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 @java.io.Serial
113 private static final long serialVersionUID = 8683452581122892189L;
114
115 /**
116 * Default initial capacity.
117 */
118 private static final int DEFAULT_CAPACITY = 10;
119
120 /**
121 * Shared empty array instance used for empty instances.
122 */
123 private static final Object[] EMPTY_ELEMENTDATA = {};
124
125 /**
126 * Shared empty array instance used for default sized empty instances. We
127 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
128 * first element is added.
129 */
130 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
131
132 /**
133 * The array buffer into which the elements of the ArrayList are stored.
134 * The capacity of the ArrayList is the length of this array buffer. Any
135 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
136 * will be expanded to DEFAULT_CAPACITY when the first element is added.
137 */
138 transient Object[] elementData; // non-private to simplify nested class access
139
140 /**
141 * The size of the ArrayList (the number of elements it contains).
142 *
143 * @serial
144 */
145 private int size;
146
147 /**
148 * Constructs an empty list with the specified initial capacity.
149 *
150 * @param initialCapacity the initial capacity of the list
151 * @throws IllegalArgumentException if the specified initial capacity
152 * is negative
153 */
154 public ArrayList(int initialCapacity) {
155 if (initialCapacity > 0) {
156 this.elementData = new Object[initialCapacity];
157 } else if (initialCapacity == 0) {
158 this.elementData = EMPTY_ELEMENTDATA;
159 } else {
160 throw new IllegalArgumentException("Illegal Capacity: "+
161 initialCapacity);
162 }
163 }
164
165 /**
166 * Constructs an empty list with an initial capacity of ten.
167 */
168 public ArrayList() {
169 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
170 }
171
172 /**
173 * Constructs a list containing the elements of the specified
174 * collection, in the order they are returned by the collection's
175 * iterator.
176 *
177 * @param c the collection whose elements are to be placed into this list
178 * @throws NullPointerException if the specified collection is null
179 */
180 public ArrayList(Collection<? extends E> c) {
181 elementData = c.toArray();
182 if ((size = elementData.length) != 0) {
183 // defend against c.toArray (incorrectly) not returning Object[]
184 // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
185 if (elementData.getClass() != Object[].class)
186 elementData = Arrays.copyOf(elementData, size, Object[].class);
187 } else {
188 // replace with empty array.
189 this.elementData = EMPTY_ELEMENTDATA;
190 }
191 }
192
193 /**
194 * Trims the capacity of this {@code ArrayList} instance to be the
195 * list's current size. An application can use this operation to minimize
196 * the storage of an {@code ArrayList} instance.
197 */
198 public void trimToSize() {
199 modCount++;
200 if (size < elementData.length) {
201 elementData = (size == 0)
202 ? EMPTY_ELEMENTDATA
203 : Arrays.copyOf(elementData, size);
204 }
205 }
206
207 /**
208 * Increases the capacity of this {@code ArrayList} instance, if
209 * necessary, to ensure that it can hold at least the number of elements
210 * specified by the minimum capacity argument.
211 *
212 * @param minCapacity the desired minimum capacity
213 */
214 public void ensureCapacity(int minCapacity) {
215 if (minCapacity > elementData.length
216 && !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
217 && minCapacity <= DEFAULT_CAPACITY)) {
218 modCount++;
219 grow(minCapacity);
220 }
221 }
222
223 /**
224 * Increases the capacity to ensure that it can hold at least the
225 * number of elements specified by the minimum capacity argument.
226 *
227 * @param minCapacity the desired minimum capacity
228 * @throws OutOfMemoryError if minCapacity is less than zero
229 */
230 private Object[] grow(int minCapacity) {
231 int oldCapacity = elementData.length;
232 if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
233 int newCapacity = ArraysSupport.newLength(oldCapacity,
234 minCapacity - oldCapacity, /* minimum growth */
235 oldCapacity >> 1 /* preferred growth */);
236 return elementData = Arrays.copyOf(elementData, newCapacity);
237 } else {
238 return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];
239 }
240 }
241
242 private Object[] grow() {
243 return grow(size + 1);
244 }
245
246 /**
247 * Returns the number of elements in this list.
248 *
249 * @return the number of elements in this list
250 */
251 public int size() {
252 return size;
253 }
254
255 /**
256 * Returns {@code true} if this list contains no elements.
257 *
258 * @return {@code true} if this list contains no elements
259 */
260 public boolean isEmpty() {
261 return size == 0;
262 }
263
264 /**
265 * Returns {@code true} if this list contains the specified element.
266 * More formally, returns {@code true} if and only if this list contains
267 * at least one element {@code e} such that
268 * {@code Objects.equals(o, e)}.
269 *
270 * @param o element whose presence in this list is to be tested
271 * @return {@code true} if this list contains the specified element
272 */
273 public boolean contains(Object o) {
274 return indexOf(o) >= 0;
275 }
276
277 /**
278 * Returns the index of the first occurrence of the specified element
279 * in this list, or -1 if this list does not contain the element.
280 * More formally, returns the lowest index {@code i} such that
281 * {@code Objects.equals(o, get(i))},
282 * or -1 if there is no such index.
283 */
284 public int indexOf(Object o) {
285 return indexOfRange(o, 0, size);
286 }
287
288 int indexOfRange(Object o, int start, int end) {
289 Object[] es = elementData;
290 if (o == null) {
291 for (int i = start; i < end; i++) {
292 if (es[i] == null) {
293 return i;
294 }
295 }
296 } else {
297 for (int i = start; i < end; i++) {
298 if (o.equals(es[i])) {
299 return i;
300 }
301 }
302 }
303 return -1;
304 }
305
306 /**
307 * Returns the index of the last occurrence of the specified element
308 * in this list, or -1 if this list does not contain the element.
309 * More formally, returns the highest index {@code i} such that
310 * {@code Objects.equals(o, get(i))},
311 * or -1 if there is no such index.
312 */
313 public int lastIndexOf(Object o) {
314 return lastIndexOfRange(o, 0, size);
315 }
316
317 int lastIndexOfRange(Object o, int start, int end) {
318 Object[] es = elementData;
319 if (o == null) {
320 for (int i = end - 1; i >= start; i--) {
321 if (es[i] == null) {
322 return i;
323 }
324 }
325 } else {
326 for (int i = end - 1; i >= start; i--) {
327 if (o.equals(es[i])) {
328 return i;
329 }
330 }
331 }
332 return -1;
333 }
334
335 /**
336 * Returns a shallow copy of this {@code ArrayList} instance. (The
337 * elements themselves are not copied.)
