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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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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 List interface. Implements all optional list operations, and permits all elements, including null. In addition to implementing the 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 Vector, except that it is unsynchronized.) 
The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, 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 LinkedList implementation. 
Each ArrayList instance has a capacity.  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.
An application can increase the capacity of an ArrayList instance before adding a large number of elements using the ensureCapacity operation. This may reduce the amount of incremental reallocation. 
Note that this implementation is not synchronized. If multiple threads access an ArrayList instance concurrently, and at least one of the threads modifies the list structurally, it must 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 Collections.synchronizedList method. This is best done at creation time, to prevent accidental unsynchronized access to the list:
  List list = Collections.synchronizedList(new ArrayList(...));
 The iterators returned by this class's iterator and listIterator methods are fail-fast: if the list is structurally modified at any time after the iterator is created, in any way except through the iterator's own remove or add methods, the iterator will throw a 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. 
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 ConcurrentModificationException on a best-effort basis. Therefore, it would be wrong to write a program that depended on this exception for its correctness: the fail-fast behavior of iterators
should be used only to detect bugs.
This class is a member of the

Java Collections Framework.
Author:
 Josh Bloch,  Neal Gafter
Type parameters:
<E> – the type of elements in this list
See Also:
Collection
List
LinkedList
Vector
Since:
  1.2/**
 * 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
{
    @java.io.Serial
    private static final long serialVersionUID = 8683452581122892189L;

    
Default initial capacity.
/**
     * Default initial capacity.
     */
    private static final int DEFAULT_CAPACITY = 10;

    
Shared empty array instance used for empty instances.
/**
     * 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.
/**
     * 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.
/**
     * 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
/**
     * The size of the ArrayList (the number of elements it contains).
     *
     * @serial
     */
    private int size;

    
Constructs an empty list with the specified initial capacity.
Params:
initialCapacity –  the initial capacity of the list
Throws:
IllegalArgumentException – if the specified initial capacity
        is negative/**
     * 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.
/**
     * 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.
Params:
c – the collection whose elements are to be placed into this list
Throws:
NullPointerException – if the specified collection is null/**
     * 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 ArrayList instance to be the list's current size. An application can use this operation to minimize the storage of an ArrayList instance. /**
     * 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 ArrayList instance, if necessary, to ensure that it can hold at least the number of elements specified by the minimum capacity argument. 
Params:
minCapacity – the desired minimum capacity/**
     * 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.
Params:
minCapacity – the desired minimum capacity
Throws:
OutOfMemoryError – if minCapacity is less than zero/**
     * 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.
Returns:
the number of elements in this list/**
     * Returns the number of elements in this list.
     *
     * @return the number of elements in this list
     */
    public int size() {
        return size;
    }

