/*

* Copyright (c) 1997, 2025, 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.access.SharedSecrets;

import jdk.internal.util.ArraysSupport;

/**

* 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 getFirst}, {@code getLast}, {@code removeLast}, {@code iterator},

* {@code listIterator}, and {@code reversed} operations run in constant time.

* The {@code add}, and {@code addLast} operations 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

{

@java.io.Serial

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) {

Object[] a = c.toArray();

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

if (c.getClass() == ArrayList.class) {

elementData = a;

} else {

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

}

} else {

// replace with empty array.

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);

}

}

/**

* 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) {

int oldCapacity = elementData.length;

if (oldCapacity > 0 || elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {

int newCapacity = ArraysSupport.newLength(oldCapacity,

minCapacity - oldCapacity, /* minimum growth */

oldCapacity >> 1 /* preferred growth */);

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

} else {

return elementData = new Object[Math.max(DEFAULT_CAPACITY, minCapacity)];

}

}

private Object[] grow() {

return grow(size + 1);

}

/**

* 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);

}

/**

* {@inheritDoc}

*

* @throws NoSuchElementException {@inheritDoc}

* @since 21

*/

public E getFirst() {

if (size == 0) {

throw new NoSuchElementException();

} else {

return elementData(0);

}

}

/**

* {@inheritDoc}

*

* @throws NoSuchElementException {@inheritDoc}

* @since 21

*/

public E getLast() {

int last = size - 1;

if (last < 0) {

throw new NoSuchElementException();

} else {

return elementData(last);

}

}

/**

* 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;

}

/**

* {@inheritDoc}

*

* @since 21

*/

public void addFirst(E element) {

add(0, element);

}

/**

* {@inheritDoc}

*

* @since 21

*/

public void addLast(E element) {

add(element);

}

/**

* 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}

*

* @throws NoSuchElementException {@inheritDoc}

* @since 21

*/

public E removeFirst() {

if (size == 0) {

throw new NoSuchElementException();

} else {

Object[] es = elementData;

@SuppressWarnings("unchecked") E oldValue = (E) es[0];

fastRemove(es, 0);

return oldValue;

}

}

/**

* {@inheritDoc}

*

* @throws NoSuchElementException {@inheritDoc}

* @since 21

*/

public E removeLast() {

int last = size - 1;

if (last < 0) {

throw new NoSuchElementException();

} else {

Object[] es = elementData;

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

fastRemove(es, last);

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;

int numNew;

if (c.getClass() == ArrayList.class) {

ArrayList<?> src = (ArrayList<?>) c;

a = src.elementData;

numNew = src.size;

} else {

a = c.toArray();

numNew = a.length;

}

modCount++;

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.

*/

@java.io.Serial

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

*/

@java.io.Serial

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);

}

}