1 /*
2 * Copyright (c) 1997, 2019, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation. Oracle designates this
8 * particular file as subject to the "Classpath" exception as provided
9 * by Oracle in the LICENSE file that accompanied this code.
10 *
11 * This code is distributed in the hope that it will be useful, but WITHOUT
12 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
13 * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
14 * version 2 for more details (a copy is included in the LICENSE file that
15 * accompanied this code).
16 *
17 * You should have received a copy of the GNU General Public License version
18 * 2 along with this work; if not, write to the Free Software Foundation,
19 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
20 *
21 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
22 * or visit www.oracle.com if you need additional information or have any
23 * questions.
24 */
25
26 package java.util;
27
28 import java.util.function.Consumer;
29 import java.util.function.Predicate;
30 import java.util.function.UnaryOperator;
31 import jdk.internal.access.SharedSecrets;
32 import jdk.internal.util.ArraysSupport;
33
34 /**
35 * Resizable-array implementation of the {@code List} interface. Implements
36 * all optional list operations, and permits all elements, including
37 * {@code null}. In addition to implementing the {@code List} interface,
38 * this class provides methods to manipulate the size of the array that is
39 * used internally to store the list. (This class is roughly equivalent to
40 * {@code Vector}, except that it is unsynchronized.)
41 *
42 * <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},
43 * {@code iterator}, and {@code listIterator} operations run in constant
44 * time. The {@code add} operation runs in <i>amortized constant time</i>,
45 * that is, adding n elements requires O(n) time. All of the other operations
46 * run in linear time (roughly speaking). The constant factor is low compared
47 * to that for the {@code LinkedList} implementation.
48 *
49 * <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is
50 * the size of the array used to store the elements in the list. It is always
51 * at least as large as the list size. As elements are added to an ArrayList,
52 * its capacity grows automatically. The details of the growth policy are not
53 * specified beyond the fact that adding an element has constant amortized
54 * time cost.
55 *
56 * <p>An application can increase the capacity of an {@code ArrayList} instance
57 * before adding a large number of elements using the {@code ensureCapacity}
58 * operation. This may reduce the amount of incremental reallocation.
59 *
60 * <p><strong>Note that this implementation is not synchronized.</strong>
61 * If multiple threads access an {@code ArrayList} instance concurrently,
62 * and at least one of the threads modifies the list structurally, it
63 * <i>must</i> be synchronized externally. (A structural modification is
64 * any operation that adds or deletes one or more elements, or explicitly
65 * resizes the backing array; merely setting the value of an element is not
66 * a structural modification.) This is typically accomplished by
67 * synchronizing on some object that naturally encapsulates the list.
68 *
69 * If no such object exists, the list should be "wrapped" using the
70 * {@link Collections#synchronizedList Collections.synchronizedList}
71 * method. This is best done at creation time, to prevent accidental
72 * unsynchronized access to the list:<pre>
73 * List list = Collections.synchronizedList(new ArrayList(...));</pre>
74 *
75 * <p id="fail-fast">
76 * The iterators returned by this class's {@link #iterator() iterator} and
77 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:
78 * if the list is structurally modified at any time after the iterator is
79 * created, in any way except through the iterator's own
80 * {@link ListIterator#remove() remove} or
81 * {@link ListIterator#add(Object) add} methods, the iterator will throw a
82 * {@link ConcurrentModificationException}. Thus, in the face of
83 * concurrent modification, the iterator fails quickly and cleanly, rather
84 * than risking arbitrary, non-deterministic behavior at an undetermined
85 * time in the future.
86 *
87 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
88 * as it is, generally speaking, impossible to make any hard guarantees in the
89 * presence of unsynchronized concurrent modification. Fail-fast iterators
90 * throw {@code ConcurrentModificationException} on a best-effort basis.
91 * Therefore, it would be wrong to write a program that depended on this
92 * exception for its correctness: <i>the fail-fast behavior of iterators
93 * should be used only to detect bugs.</i>
94 *
95 * <p>This class is a member of the
96 * <a href="{@docRoot}/java.base/java/util/package-summary.html#CollectionsFramework">
97 * Java Collections Framework</a>.
98 *
99 * @param <E> the type of elements in this list
100 *
101 * @author Josh Bloch
102 * @author Neal Gafter
103 * @see Collection
104 * @see List
105 * @see LinkedList
106 * @see Vector
107 * @since 1.2
108 */
109 public class ArrayList<E> extends AbstractList<E>
110 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
111 {
112 private static final long serialVersionUID = 8683452581122892189L;
113
114 /**
115 * Default initial capacity.
116 */
117 private static final int DEFAULT_CAPACITY = 10;
118
119 /**
120 * Shared empty array instance used for empty instances.
121 */
122 private static final Object[] EMPTY_ELEMENTDATA = {};
123
124 /**
125 * Shared empty array instance used for default sized empty instances. We
126 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
127 * first element is added.
128 */
129 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
130
131 /**
132 * The array buffer into which the elements of the ArrayList are stored.
133 * The capacity of the ArrayList is the length of this array buffer. Any
134 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
135 * will be expanded to DEFAULT_CAPACITY when the first element is added.
136 */
137 transient Object[] elementData; // non-private to simplify nested class access
138
139 /**
140 * The size of the ArrayList (the number of elements it contains).
141 *
142 * @serial
143 */
144 private int size;
145
146 /**
147 * Constructs an empty list with the specified initial capacity.
148 *
149 * @param initialCapacity the initial capacity of the list
150 * @throws IllegalArgumentException if the specified initial capacity
151 * is negative
152 */
153 public ArrayList(int initialCapacity) {
154 if (initialCapacity > 0) {
155 this.elementData = new Object[initialCapacity];
156 } else if (initialCapacity == 0) {
157 this.elementData = EMPTY_ELEMENTDATA;
158 } else {
159 throw new IllegalArgumentException("Illegal Capacity: "+
160 initialCapacity);
161 }
162 }
163
164 /**
165 * Constructs an empty list with an initial capacity of ten.
166 */
167 public ArrayList() {
168 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
169 }
170
171 /**
172 * Constructs a list containing the elements of the specified
173 * collection, in the order they are returned by the collection's
174 * iterator.
175 *
176 * @param c the collection whose elements are to be placed into this list
177 * @throws NullPointerException if the specified collection is null
178 */
179 public ArrayList(Collection<? extends E> c) {
180 elementData = c.toArray();
181 if ((size = elementData.length) != 0) {
182 // defend against c.toArray (incorrectly) not returning Object[]
183 // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
184 if (elementData.getClass() != Object[].class)
185 elementData = Arrays.copyOf(elementData, size, Object[].class);
186 } else {
187 // replace with empty array.
188 this.elementData = EMPTY_ELEMENTDATA;
189 }
190 }
191
192 /**
193 * Trims the capacity of this {@code ArrayList} instance to be the
194 * list's current size. An application can use this operation to minimize
195 * the storage of an {@code ArrayList} instance.
