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