338 *
339 * @return a clone of this {@code ArrayList} instance
340 */
341 public Object clone() {
342 try {
343 ArrayList<?> v = (ArrayList<?>) super.clone();
344 v.elementData = Arrays.copyOf(elementData, size);
345 v.modCount = 0;
346 return v;
347 } catch (CloneNotSupportedException e) {
348 // this shouldn't happen, since we are Cloneable
349 throw new InternalError(e);
350 }
351 }
352
353 /**
354 * Returns an array containing all of the elements in this list
355 * in proper sequence (from first to last element).
356 *
357 * <p>The returned array will be "safe" in that no references to it are
358 * maintained by this list. (In other words, this method must allocate
359 * a new array). The caller is thus free to modify the returned array.
360 *
361 * <p>This method acts as bridge between array-based and collection-based
362 * APIs.
363 *
364 * @return an array containing all of the elements in this list in
365 * proper sequence
366 */
367 public Object[] toArray() {
368 return Arrays.copyOf(elementData, size);
369 }
370
371 /**
372 * Returns an array containing all of the elements in this list in proper
373 * sequence (from first to last element); the runtime type of the returned
374 * array is that of the specified array. If the list fits in the
375 * specified array, it is returned therein. Otherwise, a new array is
376 * allocated with the runtime type of the specified array and the size of
377 * this list.
378 *
379 * <p>If the list fits in the specified array with room to spare
380 * (i.e., the array has more elements than the list), the element in
381 * the array immediately following the end of the collection is set to
382 * {@code null}. (This is useful in determining the length of the
383 * list <i>only</i> if the caller knows that the list does not contain
384 * any null elements.)
385 *
386 * @param a the array into which the elements of the list are to
387 * be stored, if it is big enough; otherwise, a new array of the
388 * same runtime type is allocated for this purpose.
389 * @return an array containing the elements of the list
390 * @throws ArrayStoreException if the runtime type of the specified array
391 * is not a supertype of the runtime type of every element in
392 * this list
393 * @throws NullPointerException if the specified array is null
394 */
395 @SuppressWarnings("unchecked")
396 public <T> T[] toArray(T[] a) {
397 if (a.length < size)
398 // Make a new array of a's runtime type, but my contents:
399 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
400 System.arraycopy(elementData, 0, a, 0, size);
401 if (a.length > size)
402 a[size] = null;
403 return a;
404 }
405
406 // Positional Access Operations
407
408 @SuppressWarnings("unchecked")
409 E elementData(int index) {
410 return (E) elementData[index];
411 }
412
413 @SuppressWarnings("unchecked")
414 static <E> E elementAt(Object[] es, int index) {
415 return (E) es[index];
416 }
417
418 /**
419 * Returns the element at the specified position in this list.
420 *
421 * @param index index of the element to return
422 * @return the element at the specified position in this list
423 * @throws IndexOutOfBoundsException {@inheritDoc}
424 */
425 public E get(int index) {
426 Objects.checkIndex(index, size);
427 return elementData(index);
428 }
429
430 /**
431 * Replaces the element at the specified position in this list with
432 * the specified element.
433 *
434 * @param index index of the element to replace
435 * @param element element to be stored at the specified position
436 * @return the element previously at the specified position
437 * @throws IndexOutOfBoundsException {@inheritDoc}
438 */
439 public E set(int index, E element) {
440 Objects.checkIndex(index, size);
441 E oldValue = elementData(index);
442 elementData[index] = element;
443 return oldValue;
444 }
445
446 /**
447 * This helper method split out from add(E) to keep method
448 * bytecode size under 35 (the -XX:MaxInlineSize default value),
449 * which helps when add(E) is called in a C1-compiled loop.
450 */
451 private void add(E e, Object[] elementData, int s) {
452 if (s == elementData.length)
453 elementData = grow();
454 elementData[s] = e;
455 size = s + 1;
456 }
457
458 /**
459 * Appends the specified element to the end of this list.
460 *
461 * @param e element to be appended to this list
462 * @return {@code true} (as specified by {@link Collection#add})
463 */
464 public boolean add(E e) {
465 modCount++;
466 add(e, elementData, size);
467 return true;
468 }
469
470 /**
471 * Inserts the specified element at the specified position in this
472 * list. Shifts the element currently at that position (if any) and
473 * any subsequent elements to the right (adds one to their indices).
474 *
475 * @param index index at which the specified element is to be inserted
476 * @param element element to be inserted
477 * @throws IndexOutOfBoundsException {@inheritDoc}
478 */
479 public void add(int index, E element) {
480 rangeCheckForAdd(index);
481 modCount++;
482 final int s;
483 Object[] elementData;
484 if ((s = size) == (elementData = this.elementData).length)
485 elementData = grow();
486 System.arraycopy(elementData, index,
487 elementData, index + 1,
488 s - index);
489 elementData[index] = element;
490 size = s + 1;
491 }
492
493 /**
494 * Removes the element at the specified position in this list.
495 * Shifts any subsequent elements to the left (subtracts one from their
496 * indices).
