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 * Shared empty array instance used for default sized empty instances. We
125 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
126 * first element is added.
127 */
128 private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
129
130 /**
131 * The array buffer into which the elements of the ArrayList are stored.
132 * The capacity of the ArrayList is the length of this array buffer. Any
133 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
134 * will be expanded to DEFAULT_CAPACITY when the first element is added.
135 */
136 transient Object[] elementData; // non-private to simplify nested class access
137
138 /**
139 * The size of the ArrayList (the number of elements it contains).
140 *
141 * @serial
142 */
143 private int size;
144
145 /**
146 * Constructs an empty list with the specified initial capacity.
147 *
148 * @param initialCapacity the initial capacity of the list
149 * @throws IllegalArgumentException if the specified initial capacity
150 * is negative
151 */
152 public ArrayList(int initialCapacity) {
153 if (initialCapacity > 0) {
154 this.elementData = new Object[initialCapacity];
155 } else if (initialCapacity == 0) {
156 this.elementData = EMPTY_ELEMENTDATA;
157 } else {
158 throw new IllegalArgumentException("Illegal Capacity: "+
159 initialCapacity);
160 }
161 }
162
163 /**
164 * Constructs an empty list with an initial capacity of ten.
165 */
166 public ArrayList() {
167 this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
168 }
169
170 /**
171 * Constructs a list containing the elements of the specified
172 * collection, in the order they are returned by the collection's
173 * iterator.
174 *
175 * @param c the collection whose elements are to be placed into this list
176 * @throws NullPointerException if the specified collection is null
177 */
178 public ArrayList(Collection<? extends E> c) {
179 elementData = c.toArray();
180 if ((size = elementData.length) != 0) {
181 // c.toArray might (incorrectly) not return Object[] (see 6260652)
182 if (elementData.getClass() != Object[].class)
183 elementData = Arrays.copyOf(elementData, size, Object[].class);
184 } else {
185 // replace with empty array.
186 this.elementData = EMPTY_ELEMENTDATA;
187 }
188 }
189
190 /**
191 * Trims the capacity of this {@code ArrayList} instance to be the
192 * list's current size. An application can use this operation to minimize
193 * the storage of an {@code ArrayList} instance.
194 */
195 public void trimToSize() {
196 modCount++;
197 if (size < elementData.length) {
198 elementData = (size == 0)
199 ? EMPTY_ELEMENTDATA
200 : Arrays.copyOf(elementData, size);
201 }
202 }
203
204 /**
205 * Increases the capacity of this {@code ArrayList} instance, if
206 * necessary, to ensure that it can hold at least the number of elements
207 * specified by the minimum capacity argument.
208 *
209 * @param minCapacity the desired minimum capacity
210 */
211 public void ensureCapacity(int minCapacity) {
212 int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
213 // any size if not default element table
214 ? 0
215 // larger than default for default empty table. It's already
216 // supposed to be at default size.
217 : DEFAULT_CAPACITY;
218
219 if (minCapacity > minExpand) {
220 ensureExplicitCapacity(minCapacity);
221 }
222 }
223
224 private void ensureCapacityInternal(int minCapacity) {
225 if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
226 minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
227 }
228
229 ensureExplicitCapacity(minCapacity);
230 }
231
232 private void ensureExplicitCapacity(int minCapacity) {
233 modCount++;
234
235 // overflow-conscious code
236 if (minCapacity - elementData.length > 0)
237 grow(minCapacity);
238 }
239
240 /**
241 * The maximum size of array to allocate.
242 * Some VMs reserve some header words in an array.
243 * Attempts to allocate larger arrays may result in
244 * OutOfMemoryError: Requested array size exceeds VM limit
245 */
246 private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
247
248 /**
249 * Increases the capacity to ensure that it can hold at least the
250 * number of elements specified by the minimum capacity argument.
251 *
252 * @param minCapacity the desired minimum capacity
253 */
254 private void grow(int minCapacity) {
255 // overflow-conscious code
256 int oldCapacity = elementData.length;
257 int newCapacity = oldCapacity + (oldCapacity >> 1);
258 if (newCapacity - minCapacity < 0)
259 newCapacity = minCapacity;
260 if (newCapacity - MAX_ARRAY_SIZE > 0)
261 newCapacity = hugeCapacity(minCapacity);
262 // minCapacity is usually close to size, so this is a win:
263 elementData = Arrays.copyOf(elementData, newCapacity);
264 }
265
266 private static int hugeCapacity(int minCapacity) {
267 if (minCapacity < 0) // overflow
268 throw new OutOfMemoryError();
269 return (minCapacity > MAX_ARRAY_SIZE) ?
270 Integer.MAX_VALUE :
271 MAX_ARRAY_SIZE;
272 }
273
274 /**
275 * Returns the number of elements in this list.
276 *
277 * @return the number of elements in this list
278 */
279 public int size() {
280 return size;
281 }
282
283 /**
284 * Returns {@code true} if this list contains no elements.
285 *
286 * @return {@code true} if this list contains no elements
287 */
288 public boolean isEmpty() {
289 return size == 0;
290 }
291
292 /**
293 * Returns {@code true} if this list contains the specified element.
294 * More formally, returns {@code true} if and only if this list contains
295 * at least one element {@code e} such that
296 * <tt>(o==null ? e==null : o.equals(e))</tt>.
