1084 * instead of a whole list. For example, the following idiom
1085 * removes a range of elements from a list:
1086 * <pre>
1087 * list.subList(from, to).clear();
1088 * </pre>
1089 * Similar idioms may be constructed for {@link #indexOf(Object)} and
1090 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
1091 * {@link Collections} class can be applied to a subList.
1092 *
1093 * <p>The semantics of the list returned by this method become undefined if
1094 * the backing list (i.e., this list) is <i>structurally modified</i> in
1095 * any way other than via the returned list. (Structural modifications are
1096 * those that change the size of this list, or otherwise perturb it in such
1097 * a fashion that iterations in progress may yield incorrect results.)
1098 *
1099 * @throws IndexOutOfBoundsException {@inheritDoc}
1100 * @throws IllegalArgumentException {@inheritDoc}
1101 */
1102 public List<E> subList(int fromIndex, int toIndex) {
1103 subListRangeCheck(fromIndex, toIndex, size);
1104 return new SubList<>(this, fromIndex, toIndex);
1105 }
1106
1107 private static class SubList<E> extends AbstractList<E> implements RandomAccess {
1108 private final ArrayList<E> root;
1109 private final SubList<E> parent;
1110 private final int offset;
1111 private int size;
1112
1113 /**
1114 * Constructs a sublist of an arbitrary ArrayList.
1115 */
1116 public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
1117 this.root = root;
1118 this.parent = null;
1119 this.offset = fromIndex;
1120 this.size = toIndex - fromIndex;
1121 this.modCount = root.modCount;
1122 }
1123
1124 /**
1125 * Constructs a sublist of another SubList.
1126 */
1127 private SubList(SubList<E> parent, int fromIndex, int toIndex) {
1128 this.root = parent.root;
1129 this.parent = parent;
1130 this.offset = parent.offset + fromIndex;
1131 this.size = toIndex - fromIndex;
1132 this.modCount = root.modCount;
1133 }
1134
1135 public E set(int index, E element) {
1136 Objects.checkIndex(index, size);
1137 checkForComodification();
1138 E oldValue = root.elementData(offset + index);
1139 root.elementData[offset + index] = element;
1140 return oldValue;
1141 }
1142
1143 public E get(int index) {
1144 Objects.checkIndex(index, size);
1145 checkForComodification();
1146 return root.elementData(offset + index);
1147 }
1148
1149 public int size() {
1150 checkForComodification();
1151 return size;
1152 }
1153
1154 public void add(int index, E element) {
1155 rangeCheckForAdd(index);
1156 checkForComodification();
1157 root.add(offset + index, element);
1158 updateSizeAndModCount(1);
1159 }
1160
1161 public E remove(int index) {
1162 Objects.checkIndex(index, size);
1163 checkForComodification();
1164 E result = root.remove(offset + index);
1165 updateSizeAndModCount(-1);
1166 return result;
1167 }
1168
1169 protected void removeRange(int fromIndex, int toIndex) {
1170 checkForComodification();
1171 root.removeRange(offset + fromIndex, offset + toIndex);
1172 updateSizeAndModCount(fromIndex - toIndex);
1173 }
1174
1175 public boolean addAll(Collection<? extends E> c) {
1176 return addAll(this.size, c);
1177 }
1178
1179 public boolean addAll(int index, Collection<? extends E> c) {
1180 rangeCheckForAdd(index);
1181 int cSize = c.size();
1182 if (cSize==0)
1183 return false;
1184 checkForComodification();
1185 root.addAll(offset + index, c);
1186 updateSizeAndModCount(cSize);
1187 return true;
1188 }
1189
1190 public void replaceAll(UnaryOperator<E> operator) {
1191 root.replaceAllRange(operator, offset, offset + size);
1192 }
1193
1194 public boolean removeAll(Collection<?> c) {
1195 return batchRemove(c, false);
1196 }
1197
1198 public boolean retainAll(Collection<?> c) {
1199 return batchRemove(c, true);
1200 }
1201
1202 private boolean batchRemove(Collection<?> c, boolean complement) {
1203 checkForComodification();
1204 int oldSize = root.size;
1205 boolean modified =
1206 root.batchRemove(c, complement, offset, offset + size);
1207 if (modified)
1208 updateSizeAndModCount(root.size - oldSize);
1209 return modified;
1210 }
1211
1212 public boolean removeIf(Predicate<? super E> filter) {
1213 checkForComodification();
1214 int oldSize = root.size;