196 */
197 public void trimToSize() {
198 modCount++;
199 if (size < elementData.length) {
200 elementData = (size == 0)
201 ? EMPTY_ELEMENTDATA
202 : Arrays.copyOf(elementData, size);
203 }
204 }
205
206 /**
207 * Increases the capacity of this {@code ArrayList} instance, if
208 * necessary, to ensure that it can hold at least the number of elements
209 * specified by the minimum capacity argument.
210 *
211 * @param minCapacity the desired minimum capacity
212 */
213 public void ensureCapacity(int minCapacity) {
214 if (minCapacity > elementData.length
215 && !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
216 && minCapacity <= DEFAULT_CAPACITY)) {
217 modCount++;
218 grow(minCapacity);
219 }
220 }
221
222 /**
223 * Increases the capacity to ensure that it can hold at least the
224 * number of elements specified by the minimum capacity argument.
225 *
226 * @param minCapacity the desired minimum capacity
227 * @throws OutOfMemoryError if minCapacity is less than zero
228 */
229 private Object[] grow(int minCapacity) {
230 int oldCapacity = elementData.length;
231 if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
232 int newCapacity = ArraysSupport.newLength(oldCapacity,
233 minCapacity - oldCapacity, /* minimum growth */
234 oldCapacity >> 1 /* preferred growth */);
235 return elementData = Arrays.copyOf(elementData, newCapacity);
236 } else {
237 return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];
238 }
239 }
240
241 private Object[] grow() {
242 return grow(size + 1);
243 }
244
245 /**
246 * Returns the number of elements in this list.
247 *
248 * @return the number of elements in this list
249 */
250 public int size() {
251 return size;
252 }
253
254 /**
255 * Returns {@code true} if this list contains no elements.
256 *
257 * @return {@code true} if this list contains no elements
258 */
259 public boolean isEmpty() {
260 return size == 0;
261 }
262
263 /**
264 * Returns {@code true} if this list contains the specified element.
265 * More formally, returns {@code true} if and only if this list contains
266 * at least one element {@code e} such that
267 * {@code Objects.equals(o, e)}.
268 *
269 * @param o element whose presence in this list is to be tested
270 * @return {@code true} if this list contains the specified element
271 */
272 public boolean contains(Object o) {
273 return indexOf(o) >= 0;
274 }
275
276 /**
277 * Returns the index of the first occurrence of the specified element
278 * in this list, or -1 if this list does not contain the element.
279 * More formally, returns the lowest index {@code i} such that
280 * {@code Objects.equals(o, get(i))},
281 * or -1 if there is no such index.
282 */
283 public int indexOf(Object o) {
284 return indexOfRange(o, 0, size);
285 }
286
287 int indexOfRange(Object o, int start, int end) {
288 Object[] es = elementData;
289 if (o == null) {
290 for (int i = start; i < end; i++) {
291 if (es[i] == null) {
292 return i;
293 }
294 }
295 } else {
296 for (int i = start; i < end; i++) {
297 if (o.equals(es[i])) {
298 return i;
299 }
300 }
301 }
302 return -1;
303 }
304
305 /**
306 * Returns the index of the last occurrence of the specified element
307 * in this list, or -1 if this list does not contain the element.
308 * More formally, returns the highest index {@code i} such that
309 * {@code Objects.equals(o, get(i))},
310 * or -1 if there is no such index.
311 */
312 public int lastIndexOf(Object o) {
313 return lastIndexOfRange(o, 0, size);
314 }
315
316 int lastIndexOfRange(Object o, int start, int end) {
317 Object[] es = elementData;
318 if (o == null) {
319 for (int i = end - 1; i >= start; i--) {
320 if (es[i] == null) {
321 return i;
322 }
323 }
324 } else {
325 for (int i = end - 1; i >= start; i--) {
326 if (o.equals(es[i])) {
327 return i;
328 }
329 }
330 }
331 return -1;
332 }
333
334 /**
335 * Returns a shallow copy of this {@code ArrayList} instance. (The
336 * elements themselves are not copied.)
337 *
338 * @return a clone of this {@code ArrayList} instance
339 */
340 public Object clone() {
341 try {
342 ArrayList<?> v = (ArrayList<?>) super.clone();
343 v.elementData = Arrays.copyOf(elementData, size);
344 v.modCount = 0;
345 return v;
346 } catch (CloneNotSupportedException e) {
347 // this shouldn't happen, since we are Cloneable
348 throw new InternalError(e);
349 }
350 }
351
352 /**
353 * Returns an array containing all of the elements in this list
354 * in proper sequence (from first to last element).
355 *
356 * <p>The returned array will be "safe" in that no references to it are
357 * maintained by this list. (In other words, this method must allocate
358 * a new array). The caller is thus free to modify the returned array.
359 *
360 * <p>This method acts as bridge between array-based and collection-based
361 * APIs.
362 *
363 * @return an array containing all of the elements in this list in
364 * proper sequence
365 */
366 public Object[] toArray() {
367 return Arrays.copyOf(elementData, size);
368 }
369
370 /**
371 * Returns an array containing all of the elements in this list in proper
372 * sequence (from first to last element); the runtime type of the returned
373 * array is that of the specified array. If the list fits in the
374 * specified array, it is returned therein. Otherwise, a new array is
375 * allocated with the runtime type of the specified array and the size of
376 * this list.
377 *
378 * <p>If the list fits in the specified array with room to spare
379 * (i.e., the array has more elements than the list), the element in
380 * the array immediately following the end of the collection is set to
381 * {@code null}. (This is useful in determining the length of the
382 * list <i>only</i> if the caller knows that the list does not contain
383 * any null elements.)
384 *
385 * @param a the array into which the elements of the list are to
386 * be stored, if it is big enough; otherwise, a new array of the
387 * same runtime type is allocated for this purpose.
388 * @return an array containing the elements of the list
389 * @throws ArrayStoreException if the runtime type of the specified array
390 * is not a supertype of the runtime type of every element in
391 * this list
392 * @throws NullPointerException if the specified array is null
393 */
394 @SuppressWarnings("unchecked")
395 public <T> T[] toArray(T[] a) {
396 if (a.length < size)
397 // Make a new array of a's runtime type, but my contents:
398 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
399 System.arraycopy(elementData, 0, a, 0, size);
400 if (a.length > size)
401 a[size] = null;
402 return a;
403 }
404
405 // Positional Access Operations
406
407 @SuppressWarnings("unchecked")
408 E elementData(int index) {
409 return (E) elementData[index];
410 }
411
412 @SuppressWarnings("unchecked")
413 static <E> E elementAt(Object[] es, int index) {
414 return (E) es[index];
415 }
416
417 /**
418 * Returns the element at the specified position in this list.
