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 lastRet = cursor = i;
878 checkForComodification();
879 }
880
881 final void checkForComodification() {
882 if (modCount != expectedModCount)
883 throw new ConcurrentModificationException();
884 }
885 }
886
887 /**
888 * An optimized version of AbstractList.ListItr
889 */
890 private class ListItr extends Itr implements ListIterator<E> {
891 ListItr(int index) {
892 super();
893 cursor = index;
894 }
895
896 public boolean hasPrevious() {
897 return cursor != 0;
898 }
899
900 public int nextIndex() {
901 return cursor;
902 }
903
904 public int previousIndex() {
905 return cursor - 1;
906 }
907
908 @SuppressWarnings("unchecked")
909 public E previous() {
910 checkForComodification();
911 int i = cursor - 1;
912 if (i < 0)
913 throw new NoSuchElementException();
914 Object[] elementData = ArrayList.this.elementData;
915 if (i >= elementData.length)
916 throw new ConcurrentModificationException();
917 cursor = i;
918 return (E) elementData[lastRet = i];
919 }
920
921 public void set(E e) {
922 if (lastRet < 0)
923 throw new IllegalStateException();
924 checkForComodification();
925
926 try {
927 ArrayList.this.set(lastRet, e);
928 } catch (IndexOutOfBoundsException ex) {
929 throw new ConcurrentModificationException();
930 }
931 }
932
933 public void add(E e) {
934 checkForComodification();
935
936 try {
937 int i = cursor;
938 ArrayList.this.add(i, e);
939 cursor = i + 1;
940 lastRet = -1;
941 expectedModCount = modCount;
942 } catch (IndexOutOfBoundsException ex) {
943 throw new ConcurrentModificationException();
944 }
945 }
946 }
947
948 /**
949 * Returns a view of the portion of this list between the specified
950 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
951 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
952 * empty.) The returned list is backed by this list, so non-structural
953 * changes in the returned list are reflected in this list, and vice-versa.
954 * The returned list supports all of the optional list operations.
955 *
956 * <p>This method eliminates the need for explicit range operations (of
957 * the sort that commonly exist for arrays). Any operation that expects
958 * a list can be used as a range operation by passing a subList view
959 * instead of a whole list. For example, the following idiom
960 * removes a range of elements from a list:
961 * <pre>
962 * list.subList(from, to).clear();
963 * </pre>
964 * Similar idioms may be constructed for {@link #indexOf(Object)} and
965 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
966 * {@link Collections} class can be applied to a subList.
967 *
968 * <p>The semantics of the list returned by this method become undefined if
969 * the backing list (i.e., this list) is <i>structurally modified</i> in
970 * any way other than via the returned list. (Structural modifications are
971 * those that change the size of this list, or otherwise perturb it in such
972 * a fashion that iterations in progress may yield incorrect results.)
973 *
974 * @throws IndexOutOfBoundsException {@inheritDoc}
975 * @throws IllegalArgumentException {@inheritDoc}
976 */
977 public List<E> subList(int fromIndex, int toIndex) {
978 subListRangeCheck(fromIndex, toIndex, size);
979 return new SubList(this, 0, fromIndex, toIndex);
980 }
981
982 static void subListRangeCheck(int fromIndex, int toIndex, int size) {
983 if (fromIndex < 0)
984 throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
985 if (toIndex > size)
986 throw new IndexOutOfBoundsException("toIndex = " + toIndex);
987 if (fromIndex > toIndex)
988 throw new IllegalArgumentException("fromIndex(" + fromIndex +
989 ") > toIndex(" + toIndex + ")");
990 }
991
992 private class SubList extends AbstractList<E> implements RandomAccess {
993 private final AbstractList<E> parent;
994 private final int parentOffset;
995 private final int offset;
996 int size;
997
998 SubList(AbstractList<E> parent,
999 int offset, int fromIndex, int toIndex) {
1000 this.parent = parent;
1001 this.parentOffset = fromIndex;
1002 this.offset = offset + fromIndex;
1003 this.size = toIndex - fromIndex;
1004 this.modCount = ArrayList.this.modCount;
1005 }
1006
1007 public E set(int index, E e) {