1215 boolean modified = root.removeIf(filter, offset, offset + size);
1216 if (modified)
1217 updateSizeAndModCount(root.size - oldSize);
1218 return modified;
1219 }
1220
1221 public Object[] toArray() {
1222 checkForComodification();
1223 return Arrays.copyOfRange(root.elementData, offset, offset + size);
1224 }
1225
1226 @SuppressWarnings("unchecked")
1227 public <T> T[] toArray(T[] a) {
1228 checkForComodification();
1229 if (a.length < size)
1230 return (T[]) Arrays.copyOfRange(
1231 root.elementData, offset, offset + size, a.getClass());
1232 System.arraycopy(root.elementData, offset, a, 0, size);
1233 if (a.length > size)
1234 a[size] = null;
1235 return a;
1236 }
1237
1238 public boolean equals(Object o) {
1239 if (o == this) {
1240 return true;
1241 }
1242
1243 if (!(o instanceof List)) {
1244 return false;
1245 }
1246
1247 boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
1248 checkForComodification();
1249 return equal;
1250 }
1251
1252 public int hashCode() {
1253 int hash = root.hashCodeRange(offset, offset + size);
1254 checkForComodification();
1255 return hash;
1256 }
1257
1258 public int indexOf(Object o) {
1259 int index = root.indexOfRange(o, offset, offset + size);
1260 checkForComodification();
1261 return index >= 0 ? index - offset : -1;
1262 }
1263
1264 public int lastIndexOf(Object o) {
1265 int index = root.lastIndexOfRange(o, offset, offset + size);
1266 checkForComodification();
1267 return index >= 0 ? index - offset : -1;
1268 }
1269
1270 public boolean contains(Object o) {
1271 return indexOf(o) >= 0;
1272 }
1273
1274 public Iterator<E> iterator() {
1275 return listIterator();
1276 }
1277
1278 public ListIterator<E> listIterator(int index) {
1279 checkForComodification();
1280 rangeCheckForAdd(index);
1281
1282 return new ListIterator<E>() {
1283 int cursor = index;
1284 int lastRet = -1;
1285 int expectedModCount = root.modCount;
1286
1287 public boolean hasNext() {
1288 return cursor != SubList.this.size;
1289 }
1290
1291 @SuppressWarnings("unchecked")
1292 public E next() {
1293 checkForComodification();
1294 int i = cursor;
1295 if (i >= SubList.this.size)
1296 throw new NoSuchElementException();
1297 Object[] elementData = root.elementData;
1298 if (offset + i >= elementData.length)
1299 throw new ConcurrentModificationException();
1300 cursor = i + 1;
1301 return (E) elementData[offset + (lastRet = i)];
1302 }
1303
1304 public boolean hasPrevious() {
1305 return cursor != 0;
1306 }
1307
1308 @SuppressWarnings("unchecked")
1309 public E previous() {
1310 checkForComodification();
1311 int i = cursor - 1;
1312 if (i < 0)
1313 throw new NoSuchElementException();
1314 Object[] elementData = root.elementData;
1315 if (offset + i >= elementData.length)
1316 throw new ConcurrentModificationException();
1317 cursor = i;
1318 return (E) elementData[offset + (lastRet = i)];
1319 }
1320
1321 public void forEachRemaining(Consumer<? super E> action) {
1322 Objects.requireNonNull(action);
1323 final int size = SubList.this.size;
1324 int i = cursor;
1325 if (i < size) {
1326 final Object[] es = root.elementData;
1327 if (offset + i >= es.length)
1328 throw new ConcurrentModificationException();
1329 for (; i < size && modCount == expectedModCount; i++)
1330 action.accept(elementAt(es, offset + i));
1331 // update once at end to reduce heap write traffic
1332 cursor = i;
1333 lastRet = i - 1;
1334 checkForComodification();
1335 }
1336 }
1337
1338 public int nextIndex() {
1339 return cursor;
1340 }
1341
1342 public int previousIndex() {
1343 return cursor - 1;
1344 }
1345
1346 public void remove() {
1347 if (lastRet < 0)
1348 throw new IllegalStateException();
1349 checkForComodification();
1350
1351 try {
1352 SubList.this.remove(lastRet);
1353 cursor = lastRet;
1354 lastRet = -1;
1355 expectedModCount = root.modCount;
1356 } catch (IndexOutOfBoundsException ex) {
1357 throw new ConcurrentModificationException();
1358 }
1359 }
1360
1361 public void set(E e) {
1362 if (lastRet < 0)
1363 throw new IllegalStateException();
1364 checkForComodification();
1365
1366 try {
1367 root.set(offset + lastRet, e);
1368 } catch (IndexOutOfBoundsException ex) {
1369 throw new ConcurrentModificationException();
1370 }
1371 }
1372
