1 /*
2 * Copyright (c) 1997, 2013, 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
32 /**
33 * Resizable-array implementation of the {@code List} interface. Implements
34 * all optional list operations, and permits all elements, including
35 * {@code null}. In addition to implementing the {@code List} interface,
36 * this class provides methods to manipulate the size of the array that is
37 * used internally to store the list. (This class is roughly equivalent to
38 * {@code Vector}, except that it is unsynchronized.)
39 *
40 * <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},
41 * {@code iterator}, and {@code listIterator} operations run in constant
42 * time. The {@code add} operation runs in <i>amortized constant time</i>,
43 * that is, adding n elements requires O(n) time. All of the other operations
44 * run in linear time (roughly speaking). The constant factor is low compared
45 * to that for the {@code LinkedList} implementation.
46 *
47 * <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is
48 * the size of the array used to store the elements in the list. It is always
49 * at least as large as the list size. As elements are added to an ArrayList,
50 * its capacity grows automatically. The details of the growth policy are not
51 * specified beyond the fact that adding an element has constant amortized
52 * time cost.
53 *
54 * <p>An application can increase the capacity of an {@code ArrayList} instance
55 * before adding a large number of elements using the {@code ensureCapacity}
56 * operation. This may reduce the amount of incremental reallocation.
57 *
58 * <p><strong>Note that this implementation is not synchronized.</strong>
59 * If multiple threads access an {@code ArrayList} instance concurrently,
60 * and at least one of the threads modifies the list structurally, it
61 * <i>must</i> be synchronized externally. (A structural modification is
62 * any operation that adds or deletes one or more elements, or explicitly
63 * resizes the backing array; merely setting the value of an element is not
64 * a structural modification.) This is typically accomplished by
65 * synchronizing on some object that naturally encapsulates the list.
66 *
67 * If no such object exists, the list should be "wrapped" using the
68 * {@link Collections#synchronizedList Collections.synchronizedList}
69 * method. This is best done at creation time, to prevent accidental
70 * unsynchronized access to the list:<pre>
71 * List list = Collections.synchronizedList(new ArrayList(...));</pre>
72 *
73 * <p><a name="fail-fast">
74 * The iterators returned by this class's {@link #iterator() iterator} and
75 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:</a>
76 * if the list is structurally modified at any time after the iterator is
77 * created, in any way except through the iterator's own
78 * {@link ListIterator#remove() remove} or
79 * {@link ListIterator#add(Object) add} methods, the iterator will throw a
80 * {@link ConcurrentModificationException}. Thus, in the face of
81 * concurrent modification, the iterator fails quickly and cleanly, rather
82 * than risking arbitrary, non-deterministic behavior at an undetermined
83 * time in the future.
84 *
85 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
86 * as it is, generally speaking, impossible to make any hard guarantees in the
87 * presence of unsynchronized concurrent modification. Fail-fast iterators
88 * throw {@code ConcurrentModificationException} on a best-effort basis.
89 * Therefore, it would be wrong to write a program that depended on this
90 * exception for its correctness: <i>the fail-fast behavior of iterators
91 * should be used only to detect bugs.</i>
92 *
93 * <p>This class is a member of the
94 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
95 * Java Collections Framework</a>.
96 *
97 * @param <E> the type of elements in this list
98 *
99 * @author Josh Bloch
100 * @author Neal Gafter
101 * @see Collection
102 * @see List
103 * @see LinkedList
104 * @see Vector
105 * @since 1.2
106 */
107
108 public class ArrayList<E> extends AbstractList<E>
109 implements List<E>, RandomAccess, Cloneable, java.io.Serializable
110 {
111 private static final long serialVersionUID = 8683452581122892189L;
112
113 /**
114 * Default initial capacity.
115 */
116 private static final int DEFAULT_CAPACITY = 10;
117
118 /**
119 * Shared empty array instance used for empty instances.
120 */
121 private static final Object[] EMPTY_ELEMENTDATA = {};
122
123 /**
124 * The array buffer into which the elements of the ArrayList are stored.
125 * The capacity of the ArrayList is the length of this array buffer. Any
126 * empty ArrayList with elementData == EMPTY_ELEMENTDATA will be expanded to
127 * DEFAULT_CAPACITY when the first element is added.
128 */
129 transient Object[] elementData; // non-private to simplify nested class access
130
131 /**
132 * The size of the ArrayList (the number of elements it contains).
133 *
134 * @serial
135 */
136 private int size;
137
138 /**
139 * Constructs an empty list with the specified initial capacity.
140 *
141 * @param initialCapacity the initial capacity of the list
142 * @throws IllegalArgumentException if the specified initial capacity
143 * is negative
144 */
145 public ArrayList(int initialCapacity) {
146 if (initialCapacity > 0) {
147 this.elementData = new Object[initialCapacity];
148 } else if (initialCapacity == 0) {
149 this.elementData = EMPTY_ELEMENTDATA;
150 } else {
151 throw new IllegalArgumentException("Illegal Capacity: "+
152 initialCapacity);
153 }
154 }
155
156 /**
157 * Constructs an empty list with an initial capacity of ten.
158 */
159 public ArrayList() {
160 this.elementData = EMPTY_ELEMENTDATA;
161 }
162
163 /**
164 * Constructs a list containing the elements of the specified
165 * collection, in the order they are returned by the collection's
166 * iterator.
167 *
168 * @param c the collection whose elements are to be placed into this list
169 * @throws NullPointerException if the specified collection is null
170 */
171 public ArrayList(Collection<? extends E> c) {
172 if (!c.isEmpty()) {
173 elementData = c.toArray();
174 size = elementData.length;
175 // c.toArray might (incorrectly) not return Object[] (see 6260652)
176 if (elementData.getClass() != Object[].class)
177 elementData = Arrays.copyOf(elementData, size, Object[].class);
178 } else {
179 this.elementData = EMPTY_ELEMENTDATA;
180 }
181 }
182
183 /**
184 * Trims the capacity of this {@code ArrayList} instance to be the
185 * list's current size. An application can use this operation to minimize
186 * the storage of an {@code ArrayList} instance.