297 *
298 * @param o element whose presence in this list is to be tested
299 * @return {@code true} if this list contains the specified element
300 */
301 public boolean contains(Object o) {
302 return indexOf(o) >= 0;
303 }
304
305 /**
306 * Returns the index of the first occurrence of the specified element
307 * in this list, or -1 if this list does not contain the element.
308 * More formally, returns the lowest index {@code i} such that
309 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
310 * or -1 if there is no such index.
311 */
312 public int indexOf(Object o) {
313 if (o == null) {
314 for (int i = 0; i < size; i++)
315 if (elementData[i]==null)
316 return i;
317 } else {
318 for (int i = 0; i < size; i++)
319 if (o.equals(elementData[i]))
320 return i;
321 }
322 return -1;
323 }
324
325 /**
326 * Returns the index of the last occurrence of the specified element
327 * in this list, or -1 if this list does not contain the element.
328 * More formally, returns the highest index {@code i} such that
329 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
330 * or -1 if there is no such index.
331 */
332 public int lastIndexOf(Object o) {
333 if (o == null) {
334 for (int i = size-1; i >= 0; i--)
335 if (elementData[i]==null)
336 return i;
337 } else {
338 for (int i = size-1; i >= 0; i--)
339 if (o.equals(elementData[i]))
340 return i;
341 }
342 return -1;
343 }
344
345 /**
346 * Returns a shallow copy of this {@code ArrayList} instance. (The
347 * elements themselves are not copied.)
348 *
349 * @return a clone of this {@code ArrayList} instance
350 */
351 public Object clone() {
352 try {
353 ArrayList<?> v = (ArrayList<?>) super.clone();
354 v.elementData = Arrays.copyOf(elementData, size);
355 v.modCount = 0;
356 return v;
357 } catch (CloneNotSupportedException e) {
358 // this shouldn't happen, since we are Cloneable
359 throw new InternalError(e);
360 }
361 }
362
363 /**
364 * Returns an array containing all of the elements in this list
365 * in proper sequence (from first to last element).
366 *
367 * <p>The returned array will be "safe" in that no references to it are
368 * maintained by this list. (In other words, this method must allocate
369 * a new array). The caller is thus free to modify the returned array.
370 *
371 * <p>This method acts as bridge between array-based and collection-based
372 * APIs.
373 *
374 * @return an array containing all of the elements in this list in
375 * proper sequence
376 */
377 public Object[] toArray() {
378 int sz = size;
379 return (sz != 0)
380 ? Arrays.copyOf(elementData, sz)
381 : EMPTY_ELEMENTDATA;
382 }
383
384 /**
385 * Returns an array containing all of the elements in this list in proper
386 * sequence (from first to last element); the runtime type of the returned
387 * array is that of the specified array. If the list fits in the
388 * specified array, it is returned therein. Otherwise, a new array is
389 * allocated with the runtime type of the specified array and the size of
390 * this list.
391 *
392 * <p>If the list fits in the specified array with room to spare
393 * (i.e., the array has more elements than the list), the element in
394 * the array immediately following the end of the collection is set to
395 * {@code null}. (This is useful in determining the length of the
396 * list <i>only</i> if the caller knows that the list does not contain
397 * any null elements.)
398 *
399 * @param a the array into which the elements of the list are to
400 * be stored, if it is big enough; otherwise, a new array of the
401 * same runtime type is allocated for this purpose.
402 * @return an array containing the elements of the list
403 * @throws ArrayStoreException if the runtime type of the specified array
404 * is not a supertype of the runtime type of every element in
405 * this list
406 * @throws NullPointerException if the specified array is null
407 */
408 @SuppressWarnings("unchecked")
409 public <T> T[] toArray(T[] a) {
410 if (a.length < size)
411 // Make a new array of a's runtime type, but my contents:
412 return (T[]) Arrays.copyOf(elementData, size, a.getClass());
413 System.arraycopy(elementData, 0, a, 0, size);
414 if (a.length > size)
415 a[size] = null;
416 return a;
417 }
418
419 // Positional Access Operations
420
421 @SuppressWarnings("unchecked")
422 E elementData(int index) {
423 return (E) elementData[index];
424 }
425
426 /**
427 * Returns the element at the specified position in this list.
428 *
429 * @param index index of the element to return
430 * @return the element at the specified position in this list
431 * @throws IndexOutOfBoundsException {@inheritDoc}
432 */
433 public E get(int index) {
434 rangeCheck(index);
435
436 return elementData(index);
437 }
438
439 /**
440 * Replaces the element at the specified position in this list with
441 * the specified element.
442 *
443 * @param index index of the element to replace
444 * @param element element to be stored at the specified position
445 * @return the element previously at the specified position
446 * @throws IndexOutOfBoundsException {@inheritDoc}
447 */
448 public E set(int index, E element) {
449 rangeCheck(index);
450
451 E oldValue = elementData(index);
452 elementData[index] = element;
453 return oldValue;
454 }
455
456 /**
457 * Appends the specified element to the end of this list.
458 *
459 * @param e element to be appended to this list
460 * @return {@code true} (as specified by {@link Collection#add})
461 */
462 public boolean add(E e) {
463 ensureCapacityInternal(size + 1); // Increments modCount!!
