/*

  * Copyright (c) 1997, 2010, Oracle and/or its affiliates. All rights reserved.

  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.

  *

  * This code is free software; you can redistribute it and/or modify it

  * under the terms of the GNU General Public License version 2 only, as

  * published by the Free Software Foundation.  Oracle designates this

  * particular file as subject to the "Classpath" exception as provided

  * by Oracle in the LICENSE file that accompanied this code.

  *

  * This code is distributed in the hope that it will be useful, but WITHOUT

  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License

  * version 2 for more details (a copy is included in the LICENSE file that

  * accompanied this code).

  *

  * You should have received a copy of the GNU General Public License version

  * 2 along with this work; if not, write to the Free Software Foundation,

  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.

  *

  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA

  * or visit www.oracle.com if you need additional information or have any

  * questions.

  */

 package java.util;

 /**

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

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

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

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

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

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

  *

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

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

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

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

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

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

  *

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

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

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

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

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

  * time cost.

  *

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

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

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

  *

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

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

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

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

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

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

  * a structural modification.)  This is typically accomplished by

  * synchronizing on some object that naturally encapsulates the list.

  *

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

  * {@link Collections#synchronizedList Collections.synchronizedList}

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

  * unsynchronized access to the list:<pre>

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

  *

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

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

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

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

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

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

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

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

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

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

  * time in the future.

  *

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

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

  * presence of unsynchronized concurrent modification.  Fail-fast iterators

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

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

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

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

  *

  * <p>This class is a member of the

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

  * Java Collections Framework</a>.

  *

  * @author  Josh Bloch

  * @author  Neal Gafter

  * @see     Collection

  * @see     List

  * @see     LinkedList

  * @see     Vector

  * @since   1.2

  */

 public class ArrayList<E> extends AbstractList<E>

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

 {

     private static final long serialVersionUID = 8683452581122892189L;

     /**

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

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

      */

     private transient Object[] elementData;

     /**

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

      *

      * @serial

      */

     private int size;

     /**

      * Constructs an empty list with the specified initial capacity.

      *

      * @param  initialCapacity  the initial capacity of the list

      * @throws IllegalArgumentException if the specified initial capacity

      *         is negative

      */

     public ArrayList(int initialCapacity) {

         super();

         if (initialCapacity < 0)

             throw new IllegalArgumentException("Illegal Capacity: "+

                                                initialCapacity);

         this.elementData = new Object[initialCapacity];

     }

     /**

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

      */

     public ArrayList() {

         this(10);

     }

     /**

      * Constructs a list containing the elements of the specified

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

      * iterator.

      *

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

      * @throws NullPointerException if the specified collection is null

      */

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

         elementData = c.toArray();

         size = elementData.length;

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

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

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

     }

     /**

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

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

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

      */

     public void trimToSize() {

         modCount++;

         int oldCapacity = elementData.length;

         if (size < oldCapacity) {

             elementData = Arrays.copyOf(elementData, size);

         }

     }

     /**

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

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

      * specified by the minimum capacity argument.

      *

      * @param   minCapacity   the desired minimum capacity

      */

     public void ensureCapacity(int minCapacity) {

         if (minCapacity > 0)

             ensureCapacityInternal(minCapacity);

     }

     private void ensureCapacityInternal(int minCapacity) {

         modCount++;

         // overflow-conscious code

         if (minCapacity - elementData.length > 0)

             grow(minCapacity);

     }

     /**

      * The maximum size of array to allocate.

      * Some VMs reserve some header words in an array.

      * Attempts to allocate larger arrays may result in

      * OutOfMemoryError: Requested array size exceeds VM limit

      */

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

     /**

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

      * number of elements specified by the minimum capacity argument.

      *

      * @param minCapacity the desired minimum capacity

      */

     private void grow(int minCapacity) {

         // overflow-conscious code

         int oldCapacity = elementData.length;

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

         if (newCapacity - minCapacity < 0)

             newCapacity = minCapacity;

         if (newCapacity - MAX_ARRAY_SIZE > 0)

             newCapacity = hugeCapacity(minCapacity);

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

         elementData = Arrays.copyOf(elementData, newCapacity);

     }

     private static int hugeCapacity(int minCapacity) {

         if (minCapacity < 0) // overflow

             throw new OutOfMemoryError();

         return (minCapacity > MAX_ARRAY_SIZE) ?

