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 if (DEFAULT_CAPACITY > minCapacity) {
239 return elementData = new Object[DEFAULT_CAPACITY];
240 }
241 return elementData = new Object[minCapacity];
242 }
243 }
244
245 private Object[] grow() {
246 return grow(size + 1);
247 }
248
249 /**
250 * Returns the number of elements in this list.
251 *
252 * @return the number of elements in this list
253 */
254 public int size() {
255 return size;
256 }
257
258 /**
259 * Returns {@code true} if this list contains no elements.
260 *
261 * @return {@code true} if this list contains no elements
262 */
263 public boolean isEmpty() {
264 return size == 0;
265 }
266
267 /**
268 * Returns {@code true} if this list contains the specified element.
269 * More formally, returns {@code true} if and only if this list contains
270 * at least one element {@code e} such that
271 * {@code Objects.equals(o, e)}.
272 *
273 * @param o element whose presence in this list is to be tested
274 * @return {@code true} if this list contains the specified element
275 */
276 public boolean contains(Object o) {
277 return indexOf(o) >= 0;
278 }
279
280 /**
281 * Returns the index of the first occurrence of the specified element
282 * in this list, or -1 if this list does not contain the element.
283 * More formally, returns the lowest index {@code i} such that
284 * {@code Objects.equals(o, get(i))},
285 * or -1 if there is no such index.
286 */
287 public int indexOf(Object o) {
288 return indexOfRange(o, 0, size);
289 }
290
291 int indexOfRange(Object o, int start, int end) {
292 Object[] es = elementData;
293 if (o == null) {
294 for (int i = start; i < end; i++) {
295 if (es[i] == null) {
296 return i;
297 }
298 }
299 } else {
300 for (int i = start; i < end; i++) {
301 if (o.equals(es[i])) {
302 return i;
303 }
304 }
305 }
306 return -1;
307 }
308
309 /**
310 * Returns the index of the last occurrence of the specified element
311 * in this list, or -1 if this list does not contain the element.
312 * More formally, returns the highest index {@code i} such that
313 * {@code Objects.equals(o, get(i))},
314 * or -1 if there is no such index.
315 */
316 public int lastIndexOf(Object o) {
317 return lastIndexOfRange(o, 0, size);
318 }
319
320 int lastIndexOfRange(Object o, int start, int end) {
321 Object[] es = elementData;
322 if (o == null) {
323 for (int i = end - 1; i >= start; i--) {
324 if (es[i] == null) {
325 return i;
326 }
327 }
328 } else {
329 for (int i = end - 1; i >= start; i--) {
330 if (o.equals(es[i])) {
331 return i;
332 }
333 }
334 }
335 return -1;
336 }
337
338 /**
339 * Returns a shallow copy of this {@code ArrayList} instance. (The
340 * elements themselves are not copied.)
341 *
342 * @return a clone of this {@code ArrayList} instance
343 */
344 public Object clone() {
345 try {
346 ArrayList<?> v = (ArrayList<?>) super.clone();
347 v.elementData = Arrays.copyOf(elementData, size);
348 v.modCount = 0;
349 return v;
350 } catch (CloneNotSupportedException e) {
351 // this shouldn't happen, since we are Cloneable
352 throw new InternalError(e);
353 }
354 }
355
356 /**
357 * Returns an array containing all of the elements in this list
358 * in proper sequence (from first to last element).
359 *
360 * <p>The returned array will be "safe" in that no references to it are
361 * maintained by this list. (In other words, this method must allocate
362 * a new array). The caller is thus free to modify the returned array.
363 *
364 * <p>This method acts as bridge between array-based and collection-based
365 * APIs.
366 *
367 * @return an array containing all of the elements in this list in
368 * proper sequence
369 */
370 public Object[] toArray() {
371 return Arrays.copyOf(elementData, size);
372 }
373
374 /**
375 * Returns an array containing all of the elements in this list in proper
376 * sequence (from first to last element); the runtime type of the returned
377 * array is that of the specified array. If the list fits in the
378 * specified array, it is returned therein. Otherwise, a new array is
379 * allocated with the runtime type of the specified array and the size of
380 * this list.
381 *
382 * <p>If the list fits in the specified array with room to spare
383 * (i.e., the array has more elements than the list), the element in
384 * the array immediately following the end of the collection is set to
385 * {@code null}. (This is useful in determining the length of the
386 * list <i>only</i> if the caller knows that the list does not contain
387 * any null elements.)
388 *
389 * @param a the array into which the elements of the list are to
390 * be stored, if it is big enough; otherwise, a new array of the
391 * same runtime type is allocated for this purpose.
392 * @return an array containing the elements of the list
393 * @throws ArrayStoreException if the runtime type of the specified array
394 * is not a supertype of the runtime type of every element in
395 * this list
396 * @throws NullPointerException if the specified array is null
397 */
398 @SuppressWarnings("unchecked")
399 public <T> T[] toArray(T[] a) {
400 if (a.length < size)
401 // Make a new array of a's runtime type, but my contents:
402 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
403 System.arraycopy(elementData, 0, a, 0, size);
404 if (a.length > size)
405 a[size] = null;
406 return a;
407 }
408
409 // Positional Access Operations
410
411 @SuppressWarnings("unchecked")
412 E elementData(int index) {
413 return (E) elementData[index];
414 }
415
416 @SuppressWarnings("unchecked")
417 static <E> E elementAt(Object[] es, int index) {
418 return (E) es[index];
419 }
420
421 /**
422 * Returns the element at the specified position in this list.
423 *
424 * @param index index of the element to return
425 * @return the element at the specified position in this list
426 * @throws IndexOutOfBoundsException {@inheritDoc}
427 */
428 public E get(int index) {
429 Objects.checkIndex(index, size);
430 return elementData(index);
431 }
432
433 /**
434 * Replaces the element at the specified position in this list with
435 * the specified element.