464 elementData[size++] = e;
465 return true;
466 }
467
468 /**
469 * Inserts the specified element at the specified position in this
470 * list. Shifts the element currently at that position (if any) and
471 * any subsequent elements to the right (adds one to their indices).
472 *
473 * @param index index at which the specified element is to be inserted
474 * @param element element to be inserted
475 * @throws IndexOutOfBoundsException {@inheritDoc}
476 */
477 public void add(int index, E element) {
478 rangeCheckForAdd(index);
479
480 ensureCapacityInternal(size + 1); // Increments modCount!!
481 System.arraycopy(elementData, index, elementData, index + 1,
482 size - index);
483 elementData[index] = element;
484 size++;
485 }
486
487 /**
488 * Removes the element at the specified position in this list.
489 * Shifts any subsequent elements to the left (subtracts one from their
490 * indices).
491 *
492 * @param index the index of the element to be removed
493 * @return the element that was removed from the list
494 * @throws IndexOutOfBoundsException {@inheritDoc}
495 */
496 public E remove(int index) {
497 rangeCheck(index);
498
499 modCount++;
500 E oldValue = elementData(index);
501
502 int numMoved = size - index - 1;
503 if (numMoved > 0)
504 System.arraycopy(elementData, index+1, elementData, index,
505 numMoved);
506 elementData[--size] = null; // clear to let GC do its work
507
508 return oldValue;
509 }
510
511 /**
512 * Removes the first occurrence of the specified element from this list,
513 * if it is present. If the list does not contain the element, it is
514 * unchanged. More formally, removes the element with the lowest index
515 * {@code i} such that
516 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
517 * (if such an element exists). Returns {@code true} if this list
518 * contained the specified element (or equivalently, if this list
519 * changed as a result of the call).
520 *
521 * @param o element to be removed from this list, if present
522 * @return {@code true} if this list contained the specified element
523 */
524 public boolean remove(Object o) {
525 if (o == null) {
526 for (int index = 0; index < size; index++)
527 if (elementData[index] == null) {
528 fastRemove(index);
529 return true;
530 }
531 } else {
532 for (int index = 0; index < size; index++)
533 if (o.equals(elementData[index])) {
534 fastRemove(index);
535 return true;
536 }
537 }
538 return false;
539 }
540
541 /*
542 * Private remove method that skips bounds checking and does not
543 * return the value removed.
544 */
545 private void fastRemove(int index) {
546 modCount++;
547 int numMoved = size - index - 1;
548 if (numMoved > 0)
549 System.arraycopy(elementData, index+1, elementData, index,
550 numMoved);
551 elementData[--size] = null; // clear to let GC do its work
552 }
553
554 /**
555 * Removes all of the elements from this list. The list will
556 * be empty after this call returns.
557 */
558 public void clear() {
559 modCount++;
560
561 // clear to let GC do its work
562 for (int i = 0; i < size; i++)
563 elementData[i] = null;
564
565 size = 0;
566 }
567
568 /**
569 * Appends all of the elements in the specified collection to the end of
570 * this list, in the order that they are returned by the
571 * specified collection's Iterator. The behavior of this operation is
572 * undefined if the specified collection is modified while the operation
573 * is in progress. (This implies that the behavior of this call is
574 * undefined if the specified collection is this list, and this
575 * list is nonempty.)
576 *
577 * @param c collection containing elements to be added to this list
578 * @return {@code true} if this list changed as a result of the call
579 * @throws NullPointerException if the specified collection is null
580 */
581 public boolean addAll(Collection<? extends E> c) {
582 Object[] a = c.toArray();
583 int numNew = a.length;
584 ensureCapacityInternal(size + numNew); // Increments modCount
585 System.arraycopy(a, 0, elementData, size, numNew);
586 size += numNew;
587 return numNew != 0;
588 }
589
590 /**
591 * Inserts all of the elements in the specified collection into this
592 * list, starting at the specified position. Shifts the element
593 * currently at that position (if any) and any subsequent elements to
594 * the right (increases their indices). The new elements will appear
595 * in the list in the order that they are returned by the
596 * specified collection's iterator.
597 *
598 * @param index index at which to insert the first element from the
599 * specified collection
600 * @param c collection containing elements to be added to this list
601 * @return {@code true} if this list changed as a result of the call
602 * @throws IndexOutOfBoundsException {@inheritDoc}
603 * @throws NullPointerException if the specified collection is null
604 */
605 public boolean addAll(int index, Collection<? extends E> c) {
606 rangeCheckForAdd(index);
607
608 Object[] a = c.toArray();
609 int numNew = a.length;
610 ensureCapacityInternal(size + numNew); // Increments modCount
611
612 int numMoved = size - index;
613 if (numMoved > 0)
614 System.arraycopy(elementData, index, elementData, index + numNew,
615 numMoved);
616
617 System.arraycopy(a, 0, elementData, index, numNew);
618 size += numNew;
619 return numNew != 0;
620 }
621
622 /**
623 * Removes from this list all of the elements whose index is between
624 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
625 * Shifts any succeeding elements to the left (reduces their index).
626 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
627 * (If {@code toIndex==fromIndex}, this operation has no effect.)