1373 public void add(E e) {
1374 checkForComodification();
1375
1376 try {
1377 int i = cursor;
1378 SubList.this.add(i, e);
1379 cursor = i + 1;
1380 lastRet = -1;
1381 expectedModCount = root.modCount;
1382 } catch (IndexOutOfBoundsException ex) {
1383 throw new ConcurrentModificationException();
1384 }
1385 }
1386
1387 final void checkForComodification() {
1388 if (root.modCount != expectedModCount)
1389 throw new ConcurrentModificationException();
1390 }
1391 };
1392 }
1393
1394 public List<E> subList(int fromIndex, int toIndex) {
1395 subListRangeCheck(fromIndex, toIndex, size);
1396 return new SubList<>(this, fromIndex, toIndex);
1397 }
1398
1399 private void rangeCheckForAdd(int index) {
1400 if (index < 0 || index > this.size)
1401 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1402 }
1403
1404 private String outOfBoundsMsg(int index) {
1405 return "Index: "+index+", Size: "+this.size;
1406 }
1407
1408 private void checkForComodification() {
1409 if (root.modCount != modCount)
1410 throw new ConcurrentModificationException();
1411 }
1412
1413 private void updateSizeAndModCount(int sizeChange) {
1414 SubList<E> slist = this;
1415 do {
1416 slist.size += sizeChange;
1417 slist.modCount = root.modCount;
1418 slist = slist.parent;
1419 } while (slist != null);
1420 }
1421
1422 public Spliterator<E> spliterator() {
1423 checkForComodification();
1424
1425 // ArrayListSpliterator not used here due to late-binding
1426 return new Spliterator<E>() {
1427 private int index = offset; // current index, modified on advance/split
1428 private int fence = -1; // -1 until used; then one past last index
1429 private int expectedModCount; // initialized when fence set
1430
1431 private int getFence() { // initialize fence to size on first use
1432 int hi; // (a specialized variant appears in method forEach)
1433 if ((hi = fence) < 0) {
1434 expectedModCount = modCount;
1435 hi = fence = offset + size;
1436 }
1437 return hi;
1438 }
1439
1440 public ArrayList<E>.ArrayListSpliterator trySplit() {
1441 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1442 // ArrayListSpliterator can be used here as the source is already bound
1443 return (lo >= mid) ? null : // divide range in half unless too small
1444 root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
1445 }
1446
1447 public boolean tryAdvance(Consumer<? super E> action) {
1448 Objects.requireNonNull(action);
1449 int hi = getFence(), i = index;
1450 if (i < hi) {
1451 index = i + 1;
1452 @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
1453 action.accept(e);
1454 if (root.modCount != expectedModCount)
1455 throw new ConcurrentModificationException();
1456 return true;
1457 }
1458 return false;
1459 }
1460
1461 public void forEachRemaining(Consumer<? super E> action) {
1462 Objects.requireNonNull(action);
1463 int i, hi, mc; // hoist accesses and checks from loop
1464 ArrayList<E> lst = root;
1465 Object[] a;
1466 if ((a = lst.elementData) != null) {
1467 if ((hi = fence) < 0) {
1468 mc = modCount;
1469 hi = offset + size;
1470 }
1471 else
1472 mc = expectedModCount;
1473 if ((i = index) >= 0 && (index = hi) <= a.length) {
1474 for (; i < hi; ++i) {
1475 @SuppressWarnings("unchecked") E e = (E) a[i];
1476 action.accept(e);
1477 }
1478 if (lst.modCount == mc)
1479 return;
1480 }
1481 }
1482 throw new ConcurrentModificationException();
1483 }
1484
1485 public long estimateSize() {
1486 return getFence() - index;
1487 }
1488
1489 public int characteristics() {
1490 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1491 }
1492 };
1493 }
1494 }
1495
1496 /**
1497 * @throws NullPointerException {@inheritDoc}
1498 */
1499 @Override
1500 public void forEach(Consumer<? super E> action) {
1501 Objects.requireNonNull(action);
1502 final int expectedModCount = modCount;
1503 final Object[] es = elementData;
1504 final int size = this.size;
1505 for (int i = 0; modCount == expectedModCount && i < size; i++)
1506 action.accept(elementAt(es, i));
1507 if (modCount != expectedModCount)
1508 throw new ConcurrentModificationException();
1509 }
1510
1511 /**
1512 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1513 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1514 * list.