419 *
420 * @param index index of the element to return
421 * @return the element at the specified position in this list
422 * @throws IndexOutOfBoundsException {@inheritDoc}
423 */
424 public E get(int index) {
425 Objects.checkIndex(index, size);
426 return elementData(index);
427 }
428
429 /**
430 * Replaces the element at the specified position in this list with
431 * the specified element.
432 *
433 * @param index index of the element to replace
434 * @param element element to be stored at the specified position
435 * @return the element previously at the specified position
436 * @throws IndexOutOfBoundsException {@inheritDoc}
437 */
438 public E set(int index, E element) {
439 Objects.checkIndex(index, size);
440 E oldValue = elementData(index);
441 elementData[index] = element;
442 return oldValue;
443 }
444
445 /**
446 * This helper method split out from add(E) to keep method
447 * bytecode size under 35 (the -XX:MaxInlineSize default value),
448 * which helps when add(E) is called in a C1-compiled loop.
449 */
450 private void add(E e, Object[] elementData, int s) {
451 if (s == elementData.length)
452 elementData = grow();
453 elementData[s] = e;
454 size = s + 1;
455 }
456
457 /**
458 * Appends the specified element to the end of this list.
459 *
460 * @param e element to be appended to this list
461 * @return {@code true} (as specified by {@link Collection#add})
462 */
463 public boolean add(E e) {
464 modCount++;
465 add(e, elementData, size);
466 return true;
467 }
468
469 /**
470 * Inserts the specified element at the specified position in this
471 * list. Shifts the element currently at that position (if any) and
472 * any subsequent elements to the right (adds one to their indices).
473 *
474 * @param index index at which the specified element is to be inserted
475 * @param element element to be inserted
476 * @throws IndexOutOfBoundsException {@inheritDoc}
477 */
478 public void add(int index, E element) {
479 rangeCheckForAdd(index);
480 modCount++;
481 final int s;
482 Object[] elementData;
483 if ((s = size) == (elementData = this.elementData).length)
484 elementData = grow();
485 System.arraycopy(elementData, index,
486 elementData, index + 1,
487 s - index);
488 elementData[index] = element;
489 size = s + 1;
490 }
491
492 /**
493 * Removes the element at the specified position in this list.
494 * Shifts any subsequent elements to the left (subtracts one from their
495 * indices).
496 *
497 * @param index the index of the element to be removed
498 * @return the element that was removed from the list
499 * @throws IndexOutOfBoundsException {@inheritDoc}
500 */
501 public E remove(int index) {
502 Objects.checkIndex(index, size);
503 final Object[] es = elementData;
504
505 @SuppressWarnings("unchecked") E oldValue = (E) es[index];
506 fastRemove(es, index);
507
508 return oldValue;
509 }
510
511 /**
512 * {@inheritDoc}
513 */
514 public boolean equals(Object o) {
515 if (o == this) {
516 return true;
517 }
518
519 if (!(o instanceof List)) {
520 return false;
521 }
522
523 final int expectedModCount = modCount;
524 // ArrayList can be subclassed and given arbitrary behavior, but we can
525 // still deal with the common case where o is ArrayList precisely
526 boolean equal = (o.getClass() == ArrayList.class)
527 ? equalsArrayList((ArrayList<?>) o)
528 : equalsRange((List<?>) o, 0, size);
529
530 checkForComodification(expectedModCount);
531 return equal;
532 }
533
534 boolean equalsRange(List<?> other, int from, int to) {
535 final Object[] es = elementData;
536 if (to > es.length) {
537 throw new ConcurrentModificationException();
538 }
539 var oit = other.iterator();
540 for (; from < to; from++) {
541 if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {
542 return false;
543 }
544 }
545 return !oit.hasNext();
546 }
547
548 private boolean equalsArrayList(ArrayList<?> other) {
549 final int otherModCount = other.modCount;
550 final int s = size;
551 boolean equal;
552 if (equal = (s == other.size)) {
553 final Object[] otherEs = other.elementData;
554 final Object[] es = elementData;
555 if (s > es.length || s > otherEs.length) {
556 throw new ConcurrentModificationException();
557 }
558 for (int i = 0; i < s; i++) {
559 if (!Objects.equals(es[i], otherEs[i])) {
560 equal = false;
561 break;
562 }
563 }
564 }
565 other.checkForComodification(otherModCount);
566 return equal;
567 }
568
569 private void checkForComodification(final int expectedModCount) {
570 if (modCount != expectedModCount) {
571 throw new ConcurrentModificationException();
572 }
573 }
574
575 /**
576 * {@inheritDoc}
577 */
578 public int hashCode() {
579 int expectedModCount = modCount;
580 int hash = hashCodeRange(0, size);
581 checkForComodification(expectedModCount);
582 return hash;
583 }
584
585 int hashCodeRange(int from, int to) {
586 final Object[] es = elementData;
587 if (to > es.length) {
588 throw new ConcurrentModificationException();
589 }
590 int hashCode = 1;
591 for (int i = from; i < to; i++) {
592 Object e = es[i];
593 hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());
594 }
595 return hashCode;
596 }
597
598 /**
599 * Removes the first occurrence of the specified element from this list,
600 * if it is present. If the list does not contain the element, it is
601 * unchanged. More formally, removes the element with the lowest index
602 * {@code i} such that
603 * {@code Objects.equals(o, get(i))}
604 * (if such an element exists). Returns {@code true} if this list
605 * contained the specified element (or equivalently, if this list
606 * changed as a result of the call).
607 *
608 * @param o element to be removed from this list, if present
609 * @return {@code true} if this list contained the specified element
610 */
611 public boolean remove(Object o) {
612 final Object[] es = elementData;
613 final int size = this.size;
614 int i = 0;
615 found: {
616 if (o == null) {
617 for (; i < size; i++)
618 if (es[i] == null)
619 break found;
620 } else {
621 for (; i < size; i++)
622 if (o.equals(es[i]))
623 break found;
624 }
625 return false;
626 }
627 fastRemove(es, i);
628 return true;
629 }
630
631 /**
632 * Private remove method that skips bounds checking and does not
633 * return the value removed.
634 */
635 private void fastRemove(Object[] es, int i) {
636 modCount++;
637 final int newSize;
638 if ((newSize = size - 1) > i)
639 System.arraycopy(es, i + 1, es, i, newSize - i);
640 es[size = newSize] = null;
641 }
642
643 /**
644 * Removes all of the elements from this list. The list will
645 * be empty after this call returns.
646 */
647 public void clear() {
648 modCount++;
649 final Object[] es = elementData;
650 for (int to = size, i = size = 0; i < to; i++)
651 es[i] = null;
652 }
653
654 /**
655 * Appends all of the elements in the specified collection to the end of
656 * this list, in the order that they are returned by the
657 * specified collection's Iterator. The behavior of this operation is
658 * undefined if the specified collection is modified while the operation
659 * is in progress. (This implies that the behavior of this call is
660 * undefined if the specified collection is this list, and this
661 * list is nonempty.)
