1 /*

        2  * Copyright (c) 1997, 2008, 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 /**

       29  * Resizable-array implementation of the <tt>List</tt> interface.  Implements

       30  * all optional list operations, and permits all elements, including

       31  * <tt>null</tt>.  In addition to implementing the <tt>List</tt> interface,

       32  * this class provides methods to manipulate the size of the array that is

       33  * used internally to store the list.  (This class is roughly equivalent to

       34  * <tt>Vector</tt>, except that it is unsynchronized.)

       35  *

       36  * <p>The <tt>size</tt>, <tt>isEmpty</tt>, <tt>get</tt>, <tt>set</tt>,

       37  * <tt>iterator</tt>, and <tt>listIterator</tt> operations run in constant

       38  * time.  The <tt>add</tt> operation runs in <i>amortized constant time</i>,

       39  * that is, adding n elements requires O(n) time.  All of the other operations

       40  * run in linear time (roughly speaking).  The constant factor is low compared

       41  * to that for the <tt>LinkedList</tt> implementation.

       42  *

       43  * <p>Each <tt>ArrayList</tt> instance has a <i>capacity</i>.  The capacity is

       44  * the size of the array used to store the elements in the list.  It is always

       45  * at least as large as the list size.  As elements are added to an ArrayList,

       46  * its capacity grows automatically.  The details of the growth policy are not

       47  * specified beyond the fact that adding an element has constant amortized

       48  * time cost.

       49  *

       50  * <p>An application can increase the capacity of an <tt>ArrayList</tt> instance

       51  * before adding a large number of elements using the <tt>ensureCapacity</tt>

       52  * operation.  This may reduce the amount of incremental reallocation.

       53  *

       54  * <p><strong>Note that this implementation is not synchronized.</strong>

       55  * If multiple threads access an <tt>ArrayList</tt> instance concurrently,

       56  * and at least one of the threads modifies the list structurally, it

       57  * <i>must</i> be synchronized externally.  (A structural modification is

       58  * any operation that adds or deletes one or more elements, or explicitly

       59  * resizes the backing array; merely setting the value of an element is not

       60  * a structural modification.)  This is typically accomplished by

       61  * synchronizing on some object that naturally encapsulates the list.

       62  *

       63  * If no such object exists, the list should be "wrapped" using the

       64  * {@link Collections#synchronizedList Collections.synchronizedList}

       65  * method.  This is best done at creation time, to prevent accidental

       66  * unsynchronized access to the list:<pre>

       67  *   List list = Collections.synchronizedList(new ArrayList(...));</pre>

       68  *

       69  * <p><a name="fail-fast"/>

       70  * The iterators returned by this class's {@link #iterator() iterator} and

       71  * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:

       72  * if the list is structurally modified at any time after the iterator is

       73  * created, in any way except through the iterator's own

       74  * {@link ListIterator#remove() remove} or

       75  * {@link ListIterator#add(Object) add} methods, the iterator will throw a

       76  * {@link ConcurrentModificationException}.  Thus, in the face of

       77  * concurrent modification, the iterator fails quickly and cleanly, rather

       78  * than risking arbitrary, non-deterministic behavior at an undetermined

       79  * time in the future.

       80  *

       81  * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed

       82  * as it is, generally speaking, impossible to make any hard guarantees in the

       83  * presence of unsynchronized concurrent modification.  Fail-fast iterators

       84  * throw {@code ConcurrentModificationException} on a best-effort basis.

       85  * Therefore, it would be wrong to write a program that depended on this

       86  * exception for its correctness:  <i>the fail-fast behavior of iterators

       87  * should be used only to detect bugs.</i>

       88  *

       89  * <p>This class is a member of the

       90  * <a href="{@docRoot}/../technotes/guides/collections/index.html">

       91  * Java Collections Framework</a>.

       92  *

       93  * @author  Josh Bloch

       94  * @author  Neal Gafter

       95  * @see     Collection

       96  * @see     List

       97  * @see     LinkedList

       98  * @see     Vector

       99  * @since   1.2

      100  */

      101 

      102 public class ArrayList<E> extends AbstractList<E>

      103         implements List<E>, RandomAccess, Cloneable, java.io.Serializable

      104 {

      105     private static final long serialVersionUID = 8683452581122892189L;

      106 

      107     /**

      108      * The array buffer into which the elements of the ArrayList are stored.

      109      * The capacity of the ArrayList is the length of this array buffer.

      110      */

      111     private transient Object[] elementData;

      112 

      113     /**

      114      * The size of the ArrayList (the number of elements it contains).

      115      *

      116      * @serial

      117      */

      118     private int size;

      119 

      120     /**

      121      * Constructs an empty list with the specified initial capacity.