1515 *
1516 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1517 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1518 * Overriding implementations should document the reporting of additional
1519 * characteristic values.
1520 *
1521 * @return a {@code Spliterator} over the elements in this list
1522 * @since 1.8
1523 */
1524 @Override
1525 public Spliterator<E> spliterator() {
1526 return new ArrayListSpliterator(0, -1, 0);
1527 }
1528
1529 /** Index-based split-by-two, lazily initialized Spliterator */
1530 final class ArrayListSpliterator implements Spliterator<E> {
1531
1532 /*
1533 * If ArrayLists were immutable, or structurally immutable (no
1534 * adds, removes, etc), we could implement their spliterators
1535 * with Arrays.spliterator. Instead we detect as much
1536 * interference during traversal as practical without
1537 * sacrificing much performance. We rely primarily on
1538 * modCounts. These are not guaranteed to detect concurrency
1539 * violations, and are sometimes overly conservative about
1540 * within-thread interference, but detect enough problems to
1541 * be worthwhile in practice. To carry this out, we (1) lazily
1542 * initialize fence and expectedModCount until the latest
1543 * point that we need to commit to the state we are checking
1544 * against; thus improving precision. (This doesn't apply to
1545 * SubLists, that create spliterators with current non-lazy
1546 * values). (2) We perform only a single
1547 * ConcurrentModificationException check at the end of forEach
1548 * (the most performance-sensitive method). When using forEach
1549 * (as opposed to iterators), we can normally only detect
1550 * interference after actions, not before. Further
1551 * CME-triggering checks apply to all other possible
1552 * violations of assumptions for example null or too-small
1553 * elementData array given its size(), that could only have
1554 * occurred due to interference. This allows the inner loop
1555 * of forEach to run without any further checks, and
1556 * simplifies lambda-resolution. While this does entail a
1557 * number of checks, note that in the common case of
1558 * list.stream().forEach(a), no checks or other computation
1559 * occur anywhere other than inside forEach itself. The other
1560 * less-often-used methods cannot take advantage of most of
1561 * these streamlinings.
1562 */
1563
1564 private int index; // current index, modified on advance/split
1565 private int fence; // -1 until used; then one past last index
1566 private int expectedModCount; // initialized when fence set
1567
1568 /** Creates new spliterator covering the given range. */
1569 ArrayListSpliterator(int origin, int fence, int expectedModCount) {
1570 this.index = origin;
1571 this.fence = fence;
1572 this.expectedModCount = expectedModCount;
1573 }
1574
1575 private int getFence() { // initialize fence to size on first use
1576 int hi; // (a specialized variant appears in method forEach)
1577 if ((hi = fence) < 0) {
1578 expectedModCount = modCount;
1579 hi = fence = size;
1580 }
1581 return hi;
1582 }
1583
1584 public ArrayListSpliterator trySplit() {
1585 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1586 return (lo >= mid) ? null : // divide range in half unless too small
1587 new ArrayListSpliterator(lo, index = mid, expectedModCount);
1588 }
1589
1590 public boolean tryAdvance(Consumer<? super E> action) {
1591 if (action == null)
1592 throw new NullPointerException();
1593 int hi = getFence(), i = index;
1594 if (i < hi) {
1595 index = i + 1;
1596 @SuppressWarnings("unchecked") E e = (E)elementData[i];
1597 action.accept(e);
1598 if (modCount != expectedModCount)
1599 throw new ConcurrentModificationException();
