· 9 years ago · Oct 18, 2016, 04:06 AM
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
26package java.util;
27
28import java.util.function.Consumer;
29import java.util.function.Predicate;
30import 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
106public 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 * fromIndex >= size() ||
613 * toIndex > size() ||
614 * toIndex < fromIndex})
615 */
616 protected void removeRange(int fromIndex, int toIndex) {
617 modCount++;
618 int numMoved = size - toIndex;
619 System.arraycopy(elementData, toIndex, elementData, fromIndex,
620 numMoved);
621
622 // clear to let GC do its work
623 int newSize = size - (toIndex-fromIndex);
624 for (int i = newSize; i < size; i++) {
625 elementData[i] = null;
626 }
627 size = newSize;
628 }
629
630 /**
631 * Checks if the given index is in range. If not, throws an appropriate
632 * runtime exception. This method does *not* check if the index is
633 * negative: It is always used immediately prior to an array access,
634 * which throws an ArrayIndexOutOfBoundsException if index is negative.
635 */
636 private void rangeCheck(int index) {
637 if (index >= size)
638 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
639 }
640
641 /**
642 * A version of rangeCheck used by add and addAll.
643 */
644 private void rangeCheckForAdd(int index) {
645 if (index > size || index < 0)
646 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
647 }
648
649 /**
650 * Constructs an IndexOutOfBoundsException detail message.
651 * Of the many possible refactorings of the error handling code,
652 * this "outlining" performs best with both server and client VMs.
653 */
654 private String outOfBoundsMsg(int index) {
655 return "Index: "+index+", Size: "+size;
656 }
657
658 /**
659 * Removes from this list all of its elements that are contained in the
660 * specified collection.
661 *
662 * @param c collection containing elements to be removed from this list
663 * @return {@code true} if this list changed as a result of the call
664 * @throws ClassCastException if the class of an element of this list
665 * is incompatible with the specified collection
666 * (<a href="Collection.html#optional-restrictions">optional</a>)
667 * @throws NullPointerException if this list contains a null element and the
668 * specified collection does not permit null elements
669 * (<a href="Collection.html#optional-restrictions">optional</a>),
670 * or if the specified collection is null
671 * @see Collection#contains(Object)
672 */
673 public boolean removeAll(Collection<?> c) {
674 Objects.requireNonNull(c);
675 return batchRemove(c, false);
676 }
677
678 /**
679 * Retains only the elements in this list that are contained in the
680 * specified collection. In other words, removes from this list all
681 * of its elements that are not contained in the specified collection.
682 *
683 * @param c collection containing elements to be retained in this list
684 * @return {@code true} if this list changed as a result of the call
685 * @throws ClassCastException if the class of an element of this list
686 * is incompatible with the specified collection
687 * (<a href="Collection.html#optional-restrictions">optional</a>)
688 * @throws NullPointerException if this list contains a null element and the
689 * specified collection does not permit null elements
690 * (<a href="Collection.html#optional-restrictions">optional</a>),
691 * or if the specified collection is null
692 * @see Collection#contains(Object)
693 */
694 public boolean retainAll(Collection<?> c) {
695 Objects.requireNonNull(c);
696 return batchRemove(c, true);
697 }
698
699 private boolean batchRemove(Collection<?> c, boolean complement) {
700 final Object[] elementData = this.elementData;
701 int r = 0, w = 0;
702 boolean modified = false;
703 try {
704 for (; r < size; r++)
705 if (c.contains(elementData[r]) == complement)
706 elementData[w++] = elementData[r];
707 } finally {
708 // Preserve behavioral compatibility with AbstractCollection,
709 // even if c.contains() throws.