      122      *

      123      * @param   initialCapacity   the initial capacity of the list

      124      * @exception IllegalArgumentException if the specified initial capacity

      125      *            is negative

      126      */

      127     public ArrayList(int initialCapacity) {

      128         super();

      129         if (initialCapacity < 0)

      130             throw new IllegalArgumentException("Illegal Capacity: "+

      131                                                initialCapacity);

      132         this.elementData = new Object[initialCapacity];

      133     }

      134 

      135     /**

      136      * Constructs an empty list with an initial capacity of ten.

      137      */

      138     public ArrayList() {

      139         this(10);

      140     }

      141 

      142     /**

      143      * Constructs a list containing the elements of the specified

      144      * collection, in the order they are returned by the collection's

      145      * iterator.

      146      *

      147      * @param c the collection whose elements are to be placed into this list

      148      * @throws NullPointerException if the specified collection is null

      149      */

      150     public ArrayList(Collection<? extends E> c) {

      151         elementData = c.toArray();

      152         size = elementData.length;

      153         // c.toArray might (incorrectly) not return Object[] (see 6260652)

      154         if (elementData.getClass() != Object[].class)

      155             elementData = Arrays.copyOf(elementData, size, Object[].class);

      156     }

      157 

      158     /**

      159      * Trims the capacity of this <tt>ArrayList</tt> instance to be the

      160      * list's current size.  An application can use this operation to minimize

      161      * the storage of an <tt>ArrayList</tt> instance.

      162      */

      163     public void trimToSize() {

      164         modCount++;

      165         int oldCapacity = elementData.length;

      166         if (size < oldCapacity) {

      167             elementData = Arrays.copyOf(elementData, size);

      168         }

      169     }

      170 

      171     /**

      172      * Increases the capacity of this <tt>ArrayList</tt> instance, if

      173      * necessary, to ensure that it can hold at least the number of elements

      174      * specified by the minimum capacity argument.

      175      *

      176      * @param minCapacity the desired minimum capacity

      177      */

      178     public void ensureCapacity(int minCapacity) {

      179         modCount++;

      180         // overflow-conscious code

      181         if (minCapacity - elementData.length > 0)

      182             grow(minCapacity);

      183     }

      184 

      185     /**

      186      * The maximum size of array to allocate.

      187      * Some VMs reserve some header words in an array.

      188      * Attempts to allocate larger arrays may result in

      189      * OutOfMemoryError: Requested array size exceeds VM limit

      190      */

      191     private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

      192 

      193     /**

      194      * Increases the capacity to ensure that it can hold at least the

      195      * number of elements specified by the minimum capacity argument.

      196      *

      197      * @param minCapacity the desired minimum capacity

      198      */

      199     private void grow(int minCapacity) {

      200         // overflow-conscious code

      201         int oldCapacity = elementData.length;

      202         int newCapacity = oldCapacity + (oldCapacity >> 1);

      203         if (newCapacity - minCapacity < 0)

      204             newCapacity = minCapacity;

      205         if (newCapacity - MAX_ARRAY_SIZE > 0)

      206             newCapacity = hugeCapacity(minCapacity);

      207         // minCapacity is usually close to size, so this is a win:

      208         elementData = Arrays.copyOf(elementData, newCapacity);

      209     }

      210 

      211     private static int hugeCapacity(int minCapacity) {

      212         if (minCapacity < 0) // overflow

      213             throw new OutOfMemoryError();

      214         return (minCapacity > MAX_ARRAY_SIZE) ?

      215             Integer.MAX_VALUE :

      216             MAX_ARRAY_SIZE;

      217     }

      218 

      219     /**

      220      * Returns the number of elements in this list.

      221      *

      222      * @return the number of elements in this list

      223      */

      224     public int size() {

      225         return size;

      226     }

      227 

      228     /**

      229      * Returns <tt>true</tt> if this list contains no elements.

      230      *

      231      * @return <tt>true</tt> if this list contains no elements

      232      */

      233     public boolean isEmpty() {

      234         return size == 0;

      235     }

      236 

      237     /**

      238      * Returns <tt>true</tt> if this list contains the specified element.

      239      * More formally, returns <tt>true</tt> if and only if this list contains

      240      * at least one element <tt>e</tt> such that

      241      * <tt>(o==null&nbsp;?&nbsp;e==null&nbsp;:&nbsp;o.equals(e))</tt>.

      242      *

      243      * @param o element whose presence in this list is to be tested

      244      * @return <tt>true</tt> if this list contains the specified element

      245      */

      246     public boolean contains(Object o) {

      247         return indexOf(o) >= 0;

      248     }

      249 

      250     /**

      251      * Returns the index of the first occurrence of the specified element

      252      * in this list, or -1 if this list does not contain the element.

      253      * More formally, returns the lowest index <tt>i</tt> such that

      254      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

      255      * or -1 if there is no such index.

      256      */

      257     public int indexOf(Object o) {

      258         if (o == null) {

      259             for (int i = 0; i < size; i++)

      260                 if (elementData[i]==null)

      261                     return i;

      262         } else {

      263             for (int i = 0; i < size; i++)

      264                 if (o.equals(elementData[i]))

      265                     return i;

      266         }

      267         return -1;

      268     }

      269 

      270     /**

      271      * Returns the index of the last occurrence of the specified element

      272      * in this list, or -1 if this list does not contain the element.

