/*

 * Copyright (c) 1997, 2018, 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;

import java.util.function.Consumer;

import java.util.function.Predicate;

import java.util.function.UnaryOperator;

import jdk.internal.misc.SharedSecrets;

/**

 * Resizable-array implementation of the {@code List} interface.  Implements

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

 * {@code null}.  In addition to implementing the {@code List} 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

 * {@code Vector}, except that it is unsynchronized.)

 *

 * <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},

 * {@code iterator}, and {@code listIterator} operations run in constant

 * time.  The {@code add} 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 {@code LinkedList} implementation.

 *

 * <p>Each {@code ArrayList} 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 {@code ArrayList} instance

 * before adding a large number of elements using the {@code ensureCapacity}

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

 *

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

 * If multiple threads access an {@code ArrayList} 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 id="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}/java.base/java/util/package-summary.html#CollectionsFramework">

 * Java Collections Framework</a>.

 *

 * @param <E> the type of elements in this list

 *

 * @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;

    /**

     * Default initial capacity.

     */

    private static final int DEFAULT_CAPACITY = 10;

    /**

     * Shared empty array instance used for empty instances.

     */

    private static final Object[] EMPTY_ELEMENTDATA = {};

    /**

     * Shared empty array instance used for default sized empty instances. We

     * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when

     * first element is added.

     */

    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

    /**

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

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

     * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA

     * will be expanded to DEFAULT_CAPACITY when the first element is added.

     */

    transient Object[] elementData; // non-private to simplify nested class access

    /**

     * 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) {

        if (initialCapacity > 0) {

            this.elementData = new Object[initialCapacity];

        } else if (initialCapacity == 0) {

            this.elementData = EMPTY_ELEMENTDATA;

        } else {

            throw new IllegalArgumentException("Illegal Capacity: "+

                                               initialCapacity);

        }

    }

    /**

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

     */

    public ArrayList() {

        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;

    }

    /**

     * 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();

        if ((size = elementData.length) != 0) {

            // defend against c.toArray (incorrectly) not returning Object[]

            // (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)

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

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

        } else {

            // replace with empty array.

            this.elementData = EMPTY_ELEMENTDATA;

        }

    }

    /**

     * Trims the capacity of this {@code ArrayList} instance to be the

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

     * the storage of an {@code ArrayList} instance.

     */

    public void trimToSize() {

        modCount++;

        if (size < elementData.length) {

            elementData = (size == 0)

              ? EMPTY_ELEMENTDATA

              : Arrays.copyOf(elementData, size);

        }

    }

    /**

     * Increases the capacity of this {@code ArrayList} 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 > elementData.length

            && !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA

                 && minCapacity <= DEFAULT_CAPACITY)) {

            modCount++;

            grow(minCapacity);

        }

    }

    /**

     * The maximum size of array to allocate (unless necessary).

     * 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

     * @throws OutOfMemoryError if minCapacity is less than zero

     */

    private Object[] grow(int minCapacity) {

        return elementData = Arrays.copyOf(elementData,

                                           newCapacity(minCapacity));

    }

    private Object[] grow() {

        return grow(size + 1);

    }

    /**

     * Returns a capacity at least as large as the given minimum capacity.

     * Returns the current capacity increased by 50% if that suffices.

     * Will not return a capacity greater than MAX_ARRAY_SIZE unless

     * the given minimum capacity is greater than MAX_ARRAY_SIZE.

     *

     * @param minCapacity the desired minimum capacity

     * @throws OutOfMemoryError if minCapacity is less than zero

     */

    private int newCapacity(int minCapacity) {

        // overflow-conscious code

        int oldCapacity = elementData.length;

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

        if (newCapacity - minCapacity <= 0) {

            if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA)

                return Math.max(DEFAULT_CAPACITY, minCapacity);

            if (minCapacity < 0) // overflow

                throw new OutOfMemoryError();

            return minCapacity;

        }

        return (newCapacity - MAX_ARRAY_SIZE <= 0)

            ? newCapacity

            : hugeCapacity(minCapacity);

    }

    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 {@code true} if this list contains no elements.

     *

     * @return {@code true} if this list contains no elements

     */

    public boolean isEmpty() {

        return size == 0;

    }

    /**

     * Returns {@code true} if this list contains the specified element.

     * More formally, returns {@code true} if and only if this list contains

     * at least one element {@code e} such that

     * {@code Objects.equals(o, e)}.

     *

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

     * @return {@code true} 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 {@code i} such that

     * {@code Objects.equals(o, get(i))},

     * or -1 if there is no such index.