662 *
663 * @param c collection containing elements to be added to this list
664 * @return {@code true} if this list changed as a result of the call
665 * @throws NullPointerException if the specified collection is null
666 */
667 public boolean addAll(Collection<? extends E> c) {
668 Object[] a = c.toArray();
669 modCount++;
670 int numNew = a.length;
671 if (numNew == 0)
672 return false;
673 Object[] elementData;
674 final int s;
675 if (numNew > (elementData = this.elementData).length - (s = size))
676 elementData = grow(s + numNew);
677 System.arraycopy(a, 0, elementData, s, numNew);
678 size = s + numNew;
679 return true;
680 }
681
682 /**
683 * Inserts all of the elements in the specified collection into this
684 * list, starting at the specified position. Shifts the element
685 * currently at that position (if any) and any subsequent elements to
686 * the right (increases their indices). The new elements will appear
687 * in the list in the order that they are returned by the
688 * specified collection's iterator.
689 *
690 * @param index index at which to insert the first element from the
691 * specified collection
692 * @param c collection containing elements to be added to this list
693 * @return {@code true} if this list changed as a result of the call
694 * @throws IndexOutOfBoundsException {@inheritDoc}
695 * @throws NullPointerException if the specified collection is null
696 */
697 public boolean addAll(int index, Collection<? extends E> c) {
698 rangeCheckForAdd(index);
699
700 Object[] a = c.toArray();
701 modCount++;
702 int numNew = a.length;
703 if (numNew == 0)
704 return false;
705 Object[] elementData;
706 final int s;
707 if (numNew > (elementData = this.elementData).length - (s = size))
708 elementData = grow(s + numNew);
709
710 int numMoved = s - index;
711 if (numMoved > 0)
712 System.arraycopy(elementData, index,
713 elementData, index + numNew,
714 numMoved);
715 System.arraycopy(a, 0, elementData, index, numNew);
716 size = s + numNew;
717 return true;
718 }
719
720 /**
721 * Removes from this list all of the elements whose index is between
722 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
723 * Shifts any succeeding elements to the left (reduces their index).
724 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
725 * (If {@code toIndex==fromIndex}, this operation has no effect.)
726 *
727 * @throws IndexOutOfBoundsException if {@code fromIndex} or
728 * {@code toIndex} is out of range
729 * ({@code fromIndex < 0 ||
730 * toIndex > size() ||
731 * toIndex < fromIndex})
732 */
733 protected void removeRange(int fromIndex, int toIndex) {
734 if (fromIndex > toIndex) {
735 throw new IndexOutOfBoundsException(
736 outOfBoundsMsg(fromIndex, toIndex));
737 }
738 modCount++;
739 shiftTailOverGap(elementData, fromIndex, toIndex);
740 }
741
742 /** Erases the gap from lo to hi, by sliding down following elements. */
743 private void shiftTailOverGap(Object[] es, int lo, int hi) {
744 System.arraycopy(es, hi, es, lo, size - hi);
745 for (int to = size, i = (size -= hi - lo); i < to; i++)
746 es[i] = null;
747 }
748
749 /**
750 * A version of rangeCheck used by add and addAll.
751 */
752 private void rangeCheckForAdd(int index) {
753 if (index > size || index < 0)
754 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
755 }
756
757 /**
758 * Constructs an IndexOutOfBoundsException detail message.
759 * Of the many possible refactorings of the error handling code,
760 * this "outlining" performs best with both server and client VMs.
761 */
762 private String outOfBoundsMsg(int index) {
763 return "Index: "+index+", Size: "+size;
764 }
765
766 /**
767 * A version used in checking (fromIndex > toIndex) condition
768 */
769 private static String outOfBoundsMsg(int fromIndex, int toIndex) {
770 return "From Index: " + fromIndex + " > To Index: " + toIndex;
771 }
772
773 /**
774 * Removes from this list all of its elements that are contained in the
775 * specified collection.
776 *
777 * @param c collection containing elements to be removed from this list
778 * @return {@code true} if this list changed as a result of the call
779 * @throws ClassCastException if the class of an element of this list
780 * is incompatible with the specified collection
781 * (<a href="Collection.html#optional-restrictions">optional</a>)
782 * @throws NullPointerException if this list contains a null element and the
783 * specified collection does not permit null elements
784 * (<a href="Collection.html#optional-restrictions">optional</a>),
785 * or if the specified collection is null
786 * @see Collection#contains(Object)
787 */
788 public boolean removeAll(Collection<?> c) {
789 return batchRemove(c, false, 0, size);
790 }
791
792 /**
793 * Retains only the elements in this list that are contained in the
794 * specified collection. In other words, removes from this list all
795 * of its elements that are not contained in the specified collection.
796 *
797 * @param c collection containing elements to be retained in this list
798 * @return {@code true} if this list changed as a result of the call
799 * @throws ClassCastException if the class of an element of this list
800 * is incompatible with the specified collection
801 * (<a href="Collection.html#optional-restrictions">optional</a>)
802 * @throws NullPointerException if this list contains a null element and the
803 * specified collection does not permit null elements
804 * (<a href="Collection.html#optional-restrictions">optional</a>),
805 * or if the specified collection is null
806 * @see Collection#contains(Object)
807 */
808 public boolean retainAll(Collection<?> c) {
809 return batchRemove(c, true, 0, size);
810 }
811
812 boolean batchRemove(Collection<?> c, boolean complement,
813 final int from, final int end) {
814 Objects.requireNonNull(c);
815 final Object[] es = elementData;
816 int r;
817 // Optimize for initial run of survivors
818 for (r = from;; r++) {
819 if (r == end)
820 return false;
821 if (c.contains(es[r]) != complement)
822 break;
823 }
824 int w = r++;
825 try {
826 for (Object e; r < end; r++)
827 if (c.contains(e = es[r]) == complement)
828 es[w++] = e;
829 } catch (Throwable ex) {
830 // Preserve behavioral compatibility with AbstractCollection,
831 // even if c.contains() throws.
832 System.arraycopy(es, r, es, w, end - r);
833 w += end - r;
834 throw ex;
835 } finally {
836 modCount += end - w;
837 shiftTailOverGap(es, w, end);
838 }
839 return true;
840 }
841
842 /**
843 * Saves the state of the {@code ArrayList} instance to a stream
844 * (that is, serializes it).
845 *
846 * @param s the stream
847 * @throws java.io.IOException if an I/O error occurs
848 * @serialData The length of the array backing the {@code ArrayList}
849 * instance is emitted (int), followed by all of its elements
850 * (each an {@code Object}) in the proper order.
851 */
852 private void writeObject(java.io.ObjectOutputStream s)
853 throws java.io.IOException {
854 // Write out element count, and any hidden stuff
855 int expectedModCount = modCount;
856 s.defaultWriteObject();
857
858 // Write out size as capacity for behavioral compatibility with clone()
859 s.writeInt(size);
860
861 // Write out all elements in the proper order.