628 *
629 * @throws IndexOutOfBoundsException if {@code fromIndex} or
630 * {@code toIndex} is out of range
631 * ({@code fromIndex < 0 ||
632 * fromIndex >= size() ||
633 * toIndex > size() ||
634 * toIndex < fromIndex})
635 */
636 protected void removeRange(int fromIndex, int toIndex) {
637 modCount++;
638 int numMoved = size - toIndex;
639 System.arraycopy(elementData, toIndex, elementData, fromIndex,
640 numMoved);
641
642 // clear to let GC do its work
643 int newSize = size - (toIndex-fromIndex);
644 for (int i = newSize; i < size; i++) {
645 elementData[i] = null;
646 }
647 size = newSize;
648 }
649
650 /**
651 * Checks if the given index is in range. If not, throws an appropriate
652 * runtime exception. This method does *not* check if the index is
653 * negative: It is always used immediately prior to an array access,
654 * which throws an ArrayIndexOutOfBoundsException if index is negative.
655 */
656 private void rangeCheck(int index) {
657 if (index >= size)
658 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
659 }
660
661 /**
662 * A version of rangeCheck used by add and addAll.
663 */
664 private void rangeCheckForAdd(int index) {
665 if (index > size || index < 0)
666 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
667 }
668
669 /**
670 * Constructs an IndexOutOfBoundsException detail message.
671 * Of the many possible refactorings of the error handling code,
672 * this "outlining" performs best with both server and client VMs.
673 */
674 private String outOfBoundsMsg(int index) {
675 return "Index: "+index+", Size: "+size;
676 }
677
678 /**
679 * Removes from this list all of its elements that are contained in the
680 * specified collection.
681 *
682 * @param c collection containing elements to be removed from this list
683 * @return {@code true} if this list changed as a result of the call
684 * @throws ClassCastException if the class of an element of this list
685 * is incompatible with the specified collection
686 * (<a href="Collection.html#optional-restrictions">optional</a>)
687 * @throws NullPointerException if this list contains a null element and the
688 * specified collection does not permit null elements
689 * (<a href="Collection.html#optional-restrictions">optional</a>),
690 * or if the specified collection is null
691 * @see Collection#contains(Object)
692 */
693 public boolean removeAll(Collection<?> c) {
694 Objects.requireNonNull(c);
695 return batchRemove(c, false);
696 }
697
698 /**
699 * Retains only the elements in this list that are contained in the
700 * specified collection. In other words, removes from this list all
701 * of its elements that are not contained in the specified collection.
702 *
703 * @param c collection containing elements to be retained in this list
704 * @return {@code true} if this list changed as a result of the call
705 * @throws ClassCastException if the class of an element of this list
706 * is incompatible with the specified collection
707 * (<a href="Collection.html#optional-restrictions">optional</a>)
708 * @throws NullPointerException if this list contains a null element and the
709 * specified collection does not permit null elements
710 * (<a href="Collection.html#optional-restrictions">optional</a>),
711 * or if the specified collection is null
712 * @see Collection#contains(Object)
713 */
714 public boolean retainAll(Collection<?> c) {
715 Objects.requireNonNull(c);
716 return batchRemove(c, true);
717 }
718
719 private boolean batchRemove(Collection<?> c, boolean complement) {
720 final Object[] elementData = this.elementData;
721 int r = 0, w = 0;
722 boolean modified = false;
723 try {
724 for (; r < size; r++)
725 if (c.contains(elementData[r]) == complement)
726 elementData[w++] = elementData[r];
727 } finally {
728 // Preserve behavioral compatibility with AbstractCollection,
729 // even if c.contains() throws.
730 if (r != size) {
731 System.arraycopy(elementData, r,
732 elementData, w,
733 size - r);
734 w += size - r;
735 }
736 if (w != size) {
737 // clear to let GC do its work
738 for (int i = w; i < size; i++)
739 elementData[i] = null;
740 modCount += size - w;
741 size = w;
742 modified = true;
743 }
744 }
745 return modified;
746 }
747
748 /**
749 * Save the state of the {@code ArrayList} instance to a stream (that
750 * is, serialize it).
751 *
752 * @serialData The length of the array backing the {@code ArrayList}
753 * instance is emitted (int), followed by all of its elements
754 * (each an {@code Object}) in the proper order.
755 */
756 private void writeObject(java.io.ObjectOutputStream s)
757 throws java.io.IOException{
758 // Write out element count, and any hidden stuff
759 int expectedModCount = modCount;
760 s.defaultWriteObject();
761
762 // Write out size as capacity for behavioural compatibility with clone()
763 s.writeInt(size);
764
765 // Write out all elements in the proper order.
766 for (int i=0; i<size; i++) {
767 s.writeObject(elementData[i]);
768 }
769
770 if (modCount != expectedModCount) {
771 throw new ConcurrentModificationException();
772 }
773 }
774
775 /**
776 * Reconstitute the {@code ArrayList} instance from a stream (that is,
777 * deserialize it).
778 */
779 private void readObject(java.io.ObjectInputStream s)
780 throws java.io.IOException, ClassNotFoundException {
781 elementData = EMPTY_ELEMENTDATA;
782
783 // Read in size, and any hidden stuff
784 s.defaultReadObject();
785
786 // Read in capacity
787 s.readInt(); // ignored
788
789 if (size > 0) {
790 // be like clone(), allocate array based upon size not capacity
791 ensureCapacityInternal(size);
792
793 Object[] a = elementData;
794 // Read in all elements in the proper order.