436 *
437 * @param index index of the element to replace
438 * @param element element to be stored at the specified position
439 * @return the element previously at the specified position
440 * @throws IndexOutOfBoundsException {@inheritDoc}
441 */
442 public E set(int index, E element) {
443 Objects.checkIndex(index, size);
444 E oldValue = elementData(index);
445 elementData[index] = element;
446 return oldValue;
447 }
448
449 /**
450 * This helper method split out from add(E) to keep method
451 * bytecode size under 35 (the -XX:MaxInlineSize default value),
452 * which helps when add(E) is called in a C1-compiled loop.
453 */
454 private void add(E e, Object[] elementData, int s) {
455 if (s == elementData.length)
456 elementData = grow();
457 elementData[s] = e;
458 size = s + 1;
459 }
460
461 /**
462 * Appends the specified element to the end of this list.
463 *
464 * @param e element to be appended to this list
465 * @return {@code true} (as specified by {@link Collection#add})
466 */
467 public boolean add(E e) {
468 modCount++;
469 add(e, elementData, size);
470 return true;
471 }
472
473 /**
474 * Inserts the specified element at the specified position in this
475 * list. Shifts the element currently at that position (if any) and
476 * any subsequent elements to the right (adds one to their indices).
477 *
478 * @param index index at which the specified element is to be inserted
479 * @param element element to be inserted
480 * @throws IndexOutOfBoundsException {@inheritDoc}
481 */
482 public void add(int index, E element) {
483 rangeCheckForAdd(index);
484 modCount++;
485 final int s;
486 Object[] elementData;
487 if ((s = size) == (elementData = this.elementData).length)
488 elementData = grow();
489 System.arraycopy(elementData, index,
490 elementData, index + 1,
491 s - index);
492 elementData[index] = element;
493 size = s + 1;
494 }
495
496 /**
497 * Removes the element at the specified position in this list.
498 * Shifts any subsequent elements to the left (subtracts one from their
499 * indices).
500 *
501 * @param index the index of the element to be removed
502 * @return the element that was removed from the list
503 * @throws IndexOutOfBoundsException {@inheritDoc}
504 */
505 public E remove(int index) {
506 Objects.checkIndex(index, size);
507 final Object[] es = elementData;
508
509 @SuppressWarnings("unchecked") E oldValue = (E) es[index];
510 fastRemove(es, index);
511
512 return oldValue;
513 }
514
515 /**
516 * {@inheritDoc}
517 */
518 public boolean equals(Object o) {
519 if (o == this) {
520 return true;
521 }
522
523 if (!(o instanceof List)) {
524 return false;
525 }
526
527 final int expectedModCount = modCount;
528 // ArrayList can be subclassed and given arbitrary behavior, but we can
529 // still deal with the common case where o is ArrayList precisely
530 boolean equal = (o.getClass() == ArrayList.class)
531 ? equalsArrayList((ArrayList<?>) o)
532 : equalsRange((List<?>) o, 0, size);
533
534 checkForComodification(expectedModCount);
535 return equal;
536 }
537
538 boolean equalsRange(List<?> other, int from, int to) {
539 final Object[] es = elementData;
540 if (to > es.length) {
541 throw new ConcurrentModificationException();
542 }
543 var oit = other.iterator();
544 for (; from < to; from++) {
545 if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {
546 return false;
547 }
548 }
549 return !oit.hasNext();
550 }
551
552 private boolean equalsArrayList(ArrayList<?> other) {
553 final int otherModCount = other.modCount;
554 final int s = size;
555 boolean equal;
556 if (equal = (s == other.size)) {
557 final Object[] otherEs = other.elementData;
558 final Object[] es = elementData;
559 if (s > es.length || s > otherEs.length) {
560 throw new ConcurrentModificationException();
561 }
562 for (int i = 0; i < s; i++) {
563 if (!Objects.equals(es[i], otherEs[i])) {
564 equal = false;
565 break;
566 }
567 }
568 }
569 other.checkForComodification(otherModCount);
570 return equal;
571 }
572
573 private void checkForComodification(final int expectedModCount) {
574 if (modCount != expectedModCount) {
575 throw new ConcurrentModificationException();
576 }
577 }
578
579 /**
580 * {@inheritDoc}
581 */
582 public int hashCode() {
583 int expectedModCount = modCount;
584 int hash = hashCodeRange(0, size);
585 checkForComodification(expectedModCount);
586 return hash;
587 }
588
589 int hashCodeRange(int from, int to) {
590 final Object[] es = elementData;
591 if (to > es.length) {
592 throw new ConcurrentModificationException();
593 }
594 int hashCode = 1;
595 for (int i = from; i < to; i++) {
596 Object e = es[i];
597 hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
598 }
599 return hashCode;
600 }
601
602 /**
603 * Removes the first occurrence of the specified element from this list,
604 * if it is present. If the list does not contain the element, it is
605 * unchanged. More formally, removes the element with the lowest index
606 * {@code i} such that
607 * {@code Objects.equals(o, get(i))}
608 * (if such an element exists). Returns {@code true} if this list
609 * contained the specified element (or equivalently, if this list
610 * changed as a result of the call).
611 *
612 * @param o element to be removed from this list, if present
613 * @return {@code true} if this list contained the specified element
614 */
615 public boolean remove(Object o) {
616 final Object[] es = elementData;
617 final int size = this.size;
618 int i = 0;
619 found: {
620 if (o == null) {
621 for (; i < size; i++)
622 if (es[i] == null)
623 break found;
624 } else {
625 for (; i < size; i++)
626 if (o.equals(es[i]))
627 break found;
628 }
629 return false;
630 }
631 fastRemove(es, i);
632 return true;
633 }
634
635 /**
636 * Private remove method that skips bounds checking and does not
637 * return the value removed.