187 */
188 public void trimToSize() {
189 modCount++;
190 if (size < elementData.length) {
191 elementData = Arrays.copyOf(elementData, size);
192 }
193 }
194
195 /**
196 * Increases the capacity of this {@code ArrayList} instance, if
197 * necessary, to ensure that it can hold at least the number of elements
198 * specified by the minimum capacity argument.
199 *
200 * @param minCapacity the desired minimum capacity
201 */
202 public void ensureCapacity(int minCapacity) {
203 int minExpand = (elementData != EMPTY_ELEMENTDATA)
204 // any size if real element table
205 ? 0
206 // larger than default for empty table. It's already supposed to be
207 // at default size.
208 : DEFAULT_CAPACITY;
209
210 if (minCapacity > minExpand) {
211 ensureExplicitCapacity(minCapacity);
212 }
213 }
214
215 private void ensureCapacityInternal(int minCapacity) {
216 if (elementData == EMPTY_ELEMENTDATA) {
217 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
218 }
219
220 ensureExplicitCapacity(minCapacity);
221 }
222
223 private void ensureExplicitCapacity(int minCapacity) {
224 modCount++;
225
226 // overflow-conscious code
227 if (minCapacity - elementData.length > 0)
228 grow(minCapacity);
229 }
230
231 /**
232 * The maximum size of array to allocate.
233 * Some VMs reserve some header words in an array.
234 * Attempts to allocate larger arrays may result in
235 * OutOfMemoryError: Requested array size exceeds VM limit
236 */
237 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
238
239 /**
240 * Increases the capacity to ensure that it can hold at least the
241 * number of elements specified by the minimum capacity argument.
242 *
243 * @param minCapacity the desired minimum capacity
244 */
245 private void grow(int minCapacity) {
246 // overflow-conscious code
247 int oldCapacity = elementData.length;
248 int newCapacity = oldCapacity + (oldCapacity >> 1);
249 if (newCapacity - minCapacity < 0)
250 newCapacity = minCapacity;
251 if (newCapacity - MAX_ARRAY_SIZE > 0)
252 newCapacity = hugeCapacity(minCapacity);
253 // minCapacity is usually close to size, so this is a win:
254 elementData = Arrays.copyOf(elementData, newCapacity);
255 }
256
257 private static int hugeCapacity(int minCapacity) {
258 if (minCapacity < 0) // overflow
259 throw new OutOfMemoryError();
260 return (minCapacity > MAX_ARRAY_SIZE) ?
261 Integer.MAX_VALUE :
262 MAX_ARRAY_SIZE;
263 }
264
265 /**
266 * Returns the number of elements in this list.
267 *
268 * @return the number of elements in this list
269 */
270 public int size() {
271 return size;
272 }
273
274 /**
275 * Returns {@code true} if this list contains no elements.
276 *
277 * @return {@code true} if this list contains no elements
278 */
279 public boolean isEmpty() {
280 return size == 0;
281 }
282
283 /**
284 * Returns {@code true} if this list contains the specified element.
285 * More formally, returns {@code true} if and only if this list contains
286 * at least one element {@code e} such that
287 * <tt>(o==null ? e==null : o.equals(e))</tt>.
288 *
289 * @param o element whose presence in this list is to be tested
290 * @return {@code true} if this list contains the specified element
291 */
292 public boolean contains(Object o) {
293 return indexOf(o) >= 0;
294 }
295
296 /**
297 * Returns the index of the first occurrence of the specified element
298 * in this list, or -1 if this list does not contain the element.
299 * More formally, returns the lowest index {@code i} such that
300 * {@code (o==null ? get(i)==null : o.equals(get(i)))},
301 * or -1 if there is no such index.
302 */
303 public int indexOf(Object o) {
304 if (o == null) {
305 for (int i = 0; i < size; i++)
306 if (elementData[i]==null)
307 return i;
308 } else {
309 for (int i = 0; i < size; i++)
310 if (o.equals(elementData[i]))
311 return i;
312 }
313 return -1;
314 }
315
316 /**
317 * Returns the index of the last occurrence of the specified element
318 * in this list, or -1 if this list does not contain the element.
319 * More formally, returns the highest index {@code i} such that
320 * {@code (o==null ? get(i)==null : o.equals(get(i)))},
321 * or -1 if there is no such index.
322 */
323 public int lastIndexOf(Object o) {
324 if (o == null) {
325 for (int i = size-1; i >= 0; i--)
326 if (elementData[i]==null)
327 return i;
328 } else {
329 for (int i = size-1; i >= 0; i--)
330 if (o.equals(elementData[i]))
331 return i;
332 }
333 return -1;
334 }
335
336 /**
337 * Returns a shallow copy of this {@code ArrayList} instance. (The
338 * elements themselves are not copied.)
339 *
340 * @return a clone of this {@code ArrayList} instance
341 */
342 public Object clone() {
343 try {
344 ArrayList<?> v = (ArrayList<?>) super.clone();
345 v.elementData = Arrays.copyOf(elementData, size);
346 v.modCount = 0;
347 return v;
348 } catch (CloneNotSupportedException e) {
349 // this shouldn't happen, since we are Cloneable
350 throw new InternalError(e);
351 }
352 }
353
354 /**
355 * Returns an array containing all of the elements in this list
356 * in proper sequence (from first to last element).
357 *
358 * <p>The returned array will be "safe" in that no references to it are
359 * maintained by this list. (In other words, this method must allocate
360 * a new array). The caller is thus free to modify the returned array.