    
Returns true if this list contains no elements. 
Returns:
true if this list contains no elements/**
     * 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 true if this list contains the specified element. More formally, returns true if and only if this list contains at least one element e such that Objects.equals(o, e). 
Params:
o – element whose presence in this list is to be tested
Returns:
true if this list contains the specified element/**
     * 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 i such that Objects.equals(o, get(i)), or -1 if there is no such index. /**
     * 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 i such that Objects.equals(o, get(i)), or -1 if there is no such index. /**
     * 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 ArrayList instance. (The elements themselves are not copied.) 
Returns:
a clone of this ArrayList instance/**
     * 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).
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.
This method acts as bridge between array-based and collection-based
APIs.
Returns:
an array containing all of the elements in this list in
        proper sequence/**
     * 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.
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 null. (This is useful in determining the length of the list only if the caller knows that the list does not contain
any null elements.)
Params:
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.
Throws:
ArrayStoreException – if the runtime type of the specified array
        is not a supertype of the runtime type of every element in
        this list
NullPointerException – if the specified array is null
Returns:
an array containing the elements of the list/**
     * 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.
Params:
index – index of the element to return
Throws:
IndexOutOfBoundsException – {@inheritDoc}
Returns:
the element at the specified position in this list/**
     * 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.
Params:
index – index of the element to replace
element – element to be stored at the specified position
Throws:
IndexOutOfBoundsException – {@inheritDoc}
Returns:
the element previously at the specified position/**
     * 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.
/**
     * 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.
Params:
e – element to be appended to this list
Returns:
true (as specified by Collection.add)/**
     * 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).
Params:
index – index at which the specified element is to be inserted
element – element to be inserted
Throws:
IndexOutOfBoundsException – {@inheritDoc}/**
     * 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).
Params:
index – the index of the element to be removed
Throws:
IndexOutOfBoundsException – {@inheritDoc}
Returns:
the element that was removed from the list/**
     * 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}
/**
     * {@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}
/**
     * {@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 i such that Objects.equals(o, get(i)) (if such an element exists). Returns true if this list contained the specified element (or equivalently, if this list changed as a result of the call). 
Params:
o – element to be removed from this list, if present
Returns:
true if this list contained the specified element/**
     * 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 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.
/**
     * 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.)
Params:
c – collection containing elements to be added to this list
Throws:
NullPointerException – if the specified collection is null
Returns:
true if this list changed as a result of the call/**
     * 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.
Params:
index – index at which to insert the first element from the
             specified collection
c – collection containing elements to be added to this list
Throws:
IndexOutOfBoundsException – {@inheritDoc}
NullPointerException – if the specified collection is null
Returns:
true if this list changed as a result of the call/**
     * 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 fromIndex, inclusive, and toIndex, exclusive. Shifts any succeeding elements to the left (reduces their index). This call shortens the list by (toIndex - fromIndex) elements. (If toIndex==fromIndex, this operation has no effect.) 
Throws:
IndexOutOfBoundsException – if fromIndex or toIndex is out of range (fromIndex < 0 ||
         toIndex > size() ||
         toIndex < fromIndex)/**
     * 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. /** 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.
/**
     * 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.
/**
     * 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
/**
     * 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.
Params:
c – collection containing elements to be removed from this list
Throws:
ClassCastException – if the class of an element of this list
        is incompatible with the specified collection
(optional)
NullPointerException – if this list contains a null element and the
        specified collection does not permit null elements
(optional),
        or if the specified collection is null
See Also:
Collection.contains(Object)
Returns:
true if this list changed as a result of the call/**
     * 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.
Params:
c – collection containing elements to be retained in this list
Throws:
ClassCastException – if the class of an element of this list
        is incompatible with the specified collection
(optional)
NullPointerException – if this list contains a null element and the
        specified collection does not permit null elements
(optional),
        or if the specified collection is null
See Also:
Collection.contains(Object)
Returns:
true if this list changed as a result of the call/**
     * 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 ArrayList instance to a stream (that is, serializes it). 
Params:
s – the stream
Throws:
IOException – if an I/O error occurs
@serialData
The length of the array backing the ArrayList instance is emitted (int), followed by all of its elements (each an Object) in the proper order./**
     * 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 ArrayList instance from a stream (that is, deserializes it). 
Params:
s – the stream
Throws:
ClassNotFoundException – if the class of a serialized object
        could not be found
IOException – if an I/O error occurs/**
     * 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);
        }
    }

    
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 next. An initial call to previous would return the element with the specified index minus one. 
The returned list iterator is fail-fast.
Throws:
IndexOutOfBoundsException – {@inheritDoc}/**
     * 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).
The returned list iterator is fail-fast.
See Also:
listIterator(int)/**
     * 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.
The returned iterator is fail-fast.
Returns:
an iterator over the elements in this list in proper sequence/**
     * 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
/**
     * 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
/**
     * 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 fromIndex, inclusive, and toIndex, exclusive. (If fromIndex and 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. 
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:
     list.subList(from, to).clear();
 Similar idioms may be constructed for indexOf(Object) and lastIndexOf(Object), and all of the algorithms in the Collections class can be applied to a subList. 
The semantics of the list returned by this method become undefined if
the backing list (i.e., this list) is structurally modified 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}
IllegalArgumentException – {@inheritDoc}/**
     * 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.
/**
         * 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.
/**
         * 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 = parent.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;
            }

            if (!(o instanceof List)) {
                return false;
            }

            boolean equal = root.equalsRange((List<?>)o, offset, offset + size);
            checkForComodification();
            return equal;
        }

        public int hashCode() {
            int hash = root.hashCodeRange(offset, offset + size);
            checkForComodification();
            return hash;
        }

        public int indexOf(Object o) {
            int index = root.indexOfRange(o, offset, offset + size);
            checkForComodification();
            return index >= 0 ? index - offset : -1;
        }

        public int lastIndexOf(Object o) {
            int index = root.lastIndexOfRange(o, offset, offset + size);
            checkForComodification();
            return index >= 0 ? index - offset : -1;
        }

        public boolean contains(Object o) {
            return indexOf(o) >= 0;
        }

        public Iterator<E> iterator() {
            return listIterator();
        }

        public ListIterator<E> listIterator(int index) {
            checkForComodification();
            rangeCheckForAdd(index);

            return new ListIterator<E>() {
                int cursor = index;
                int lastRet = -1;
                int expectedModCount = SubList.this.modCount;

                public boolean hasNext() {
                    return cursor != SubList.this.size;
                }