638 */
639 private void fastRemove(Object[] es, int i) {
640 modCount++;
641 final int newSize;
642 if ((newSize = size - 1) > i)
643 System.arraycopy(es, i + 1, es, i, newSize - i);
644 es[size = newSize] = null;
645 }
646
647 /**
648 * Removes all of the elements from this list. The list will
649 * be empty after this call returns.
650 */
651 public void clear() {
652 modCount++;
653 final Object[] es = elementData;
654 for (int to = size, i = size = 0; i < to; i++)
655 es[i] = null;
656 }
657
658 /**
659 * Appends all of the elements in the specified collection to the end of
660 * this list, in the order that they are returned by the
661 * specified collection's Iterator. The behavior of this operation is
662 * undefined if the specified collection is modified while the operation
663 * is in progress. (This implies that the behavior of this call is
664 * undefined if the specified collection is this list, and this
665 * list is nonempty.)
666 *
667 * @param c collection containing elements to be added to this list
668 * @return {@code true} if this list changed as a result of the call
669 * @throws NullPointerException if the specified collection is null
670 */
671 public boolean addAll(Collection<? extends E> c) {
672 Object[] a = c.toArray();
673 modCount++;
674 int numNew = a.length;
675 if (numNew == 0)
676 return false;
677 Object[] elementData;
678 final int s;
679 if (numNew > (elementData = this.elementData).length - (s = size))
680 elementData = grow(s + numNew);
681 System.arraycopy(a, 0, elementData, s, numNew);
682 size = s + numNew;
683 return true;
684 }
685
686 /**
687 * Inserts all of the elements in the specified collection into this
688 * list, starting at the specified position. Shifts the element
689 * currently at that position (if any) and any subsequent elements to
690 * the right (increases their indices). The new elements will appear
691 * in the list in the order that they are returned by the
692 * specified collection's iterator.
693 *
694 * @param index index at which to insert the first element from the
695 * specified collection
696 * @param c collection containing elements to be added to this list
697 * @return {@code true} if this list changed as a result of the call
698 * @throws IndexOutOfBoundsException {@inheritDoc}
699 * @throws NullPointerException if the specified collection is null
700 */
701 public boolean addAll(int index, Collection<? extends E> c) {
702 rangeCheckForAdd(index);
703
704 Object[] a = c.toArray();
705 modCount++;
706 int numNew = a.length;
707 if (numNew == 0)
708 return false;
709 Object[] elementData;
710 final int s;
711 if (numNew > (elementData = this.elementData).length - (s = size))
712 elementData = grow(s + numNew);
713
714 int numMoved = s - index;
715 if (numMoved > 0)
716 System.arraycopy(elementData, index,
717 elementData, index + numNew,
718 numMoved);
719 System.arraycopy(a, 0, elementData, index, numNew);
720 size = s + numNew;
721 return true;
722 }
723
724 /**
725 * Removes from this list all of the elements whose index is between
726 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
727 * Shifts any succeeding elements to the left (reduces their index).
728 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
729 * (If {@code toIndex==fromIndex}, this operation has no effect.)
730 *
731 * @throws IndexOutOfBoundsException if {@code fromIndex} or
732 * {@code toIndex} is out of range
733 * ({@code fromIndex < 0 ||
734 * toIndex > size() ||
735 * toIndex < fromIndex})
736 */
737 protected void removeRange(int fromIndex, int toIndex) {
738 if (fromIndex > toIndex) {
739 throw new IndexOutOfBoundsException(
740 outOfBoundsMsg(fromIndex, toIndex));
741 }
742 modCount++;
743 shiftTailOverGap(elementData, fromIndex, toIndex);
744 }
745
746 /** Erases the gap from lo to hi, by sliding down following elements. */
747 private void shiftTailOverGap(Object[] es, int lo, int hi) {
748 System.arraycopy(es, hi, es, lo, size - hi);
749 for (int to = size, i = (size -= hi - lo); i < to; i++)
750 es[i] = null;
751 }
752
753 /**
754 * A version of rangeCheck used by add and addAll.
755 */
756 private void rangeCheckForAdd(int index) {
757 if (index > size || index < 0)
758 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
759 }
760
761 /**
762 * Constructs an IndexOutOfBoundsException detail message.
763 * Of the many possible refactorings of the error handling code,
764 * this "outlining" performs best with both server and client VMs.
765 */
766 private String outOfBoundsMsg(int index) {
767 return "Index: "+index+", Size: "+size;
768 }
769
770 /**
771 * A version used in checking (fromIndex > toIndex) condition
772 */
773 private static String outOfBoundsMsg(int fromIndex, int toIndex) {
774 return "From Index: " + fromIndex + " > To Index: " + toIndex;
775 }
776
777 /**
778 * Removes from this list all of its elements that are contained in the
779 * specified collection.
780 *
781 * @param c collection containing elements to be removed from this list
782 * @return {@code true} if this list changed as a result of the call
783 * @throws ClassCastException if the class of an element of this list
784 * is incompatible with the specified collection
785 * (<a href="Collection.html#optional-restrictions">optional</a>)
786 * @throws NullPointerException if this list contains a null element and the
787 * specified collection does not permit null elements
788 * (<a href="Collection.html#optional-restrictions">optional</a>),
789 * or if the specified collection is null
790 * @see Collection#contains(Object)
791 */
792 public boolean removeAll(Collection<?> c) {
793 return batchRemove(c, false, 0, size);
794 }
795
796 /**
797 * Retains only the elements in this list that are contained in the
798 * specified collection. In other words, removes from this list all
799 * of its elements that are not contained in the specified collection.