361 *
362 * <p>This method acts as bridge between array-based and collection-based
363 * APIs.
364 *
365 * @return an array containing all of the elements in this list in
366 * proper sequence
367 */
368 public Object[] toArray() {
369 return Arrays.copyOf(elementData, size);
370 }
371
372 /**
373 * Returns an array containing all of the elements in this list in proper
374 * sequence (from first to last element); the runtime type of the returned
375 * array is that of the specified array. If the list fits in the
376 * specified array, it is returned therein. Otherwise, a new array is
377 * allocated with the runtime type of the specified array and the size of
378 * this list.
379 *
380 * <p>If the list fits in the specified array with room to spare
381 * (i.e., the array has more elements than the list), the element in
382 * the array immediately following the end of the collection is set to
383 * {@code null}. (This is useful in determining the length of the
384 * list <i>only</i> if the caller knows that the list does not contain
385 * any null elements.)
386 *
387 * @param a the array into which the elements of the list are to
388 * be stored, if it is big enough; otherwise, a new array of the
389 * same runtime type is allocated for this purpose.
390 * @return an array containing the elements of the list
391 * @throws ArrayStoreException if the runtime type of the specified array
392 * is not a supertype of the runtime type of every element in
393 * this list
394 * @throws NullPointerException if the specified array is null
395 */
396 @SuppressWarnings("unchecked")
397 public <T> T[] toArray(T[] a) {
398 if (a.length < size)
399 // Make a new array of a's runtime type, but my contents:
400 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
401 System.arraycopy(elementData, 0, a, 0, size);
402 if (a.length > size)
403 a[size] = null;
404 return a;
405 }
406
407 // Positional Access Operations
408
409 @SuppressWarnings("unchecked")
410 E elementData(int index) {
411 return (E) elementData[index];
412 }
413
414 /**
415 * Returns the element at the specified position in this list.
416 *
417 * @param index index of the element to return
418 * @return the element at the specified position in this list
419 * @throws IndexOutOfBoundsException {@inheritDoc}
420 */
421 public E get(int index) {
422 rangeCheck(index);
423
424 return elementData(index);
425 }
426
427 /**
428 * Replaces the element at the specified position in this list with
429 * the specified element.
430 *
431 * @param index index of the element to replace
432 * @param element element to be stored at the specified position
433 * @return the element previously at the specified position
434 * @throws IndexOutOfBoundsException {@inheritDoc}
435 */
436 public E set(int index, E element) {
437 rangeCheck(index);
438
439 E oldValue = elementData(index);
440 elementData[index] = element;
441 return oldValue;
442 }
443
444 /**
445 * Appends the specified element to the end of this list.
446 *
447 * @param e element to be appended to this list
448 * @return {@code true} (as specified by {@link Collection#add})
449 */
450 public boolean add(E e) {
451 ensureCapacityInternal(size + 1); // Increments modCount!!
452 elementData[size++] = e;
453 return true;
454 }
455
456 /**
457 * Inserts the specified element at the specified position in this
458 * list. Shifts the element currently at that position (if any) and
459 * any subsequent elements to the right (adds one to their indices).
460 *
461 * @param index index at which the specified element is to be inserted
462 * @param element element to be inserted
463 * @throws IndexOutOfBoundsException {@inheritDoc}
464 */
465 public void add(int index, E element) {
466 rangeCheckForAdd(index);
467
468 ensureCapacityInternal(size + 1); // Increments modCount!!
469 System.arraycopy(elementData, index, elementData, index + 1,
470 size - index);
471 elementData[index] = element;
472 size++;
473 }
474
475 /**
476 * Removes the element at the specified position in this list.
477 * Shifts any subsequent elements to the left (subtracts one from their
478 * indices).
479 *
480 * @param index the index of the element to be removed
481 * @return the element that was removed from the list
482 * @throws IndexOutOfBoundsException {@inheritDoc}
483 */
484 public E remove(int index) {
485 rangeCheck(index);
486
487 modCount++;
488 E oldValue = elementData(index);
489
490 int numMoved = size - index - 1;
491 if (numMoved > 0)
492 System.arraycopy(elementData, index+1, elementData, index,
493 numMoved);
494 elementData[--size] = null; // clear to let GC do its work
495
496 return oldValue;
497 }
498
499 /**
500 * Removes the first occurrence of the specified element from this list,
501 * if it is present. If the list does not contain the element, it is
502 * unchanged. More formally, removes the element with the lowest index
503 * {@code i} such that
504 * {@code (o==null ? get(i)==null : o.equals(get(i)))}
505 * (if such an element exists). Returns {@code true} if this list
506 * contained the specified element (or equivalently, if this list
507 * changed as a result of the call).
508 *
509 * @param o element to be removed from this list, if present
510 * @return {@code true} if this list contained the specified element
511 */
512 public boolean remove(Object o) {
513 if (o == null) {
514 for (int index = 0; index < size; index++)
515 if (elementData[index] == null) {
516 fastRemove(index);
517 return true;
518 }
519 } else {
520 for (int index = 0; index < size; index++)
521 if (o.equals(elementData[index])) {
522 fastRemove(index);
523 return true;
524 }
525 }
526 return false;
527 }
528
529 /*
530 * Private remove method that skips bounds checking and does not
531 * return the value removed.
532 */
533 private void fastRemove(int index) {
534 modCount++;
535 int numMoved = size - index - 1;
536 if (numMoved > 0)
537 System.arraycopy(elementData, index+1, elementData, index,
538 numMoved);
539 elementData[--size] = null; // clear to let GC do its work
540 }
541
542 /**
543 * Removes all of the elements from this list. The list will
544 * be empty after this call returns.