     */

    public int indexOf(Object o) {

        return indexOfRange(o, 0, size);

    }

    int indexOfRange(Object o, int start, int end) {

        Object[] es = elementData;

        if (o == null) {

            for (int i = start; i < end; i++) {

                if (es[i] == null) {

                    return i;

                }

            }

        } else {

            for (int i = start; i < end; i++) {

                if (o.equals(es[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 {@code i} such that

     * {@code Objects.equals(o, get(i))},

     * or -1 if there is no such index.

     */

    public int lastIndexOf(Object o) {

        return lastIndexOfRange(o, 0, size);

    }

    int lastIndexOfRange(Object o, int start, int end) {

        Object[] es = elementData;

        if (o == null) {

            for (int i = end - 1; i >= start; i--) {

                if (es[i] == null) {

                    return i;

                }

            }

        } else {

            for (int i = end - 1; i >= start; i--) {

                if (o.equals(es[i])) {

                    return i;

                }

            }

        }

        return -1;

    }

    /**

     * Returns a shallow copy of this {@code ArrayList} instance.  (The

     * elements themselves are not copied.)

     *

     * @return a clone of this {@code ArrayList} instance

     */

    public Object clone() {

        try {

            ArrayList<?> v = (ArrayList<?>) 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(e);

        }

    }

    /**

     * 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

     * {@code null}.  (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];

    }

    @SuppressWarnings("unchecked")

    static <E> E elementAt(Object[] es, int index) {

        return (E) es[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) {

        Objects.checkIndex(index, size);

        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) {

        Objects.checkIndex(index, size);

        E oldValue = elementData(index);

        elementData[index] = element;

        return oldValue;

    }

    /**

     * This helper method split out from add(E) to keep method

     * bytecode size under 35 (the -XX:MaxInlineSize default value),

     * which helps when add(E) is called in a C1-compiled loop.

     */

    private void add(E e, Object[] elementData, int s) {

        if (s == elementData.length)

            elementData = grow();

        elementData[s] = e;

        size = s + 1;

    }

    /**

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

     *

     * @param e element to be appended to this list

     * @return {@code true} (as specified by {@link Collection#add})

     */

    public boolean add(E e) {

        modCount++;

        add(e, elementData, size);

        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);

        modCount++;

        final int s;

        Object[] elementData;

        if ((s = size) == (elementData = this.elementData).length)

            elementData = grow();

        System.arraycopy(elementData, index,

                         elementData, index + 1,

                         s - index);

        elementData[index] = element;

        size = s + 1;

    }

    /**

     * 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) {

        Objects.checkIndex(index, size);

        final Object[] es = elementData;

        @SuppressWarnings("unchecked") E oldValue = (E) es[index];

        fastRemove(es, index);

        return oldValue;

    }

    /**

     * {@inheritDoc}

     */

    public boolean equals(Object o) {

        if (o == this) {

            return true;

        }

        if (!(o instanceof List)) {

            return false;

        }

        final int expectedModCount = modCount;

        // ArrayList can be subclassed and given arbitrary behavior, but we can

        // still deal with the common case where o is ArrayList precisely

        boolean equal = (o.getClass() == ArrayList.class)

            ? equalsArrayList((ArrayList<?>) o)

            : equalsRange((List<?>) o, 0, size);

        checkForComodification(expectedModCount);

        return equal;

    }

    boolean equalsRange(List<?> other, int from, int to) {

        final Object[] es = elementData;

        if (to > es.length) {

            throw new ConcurrentModificationException();

        }

        var oit = other.iterator();

        for (; from < to; from++) {

            if (!oit.hasNext() || !Objects.equals(es[from], oit.next())) {

                return false;

            }

        }

        return !oit.hasNext();

    }

    private boolean equalsArrayList(ArrayList<?> other) {

        final int otherModCount = other.modCount;

        final int s = size;

        boolean equal;

        if (equal = (s == other.size)) {

            final Object[] otherEs = other.elementData;

            final Object[] es = elementData;

            if (s > es.length || s > otherEs.length) {

                throw new ConcurrentModificationException();

            }

            for (int i = 0; i < s; i++) {

                if (!Objects.equals(es[i], otherEs[i])) {

                    equal = false;

                    break;

                }

            }

        }

        other.checkForComodification(otherModCount);

        return equal;

    }

    private void checkForComodification(final int expectedModCount) {

        if (modCount != expectedModCount) {

            throw new ConcurrentModificationException();

        }

    }

    /**

     * {@inheritDoc}

     */

    public int hashCode() {

        int expectedModCount = modCount;

        int hash = hashCodeRange(0, size);

        checkForComodification(expectedModCount);

        return hash;

    }

    int hashCodeRange(int from, int to) {

        final Object[] es = elementData;

        if (to > es.length) {

            throw new ConcurrentModificationException();

