2 * Copyright (c) 2003, 2011, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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.
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).
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.
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
27 * Written by Doug Lea with assistance from members of JCP JSR-166
28 * Expert Group. Adapted and released, under explicit permission,
29 * from JDK ArrayList.java which carries the following copyright:
31 * Copyright 1997 by Sun Microsystems, Inc.,
32 * 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
33 * All rights reserved.
36 package java.util.concurrent;
38 import java.util.concurrent.locks.*;
39 import sun.misc.Unsafe;
42 * A thread-safe variant of {@link java.util.ArrayList} in which all mutative
43 * operations (<tt>add</tt>, <tt>set</tt>, and so on) are implemented by
44 * making a fresh copy of the underlying array.
46 * <p> This is ordinarily too costly, but may be <em>more</em> efficient
47 * than alternatives when traversal operations vastly outnumber
48 * mutations, and is useful when you cannot or don't want to
49 * synchronize traversals, yet need to preclude interference among
50 * concurrent threads. The "snapshot" style iterator method uses a
51 * reference to the state of the array at the point that the iterator
52 * was created. This array never changes during the lifetime of the
53 * iterator, so interference is impossible and the iterator is
54 * guaranteed not to throw <tt>ConcurrentModificationException</tt>.
55 * The iterator will not reflect additions, removals, or changes to
56 * the list since the iterator was created. Element-changing
57 * operations on iterators themselves (<tt>remove</tt>, <tt>set</tt>, and
58 * <tt>add</tt>) are not supported. These methods throw
59 * <tt>UnsupportedOperationException</tt>.
61 * <p>All elements are permitted, including <tt>null</tt>.
63 * <p>Memory consistency effects: As with other concurrent
64 * collections, actions in a thread prior to placing an object into a
65 * {@code CopyOnWriteArrayList}
66 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
67 * actions subsequent to the access or removal of that element from
68 * the {@code CopyOnWriteArrayList} in another thread.
70 * <p>This class is a member of the
71 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
72 * Java Collections Framework</a>.
76 * @param <E> the type of elements held in this collection
78 public class CopyOnWriteArrayList<E>
79 implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
80 private static final long serialVersionUID = 8673264195747942595L;
82 /** The lock protecting all mutators */
83 transient final ReentrantLock lock = new ReentrantLock();
85 /** The array, accessed only via getArray/setArray. */
86 private volatile transient Object[] array;
89 * Gets the array. Non-private so as to also be accessible
90 * from CopyOnWriteArraySet class.
92 final Object[] getArray() {
99 final void setArray(Object[] a) {
104 * Creates an empty list.
106 public CopyOnWriteArrayList() {
107 setArray(new Object[0]);
111 * Creates a list containing the elements of the specified
112 * collection, in the order they are returned by the collection's
115 * @param c the collection of initially held elements
116 * @throws NullPointerException if the specified collection is null
118 public CopyOnWriteArrayList(Collection<? extends E> c) {
119 Object[] elements = c.toArray();
120 // c.toArray might (incorrectly) not return Object[] (see 6260652)
121 if (elements.getClass() != Object[].class)
122 elements = Arrays.copyOf(elements, elements.length, Object[].class);
127 * Creates a list holding a copy of the given array.
129 * @param toCopyIn the array (a copy of this array is used as the
131 * @throws NullPointerException if the specified array is null
133 public CopyOnWriteArrayList(E[] toCopyIn) {
134 setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class));
138 * Returns the number of elements in this list.
140 * @return the number of elements in this list
143 return getArray().length;
147 * Returns <tt>true</tt> if this list contains no elements.
149 * @return <tt>true</tt> if this list contains no elements
151 public boolean isEmpty() {
156 * Test for equality, coping with nulls.
158 private static boolean eq(Object o1, Object o2) {
159 return (o1 == null ? o2 == null : o1.equals(o2));
163 * static version of indexOf, to allow repeated calls without
164 * needing to re-acquire array each time.
165 * @param o element to search for
166 * @param elements the array
167 * @param index first index to search
168 * @param fence one past last index to search
169 * @return index of element, or -1 if absent
171 private static int indexOf(Object o, Object[] elements,
172 int index, int fence) {
174 for (int i = index; i < fence; i++)
175 if (elements[i] == null)
178 for (int i = index; i < fence; i++)
179 if (o.equals(elements[i]))
186 * static version of lastIndexOf.