862 for (int i=0; i<size; i++) {
863 s.writeObject(elementData[i]);
864 }
865
866 if (modCount != expectedModCount) {
867 throw new ConcurrentModificationException();
868 }
869 }
870
871 /**
872 * Reconstitutes the {@code ArrayList} instance from a stream (that is,
873 * deserializes it).
874 * @param s the stream
875 * @throws ClassNotFoundException if the class of a serialized object
876 * could not be found
877 * @throws java.io.IOException if an I/O error occurs
878 */
879 private void readObject(java.io.ObjectInputStream s)
880 throws java.io.IOException, ClassNotFoundException {
881
882 // Read in size, and any hidden stuff
883 s.defaultReadObject();
884
885 // Read in capacity
886 s.readInt(); // ignored
887
888 if (size > 0) {
889 // like clone(), allocate array based upon size not capacity
890 SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);
891 Object[] elements = new Object[size];
892
893 // Read in all elements in the proper order.
894 for (int i = 0; i < size; i++) {
895 elements[i] = s.readObject();
896 }
897
898 elementData = elements;
899 } else if (size == 0) {
900 elementData = EMPTY_ELEMENTDATA;
901 } else {
902 throw new java.io.InvalidObjectException("Invalid size: " + size);
903 }
904 }
905
906 /**
907 * Returns a list iterator over the elements in this list (in proper
908 * sequence), starting at the specified position in the list.
909 * The specified index indicates the first element that would be
910 * returned by an initial call to {@link ListIterator#next next}.
911 * An initial call to {@link ListIterator#previous previous} would
912 * return the element with the specified index minus one.
913 *
914 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
915 *
916 * @throws IndexOutOfBoundsException {@inheritDoc}
917 */
918 public ListIterator<E> listIterator(int index) {
919 rangeCheckForAdd(index);
920 return new ListItr(index);
921 }
922
923 /**
924 * Returns a list iterator over the elements in this list (in proper
925 * sequence).
926 *
927 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
928 *
929 * @see #listIterator(int)
930 */
931 public ListIterator<E> listIterator() {
932 return new ListItr(0);
933 }
934
935 /**
936 * Returns an iterator over the elements in this list in proper sequence.
937 *
938 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
939 *
940 * @return an iterator over the elements in this list in proper sequence
941 */
942 public Iterator<E> iterator() {
943 return new Itr();
944 }
945
946 /**
947 * An optimized version of AbstractList.Itr
948 */
949 private class Itr implements Iterator<E> {
950 int cursor; // index of next element to return
951 int lastRet = -1; // index of last element returned; -1 if no such
952 int expectedModCount = modCount;
953
954 // prevent creating a synthetic constructor
955 Itr() {}
956
957 public boolean hasNext() {
958 return cursor != size;
959 }
960
961 @SuppressWarnings("unchecked")
962 public E next() {
963 checkForComodification();
964 int i = cursor;
965 if (i >= size)
966 throw new NoSuchElementException();
967 Object[] elementData = ArrayList.this.elementData;
968 if (i >= elementData.length)
969 throw new ConcurrentModificationException();
970 cursor = i + 1;
971 return (E) elementData[lastRet = i];
972 }
973
974 public void remove() {
975 if (lastRet < 0)
976 throw new IllegalStateException();
977 checkForComodification();
978
979 try {
980 ArrayList.this.remove(lastRet);
981 cursor = lastRet;
982 lastRet = -1;
983 expectedModCount = modCount;
984 } catch (IndexOutOfBoundsException ex) {
985 throw new ConcurrentModificationException();
986 }
987 }
988
989 @Override
990 public void forEachRemaining(Consumer<? super E> action) {
991 Objects.requireNonNull(action);
992 final int size = ArrayList.this.size;
993 int i = cursor;
994 if (i < size) {
995 final Object[] es = elementData;
996 if (i >= es.length)
997 throw new ConcurrentModificationException();
998 for (; i < size && modCount == expectedModCount; i++)
999 action.accept(elementAt(es, i));
1000 // update once at end to reduce heap write traffic
1001 cursor = i;
1002 lastRet = i - 1;
1003 checkForComodification();
1004 }
1005 }
1006
1007 final void checkForComodification() {
1008 if (modCount != expectedModCount)
1009 throw new ConcurrentModificationException();
1010 }
1011 }
1012
1013 /**
1014 * An optimized version of AbstractList.ListItr
1015 */
1016 private class ListItr extends Itr implements ListIterator<E> {
1017 ListItr(int index) {
1018 super();
1019 cursor = index;
1020 }
1021
1022 public boolean hasPrevious() {
1023 return cursor != 0;
1024 }
1025
1026 public int nextIndex() {
1027 return cursor;
1028 }
1029
1030 public int previousIndex() {
1031 return cursor - 1;
1032 }
1033
1034 @SuppressWarnings("unchecked")
1035 public E previous() {
1036 checkForComodification();
1037 int i = cursor - 1;
1038 if (i < 0)
1039 throw new NoSuchElementException();
1040 Object[] elementData = ArrayList.this.elementData;
1041 if (i >= elementData.length)
1042 throw new ConcurrentModificationException();
1043 cursor = i;
1044 return (E) elementData[lastRet = i];
1045 }
1046
1047 public void set(E e) {
1048 if (lastRet < 0)
1049 throw new IllegalStateException();
1050 checkForComodification();
1051
1052 try {
1053 ArrayList.this.set(lastRet, e);
1054 } catch (IndexOutOfBoundsException ex) {
1055 throw new ConcurrentModificationException();
1056 }
1057 }
1058
1059 public void add(E e) {
1060 checkForComodification();
1061
1062 try {
1063 int i = cursor;
1064 ArrayList.this.add(i, e);
1065 cursor = i + 1;
1066 lastRet = -1;
1067 expectedModCount = modCount;
1068 } catch (IndexOutOfBoundsException ex) {
1069 throw new ConcurrentModificationException();
1070 }
1071 }
1072 }
1073
1074 /**
1075 * Returns a view of the portion of this list between the specified
1076 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
1077 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
1078 * empty.) The returned list is backed by this list, so non-structural
1079 * changes in the returned list are reflected in this list, and vice-versa.
1080 * The returned list supports all of the optional list operations.
1081 *
1082 * <p>This method eliminates the need for explicit range operations (of
1083 * the sort that commonly exist for arrays). Any operation that expects
1084 * a list can be used as a range operation by passing a subList view
1085 * instead of a whole list. For example, the following idiom
1086 * removes a range of elements from a list:
1087 * <pre>
1088 * list.subList(from, to).clear();
1089 * </pre>
1090 * Similar idioms may be constructed for {@link #indexOf(Object)} and
1091 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
1092 * {@link Collections} class can be applied to a subList.