        }

        int hashCode = 1;

        for (int i = from; i < to; i++) {

            Object e = es[i];

            hashCode = 31 * hashCode + (e == null ? 0 : e.hashCode());

        }

        return hashCode;

    }

    /**

     * 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

     * {@code i} such that

     * {@code Objects.equals(o, get(i))}

     * (if such an element exists).  Returns {@code true} 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 {@code true} if this list contained the specified element

     */

    public boolean remove(Object o) {

        final Object[] es = elementData;

        final int size = this.size;

        int i = 0;

        found: {

            if (o == null) {

                for (; i < size; i++)

                    if (es[i] == null)

                        break found;

            } else {

                for (; i < size; i++)

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

                        break found;

            }

            return false;

        }

        fastRemove(es, i);

        return true;

    }

    /**

     * Private remove method that skips bounds checking and does not

     * return the value removed.

     */

    private void fastRemove(Object[] es, int i) {

        modCount++;

        final int newSize;

        if ((newSize = size - 1) > i)

            System.arraycopy(es, i + 1, es, i, newSize - i);

        es[size = newSize] = null;

    }

    /**

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

     * be empty after this call returns.

     */

    public void clear() {

        modCount++;

        final Object[] es = elementData;

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

            es[i] = null;

    }

    /**

     * 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 {@code true} 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();

        modCount++;

        int numNew = a.length;

        if (numNew == 0)

            return false;

        Object[] elementData;

        final int s;

        if (numNew > (elementData = this.elementData).length - (s = size))

            elementData = grow(s + numNew);

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

        size = s + numNew;

        return true;

    }

    /**

     * 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 {@code true} 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();

        modCount++;

        int numNew = a.length;

        if (numNew == 0)

            return false;

        Object[] elementData;

        final int s;

        if (numNew > (elementData = this.elementData).length - (s = size))

            elementData = grow(s + numNew);

        int numMoved = s - index;

        if (numMoved > 0)

            System.arraycopy(elementData, index,

                             elementData, index + numNew,

                             numMoved);

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

        size = s + numNew;

        return true;

    }

    /**

     * 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 ||

     *          toIndex > size() ||

     *          toIndex < fromIndex})

     */

    protected void removeRange(int fromIndex, int toIndex) {

        if (fromIndex > toIndex) {

            throw new IndexOutOfBoundsException(

                    outOfBoundsMsg(fromIndex, toIndex));

        }

        modCount++;

        shiftTailOverGap(elementData, fromIndex, toIndex);

    }

    /** Erases the gap from lo to hi, by sliding down following elements. */

    private void shiftTailOverGap(Object[] es, int lo, int hi) {

        System.arraycopy(es, hi, es, lo, size - hi);

        for (int to = size, i = (size -= hi - lo); i < to; i++)

            es[i] = null;

    }

    /**

     * 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;

    }

    /**

     * A version used in checking (fromIndex > toIndex) condition

     */

    private static String outOfBoundsMsg(int fromIndex, int toIndex) {

        return "From Index: " + fromIndex + " > To Index: " + toIndex;

    }

    /**

     * 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, 0, size);

    }

    /**

     * 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, 0, size);

    }

    boolean batchRemove(Collection<?> c, boolean complement,

                        final int from, final int end) {

        Objects.requireNonNull(c);

        final Object[] es = elementData;

        int r;

        // Optimize for initial run of survivors

        for (r = from;; r++) {

            if (r == end)

                return false;

            if (c.contains(es[r]) != complement)

                break;

        }

        int w = r++;

        try {

            for (Object e; r < end; r++)

                if (c.contains(e = es[r]) == complement)

                    es[w++] = e;

        } catch (Throwable ex) {

            // Preserve behavioral compatibility with AbstractCollection,

            // even if c.contains() throws.

            System.arraycopy(es, r, es, w, end - r);

            w += end - r;

            throw ex;

        } finally {

            modCount += end - w;

            shiftTailOverGap(es, w, end);

        }

        return true;

    }

    /**

     * Saves the state of the {@code ArrayList} instance to a stream

     * (that is, serializes it).

     *

     * @param s the stream

     * @throws java.io.IOException if an I/O error occurs

     * @serialData The length of the array backing the {@code ArrayList}

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

     *             (each an {@code Object}) 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 size as capacity for behavioral compatibility with clone()

        s.writeInt(size);

        // 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();

        }

    }

    /**

     * Reconstitutes the {@code ArrayList} instance from a stream (that is,

     * deserializes it).