795 for (int i=0; i<size; i++) {
796 a[i] = s.readObject();
797 }
798 }
799 }
800
801 /**
802 * Returns a list iterator over the elements in this list (in proper
803 * sequence), starting at the specified position in the list.
804 * The specified index indicates the first element that would be
805 * returned by an initial call to {@link ListIterator#next next}.
806 * An initial call to {@link ListIterator#previous previous} would
807 * return the element with the specified index minus one.
808 *
809 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
810 *
811 * @throws IndexOutOfBoundsException {@inheritDoc}
812 */
813 public ListIterator<E> listIterator(int index) {
814 if (index < 0 || index > size)
815 throw new IndexOutOfBoundsException("Index: "+index);
816 return new ListItr(index);
817 }
818
819 /**
820 * Returns a list iterator over the elements in this list (in proper
821 * sequence).
822 *
823 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
824 *
825 * @see #listIterator(int)
826 */
827 public ListIterator<E> listIterator() {
828 return new ListItr(0);
829 }
830
831 /**
832 * Returns an iterator over the elements in this list in proper sequence.
833 *
834 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
835 *
836 * @return an iterator over the elements in this list in proper sequence
837 */
838 public Iterator<E> iterator() {
839 return new Itr();
840 }
841
842 /**
843 * An optimized version of AbstractList.Itr
844 */
845 private class Itr implements Iterator<E> {
846 int cursor; // index of next element to return
847 int lastRet = -1; // index of last element returned; -1 if no such
848 int expectedModCount = modCount;
849
850 public boolean hasNext() {
851 return cursor != size;
852 }
853
854 @SuppressWarnings("unchecked")
855 public E next() {
856 checkForComodification();
857 int i = cursor;
858 if (i >= size)
859 throw new NoSuchElementException();
860 Object[] elementData = ArrayList.this.elementData;
861 if (i >= elementData.length)
862 throw new ConcurrentModificationException();
863 cursor = i + 1;
864 return (E) elementData[lastRet = i];
865 }
866
867 public void remove() {
868 if (lastRet < 0)
869 throw new IllegalStateException();
870 checkForComodification();
871
872 try {
873 ArrayList.this.remove(lastRet);
874 cursor = lastRet;
875 lastRet = -1;
876 expectedModCount = modCount;
877 } catch (IndexOutOfBoundsException ex) {
878 throw new ConcurrentModificationException();
879 }
880 }
881
882 @Override
883 @SuppressWarnings("unchecked")
884 public void forEachRemaining(Consumer<? super E> consumer) {
885 Objects.requireNonNull(consumer);
886 final int size = ArrayList.this.size;
887 int i = cursor;
888 if (i >= size) {
889 return;
890 }
891 final Object[] elementData = ArrayList.this.elementData;
892 if (i >= elementData.length) {
893 throw new ConcurrentModificationException();
894 }
895 while (i != size && modCount == expectedModCount) {
896 consumer.accept((E) elementData[i++]);
897 }
898 // update once at end of iteration to reduce heap write traffic
899 cursor = i;
900 lastRet = i - 1;
901 checkForComodification();
902 }
903
904 final void checkForComodification() {
905 if (modCount != expectedModCount)
906 throw new ConcurrentModificationException();
907 }
908 }
909
910 /**
911 * An optimized version of AbstractList.ListItr
912 */
913 private class ListItr extends Itr implements ListIterator<E> {
914 ListItr(int index) {
915 super();
916 cursor = index;
917 }
918
919 public boolean hasPrevious() {
920 return cursor != 0;
921 }
922
923 public int nextIndex() {
924 return cursor;
925 }
926
927 public int previousIndex() {
928 return cursor - 1;
929 }
930
931 @SuppressWarnings("unchecked")
932 public E previous() {
933 checkForComodification();
934 int i = cursor - 1;
935 if (i < 0)
936 throw new NoSuchElementException();
937 Object[] elementData = ArrayList.this.elementData;
938 if (i >= elementData.length)
939 throw new ConcurrentModificationException();
940 cursor = i;
941 return (E) elementData[lastRet = i];
942 }
943
944 public void set(E e) {
945 if (lastRet < 0)
946 throw new IllegalStateException();
947 checkForComodification();
948
949 try {
950 ArrayList.this.set(lastRet, e);
951 } catch (IndexOutOfBoundsException ex) {
952 throw new ConcurrentModificationException();
953 }
954 }
955
956 public void add(E e) {
957 checkForComodification();
958
959 try {
960 int i = cursor;
961 ArrayList.this.add(i, e);
962 cursor = i + 1;
963 lastRet = -1;
964 expectedModCount = modCount;
965 } catch (IndexOutOfBoundsException ex) {
966 throw new ConcurrentModificationException();
967 }
968 }
969 }
970
971 /**
972 * Returns a view of the portion of this list between the specified
973 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
974 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
975 * empty.) The returned list is backed by this list, so non-structural
976 * changes in the returned list are reflected in this list, and vice-versa.
977 * The returned list supports all of the optional list operations.
978 *
979 * <p>This method eliminates the need for explicit range operations (of
980 * the sort that commonly exist for arrays). Any operation that expects
981 * a list can be used as a range operation by passing a subList view
982 * instead of a whole list. For example, the following idiom
983 * removes a range of elements from a list:
984 * <pre>
985 * list.subList(from, to).clear();
986 * </pre>
987 * Similar idioms may be constructed for {@link #indexOf(Object)} and
988 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
989 * {@link Collections} class can be applied to a subList.