710 if (r != size) {
711 System.arraycopy(elementData, r,
712 elementData, w,
713 size - r);
714 w += size - r;
715 }
716 if (w != size) {
717 // clear to let GC do its work
718 for (int i = w; i < size; i++)
719 elementData[i] = null;
720 modCount += size - w;
721 size = w;
722 modified = true;
723 }
724 }
725 return modified;
726 }
727
728 /**
729 * Save the state of the <tt>ArrayList</tt> instance to a stream (that
730 * is, serialize it).
731 *
732 * @serialData The length of the array backing the <tt>ArrayList</tt>
733 * instance is emitted (int), followed by all of its elements
734 * (each an <tt>Object</tt>) in the proper order.
735 */
736 private void writeObject(java.io.ObjectOutputStream s)
737 throws java.io.IOException{
738 // Write out element count, and any hidden stuff
739 int expectedModCount = modCount;
740 s.defaultWriteObject();
741
742 // Write out size as capacity for behavioural compatibility with clone()
743 s.writeInt(size);
744
745 // Write out all elements in the proper order.
746 for (int i=0; i<size; i++) {
747 s.writeObject(elementData[i]);
748 }
749
750 if (modCount != expectedModCount) {
751 throw new ConcurrentModificationException();
752 }
753 }
754
755 /**
756 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
757 * deserialize it).
758 */
759 private void readObject(java.io.ObjectInputStream s)
760 throws java.io.IOException, ClassNotFoundException {
761 elementData = EMPTY_ELEMENTDATA;
762
763 // Read in size, and any hidden stuff
764 s.defaultReadObject();
765
766 // Read in capacity
767 s.readInt(); // ignored
768
769 if (size > 0) {
770 // be like clone(), allocate array based upon size not capacity
771 ensureCapacityInternal(size);
772
773 Object[] a = elementData;
774 // Read in all elements in the proper order.
775 for (int i=0; i<size; i++) {
776 a[i] = s.readObject();
777 }
778 }
779 }
780
781 /**
782 * Returns a list iterator over the elements in this list (in proper
783 * sequence), starting at the specified position in the list.
784 * The specified index indicates the first element that would be
785 * returned by an initial call to {@link ListIterator#next next}.
786 * An initial call to {@link ListIterator#previous previous} would
787 * return the element with the specified index minus one.
788 *
789 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
790 *
791 * @throws IndexOutOfBoundsException {@inheritDoc}
792 */
793 public ListIterator<E> listIterator(int index) {
794 if (index < 0 || index > size)
795 throw new IndexOutOfBoundsException("Index: "+index);
796 return new ListItr(index);
797 }
798
799 /**
800 * Returns a list iterator over the elements in this list (in proper
801 * sequence).
802 *
803 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
804 *
805 * @see #listIterator(int)
806 */
807 public ListIterator<E> listIterator() {
808 return new ListItr(0);
809 }
810
811 /**
812 * Returns an iterator over the elements in this list in proper sequence.