497 *
498 * @param index the index of the element to be removed
499 * @return the element that was removed from the list
500 * @throws IndexOutOfBoundsException {@inheritDoc}
501 */
502 public E remove(int index) {
503 Objects.checkIndex(index, size);
504 final Object[] es = elementData;
505
506 @SuppressWarnings("unchecked") E oldValue = (E) es[index];
507 fastRemove(es, index);
508
509 return oldValue;
510 }
511
512 /**
513 * {@inheritDoc}
514 */
515 public boolean equals(Object o) {
516 if (o == this) {
517 return true;
518 }
519
520 if (!(o instanceof List)) {
521 return false;
522 }
523
524 final int expectedModCount = modCount;
525 // ArrayList can be subclassed and given arbitrary behavior, but we can
526 // still deal with the common case where o is ArrayList precisely
527 boolean equal = (o.getClass() == ArrayList.class)
528 ? equalsArrayList((ArrayList<?>) o)
529 : equalsRange((List<?>) o, 0, size);
530
531 checkForComodification(expectedModCount);
532 return equal;
533 }
534
535 boolean equalsRange(List<?> other, int from, int to) {
536 final Object[] es = elementData;
537 if (to > es.length) {
538 throw new ConcurrentModificationException();
539 }
540 var oit = other.iterator();
541 for (; from < to; from++) {
542 if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {
543 return false;
544 }
545 }
546 return !oit.hasNext();
547 }
548
549 private boolean equalsArrayList(ArrayList<?> other) {
550 final int otherModCount = other.modCount;
551 final int s = size;
552 boolean equal;
553 if (equal = (s == other.size)) {
554 final Object[] otherEs = other.elementData;
555 final Object[] es = elementData;
556 if (s > es.length || s > otherEs.length) {
557 throw new ConcurrentModificationException();
558 }
559 for (int i = 0; i < s; i++) {
560 if (!Objects.equals(es[i], otherEs[i])) {
561 equal = false;
562 break;
563 }
564 }
565 }
566 other.checkForComodification(otherModCount);
567 return equal;
568 }
569
570 private void checkForComodification(final int expectedModCount) {
571 if (modCount != expectedModCount) {
572 throw new ConcurrentModificationException();
573 }
574 }
575
576 /**
577 * {@inheritDoc}
578 */
579 public int hashCode() {
580 int expectedModCount = modCount;
581 int hash = hashCodeRange(0, size);
582 checkForComodification(expectedModCount);
583 return hash;
584 }
585
586 int hashCodeRange(int from, int to) {
587 final Object[] es = elementData;
588 if (to > es.length) {
589 throw new ConcurrentModificationException();
590 }
591 int hashCode = 1;
592 for (int i = from; i < to; i++) {
593 Object e = es[i];
594 hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
595 }
596 return hashCode;
597 }
598
599 /**
600 * Removes the first occurrence of the specified element from this list,
601 * if it is present. If the list does not contain the element, it is
602 * unchanged. More formally, removes the element with the lowest index
603 * {@code i} such that
604 * {@code Objects.equals(o, get(i))}
605 * (if such an element exists). Returns {@code true} if this list
606 * contained the specified element (or equivalently, if this list
607 * changed as a result of the call).
608 *
609 * @param o element to be removed from this list, if present
610 * @return {@code true} if this list contained the specified element
611 */
612 public boolean remove(Object o) {
613 final Object[] es = elementData;
614 final int size = this.size;
615 int i = 0;
616 found: {
617 if (o == null) {
618 for (; i < size; i++)
619 if (es[i] == null)
620 break found;
621 } else {
622 for (; i < size; i++)
623 if (o.equals(es[i]))
624 break found;
625 }
626 return false;
627 }
628 fastRemove(es, i);
629 return true;
630 }
631
632 /**
633 * Private remove method that skips bounds checking and does not
634 * return the value removed.
635 */
636 private void fastRemove(Object[] es, int i) {
637 modCount++;
638 final int newSize;
639 if ((newSize = size - 1) > i)
640 System.arraycopy(es, i + 1, es, i, newSize - i);
641 es[size = newSize] = null;
642 }
643
644 /**
645 * Removes all of the elements from this list. The list will
646 * be empty after this call returns.
647 */
648 public void clear() {
649 modCount++;
650 final Object[] es = elementData;
651 for (int to = size, i = size = 0; i < to; i++)
652 es[i] = null;
653 }
654
655 /**
656 * Appends all of the elements in the specified collection to the end of
657 * this list, in the order that they are returned by the
658 * specified collection's Iterator. The behavior of this operation is
659 * undefined if the specified collection is modified while the operation
660 * is in progress. (This implies that the behavior of this call is
661 * undefined if the specified collection is this list, and this
662 * list is nonempty.)
663 *
664 * @param c collection containing elements to be added to this list
665 * @return {@code true} if this list changed as a result of the call
666 * @throws NullPointerException if the specified collection is null
667 */
668 public boolean addAll(Collection<? extends E> c) {
669 Object[] a = c.toArray();
670 modCount++;
671 int numNew = a.length;
672 if (numNew == 0)
673 return false;
674 Object[] elementData;
675 final int s;
676 if (numNew > (elementData = this.elementData).length - (s = size))
677 elementData = grow(s + numNew);
678 System.arraycopy(a, 0, elementData, s, numNew);
679 size = s + numNew;
680 return true;
681 }
682
683 /**
684 * Inserts all of the elements in the specified collection into this
685 * list, starting at the specified position. Shifts the element
686 * currently at that position (if any) and any subsequent elements to
687 * the right (increases their indices). The new elements will appear
688 * in the list in the order that they are returned by the
689 * specified collection's iterator.
690 *
691 * @param index index at which to insert the first element from the
692 * specified collection
693 * @param c collection containing elements to be added to this list
694 * @return {@code true} if this list changed as a result of the call
695 * @throws IndexOutOfBoundsException {@inheritDoc}
696 * @throws NullPointerException if the specified collection is null
697 */
698 public boolean addAll(int index, Collection<? extends E> c) {
699 rangeCheckForAdd(index);
700
701 Object[] a = c.toArray();
702 modCount++;
703 int numNew = a.length;
704 if (numNew == 0)
705 return false;
706 Object[] elementData;
707 final int s;
708 if (numNew > (elementData = this.elementData).length - (s = size))
709 elementData = grow(s + numNew);
710
711 int numMoved = s - index;
712 if (numMoved > 0)
713 System.arraycopy(elementData, index,
714 elementData, index + numNew,
715 numMoved);
716 System.arraycopy(a, 0, elementData, index, numNew);
717 size = s + numNew;
718 return true;
719 }
720
721 /**
722 * Removes from this list all of the elements whose index is between
723 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
724 * Shifts any succeeding elements to the left (reduces their index).
725 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
726 * (If {@code toIndex==fromIndex}, this operation has no effect.)
727 *
728 * @throws IndexOutOfBoundsException if {@code fromIndex} or
729 * {@code toIndex} is out of range
730 * ({@code fromIndex < 0 ||
731 * toIndex > size() ||
732 * toIndex < fromIndex})
733 */
734 protected void removeRange(int fromIndex, int toIndex) {
735 if (fromIndex > toIndex) {
736 throw new IndexOutOfBoundsException(
737 outOfBoundsMsg(fromIndex, toIndex));
738 }
739 modCount++;
740 shiftTailOverGap(elementData, fromIndex, toIndex);
741 }
742
743 /** Erases the gap from lo to hi, by sliding down following elements. */
744 private void shiftTailOverGap(Object[] es, int lo, int hi) {
745 System.arraycopy(es, hi, es, lo, size - hi);
746 for (int to = size, i = (size -= hi - lo); i < to; i++)
747 es[i] = null;
748 }
749
750 /**
751 * A version of rangeCheck used by add and addAll.