800 *
801 * @param c collection containing elements to be retained in this list
802 * @return {@code true} if this list changed as a result of the call
803 * @throws ClassCastException if the class of an element of this list
804 * is incompatible with the specified collection
805 * (<a href="Collection.html#optional-restrictions">optional</a>)
806 * @throws NullPointerException if this list contains a null element and the
807 * specified collection does not permit null elements
808 * (<a href="Collection.html#optional-restrictions">optional</a>),
809 * or if the specified collection is null
810 * @see Collection#contains(Object)
811 */
812 public boolean retainAll(Collection<?> c) {
813 return batchRemove(c, true, 0, size);
814 }
815
816 boolean batchRemove(Collection<?> c, boolean complement,
817 final int from, final int end) {
818 Objects.requireNonNull(c);
819 final Object[] es = elementData;
820 int r;
821 // Optimize for initial run of survivors
822 for (r = from;; r++) {
823 if (r == end)
824 return false;
825 if (c.contains(es[r]) != complement)
826 break;
827 }
828 int w = r++;
829 try {
830 for (Object e; r < end; r++)
831 if (c.contains(e = es[r]) == complement)
832 es[w++] = e;
833 } catch (Throwable ex) {
834 // Preserve behavioral compatibility with AbstractCollection,
835 // even if c.contains() throws.
836 System.arraycopy(es, r, es, w, end - r);
837 w += end - r;
838 throw ex;
839 } finally {
840 modCount += end - w;
841 shiftTailOverGap(es, w, end);
842 }
843 return true;
844 }
845
846 /**
847 * Saves the state of the {@code ArrayList} instance to a stream
848 * (that is, serializes it).
849 *
850 * @param s the stream
851 * @throws java.io.IOException if an I/O error occurs
852 * @serialData The length of the array backing the {@code ArrayList}
853 * instance is emitted (int), followed by all of its elements
854 * (each an {@code Object}) in the proper order.
855 */
856 @java.io.Serial
857 private void writeObject(java.io.ObjectOutputStream s)
858 throws java.io.IOException {
859 // Write out element count, and any hidden stuff
860 int expectedModCount = modCount;
861 s.defaultWriteObject();
862
863 // Write out size as capacity for behavioral compatibility with clone()
864 s.writeInt(size);
865
866 // Write out all elements in the proper order.
867 for (int i=0; i<size; i++) {
868 s.writeObject(elementData[i]);
869 }
870
871 if (modCount != expectedModCount) {
872 throw new ConcurrentModificationException();
873 }
874 }
875
876 /**
877 * Reconstitutes the {@code ArrayList} instance from a stream (that is,
878 * deserializes it).
879 * @param s the stream
880 * @throws ClassNotFoundException if the class of a serialized object
881 * could not be found
882 * @throws java.io.IOException if an I/O error occurs
883 */
884 @java.io.Serial
885 private void readObject(java.io.ObjectInputStream s)
886 throws java.io.IOException, ClassNotFoundException {
887
888 // Read in size, and any hidden stuff
889 s.defaultReadObject();
890
891 // Read in capacity
892 s.readInt(); // ignored
893
894 if (size > 0) {
895 // like clone(), allocate array based upon size not capacity
896 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
897 Object[] elements = new Object[size];
898
899 // Read in all elements in the proper order.
900 for (int i = 0; i < size; i++) {
901 elements[i] = s.readObject();
902 }
903
904 elementData = elements;
905 } else if (size == 0) {
906 elementData = EMPTY_ELEMENTDATA;
907 } else {
908 throw new java.io.InvalidObjectException("Invalid size: " + size);
909 }
910 }
911
912 /**
913 * Returns a list iterator over the elements in this list (in proper
914 * sequence), starting at the specified position in the list.
915 * The specified index indicates the first element that would be
916 * returned by an initial call to {@link ListIterator#next next}.
917 * An initial call to {@link ListIterator#previous previous} would
918 * return the element with the specified index minus one.
919 *
920 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
921 *
922 * @throws IndexOutOfBoundsException {@inheritDoc}
923 */
924 public ListIterator<E> listIterator(int index) {
925 rangeCheckForAdd(index);
926 return new ListItr(index);
927 }
928
929 /**
930 * Returns a list iterator over the elements in this list (in proper
931 * sequence).
932 *
933 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
934 *
935 * @see #listIterator(int)
936 */
937 public ListIterator<E> listIterator() {
938 return new ListItr(0);
939 }
940
941 /**
942 * Returns an iterator over the elements in this list in proper sequence.
943 *
944 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
945 *
946 * @return an iterator over the elements in this list in proper sequence
947 */
948 public Iterator<E> iterator() {
949 return new Itr();
950 }
951
952 /**
953 * An optimized version of AbstractList.Itr
954 */
955 private class Itr implements Iterator<E> {
956 int cursor; // index of next element to return
957 int lastRet = -1; // index of last element returned; -1 if no such
958 int expectedModCount = modCount;
959
960 // prevent creating a synthetic constructor
961 Itr() {}
962
963 public boolean hasNext() {
964 return cursor != size;
965 }
966
967 @SuppressWarnings("unchecked")
968 public E next() {
969 checkForComodification();
970 int i = cursor;
971 if (i >= size)
972 throw new NoSuchElementException();
973 Object[] elementData = ArrayList.this.elementData;
974 if (i >= elementData.length)
975 throw new ConcurrentModificationException();
976 cursor = i + 1;
977 return (E) elementData[lastRet = i];
978 }
979
980 public void remove() {
981 if (lastRet < 0)
982 throw new IllegalStateException();
983 checkForComodification();
984
985 try {
986 ArrayList.this.remove(lastRet);
987 cursor = lastRet;
988 lastRet = -1;
989 expectedModCount = modCount;
990 } catch (IndexOutOfBoundsException ex) {
991 throw new ConcurrentModificationException();