      273      * More formally, returns the highest index <tt>i</tt> such that

      274      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>,

      275      * or -1 if there is no such index.

      276      */

      277     public int lastIndexOf(Object o) {

      278         if (o == null) {

      279             for (int i = size-1; i >= 0; i--)

      280                 if (elementData[i]==null)

      281                     return i;

      282         } else {

      283             for (int i = size-1; i >= 0; i--)

      284                 if (o.equals(elementData[i]))

      285                     return i;

      286         }

      287         return -1;

      288     }

      289 

      290     /**

      291      * Returns a shallow copy of this <tt>ArrayList</tt> instance.  (The

      292      * elements themselves are not copied.)

      293      *

      294      * @return a clone of this <tt>ArrayList</tt> instance

      295      */

      296     public Object clone() {

      297         try {

      298             @SuppressWarnings("unchecked")

      299                 ArrayList<E> v = (ArrayList<E>) super.clone();

      300             v.elementData = Arrays.copyOf(elementData, size);

      301             v.modCount = 0;

      302             return v;

      303         } catch (CloneNotSupportedException e) {

      304             // this shouldn't happen, since we are Cloneable

      305             throw new InternalError();

      306         }

      307     }

      308 

      309     /**

      310      * Returns an array containing all of the elements in this list

      311      * in proper sequence (from first to last element).

      312      *

      313      * <p>The returned array will be "safe" in that no references to it are

      314      * maintained by this list.  (In other words, this method must allocate

      315      * a new array).  The caller is thus free to modify the returned array.

      316      *

      317      * <p>This method acts as bridge between array-based and collection-based

      318      * APIs.

      319      *

      320      * @return an array containing all of the elements in this list in

      321      *         proper sequence

      322      */

      323     public Object[] toArray() {

      324         return Arrays.copyOf(elementData, size);

      325     }

      326 

      327     /**

      328      * Returns an array containing all of the elements in this list in proper

      329      * sequence (from first to last element); the runtime type of the returned

      330      * array is that of the specified array.  If the list fits in the

      331      * specified array, it is returned therein.  Otherwise, a new array is

      332      * allocated with the runtime type of the specified array and the size of

      333      * this list.

      334      *

      335      * <p>If the list fits in the specified array with room to spare

      336      * (i.e., the array has more elements than the list), the element in

      337      * the array immediately following the end of the collection is set to

      338      * <tt>null</tt>.  (This is useful in determining the length of the

      339      * list <i>only</i> if the caller knows that the list does not contain

      340      * any null elements.)

      341      *

      342      * @param a the array into which the elements of the list are to

      343      *          be stored, if it is big enough; otherwise, a new array of the

      344      *          same runtime type is allocated for this purpose.

      345      * @return an array containing the elements of the list

      346      * @throws ArrayStoreException if the runtime type of the specified array

      347      *         is not a supertype of the runtime type of every element in

      348      *         this list

      349      * @throws NullPointerException if the specified array is null

      350      */

      351     @SuppressWarnings("unchecked")

      352     public <T> T[] toArray(T[] a) {

      353         if (a.length < size)

      354             // Make a new array of a's runtime type, but my contents:

      355             return (T[]) Arrays.copyOf(elementData, size, a.getClass());

      356         System.arraycopy(elementData, 0, a, 0, size);

      357         if (a.length > size)

      358             a[size] = null;

      359         return a;

      360     }

      361 

      362     // Positional Access Operations

      363 

      364     @SuppressWarnings("unchecked")

      365     E elementData(int index) {

      366         return (E) elementData[index];

      367     }

      368 

      369     /**

      370      * Returns the element at the specified position in this list.

      371      *

      372      * @param  index index of the element to return

      373      * @return the element at the specified position in this list

      374      * @throws IndexOutOfBoundsException {@inheritDoc}

      375      */

      376     public E get(int index) {

      377         rangeCheck(index);

      378 

      379         return elementData(index);

      380     }

      381 

      382     /**

      383      * Replaces the element at the specified position in this list with

      384      * the specified element.

      385      *

      386      * @param index index of the element to replace

      387      * @param element element to be stored at the specified position

      388      * @return the element previously at the specified position

      389      * @throws IndexOutOfBoundsException {@inheritDoc}

      390      */

      391     public E set(int index, E element) {

      392         rangeCheck(index);

      393 

      394         E oldValue = elementData(index);

      395         elementData[index] = element;

      396         return oldValue;

      397     }

      398 

      399     /**

      400      * Appends the specified element to the end of this list.

      401      *

      402      * @param e element to be appended to this list

      403      * @return <tt>true</tt> (as specified by {@link Collection#add})

      404      */

      405     public boolean add(E e) {

      406         ensureCapacity(size + 1);  // Increments modCount!!