752 */
753 private void rangeCheckForAdd(int index) {
754 if (index > size || index < 0)
755 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
756 }
757
758 /**
759 * Constructs an IndexOutOfBoundsException detail message.
760 * Of the many possible refactorings of the error handling code,
761 * this "outlining" performs best with both server and client VMs.
762 */
763 private String outOfBoundsMsg(int index) {
764 return "Index: "+index+", Size: "+size;
765 }
766
767 /**
768 * A version used in checking (fromIndex > toIndex) condition
769 */
770 private static String outOfBoundsMsg(int fromIndex, int toIndex) {
771 return "From Index: " + fromIndex + " > To Index: " + toIndex;
772 }
773
774 /**
775 * Removes from this list all of its elements that are contained in the
776 * specified collection.
777 *
778 * @param c collection containing elements to be removed from this list
779 * @return {@code true} if this list changed as a result of the call
780 * @throws ClassCastException if the class of an element of this list
781 * is incompatible with the specified collection
782 * (<a href="Collection.html#optional-restrictions">optional</a>)
783 * @throws NullPointerException if this list contains a null element and the
784 * specified collection does not permit null elements
785 * (<a href="Collection.html#optional-restrictions">optional</a>),
786 * or if the specified collection is null
787 * @see Collection#contains(Object)
788 */
789 public boolean removeAll(Collection<?> c) {
790 return batchRemove(c, false, 0, size);
791 }
792
793 /**
794 * Retains only the elements in this list that are contained in the
795 * specified collection. In other words, removes from this list all
796 * of its elements that are not contained in the specified collection.
797 *
798 * @param c collection containing elements to be retained in this list
799 * @return {@code true} if this list changed as a result of the call
800 * @throws ClassCastException if the class of an element of this list
801 * is incompatible with the specified collection
802 * (<a href="Collection.html#optional-restrictions">optional</a>)
803 * @throws NullPointerException if this list contains a null element and the
804 * specified collection does not permit null elements
805 * (<a href="Collection.html#optional-restrictions">optional</a>),
806 * or if the specified collection is null
807 * @see Collection#contains(Object)
808 */
809 public boolean retainAll(Collection<?> c) {
810 return batchRemove(c, true, 0, size);
811 }
812
813 boolean batchRemove(Collection<?> c, boolean complement,
814 final int from, final int end) {
815 Objects.requireNonNull(c);
816 final Object[] es = elementData;
817 int r;
818 // Optimize for initial run of survivors
819 for (r = from;; r++) {
820 if (r == end)
821 return false;
822 if (c.contains(es[r]) != complement)
823 break;
824 }
825 int w = r++;
826 try {
827 for (Object e; r < end; r++)
828 if (c.contains(e = es[r]) == complement)
829 es[w++] = e;
830 } catch (Throwable ex) {
831 // Preserve behavioral compatibility with AbstractCollection,
832 // even if c.contains() throws.
833 System.arraycopy(es, r, es, w, end - r);
834 w += end - r;
835 throw ex;
836 } finally {
837 modCount += end - w;
838 shiftTailOverGap(es, w, end);
839 }
840 return true;
841 }
842
843 /**
844 * Saves the state of the {@code ArrayList} instance to a stream
845 * (that is, serializes it).
846 *
847 * @param s the stream
848 * @throws java.io.IOException if an I/O error occurs
849 * @serialData The length of the array backing the {@code ArrayList}
850 * instance is emitted (int), followed by all of its elements
851 * (each an {@code Object}) in the proper order.
852 */
853 @java.io.Serial
854 private void writeObject(java.io.ObjectOutputStream s)
855 throws java.io.IOException {
856 // Write out element count, and any hidden stuff
857 int expectedModCount = modCount;
858 s.defaultWriteObject();
859
860 // Write out size as capacity for behavioral compatibility with clone()
861 s.writeInt(size);
862
863 // Write out all elements in the proper order.
864 for (int i=0; i<size; i++) {
865 s.writeObject(elementData[i]);
866 }
867
868 if (modCount != expectedModCount) {
869 throw new ConcurrentModificationException();
870 }
871 }
872
873 /**
874 * Reconstitutes the {@code ArrayList} instance from a stream (that is,
875 * deserializes it).
876 * @param s the stream
877 * @throws ClassNotFoundException if the class of a serialized object
878 * could not be found
879 * @throws java.io.IOException if an I/O error occurs
880 */
881 @java.io.Serial
882 private void readObject(java.io.ObjectInputStream s)
883 throws java.io.IOException, ClassNotFoundException {
884
885 // Read in size, and any hidden stuff
886 s.defaultReadObject();
887
888 // Read in capacity
889 s.readInt(); // ignored
890
891 if (size > 0) {
892 // like clone(), allocate array based upon size not capacity
893 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
894 Object[] elements = new Object[size];
895
896 // Read in all elements in the proper order.
897 for (int i = 0; i < size; i++) {
898 elements[i] = s.readObject();
899 }
900
901 elementData = elements;
902 } else if (size == 0) {
903 elementData = EMPTY_ELEMENTDATA;
904 } else {
905 throw new java.io.InvalidObjectException("Invalid size: " + size);
906 }
907 }
908
909 /**
910 * Returns a list iterator over the elements in this list (in proper
911 * sequence), starting at the specified position in the list.
912 * The specified index indicates the first element that would be
913 * returned by an initial call to {@link ListIterator#next next}.
914 * An initial call to {@link ListIterator#previous previous} would
915 * return the element with the specified index minus one.
916 *
917 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
918 *
919 * @throws IndexOutOfBoundsException {@inheritDoc}
920 */
921 public ListIterator<E> listIterator(int index) {
922 rangeCheckForAdd(index);
923 return new ListItr(index);
924 }
925
926 /**
927 * Returns a list iterator over the elements in this list (in proper
928 * sequence).
929 *
930 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
931 *
932 * @see #listIterator(int)
933 */
934 public ListIterator<E> listIterator() {
935 return new ListItr(0);
936 }
937
938 /**
939 * Returns an iterator over the elements in this list in proper sequence.