990 *
991 * <p>The semantics of the list returned by this method become undefined if
992 * the backing list (i.e., this list) is <i>structurally modified</i> in
993 * any way other than via the returned list. (Structural modifications are
994 * those that change the size of this list, or otherwise perturb it in such
995 * a fashion that iterations in progress may yield incorrect results.)
996 *
997 * @throws IndexOutOfBoundsException {@inheritDoc}
998 * @throws IllegalArgumentException {@inheritDoc}
999 */
1000 public List<E> subList(int fromIndex, int toIndex) {
1001 subListRangeCheck(fromIndex, toIndex, size);
1002 return new SubList(this, 0, fromIndex, toIndex);
1003 }
1004
1005 static void subListRangeCheck(int fromIndex, int toIndex, int size) {
1006 if (fromIndex < 0)
1007 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
1008 if (toIndex > size)
1009 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
1010 if (fromIndex > toIndex)
1011 throw new IllegalArgumentException("fromIndex(" + fromIndex +
1012 ") > toIndex(" + toIndex + ")");
1013 }
1014
1015 private class SubList extends AbstractList<E> implements RandomAccess {
1016 private final AbstractList<E> parent;
1017 private final int parentOffset;
1018 private final int offset;
1019 int size;
1020
1021 SubList(AbstractList<E> parent,
1022 int offset, int fromIndex, int toIndex) {
1023 this.parent = parent;
1024 this.parentOffset = fromIndex;
1025 this.offset = offset + fromIndex;
1026 this.size = toIndex - fromIndex;
1027 this.modCount = ArrayList.this.modCount;
1028 }
1029
1030 public E set(int index, E e) {
1031 rangeCheck(index);
1032 checkForComodification();
1033 E oldValue = ArrayList.this.elementData(offset + index);
1034 ArrayList.this.elementData[offset + index] = e;
1035 return oldValue;
1036 }
1037
1038 public E get(int index) {
1039 rangeCheck(index);
1040 checkForComodification();
1041 return ArrayList.this.elementData(offset + index);
1042 }
1043
1044 public int size() {
1045 checkForComodification();
1046 return this.size;
1047 }
1048
1049 public void add(int index, E e) {
1050 rangeCheckForAdd(index);
1051 checkForComodification();
1052 parent.add(parentOffset + index, e);
1053 this.modCount = parent.modCount;
1054 this.size++;
1055 }
1056
1057 public E remove(int index) {
1058 rangeCheck(index);
1059 checkForComodification();
1060 E result = parent.remove(parentOffset + index);
1061 this.modCount = parent.modCount;
1062 this.size--;
1063 return result;
1064 }
1065
1066 protected void removeRange(int fromIndex, int toIndex) {
1067 checkForComodification();
1068 parent.removeRange(parentOffset + fromIndex,
1069 parentOffset + toIndex);
1070 this.modCount = parent.modCount;
1071 this.size -= toIndex - fromIndex;
1072 }
1073
1074 public boolean addAll(Collection<? extends E> c) {
1075 return addAll(this.size, c);
1076 }
1077
1078 public boolean addAll(int index, Collection<? extends E> c) {
1079 rangeCheckForAdd(index);
1080 int cSize = c.size();
1081 if (cSize==0)
1082 return false;
1083
1084 checkForComodification();
1085 parent.addAll(parentOffset + index, c);
1086 this.modCount = parent.modCount;
1087 this.size += cSize;
1088 return true;
1089 }
1090
1091 public Iterator<E> iterator() {
1092 return listIterator();
1093 }
1094
1095 public ListIterator<E> listIterator(final int index) {
1096 checkForComodification();
1097 rangeCheckForAdd(index);
1098 final int offset = this.offset;
1099
1100 return new ListIterator<E>() {
1101 int cursor = index;
1102 int lastRet = -1;
1103 int expectedModCount = ArrayList.this.modCount;
1104
1105 public boolean hasNext() {
1106 return cursor != SubList.this.size;
1107 }
1108
1109 @SuppressWarnings("unchecked")
1110 public E next() {
1111 checkForComodification();
1112 int i = cursor;
1113 if (i >= SubList.this.size)
1114 throw new NoSuchElementException();
1115 Object[] elementData = ArrayList.this.elementData;
1116 if (offset + i >= elementData.length)
1117 throw new ConcurrentModificationException();
1118 cursor = i + 1;
1119 return (E) elementData[offset + (lastRet = i)];
1120 }
1121
1122 public boolean hasPrevious() {
1123 return cursor != 0;
1124 }
1125
1126 @SuppressWarnings("unchecked")
1127 public E previous() {
1128 checkForComodification();
1129 int i = cursor - 1;
1130 if (i < 0)
1131 throw new NoSuchElementException();
1132 Object[] elementData = ArrayList.this.elementData;
1133 if (offset + i >= elementData.length)
1134 throw new ConcurrentModificationException();
1135 cursor = i;
1136 return (E) elementData[offset + (lastRet = i)];
1137 }
1138
1139 @SuppressWarnings("unchecked")
1140 public void forEachRemaining(Consumer<? super E> consumer) {
1141 Objects.requireNonNull(consumer);
1142 final int size = SubList.this.size;
1143 int i = cursor;
1144 if (i >= size) {
1145 return;
1146 }
1147 final Object[] elementData = ArrayList.this.elementData;
1148 if (offset + i >= elementData.length) {
1149 throw new ConcurrentModificationException();
1150 }
1151 while (i != size && modCount == expectedModCount) {
1152 consumer.accept((E) elementData[offset + (i++)]);
1153 }
1154 // update once at end of iteration to reduce heap write traffic
1155 lastRet = cursor = i;
1156 checkForComodification();
1157 }
1158
1159 public int nextIndex() {