813 *
814 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
815 *
816 * @return an iterator over the elements in this list in proper sequence
817 */
818 public Iterator<E> iterator() {
819 return new Itr();
820 }
821
822 /**
823 * An optimized version of AbstractList.Itr
824 */
825 private class Itr implements Iterator<E> {
826 int cursor; // index of next element to return
827 int lastRet = -1; // index of last element returned; -1 if no such
828 int expectedModCount = modCount;
829
830 public boolean hasNext() {
831 return cursor != size;
832 }
833
834 @SuppressWarnings("unchecked")
835 public E next() {
836 checkForComodification();
837 int i = cursor;
838 if (i >= size)
839 throw new NoSuchElementException();
840 Object[] elementData = ArrayList.this.elementData;
841 if (i >= elementData.length)
842 throw new ConcurrentModificationException();
843 cursor = i + 1;
844 return (E) elementData[lastRet = i];
845 }
846
847 public void remove() {
848 if (lastRet < 0)
849 throw new IllegalStateException();
850 checkForComodification();
851
852 try {
853 ArrayList.this.remove(lastRet);
854 cursor = lastRet;
855 lastRet = -1;
856 expectedModCount = modCount;
857 } catch (IndexOutOfBoundsException ex) {
858 throw new ConcurrentModificationException();
859 }
860 }
861
862 @Override
863 @SuppressWarnings("unchecked")
864 public void forEachRemaining(Consumer<? super E> consumer) {
865 Objects.requireNonNull(consumer);
866 final int size = ArrayList.this.size;
867 int i = cursor;
868 if (i >= size) {
869 return;
870 }
871 final Object[] elementData = ArrayList.this.elementData;
872 if (i >= elementData.length) {
873 throw new ConcurrentModificationException();
874 }
875 while (i != size && modCount == expectedModCount) {
876 consumer.accept((E) elementData[i++]);
877 }
878 // update once at end of iteration to reduce heap write traffic
879 cursor = i;
880 lastRet = i - 1;
881 checkForComodification();
882 }
883
884 final void checkForComodification() {
885 if (modCount != expectedModCount)
886 throw new ConcurrentModificationException();
887 }
888 }
889
890 /**
891 * An optimized version of AbstractList.ListItr
892 */
893 private class ListItr extends Itr implements ListIterator<E> {
894 ListItr(int index) {
895 super();
896 cursor = index;
897 }
898
899 public boolean hasPrevious() {
900 return cursor != 0;
901 }
902
903 public int nextIndex() {
904 return cursor;
905 }
906
907 public int previousIndex() {
908 return cursor - 1;
909 }
910
911 @SuppressWarnings("unchecked")
912 public E previous() {
913 checkForComodification();
914 int i = cursor - 1;
915 if (i < 0)
916 throw new NoSuchElementException();
917 Object[] elementData = ArrayList.this.elementData;
918 if (i >= elementData.length)
919 throw new ConcurrentModificationException();
920 cursor = i;
921 return (E) elementData[lastRet = i];
922 }
923
924 public void set(E e) {
925 if (lastRet < 0)
926 throw new IllegalStateException();
927 checkForComodification();
928
929 try {
930 ArrayList.this.set(lastRet, e);
931 } catch (IndexOutOfBoundsException ex) {
932 throw new ConcurrentModificationException();
933 }
934 }
935
936 public void add(E e) {
937 checkForComodification();
938
939 try {
940 int i = cursor;
941 ArrayList.this.add(i, e);
942 cursor = i + 1;
943 lastRet = -1;
944 expectedModCount = modCount;
945 } catch (IndexOutOfBoundsException ex) {
946 throw new ConcurrentModificationException();
947 }
948 }
949 }
950
951 /**
952 * Returns a view of the portion of this list between the specified
953 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
954 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
955 * empty.) The returned list is backed by this list, so non-structural
956 * changes in the returned list are reflected in this list, and vice-versa.
957 * The returned list supports all of the optional list operations.
958 *
959 * <p>This method eliminates the need for explicit range operations (of
960 * the sort that commonly exist for arrays). Any operation that expects
961 * a list can be used as a range operation by passing a subList view
962 * instead of a whole list. For example, the following idiom
963 * removes a range of elements from a list:
964 * <pre>
965 * list.subList(from, to).clear();
966 * </pre>
967 * Similar idioms may be constructed for {@link #indexOf(Object)} and
968 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
969 * {@link Collections} class can be applied to a subList.
970 *
971 * <p>The semantics of the list returned by this method become undefined if
972 * the backing list (i.e., this list) is <i>structurally modified</i> in
973 * any way other than via the returned list. (Structural modifications are
974 * those that change the size of this list, or otherwise perturb it in such
975 * a fashion that iterations in progress may yield incorrect results.)