             Integer.MAX_VALUE :

             MAX_ARRAY_SIZE;

     }

     /**

      * Returns the number of elements in this list.

      *

      * @return the number of elements in this list

      */

     public int size() {

         return size;

     }

     /**

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

      *

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

      */

     public boolean isEmpty() {

         return size == 0;

     }

     /**

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

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

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

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

      *

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

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

      */

     public boolean contains(Object o) {

         return indexOf(o) >= 0;

     }

     /**

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

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

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

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

      * or -1 if there is no such index.

      */

     public int indexOf(Object o) {

         if (o == null) {

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

                 if (elementData[i]==null)

                     return i;

         } else {

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

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

                     return i;

         }

         return -1;

     }

     /**

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

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

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

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

      * or -1 if there is no such index.

      */

     public int lastIndexOf(Object o) {

         if (o == null) {

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

                 if (elementData[i]==null)

                     return i;

         } else {

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

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

                     return i;

         }

         return -1;

     }

     /**

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

      * elements themselves are not copied.)

      *

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

      */

     public Object clone() {

         try {

             @SuppressWarnings("unchecked")

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

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

             v.modCount = 0;

             return v;

         } catch (CloneNotSupportedException e) {

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

             throw new InternalError();

         }

     }

     /**

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

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

      *

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

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

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

      *

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

      * APIs.

      *

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

      *         proper sequence

      */

     public Object[] toArray() {

         return Arrays.copyOf(elementData, size);

     }

     /**

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

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

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

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

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

      * this list.

      *

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

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

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

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

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

      * any null elements.)

      *

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

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

      *          same runtime type is allocated for this purpose.

      * @return an array containing the elements of the list

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

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

      *         this list

      * @throws NullPointerException if the specified array is null

      */

     @SuppressWarnings("unchecked")

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

         if (a.length < size)

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

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

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

         if (a.length > size)

             a[size] = null;

         return a;

     }

     // Positional Access Operations

     @SuppressWarnings("unchecked")

     E elementData(int index) {

         return (E) elementData[index];

     }

     /**

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

      *

      * @param  index index of the element to return

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

      * @throws IndexOutOfBoundsException {@inheritDoc}

      */

     public E get(int index) {

         rangeCheck(index);

         return elementData(index);

     }

     /**

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

      * the specified element.

      *

      * @param index index of the element to replace

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

      * @return the element previously at the specified position

      * @throws IndexOutOfBoundsException {@inheritDoc}

      */

     public E set(int index, E element) {

         rangeCheck(index);

         E oldValue = elementData(index);

         elementData[index] = element;

         return oldValue;

     }

     /**

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

      *

      * @param e element to be appended to this list

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

      */

     public boolean add(E e) {

         ensureCapacityInternal(size + 1);  // Increments modCount!!

         elementData[size++] = e;

         return true;

     }

     /**

      * Inserts the specified element at the specified position in this

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

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

      *

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

      * @param element element to be inserted

      * @throws IndexOutOfBoundsException {@inheritDoc}

      */

     public void add(int index, E element) {

         rangeCheckForAdd(index);

         ensureCapacityInternal(size + 1);  // Increments modCount!!

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

                          size - index);

         elementData[index] = element;

         size++;

     }

     /**

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

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

      * indices).

      *

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

      * @return the element that was removed from the list

      * @throws IndexOutOfBoundsException {@inheritDoc}

      */

     public E remove(int index) {

         rangeCheck(index);

         modCount++;

         E oldValue = elementData(index);

         int numMoved = size - index - 1;

         if (numMoved > 0)

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

                              numMoved);

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

         return oldValue;

     }

     /**

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

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

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

      * <tt>i</tt> such that

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

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

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

      * changed as a result of the call).

      *

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

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

      */

     public boolean remove(Object o) {

         if (o == null) {

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

                 if (elementData[index] == null) {

                     fastRemove(index);

                     return true;

                 }

         } else {

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

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

                     fastRemove(index);

                     return true;

                 }

         }

         return false;

     }

     /*

      * Private remove method that skips bounds checking and does not

      * return the value removed.

      */

     private void fastRemove(int index) {

         modCount++;

         int numMoved = size - index - 1;

         if (numMoved > 0)

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

                              numMoved);

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

     }

     /**

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

      * be empty after this call returns.