187 * @param o element to search for
188 * @param elements the array
189 * @param index first index to search
190 * @return index of element, or -1 if absent
192 private static int lastIndexOf(Object o, Object[] elements, int index) {
194 for (int i = index; i >= 0; i--)
195 if (elements[i] == null)
198 for (int i = index; i >= 0; i--)
199 if (o.equals(elements[i]))
206 * Returns <tt>true</tt> if this list contains the specified element.
207 * More formally, returns <tt>true</tt> if and only if this list contains
208 * at least one element <tt>e</tt> such that
209 * <tt>(o==null ? e==null : o.equals(e))</tt>.
211 * @param o element whose presence in this list is to be tested
212 * @return <tt>true</tt> if this list contains the specified element
214 public boolean contains(Object o) {
215 Object[] elements = getArray();
216 return indexOf(o, elements, 0, elements.length) >= 0;
222 public int indexOf(Object o) {
223 Object[] elements = getArray();
224 return indexOf(o, elements, 0, elements.length);
228 * Returns the index of the first occurrence of the specified element in
229 * this list, searching forwards from <tt>index</tt>, or returns -1 if
230 * the element is not found.
231 * More formally, returns the lowest index <tt>i</tt> such that
232 * <tt>(i >= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>,
233 * or -1 if there is no such index.
235 * @param e element to search for
236 * @param index index to start searching from
237 * @return the index of the first occurrence of the element in
238 * this list at position <tt>index</tt> or later in the list;
239 * <tt>-1</tt> if the element is not found.
240 * @throws IndexOutOfBoundsException if the specified index is negative
242 public int indexOf(E e, int index) {
243 Object[] elements = getArray();
244 return indexOf(e, elements, index, elements.length);
250 public int lastIndexOf(Object o) {
251 Object[] elements = getArray();
252 return lastIndexOf(o, elements, elements.length - 1);
256 * Returns the index of the last occurrence of the specified element in
257 * this list, searching backwards from <tt>index</tt>, or returns -1 if
258 * the element is not found.
259 * More formally, returns the highest index <tt>i</tt> such that
260 * <tt>(i <= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>,
261 * or -1 if there is no such index.
263 * @param e element to search for
264 * @param index index to start searching backwards from
265 * @return the index of the last occurrence of the element at position
266 * less than or equal to <tt>index</tt> in this list;
267 * -1 if the element is not found.
268 * @throws IndexOutOfBoundsException if the specified index is greater
269 * than or equal to the current size of this list
271 public int lastIndexOf(E e, int index) {
272 Object[] elements = getArray();
273 return lastIndexOf(e, elements, index);
277 * Returns a shallow copy of this list. (The elements themselves
280 * @return a clone of this list
282 public Object clone() {
284 CopyOnWriteArrayList c = (CopyOnWriteArrayList)(super.clone());
287 } catch (CloneNotSupportedException e) {
288 // this shouldn't happen, since we are Cloneable
289 throw new InternalError();
294 * Returns an array containing all of the elements in this list
295 * in proper sequence (from first to last element).
297 * <p>The returned array will be "safe" in that no references to it are
298 * maintained by this list. (In other words, this method must allocate
299 * a new array). The caller is thus free to modify the returned array.
301 * <p>This method acts as bridge between array-based and collection-based
304 * @return an array containing all the elements in this list
306 public Object[] toArray() {
307 Object[] elements = getArray();
308 return Arrays.copyOf(elements, elements.length);
312 * Returns an array containing all of the elements in this list in
313 * proper sequence (from first to last element); the runtime type of
314 * the returned array is that of the specified array. If the list fits
315 * in the specified array, it is returned therein. Otherwise, a new
316 * array is allocated with the runtime type of the specified array and
317 * the size of this list.
319 * <p>If this list fits in the specified array with room to spare
320 * (i.e., the array has more elements than this list), the element in
321 * the array immediately following the end of the list is set to
322 * <tt>null</tt>. (This is useful in determining the length of this
323 * list <i>only</i> if the caller knows that this list does not contain
324 * any null elements.)
