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 * Copyright (c) 1997, 2017, 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

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 */

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/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) {

        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 {@code i} such that

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

     * 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 {@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.