      */

     public void clear() {

         modCount++;

         // Let gc do its work

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

             elementData[i] = null;

         size = 0;

     }

     /**

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

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

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

      * undefined if the specified collection is modified while the operation

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

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

      * list is nonempty.)

      *

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

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

      * @throws NullPointerException if the specified collection is null

      */

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

         Object[] a = c.toArray();

         int numNew = a.length;

         ensureCapacityInternal(size + numNew);  // Increments modCount

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

         size += numNew;

         return numNew != 0;

     }

     /**

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

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

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

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

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

      * specified collection's iterator.

      *

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

      *              specified collection

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

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

      * @throws IndexOutOfBoundsException {@inheritDoc}

      * @throws NullPointerException if the specified collection is null

      */

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

         rangeCheckForAdd(index);

         Object[] a = c.toArray();

         int numNew = a.length;

         ensureCapacityInternal(size + numNew);  // Increments modCount

         int numMoved = size - index;

         if (numMoved > 0)

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

                              numMoved);

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

         size += numNew;

         return numNew != 0;

     }

     /**

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

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

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

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

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

      *

      * @throws IndexOutOfBoundsException if {@code fromIndex} or

      *         {@code toIndex} is out of range

      *         ({@code fromIndex < 0 ||

      *          fromIndex >= size() ||

      *          toIndex > size() ||

      *          toIndex < fromIndex})

      */

     protected void removeRange(int fromIndex, int toIndex) {

         modCount++;

         int numMoved = size - toIndex;

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

                          numMoved);

         // Let gc do its work

         int newSize = size - (toIndex-fromIndex);

         while (size != newSize)

             elementData[--size] = null;

     }

     /**

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

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

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

      * which throws an ArrayIndexOutOfBoundsException if index is negative.

      */

     private void rangeCheck(int index) {

         if (index >= size)

             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

     }

     /**

      * A version of rangeCheck used by add and addAll.

      */

     private void rangeCheckForAdd(int index) {

         if (index > size || index < 0)

             throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

     }

     /**

      * Constructs an IndexOutOfBoundsException detail message.

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

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

      */

     private String outOfBoundsMsg(int index) {

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

     }

     /**

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

      * specified collection.

      *

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

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

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

      *         is incompatible with the specified collection

      * (<a href="Collection.html#optional-restrictions">optional</a>)

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

      *         specified collection does not permit null elements

      * (<a href="Collection.html#optional-restrictions">optional</a>),

      *         or if the specified collection is null

      * @see Collection#contains(Object)

      */

     public boolean removeAll(Collection<?> c) {

         return batchRemove(c, false);

     }

     /**

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

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

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

      *

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

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

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

      *         is incompatible with the specified collection

      * (<a href="Collection.html#optional-restrictions">optional</a>)

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

      *         specified collection does not permit null elements

      * (<a href="Collection.html#optional-restrictions">optional</a>),

      *         or if the specified collection is null

      * @see Collection#contains(Object)

      */

     public boolean retainAll(Collection<?> c) {

         return batchRemove(c, true);

     }

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

         final Object[] elementData = this.elementData;

         int r = 0, w = 0;

         boolean modified = false;

         try {

             for (; r < size; r++)

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

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

         } finally {

             // Preserve behavioral compatibility with AbstractCollection,

             // even if c.contains() throws.

             if (r != size) {

                 System.arraycopy(elementData, r,

                                  elementData, w,

                                  size - r);

                 w += size - r;

             }

             if (w != size) {

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

                     elementData[i] = null;

                 modCount += size - w;

                 size = w;

                 modified = true;

             }

         }

         return modified;

     }

     /**

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

      * is, serialize it).

      *

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

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

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

      */

     private void writeObject(java.io.ObjectOutputStream s)

         throws java.io.IOException{

         // Write out element count, and any hidden stuff

         int expectedModCount = modCount;

         s.defaultWriteObject();

         // Write out array length

         s.writeInt(elementData.length);

         // Write out all elements in the proper order.

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

             s.writeObject(elementData[i]);

         if (modCount != expectedModCount) {

             throw new ConcurrentModificationException();

         }

     }

     /**

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

      * deserialize it).