976 *
977 * @throws IndexOutOfBoundsException {@inheritDoc}
978 * @throws IllegalArgumentException {@inheritDoc}
979 */
980 public List<E> subList(int fromIndex, int toIndex) {
981 subListRangeCheck(fromIndex, toIndex, size);
982 return new SubList(this, 0, fromIndex, toIndex);
983 }
984
985 static void subListRangeCheck(int fromIndex, int toIndex, int size) {
986 if (fromIndex < 0)
987 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
988 if (toIndex > size)
989 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
990 if (fromIndex > toIndex)
991 throw new IllegalArgumentException("fromIndex(" + fromIndex +
992 ") > toIndex(" + toIndex + ")");
993 }
994
995 private class SubList extends AbstractList<E> implements RandomAccess {
996 private final AbstractList<E> parent;
997 private final int parentOffset;
998 private final int offset;
999 int size;
1000
1001 SubList(AbstractList<E> parent,
1002 int offset, int fromIndex, int toIndex) {
1003 this.parent = parent;
1004 this.parentOffset = fromIndex;
1005 this.offset = offset + fromIndex;
1006 this.size = toIndex - fromIndex;
1007 this.modCount = ArrayList.this.modCount;
1008 }
1009
1010 public E set(int index, E e) {
1011 rangeCheck(index);
1012 checkForComodification();
1013 E oldValue = ArrayList.this.elementData(offset + index);
1014 ArrayList.this.elementData[offset + index] = e;
1015 return oldValue;
1016 }
1017
1018 public E get(int index) {
1019 rangeCheck(index);
1020 checkForComodification();
1021 return ArrayList.this.elementData(offset + index);
1022 }
1023
1024 public int size() {
1025 checkForComodification();
1026 return this.size;
1027 }
1028
1029 public void add(int index, E e) {
1030 rangeCheckForAdd(index);
1031 checkForComodification();
1032 parent.add(parentOffset + index, e);
1033 this.modCount = parent.modCount;
1034 this.size++;
1035 }
1036
1037 public E remove(int index) {
1038 rangeCheck(index);
1039 checkForComodification();
1040 E result = parent.remove(parentOffset + index);
1041 this.modCount = parent.modCount;
1042 this.size--;
1043 return result;
1044 }
1045
1046 protected void removeRange(int fromIndex, int toIndex) {
1047 checkForComodification();
1048 parent.removeRange(parentOffset + fromIndex,
1049 parentOffset + toIndex);
1050 this.modCount = parent.modCount;
1051 this.size -= toIndex - fromIndex;
1052 }
1053
1054 public boolean addAll(Collection<? extends E> c) {
1055 return addAll(this.size, c);
1056 }
1057
1058 public boolean addAll(int index, Collection<? extends E> c) {
1059 rangeCheckForAdd(index);
1060 int cSize = c.size();
1061 if (cSize==0)
1062 return false;
1063
1064 checkForComodification();
1065 parent.addAll(parentOffset + index, c);
1066 this.modCount = parent.modCount;
1067 this.size += cSize;
1068 return true;
1069 }
1070
1071 public Iterator<E> iterator() {
1072 return listIterator();
1073 }
1074
1075 public ListIterator<E> listIterator(final int index) {
1076 checkForComodification();
1077 rangeCheckForAdd(index);
1078 final int offset = this.offset;
1079
1080 return new ListIterator<E>() {
1081 int cursor = index;
1082 int lastRet = -1;
1083 int expectedModCount = ArrayList.this.modCount;
1084
1085 public boolean hasNext() {
1086 return cursor != SubList.this.size;
1087 }
1088
1089 @SuppressWarnings("unchecked")
1090 public E next() {
1091 checkForComodification();
1092 int i = cursor;
1093 if (i >= SubList.this.size)
1094 throw new NoSuchElementException();
1095 Object[] elementData = ArrayList.this.elementData;
1096 if (offset + i >= elementData.length)
1097 throw new ConcurrentModificationException();
1098 cursor = i + 1;
1099 return (E) elementData[offset + (lastRet = i)];
1100 }
1101
1102 public boolean hasPrevious() {
1103 return cursor != 0;
1104 }
1105
1106 @SuppressWarnings("unchecked")
1107 public E previous() {
1108 checkForComodification();
1109 int i = cursor - 1;
1110 if (i < 0)