992 }
993 }
994
995 @Override
996 public void forEachRemaining(Consumer<? super E> action) {
997 Objects.requireNonNull(action);
998 final int size = ArrayList.this.size;
999 int i = cursor;
1000 if (i < size) {
1001 final Object[] es = elementData;
1002 if (i >= es.length)
1003 throw new ConcurrentModificationException();
1004 for (; i < size && modCount == expectedModCount; i++)
1005 action.accept(elementAt(es, i));
1006 // update once at end to reduce heap write traffic
1007 cursor = i;
1008 lastRet = i - 1;
1009 checkForComodification();
1010 }
1011 }
1012
1013 final void checkForComodification() {
1014 if (modCount != expectedModCount)
1015 throw new ConcurrentModificationException();
1016 }
1017 }
1018
1019 /**
1020 * An optimized version of AbstractList.ListItr
1021 */
1022 private class ListItr extends Itr implements ListIterator<E> {
1023 ListItr(int index) {
1024 super();
1025 cursor = index;
1026 }
1027
1028 public boolean hasPrevious() {
1029 return cursor != 0;
1030 }
1031
1032 public int nextIndex() {
1033 return cursor;
1034 }
1035
1036 public int previousIndex() {
1037 return cursor - 1;
1038 }
1039
1040 @SuppressWarnings("unchecked")
1041 public E previous() {
1042 checkForComodification();
1043 int i = cursor - 1;
1044 if (i < 0)
1045 throw new NoSuchElementException();
1046 Object[] elementData = ArrayList.this.elementData;
1047 if (i >= elementData.length)
1048 throw new ConcurrentModificationException();
1049 cursor = i;
1050 return (E) elementData[lastRet = i];
1051 }
1052
1053 public void set(E e) {
1054 if (lastRet < 0)
1055 throw new IllegalStateException();
1056 checkForComodification();
1057
1058 try {
1059 ArrayList.this.set(lastRet, e);
1060 } catch (IndexOutOfBoundsException ex) {
1061 throw new ConcurrentModificationException();
1062 }
1063 }
1064
1065 public void add(E e) {
1066 checkForComodification();
1067
1068 try {
1069 int i = cursor;
1070 ArrayList.this.add(i, e);
1071 cursor = i + 1;
1072 lastRet = -1;
1073 expectedModCount = modCount;
1074 } catch (IndexOutOfBoundsException ex) {
1075 throw new ConcurrentModificationException();
1076 }
1077 }
1078 }
1079
1080 /**
1081 * Returns a view of the portion of this list between the specified
1082 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
1083 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
1084 * empty.) The returned list is backed by this list, so non-structural
1085 * changes in the returned list are reflected in this list, and vice-versa.
1086 * The returned list supports all of the optional list operations.
1087 *
1088 * <p>This method eliminates the need for explicit range operations (of
1089 * the sort that commonly exist for arrays). Any operation that expects
1090 * a list can be used as a range operation by passing a subList view
1091 * instead of a whole list. For example, the following idiom
1092 * removes a range of elements from a list:
1093 * <pre>
1094 * list.subList(from, to).clear();
1095 * </pre>
1096 * Similar idioms may be constructed for {@link #indexOf(Object)} and
1097 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
1098 * {@link Collections} class can be applied to a subList.
1099 *
1100 * <p>The semantics of the list returned by this method become undefined if
1101 * the backing list (i.e., this list) is <i>structurally modified</i> in
1102 * any way other than via the returned list. (Structural modifications are
1103 * those that change the size of this list, or otherwise perturb it in such
1104 * a fashion that iterations in progress may yield incorrect results.)
1105 *
1106 * @throws IndexOutOfBoundsException {@inheritDoc}
1107 * @throws IllegalArgumentException {@inheritDoc}
1108 */
1109 public List<E> subList(int fromIndex, int toIndex) {
1110 subListRangeCheck(fromIndex, toIndex, size);
1111 return new SubList<>(this, fromIndex, toIndex);
1112 }
1113
1114 private static class SubList<E> extends AbstractList<E> implements RandomAccess {
1115 private final ArrayList<E> root;
1116 private final SubList<E> parent;
1117 private final int offset;
1118 private int size;
1119
1120 /**
1121 * Constructs a sublist of an arbitrary ArrayList.
1122 */
1123 public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
1124 this.root = root;
1125 this.parent = null;
1126 this.offset = fromIndex;
1127 this.size = toIndex - fromIndex;
1128 this.modCount = root.modCount;
1129 }
1130
1131 /**
1132 * Constructs a sublist of another SubList.
1133 */
1134 private SubList(SubList<E> parent, int fromIndex, int toIndex) {
1135 this.root = parent.root;
1136 this.parent = parent;
1137 this.offset = parent.offset + fromIndex;
1138 this.size = toIndex - fromIndex;
1139 this.modCount = parent.modCount;
1140 }
1141
1142 public E set(int index, E element) {
1143 Objects.checkIndex(index, size);
1144 checkForComodification();
1145 E oldValue = root.elementData(offset + index);
1146 root.elementData[offset + index] = element;
1147 return oldValue;
1148 }
1149
1150 public E get(int index) {
1151 Objects.checkIndex(index, size);
1152 checkForComodification();
1153 return root.elementData(offset + index);
1154 }
1155
1156 public int size() {
1157 checkForComodification();
1158 return size;
1159 }
1160
1161 public void add(int index, E element) {
1162 rangeCheckForAdd(index);
1163 checkForComodification();
1164 root.add(offset + index, element);
1165 updateSizeAndModCount(1);
1166 }
1167
1168 public E remove(int index) {
1169 Objects.checkIndex(index, size);
1170 checkForComodification();
1171 E result = root.remove(offset + index);
1172 updateSizeAndModCount(-1);
1173 return result;
1174 }
1175
1176 protected void removeRange(int fromIndex, int toIndex) {
1177 checkForComodification();
1178 root.removeRange(offset + fromIndex, offset + toIndex);
1179 updateSizeAndModCount(fromIndex - toIndex);
1180 }
1181
1182 public boolean addAll(Collection<? extends E> c) {
1183 return addAll(this.size, c);
1184 }
1185