545 */
546 public void clear() {
547 modCount++;
548
549 // clear to let GC do its work
550 for (int i = 0; i < size; i++)
551 elementData[i] = null;
552
553 size = 0;
554 }
555
556 /**
557 * Appends all of the elements in the specified collection to the end of
558 * this list, in the order that they are returned by the
559 * specified collection's Iterator. The behavior of this operation is
560 * undefined if the specified collection is modified while the operation
561 * is in progress. (This implies that the behavior of this call is
562 * undefined if the specified collection is this list, and this
563 * list is nonempty.)
564 *
565 * @param c collection containing elements to be added to this list
566 * @return {@code true} if this list changed as a result of the call
567 * @throws NullPointerException if the specified collection is null
568 */
569 public boolean addAll(Collection<? extends E> c) {
570 Object[] a = c.toArray();
571 int numNew = a.length;
572 ensureCapacityInternal(size + numNew); // Increments modCount
573 System.arraycopy(a, 0, elementData, size, numNew);
574 size += numNew;
575 return numNew != 0;
576 }
577
578 /**
579 * Inserts all of the elements in the specified collection into this
580 * list, starting at the specified position. Shifts the element
581 * currently at that position (if any) and any subsequent elements to
582 * the right (increases their indices). The new elements will appear
583 * in the list in the order that they are returned by the
584 * specified collection's iterator.
585 *
586 * @param index index at which to insert the first element from the
587 * specified collection
588 * @param c collection containing elements to be added to this list
589 * @return {@code true} if this list changed as a result of the call
590 * @throws IndexOutOfBoundsException {@inheritDoc}
591 * @throws NullPointerException if the specified collection is null
592 */
593 public boolean addAll(int index, Collection<? extends E> c) {
594 rangeCheckForAdd(index);
595
596 Object[] a = c.toArray();
597 int numNew = a.length;
598 ensureCapacityInternal(size + numNew); // Increments modCount
599
600 int numMoved = size - index;
601 if (numMoved > 0)
602 System.arraycopy(elementData, index, elementData, index + numNew,
603 numMoved);
604
605 System.arraycopy(a, 0, elementData, index, numNew);
606 size += numNew;
607 return numNew != 0;
608 }
609
610 /**
611 * Removes from this list all of the elements whose index is between
612 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
613 * Shifts any succeeding elements to the left (reduces their index).
614 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
615 * (If {@code toIndex==fromIndex}, this operation has no effect.)
616 *
617 * @throws IndexOutOfBoundsException if {@code fromIndex} or
618 * {@code toIndex} is out of range
619 * ({@code fromIndex < 0 ||
620 * fromIndex >= size() ||
621 * toIndex > size() ||
622 * toIndex < fromIndex})
623 */
624 protected void removeRange(int fromIndex, int toIndex) {
625 modCount++;
626 int numMoved = size - toIndex;
627 System.arraycopy(elementData, toIndex, elementData, fromIndex,
628 numMoved);
629
630 // clear to let GC do its work
631 int newSize = size - (toIndex-fromIndex);
632 for (int i = newSize; i < size; i++) {
633 elementData[i] = null;
634 }
635 size = newSize;
636 }
637
638 /**
639 * Checks if the given index is in range. If not, throws an appropriate
640 * runtime exception. This method does *not* check if the index is
641 * negative: It is always used immediately prior to an array access,
642 * which throws an ArrayIndexOutOfBoundsException if index is negative.
643 */
644 private void rangeCheck(int index) {
645 if (index >= size)
646 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
647 }
648
649 /**
650 * A version of rangeCheck used by add and addAll.
651 */
652 private void rangeCheckForAdd(int index) {
653 if (index > size || index < 0)
654 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
655 }
656
657 /**
658 * Constructs an IndexOutOfBoundsException detail message.
659 * Of the many possible refactorings of the error handling code,
660 * this "outlining" performs best with both server and client VMs.
661 */
662 private String outOfBoundsMsg(int index) {
663 return "Index: "+index+", Size: "+size;
664 }
665
666 /**
667 * Removes from this list all of its elements that are contained in the
668 * specified collection.
669 *
670 * @param c collection containing elements to be removed from this list
671 * @return {@code true} if this list changed as a result of the call
672 * @throws ClassCastException if the class of an element of this list
673 * is incompatible with the specified collection
674 * (<a href="Collection.html#optional-restrictions">optional</a>)
675 * @throws NullPointerException if this list contains a null element and the
676 * specified collection does not permit null elements
677 * (<a href="Collection.html#optional-restrictions">optional</a>),
678 * or if the specified collection is null
679 * @see Collection#contains(Object)
680 */
681 public boolean removeAll(Collection<?> c) {
682 Objects.requireNonNull(c);
683 return batchRemove(c, false);
684 }
685
686 /**
687 * Retains only the elements in this list that are contained in the
688 * specified collection. In other words, removes from this list all
689 * of its elements that are not contained in the specified collection.
690 *
691 * @param c collection containing elements to be retained in this list
692 * @return {@code true} if this list changed as a result of the call
693 * @throws ClassCastException if the class of an element of this list
694 * is incompatible with the specified collection
695 * (<a href="Collection.html#optional-restrictions">optional</a>)
696 * @throws NullPointerException if this list contains a null element and the
697 * specified collection does not permit null elements
698 * (<a href="Collection.html#optional-restrictions">optional</a>),
699 * or if the specified collection is null
700 * @see Collection#contains(Object)
701 */
702 public boolean retainAll(Collection<?> c) {
703 Objects.requireNonNull(c);
704 return batchRemove(c, true);
705 }
706
707 private boolean batchRemove(Collection<?> c, boolean complement) {
708 final Object[] elementData = this.elementData;
709 int r = 0, w = 0;
710 boolean modified = false;
711 try {
712 for (; r < size; r++)
713 if (c.contains(elementData[r]) == complement)
714 elementData[w++] = elementData[r];
715 } finally {
716 // Preserve behavioral compatibility with AbstractCollection,
717 // even if c.contains() throws.