1093 *
1094 * <p>The semantics of the list returned by this method become undefined if
1095 * the backing list (i.e., this list) is <i>structurally modified</i> in
1096 * any way other than via the returned list. (Structural modifications are
1097 * those that change the size of this list, or otherwise perturb it in such
1098 * a fashion that iterations in progress may yield incorrect results.)
1099 *
1100 * @throws IndexOutOfBoundsException {@inheritDoc}
1101 * @throws IllegalArgumentException {@inheritDoc}
1102 */
1103 public List<E> subList(int fromIndex, int toIndex) {
1104 subListRangeCheck(fromIndex, toIndex, size);
1105 return new SubList<>(this, fromIndex, toIndex);
1106 }
1107
1108 private static class SubList<E> extends AbstractList<E> implements RandomAccess {
1109 private final ArrayList<E> root;
1110 private final SubList<E> parent;
1111 private final int offset;
1112 private int size;
1113
1114 /**
1115 * Constructs a sublist of an arbitrary ArrayList.
1116 */
1117 public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
1118 this.root = root;
1119 this.parent = null;
1120 this.offset = fromIndex;
1121 this.size = toIndex - fromIndex;
1122 this.modCount = root.modCount;
1123 }
1124
1125 /**
1126 * Constructs a sublist of another SubList.
1127 */
1128 private SubList(SubList<E> parent, int fromIndex, int toIndex) {
1129 this.root = parent.root;
1130 this.parent = parent;
1131 this.offset = parent.offset + fromIndex;
1132 this.size = toIndex - fromIndex;
1133 this.modCount = root.modCount;
1134 }
1135
1136 public E set(int index, E element) {
1137 Objects.checkIndex(index, size);
1138 checkForComodification();
1139 E oldValue = root.elementData(offset + index);
1140 root.elementData[offset + index] = element;
1141 return oldValue;
1142 }
1143
1144 public E get(int index) {
1145 Objects.checkIndex(index, size);
1146 checkForComodification();
1147 return root.elementData(offset + index);
1148 }
1149
1150 public int size() {
1151 checkForComodification();
1152 return size;
1153 }
1154
1155 public void add(int index, E element) {
1156 rangeCheckForAdd(index);
1157 checkForComodification();
1158 root.add(offset + index, element);
1159 updateSizeAndModCount(1);
1160 }
1161
1162 public E remove(int index) {
1163 Objects.checkIndex(index, size);
1164 checkForComodification();
1165 E result = root.remove(offset + index);
1166 updateSizeAndModCount(-1);
1167 return result;
1168 }
1169
1170 protected void removeRange(int fromIndex, int toIndex) {
1171 checkForComodification();
1172 root.removeRange(offset + fromIndex, offset + toIndex);
1173 updateSizeAndModCount(fromIndex - toIndex);
1174 }
1175
1176 public boolean addAll(Collection<? extends E> c) {
1177 return addAll(this.size, c);
1178 }
1179
1180 public boolean addAll(int index, Collection<? extends E> c) {
1181 rangeCheckForAdd(index);
1182 int cSize = c.size();
1183 if (cSize==0)
1184 return false;
1185 checkForComodification();
1186 root.addAll(offset + index, c);
1187 updateSizeAndModCount(cSize);
1188 return true;
1189 }
1190
1191 public void replaceAll(UnaryOperator<E> operator) {
1192 root.replaceAllRange(operator, offset, offset + size);
1193 }
1194
1195 public boolean removeAll(Collection<?> c) {
1196 return batchRemove(c, false);
1197 }
1198
1199 public boolean retainAll(Collection<?> c) {
1200 return batchRemove(c, true);
1201 }
1202
1203 private boolean batchRemove(Collection<?> c, boolean complement) {
1204 checkForComodification();
1205 int oldSize = root.size;
1206 boolean modified =
1207 root.batchRemove(c, complement, offset, offset + size);
1208 if (modified)
1209 updateSizeAndModCount(root.size - oldSize);
1210 return modified;
1211 }
1212
1213 public boolean removeIf(Predicate<? super E> filter) {
1214 checkForComodification();
1215 int oldSize = root.size;
1216 boolean modified = root.removeIf(filter, offset, offset + size);
1217 if (modified)
1218 updateSizeAndModCount(root.size - oldSize);
1219 return modified;
1220 }
1221
1222 public Object[] toArray() {
1223 checkForComodification();
1224 return Arrays.copyOfRange(root.elementData, offset, offset + size);
1225 }
1226
1227 @SuppressWarnings("unchecked")
1228 public <T> T[] toArray(T[] a) {
1229 checkForComodification();
1230 if (a.length < size)
1231 return (T[]) Arrays.copyOfRange(
1232 root.elementData, offset, offset + size, a.getClass());
1233 System.arraycopy(root.elementData, offset, a, 0, size);
1234 if (a.length > size)
1235 a[size] = null;
1236 return a;
1237 }
1238
1239 public boolean equals(Object o) {
1240 if (o == this) {
1241 return true;
1242 }
1243
1244 if (!(o instanceof List)) {
1245 return false;
1246 }
1247
1248 boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
1249 checkForComodification();
1250 return equal;
1251 }
1252
1253 public int hashCode() {
1254 int hash = root.hashCodeRange(offset, offset + size);
1255 checkForComodification();
1256 return hash;
1257 }
1258
1259 public int indexOf(Object o) {
1260 int index = root.indexOfRange(o, offset, offset + size);
1261 checkForComodification();
1262 return index >= 0 ? index - offset : -1;
1263 }
1264
1265 public int lastIndexOf(Object o) {
1266 int index = root.lastIndexOfRange(o, offset, offset + size);
1267 checkForComodification();
1268 return index >= 0 ? index - offset : -1;
1269 }
1270
1271 public boolean contains(Object o) {
1272 return indexOf(o) >= 0;
1273 }
1274
1275 public Iterator<E> iterator() {
1276 return listIterator();
1277 }
1278
1279 public ListIterator<E> listIterator(int index) {
1280 checkForComodification();
1281 rangeCheckForAdd(index);
1282
1283 return new ListIterator<E>() {
1284 int cursor = index;
1285 int lastRet = -1;
1286 int expectedModCount = root.modCount;
1287
1288 public boolean hasNext() {
1289 return cursor != SubList.this.size;
1290 }
1291
1292 @SuppressWarnings("unchecked")
1293 public E next() {
1294 checkForComodification();
1295 int i = cursor;
1296 if (i >= SubList.this.size)
1297 throw new NoSuchElementException();
1298 Object[] elementData = root.elementData;
1299 if (offset + i >= elementData.length)
1300 throw new ConcurrentModificationException();
1301 cursor = i + 1;
1302 return (E) elementData[offset + (lastRet = i)];
1303 }
1304
1305 public boolean hasPrevious() {