326 * <p>Like the {@link #toArray()} method, this method acts as bridge between
327 * array-based and collection-based APIs. Further, this method allows
328 * precise control over the runtime type of the output array, and may,
329 * under certain circumstances, be used to save allocation costs.
331 * <p>Suppose <tt>x</tt> is a list known to contain only strings.
332 * The following code can be used to dump the list into a newly
333 * allocated array of <tt>String</tt>:
336 * String[] y = x.toArray(new String[0]);</pre>
338 * Note that <tt>toArray(new Object[0])</tt> is identical in function to
339 * <tt>toArray()</tt>.
341 * @param a the array into which the elements of the list are to
342 * be stored, if it is big enough; otherwise, a new array of the
343 * same runtime type is allocated for this purpose.
344 * @return an array containing all the elements in this list
345 * @throws ArrayStoreException if the runtime type of the specified array
346 * is not a supertype of the runtime type of every element in
348 * @throws NullPointerException if the specified array is null
350 @SuppressWarnings("unchecked")
351 public <T> T[] toArray(T a[]) {
352 Object[] elements = getArray();
353 int len = elements.length;
355 return (T[]) Arrays.copyOf(elements, len, a.getClass());
357 System.arraycopy(elements, 0, a, 0, len);
364 // Positional Access Operations
366 @SuppressWarnings("unchecked")
367 private E get(Object[] a, int index) {
374 * @throws IndexOutOfBoundsException {@inheritDoc}
376 public E get(int index) {
377 return get(getArray(), index);
381 * Replaces the element at the specified position in this list with the
384 * @throws IndexOutOfBoundsException {@inheritDoc}
386 public E set(int index, E element) {
387 final ReentrantLock lock = this.lock;
390 Object[] elements = getArray();
391 E oldValue = get(elements, index);
393 if (oldValue != element) {
394 int len = elements.length;
395 Object[] newElements = Arrays.copyOf(elements, len);
396 newElements[index] = element;
397 setArray(newElements);
399 // Not quite a no-op; ensures volatile write semantics
409 * Appends the specified element to the end of this list.
411 * @param e element to be appended to this list
412 * @return <tt>true</tt> (as specified by {@link Collection#add})
414 public boolean add(E e) {
415 final ReentrantLock lock = this.lock;
418 Object[] elements = getArray();
419 int len = elements.length;
420 Object[] newElements = Arrays.copyOf(elements, len + 1);
421 newElements[len] = e;
422 setArray(newElements);
430 * Inserts the specified element at the specified position in this
431 * list. Shifts the element currently at that position (if any) and
432 * any subsequent elements to the right (adds one to their indices).
434 * @throws IndexOutOfBoundsException {@inheritDoc}
436 public void add(int index, E element) {
437 final ReentrantLock lock = this.lock;
440 Object[] elements = getArray();
441 int len = elements.length;
442 if (index > len || index < 0)
443 throw new IndexOutOfBoundsException("Index: "+index+
445 Object[] newElements;
446 int numMoved = len - index;
448 newElements = Arrays.copyOf(elements, len + 1);
450 newElements = new Object[len + 1];
451 System.arraycopy(elements, 0, newElements, 0, index);
452 System.arraycopy(elements, index, newElements, index + 1,
455 newElements[index] = element;
456 setArray(newElements);
463 * Removes the element at the specified position in this list.
464 * Shifts any subsequent elements to the left (subtracts one from their
465 * indices). Returns the element that was removed from the list.
467 * @throws IndexOutOfBoundsException {@inheritDoc}
469 public E remove(int index) {
470 final ReentrantLock lock = this.lock;
473 Object[] elements = getArray();
474 int len = elements.length;
475 E oldValue = get(elements, index);
476 int numMoved = len - index - 1;
478 setArray(Arrays.copyOf(elements, len - 1));
480 Object[] newElements = new Object[len - 1];
481 System.arraycopy(elements, 0, newElements, 0, index);
482 System.arraycopy(elements, index + 1, newElements, index,
484 setArray(newElements);
493 * Removes the first occurrence of the specified element from this list,
494 * if it is present. If this list does not contain the element, it is
495 * unchanged. More formally, removes the element with the lowest index
496 * <tt>i</tt> such that
497 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
498 * (if such an element exists). Returns <tt>true</tt> if this list
499 * contained the specified element (or equivalently, if this list
500 * changed as a result of the call).