1111 throw new NoSuchElementException();
1112 Object[] elementData = ArrayList.this.elementData;
1113 if (offset + i >= elementData.length)
1114 throw new ConcurrentModificationException();
1115 cursor = i;
1116 return (E) elementData[offset + (lastRet = i)];
1117 }
1118
1119 @SuppressWarnings("unchecked")
1120 public void forEachRemaining(Consumer<? super E> consumer) {
1121 Objects.requireNonNull(consumer);
1122 final int size = SubList.this.size;
1123 int i = cursor;
1124 if (i >= size) {
1125 return;
1126 }
1127 final Object[] elementData = ArrayList.this.elementData;
1128 if (offset + i >= elementData.length) {
1129 throw new ConcurrentModificationException();
1130 }
1131 while (i != size && modCount == expectedModCount) {
1132 consumer.accept((E) elementData[offset + (i++)]);
1133 }
1134 // update once at end of iteration to reduce heap write traffic
1135 lastRet = cursor = i;
1136 checkForComodification();
1137 }
1138
1139 public int nextIndex() {
1140 return cursor;
1141 }
1142
1143 public int previousIndex() {
1144 return cursor - 1;
1145 }
1146
1147 public void remove() {
1148 if (lastRet < 0)
1149 throw new IllegalStateException();
1150 checkForComodification();
1151
1152 try {
1153 SubList.this.remove(lastRet);
1154 cursor = lastRet;
1155 lastRet = -1;
1156 expectedModCount = ArrayList.this.modCount;
1157 } catch (IndexOutOfBoundsException ex) {
1158 throw new ConcurrentModificationException();
1159 }
1160 }
1161
1162 public void set(E e) {
1163 if (lastRet < 0)
1164 throw new IllegalStateException();
1165 checkForComodification();
1166
1167 try {
1168 ArrayList.this.set(offset + lastRet, e);
1169 } catch (IndexOutOfBoundsException ex) {
1170 throw new ConcurrentModificationException();
1171 }
1172 }
1173
1174 public void add(E e) {
1175 checkForComodification();
1176
1177 try {
1178 int i = cursor;
1179 SubList.this.add(i, e);
1180 cursor = i + 1;
1181 lastRet = -1;
1182 expectedModCount = ArrayList.this.modCount;
1183 } catch (IndexOutOfBoundsException ex) {
1184 throw new ConcurrentModificationException();
1185 }
1186 }
1187
1188 final void checkForComodification() {
1189 if (expectedModCount != ArrayList.this.modCount)
1190 throw new ConcurrentModificationException();
1191 }
1192 };
1193 }
1194
1195 public List<E> subList(int fromIndex, int toIndex) {
1196 subListRangeCheck(fromIndex, toIndex, size);
1197 return new SubList(this, offset, fromIndex, toIndex);
1198 }
1199
1200 private void rangeCheck(int index) {
1201 if (index < 0 || index >= this.size)
1202 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1203 }
1204
1205 private void rangeCheckForAdd(int index) {
1206 if (index < 0 || index > this.size)
1207 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1208 }
1209
1210 private String outOfBoundsMsg(int index) {
1211 return "Index: "+index+", Size: "+this.size;
1212 }
1213
1214 private void checkForComodification() {
1215 if (ArrayList.this.modCount != this.modCount)
1216 throw new ConcurrentModificationException();
1217 }
1218
1219 public Spliterator<E> spliterator() {
1220 checkForComodification();
1221 return new ArrayListSpliterator<E>(ArrayList.this, offset,
1222 offset + this.size, this.modCount);
1223 }
1224 }
1225
1226 @Override
1227 public void forEach(Consumer<? super E> action) {
1228 Objects.requireNonNull(action);
1229 final int expectedModCount = modCount;
1230 @SuppressWarnings("unchecked")
1231 final E[] elementData = (E[]) this.elementData;
1232 final int size = this.size;
1233 for (int i=0; modCount == expectedModCount && i < size; i++) {
1234 action.accept(elementData[i]);
1235 }
1236 if (modCount != expectedModCount) {
1237 throw new ConcurrentModificationException();
1238 }
1239 }
1240
1241 /**
1242 * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
1243 * and <em>fail-fast</em> {@link Spliterator} over the elements in this
1244 * list.