1306 return cursor != 0;
1307 }
1308
1309 @SuppressWarnings("unchecked")
1310 public E previous() {
1311 checkForComodification();
1312 int i = cursor - 1;
1313 if (i < 0)
1314 throw new NoSuchElementException();
1315 Object[] elementData = root.elementData;
1316 if (offset + i >= elementData.length)
1317 throw new ConcurrentModificationException();
1318 cursor = i;
1319 return (E) elementData[offset + (lastRet = i)];
1320 }
1321
1322 public void forEachRemaining(Consumer<? super E> action) {
1323 Objects.requireNonNull(action);
1324 final int size = SubList.this.size;
1325 int i = cursor;
1326 if (i < size) {
1327 final Object[] es = root.elementData;
1328 if (offset + i >= es.length)
1329 throw new ConcurrentModificationException();
1330 for (; i < size && modCount == expectedModCount; i++)
1331 action.accept(elementAt(es, offset + i));
1332 // update once at end to reduce heap write traffic
1333 cursor = i;
1334 lastRet = i - 1;
1335 checkForComodification();
1336 }
1337 }
1338
1339 public int nextIndex() {
1340 return cursor;
1341 }
1342
1343 public int previousIndex() {
1344 return cursor - 1;
1345 }
1346
1347 public void remove() {
1348 if (lastRet < 0)
1349 throw new IllegalStateException();
1350 checkForComodification();
1351
1352 try {
1353 SubList.this.remove(lastRet);
1354 cursor = lastRet;
1355 lastRet = -1;
1356 expectedModCount = root.modCount;
1357 } catch (IndexOutOfBoundsException ex) {
1358 throw new ConcurrentModificationException();
1359 }
1360 }
1361
1362 public void set(E e) {
1363 if (lastRet < 0)
1364 throw new IllegalStateException();
1365 checkForComodification();
1366
1367 try {
1368 root.set(offset + lastRet, e);
1369 } catch (IndexOutOfBoundsException ex) {
1370 throw new ConcurrentModificationException();
1371 }
1372 }
1373
1374 public void add(E e) {
1375 checkForComodification();
1376
1377 try {
1378 int i = cursor;
1379 SubList.this.add(i, e);
1380 cursor = i + 1;
1381 lastRet = -1;
1382 expectedModCount = root.modCount;
1383 } catch (IndexOutOfBoundsException ex) {
1384 throw new ConcurrentModificationException();
1385 }
1386 }
1387
1388 final void checkForComodification() {
1389 if (root.modCount != expectedModCount)
1390 throw new ConcurrentModificationException();
1391 }
1392 };
1393 }
1394
1395 public List<E> subList(int fromIndex, int toIndex) {
1396 subListRangeCheck(fromIndex, toIndex, size);
1397 return new SubList<>(this, fromIndex, toIndex);
1398 }
1399
1400 private void rangeCheckForAdd(int index) {
1401 if (index < 0 || index > this.size)
1402 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1403 }
1404
1405 private String outOfBoundsMsg(int index) {
1406 return "Index: "+index+", Size: "+this.size;
1407 }
1408
1409 private void checkForComodification() {
1410 if (root.modCount != modCount)
1411 throw new ConcurrentModificationException();
1412 }
1413
1414 private void updateSizeAndModCount(int sizeChange) {
1415 SubList<E> slist = this;
1416 do {
1417 slist.size += sizeChange;
1418 slist.modCount = root.modCount;
1419 slist = slist.parent;
1420 } while (slist != null);
1421 }
1422
1423 public Spliterator<E> spliterator() {
1424 checkForComodification();
1425
1426 // ArrayListSpliterator not used here due to late-binding
1427 return new Spliterator<E>() {
1428 private int index = offset; // current index, modified on advance/split
1429 private int fence = -1; // -1 until used; then one past last index
1430 private int expectedModCount; // initialized when fence set
1431
1432 private int getFence() { // initialize fence to size on first use
1433 int hi; // (a specialized variant appears in method forEach)
1434 if ((hi = fence) < 0) {
1435 expectedModCount = modCount;
1436 hi = fence = offset + size;
1437 }
1438 return hi;
1439 }
1440
1441 public ArrayList<E>.ArrayListSpliterator trySplit() {
1442 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1443 // ArrayListSpliterator can be used here as the source is already bound
1444 return (lo >= mid) ? null : // divide range in half unless too small
1445 root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
1446 }
1447
1448 public boolean tryAdvance(Consumer<? super E> action) {
1449 Objects.requireNonNull(action);
1450 int hi = getFence(), i = index;
1451 if (i < hi) {
1452 index = i + 1;
1453 @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
1454 action.accept(e);
1455 if (root.modCount != expectedModCount)
1456 throw new ConcurrentModificationException();
1457 return true;
1458 }
1459 return false;
1460 }
1461
1462 public void forEachRemaining(Consumer<? super E> action) {
1463 Objects.requireNonNull(action);
1464 int i, hi, mc; // hoist accesses and checks from loop
1465 ArrayList<E> lst = root;
1466 Object[] a;
1467 if ((a = lst.elementData) != null) {
1468 if ((hi = fence) < 0) {
1469 mc = modCount;
1470 hi = offset + size;
1471 }
1472 else
1473 mc = expectedModCount;
1474 if ((i = index) >= 0 && (index = hi) <= a.length) {
1475 for (; i < hi; ++i) {
1476 @SuppressWarnings("unchecked") E e = (E) a[i];
1477 action.accept(e);
1478 }
1479 if (lst.modCount == mc)
1480 return;
1481 }
1482 }
1483 throw new ConcurrentModificationException();
1484 }
1485
1486 public long estimateSize() {
1487 return getFence() - index;
1488 }
1489
1490 public int characteristics() {
1491 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1492 }
1493 };
1494 }
1495 }
1496
1497 /**
1498 * @throws NullPointerException {@inheritDoc}
1499 */
1500 @Override
1501 public void forEach(Consumer<? super E> action) {
1502 Objects.requireNonNull(action);
1503 final int expectedModCount = modCount;
1504 final Object[] es = elementData;
1505 final int size = this.size;
1506 for (int i = 0; modCount == expectedModCount && i < size; i++)
1507 action.accept(elementAt(es, i));
1508 if (modCount != expectedModCount)
1509 throw new ConcurrentModificationException();
1510 }
1511
1512 /**
1513 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1514 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1515 * list.
1516 *
1517 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1518 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1519 * Overriding implementations should document the reporting of additional
1520 * characteristic values.