      */

     private void readObject(java.io.ObjectInputStream s)

         throws java.io.IOException, ClassNotFoundException {

         // Read in size, and any hidden stuff

         s.defaultReadObject();

         // Read in array length and allocate array

         int arrayLength = s.readInt();

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

         // Read in all elements in the proper order.

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

             a[i] = s.readObject();

     }

     /**

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

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

      * The specified index indicates the first element that would be

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

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

      * return the element with the specified index minus one.

      *

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

      *

      * @throws IndexOutOfBoundsException {@inheritDoc}

      */

     public ListIterator<E> listIterator(int index) {

         if (index < 0 || index > size)

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

         return new ListItr(index);

     }

     /**

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

      * sequence).

      *

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

      *

      * @see #listIterator(int)

      */

     public ListIterator<E> listIterator() {

         return new ListItr(0);

     }

     /**

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

      *

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

      *

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

      */

     public Iterator<E> iterator() {

         return new Itr();

     }

     /**

      * An optimized version of AbstractList.Itr

      */

     private class Itr implements Iterator<E> {

         int cursor;       // index of next element to return

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

         int expectedModCount = modCount;

         public boolean hasNext() {

             return cursor != size;

         }

         @SuppressWarnings("unchecked")

         public E next() {

             checkForComodification();

             int i = cursor;

             if (i >= size)

                 throw new NoSuchElementException();

             Object[] elementData = ArrayList.this.elementData;

             if (i >= elementData.length)

                 throw new ConcurrentModificationException();

             cursor = i + 1;

             return (E) elementData[lastRet = i];

         }

         public void remove() {

             if (lastRet < 0)

                 throw new IllegalStateException();

             checkForComodification();

             try {

                 ArrayList.this.remove(lastRet);

                 cursor = lastRet;

                 lastRet = -1;

                 expectedModCount = modCount;

             } catch (IndexOutOfBoundsException ex) {

                 throw new ConcurrentModificationException();

             }

         }

         final void checkForComodification() {

             if (modCount != expectedModCount)

                 throw new ConcurrentModificationException();

         }

     }

     /**

      * An optimized version of AbstractList.ListItr

      */

     private class ListItr extends Itr implements ListIterator<E> {

         ListItr(int index) {

             super();

             cursor = index;

         }

         public boolean hasPrevious() {

             return cursor != 0;

         }

         public int nextIndex() {

             return cursor;

         }

         public int previousIndex() {

             return cursor - 1;

         }

         @SuppressWarnings("unchecked")

         public E previous() {

             checkForComodification();

             int i = cursor - 1;

             if (i < 0)

                 throw new NoSuchElementException();

             Object[] elementData = ArrayList.this.elementData;

             if (i >= elementData.length)

                 throw new ConcurrentModificationException();

             cursor = i;

             return (E) elementData[lastRet = i];

         }

         public void set(E e) {

             if (lastRet < 0)

                 throw new IllegalStateException();

             checkForComodification();

             try {

                 ArrayList.this.set(lastRet, e);

             } catch (IndexOutOfBoundsException ex) {

                 throw new ConcurrentModificationException();

             }

         }

         public void add(E e) {

             checkForComodification();

             try {

                 int i = cursor;

                 ArrayList.this.add(i, e);

                 cursor = i + 1;

                 lastRet = -1;

                 expectedModCount = modCount;

             } catch (IndexOutOfBoundsException ex) {

                 throw new ConcurrentModificationException();

             }

         }

     }

     /**

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

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

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

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

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

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

      *

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

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

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

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

      * removes a range of elements from a list:

      * <pre>

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

      * </pre>

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

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

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

      *

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

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

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

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

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

      *

      * @throws IndexOutOfBoundsException {@inheritDoc}

      * @throws IllegalArgumentException {@inheritDoc}

      */

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

         subListRangeCheck(fromIndex, toIndex, size);

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

     }

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

         if (fromIndex < 0)

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

         if (toIndex > size)

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

         if (fromIndex > toIndex)

             throw new IllegalArgumentException("fromIndex(" + fromIndex +

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

     }

     private class SubList extends AbstractList<E> implements RandomAccess {

         private final AbstractList<E> parent;

         private final int parentOffset;

         private final int offset;

         int size;

         SubList(AbstractList<E> parent,

                 int offset, int fromIndex, int toIndex) {

             this.parent = parent;

             this.parentOffset = fromIndex;

             this.offset = offset + fromIndex;

             this.size = toIndex - fromIndex;

             this.modCount = ArrayList.this.modCount;