940 *
941 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
942 *
943 * @return an iterator over the elements in this list in proper sequence
944 */
945 public Iterator<E> iterator() {
946 return new Itr();
947 }
948
949 /**
950 * An optimized version of AbstractList.Itr
951 */
952 private class Itr implements Iterator<E> {
953 int cursor; // index of next element to return
954 int lastRet = -1; // index of last element returned; -1 if no such
955 int expectedModCount = modCount;
956
957 // prevent creating a synthetic constructor
958 Itr() {}
959
960 public boolean hasNext() {
961 return cursor != size;
962 }
963
964 @SuppressWarnings("unchecked")
965 public E next() {
966 checkForComodification();
967 int i = cursor;
968 if (i >= size)
969 throw new NoSuchElementException();
970 Object[] elementData = ArrayList.this.elementData;
971 if (i >= elementData.length)
972 throw new ConcurrentModificationException();
973 cursor = i + 1;
974 return (E) elementData[lastRet = i];
975 }
976
977 public void remove() {
978 if (lastRet < 0)
979 throw new IllegalStateException();
980 checkForComodification();
981
982 try {
983 ArrayList.this.remove(lastRet);
984 cursor = lastRet;
985 lastRet = -1;
986 expectedModCount = modCount;
987 } catch (IndexOutOfBoundsException ex) {
988 throw new ConcurrentModificationException();
989 }
990 }
991
992 @Override
993 public void forEachRemaining(Consumer<? super E> action) {
994 Objects.requireNonNull(action);
995 final int size = ArrayList.this.size;
996 int i = cursor;
997 if (i < size) {
998 final Object[] es = elementData;
999 if (i >= es.length)
1000 throw new ConcurrentModificationException();
1001 for (; i < size && modCount == expectedModCount; i++)
1002 action.accept(elementAt(es, i));
1003 // update once at end to reduce heap write traffic
1004 cursor = i;
1005 lastRet = i - 1;
1006 checkForComodification();
1007 }
1008 }
1009
1010 final void checkForComodification() {
1011 if (modCount != expectedModCount)
1012 throw new ConcurrentModificationException();
1013 }
1014 }
1015
1016 /**
1017 * An optimized version of AbstractList.ListItr
1018 */
1019 private class ListItr extends Itr implements ListIterator<E> {
1020 ListItr(int index) {
1021 super();
1022 cursor = index;
1023 }
1024
1025 public boolean hasPrevious() {
1026 return cursor != 0;
1027 }
1028
1029 public int nextIndex() {
1030 return cursor;
1031 }
1032
1033 public int previousIndex() {
1034 return cursor - 1;
1035 }
1036
1037 @SuppressWarnings("unchecked")
1038 public E previous() {
1039 checkForComodification();
1040 int i = cursor - 1;
1041 if (i < 0)
1042 throw new NoSuchElementException();
1043 Object[] elementData = ArrayList.this.elementData;
1044 if (i >= elementData.length)
1045 throw new ConcurrentModificationException();
1046 cursor = i;
1047 return (E) elementData[lastRet = i];
1048 }
1049
1050 public void set(E e) {
1051 if (lastRet < 0)
1052 throw new IllegalStateException();
1053 checkForComodification();
1054
1055 try {
1056 ArrayList.this.set(lastRet, e);
1057 } catch (IndexOutOfBoundsException ex) {
1058 throw new ConcurrentModificationException();
1059 }
1060 }
1061
1062 public void add(E e) {
1063 checkForComodification();
1064
1065 try {
1066 int i = cursor;
1067 ArrayList.this.add(i, e);
1068 cursor = i + 1;
1069 lastRet = -1;
1070 expectedModCount = modCount;
1071 } catch (IndexOutOfBoundsException ex) {
1072 throw new ConcurrentModificationException();
1073 }
1074 }
1075 }
1076
1077 /**
1078 * Returns a view of the portion of this list between the specified
1079 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
1080 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
1081 * empty.) The returned list is backed by this list, so non-structural
1082 * changes in the returned list are reflected in this list, and vice-versa.
1083 * The returned list supports all of the optional list operations.
1084 *
1085 * <p>This method eliminates the need for explicit range operations (of
1086 * the sort that commonly exist for arrays). Any operation that expects
1087 * a list can be used as a range operation by passing a subList view
1088 * instead of a whole list. For example, the following idiom
1089 * removes a range of elements from a list:
1090 * <pre>
1091 * list.subList(from, to).clear();
1092 * </pre>
1093 * Similar idioms may be constructed for {@link #indexOf(Object)} and
1094 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
1095 * {@link Collections} class can be applied to a subList.
1096 *
1097 * <p>The semantics of the list returned by this method become undefined if
1098 * the backing list (i.e., this list) is <i>structurally modified</i> in
1099 * any way other than via the returned list. (Structural modifications are
1100 * those that change the size of this list, or otherwise perturb it in such
1101 * a fashion that iterations in progress may yield incorrect results.)
1102 *
1103 * @throws IndexOutOfBoundsException {@inheritDoc}
1104 * @throws IllegalArgumentException {@inheritDoc}
1105 */
1106 public List<E> subList(int fromIndex, int toIndex) {
1107 subListRangeCheck(fromIndex, toIndex, size);
1108 return new SubList<>(this, fromIndex, toIndex);
1109 }
1110
1111 private static class SubList<E> extends AbstractList<E> implements RandomAccess {
1112 private final ArrayList<E> root;
1113 private final SubList<E> parent;
1114 private final int offset;
1115 private int size;
1116
1117 /**
1118 * Constructs a sublist of an arbitrary ArrayList.
1119 */
1120 public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
1121 this.root = root;
1122 this.parent = null;
1123 this.offset = fromIndex;
1124 this.size = toIndex - fromIndex;
1125 this.modCount = root.modCount;
1126 }
1127
1128 /**
1129 * Constructs a sublist of another SubList.