      407         elementData[size++] = e;

      408         return true;

      409     }

      410 

      411     /**

      412      * Inserts the specified element at the specified position in this

      413      * list. Shifts the element currently at that position (if any) and

      414      * any subsequent elements to the right (adds one to their indices).

      415      *

      416      * @param index index at which the specified element is to be inserted

      417      * @param element element to be inserted

      418      * @throws IndexOutOfBoundsException {@inheritDoc}

      419      */

      420     public void add(int index, E element) {

      421         rangeCheckForAdd(index);

      422 

      423         ensureCapacity(size + 1);  // Increments modCount!!

      424         System.arraycopy(elementData, index, elementData, index + 1,

      425                          size - index);

      426         elementData[index] = element;

      427         size++;

      428     }

      429 

      430     /**

      431      * Removes the element at the specified position in this list.

      432      * Shifts any subsequent elements to the left (subtracts one from their

      433      * indices).

      434      *

      435      * @param index the index of the element to be removed

      436      * @return the element that was removed from the list

      437      * @throws IndexOutOfBoundsException {@inheritDoc}

      438      */

      439     public E remove(int index) {

      440         rangeCheck(index);

      441 

      442         modCount++;

      443         E oldValue = elementData(index);

      444 

      445         int numMoved = size - index - 1;

      446         if (numMoved > 0)

      447             System.arraycopy(elementData, index+1, elementData, index,

      448                              numMoved);

      449         elementData[--size] = null; // Let gc do its work

      450 

      451         return oldValue;

      452     }

      453 

      454     /**

      455      * Removes the first occurrence of the specified element from this list,

      456      * if it is present.  If the list does not contain the element, it is

      457      * unchanged.  More formally, removes the element with the lowest index

      458      * <tt>i</tt> such that

      459      * <tt>(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;o.equals(get(i)))</tt>

      460      * (if such an element exists).  Returns <tt>true</tt> if this list

      461      * contained the specified element (or equivalently, if this list

      462      * changed as a result of the call).

      463      *

      464      * @param o element to be removed from this list, if present

      465      * @return <tt>true</tt> if this list contained the specified element

      466      */

      467     public boolean remove(Object o) {

      468         if (o == null) {

      469             for (int index = 0; index < size; index++)

      470                 if (elementData[index] == null) {

      471                     fastRemove(index);

      472                     return true;

      473                 }

      474         } else {

      475             for (int index = 0; index < size; index++)

      476                 if (o.equals(elementData[index])) {

      477                     fastRemove(index);

      478                     return true;

      479                 }

      480         }

      481         return false;

      482     }

      483 

      484     /*

      485      * Private remove method that skips bounds checking and does not

      486      * return the value removed.

      487      */

      488     private void fastRemove(int index) {

      489         modCount++;

      490         int numMoved = size - index - 1;

      491         if (numMoved > 0)

      492             System.arraycopy(elementData, index+1, elementData, index,

      493                              numMoved);

      494         elementData[--size] = null; // Let gc do its work

      495     }

      496 

      497     /**

      498      * Removes all of the elements from this list.  The list will

      499      * be empty after this call returns.

      500      */

      501     public void clear() {

      502         modCount++;

      503 

      504         // Let gc do its work

      505         for (int i = 0; i < size; i++)

      506             elementData[i] = null;

      507 

      508         size = 0;

      509     }

      510 

      511     /**

      512      * Appends all of the elements in the specified collection to the end of

      513      * this list, in the order that they are returned by the

      514      * specified collection's Iterator.  The behavior of this operation is

      515      * undefined if the specified collection is modified while the operation

      516      * is in progress.  (This implies that the behavior of this call is

      517      * undefined if the specified collection is this list, and this

      518      * list is nonempty.)

      519      *

      520      * @param c collection containing elements to be added to this list

      521      * @return <tt>true</tt> if this list changed as a result of the call

      522      * @throws NullPointerException if the specified collection is null

      523      */

      524     public boolean addAll(Collection<? extends E> c) {

      525         Object[] a = c.toArray();

      526         int numNew = a.length;

      527         ensureCapacity(size + numNew);  // Increments modCount

      528         System.arraycopy(a, 0, elementData, size, numNew);

      529         size += numNew;

      530         return numNew != 0;

      531     }

      532 

      533     /**

      534      * Inserts all of the elements in the specified collection into this

      535      * list, starting at the specified position.  Shifts the element

      536      * currently at that position (if any) and any subsequent elements to

      537      * the right (increases their indices).  The new elements will appear

      538      * in the list in the order that they are returned by the

      539      * specified collection's iterator.