                @SuppressWarnings("unchecked")
                public E next() {
                    checkForComodification();
                    int i = cursor;
                    if (i >= SubList.this.size)
                        throw new NoSuchElementException();
                    Object[] elementData = root.elementData;
                    if (offset + i >= elementData.length)
                        throw new ConcurrentModificationException();
                    cursor = i + 1;
                    return (E) elementData[offset + (lastRet = i)];
                }

                public boolean hasPrevious() {
                    return cursor != 0;
                }

                @SuppressWarnings("unchecked")
                public E previous() {
                    checkForComodification();
                    int i = cursor - 1;
                    if (i < 0)
                        throw new NoSuchElementException();
                    Object[] elementData = root.elementData;
                    if (offset + i >= elementData.length)
                        throw new ConcurrentModificationException();
                    cursor = i;
                    return (E) elementData[offset + (lastRet = i)];
                }

                public void forEachRemaining(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    final int size = SubList.this.size;
                    int i = cursor;
                    if (i < size) {
                        final Object[] es = root.elementData;
                        if (offset + i >= es.length)
                            throw new ConcurrentModificationException();
                        for (; i < size && root.modCount == expectedModCount; i++)
                            action.accept(elementAt(es, offset + i));
                        // update once at end to reduce heap write traffic
                        cursor = i;
                        lastRet = i - 1;
                        checkForComodification();
                    }
                }

                public int nextIndex() {
                    return cursor;
                }

                public int previousIndex() {
                    return cursor - 1;
                }

                public void remove() {
                    if (lastRet < 0)
                        throw new IllegalStateException();
                    checkForComodification();

                    try {
                        SubList.this.remove(lastRet);
                        cursor = lastRet;
                        lastRet = -1;
                        expectedModCount = SubList.this.modCount;
                    } catch (IndexOutOfBoundsException ex) {
                        throw new ConcurrentModificationException();
                    }
                }

                public void set(E e) {
                    if (lastRet < 0)
                        throw new IllegalStateException();
                    checkForComodification();

                    try {
                        root.set(offset + lastRet, e);
                    } catch (IndexOutOfBoundsException ex) {
                        throw new ConcurrentModificationException();
                    }
                }

                public void add(E e) {
                    checkForComodification();

                    try {
                        int i = cursor;
                        SubList.this.add(i, e);
                        cursor = i + 1;
                        lastRet = -1;
                        expectedModCount = SubList.this.modCount;
                    } catch (IndexOutOfBoundsException ex) {
                        throw new ConcurrentModificationException();
                    }
                }

                final void checkForComodification() {
                    if (root.modCount != expectedModCount)
                        throw new ConcurrentModificationException();
                }
            };
        }

        public List<E> subList(int fromIndex, int toIndex) {
            subListRangeCheck(fromIndex, toIndex, size);
            return new SubList<>(this, fromIndex, toIndex);
        }

        private void rangeCheckForAdd(int index) {
            if (index < 0 || index > this.size)
                throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
        }

        private String outOfBoundsMsg(int index) {
            return "Index: "+index+", Size: "+this.size;
        }

        private void checkForComodification() {
            if (root.modCount != modCount)
                throw new ConcurrentModificationException();
        }

        private void updateSizeAndModCount(int sizeChange) {
            SubList<E> slist = this;
            do {
                slist.size += sizeChange;
                slist.modCount = root.modCount;
                slist = slist.parent;
            } while (slist != null);
        }

        public Spliterator<E> spliterator() {
            checkForComodification();