     * @param s the stream

     * @throws ClassNotFoundException if the class of a serialized object

     *         could not be found

     * @throws java.io.IOException if an I/O error occurs

     */

    private void readObject(java.io.ObjectInputStream s)

        throws java.io.IOException, ClassNotFoundException {

        // Read in size, and any hidden stuff

        s.defaultReadObject();

        // Read in capacity

        s.readInt(); // ignored

        if (size > 0) {

            // like clone(), allocate array based upon size not capacity

            SharedSecrets.getJavaObjectInputStreamAccess().checkArray(s, Object[].class, size);

            Object[] elements = new Object[size];

            // Read in all elements in the proper order.

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

                elements[i] = s.readObject();

            }

            elementData = elements;

        } else if (size == 0) {

            elementData = EMPTY_ELEMENTDATA;

        } else {

            throw new java.io.InvalidObjectException("Invalid size: " + size);

        }

    }

    /**

     * 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) {

        rangeCheckForAdd(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;

        // prevent creating a synthetic constructor

        Itr() {}

        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();

            }

        }

        @Override

        public void forEachRemaining(Consumer<? super E> action) {

            Objects.requireNonNull(action);

            final int size = ArrayList.this.size;

            int i = cursor;

            if (i < size) {

                final Object[] es = elementData;

                if (i >= es.length)

                    throw new ConcurrentModificationException();

                for (; i < size && modCount == expectedModCount; i++)

                    action.accept(elementAt(es, i));

                // update once at end to reduce heap write traffic

                cursor = i;

                lastRet = i - 1;

                checkForComodification();

            }

        }

        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, fromIndex, toIndex);

    }

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

        private final ArrayList<E> root;

        private final SubList<E> parent;

        private final int offset;

        private int size;

        /**

         * Constructs a sublist of an arbitrary ArrayList.

         */

        public SubList(ArrayList<E> root, int fromIndex, int toIndex) {

            this.root = root;

            this.parent = null;

            this.offset = fromIndex;

            this.size = toIndex - fromIndex;

            this.modCount = root.modCount;

        }

        /**

         * Constructs a sublist of another SubList.

         */

        private SubList(SubList<E> parent, int fromIndex, int toIndex) {

            this.root = parent.root;

            this.parent = parent;

            this.offset = parent.offset + fromIndex;

            this.size = toIndex - fromIndex;

            this.modCount = root.modCount;

        }

        public E set(int index, E element) {

            Objects.checkIndex(index, size);

            checkForComodification();

            E oldValue = root.elementData(offset + index);

            root.elementData[offset + index] = element;

            return oldValue;

        }

        public E get(int index) {

            Objects.checkIndex(index, size);

            checkForComodification();

            return root.elementData(offset + index);

        }

        public int size() {

            checkForComodification();

            return size;

        }

        public void add(int index, E element) {

            rangeCheckForAdd(index);

            checkForComodification();

            root.add(offset + index, element);

            updateSizeAndModCount(1);

        }

        public E remove(int index) {

            Objects.checkIndex(index, size);

            checkForComodification();

            E result = root.remove(offset + index);

            updateSizeAndModCount(-1);

            return result;

        }

        protected void removeRange(int fromIndex, int toIndex) {

            checkForComodification();

            root.removeRange(offset + fromIndex, offset + toIndex);

            updateSizeAndModCount(fromIndex - toIndex);

        }

        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();

            root.addAll(offset + index, c);

            updateSizeAndModCount(cSize);

            return true;

        }

        public void replaceAll(UnaryOperator<E> operator) {

            root.replaceAllRange(operator, offset, offset + size);

        }

        public boolean removeAll(Collection<?> c) {

            return batchRemove(c, false);

        }

        public boolean retainAll(Collection<?> c) {

            return batchRemove(c, true);

        }

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

            checkForComodification();

            int oldSize = root.size;

            boolean modified =

                root.batchRemove(c, complement, offset, offset + size);

            if (modified)

                updateSizeAndModCount(root.size - oldSize);

            return modified;

        }

        public boolean removeIf(Predicate<? super E> filter) {

            checkForComodification();

            int oldSize = root.size;

            boolean modified = root.removeIf(filter, offset, offset + size);

            if (modified)

                updateSizeAndModCount(root.size - oldSize);

            return modified;

        }

        public Object[] toArray() {

            checkForComodification();

            return Arrays.copyOfRange(root.elementData, offset, offset + size);

        }

        @SuppressWarnings("unchecked")

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

            checkForComodification();

            if (a.length < size)

                return (T[]) Arrays.copyOfRange(

                        root.elementData, offset, offset + size, a.getClass());

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

            if (a.length > size)

                a[size] = null;

            return a;

        }

        public boolean equals(Object o) {

            if (o == this) {

                return true;