      540      *

      541      * @param index index at which to insert the first element from the

      542      *              specified collection

      543      * @param c collection containing elements to be added to this list

      544      * @return <tt>true</tt> if this list changed as a result of the call

      545      * @throws IndexOutOfBoundsException {@inheritDoc}

      546      * @throws NullPointerException if the specified collection is null

      547      */

      548     public boolean addAll(int index, Collection<? extends E> c) {

      549         rangeCheckForAdd(index);

      550 

      551         Object[] a = c.toArray();

      552         int numNew = a.length;

      553         ensureCapacity(size + numNew);  // Increments modCount

      554 

      555         int numMoved = size - index;

      556         if (numMoved > 0)

      557             System.arraycopy(elementData, index, elementData, index + numNew,

      558                              numMoved);

      559 

      560         System.arraycopy(a, 0, elementData, index, numNew);

      561         size += numNew;

      562         return numNew != 0;

      563     }

      564 

      565     /**

      566      * Removes from this list all of the elements whose index is between

      567      * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.

      568      * Shifts any succeeding elements to the left (reduces their index).

      569      * This call shortens the list by {@code (toIndex - fromIndex)} elements.

      570      * (If {@code toIndex==fromIndex}, this operation has no effect.)

      571      *

      572      * @throws IndexOutOfBoundsException if {@code fromIndex} or

      573      *         {@code toIndex} is out of range

      574      *         ({@code fromIndex < 0 ||

      575      *          fromIndex >= size() ||

      576      *          toIndex > size() ||

      577      *          toIndex < fromIndex})

      578      */

      579     protected void removeRange(int fromIndex, int toIndex) {

      580         modCount++;

      581         int numMoved = size - toIndex;

      582         System.arraycopy(elementData, toIndex, elementData, fromIndex,

      583                          numMoved);

      584 

      585         // Let gc do its work

      586         int newSize = size - (toIndex-fromIndex);

      587         while (size != newSize)

      588             elementData[--size] = null;

      589     }

      590 

      591     /**

      592      * Checks if the given index is in range.  If not, throws an appropriate

      593      * runtime exception.  This method does *not* check if the index is

      594      * negative: It is always used immediately prior to an array access,

      595      * which throws an ArrayIndexOutOfBoundsException if index is negative.

      596      */

      597     private void rangeCheck(int index) {

      598         if (index >= size)

      599             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

      600     }

      601 

      602     /**

      603      * A version of rangeCheck used by add and addAll.

      604      */

      605     private void rangeCheckForAdd(int index) {

      606         if (index > size || index < 0)

      607             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

      608     }

      609 

      610     /**

      611      * Constructs an IndexOutOfBoundsException detail message.

      612      * Of the many possible refactorings of the error handling code,

      613      * this "outlining" performs best with both server and client VMs.

      614      */

      615     private String outOfBoundsMsg(int index) {

      616         return "Index: "+index+", Size: "+size;

      617     }

      618 

      619     /**

      620      * Removes from this list all of its elements that are contained in the

      621      * specified collection.

      622      *

      623      * @param c collection containing elements to be removed from this list

      624      * @return {@code true} if this list changed as a result of the call

      625      * @throws ClassCastException if the class of an element of this list

      626      *         is incompatible with the specified collection (optional)

      627      * @throws NullPointerException if this list contains a null element and the

      628      *         specified collection does not permit null elements (optional),

      629      *         or if the specified collection is null

      630      * @see Collection#contains(Object)

      631      */

      632     public boolean removeAll(Collection<?> c) {

      633         return batchRemove(c, false);

      634     }

      635 

      636     /**

      637      * Retains only the elements in this list that are contained in the

      638      * specified collection.  In other words, removes from this list all

      639      * of its elements that are not contained in the specified collection.

      640      *

      641      * @param c collection containing elements to be retained in this list

      642      * @return {@code true} if this list changed as a result of the call

      643      * @throws ClassCastException if the class of an element of this list

      644      *         is incompatible with the specified collection (optional)

      645      * @throws NullPointerException if this list contains a null element and the

      646      *         specified collection does not permit null elements (optional),

      647      *         or if the specified collection is null

      648      * @see Collection#contains(Object)

      649      */

      650     public boolean retainAll(Collection<?> c) {

      651         return batchRemove(c, true);

      652     }

      653 

      654     private boolean batchRemove(Collection<?> c, boolean complement) {

      655         final Object[] elementData = this.elementData;

      656         int r = 0, w = 0;

      657         boolean modified = false;

      658         try {

      659             for (; r < size; r++)

      660                 if (c.contains(elementData[r]) == complement)

      661                     elementData[w++] = elementData[r];

      662         } finally {

      663             // Preserve behavioral compatibility with AbstractCollection,

      664             // even if c.contains() throws.

      665             if (r != size) {

      666                 System.arraycopy(elementData, r,

      667                                  elementData, w,

      668                                  size - r);

      669                 w += size - r;

      670             }

      671             if (w != size) {

      672                 for (int i = w; i < size; i++)

      673                     elementData[i] = null;

      674                 modCount += size - w;

      675                 size = w;

      676                 modified = true;

      677             }

      678         }

      679         return modified;

      680     }

      681 

      682     /**

      683      * Save the state of the <tt>ArrayList</tt> instance to a stream (that

      684      * is, serialize it).