1130 */
1131 private SubList(SubList<E> parent, int fromIndex, int toIndex) {
1132 this.root = parent.root;
1133 this.parent = parent;
1134 this.offset = parent.offset + fromIndex;
1135 this.size = toIndex - fromIndex;
1136 this.modCount = root.modCount;
1137 }
1138
1139 public E set(int index, E element) {
1140 Objects.checkIndex(index, size);
1141 checkForComodification();
1142 E oldValue = root.elementData(offset + index);
1143 root.elementData[offset + index] = element;
1144 return oldValue;
1145 }
1146
1147 public E get(int index) {
1148 Objects.checkIndex(index, size);
1149 checkForComodification();
1150 return root.elementData(offset + index);
1151 }
1152
1153 public int size() {
1154 checkForComodification();
1155 return size;
1156 }
1157
1158 public void add(int index, E element) {
1159 rangeCheckForAdd(index);
1160 checkForComodification();
1161 root.add(offset + index, element);
1162 updateSizeAndModCount(1);
1163 }
1164
1165 public E remove(int index) {
1166 Objects.checkIndex(index, size);
1167 checkForComodification();
1168 E result = root.remove(offset + index);
1169 updateSizeAndModCount(-1);
1170 return result;
1171 }
1172
1173 protected void removeRange(int fromIndex, int toIndex) {
1174 checkForComodification();
1175 root.removeRange(offset + fromIndex, offset + toIndex);
1176 updateSizeAndModCount(fromIndex - toIndex);
1177 }
1178
1179 public boolean addAll(Collection<? extends E> c) {
1180 return addAll(this.size, c);
1181 }
1182
1183 public boolean addAll(int index, Collection<? extends E> c) {
1184 rangeCheckForAdd(index);
1185 int cSize = c.size();
1186 if (cSize==0)
1187 return false;
1188 checkForComodification();
1189 root.addAll(offset + index, c);
1190 updateSizeAndModCount(cSize);
1191 return true;
1192 }
1193
1194 public void replaceAll(UnaryOperator<E> operator) {
1195 root.replaceAllRange(operator, offset, offset + size);
1196 }
1197
1198 public boolean removeAll(Collection<?> c) {
1199 return batchRemove(c, false);
1200 }
1201
1202 public boolean retainAll(Collection<?> c) {
1203 return batchRemove(c, true);
1204 }
1205
1206 private boolean batchRemove(Collection<?> c, boolean complement) {
1207 checkForComodification();
1208 int oldSize = root.size;
1209 boolean modified =
1210 root.batchRemove(c, complement, offset, offset + size);
1211 if (modified)
1212 updateSizeAndModCount(root.size - oldSize);
1213 return modified;
1214 }
1215
1216 public boolean removeIf(Predicate<? super E> filter) {
1217 checkForComodification();
1218 int oldSize = root.size;
1219 boolean modified = root.removeIf(filter, offset, offset + size);
1220 if (modified)
1221 updateSizeAndModCount(root.size - oldSize);
1222 return modified;
1223 }
1224
1225 public Object[] toArray() {
1226 checkForComodification();
1227 return Arrays.copyOfRange(root.elementData, offset, offset + size);
1228 }
1229
1230 @SuppressWarnings("unchecked")
1231 public <T> T[] toArray(T[] a) {
1232 checkForComodification();
1233 if (a.length < size)
1234 return (T[]) Arrays.copyOfRange(
1235 root.elementData, offset, offset + size, a.getClass());
1236 System.arraycopy(root.elementData, offset, a, 0, size);
1237 if (a.length > size)
1238 a[size] = null;
1239 return a;
1240 }
1241
1242 public boolean equals(Object o) {
1243 if (o == this) {
1244 return true;
1245 }
1246
1247 if (!(o instanceof List)) {
1248 return false;
1249 }
1250
1251 boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
1252 checkForComodification();
1253 return equal;
1254 }
1255
1256 public int hashCode() {
1257 int hash = root.hashCodeRange(offset, offset + size);
1258 checkForComodification();
1259 return hash;
1260 }
1261
1262 public int indexOf(Object o) {
1263 int index = root.indexOfRange(o, offset, offset + size);
1264 checkForComodification();
1265 return index >= 0 ? index - offset : -1;
1266 }
1267
1268 public int lastIndexOf(Object o) {
1269 int index = root.lastIndexOfRange(o, offset, offset + size);
1270 checkForComodification();
1271 return index >= 0 ? index - offset : -1;
1272 }
1273
1274 public boolean contains(Object o) {
1275 return indexOf(o) >= 0;
1276 }
1277
1278 public Iterator<E> iterator() {
1279 return listIterator();
1280 }
1281
1282 public ListIterator<E> listIterator(int index) {
1283 checkForComodification();
1284 rangeCheckForAdd(index);
1285
1286 return new ListIterator<E>() {
1287 int cursor = index;
1288 int lastRet = -1;
1289 int expectedModCount = root.modCount;
1290
1291 public boolean hasNext() {
1292 return cursor != SubList.this.size;
1293 }
1294
1295 @SuppressWarnings("unchecked")
1296 public E next() {
1297 checkForComodification();
1298 int i = cursor;
1299 if (i >= SubList.this.size)
1300 throw new NoSuchElementException();
1301 Object[] elementData = root.elementData;
1302 if (offset + i >= elementData.length)
1303 throw new ConcurrentModificationException();
1304 cursor = i + 1;
1305 return (E) elementData[offset + (lastRet = i)];
1306 }
1307
1308 public boolean hasPrevious() {
1309 return cursor != 0;
1310 }
1311
1312 @SuppressWarnings("unchecked")
1313 public E previous() {
1314 checkForComodification();
1315 int i = cursor - 1;
1316 if (i < 0)
1317 throw new NoSuchElementException();
1318 Object[] elementData = root.elementData;
1319 if (offset + i >= elementData.length)
1320 throw new ConcurrentModificationException();
1321 cursor = i;
1322 return (E) elementData[offset + (lastRet = i)];
1323 }
1324
1325 public void forEachRemaining(Consumer<? super E> action) {
1326 Objects.requireNonNull(action);
1327 final int size = SubList.this.size;
1328 int i = cursor;
1329 if (i < size) {
1330 final Object[] es = root.elementData;
1331 if (offset + i >= es.length)
1332 throw new ConcurrentModificationException();
1333 for (; i < size && modCount == expectedModCount; i++)
1334 action.accept(elementAt(es, offset + i));
1335 // update once at end to reduce heap write traffic
1336 cursor = i;
1337 lastRet = i - 1;
1338 checkForComodification();
1339 }
1340 }
1341
1342 public int nextIndex() {
1343 return cursor;
1344 }
1345
1346 public int previousIndex() {
1347 return cursor - 1;
1348 }
1349
1350 public void remove() {
1351 if (lastRet < 0)
1352 throw new IllegalStateException();
1353 checkForComodification();
1354
1355 try {
1356 SubList.this.remove(lastRet);
1357 cursor = lastRet;
1358 lastRet = -1;
1359 expectedModCount = root.modCount;
1360 } catch (IndexOutOfBoundsException ex) {
1361 throw new ConcurrentModificationException();
1362 }
1363 }
1364
1365 public void set(E e) {
1366 if (lastRet < 0)
1367 throw new IllegalStateException();
1368 checkForComodification();
1369
1370 try {
1371 root.set(offset + lastRet, e);
1372 } catch (IndexOutOfBoundsException ex) {