1160 return cursor;
1161 }
1162
1163 public int previousIndex() {
1164 return cursor - 1;
1165 }
1166
1167 public void remove() {
1168 if (lastRet < 0)
1169 throw new IllegalStateException();
1170 checkForComodification();
1171
1172 try {
1173 SubList.this.remove(lastRet);
1174 cursor = lastRet;
1175 lastRet = -1;
1176 expectedModCount = ArrayList.this.modCount;
1177 } catch (IndexOutOfBoundsException ex) {
1178 throw new ConcurrentModificationException();
1179 }
1180 }
1181
1182 public void set(E e) {
1183 if (lastRet < 0)
1184 throw new IllegalStateException();
1185 checkForComodification();
1186
1187 try {
1188 ArrayList.this.set(offset + lastRet, e);
1189 } catch (IndexOutOfBoundsException ex) {
1190 throw new ConcurrentModificationException();
1191 }
1192 }
1193
1194 public void add(E e) {
1195 checkForComodification();
1196
1197 try {
1198 int i = cursor;
1199 SubList.this.add(i, e);
1200 cursor = i + 1;
1201 lastRet = -1;
1202 expectedModCount = ArrayList.this.modCount;
1203 } catch (IndexOutOfBoundsException ex) {
1204 throw new ConcurrentModificationException();
1205 }
1206 }
1207
1208 final void checkForComodification() {
1209 if (expectedModCount != ArrayList.this.modCount)
1210 throw new ConcurrentModificationException();
1211 }
1212 };
1213 }
1214
1215 public List<E> subList(int fromIndex, int toIndex) {
1216 subListRangeCheck(fromIndex, toIndex, size);
1217 return new SubList(this, offset, fromIndex, toIndex);
1218 }
1219
1220 private void rangeCheck(int index) {
1221 if (index < 0 || index >= this.size)
1222 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1223 }
1224
1225 private void rangeCheckForAdd(int index) {
1226 if (index < 0 || index > this.size)
1227 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1228 }
1229
1230 private String outOfBoundsMsg(int index) {
1231 return "Index: "+index+", Size: "+this.size;
1232 }
1233
1234 private void checkForComodification() {
1235 if (ArrayList.this.modCount != this.modCount)
1236 throw new ConcurrentModificationException();
1237 }
1238
1239 public Spliterator<E> spliterator() {
1240 checkForComodification();
1241 return new ArrayListSpliterator<>(ArrayList.this, offset,
1242 offset + this.size, this.modCount);
1243 }
1244 }
1245
1246 @Override
1247 public void forEach(Consumer<? super E> action) {
1248 Objects.requireNonNull(action);
1249 final int expectedModCount = modCount;
1250 @SuppressWarnings("unchecked")
1251 final E[] elementData = (E[]) this.elementData;
1252 final int size = this.size;
1253 for (int i=0; modCount == expectedModCount && i < size; i++) {
1254 action.accept(elementData[i]);
1255 }
1256 if (modCount != expectedModCount) {
1257 throw new ConcurrentModificationException();
1258 }
1259 }
1260
1261 /**
1262 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1263 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1264 * list.
1265 *
1266 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1267 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1268 * Overriding implementations should document the reporting of additional
1269 * characteristic values.
1270 *
1271 * @return a {@code Spliterator} over the elements in this list
1272 * @since 1.8
1273 */
1274 @Override
1275 public Spliterator<E> spliterator() {
1276 return new ArrayListSpliterator<>(this, 0, -1, 0);
1277 }
1278
1279 /** Index-based split-by-two, lazily initialized Spliterator */
1280 static final class ArrayListSpliterator<E> implements Spliterator<E> {
1281
1282 /*
1283 * If ArrayLists were immutable, or structurally immutable (no
1284 * adds, removes, etc), we could implement their spliterators
1285 * with Arrays.spliterator. Instead we detect as much
1286 * interference during traversal as practical without
1287 * sacrificing much performance. We rely primarily on
1288 * modCounts. These are not guaranteed to detect concurrency
1289 * violations, and are sometimes overly conservative about
1290 * within-thread interference, but detect enough problems to
1291 * be worthwhile in practice. To carry this out, we (1) lazily
1292 * initialize fence and expectedModCount until the latest
1293 * point that we need to commit to the state we are checking
1294 * against; thus improving precision. (This doesn't apply to
1295 * SubLists, that create spliterators with current non-lazy
1296 * values). (2) We perform only a single
1297 * ConcurrentModificationException check at the end of forEach
1298 * (the most performance-sensitive method). When using forEach
1299 * (as opposed to iterators), we can normally only detect
1300 * interference after actions, not before. Further
1301 * CME-triggering checks apply to all other possible
1302 * violations of assumptions for example null or too-small
1303 * elementData array given its size(), that could only have
1304 * occurred due to interference. This allows the inner loop
1305 * of forEach to run without any further checks, and
1306 * simplifies lambda-resolution. While this does entail a
1307 * number of checks, note that in the common case of
1308 * list.stream().forEach(a), no checks or other computation
1309 * occur anywhere other than inside forEach itself. The other
1310 * less-often-used methods cannot take advantage of most of
1311 * these streamlinings.