      685      *

      686      * @serialData The length of the array backing the <tt>ArrayList</tt>

      687      *             instance is emitted (int), followed by all of its elements

      688      *             (each an <tt>Object</tt>) in the proper order.

      689      */

      690     private void writeObject(java.io.ObjectOutputStream s)

      691         throws java.io.IOException{

      692         // Write out element count, and any hidden stuff

      693         int expectedModCount = modCount;

      694         s.defaultWriteObject();

      695 

      696         // Write out array length

      697         s.writeInt(elementData.length);

      698 

      699         // Write out all elements in the proper order.

      700         for (int i=0; i<size; i++)

      701             s.writeObject(elementData[i]);

      702 

      703         if (modCount != expectedModCount) {

      704             throw new ConcurrentModificationException();

      705         }

      706 

      707     }

      708 

      709     /**

      710      * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,

      711      * deserialize it).

      712      */

      713     private void readObject(java.io.ObjectInputStream s)

      714         throws java.io.IOException, ClassNotFoundException {

      715         // Read in size, and any hidden stuff

      716         s.defaultReadObject();

      717 

      718         // Read in array length and allocate array

      719         int arrayLength = s.readInt();

      720         Object[] a = elementData = new Object[arrayLength];

      721 

      722         // Read in all elements in the proper order.

      723         for (int i=0; i<size; i++)

      724             a[i] = s.readObject();

      725     }

      726 

      727     /**

      728      * Returns a list iterator over the elements in this list (in proper

      729      * sequence), starting at the specified position in the list.

      730      * The specified index indicates the first element that would be

      731      * returned by an initial call to {@link ListIterator#next next}.

      732      * An initial call to {@link ListIterator#previous previous} would

      733      * return the element with the specified index minus one.

      734      *

      735      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.

      736      *

      737      * @throws IndexOutOfBoundsException {@inheritDoc}

      738      */

      739     public ListIterator<E> listIterator(int index) {

      740         if (index < 0 || index > size)

      741             throw new IndexOutOfBoundsException("Index: "+index);

      742         return new ListItr(index);

      743     }

      744 

      745     /**

      746      * Returns a list iterator over the elements in this list (in proper

      747      * sequence).

      748      *

      749      * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.

      750      *

      751      * @see #listIterator(int)

      752      */

      753     public ListIterator<E> listIterator() {

      754         return new ListItr(0);

      755     }

      756 

      757     /**

      758      * Returns an iterator over the elements in this list in proper sequence.

      759      *

      760      * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.

      761      *

      762      * @return an iterator over the elements in this list in proper sequence

      763      */

      764     public Iterator<E> iterator() {

      765         return new Itr();

      766     }

      767 

      768     /**

      769      * An optimized version of AbstractList.Itr

      770      */

      771     private class Itr implements Iterator<E> {

      772         int cursor;       // index of next element to return

      773         int lastRet = -1; // index of last element returned; -1 if no such

      774         int expectedModCount = modCount;

      775 

      776         public boolean hasNext() {

      777             return cursor != size;

      778         }

      779 

      780         @SuppressWarnings("unchecked")

      781         public E next() {

      782             checkForComodification();

      783             int i = cursor;

      784             if (i >= size)

      785                 throw new NoSuchElementException();

      786             Object[] elementData = ArrayList.this.elementData;

      787             if (i >= elementData.length)

      788                 throw new ConcurrentModificationException();

      789             cursor = i + 1;

      790             return (E) elementData[lastRet = i];

      791         }

      792 

      793         public void remove() {

      794             if (lastRet < 0)

      795                 throw new IllegalStateException();

      796             checkForComodification();

      797 

      798             try {

      799                 ArrayList.this.remove(lastRet);

      800                 cursor = lastRet;

      801                 lastRet = -1;

      802                 expectedModCount = modCount;

      803             } catch (IndexOutOfBoundsException ex) {

      804                 throw new ConcurrentModificationException();

      805             }

      806         }

      807 

      808         final void checkForComodification() {

      809             if (modCount != expectedModCount)

      810                 throw new ConcurrentModificationException();

      811         }

      812     }

      813 

      814     /**

      815      * An optimized version of AbstractList.ListItr

      816      */

      817     private class ListItr extends Itr implements ListIterator<E> {

      818         ListItr(int index) {

      819             super();

      820             cursor = index;

      821         }

      822 

      823         public boolean hasPrevious() {

      824             return cursor != 0;

      825         }

      826 

      827         public int nextIndex() {

      828             return cursor;

      829         }

      830 

      831         public int previousIndex() {

      832             return cursor - 1;

      833         }

      834 

      835         @SuppressWarnings("unchecked")

      836         public E previous() {

      837             checkForComodification();

      838             int i = cursor - 1;

      839             if (i < 0)

      840                 throw new NoSuchElementException();

      841             Object[] elementData = ArrayList.this.elementData;

      842             if (i >= elementData.length)

      843                 throw new ConcurrentModificationException();