718 if (r != size) {
719 System.arraycopy(elementData, r,
720 elementData, w,
721 size - r);
722 w += size - r;
723 }
724 if (w != size) {
725 // clear to let GC do its work
726 for (int i = w; i < size; i++)
727 elementData[i] = null;
728 modCount += size - w;
729 size = w;
730 modified = true;
731 }
732 }
733 return modified;
734 }
735
736 /**
737 * Save the state of the {@code ArrayList} instance to a stream (that
738 * is, serialize it).
739 *
740 * @serialData The length of the array backing the {@code ArrayList}
741 * instance is emitted (int), followed by all of its elements
742 * (each an {@code Object}) in the proper order.
743 */
744 private void writeObject(java.io.ObjectOutputStream s)
745 throws java.io.IOException{
746 // Write out element count, and any hidden stuff
747 int expectedModCount = modCount;
748 s.defaultWriteObject();
749
750 // Write out size as capacity for behavioural compatibility with clone()
751 s.writeInt(size);
752
753 // Write out all elements in the proper order.
754 for (int i=0; i<size; i++) {
755 s.writeObject(elementData[i]);
756 }
757
758 if (modCount != expectedModCount) {
759 throw new ConcurrentModificationException();
760 }
761 }
762
763 /**
764 * Reconstitute the {@code ArrayList} instance from a stream (that is,
765 * deserialize it).
766 */
767 private void readObject(java.io.ObjectInputStream s)
768 throws java.io.IOException, ClassNotFoundException {
769 elementData = EMPTY_ELEMENTDATA;
770
771 // Read in size, and any hidden stuff
772 s.defaultReadObject();
773
774 // Read in capacity
775 s.readInt(); // ignored
776
777 if (size > 0) {
778 // be like clone(), allocate array based upon size not capacity
779 ensureCapacityInternal(size);
780
781 Object[] a = elementData;
782 // Read in all elements in the proper order.
783 for (int i=0; i<size; i++) {
784 a[i] = s.readObject();
785 }
786 }
787 }
788
789 /**
790 * Returns a list iterator over the elements in this list (in proper
791 * sequence), starting at the specified position in the list.
792 * The specified index indicates the first element that would be
793 * returned by an initial call to {@link ListIterator#next next}.
794 * An initial call to {@link ListIterator#previous previous} would
795 * return the element with the specified index minus one.
796 *
797 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
798 *
799 * @throws IndexOutOfBoundsException {@inheritDoc}
800 */
801 public ListIterator<E> listIterator(int index) {
802 if (index < 0 || index > size)
803 throw new IndexOutOfBoundsException("Index: "+index);
804 return new ListItr(index);
805 }
806
807 /**
808 * Returns a list iterator over the elements in this list (in proper
809 * sequence).
810 *
811 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
812 *
813 * @see #listIterator(int)
814 */
815 public ListIterator<E> listIterator() {
816 return new ListItr(0);
817 }
818
819 /**
820 * Returns an iterator over the elements in this list in proper sequence.
821 *
822 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
823 *
824 * @return an iterator over the elements in this list in proper sequence
825 */
826 public Iterator<E> iterator() {
827 return new Itr();
828 }
829
830 /**
831 * An optimized version of AbstractList.Itr
832 */
833 private class Itr implements Iterator<E> {
834 int cursor; // index of next element to return
835 int lastRet = -1; // index of last element returned; -1 if no such
836 int expectedModCount = modCount;
837
838 public boolean hasNext() {
839 return cursor != size;
840 }
841
842 @SuppressWarnings("unchecked")
843 public E next() {
844 checkForComodification();
845 int i = cursor;
846 if (i >= size)
847 throw new NoSuchElementException();
848 Object[] elementData = ArrayList.this.elementData;
849 if (i >= elementData.length)
850 throw new ConcurrentModificationException();
851 cursor = i + 1;
852 return (E) elementData[lastRet = i];
853 }
854
855 public void remove() {
856 if (lastRet < 0)
857 throw new IllegalStateException();
858 checkForComodification();
859
860 try {
861 ArrayList.this.remove(lastRet);
862 cursor = lastRet;
863 lastRet = -1;
864 expectedModCount = modCount;
865 } catch (IndexOutOfBoundsException ex) {
866 throw new ConcurrentModificationException();
867 }
868 }
869
870 @Override
871 @SuppressWarnings("unchecked")
872 public void forEachRemaining(Consumer<? super E> consumer) {
873 Objects.requireNonNull(consumer);
874 final int size = ArrayList.this.size;
875 int i = cursor;
876 if (i >= size) {
877 return;
878 }
879 final Object[] elementData = ArrayList.this.elementData;
880 if (i >= elementData.length) {
881 throw new ConcurrentModificationException();
882 }
883 while (i != size && modCount == expectedModCount) {
884 consumer.accept((E) elementData[i++]);
885 }
886 // update once at end of iteration to reduce heap write traffic
887 cursor = i;
888 lastRet = i - 1;
889 checkForComodification();
890 }
891
892 final void checkForComodification() {
893 if (modCount != expectedModCount)
894 throw new ConcurrentModificationException();
895 }
896 }
897
898 /**
899 * An optimized version of AbstractList.ListItr
900 */
901 private class ListItr extends Itr implements ListIterator<E> {
902 ListItr(int index) {
903 super();
904 cursor = index;
905 }
906
907 public boolean hasPrevious() {
908 return cursor != 0;
909 }
910
911 public int nextIndex() {
912 return cursor;
913 }
914
915 public int previousIndex() {
916 return cursor - 1;
917 }
918
919 @SuppressWarnings("unchecked")
920 public E previous() {
921 checkForComodification();
922 int i = cursor - 1;
923 if (i < 0)
924 throw new NoSuchElementException();
925 Object[] elementData = ArrayList.this.elementData;
926 if (i >= elementData.length)
927 throw new ConcurrentModificationException();
928 cursor = i;
929 return (E) elementData[lastRet = i];
930 }
931
932 public void set(E e) {
933 if (lastRet < 0)
934 throw new IllegalStateException();
935 checkForComodification();
936
937 try {
938 ArrayList.this.set(lastRet, e);
939 } catch (IndexOutOfBoundsException ex) {
940 throw new ConcurrentModificationException();
941 }
942 }
943
944 public void add(E e) {
945 checkForComodification();
946
947 try {
948 int i = cursor;
949 ArrayList.this.add(i, e);
950 cursor = i + 1;
951 lastRet = -1;
952 expectedModCount = modCount;
953 } catch (IndexOutOfBoundsException ex) {
954 throw new ConcurrentModificationException();
955 }
956 }
957 }
958
959 /**
960 * Returns a view of the portion of this list between the specified
961 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
962 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
963 * empty.) The returned list is backed by this list, so non-structural
964 * changes in the returned list are reflected in this list, and vice-versa.