1008 rangeCheck(index);
1009 checkForComodification();
1010 E oldValue = ArrayList.this.elementData(offset + index);
1011 ArrayList.this.elementData[offset + index] = e;
1012 return oldValue;
1013 }
1014
1015 public E get(int index) {
1016 rangeCheck(index);
1017 checkForComodification();
1018 return ArrayList.this.elementData(offset + index);
1019 }
1020
1021 public int size() {
1022 checkForComodification();
1023 return this.size;
1024 }
1025
1026 public void add(int index, E e) {
1027 rangeCheckForAdd(index);
1028 checkForComodification();
1029 parent.add(parentOffset + index, e);
1030 this.modCount = parent.modCount;
1031 this.size++;
1032 }
1033
1034 public E remove(int index) {
1035 rangeCheck(index);
1036 checkForComodification();
1037 E result = parent.remove(parentOffset + index);
1038 this.modCount = parent.modCount;
1039 this.size--;
1040 return result;
1041 }
1042
1043 protected void removeRange(int fromIndex, int toIndex) {
1044 checkForComodification();
1045 parent.removeRange(parentOffset + fromIndex,
1046 parentOffset + toIndex);
1047 this.modCount = parent.modCount;
1048 this.size -= toIndex - fromIndex;
1049 }
1050
1051 public boolean addAll(Collection<? extends E> c) {
1052 return addAll(this.size, c);
1053 }
1054
1055 public boolean addAll(int index, Collection<? extends E> c) {
1056 rangeCheckForAdd(index);
1057 int cSize = c.size();
1058 if (cSize==0)
1059 return false;
1060
1061 checkForComodification();
1062 parent.addAll(parentOffset + index, c);
1063 this.modCount = parent.modCount;
1064 this.size += cSize;
1065 return true;
1066 }
1067
1068 public Iterator<E> iterator() {
1069 return listIterator();
1070 }
1071
1072 public ListIterator<E> listIterator(final int index) {
1073 checkForComodification();
1074 rangeCheckForAdd(index);
1075 final int offset = this.offset;
1076
1077 return new ListIterator<E>() {
1078 int cursor = index;
1079 int lastRet = -1;
1080 int expectedModCount = ArrayList.this.modCount;
1081
1082 public boolean hasNext() {
1083 return cursor != SubList.this.size;
1084 }
1085
1086 @SuppressWarnings("unchecked")
1087 public E next() {
1088 checkForComodification();
1089 int i = cursor;
1090 if (i >= SubList.this.size)
1091 throw new NoSuchElementException();
1092 Object[] elementData = ArrayList.this.elementData;
1093 if (offset + i >= elementData.length)
1094 throw new ConcurrentModificationException();
1095 cursor = i + 1;
1096 return (E) elementData[offset + (lastRet = i)];
1097 }
1098
1099 public boolean hasPrevious() {
1100 return cursor != 0;
1101 }
1102
1103 @SuppressWarnings("unchecked")
1104 public E previous() {
1105 checkForComodification();
1106 int i = cursor - 1;
1107 if (i < 0)
1108 throw new NoSuchElementException();
1109 Object[] elementData = ArrayList.this.elementData;
1110 if (offset + i >= elementData.length)
1111 throw new ConcurrentModificationException();
1112 cursor = i;
1113 return (E) elementData[offset + (lastRet = i)];
1114 }
1115
1116 @SuppressWarnings("unchecked")
1117 public void forEachRemaining(Consumer<? super E> consumer) {
1118 Objects.requireNonNull(consumer);
1119 final int size = SubList.this.size;
1120 int i = cursor;
1121 if (i >= size) {
1122 return;
1123 }
1124 final Object[] elementData = ArrayList.this.elementData;
1125 if (offset + i >= elementData.length) {
1126 throw new ConcurrentModificationException();
1127 }
1128 while (i != size && modCount == expectedModCount) {
1129 consumer.accept((E) elementData[offset + (i++)]);
1130 }
1131 // update once at end of iteration to reduce heap write traffic
1132 lastRet = cursor = i;
1133 checkForComodification();
1134 }
1135
1136 public int nextIndex() {
1137 return cursor;
1138 }
1139
1140 public int previousIndex() {
1141 return cursor - 1;
1142 }
1143
1144 public void remove() {
1145 if (lastRet < 0)
1146 throw new IllegalStateException();
1147 checkForComodification();
1148
1149 try {
1150 SubList.this.remove(lastRet);
1151 cursor = lastRet;
1152 lastRet = -1;
1153 expectedModCount = ArrayList.this.modCount;
1154 } catch (IndexOutOfBoundsException ex) {
1155 throw new ConcurrentModificationException();
1156 }
1157 }
1158
1159 public void set(E e) {
1160 if (lastRet < 0)
1161 throw new IllegalStateException();