      844             cursor = i;

      845             return (E) elementData[lastRet = i];

      846         }

      847 

      848         public void set(E e) {

      849             if (lastRet < 0)

      850                 throw new IllegalStateException();

      851             checkForComodification();

      852 

      853             try {

      854                 ArrayList.this.set(lastRet, e);

      855             } catch (IndexOutOfBoundsException ex) {

      856                 throw new ConcurrentModificationException();

      857             }

      858         }

      859 

      860         public void add(E e) {

      861             checkForComodification();

      862 

      863             try {

      864                 int i = cursor;

      865                 ArrayList.this.add(i, e);

      866                 cursor = i + 1;

      867                 lastRet = -1;

      868                 expectedModCount = modCount;

      869             } catch (IndexOutOfBoundsException ex) {

      870                 throw new ConcurrentModificationException();

      871             }

      872         }

      873     }

      874 

      875     /**

      876      * Returns a view of the portion of this list between the specified

      877      * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.  (If

      878      * {@code fromIndex} and {@code toIndex} are equal, the returned list is

      879      * empty.)  The returned list is backed by this list, so non-structural

      880      * changes in the returned list are reflected in this list, and vice-versa.

      881      * The returned list supports all of the optional list operations.

      882      *

      883      * <p>This method eliminates the need for explicit range operations (of

      884      * the sort that commonly exist for arrays).  Any operation that expects

      885      * a list can be used as a range operation by passing a subList view

      886      * instead of a whole list.  For example, the following idiom

      887      * removes a range of elements from a list:

      888      * <pre>

      889      *      list.subList(from, to).clear();

      890      * </pre>

      891      * Similar idioms may be constructed for {@link #indexOf(Object)} and

      892      * {@link #lastIndexOf(Object)}, and all of the algorithms in the

      893      * {@link Collections} class can be applied to a subList.

      894      *

      895      * <p>The semantics of the list returned by this method become undefined if

      896      * the backing list (i.e., this list) is <i>structurally modified</i> in

      897      * any way other than via the returned list.  (Structural modifications are

      898      * those that change the size of this list, or otherwise perturb it in such

      899      * a fashion that iterations in progress may yield incorrect results.)

      900      *

      901      * @throws IndexOutOfBoundsException {@inheritDoc}

      902      * @throws IllegalArgumentException {@inheritDoc}

      903      */

      904     public List<E> subList(int fromIndex, int toIndex) {

      905         subListRangeCheck(fromIndex, toIndex, size);

      906         return new SubList(this, 0, fromIndex, toIndex);

      907     }

      908 

      909     static void subListRangeCheck(int fromIndex, int toIndex, int size) {

      910         if (fromIndex < 0)

      911             throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);

      912         if (toIndex > size)

      913             throw new IndexOutOfBoundsException("toIndex = " + toIndex);

      914         if (fromIndex > toIndex)

      915             throw new IllegalArgumentException("fromIndex(" + fromIndex +

      916                                                ") > toIndex(" + toIndex + ")");

      917     }

      918 

      919     private class SubList extends AbstractList<E> implements RandomAccess {

      920         private final AbstractList<E> parent;

      921         private final int parentOffset;

      922         private final int offset;

      923         int size;

      924 

      925         SubList(AbstractList<E> parent,

      926                 int offset, int fromIndex, int toIndex) {

      927             this.parent = parent;

      928             this.parentOffset = fromIndex;

      929             this.offset = offset + fromIndex;

      930             this.size = toIndex - fromIndex;

      931             this.modCount = ArrayList.this.modCount;

      932         }

      933 

      934         public E set(int index, E e) {

      935             rangeCheck(index);

      936             checkForComodification();

      937             E oldValue = ArrayList.this.elementData(offset + index);

      938             ArrayList.this.elementData[offset + index] = e;

      939             return oldValue;

      940         }

      941 

      942         public E get(int index) {

      943             rangeCheck(index);

      944             checkForComodification();

      945             return ArrayList.this.elementData(offset + index);

      946         }

      947 

      948         public int size() {

      949             checkForComodification();

      950             return this.size;

      951         }

      952 

      953         public void add(int index, E e) {

      954             rangeCheckForAdd(index);

      955             checkForComodification();

      956             parent.add(parentOffset + index, e);

      957             this.modCount = parent.modCount;

      958             this.size++;

      959         }

      960 

      961         public E remove(int index) {

      962             rangeCheck(index);

      963             checkForComodification();

      964             E result = parent.remove(parentOffset + index);

      965             this.modCount = parent.modCount;

      966             this.size--;

      967             return result;

      968         }

      969 

      970         protected void removeRange(int fromIndex, int toIndex) {

      971             checkForComodification();

      972             parent.removeRange(parentOffset + fromIndex,

      973                                parentOffset + toIndex);

      974             this.modCount = parent.modCount;

      975             this.size -= toIndex - fromIndex;