965 * The returned list supports all of the optional list operations.
966 *
967 * <p>This method eliminates the need for explicit range operations (of
968 * the sort that commonly exist for arrays). Any operation that expects
969 * a list can be used as a range operation by passing a subList view
970 * instead of a whole list. For example, the following idiom
971 * removes a range of elements from a list:
972 * <pre>
973 * list.subList(from, to).clear();
974 * </pre>
975 * Similar idioms may be constructed for {@link #indexOf(Object)} and
976 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
977 * {@link Collections} class can be applied to a subList.
978 *
979 * <p>The semantics of the list returned by this method become undefined if
980 * the backing list (i.e., this list) is <i>structurally modified</i> in
981 * any way other than via the returned list. (Structural modifications are
982 * those that change the size of this list, or otherwise perturb it in such
983 * a fashion that iterations in progress may yield incorrect results.)
984 *
985 * @throws IndexOutOfBoundsException {@inheritDoc}
986 * @throws IllegalArgumentException {@inheritDoc}
987 */
988 public List<E> subList(int fromIndex, int toIndex) {
989 subListRangeCheck(fromIndex, toIndex, size);
990 return new SubList(this, 0, fromIndex, toIndex);
991 }
992
993 static void subListRangeCheck(int fromIndex, int toIndex, int size) {
994 if (fromIndex < 0)
995 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
996 if (toIndex > size)
997 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
998 if (fromIndex > toIndex)
999 throw new IllegalArgumentException("fromIndex(" + fromIndex +
1000 ") > toIndex(" + toIndex + ")");
1001 }
1002
1003 private class SubList extends AbstractList<E> implements RandomAccess {
1004 private final AbstractList<E> parent;
1005 private final int parentOffset;
1006 private final int offset;
1007 int size;
1008
1009 SubList(AbstractList<E> parent,
1010 int offset, int fromIndex, int toIndex) {
1011 this.parent = parent;
1012 this.parentOffset = fromIndex;
1013 this.offset = offset + fromIndex;
1014 this.size = toIndex - fromIndex;
1015 this.modCount = ArrayList.this.modCount;
1016 }
1017
1018 public E set(int index, E e) {
1019 rangeCheck(index);
1020 checkForComodification();
1021 E oldValue = ArrayList.this.elementData(offset + index);
1022 ArrayList.this.elementData[offset + index] = e;
1023 return oldValue;
1024 }
1025
1026 public E get(int index) {
1027 rangeCheck(index);
1028 checkForComodification();
1029 return ArrayList.this.elementData(offset + index);
1030 }
1031
1032 public int size() {
1033 checkForComodification();
1034 return this.size;
1035 }
1036
1037 public void add(int index, E e) {
1038 rangeCheckForAdd(index);
1039 checkForComodification();
1040 parent.add(parentOffset + index, e);
1041 this.modCount = parent.modCount;
1042 this.size++;
1043 }
1044
1045 public E remove(int index) {
1046 rangeCheck(index);
1047 checkForComodification();
1048 E result = parent.remove(parentOffset + index);
1049 this.modCount = parent.modCount;
1050 this.size--;
1051 return result;
1052 }
1053
1054 protected void removeRange(int fromIndex, int toIndex) {
1055 checkForComodification();
1056 parent.removeRange(parentOffset + fromIndex,
1057 parentOffset + toIndex);
1058 this.modCount = parent.modCount;
1059 this.size -= toIndex - fromIndex;
1060 }
1061
1062 public boolean addAll(Collection<? extends E> c) {
1063 return addAll(this.size, c);
1064 }
1065
1066 public boolean addAll(int index, Collection<? extends E> c) {
1067 rangeCheckForAdd(index);
1068 int cSize = c.size();
1069 if (cSize==0)
1070 return false;
1071
1072 checkForComodification();
1073 parent.addAll(parentOffset + index, c);
1074 this.modCount = parent.modCount;
1075 this.size += cSize;
1076 return true;
1077 }
1078
1079 public Iterator<E> iterator() {
1080 return listIterator();
1081 }
1082
1083 public ListIterator<E> listIterator(final int index) {
1084 checkForComodification();
1085 rangeCheckForAdd(index);
1086 final int offset = this.offset;
1087
1088 return new ListIterator<E>() {
1089 int cursor = index;
1090 int lastRet = -1;
1091 int expectedModCount = ArrayList.this.modCount;
1092
1093 public boolean hasNext() {
1094 return cursor != SubList.this.size;
1095 }
1096
1097 @SuppressWarnings("unchecked")
1098 public E next() {
1099 checkForComodification();
1100 int i = cursor;
1101 if (i >= SubList.this.size)
1102 throw new NoSuchElementException();
1103 Object[] elementData = ArrayList.this.elementData;
1104 if (offset + i >= elementData.length)
1105 throw new ConcurrentModificationException();
1106 cursor = i + 1;
1107 return (E) elementData[offset + (lastRet = i)];
1108 }
1109
1110 public boolean hasPrevious() {
1111 return cursor != 0;
1112 }
1113
1114 @SuppressWarnings("unchecked")
1115 public E previous() {
1116 checkForComodification();
1117 int i = cursor - 1;
1118 if (i < 0)
1119 throw new NoSuchElementException();
1120 Object[] elementData = ArrayList.this.elementData;
1121 if (offset + i >= elementData.length)
1122 throw new ConcurrentModificationException();
1123 cursor = i;
1124 return (E) elementData[offset + (lastRet = i)];
1125 }
1126
1127 @SuppressWarnings("unchecked")
1128 public void forEachRemaining(Consumer<? super E> consumer) {
1129 Objects.requireNonNull(consumer);
1130 final int size = SubList.this.size;
1131 int i = cursor;
1132 if (i >= size) {
1133 return;
1134 }
1135 final Object[] elementData = ArrayList.this.elementData;
1136 if (offset + i >= elementData.length) {