502 * @param o element to be removed from this list, if present
503 * @return <tt>true</tt> if this list contained the specified element
505 public boolean remove(Object o) {
506 final ReentrantLock lock = this.lock;
509 Object[] elements = getArray();
510 int len = elements.length;
512 // Copy while searching for element to remove
513 // This wins in the normal case of element being present
514 int newlen = len - 1;
515 Object[] newElements = new Object[newlen];
517 for (int i = 0; i < newlen; ++i) {
518 if (eq(o, elements[i])) {
519 // found one; copy remaining and exit
520 for (int k = i + 1; k < len; ++k)
521 newElements[k-1] = elements[k];
522 setArray(newElements);
525 newElements[i] = elements[i];
528 // special handling for last cell
529 if (eq(o, elements[newlen])) {
530 setArray(newElements);
541 * Removes from this list all of the elements whose index is between
542 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.
543 * Shifts any succeeding elements to the left (reduces their index).
544 * This call shortens the list by <tt>(toIndex - fromIndex)</tt> elements.
545 * (If <tt>toIndex==fromIndex</tt>, this operation has no effect.)
547 * @param fromIndex index of first element to be removed
548 * @param toIndex index after last element to be removed
549 * @throws IndexOutOfBoundsException if fromIndex or toIndex out of range
550 * ({@code{fromIndex < 0 || toIndex > size() || toIndex < fromIndex})
552 private void removeRange(int fromIndex, int toIndex) {
553 final ReentrantLock lock = this.lock;
556 Object[] elements = getArray();
557 int len = elements.length;
559 if (fromIndex < 0 || toIndex > len || toIndex < fromIndex)
560 throw new IndexOutOfBoundsException();
561 int newlen = len - (toIndex - fromIndex);
562 int numMoved = len - toIndex;
564 setArray(Arrays.copyOf(elements, newlen));
566 Object[] newElements = new Object[newlen];
567 System.arraycopy(elements, 0, newElements, 0, fromIndex);
568 System.arraycopy(elements, toIndex, newElements,
569 fromIndex, numMoved);
570 setArray(newElements);
578 * Append the element if not present.
580 * @param e element to be added to this list, if absent
581 * @return <tt>true</tt> if the element was added
583 public boolean addIfAbsent(E e) {
584 final ReentrantLock lock = this.lock;
587 // Copy while checking if already present.
588 // This wins in the most common case where it is not present
589 Object[] elements = getArray();
590 int len = elements.length;
591 Object[] newElements = new Object[len + 1];
592 for (int i = 0; i < len; ++i) {
593 if (eq(e, elements[i]))
594 return false; // exit, throwing away copy
596 newElements[i] = elements[i];
598 newElements[len] = e;
599 setArray(newElements);
607 * Returns <tt>true</tt> if this list contains all of the elements of the
608 * specified collection.
610 * @param c collection to be checked for containment in this list
611 * @return <tt>true</tt> if this list contains all of the elements of the
612 * specified collection
613 * @throws NullPointerException if the specified collection is null
614 * @see #contains(Object)
616 public boolean containsAll(Collection<?> c) {
617 Object[] elements = getArray();
618 int len = elements.length;
620 if (indexOf(e, elements, 0, len) < 0)
627 * Removes from this list all of its elements that are contained in
628 * the specified collection. This is a particularly expensive operation
629 * in this class because of the need for an internal temporary array.