1245 *
1246 * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
1247 * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
1248 * Overriding implementations should document the reporting of additional
1249 * characteristic values.
1250 *
1251 * @return a {@code Spliterator} over the elements in this list
1252 * @since 1.8
1253 */
1254 @Override
1255 public Spliterator<E> spliterator() {
1256 return new ArrayListSpliterator<>(this, 0, -1, 0);
1257 }
1258
1259 /** Index-based split-by-two, lazily initialized Spliterator */
1260 static final class ArrayListSpliterator<E> implements Spliterator<E> {
1261
1262 /*
1263 * If ArrayLists were immutable, or structurally immutable (no
1264 * adds, removes, etc), we could implement their spliterators
1265 * with Arrays.spliterator. Instead we detect as much
1266 * interference during traversal as practical without
1267 * sacrificing much performance. We rely primarily on
1268 * modCounts. These are not guaranteed to detect concurrency
1269 * violations, and are sometimes overly conservative about
1270 * within-thread interference, but detect enough problems to
1271 * be worthwhile in practice. To carry this out, we (1) lazily
1272 * initialize fence and expectedModCount until the latest
1273 * point that we need to commit to the state we are checking
1274 * against; thus improving precision. (This doesn't apply to
1275 * SubLists, that create spliterators with current non-lazy
1276 * values). (2) We perform only a single
1277 * ConcurrentModificationException check at the end of forEach
1278 * (the most performance-sensitive method). When using forEach
1279 * (as opposed to iterators), we can normally only detect
1280 * interference after actions, not before. Further
1281 * CME-triggering checks apply to all other possible
1282 * violations of assumptions for example null or too-small
1283 * elementData array given its size(), that could only have
1284 * occurred due to interference. This allows the inner loop
1285 * of forEach to run without any further checks, and
1286 * simplifies lambda-resolution. While this does entail a
1287 * number of checks, note that in the common case of
1288 * list.stream().forEach(a), no checks or other computation
1289 * occur anywhere other than inside forEach itself. The other
1290 * less-often-used methods cannot take advantage of most of
1291 * these streamlinings.
1292 */
1293
1294 private final ArrayList<E> list;
1295 private int index; // current index, modified on advance/split
1296 private int fence; // -1 until used; then one past last index
1297 private int expectedModCount; // initialized when fence set
1298
1299 /** Create new spliterator covering the given range */
1300 ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
1301 int expectedModCount) {
1302 this.list = list; // OK if null unless traversed
1303 this.index = origin;
1304 this.fence = fence;
1305 this.expectedModCount = expectedModCount;
1306 }
1307
1308 private int getFence() { // initialize fence to size on first use
1309 int hi; // (a specialized variant appears in method forEach)
1310 ArrayList<E> lst;
1311 if ((hi = fence) < 0) {
1312 if ((lst = list) == null)
1313 hi = fence = 0;
1314 else {
1315 expectedModCount = lst.modCount;
1316 hi = fence = lst.size;
1317 }
1318 }
1319 return hi;
1320 }
1321
1322 public ArrayListSpliterator<E> trySplit() {
1323 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1324 return (lo >= mid) ? null : // divide range in half unless too small
1325 new ArrayListSpliterator<E>(list, lo, index = mid,