1137 throw new ConcurrentModificationException();
1138 }
1139 while (i != size && modCount == expectedModCount) {
1140 consumer.accept((E) elementData[offset + (i++)]);
1141 }
1142 // update once at end of iteration to reduce heap write traffic
1143 lastRet = cursor = i;
1144 checkForComodification();
1145 }
1146
1147 public int nextIndex() {
1148 return cursor;
1149 }
1150
1151 public int previousIndex() {
1152 return cursor - 1;
1153 }
1154
1155 public void remove() {
1156 if (lastRet < 0)
1157 throw new IllegalStateException();
1158 checkForComodification();
1159
1160 try {
1161 SubList.this.remove(lastRet);
1162 cursor = lastRet;
1163 lastRet = -1;
1164 expectedModCount = ArrayList.this.modCount;
1165 } catch (IndexOutOfBoundsException ex) {
1166 throw new ConcurrentModificationException();
1167 }
1168 }
1169
1170 public void set(E e) {
1171 if (lastRet < 0)
1172 throw new IllegalStateException();
1173 checkForComodification();
1174
1175 try {
1176 ArrayList.this.set(offset + lastRet, e);
1177 } catch (IndexOutOfBoundsException ex) {
1178 throw new ConcurrentModificationException();
1179 }
1180 }
1181
1182 public void add(E e) {
1183 checkForComodification();
1184
1185 try {
1186 int i = cursor;
1187 SubList.this.add(i, e);
1188 cursor = i + 1;
1189 lastRet = -1;
1190 expectedModCount = ArrayList.this.modCount;
1191 } catch (IndexOutOfBoundsException ex) {
1192 throw new ConcurrentModificationException();
1193 }
1194 }
1195
1196 final void checkForComodification() {
1197 if (expectedModCount != ArrayList.this.modCount)
1198 throw new ConcurrentModificationException();
1199 }
1200 };
1201 }
1202
1203 public List<E> subList(int fromIndex, int toIndex) {
1204 subListRangeCheck(fromIndex, toIndex, size);
1205 return new SubList(this, offset, fromIndex, toIndex);
1206 }
1207
1208 private void rangeCheck(int index) {
1209 if (index < 0 || index >= this.size)
1210 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1211 }
1212
1213 private void rangeCheckForAdd(int index) {
1214 if (index < 0 || index > this.size)
1215 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1216 }
1217
1218 private String outOfBoundsMsg(int index) {
1219 return "Index: "+index+", Size: "+this.size;
1220 }
1221
1222 private void checkForComodification() {
1223 if (ArrayList.this.modCount != this.modCount)
1224 throw new ConcurrentModificationException();
1225 }
1226
1227 public Spliterator<E> spliterator() {
1228 checkForComodification();
1229 return new ArrayListSpliterator<>(ArrayList.this, offset,
1230 offset + this.size, this.modCount);
1231 }
1232 }
1233
1234 @Override
1235 public void forEach(Consumer<? super E> action) {
1236 Objects.requireNonNull(action);
1237 final int expectedModCount = modCount;
1238 @SuppressWarnings("unchecked")
1239 final E[] elementData = (E[]) this.elementData;
1240 final int size = this.size;
1241 for (int i=0; modCount == expectedModCount && i < size; i++) {
1242 action.accept(elementData[i]);
1243 }
1244 if (modCount != expectedModCount) {
1245 throw new ConcurrentModificationException();
1246 }
1247 }
1248
1249 /**
1250 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1251 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1252 * list.
1253 *
1254 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1255 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1256 * Overriding implementations should document the reporting of additional
1257 * characteristic values.
1258 *
1259 * @return a {@code Spliterator} over the elements in this list
1260 * @since 1.8
1261 */
1262 @Override
1263 public Spliterator<E> spliterator() {
1264 return new ArrayListSpliterator<>(this, 0, -1, 0);
1265 }
1266
1267 /** Index-based split-by-two, lazily initialized Spliterator */
1268 static final class ArrayListSpliterator<E> implements Spliterator<E> {
1269
1270 /*
1271 * If ArrayLists were immutable, or structurally immutable (no
1272 * adds, removes, etc), we could implement their spliterators
1273 * with Arrays.spliterator. Instead we detect as much
1274 * interference during traversal as practical without
1275 * sacrificing much performance. We rely primarily on
1276 * modCounts. These are not guaranteed to detect concurrency
1277 * violations, and are sometimes overly conservative about
1278 * within-thread interference, but detect enough problems to
1279 * be worthwhile in practice. To carry this out, we (1) lazily
1280 * initialize fence and expectedModCount until the latest
1281 * point that we need to commit to the state we are checking
1282 * against; thus improving precision. (This doesn't apply to
1283 * SubLists, that create spliterators with current non-lazy
1284 * values). (2) We perform only a single
1285 * ConcurrentModificationException check at the end of forEach
1286 * (the most performance-sensitive method). When using forEach
1287 * (as opposed to iterators), we can normally only detect
1288 * interference after actions, not before. Further
1289 * CME-triggering checks apply to all other possible
1290 * violations of assumptions for example null or too-small
1291 * elementData array given its size(), that could only have
1292 * occurred due to interference. This allows the inner loop
1293 * of forEach to run without any further checks, and
1294 * simplifies lambda-resolution. While this does entail a
1295 * number of checks, note that in the common case of
1296 * list.stream().forEach(a), no checks or other computation
1297 * occur anywhere other than inside forEach itself. The other
1298 * less-often-used methods cannot take advantage of most of
1299 * these streamlinings.