631 * @param c collection containing elements to be removed from this list
632 * @return <tt>true</tt> if this list changed as a result of the call
633 * @throws ClassCastException if the class of an element of this list
634 * is incompatible with the specified collection
635 * (<a href="../Collection.html#optional-restrictions">optional</a>)
636 * @throws NullPointerException if this list contains a null element and the
637 * specified collection does not permit null elements
638 * (<a href="../Collection.html#optional-restrictions">optional</a>),
639 * or if the specified collection is null
640 * @see #remove(Object)
642 public boolean removeAll(Collection<?> c) {
643 final ReentrantLock lock = this.lock;
646 Object[] elements = getArray();
647 int len = elements.length;
649 // temp array holds those elements we know we want to keep
651 Object[] temp = new Object[len];
652 for (int i = 0; i < len; ++i) {
653 Object element = elements[i];
654 if (!c.contains(element))
655 temp[newlen++] = element;
658 setArray(Arrays.copyOf(temp, newlen));
669 * Retains only the elements in this list that are contained in the
670 * specified collection. In other words, removes from this list all of
671 * its elements that are not contained in the specified collection.
673 * @param c collection containing elements to be retained in this list
674 * @return <tt>true</tt> if this list changed as a result of the call
675 * @throws ClassCastException if the class of an element of this list
676 * is incompatible with the specified collection
677 * (<a href="../Collection.html#optional-restrictions">optional</a>)
678 * @throws NullPointerException if this list contains a null element and the
679 * specified collection does not permit null elements
680 * (<a href="../Collection.html#optional-restrictions">optional</a>),
681 * or if the specified collection is null
682 * @see #remove(Object)
684 public boolean retainAll(Collection<?> c) {
685 final ReentrantLock lock = this.lock;
688 Object[] elements = getArray();
689 int len = elements.length;
691 // temp array holds those elements we know we want to keep
693 Object[] temp = new Object[len];
694 for (int i = 0; i < len; ++i) {
695 Object element = elements[i];
696 if (c.contains(element))
697 temp[newlen++] = element;
700 setArray(Arrays.copyOf(temp, newlen));
711 * Appends all of the elements in the specified collection that
712 * are not already contained in this list, to the end of
713 * this list, in the order that they are returned by the
714 * specified collection's iterator.
716 * @param c collection containing elements to be added to this list
717 * @return the number of elements added
718 * @throws NullPointerException if the specified collection is null
719 * @see #addIfAbsent(Object)
721 public int addAllAbsent(Collection<? extends E> c) {
722 Object[] cs = c.toArray();
725 Object[] uniq = new Object[cs.length];
726 final ReentrantLock lock = this.lock;
729 Object[] elements = getArray();
730 int len = elements.length;
732 for (int i = 0; i < cs.length; ++i) { // scan for duplicates
734 if (indexOf(e, elements, 0, len) < 0 &&
735 indexOf(e, uniq, 0, added) < 0)
739 Object[] newElements = Arrays.copyOf(elements, len + added);
740 System.arraycopy(uniq, 0, newElements, len, added);
741 setArray(newElements);
750 * Removes all of the elements from this list.
751 * The list will be empty after this call returns.
753 public void clear() {
754 final ReentrantLock lock = this.lock;
757 setArray(new Object[0]);
764 * Appends all of the elements in the specified collection to the end
765 * of this list, in the order that they are returned by the specified
766 * collection's iterator.
768 * @param c collection containing elements to be added to this list
769 * @return <tt>true</tt> if this list changed as a result of the call
770 * @throws NullPointerException if the specified collection is null
773 public boolean addAll(Collection<? extends E> c) {
774 Object[] cs = c.toArray();
777 final ReentrantLock lock = this.lock;
780 Object[] elements = getArray();
781 int len = elements.length;
782 Object[] newElements = Arrays.copyOf(elements, len + cs.length);
783 System.arraycopy(cs, 0, newElements, len, cs.length);
784 setArray(newElements);
792 * Inserts all of the elements in the specified collection into this
793 * list, starting at the specified position. Shifts the element
794 * currently at that position (if any) and any subsequent elements to
795 * the right (increases their indices). The new elements will appear
796 * in this list in the order that they are returned by the
797 * specified collection's iterator.