1162 checkForComodification();
1163
1164 try {
1165 ArrayList.this.set(offset + lastRet, e);
1166 } catch (IndexOutOfBoundsException ex) {
1167 throw new ConcurrentModificationException();
1168 }
1169 }
1170
1171 public void add(E e) {
1172 checkForComodification();
1173
1174 try {
1175 int i = cursor;
1176 SubList.this.add(i, e);
1177 cursor = i + 1;
1178 lastRet = -1;
1179 expectedModCount = ArrayList.this.modCount;
1180 } catch (IndexOutOfBoundsException ex) {
1181 throw new ConcurrentModificationException();
1182 }
1183 }
1184
1185 final void checkForComodification() {
1186 if (expectedModCount != ArrayList.this.modCount)
1187 throw new ConcurrentModificationException();
1188 }
1189 };
1190 }
1191
1192 public List<E> subList(int fromIndex, int toIndex) {
1193 subListRangeCheck(fromIndex, toIndex, size);
1194 return new SubList(this, offset, fromIndex, toIndex);
1195 }
1196
1197 private void rangeCheck(int index) {
1198 if (index < 0 || index >= this.size)
1199 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1200 }
1201
1202 private void rangeCheckForAdd(int index) {
1203 if (index < 0 || index > this.size)
1204 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
1205 }
1206
1207 private String outOfBoundsMsg(int index) {
1208 return "Index: "+index+", Size: "+this.size;
1209 }
1210
1211 private void checkForComodification() {
1212 if (ArrayList.this.modCount != this.modCount)
1213 throw new ConcurrentModificationException();
1214 }
1215
1216 public Spliterator<E> spliterator() {
1217 checkForComodification();
1218 return new ArrayListSpliterator<E>(ArrayList.this, offset,
1219 offset + this.size, this.modCount);
1220 }
1221 }
1222
1223 @Override
1224 public void forEach(Consumer<? super E> action) {
1225 Objects.requireNonNull(action);
1226 final int expectedModCount = modCount;
1227 @SuppressWarnings("unchecked")
1228 final E[] elementData = (E[]) this.elementData;
1229 final int size = this.size;
1230 for (int i=0; modCount == expectedModCount && i < size; i++) {
1231 action.accept(elementData[i]);
1232 }
1233 if (modCount != expectedModCount) {
1234 throw new ConcurrentModificationException();
1235 }
1236 }
1237
1238 public Spliterator<E> spliterator() {
1239 return new ArrayListSpliterator<>(this, 0, -1, 0);
1240 }
1241
1242 /** Index-based split-by-two, lazily initialized Spliterator */
1243 static final class ArrayListSpliterator<E> implements Spliterator<E> {
1244
1245 /*
1246 * If ArrayLists were immutable, or structurally immutable (no
1247 * adds, removes, etc), we could implement their spliterators
1248 * with Arrays.spliterator. Instead we detect as much
1249 * interference during traversal as practical without
1250 * sacrificing much performance. We rely primarily on
1251 * modCounts. These are not guaranteed to detect concurrency
1252 * violations, and are sometimes overly conservative about
1253 * within-thread interference, but detect enough problems to
1254 * be worthwhile in practice. To carry this out, we (1) lazily
1255 * initialize fence and expectedModCount until the latest
1256 * point that we need to commit to the state we are checking
1257 * against; thus improving precision. (This doesn't apply to
1258 * SubLists, that create spliterators with current non-lazy
1259 * values). (2) We perform only a single
1260 * ConcurrentModificationException check at the end of forEach
1261 * (the most performance-sensitive method). When using forEach
1262 * (as opposed to iterators), we can normally only detect
1263 * interference after actions, not before. Further
1264 * CME-triggering checks apply to all other possible
1265 * violations of assumptions for example null or too-small
1266 * elementData array given its size(), that could only have
1267 * occurred due to interference. This allows the inner loop
1268 * of forEach to run without any further checks, and
1269 * simplifies lambda-resolution. While this does entail a
1270 * number of checks, note that in the common case of
1271 * list.stream().forEach(a), no checks or other computation
1272 * occur anywhere other than inside forEach itself. The other
1273 * less-often-used methods cannot take advantage of most of
1274 * these streamlinings.