1373 throw new ConcurrentModificationException();
1374 }
1375 }
1376
1377 public void add(E e) {
1378 checkForComodification();
1379
1380 try {
1381 int i = cursor;
1382 SubList.this.add(i, e);
1383 cursor = i + 1;
1384 lastRet = -1;
1385 expectedModCount = root.modCount;
1386 } catch (IndexOutOfBoundsException ex) {
1387 throw new ConcurrentModificationException();
1388 }
1389 }
1390
1391 final void checkForComodification() {
1392 if (root.modCount != expectedModCount)
1393 throw new ConcurrentModificationException();
1394 }
1395 };
1396 }
1397
1398 public List<E> subList(int fromIndex, int toIndex) {
1399 subListRangeCheck(fromIndex, toIndex, size);
1400 return new SubList<>(this, fromIndex, toIndex);
1401 }
1402
1403 private void rangeCheckForAdd(int index) {
1404 if (index < 0 || index > this.size)
1405 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1406 }
1407
1408 private String outOfBoundsMsg(int index) {
1409 return "Index: "+index+", Size: "+this.size;
1410 }
1411
1412 private void checkForComodification() {
1413 if (root.modCount != modCount)
1414 throw new ConcurrentModificationException();
1415 }
1416
1417 private void updateSizeAndModCount(int sizeChange) {
1418 SubList<E> slist = this;
1419 do {
1420 slist.size += sizeChange;
1421 slist.modCount = root.modCount;
1422 slist = slist.parent;
1423 } while (slist != null);
1424 }
1425
1426 public Spliterator<E> spliterator() {
1427 checkForComodification();
1428
1429 // ArrayListSpliterator not used here due to late-binding
1430 return new Spliterator<E>() {
1431 private int index = offset; // current index, modified on advance/split
1432 private int fence = -1; // -1 until used; then one past last index
1433 private int expectedModCount; // initialized when fence set
1434
1435 private int getFence() { // initialize fence to size on first use
1436 int hi; // (a specialized variant appears in method forEach)
1437 if ((hi = fence) < 0) {
1438 expectedModCount = modCount;
1439 hi = fence = offset + size;
1440 }
1441 return hi;
1442 }
1443
1444 public ArrayList<E>.ArrayListSpliterator trySplit() {
1445 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1446 // ArrayListSpliterator can be used here as the source is already bound
1447 return (lo >= mid) ? null : // divide range in half unless too small
1448 root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
1449 }
1450
1451 public boolean tryAdvance(Consumer<? super E> action) {
1452 Objects.requireNonNull(action);
1453 int hi = getFence(), i = index;
1454 if (i < hi) {
1455 index = i + 1;
1456 @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
1457 action.accept(e);
1458 if (root.modCount != expectedModCount)
1459 throw new ConcurrentModificationException();
1460 return true;
1461 }
1462 return false;
1463 }
1464
1465 public void forEachRemaining(Consumer<? super E> action) {
1466 Objects.requireNonNull(action);
1467 int i, hi, mc; // hoist accesses and checks from loop
1468 ArrayList<E> lst = root;
1469 Object[] a;
1470 if ((a = lst.elementData) != null) {
1471 if ((hi = fence) < 0) {
1472 mc = modCount;
1473 hi = offset + size;
1474 }
1475 else
1476 mc = expectedModCount;
1477 if ((i = index) >= 0 && (index = hi) <= a.length) {
1478 for (; i < hi; ++i) {
1479 @SuppressWarnings("unchecked") E e = (E) a[i];
1480 action.accept(e);
1481 }
1482 if (lst.modCount == mc)
1483 return;
1484 }
1485 }
1486 throw new ConcurrentModificationException();
1487 }
1488
1489 public long estimateSize() {
1490 return getFence() - index;
1491 }
1492
1493 public int characteristics() {
1494 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1495 }
1496 };
1497 }
1498 }
1499
1500 /**
1501 * @throws NullPointerException {@inheritDoc}
1502 */
1503 @Override
1504 public void forEach(Consumer<? super E> action) {
1505 Objects.requireNonNull(action);
1506 final int expectedModCount = modCount;
1507 final Object[] es = elementData;
1508 final int size = this.size;
1509 for (int i = 0; modCount == expectedModCount && i < size; i++)
1510 action.accept(elementAt(es, i));
1511 if (modCount != expectedModCount)
1512 throw new ConcurrentModificationException();
1513 }
1514
1515 /**
1516 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1517 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1518 * list.
1519 *
1520 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1521 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1522 * Overriding implementations should document the reporting of additional
1523 * characteristic values.
1524 *
1525 * @return a {@code Spliterator} over the elements in this list
1526 * @since 1.8
1527 */
1528 @Override
1529 public Spliterator<E> spliterator() {
1530 return new ArrayListSpliterator(0, -1, 0);
1531 }
1532
1533 /** Index-based split-by-two, lazily initialized Spliterator */
1534 final class ArrayListSpliterator implements Spliterator<E> {
1535
1536 /*
1537 * If ArrayLists were immutable, or structurally immutable (no
1538 * adds, removes, etc), we could implement their spliterators
1539 * with Arrays.spliterator. Instead we detect as much
1540 * interference during traversal as practical without
1541 * sacrificing much performance. We rely primarily on
1542 * modCounts. These are not guaranteed to detect concurrency
1543 * violations, and are sometimes overly conservative about
1544 * within-thread interference, but detect enough problems to
1545 * be worthwhile in practice. To carry this out, we (1) lazily
1546 * initialize fence and expectedModCount until the latest
1547 * point that we need to commit to the state we are checking
1548 * against; thus improving precision. (This doesn't apply to
1549 * SubLists, that create spliterators with current non-lazy
1550 * values). (2) We perform only a single
1551 * ConcurrentModificationException check at the end of forEach
1552 * (the most performance-sensitive method). When using forEach
1553 * (as opposed to iterators), we can normally only detect
1554 * interference after actions, not before. Further
1555 * CME-triggering checks apply to all other possible
1556 * violations of assumptions for example null or too-small
1557 * elementData array given its size(), that could only have
1558 * occurred due to interference. This allows the inner loop
1559 * of forEach to run without any further checks, and
1560 * simplifies lambda-resolution. While this does entail a
1561 * number of checks, note that in the common case of
1562 * list.stream().forEach(a), no checks or other computation
1563 * occur anywhere other than inside forEach itself. The other
1564 * less-often-used methods cannot take advantage of most of
1565 * these streamlinings.