799 * @param index index at which to insert the first element
800 * from the specified collection
801 * @param c collection containing elements to be added to this list
802 * @return <tt>true</tt> if this list changed as a result of the call
803 * @throws IndexOutOfBoundsException {@inheritDoc}
804 * @throws NullPointerException if the specified collection is null
805 * @see #add(int,Object)
807 public boolean addAll(int index, Collection<? extends E> c) {
808 Object[] cs = c.toArray();
809 final ReentrantLock lock = this.lock;
812 Object[] elements = getArray();
813 int len = elements.length;
814 if (index > len || index < 0)
815 throw new IndexOutOfBoundsException("Index: "+index+
819 int numMoved = len - index;
820 Object[] newElements;
822 newElements = Arrays.copyOf(elements, len + cs.length);
824 newElements = new Object[len + cs.length];
825 System.arraycopy(elements, 0, newElements, 0, index);
826 System.arraycopy(elements, index,
827 newElements, index + cs.length,
830 System.arraycopy(cs, 0, newElements, index, cs.length);
831 setArray(newElements);
839 * Saves the state of the list to a stream (that is, serializes it).
841 * @serialData The length of the array backing the list is emitted
842 * (int), followed by all of its elements (each an Object)
843 * in the proper order.
844 * @param s the stream
846 private void writeObject(java.io.ObjectOutputStream s)
847 throws java.io.IOException{
849 s.defaultWriteObject();
851 Object[] elements = getArray();
852 // Write out array length
853 s.writeInt(elements.length);
855 // Write out all elements in the proper order.
856 for (Object element : elements)
857 s.writeObject(element);
861 * Reconstitutes the list from a stream (that is, deserializes it).
863 * @param s the stream
865 private void readObject(java.io.ObjectInputStream s)
866 throws java.io.IOException, ClassNotFoundException {
868 s.defaultReadObject();
873 // Read in array length and allocate array
874 int len = s.readInt();
875 Object[] elements = new Object[len];
877 // Read in all elements in the proper order.
878 for (int i = 0; i < len; i++)
879 elements[i] = s.readObject();
884 * Returns a string representation of this list. The string
885 * representation consists of the string representations of the list's
886 * elements in the order they are returned by its iterator, enclosed in
887 * square brackets (<tt>"[]"</tt>). Adjacent elements are separated by
888 * the characters <tt>", "</tt> (comma and space). Elements are
889 * converted to strings as by {@link String#valueOf(Object)}.
891 * @return a string representation of this list
893 public String toString() {
894 return Arrays.toString(getArray());
898 * Compares the specified object with this list for equality.
899 * Returns {@code true} if the specified object is the same object
900 * as this object, or if it is also a {@link List} and the sequence
901 * of elements returned by an {@linkplain List#iterator() iterator}
902 * over the specified list is the same as the sequence returned by
903 * an iterator over this list. The two sequences are considered to
904 * be the same if they have the same length and corresponding
905 * elements at the same position in the sequence are <em>equal</em>.
906 * Two elements {@code e1} and {@code e2} are considered
907 * <em>equal</em> if {@code (e1==null ? e2==null : e1.equals(e2))}.
909 * @param o the object to be compared for equality with this list
910 * @return {@code true} if the specified object is equal to this list
912 public boolean equals(Object o) {
915 if (!(o instanceof List))
918 List<?> list = (List<?>)(o);
919 Iterator<?> it = list.iterator();
920 Object[] elements = getArray();
921 int len = elements.length;
922 for (int i = 0; i < len; ++i)
923 if (!it.hasNext() || !eq(elements[i], it.next()))
931 * Returns the hash code value for this list.
933 * <p>This implementation uses the definition in {@link List#hashCode}.
935 * @return the hash code value for this list
937 public int hashCode() {
939 Object[] elements = getArray();
940 int len = elements.length;
941 for (int i = 0; i < len; ++i) {
942 Object obj = elements[i];
943 hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
949 * Returns an iterator over the elements in this list in proper sequence.
951 * <p>The returned iterator provides a snapshot of the state of the list
952 * when the iterator was constructed. No synchronization is needed while
953 * traversing the iterator. The iterator does <em>NOT</em> support the
954 * <tt>remove</tt> method.
956 * @return an iterator over the elements in this list in proper sequence
958 public Iterator<E> iterator() {
959 return new COWIterator<E>(getArray(), 0);
965 * <p>The returned iterator provides a snapshot of the state of the list
966 * when the iterator was constructed. No synchronization is needed while
967 * traversing the iterator. The iterator does <em>NOT</em> support the
968 * <tt>remove</tt>, <tt>set</tt> or <tt>add</tt> methods.