            // ArrayListSpliterator not used here due to late-binding
            return new Spliterator<E>() {
                private int index = offset; // current index, modified on advance/split
                private int fence = -1; // -1 until used; then one past last index
                private int expectedModCount; // initialized when fence set

                private int getFence() { // initialize fence to size on first use
                    int hi; // (a specialized variant appears in method forEach)
                    if ((hi = fence) < 0) {
                        expectedModCount = modCount;
                        hi = fence = offset + size;
                    }
                    return hi;
                }

                public ArrayList<E>.ArrayListSpliterator trySplit() {
                    int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
                    // ArrayListSpliterator can be used here as the source is already bound
                    return (lo >= mid) ? null : // divide range in half unless too small
                        root.new ArrayListSpliterator(lo, index = mid, expectedModCount);
                }

                public boolean tryAdvance(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    int hi = getFence(), i = index;
                    if (i < hi) {
                        index = i + 1;
                        @SuppressWarnings("unchecked") E e = (E)root.elementData[i];
                        action.accept(e);
                        if (root.modCount != expectedModCount)
                            throw new ConcurrentModificationException();
                        return true;
                    }
                    return false;
                }

                public void forEachRemaining(Consumer<? super E> action) {
                    Objects.requireNonNull(action);
                    int i, hi, mc; // hoist accesses and checks from loop
                    ArrayList<E> lst = root;
                    Object[] a;
                    if ((a = lst.elementData) != null) {
                        if ((hi = fence) < 0) {
                            mc = modCount;
                            hi = offset + size;
                        }
                        else
                            mc = expectedModCount;
                        if ((i = index) >= 0 && (index = hi) <= a.length) {
                            for (; i < hi; ++i) {
                                @SuppressWarnings("unchecked") E e = (E) a[i];
                                action.accept(e);
                            }
                            if (lst.modCount == mc)
                                return;
                        }
                    }
                    throw new ConcurrentModificationException();
                }

                public long estimateSize() {
                    return getFence() - index;
                }

                public int characteristics() {
                    return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
                }
            };
        }
    }

    
Throws:
NullPointerException – {@inheritDoc}/**
     * @throws NullPointerException {@inheritDoc}
     */
    @Override
    public void forEach(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        final int expectedModCount = modCount;
        final Object[] es = elementData;
        final int size = this.size;
        for (int i = 0; modCount == expectedModCount && i < size; i++)
            action.accept(elementAt(es, i));
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }

    
Creates a late-binding
and fail-fast Spliterator over the elements in this list. 
The Spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, and Spliterator.ORDERED. Overriding implementations should document the reporting of additional characteristic values. 
Returns:
a Spliterator over the elements in this list
Since:
1.8/**
     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
     * and <em>fail-fast</em> {@link Spliterator} over the elements in this
     * list.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
     * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
     * Overriding implementations should document the reporting of additional
     * characteristic values.
     *
     * @return a {@code Spliterator} over the elements in this list
     * @since 1.8
     */
    @Override
    public Spliterator<E> spliterator() {
        return new ArrayListSpliterator(0, -1, 0);
    }

    
Index-based split-by-two, lazily initialized Spliterator /** Index-based split-by-two, lazily initialized Spliterator */
    final class ArrayListSpliterator implements Spliterator<E> {

        /*
         * If ArrayLists were immutable, or structurally immutable (no
         * adds, removes, etc), we could implement their spliterators
         * with Arrays.spliterator. Instead we detect as much
         * interference during traversal as practical without
         * sacrificing much performance. We rely primarily on
         * modCounts. These are not guaranteed to detect concurrency
         * violations, and are sometimes overly conservative about
         * within-thread interference, but detect enough problems to
         * be worthwhile in practice. To carry this out, we (1) lazily
         * initialize fence and expectedModCount until the latest
         * point that we need to commit to the state we are checking
         * against; thus improving precision.  (This doesn't apply to
         * SubLists, that create spliterators with current non-lazy
         * values).  (2) We perform only a single
         * ConcurrentModificationException check at the end of forEach
         * (the most performance-sensitive method). When using forEach
         * (as opposed to iterators), we can normally only detect
         * interference after actions, not before. Further
         * CME-triggering checks apply to all other possible
         * violations of assumptions for example null or too-small
         * elementData array given its size(), that could only have
         * occurred due to interference.  This allows the inner loop
         * of forEach to run without any further checks, and
         * simplifies lambda-resolution. While this does entail a
         * number of checks, note that in the common case of
         * list.stream().forEach(a), no checks or other computation
         * occur anywhere other than inside forEach itself.  The other
         * less-often-used methods cannot take advantage of most of
         * these streamlinings.
         */

        private int index; // current index, modified on advance/split
        private int fence; // -1 until used; then one past last index
        private int expectedModCount; // initialized when fence set

