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