970 public ListIterator<E> listIterator() {
971 return new COWIterator<E>(getArray(), 0);
977 * <p>The returned iterator provides a snapshot of the state of the list
978 * when the iterator was constructed. No synchronization is needed while
979 * traversing the iterator. The iterator does <em>NOT</em> support the
980 * <tt>remove</tt>, <tt>set</tt> or <tt>add</tt> methods.
982 * @throws IndexOutOfBoundsException {@inheritDoc}
984 public ListIterator<E> listIterator(final int index) {
985 Object[] elements = getArray();
986 int len = elements.length;
987 if (index<0 || index>len)
988 throw new IndexOutOfBoundsException("Index: "+index);
990 return new COWIterator<E>(elements, index);
993 private static class COWIterator<E> implements ListIterator<E> {
994 /** Snapshot of the array */
995 private final Object[] snapshot;
996 /** Index of element to be returned by subsequent call to next. */
999 private COWIterator(Object[] elements, int initialCursor) {
1000 cursor = initialCursor;
1001 snapshot = elements;
1004 public boolean hasNext() {
1005 return cursor < snapshot.length;
1008 public boolean hasPrevious() {
1012 @SuppressWarnings("unchecked")
1015 throw new NoSuchElementException();
1016 return (E) snapshot[cursor++];
1019 @SuppressWarnings("unchecked")
1020 public E previous() {
1021 if (! hasPrevious())
1022 throw new NoSuchElementException();
1023 return (E) snapshot[--cursor];
1026 public int nextIndex() {
1030 public int previousIndex() {
1035 * Not supported. Always throws UnsupportedOperationException.
1036 * @throws UnsupportedOperationException always; <tt>remove</tt>
1037 * is not supported by this iterator.
1039 public void remove() {
1040 throw new UnsupportedOperationException();
1044 * Not supported. Always throws UnsupportedOperationException.
1045 * @throws UnsupportedOperationException always; <tt>set</tt>
1046 * is not supported by this iterator.
1048 public void set(E e) {
1049 throw new UnsupportedOperationException();
1053 * Not supported. Always throws UnsupportedOperationException.
1054 * @throws UnsupportedOperationException always; <tt>add</tt>
1055 * is not supported by this iterator.
1057 public void add(E e) {
1058 throw new UnsupportedOperationException();
1063 * Returns a view of the portion of this list between
1064 * <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.
1065 * The returned list is backed by this list, so changes in the
1066 * returned list are reflected in this list.
1068 * <p>The semantics of the list returned by this method become
1069 * undefined if the backing list (i.e., this list) is modified in
1070 * any way other than via the returned list.
1072 * @param fromIndex low endpoint (inclusive) of the subList
1073 * @param toIndex high endpoint (exclusive) of the subList
1074 * @return a view of the specified range within this list
1075 * @throws IndexOutOfBoundsException {@inheritDoc}
1077 public List<E> subList(int fromIndex, int toIndex) {
1078 final ReentrantLock lock = this.lock;
1081 Object[] elements = getArray();
1082 int len = elements.length;
1083 if (fromIndex < 0 || toIndex > len || fromIndex > toIndex)
1084 throw new IndexOutOfBoundsException();
1085 return new COWSubList<E>(this, fromIndex, toIndex);
1092 * Sublist for CopyOnWriteArrayList.
1093 * This class extends AbstractList merely for convenience, to
1094 * avoid having to define addAll, etc. This doesn't hurt, but
1095 * is wasteful. This class does not need or use modCount
1096 * mechanics in AbstractList, but does need to check for
1097 * concurrent modification using similar mechanics. On each
1098 * operation, the array that we expect the backing list to use
1099 * is checked and updated. Since we do this for all of the
1100 * base operations invoked by those defined in AbstractList,
1101 * all is well. While inefficient, this is not worth
1102 * improving. The kinds of list operations inherited from
1103 * AbstractList are already so slow on COW sublists that
1104 * adding a bit more space/time doesn't seem even noticeable.