1300 */
1301
1302 private final ArrayList<E> list;
1303 private int index; // current index, modified on advance/split
1304 private int fence; // -1 until used; then one past last index
1305 private int expectedModCount; // initialized when fence set
1306
1307 /** Create new spliterator covering the given range */
1308 ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
1309 int expectedModCount) {
1310 this.list = list; // OK if null unless traversed
1311 this.index = origin;
1312 this.fence = fence;
1313 this.expectedModCount = expectedModCount;
1314 }
1315
1316 private int getFence() { // initialize fence to size on first use
1317 int hi; // (a specialized variant appears in method forEach)
1318 ArrayList<E> lst;
1319 if ((hi = fence) < 0) {
1320 if ((lst = list) == null)
1321 hi = fence = 0;
1322 else {
1323 expectedModCount = lst.modCount;
1324 hi = fence = lst.size;
1325 }
1326 }
1327 return hi;
1328 }
1329
1330 public ArrayListSpliterator<E> trySplit() {
1331 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1332 return (lo >= mid) ? null : // divide range in half unless too small
1333 new ArrayListSpliterator<>(list, lo, index = mid,
1334 expectedModCount);
1335 }
1336
1337 public boolean tryAdvance(Consumer<? super E> action) {
1338 if (action == null)
1339 throw new NullPointerException();
1340 int hi = getFence(), i = index;
1341 if (i < hi) {
1342 index = i + 1;
1343 @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
1344 action.accept(e);
1345 if (list.modCount != expectedModCount)
1346 throw new ConcurrentModificationException();
1347 return true;
1348 }
1349 return false;
1350 }
1351
1352 public void forEachRemaining(Consumer<? super E> action) {
1353 int i, hi, mc; // hoist accesses and checks from loop
1354 ArrayList<E> lst; Object[] a;
1355 if (action == null)
1356 throw new NullPointerException();
1357 if ((lst = list) != null && (a = lst.elementData) != null) {
1358 if ((hi = fence) < 0) {
1359 mc = lst.modCount;
1360 hi = lst.size;
1361 }
1362 else
1363 mc = expectedModCount;
1364 if ((i = index) >= 0 && (index = hi) <= a.length) {
1365 for (; i < hi; ++i) {
1366 @SuppressWarnings("unchecked") E e = (E) a[i];
1367 action.accept(e);
1368 }
1369 if (lst.modCount == mc)
1370 return;
1371 }
1372 }
1373 throw new ConcurrentModificationException();
1374 }
1375
1376 public long estimateSize() {
1377 return (long) (getFence() - index);
1378 }
1379
1380 public int characteristics() {
1381 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1382 }
1383 }
1384
1385 @Override
1386 public boolean removeIf(Predicate<? super E> filter) {
1387 Objects.requireNonNull(filter);
1388 // figure out which elements are to be removed
1389 // any exception thrown from the filter predicate at this stage
1390 // will leave the collection unmodified
1391 int removeCount = 0;
1392 final BitSet removeSet = new BitSet(size);
1393 final int expectedModCount = modCount;
1394 final int size = this.size;
1395 for (int i=0; modCount == expectedModCount && i < size; i++) {
1396 @SuppressWarnings("unchecked")
1397 final E element = (E) elementData[i];
1398 if (filter.test(element)) {
1399 removeSet.set(i);
1400 removeCount++;
1401 }
1402 }
1403 if (modCount != expectedModCount) {
1404 throw new ConcurrentModificationException();
1405 }
1406
1407 // shift surviving elements left over the spaces left by removed elements
1408 final boolean anyToRemove = removeCount > 0;
1409 if (anyToRemove) {
1410 final int newSize = size - removeCount;
1411 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
1412 i = removeSet.nextClearBit(i);
1413 elementData[j] = elementData[i];
1414 }
1415 for (int k=newSize; k < size; k++) {
1416 elementData[k] = null; // Let gc do its work
1417 }
1418 this.size = newSize;
1419 if (modCount != expectedModCount) {
1420 throw new ConcurrentModificationException();
1421 }
1422 modCount++;
1423 }
1424
1425 return anyToRemove;
1426 }
1427
1428 @Override
1429 @SuppressWarnings("unchecked")
1430 public void replaceAll(UnaryOperator<E> operator) {
1431 Objects.requireNonNull(operator);
1432 final int expectedModCount = modCount;
1433 final int size = this.size;
1434 for (int i=0; modCount == expectedModCount && i < size; i++) {
1435 elementData[i] = operator.apply((E) elementData[i]);
1436 }
1437 if (modCount != expectedModCount) {
1438 throw new ConcurrentModificationException();
1439 }
1440 modCount++;
1441 }
1442
1443 @Override
1444 @SuppressWarnings("unchecked")
1445 public void sort(Comparator<? super E> c) {
1446 final int expectedModCount = modCount;
1447 Arrays.sort((E[]) elementData, 0, size, c);
1448 if (modCount != expectedModCount) {
1449 throw new ConcurrentModificationException();
1450 }
1451 modCount++;
1452 }
1453 }