1186 public boolean addAll(int index, Collection<? extends E> c) {
1187 rangeCheckForAdd(index);
1188 int cSize = c.size();
1189 if (cSize==0)
1190 return false;
1191 checkForComodification();
1192 root.addAll(offset + index, c);
1193 updateSizeAndModCount(cSize);
1194 return true;
1195 }
1196
1197 public void replaceAll(UnaryOperator<E> operator) {
1198 root.replaceAllRange(operator, offset, offset + size);
1199 }
1200
1201 public boolean removeAll(Collection<?> c) {
1202 return batchRemove(c, false);
1203 }
1204
1205 public boolean retainAll(Collection<?> c) {
1206 return batchRemove(c, true);
1207 }
1208
1209 private boolean batchRemove(Collection<?> c, boolean complement) {
1210 checkForComodification();
1211 int oldSize = root.size;
1212 boolean modified =
1213 root.batchRemove(c, complement, offset, offset + size);
1214 if (modified)
1215 updateSizeAndModCount(root.size - oldSize);
1216 return modified;
1217 }
1218
1219 public boolean removeIf(Predicate<? super E> filter) {
1220 checkForComodification();
1221 int oldSize = root.size;
1222 boolean modified = root.removeIf(filter, offset, offset + size);
1223 if (modified)
1224 updateSizeAndModCount(root.size - oldSize);
1225 return modified;
1226 }
1227
1228 public Object[] toArray() {
1229 checkForComodification();
1230 return Arrays.copyOfRange(root.elementData, offset, offset + size);
1231 }
1232
1233 @SuppressWarnings("unchecked")
1234 public <T> T[] toArray(T[] a) {
1235 checkForComodification();
1236 if (a.length < size)
1237 return (T[]) Arrays.copyOfRange(
1238 root.elementData, offset, offset + size, a.getClass());
1239 System.arraycopy(root.elementData, offset, a, 0, size);
1240 if (a.length > size)
1241 a[size] = null;
1242 return a;
1243 }
1244
1245 public boolean equals(Object o) {
1246 if (o == this) {
1247 return true;
1248 }
1249
1250 if (!(o instanceof List)) {
1251 return false;
1252 }
1253
1254 boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
1255 checkForComodification();
1256 return equal;
1257 }
1258
1259 public int hashCode() {
1260 int hash = root.hashCodeRange(offset, offset + size);
1261 checkForComodification();
1262 return hash;
1263 }
1264
1265 public int indexOf(Object o) {
1266 int index = root.indexOfRange(o, offset, offset + size);
1267 checkForComodification();
1268 return index >= 0 ? index - offset : -1;
1269 }
1270
1271 public int lastIndexOf(Object o) {
1272 int index = root.lastIndexOfRange(o, offset, offset + size);
1273 checkForComodification();
1274 return index >= 0 ? index - offset : -1;
1275 }
1276
1277 public boolean contains(Object o) {
1278 return indexOf(o) >= 0;
1279 }
1280
1281 public Iterator<E> iterator() {
1282 return listIterator();
1283 }
1284
1285 public ListIterator<E> listIterator(int index) {
1286 checkForComodification();
1287 rangeCheckForAdd(index);
1288
1289 return new ListIterator<E>() {
1290 int cursor = index;
1291 int lastRet = -1;
1292 int expectedModCount = SubList.this.modCount;
1293
1294 public boolean hasNext() {
1295 return cursor != SubList.this.size;
1296 }
1297
1298 @SuppressWarnings("unchecked")
1299 public E next() {
1300 checkForComodification();
1301 int i = cursor;
1302 if (i >= SubList.this.size)
1303 throw new NoSuchElementException();
1304 Object[] elementData = root.elementData;
1305 if (offset + i >= elementData.length)
1306 throw new ConcurrentModificationException();
1307 cursor = i + 1;
1308 return (E) elementData[offset + (lastRet = i)];
1309 }
1310
1311 public boolean hasPrevious() {
1312 return cursor != 0;
1313 }
1314
1315 @SuppressWarnings("unchecked")
1316 public E previous() {
1317 checkForComodification();
1318 int i = cursor - 1;
1319 if (i < 0)
1320 throw new NoSuchElementException();
1321 Object[] elementData = root.elementData;
1322 if (offset + i >= elementData.length)
1323 throw new ConcurrentModificationException();
1324 cursor = i;
1325 return (E) elementData[offset + (lastRet = i)];
1326 }
1327
1328 public void forEachRemaining(Consumer<? super E> action) {
1329 Objects.requireNonNull(action);
1330 final int size = SubList.this.size;
1331 int i = cursor;
1332 if (i < size) {
1333 final Object[] es = root.elementData;
1334 if (offset + i >= es.length)
1335 throw new ConcurrentModificationException();
1336 for (; i < size && root.modCount == expectedModCount; i++)
1337 action.accept(elementAt(es, offset + i));
1338 // update once at end to reduce heap write traffic
1339 cursor = i;
1340 lastRet = i - 1;
1341 checkForComodification();
1342 }
1343 }
1344
1345 public int nextIndex() {
1346 return cursor;
1347 }
1348
1349 public int previousIndex() {
1350 return cursor - 1;
1351 }
1352
1353 public void remove() {
1354 if (lastRet < 0)
1355 throw new IllegalStateException();
1356 checkForComodification();
1357
1358 try {
1359 SubList.this.remove(lastRet);
1360 cursor = lastRet;
1361 lastRet = -1;
1362 expectedModCount = SubList.this.modCount;
1363 } catch (IndexOutOfBoundsException ex) {
1364 throw new ConcurrentModificationException();
1365 }
1366 }
1367
1368 public void set(E e) {
1369 if (lastRet < 0)
1370 throw new IllegalStateException();
1371 checkForComodification();
1372
1373 try {
1374 root.set(offset + lastRet, e);
1375 } catch (IndexOutOfBoundsException ex) {
1376 throw new ConcurrentModificationException();
1377 }
1378 }
1379
1380 public void add(E e) {
1381 checkForComodification();
1382
1383 try {
1384 int i = cursor;
1385 SubList.this.add(i, e);
1386 cursor = i + 1;
1387 lastRet = -1;
1388 expectedModCount = SubList.this.modCount;
1389 } catch (IndexOutOfBoundsException ex) {
1390 throw new ConcurrentModificationException();
1391 }
1392 }
1393
1394 final void checkForComodification() {
1395 if (root.modCount != expectedModCount)
1396 throw new ConcurrentModificationException();
1397 }
1398 };
1399 }
1400
1401 public List<E> subList(int fromIndex, int toIndex) {
1402 subListRangeCheck(fromIndex, toIndex, size);
1403 return new SubList<>(this, fromIndex, toIndex);