      976         }

      977 

      978         public boolean addAll(Collection<? extends E> c) {

      979             return addAll(this.size, c);

      980         }

      981 

      982         public boolean addAll(int index, Collection<? extends E> c) {

      983             rangeCheckForAdd(index);

      984             int cSize = c.size();

      985             if (cSize==0)

      986                 return false;

      987 

      988             checkForComodification();

      989             parent.addAll(parentOffset + index, c);

      990             this.modCount = parent.modCount;

      991             this.size += cSize;

      992             return true;

      993         }

      994 

      995         public Iterator<E> iterator() {

      996             return listIterator();

      997         }

      998 

      999         public ListIterator<E> listIterator(final int index) {

     1000             checkForComodification();

     1001             rangeCheckForAdd(index);

     1002             final int offset = this.offset;

     1003 

     1004             return new ListIterator<E>() {

     1005                 int cursor = index;

     1006                 int lastRet = -1;

     1007                 int expectedModCount = ArrayList.this.modCount;

     1008 

     1009                 public boolean hasNext() {

     1010                     return cursor != SubList.this.size;

     1011                 }

     1012 

     1013                 @SuppressWarnings("unchecked")

     1014                 public E next() {

     1015                     checkForComodification();

     1016                     int i = cursor;

     1017                     if (i >= SubList.this.size)

     1018                         throw new NoSuchElementException();

     1019                     Object[] elementData = ArrayList.this.elementData;

     1020                     if (offset + i >= elementData.length)

     1021                         throw new ConcurrentModificationException();

     1022                     cursor = i + 1;

     1023                     return (E) elementData[offset + (lastRet = i)];

     1024                 }

     1025 

     1026                 public boolean hasPrevious() {

     1027                     return cursor != 0;

     1028                 }

     1029 

     1030                 @SuppressWarnings("unchecked")

     1031                 public E previous() {

     1032                     checkForComodification();

     1033                     int i = cursor - 1;

     1034                     if (i < 0)

     1035                         throw new NoSuchElementException();

     1036                     Object[] elementData = ArrayList.this.elementData;

     1037                     if (offset + i >= elementData.length)

     1038                         throw new ConcurrentModificationException();

     1039                     cursor = i;

     1040                     return (E) elementData[offset + (lastRet = i)];

     1041                 }

     1042 

     1043                 public int nextIndex() {

     1044                     return cursor;

     1045                 }

     1046 

     1047                 public int previousIndex() {

     1048                     return cursor - 1;

     1049                 }

     1050 

     1051                 public void remove() {

     1052                     if (lastRet < 0)

     1053                         throw new IllegalStateException();

     1054                     checkForComodification();

     1055 

     1056                     try {

     1057                         SubList.this.remove(lastRet);

     1058                         cursor = lastRet;

     1059                         lastRet = -1;

     1060                         expectedModCount = ArrayList.this.modCount;

     1061                     } catch (IndexOutOfBoundsException ex) {

     1062                         throw new ConcurrentModificationException();

     1063                     }

     1064                 }

     1065 

     1066                 public void set(E e) {

     1067                     if (lastRet < 0)

     1068                         throw new IllegalStateException();

     1069                     checkForComodification();

     1070 

     1071                     try {

     1072                         ArrayList.this.set(offset + lastRet, e);

     1073                     } catch (IndexOutOfBoundsException ex) {

     1074                         throw new ConcurrentModificationException();

     1075                     }

     1076                 }

     1077 

     1078                 public void add(E e) {

     1079                     checkForComodification();

     1080 

     1081                     try {

     1082                         int i = cursor;

     1083                         SubList.this.add(i, e);

     1084                         cursor = i + 1;

     1085                         lastRet = -1;

     1086                         expectedModCount = ArrayList.this.modCount;

     1087                     } catch (IndexOutOfBoundsException ex) {

     1088                         throw new ConcurrentModificationException();

     1089                     }

     1090                 }

     1091 

     1092                 final void checkForComodification() {

     1093                     if (expectedModCount != ArrayList.this.modCount)

     1094                         throw new ConcurrentModificationException();

     1095                 }

     1096             };

     1097         }

     1098 

     1099         public List<E> subList(int fromIndex, int toIndex) {

     1100             subListRangeCheck(fromIndex, toIndex, size);

     1101             return new SubList(this, offset, fromIndex, toIndex);

     1102         }

     1103 

     1104         private void rangeCheck(int index) {

     1105             if (index < 0 || index >= this.size)

     1106                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

     1107         }

     1108 

     1109         private void rangeCheckForAdd(int index) {

     1110             if (index < 0 || index > this.size)

     1111                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

     1112         }

     1113 

     1114         private String outOfBoundsMsg(int index) {

     1115             return "Index: "+index+", Size: "+this.size;

     1116         }

     1117 

     1118         private void checkForComodification() {

     1119             if (ArrayList.this.modCount != this.modCount)

     1120                 throw new ConcurrentModificationException();

     1121         }

     1122     }

     1123 }