1326 expectedModCount);
1327 }
1328
1329 public boolean tryAdvance(Consumer<? super E> action) {
1330 if (action == null)
1331 throw new NullPointerException();
1332 int hi = getFence(), i = index;
1333 if (i < hi) {
1334 index = i + 1;
1335 @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
1336 action.accept(e);
1337 if (list.modCount != expectedModCount)
1338 throw new ConcurrentModificationException();
1339 return true;
1340 }
1341 return false;
1342 }
1343
1344 public void forEachRemaining(Consumer<? super E> action) {
1345 int i, hi, mc; // hoist accesses and checks from loop
1346 ArrayList<E> lst; Object[] a;
1347 if (action == null)
1348 throw new NullPointerException();
1349 if ((lst = list) != null && (a = lst.elementData) != null) {
1350 if ((hi = fence) < 0) {
1351 mc = lst.modCount;
1352 hi = lst.size;
1353 }
1354 else
1355 mc = expectedModCount;
1356 if ((i = index) >= 0 && (index = hi) <= a.length) {
1357 for (; i < hi; ++i) {
1358 @SuppressWarnings("unchecked") E e = (E) a[i];
1359 action.accept(e);
1360 }
1361 if (lst.modCount == mc)
1362 return;
1363 }
1364 }
1365 throw new ConcurrentModificationException();
1366 }
1367
1368 public long estimateSize() {
1369 return (long) (getFence() - index);
1370 }
1371
1372 public int characteristics() {
1373 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1374 }
1375 }
1376
1377 @Override
1378 public boolean removeIf(Predicate<? super E> filter) {
1379 Objects.requireNonNull(filter);
1380 // figure out which elements are to be removed
1381 // any exception thrown from the filter predicate at this stage
1382 // will leave the collection unmodified
1383 int removeCount = 0;
1384 final BitSet removeSet = new BitSet(size);
1385 final int expectedModCount = modCount;
1386 final int size = this.size;
1387 for (int i=0; modCount == expectedModCount && i < size; i++) {
1388 @SuppressWarnings("unchecked")
1389 final E element = (E) elementData[i];
1390 if (filter.test(element)) {
1391 removeSet.set(i);
1392 removeCount++;
1393 }
1394 }
1395 if (modCount != expectedModCount) {
1396 throw new ConcurrentModificationException();
1397 }
1398
1399 // shift surviving elements left over the spaces left by removed elements
1400 final boolean anyToRemove = removeCount > 0;
1401 if (anyToRemove) {
1402 final int newSize = size - removeCount;
1403 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
1404 i = removeSet.nextClearBit(i);
1405 elementData[j] = elementData[i];
1406 }
1407 for (int k=newSize; k < size; k++) {
1408 elementData[k] = null; // Let gc do its work
1409 }
1410 this.size = newSize;
1411 if (modCount != expectedModCount) {
1412 throw new ConcurrentModificationException();
1413 }
1414 modCount++;
1415 }
1416
1417 return anyToRemove;
1418 }
1419
1420 @Override
1421 @SuppressWarnings("unchecked")
1422 public void replaceAll(UnaryOperator<E> operator) {
1423 Objects.requireNonNull(operator);
1424 final int expectedModCount = modCount;
1425 final int size = this.size;
1426 for (int i=0; modCount == expectedModCount && i < size; i++) {
1427 elementData[i] = operator.apply((E) elementData[i]);
1428 }
1429 if (modCount != expectedModCount) {
1430 throw new ConcurrentModificationException();
1431 }
1432 modCount++;
1433 }
1434
1435 @Override
1436 @SuppressWarnings("unchecked")
1437 public void sort(Comparator<? super E> c) {
1438 final int expectedModCount = modCount;
1439 Arrays.sort((E[]) elementData, 0, size, c);
1440 if (modCount != expectedModCount) {
1441 throw new ConcurrentModificationException();
1442 }
1443 modCount++;
1444 }
1445}