1600 return true;
1601 }
1602 return false;
1603 }
1604
1605 public void forEachRemaining(Consumer<? super E> action) {
1606 int i, hi, mc; // hoist accesses and checks from loop
1607 Object[] a;
1608 if (action == null)
1609 throw new NullPointerException();
1610 if ((a = elementData) != null) {
1611 if ((hi = fence) < 0) {
1612 mc = modCount;
1613 hi = size;
1614 }
1615 else
1616 mc = expectedModCount;
1617 if ((i = index) >= 0 && (index = hi) <= a.length) {
1618 for (; i < hi; ++i) {
1619 @SuppressWarnings("unchecked") E e = (E) a[i];
1620 action.accept(e);
1621 }
1622 if (modCount == mc)
1623 return;
1624 }
1625 }
1626 throw new ConcurrentModificationException();
1627 }
1628
1629 public long estimateSize() {
1630 return getFence() - index;
1631 }
1632
1633 public int characteristics() {
1634 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1635 }
1636 }
1637
1638 // A tiny bit set implementation
1639
1640 private static long[] nBits(int n) {
1641 return new long[((n - 1) >> 6) + 1];
1642 }
1643 private static void setBit(long[] bits, int i) {
1644 bits[i >> 6] |= 1L << i;
1645 }
1646 private static boolean isClear(long[] bits, int i) {
1647 return (bits[i >> 6] & (1L << i)) == 0;
1648 }
1649
1650 /**
1651 * @throws NullPointerException {@inheritDoc}
1652 */
1653 @Override
1654 public boolean removeIf(Predicate<? super E> filter) {
1655 return removeIf(filter, 0, size);
1656 }
1657
1658 /**
1659 * Removes all elements satisfying the given predicate, from index
1660 * i (inclusive) to index end (exclusive).
1661 */
1662 boolean removeIf(Predicate<? super E> filter, int i, final int end) {
1663 Objects.requireNonNull(filter);
1664 int expectedModCount = modCount;
1665 final Object[] es = elementData;
1666 // Optimize for initial run of survivors
1667 for (; i < end && !filter.test(elementAt(es, i)); i++)
1668 ;
1669 // Tolerate predicates that reentrantly access the collection for
1670 // read (but writers still get CME), so traverse once to find
1671 // elements to delete, a second pass to physically expunge.
1672 if (i < end) {
1673 final int beg = i;
1674 final long[] deathRow = nBits(end - beg);
1675 deathRow[0] = 1L; // set bit 0
1676 for (i = beg + 1; i < end; i++)
1677 if (filter.test(elementAt(es, i)))
1678 setBit(deathRow, i - beg);
1679 if (modCount != expectedModCount)
1680 throw new ConcurrentModificationException();
1681 modCount++;
1682 int w = beg;
1683 for (i = beg; i < end; i++)
1684 if (isClear(deathRow, i - beg))
1685 es[w++] = es[i];
1686 shiftTailOverGap(es, w, end);
1687 return true;
1688 } else {
1689 if (modCount != expectedModCount)
1690 throw new ConcurrentModificationException();
1691 return false;
1692 }
1693 }
1694
1695 @Override
1696 public void replaceAll(UnaryOperator<E> operator) {
1697 replaceAllRange(operator, 0, size);
1698 modCount++;
1699 }
1700
1701 private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
1702 Objects.requireNonNull(operator);
1703 final int expectedModCount = modCount;
1704 final Object[] es = elementData;
1705 for (; modCount == expectedModCount && i < end; i++)
1706 es[i] = operator.apply(elementAt(es, i));
1707 if (modCount != expectedModCount)
1708 throw new ConcurrentModificationException();
1709 }
1710
1711 @Override
1712 @SuppressWarnings("unchecked")
1713 public void sort(Comparator<? super E> c) {
1714 final int expectedModCount = modCount;
1715 Arrays.sort((E[]) elementData, 0, size, c);
1716 if (modCount != expectedModCount)
1717 throw new ConcurrentModificationException();
1718 modCount++;
1719 }
1720
1721 void checkInvariants() {
1722 // assert size >= 0;
1723 // assert size == elementData.length || elementData[size] == null;
1724 }
1725 }