1404 }
1405
1406 private void rangeCheckForAdd(int index) {
1407 if (index < 0 || index > this.size)
1408 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1409 }
1410
1411 private String outOfBoundsMsg(int index) {
1412 return "Index: "+index+", Size: "+this.size;
1413 }
1414
1415 private void checkForComodification() {
1416 if (root.modCount != modCount)
1417 throw new ConcurrentModificationException();
1418 }
1419
1420 private void updateSizeAndModCount(int sizeChange) {
1421 SubList<E> slist = this;
1422 do {
1423 slist.size += sizeChange;
1424 slist.modCount = root.modCount;
1425 slist = slist.parent;
1426 } while (slist != null);
1427 }
1428
1429 public Spliterator<E> spliterator() {
1430 checkForComodification();
1431
1432 // ArrayListSpliterator not used here due to late-binding
1433 return new Spliterator<E>() {
1434 private int index = offset; // current index, modified on advance/split
1435 private int fence = -1; // -1 until used; then one past last index
1436 private int expectedModCount; // initialized when fence set
1437
1438 private int getFence() { // initialize fence to size on first use
1439 int hi; // (a specialized variant appears in method forEach)
1440 if ((hi = fence) < 0) {
1441 expectedModCount = modCount;
1442 hi = fence = offset + size;
1443 }
1444 return hi;
1445 }
1446
1447 public ArrayList<E>.ArrayListSpliterator trySplit() {
1448 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1449 // ArrayListSpliterator can be used here as the source is already bound
1450 return (lo >= mid) ? null : // divide range in half unless too small
1451 root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
1452 }
1453
1454 public boolean tryAdvance(Consumer<? super E> action) {
1455 Objects.requireNonNull(action);
1456 int hi = getFence(), i = index;
1457 if (i < hi) {
1458 index = i + 1;
1459 @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
1460 action.accept(e);
1461 if (root.modCount != expectedModCount)
1462 throw new ConcurrentModificationException();
1463 return true;
1464 }
1465 return false;
1466 }
1467
1468 public void forEachRemaining(Consumer<? super E> action) {
1469 Objects.requireNonNull(action);
1470 int i, hi, mc; // hoist accesses and checks from loop
1471 ArrayList<E> lst = root;
1472 Object[] a;
1473 if ((a = lst.elementData) != null) {
1474 if ((hi = fence) < 0) {
1475 mc = modCount;
1476 hi = offset + size;
1477 }
1478 else
1479 mc = expectedModCount;
1480 if ((i = index) >= 0 && (index = hi) <= a.length) {
1481 for (; i < hi; ++i) {
1482 @SuppressWarnings("unchecked") E e = (E) a[i];
1483 action.accept(e);
1484 }
1485 if (lst.modCount == mc)
1486 return;
1487 }
1488 }
1489 throw new ConcurrentModificationException();
1490 }
1491
1492 public long estimateSize() {
1493 return getFence() - index;
1494 }
1495
1496 public int characteristics() {
1497 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1498 }
1499 };
1500 }
1501 }
1502
1503 /**
1504 * @throws NullPointerException {@inheritDoc}
1505 */
1506 @Override
1507 public void forEach(Consumer<? super E> action) {
1508 Objects.requireNonNull(action);
1509 final int expectedModCount = modCount;
1510 final Object[] es = elementData;
1511 final int size = this.size;
1512 for (int i = 0; modCount == expectedModCount && i < size; i++)
1513 action.accept(elementAt(es, i));
1514 if (modCount != expectedModCount)
1515 throw new ConcurrentModificationException();
1516 }
1517
1518 /**
1519 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1520 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1521 * list.
1522 *
1523 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1524 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1525 * Overriding implementations should document the reporting of additional
1526 * characteristic values.
1527 *
1528 * @return a {@code Spliterator} over the elements in this list
1529 * @since 1.8
1530 */
1531 @Override
1532 public Spliterator<E> spliterator() {
1533 return new ArrayListSpliterator(0, -1, 0);
1534 }
1535
1536 /** Index-based split-by-two, lazily initialized Spliterator */
1537 final class ArrayListSpliterator implements Spliterator<E> {
1538
1539 /*
1540 * If ArrayLists were immutable, or structurally immutable (no
1541 * adds, removes, etc), we could implement their spliterators
1542 * with Arrays.spliterator. Instead we detect as much
1543 * interference during traversal as practical without
1544 * sacrificing much performance. We rely primarily on
1545 * modCounts. These are not guaranteed to detect concurrency
1546 * violations, and are sometimes overly conservative about
1547 * within-thread interference, but detect enough problems to
1548 * be worthwhile in practice. To carry this out, we (1) lazily
1549 * initialize fence and expectedModCount until the latest
1550 * point that we need to commit to the state we are checking
1551 * against; thus improving precision. (This doesn't apply to
1552 * SubLists, that create spliterators with current non-lazy
1553 * values). (2) We perform only a single
1554 * ConcurrentModificationException check at the end of forEach
1555 * (the most performance-sensitive method). When using forEach
1556 * (as opposed to iterators), we can normally only detect
1557 * interference after actions, not before. Further
1558 * CME-triggering checks apply to all other possible
1559 * violations of assumptions for example null or too-small
1560 * elementData array given its size(), that could only have
1561 * occurred due to interference. This allows the inner loop
1562 * of forEach to run without any further checks, and
1563 * simplifies lambda-resolution. While this does entail a
1564 * number of checks, note that in the common case of
1565 * list.stream().forEach(a), no checks or other computation
1566 * occur anywhere other than inside forEach itself. The other
1567 * less-often-used methods cannot take advantage of most of
1568 * these streamlinings.
