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