1106 private static class COWSubList<E>
1107 extends AbstractList<E>
1108 implements RandomAccess
1110 private final CopyOnWriteArrayList<E> l;
1111 private final int offset;
1113 private Object[] expectedArray;
1115 // only call this holding l's lock
1116 COWSubList(CopyOnWriteArrayList<E> list,
1117 int fromIndex, int toIndex) {
1119 expectedArray = l.getArray();
1121 size = toIndex - fromIndex;
1124 // only call this holding l's lock
1125 private void checkForComodification() {
1126 if (l.getArray() != expectedArray)
1127 throw new ConcurrentModificationException();
1130 // only call this holding l's lock
1131 private void rangeCheck(int index) {
1132 if (index<0 || index>=size)
1133 throw new IndexOutOfBoundsException("Index: "+index+
1137 public E set(int index, E element) {
1138 final ReentrantLock lock = l.lock;
1142 checkForComodification();
1143 E x = l.set(index+offset, element);
1144 expectedArray = l.getArray();
1151 public E get(int index) {
1152 final ReentrantLock lock = l.lock;
1156 checkForComodification();
1157 return l.get(index+offset);
1164 final ReentrantLock lock = l.lock;
1167 checkForComodification();
1174 public void add(int index, E element) {
1175 final ReentrantLock lock = l.lock;
1178 checkForComodification();
1179 if (index<0 || index>size)
1180 throw new IndexOutOfBoundsException();
1181 l.add(index+offset, element);
1182 expectedArray = l.getArray();
1189 public void clear() {
1190 final ReentrantLock lock = l.lock;
1193 checkForComodification();
1194 l.removeRange(offset, offset+size);
1195 expectedArray = l.getArray();
1202 public E remove(int index) {
1203 final ReentrantLock lock = l.lock;
1207 checkForComodification();
1208 E result = l.remove(index+offset);
1209 expectedArray = l.getArray();
1217 public boolean remove(Object o) {
1218 int index = indexOf(o);
1225 public Iterator<E> iterator() {
1226 final ReentrantLock lock = l.lock;
1229 checkForComodification();
1230 return new COWSubListIterator<E>(l, 0, offset, size);
1236 public ListIterator<E> listIterator(final int index) {
1237 final ReentrantLock lock = l.lock;
1240 checkForComodification();
1241 if (index<0 || index>size)
1242 throw new IndexOutOfBoundsException("Index: "+index+
1244 return new COWSubListIterator<E>(l, index, offset, size);
1250 public List<E> subList(int fromIndex, int toIndex) {
1251 final ReentrantLock lock = l.lock;
1254 checkForComodification();
1255 if (fromIndex<0 || toIndex>size)
1256 throw new IndexOutOfBoundsException();
1257 return new COWSubList<E>(l, fromIndex + offset,
1267 private static class COWSubListIterator<E> implements ListIterator<E> {
1268 private final ListIterator<E> i;
1269 private final int index;
1270 private final int offset;
1271 private final int size;
1273 COWSubListIterator(List<E> l, int index, int offset,
1276 this.offset = offset;
1278 i = l.listIterator(index+offset);
1281 public boolean hasNext() {
1282 return nextIndex() < size;
1289 throw new NoSuchElementException();
1292 public boolean hasPrevious() {
1293 return previousIndex() >= 0;
1296 public E previous() {
1298 return i.previous();
1300 throw new NoSuchElementException();
1303 public int nextIndex() {
1304 return i.nextIndex() - offset;
1307 public int previousIndex() {
1308 return i.previousIndex() - offset;
1311 public void remove() {
1312 throw new UnsupportedOperationException();
1315 public void set(E e) {
1316 throw new UnsupportedOperationException();
1319 public void add(E e) {
1320 throw new UnsupportedOperationException();
1324 // Support for resetting lock while deserializing
1325 private void resetLock() {
1326 UNSAFE.putObjectVolatile(this, lockOffset, new ReentrantLock());
1328 private static final sun.misc.Unsafe UNSAFE;
1329 private static final long lockOffset;
1332 UNSAFE = sun.misc.Unsafe.getUnsafe();
1333 Class k = CopyOnWriteArrayList.class;
1334 lockOffset = UNSAFE.objectFieldOffset
1335 (k.getDeclaredField("lock"));
1336 } catch (Exception e) {