1566 */
1567
1568 private int index; // current index, modified on advance/split
1569 private int fence; // -1 until used; then one past last index
1570 private int expectedModCount; // initialized when fence set
1571
1572 /** Creates new spliterator covering the given range. */
1573 ArrayListSpliterator(int origin, int fence, int expectedModCount) {
1574 this.index = origin;
1575 this.fence = fence;
1576 this.expectedModCount = expectedModCount;
1577 }
1578
1579 private int getFence() { // initialize fence to size on first use
1580 int hi; // (a specialized variant appears in method forEach)
1581 if ((hi = fence) < 0) {
1582 expectedModCount = modCount;
1583 hi = fence = size;
1584 }
1585 return hi;
1586 }
1587
1588 public ArrayListSpliterator trySplit() {
1589 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1590 return (lo >= mid) ? null : // divide range in half unless too small
1591 new ArrayListSpliterator(lo, index = mid, expectedModCount);
1592 }
1593
1594 public boolean tryAdvance(Consumer<? super E> action) {
1595 if (action == null)
1596 throw new NullPointerException();
1597 int hi = getFence(), i = index;
1598 if (i < hi) {
1599 index = i + 1;
1600 @SuppressWarnings("unchecked") E e = (E)elementData[i];
1601 action.accept(e);
1602 if (modCount != expectedModCount)
1603 throw new ConcurrentModificationException();
1604 return true;
1605 }
1606 return false;
1607 }
1608
1609 public void forEachRemaining(Consumer<? super E> action) {
1610 int i, hi, mc; // hoist accesses and checks from loop
1611 Object[] a;
1612 if (action == null)
1613 throw new NullPointerException();
1614 if ((a = elementData) != null) {
1615 if ((hi = fence) < 0) {
1616 mc = modCount;
1617 hi = size;
1618 }
1619 else
1620 mc = expectedModCount;
1621 if ((i = index) >= 0 && (index = hi) <= a.length) {
1622 for (; i < hi; ++i) {
1623 @SuppressWarnings("unchecked") E e = (E) a[i];
1624 action.accept(e);
1625 }
1626 if (modCount == mc)
1627 return;
1628 }
1629 }
1630 throw new ConcurrentModificationException();
1631 }
1632
1633 public long estimateSize() {
1634 return getFence() - index;
1635 }
1636
1637 public int characteristics() {
1638 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1639 }
1640 }
1641
1642 // A tiny bit set implementation
1643
1644 private static long[] nBits(int n) {
1645 return new long[((n - 1) >> 6) + 1];
1646 }
1647 private static void setBit(long[] bits, int i) {
1648 bits[i >> 6] |= 1L << i;
1649 }
1650 private static boolean isClear(long[] bits, int i) {
1651 return (bits[i >> 6] & (1L << i)) == 0;
1652 }
1653
1654 /**
1655 * @throws NullPointerException {@inheritDoc}
1656 */
1657 @Override
1658 public boolean removeIf(Predicate<? super E> filter) {
1659 return removeIf(filter, 0, size);
1660 }
1661
1662 /**
1663 * Removes all elements satisfying the given predicate, from index
1664 * i (inclusive) to index end (exclusive).
1665 */
1666 boolean removeIf(Predicate<? super E> filter, int i, final int end) {
1667 Objects.requireNonNull(filter);
1668 int expectedModCount = modCount;
1669 final Object[] es = elementData;
1670 // Optimize for initial run of survivors
1671 for (; i < end && !filter.test(elementAt(es, i)); i++)
1672 ;
1673 // Tolerate predicates that reentrantly access the collection for
1674 // read (but writers still get CME), so traverse once to find
1675 // elements to delete, a second pass to physically expunge.
1676 if (i < end) {
1677 final int beg = i;
1678 final long[] deathRow = nBits(end - beg);
1679 deathRow[0] = 1L; // set bit 0
1680 for (i = beg + 1; i < end; i++)
1681 if (filter.test(elementAt(es, i)))
1682 setBit(deathRow, i - beg);
1683 if (modCount != expectedModCount)
1684 throw new ConcurrentModificationException();
1685 modCount++;
1686 int w = beg;
1687 for (i = beg; i < end; i++)
1688 if (isClear(deathRow, i - beg))
1689 es[w++] = es[i];
1690 shiftTailOverGap(es, w, end);
1691 return true;
1692 } else {
1693 if (modCount != expectedModCount)
1694 throw new ConcurrentModificationException();
1695 return false;
1696 }
1697 }
1698
1699 @Override
1700 public void replaceAll(UnaryOperator<E> operator) {
1701 replaceAllRange(operator, 0, size);
1702 // TODO(8203662): remove increment of modCount from ...
1703 modCount++;
1704 }
1705
1706 private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
1707 Objects.requireNonNull(operator);
1708 final int expectedModCount = modCount;
1709 final Object[] es = elementData;
1710 for (; modCount == expectedModCount && i < end; i++)
1711 es[i] = operator.apply(elementAt(es, i));
1712 if (modCount != expectedModCount)
1713 throw new ConcurrentModificationException();
1714 }
1715
1716 @Override
1717 @SuppressWarnings("unchecked")
1718 public void sort(Comparator<? super E> c) {
1719 final int expectedModCount = modCount;
1720 Arrays.sort((E[]) elementData, 0, size, c);
1721 if (modCount != expectedModCount)
1722 throw new ConcurrentModificationException();
1723 modCount++;
1724 }
1725
1726 void checkInvariants() {
1727 // assert size >= 0;
1728 // assert size == elementData.length || elementData[size] == null;
1729 }
1730 }