1569 */
1570
1571 private int index; // current index, modified on advance/split
1572 private int fence; // -1 until used; then one past last index
1573 private int expectedModCount; // initialized when fence set
1574
1575 /** Creates new spliterator covering the given range. */
1576 ArrayListSpliterator(int origin, int fence, int expectedModCount) {
1577 this.index = origin;
1578 this.fence = fence;
1579 this.expectedModCount = expectedModCount;
1580 }
1581
1582 private int getFence() { // initialize fence to size on first use
1583 int hi; // (a specialized variant appears in method forEach)
1584 if ((hi = fence) < 0) {
1585 expectedModCount = modCount;
1586 hi = fence = size;
1587 }
1588 return hi;
1589 }
1590
1591 public ArrayListSpliterator trySplit() {
1592 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1593 return (lo >= mid) ? null : // divide range in half unless too small
1594 new ArrayListSpliterator(lo, index = mid, expectedModCount);
1595 }
1596
1597 public boolean tryAdvance(Consumer<? super E> action) {
1598 if (action == null)
1599 throw new NullPointerException();
1600 int hi = getFence(), i = index;
1601 if (i < hi) {
1602 index = i + 1;
1603 @SuppressWarnings("unchecked") E e = (E)elementData[i];
1604 action.accept(e);
1605 if (modCount != expectedModCount)
1606 throw new ConcurrentModificationException();
1607 return true;
1608 }
1609 return false;
1610 }
1611
1612 public void forEachRemaining(Consumer<? super E> action) {
1613 int i, hi, mc; // hoist accesses and checks from loop
1614 Object[] a;
1615 if (action == null)
1616 throw new NullPointerException();
1617 if ((a = elementData) != null) {
1618 if ((hi = fence) < 0) {
1619 mc = modCount;
1620 hi = size;
1621 }
1622 else
1623 mc = expectedModCount;
1624 if ((i = index) >= 0 && (index = hi) <= a.length) {
1625 for (; i < hi; ++i) {
1626 @SuppressWarnings("unchecked") E e = (E) a[i];
1627 action.accept(e);
1628 }
1629 if (modCount == mc)
1630 return;
1631 }
1632 }
1633 throw new ConcurrentModificationException();
1634 }
1635
1636 public long estimateSize() {
1637 return getFence() - index;
1638 }
1639
1640 public int characteristics() {
1641 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1642 }
1643 }
1644
1645 // A tiny bit set implementation
1646
1647 private static long[] nBits(int n) {
1648 return new long[((n - 1) >> 6) + 1];
1649 }
1650 private static void setBit(long[] bits, int i) {
1651 bits[i >> 6] |= 1L << i;
1652 }
1653 private static boolean isClear(long[] bits, int i) {
1654 return (bits[i >> 6] & (1L << i)) == 0;
1655 }
1656
1657 /**
1658 * @throws NullPointerException {@inheritDoc}
1659 */
1660 @Override
1661 public boolean removeIf(Predicate<? super E> filter) {
1662 return removeIf(filter, 0, size);
1663 }
1664
1665 /**
1666 * Removes all elements satisfying the given predicate, from index
1667 * i (inclusive) to index end (exclusive).
1668 */
1669 boolean removeIf(Predicate<? super E> filter, int i, final int end) {
1670 Objects.requireNonNull(filter);
1671 int expectedModCount = modCount;
1672 final Object[] es = elementData;
1673 // Optimize for initial run of survivors
1674 for (; i < end && !filter.test(elementAt(es, i)); i++)
1675 ;
1676 // Tolerate predicates that reentrantly access the collection for
1677 // read (but writers still get CME), so traverse once to find
1678 // elements to delete, a second pass to physically expunge.
1679 if (i < end) {
1680 final int beg = i;
1681 final long[] deathRow = nBits(end - beg);
1682 deathRow[0] = 1L; // set bit 0
1683 for (i = beg + 1; i < end; i++)
1684 if (filter.test(elementAt(es, i)))
1685 setBit(deathRow, i - beg);
1686 if (modCount != expectedModCount)
1687 throw new ConcurrentModificationException();
1688 modCount++;
1689 int w = beg;
1690 for (i = beg; i < end; i++)
1691 if (isClear(deathRow, i - beg))
1692 es[w++] = es[i];
1693 shiftTailOverGap(es, w, end);
1694 return true;
1695 } else {
1696 if (modCount != expectedModCount)
1697 throw new ConcurrentModificationException();
1698 return false;
1699 }
1700 }
1701
1702 @Override
1703 public void replaceAll(UnaryOperator<E> operator) {
1704 replaceAllRange(operator, 0, size);
1705 // TODO(8203662): remove increment of modCount from ...
1706 modCount++;
1707 }
1708
1709 private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
1710 Objects.requireNonNull(operator);
1711 final int expectedModCount = modCount;
1712 final Object[] es = elementData;
1713 for (; modCount == expectedModCount && i < end; i++)
1714 es[i] = operator.apply(elementAt(es, i));
1715 if (modCount != expectedModCount)
1716 throw new ConcurrentModificationException();
1717 }
1718
1719 @Override
1720 @SuppressWarnings("unchecked")
1721 public void sort(Comparator<? super E> c) {
1722 final int expectedModCount = modCount;
1723 Arrays.sort((E[]) elementData, 0, size, c);
1724 if (modCount != expectedModCount)
1725 throw new ConcurrentModificationException();
1726 modCount++;
1727 }
1728
1729 void checkInvariants() {
1730 // assert size >= 0;
1731 // assert size == elementData.length || elementData[size] == null;
1732 }
1733 }