1275 */
1276
1277 private final ArrayList<E> list;
1278 private int index; // current index, modified on advance/split
1279 private int fence; // -1 until used; then one past last index
1280 private int expectedModCount; // initialized when fence set
1281
1282 /** Create new spliterator covering the given range */
1283 ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
1284 int expectedModCount) {
1285 this.list = list; // OK if null unless traversed
1286 this.index = origin;
1287 this.fence = fence;
1288 this.expectedModCount = expectedModCount;
1289 }
1290
1291 private int getFence() { // initialize fence to size on first use
1292 int hi; // (a specialized variant appears in method forEach)
1293 ArrayList<E> lst;
1294 if ((hi = fence) < 0) {
1295 if ((lst = list) == null)
1296 hi = fence = 0;
1297 else {
1298 expectedModCount = lst.modCount;
1299 hi = fence = lst.size;
1300 }
1301 }
1302 return hi;
1303 }
1304
1305 public ArrayListSpliterator<E> trySplit() {
1306 int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
1307 return (lo >= mid) ? null : // divide range in half unless too small
1308 new ArrayListSpliterator<E>(list, lo, index = mid,
1309 expectedModCount);
1310 }
1311
1312 public boolean tryAdvance(Consumer<? super E> action) {
1313 if (action == null)
1314 throw new NullPointerException();
1315 int hi = getFence(), i = index;
1316 if (i < hi) {
1317 index = i + 1;
1318 @SuppressWarnings("unchecked") E e = (E)list.elementData[i];
1319 action.accept(e);
1320 if (list.modCount != expectedModCount)
1321 throw new ConcurrentModificationException();
1322 return true;
1323 }
1324 return false;
1325 }
1326
1327 public void forEachRemaining(Consumer<? super E> action) {
1328 int i, hi, mc; // hoist accesses and checks from loop
1329 ArrayList<E> lst; Object[] a;
1330 if (action == null)
1331 throw new NullPointerException();
1332 if ((lst = list) != null && (a = lst.elementData) != null) {
1333 if ((hi = fence) < 0) {
1334 mc = lst.modCount;
1335 hi = lst.size;
1336 }
1337 else
1338 mc = expectedModCount;
1339 if ((i = index) >= 0 && (index = hi) <= a.length) {
1340 for (; i < hi; ++i) {
1341 @SuppressWarnings("unchecked") E e = (E) a[i];
1342 action.accept(e);
1343 }
1344 if (lst.modCount == mc)
1345 return;
1346 }
1347 }
1348 throw new ConcurrentModificationException();
1349 }
1350
1351 public long estimateSize() {
1352 return (long) (getFence() - index);
1353 }
1354
1355 public int characteristics() {
1356 return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
1357 }
1358 }
1359
1360 @Override
1361 public boolean removeIf(Predicate<? super E> filter) {
1362 Objects.requireNonNull(filter);
1363 // figure out which elements are to be removed
1364 // any exception thrown from the filter predicate at this stage
1365 // will leave the collection unmodified
1366 int removeCount = 0;
1367 final BitSet removeSet = new BitSet(size);
1368 final int expectedModCount = modCount;
1369 final int size = this.size;
1370 for (int i=0; modCount == expectedModCount && i < size; i++) {
1371 @SuppressWarnings("unchecked")
1372 final E element = (E) elementData[i];
1373 if (filter.test(element)) {
1374 removeSet.set(i);
1375 removeCount++;
1376 }
1377 }
1378 if (modCount != expectedModCount) {
1379 throw new ConcurrentModificationException();
1380 }
1381
1382 // shift surviving elements left over the spaces left by removed elements
1383 final boolean anyToRemove = removeCount > 0;
1384 if (anyToRemove) {
1385 final int newSize = size - removeCount;
1386 for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
1387 i = removeSet.nextClearBit(i);
1388 elementData[j] = elementData[i];
1389 }
1390 for (int k=newSize; k < size; k++) {
1391 elementData[k] = null; // Let gc do its work
1392 }
1393 this.size = newSize;
1394 if (modCount != expectedModCount) {
1395 throw new ConcurrentModificationException();
1396 }
1397 modCount++;
1398 }
1399
1400 return anyToRemove;
1401 }
1402
1403 @Override
1404 @SuppressWarnings("unchecked")
1405 public void replaceAll(UnaryOperator<E> operator) {
1406 Objects.requireNonNull(operator);
1407 final int expectedModCount = modCount;
1408 final int size = this.size;
1409 for (int i=0; modCount == expectedModCount && i < size; i++) {
1410 elementData[i] = operator.apply((E) elementData[i]);
1411 }
1412 if (modCount != expectedModCount) {
1413 throw new ConcurrentModificationException();
1414 }
1415 modCount++;
1416 }
1417
1418 @Override
1419 @SuppressWarnings("unchecked")
1420 public void sort(Comparator<? super E> c) {
1421 final int expectedModCount = modCount;
1422 Arrays.sort((E[]) elementData, 0, size, c);
1423 if (modCount != expectedModCount) {
1424 throw new ConcurrentModificationException();
1425 }
1426 modCount++;
1427 }
1428 }