1521 *
1522 * @return a {@code Spliterator} over the elements in this list
1523 * @since 1.8
1524 */
1525 @Override
1526 public Spliterator<E> spliterator() {
1527 return new ArrayListSpliterator(0, -1, 0);
1528 }
1529
1530 /** Index-based split-by-two, lazily initialized Spliterator */
1531 final class ArrayListSpliterator implements Spliterator<E> {
1532
1533 /*
1534 * If ArrayLists were immutable, or structurally immutable (no
1535 * adds, removes, etc), we could implement their spliterators
1536 * with Arrays.spliterator. Instead we detect as much
1537 * interference during traversal as practical without
1538 * sacrificing much performance. We rely primarily on
1539 * modCounts. These are not guaranteed to detect concurrency
1540 * violations, and are sometimes overly conservative about
1541 * within-thread interference, but detect enough problems to
1542 * be worthwhile in practice. To carry this out, we (1) lazily
1543 * initialize fence and expectedModCount until the latest
1544 * point that we need to commit to the state we are checking
1545 * against; thus improving precision. (This doesn't apply to
1546 * SubLists, that create spliterators with current non-lazy
1547 * values). (2) We perform only a single
1548 * ConcurrentModificationException check at the end of forEach
1549 * (the most performance-sensitive method). When using forEach
1550 * (as opposed to iterators), we can normally only detect
1551 * interference after actions, not before. Further
1552 * CME-triggering checks apply to all other possible
1553 * violations of assumptions for example null or too-small
1554 * elementData array given its size(), that could only have
1555 * occurred due to interference. This allows the inner loop
1556 * of forEach to run without any further checks, and
1557 * simplifies lambda-resolution. While this does entail a
1558 * number of checks, note that in the common case of
1559 * list.stream().forEach(a), no checks or other computation
1560 * occur anywhere other than inside forEach itself. The other
1561 * less-often-used methods cannot take advantage of most of
1562 * these streamlinings.
1563 */
1564
1565 private int index; // current index, modified on advance/split
1566 private int fence; // -1 until used; then one past last index
1567 private int expectedModCount; // initialized when fence set
1568
1569 /** Creates new spliterator covering the given range. */
1570 ArrayListSpliterator(int origin, int fence, int expectedModCount) {
1571 this.index = origin;
1572 this.fence = fence;
1573 this.expectedModCount = expectedModCount;
1574 }
1575
1576 private int getFence() { // initialize fence to size on first use
1577 int hi; // (a specialized variant appears in method forEach)
1578 if ((hi = fence) < 0) {
1579 expectedModCount = modCount;
1580 hi = fence = size;
1581 }
1582 return hi;
1583 }
1584
1585 public ArrayListSpliterator trySplit() {
1586 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1587 return (lo >= mid) ? null : // divide range in half unless too small
1588 new ArrayListSpliterator(lo, index = mid, expectedModCount);
1589 }
1590
1591 public boolean tryAdvance(Consumer<? super E> action) {
1592 if (action == null)
1593 throw new NullPointerException();
1594 int hi = getFence(), i = index;
1595 if (i < hi) {
1596 index = i + 1;
1597 @SuppressWarnings("unchecked") E e = (E)elementData[i];
1598 action.accept(e);
1599 if (modCount != expectedModCount)
1600 throw new ConcurrentModificationException();
1601 return true;
1602 }
1603 return false;
1604 }
1605
1606 public void forEachRemaining(Consumer<? super E> action) {
1607 int i, hi, mc; // hoist accesses and checks from loop
1608 Object[] a;
1609 if (action == null)
1610 throw new NullPointerException();
1611 if ((a = elementData) != null) {
1612 if ((hi = fence) < 0) {
1613 mc = modCount;
1614 hi = size;
1615 }
1616 else
1617 mc = expectedModCount;
1618 if ((i = index) >= 0 && (index = hi) <= a.length) {
1619 for (; i < hi; ++i) {
1620 @SuppressWarnings("unchecked") E e = (E) a[i];
1621 action.accept(e);
1622 }
1623 if (modCount == mc)
1624 return;
1625 }
1626 }
1627 throw new ConcurrentModificationException();
1628 }
1629
1630 public long estimateSize() {
1631 return getFence() - index;
1632 }
1633
1634 public int characteristics() {
1635 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1636 }
1637 }
1638
1639 // A tiny bit set implementation
1640
1641 private static long[] nBits(int n) {
1642 return new long[((n - 1) >> 6) + 1];
1643 }
1644 private static void setBit(long[] bits, int i) {
1645 bits[i >> 6] |= 1L << i;
1646 }
1647 private static boolean isClear(long[] bits, int i) {
1648 return (bits[i >> 6] & (1L << i)) == 0;
1649 }
1650
1651 /**
1652 * @throws NullPointerException {@inheritDoc}
1653 */
1654 @Override
1655 public boolean removeIf(Predicate<? super E> filter) {
1656 return removeIf(filter, 0, size);
1657 }
1658
1659 /**
1660 * Removes all elements satisfying the given predicate, from index
1661 * i (inclusive) to index end (exclusive).
1662 */
1663 boolean removeIf(Predicate<? super E> filter, int i, final int end) {
1664 Objects.requireNonNull(filter);
1665 int expectedModCount = modCount;
1666 final Object[] es = elementData;
1667 // Optimize for initial run of survivors
1668 for (; i < end && !filter.test(elementAt(es, i)); i++)
1669 ;
1670 // Tolerate predicates that reentrantly access the collection for
1671 // read (but writers still get CME), so traverse once to find
1672 // elements to delete, a second pass to physically expunge.
1673 if (i < end) {
1674 final int beg = i;
1675 final long[] deathRow = nBits(end - beg);
1676 deathRow[0] = 1L; // set bit 0
1677 for (i = beg + 1; i < end; i++)
1678 if (filter.test(elementAt(es, i)))
1679 setBit(deathRow, i - beg);
1680 if (modCount != expectedModCount)
1681 throw new ConcurrentModificationException();
1682 modCount++;
1683 int w = beg;
1684 for (i = beg; i < end; i++)
1685 if (isClear(deathRow, i - beg))
1686 es[w++] = es[i];
1687 shiftTailOverGap(es, w, end);
1688 return true;
1689 } else {
1690 if (modCount != expectedModCount)
1691 throw new ConcurrentModificationException();
1692 return false;
1693 }
1694 }
1695
1696 @Override
1697 public void replaceAll(UnaryOperator<E> operator) {
1698 replaceAllRange(operator, 0, size);
1699 // TODO(8203662): remove increment of modCount from ...
1700 modCount++;
1701 }
1702
1703 private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
1704 Objects.requireNonNull(operator);
1705 final int expectedModCount = modCount;
1706 final Object[] es = elementData;
1707 for (; modCount == expectedModCount && i < end; i++)
1708 es[i] = operator.apply(elementAt(es, i));
1709 if (modCount != expectedModCount)
1710 throw new ConcurrentModificationException();
1711 }
1712
1713 @Override
1714 @SuppressWarnings("unchecked")
1715 public void sort(Comparator<? super E> c) {
1716 final int expectedModCount = modCount;
1717 Arrays.sort((E[]) elementData, 0, size, c);
1718 if (modCount != expectedModCount)
1719 throw new ConcurrentModificationException();
1720 modCount++;
1721 }
1722
1723 void checkInvariants() {
1724 // assert size >= 0;
1725 // assert size == elementData.length || elementData[size] == null;
1726 }
1727 }