         }

         public E set(int index, E e) {

             rangeCheck(index);

             checkForComodification();

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

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

             return oldValue;

         }

         public E get(int index) {

             rangeCheck(index);

             checkForComodification();

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

         }

         public int size() {

             checkForComodification();

             return this.size;

         }

         public void add(int index, E e) {

             rangeCheckForAdd(index);

             checkForComodification();

             parent.add(parentOffset + index, e);

             this.modCount = parent.modCount;

             this.size++;

         }

         public E remove(int index) {

             rangeCheck(index);

             checkForComodification();

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

             this.modCount = parent.modCount;

             this.size--;

             return result;

         }

         protected void removeRange(int fromIndex, int toIndex) {

             checkForComodification();

             parent.removeRange(parentOffset + fromIndex,

                                parentOffset + toIndex);

             this.modCount = parent.modCount;

             this.size -= toIndex - fromIndex;

         }

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

             return addAll(this.size, c);

         }

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

             rangeCheckForAdd(index);

             int cSize = c.size();

             if (cSize==0)

                 return false;

             checkForComodification();

             parent.addAll(parentOffset + index, c);

             this.modCount = parent.modCount;

             this.size += cSize;

             return true;

         }

         public Iterator<E> iterator() {

             return listIterator();

         }

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

             checkForComodification();

             rangeCheckForAdd(index);

             final int offset = this.offset;

             return new ListIterator<E>() {

                 int cursor = index;

                 int lastRet = -1;

                 int expectedModCount = ArrayList.this.modCount;

                 public boolean hasNext() {

                     return cursor != SubList.this.size;

                 }

                 @SuppressWarnings("unchecked")

                 public E next() {

                     checkForComodification();

                     int i = cursor;

                     if (i >= SubList.this.size)

                         throw new NoSuchElementException();

                     Object[] elementData = ArrayList.this.elementData;

                     if (offset + i >= elementData.length)

                         throw new ConcurrentModificationException();

                     cursor = i + 1;

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

                 }

                 public boolean hasPrevious() {

                     return cursor != 0;

                 }

                 @SuppressWarnings("unchecked")

                 public E previous() {

                     checkForComodification();

                     int i = cursor - 1;

                     if (i < 0)

                         throw new NoSuchElementException();

                     Object[] elementData = ArrayList.this.elementData;

                     if (offset + i >= elementData.length)

                         throw new ConcurrentModificationException();

                     cursor = i;

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

                 }

                 public int nextIndex() {

                     return cursor;

                 }

                 public int previousIndex() {

                     return cursor - 1;

                 }

                 public void remove() {

                     if (lastRet < 0)

                         throw new IllegalStateException();

                     checkForComodification();

                     try {

                         SubList.this.remove(lastRet);

                         cursor = lastRet;

                         lastRet = -1;

                         expectedModCount = ArrayList.this.modCount;

                     } catch (IndexOutOfBoundsException ex) {

                         throw new ConcurrentModificationException();

                     }

                 }

                 public void set(E e) {

                     if (lastRet < 0)

                         throw new IllegalStateException();

                     checkForComodification();

                     try {

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

                     } catch (IndexOutOfBoundsException ex) {

                         throw new ConcurrentModificationException();

                     }

                 }

                 public void add(E e) {

                     checkForComodification();

                     try {

                         int i = cursor;

                         SubList.this.add(i, e);

                         cursor = i + 1;

                         lastRet = -1;

                         expectedModCount = ArrayList.this.modCount;

                     } catch (IndexOutOfBoundsException ex) {

                         throw new ConcurrentModificationException();

                     }

                 }

                 final void checkForComodification() {

                     if (expectedModCount != ArrayList.this.modCount)

                         throw new ConcurrentModificationException();

                 }

             };

         }

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

             subListRangeCheck(fromIndex, toIndex, size);

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

         }

         private void rangeCheck(int index) {

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

                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

         }

         private void rangeCheckForAdd(int index) {

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

                 throw new IndexOutOfBoundsException(outOfBoundsMsg(index));

         }

         private String outOfBoundsMsg(int index) {

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

         }

         private void checkForComodification() {

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

                 throw new ConcurrentModificationException();

         }

     }

 }