1312 */
1313
1314 private final ArrayList<E> list;
1315 private int index; // current index, modified on advance/split
1316 private int fence; // -1 until used; then one past last index
1317 private int expectedModCount; // initialized when fence set
1318
1319 /** Create new spliterator covering the given range */
1320 ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
1321 int expectedModCount) {
1322 this.list = list; // OK if null unless traversed
1323 this.index = origin;
1324 this.fence = fence;
1325 this.expectedModCount = expectedModCount;
1326 }
1327
1328 private int getFence() { // initialize fence to size on first use
1329 int hi; // (a specialized variant appears in method forEach)
1330 ArrayList<E> lst;
1331 if ((hi = fence) < 0) {
1332 if ((lst = list) == null)
1333 hi = fence = 0;
1334 else {
1335 expectedModCount = lst.modCount;
1336 hi = fence = lst.size;
1337 }
1338 }
1339 return hi;
1340 }
1341
1342 public ArrayListSpliterator<E> trySplit() {
1343 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1344 return (lo >= mid) ? null : // divide range in half unless too small
1345 new ArrayListSpliterator<>(list, lo, index = mid,
1346 expectedModCount);
1347 }
1348
1349 public boolean tryAdvance(Consumer<? super E> action) {
1350 if (action == null)
1351 throw new NullPointerException();
1352 int hi = getFence(), i = index;
1353 if (i < hi) {
1354 index = i + 1;
1355 @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
1356 action.accept(e);
1357 if (list.modCount != expectedModCount)
1358 throw new ConcurrentModificationException();
1359 return true;
1360 }
1361 return false;
1362 }
1363
1364 public void forEachRemaining(Consumer<? super E> action) {
1365 int i, hi, mc; // hoist accesses and checks from loop
1366 ArrayList<E> lst; Object[] a;
1367 if (action == null)
1368 throw new NullPointerException();
1369 if ((lst = list) != null && (a = lst.elementData) != null) {
1370 if ((hi = fence) < 0) {
1371 mc = lst.modCount;
1372 hi = lst.size;
1373 }
1374 else
1375 mc = expectedModCount;
1376 if ((i = index) >= 0 && (index = hi) <= a.length) {
1377 for (; i < hi; ++i) {
1378 @SuppressWarnings("unchecked") E e = (E) a[i];
1379 action.accept(e);
1380 }
1381 if (lst.modCount == mc)
1382 return;
1383 }
1384 }
1385 throw new ConcurrentModificationException();
1386 }
1387
1388 public long estimateSize() {
1389 return (long) (getFence() - index);
1390 }
1391
1392 public int characteristics() {
1393 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1394 }
1395 }
1396
1397 @Override
1398 public boolean removeIf(Predicate<? super E> filter) {
1399 Objects.requireNonNull(filter);
1400 // figure out which elements are to be removed
1401 // any exception thrown from the filter predicate at this stage
1402 // will leave the collection unmodified
1403 int removeCount = 0;
1404 final BitSet removeSet = new BitSet(size);
1405 final int expectedModCount = modCount;
1406 final int size = this.size;
1407 for (int i=0; modCount == expectedModCount && i < size; i++) {
1408 @SuppressWarnings("unchecked")
1409 final E element = (E) elementData[i];
1410 if (filter.test(element)) {
1411 removeSet.set(i);
1412 removeCount++;
1413 }
1414 }
1415 if (modCount != expectedModCount) {
1416 throw new ConcurrentModificationException();
1417 }
1418
1419 // shift surviving elements left over the spaces left by removed elements
1420 final boolean anyToRemove = removeCount > 0;
1421 if (anyToRemove) {
1422 final int newSize = size - removeCount;
1423 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
1424 i = removeSet.nextClearBit(i);
1425 elementData[j] = elementData[i];
1426 }
1427 for (int k=newSize; k < size; k++) {
1428 elementData[k] = null; // Let gc do its work
1429 }
1430 this.size = newSize;
1431 if (modCount != expectedModCount) {
1432 throw new ConcurrentModificationException();
1433 }
1434 modCount++;
1435 }
1436
1437 return anyToRemove;
1438 }
1439
1440 @Override
1441 @SuppressWarnings("unchecked")
1442 public void replaceAll(UnaryOperator<E> operator) {
1443 Objects.requireNonNull(operator);
1444 final int expectedModCount = modCount;
1445 final int size = this.size;
1446 for (int i=0; modCount == expectedModCount && i < size; i++) {
1447 elementData[i] = operator.apply((E) elementData[i]);
1448 }
1449 if (modCount != expectedModCount) {
1450 throw new ConcurrentModificationException();
1451 }
1452 modCount++;
1453 }
1454
1455 @Override
1456 @SuppressWarnings("unchecked")
1457 public void sort(Comparator<? super E> c) {
1458 final int expectedModCount = modCount;
1459 Arrays.sort((E[]) elementData, 0, size, c);
1460 if (modCount != expectedModCount) {
1461 throw new ConcurrentModificationException();
1462 }
1463 modCount++;
1464 }
1465 }