        
Creates new spliterator covering the given range. /** Creates new spliterator covering the given range. */
        ArrayListSpliterator(int origin, int fence, int expectedModCount) {
            this.index = origin;
            this.fence = fence;
            this.expectedModCount = expectedModCount;
        }

        private int getFence() { // initialize fence to size on first use
            int hi; // (a specialized variant appears in method forEach)
            if ((hi = fence) < 0) {
                expectedModCount = modCount;
                hi = fence = size;
            }
            return hi;
        }

        public ArrayListSpliterator trySplit() {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null : // divide range in half unless too small
                new ArrayListSpliterator(lo, index = mid, expectedModCount);
        }

        public boolean tryAdvance(Consumer<? super E> action) {
            if (action == null)
                throw new NullPointerException();
            int hi = getFence(), i = index;
            if (i < hi) {
                index = i + 1;
                @SuppressWarnings("unchecked") E e = (E)elementData[i];
                action.accept(e);
                if (modCount != expectedModCount)
                    throw new ConcurrentModificationException();
                return true;
            }
            return false;
        }

        public void forEachRemaining(Consumer<? super E> action) {
            int i, hi, mc; // hoist accesses and checks from loop
            Object[] a;
            if (action == null)
                throw new NullPointerException();
            if ((a = elementData) != null) {
                if ((hi = fence) < 0) {
                    mc = modCount;
                    hi = size;
                }
                else
                    mc = expectedModCount;
                if ((i = index) >= 0 && (index = hi) <= a.length) {
                    for (; i < hi; ++i) {
                        @SuppressWarnings("unchecked") E e = (E) a[i];
                        action.accept(e);
                    }
                    if (modCount == mc)
                        return;
                }
            }
            throw new ConcurrentModificationException();
        }

        public long estimateSize() {
            return getFence() - index;
        }

        public int characteristics() {
            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
        }
    }

    // A tiny bit set implementation

    private static long[] nBits(int n) {
        return new long[((n - 1) >> 6) + 1];
    }
    private static void setBit(long[] bits, int i) {
        bits[i >> 6] |= 1L << i;
    }
    private static boolean isClear(long[] bits, int i) {
        return (bits[i >> 6] & (1L << i)) == 0;
    }

    
Throws:
NullPointerException – {@inheritDoc}/**
     * @throws NullPointerException {@inheritDoc}
     */
    @Override
    public boolean removeIf(Predicate<? super E> filter) {
        return removeIf(filter, 0, size);
    }

    
Removes all elements satisfying the given predicate, from index
i (inclusive) to index end (exclusive).
/**
     * Removes all elements satisfying the given predicate, from index
     * i (inclusive) to index end (exclusive).
     */
    boolean removeIf(Predicate<? super E> filter, int i, final int end) {
        Objects.requireNonNull(filter);
        int expectedModCount = modCount;
        final Object[] es = elementData;
        // Optimize for initial run of survivors
        for (; i < end && !filter.test(elementAt(es, i)); i++)
            ;
        // Tolerate predicates that reentrantly access the collection for
        // read (but writers still get CME), so traverse once to find
        // elements to delete, a second pass to physically expunge.
        if (i < end) {
            final int beg = i;
            final long[] deathRow = nBits(end - beg);
            deathRow[0] = 1L;   // set bit 0
            for (i = beg + 1; i < end; i++)
                if (filter.test(elementAt(es, i)))
                    setBit(deathRow, i - beg);
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            modCount++;
            int w = beg;
            for (i = beg; i < end; i++)
                if (isClear(deathRow, i - beg))
                    es[w++] = es[i];
            shiftTailOverGap(es, w, end);
            return true;
        } else {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
            return false;
        }
    }

    @Override
    public void replaceAll(UnaryOperator<E> operator) {
        replaceAllRange(operator, 0, size);
        // TODO(8203662): remove increment of modCount from ...
        modCount++;
    }

    private void replaceAllRange(UnaryOperator<E> operator, int i, int end) {
        Objects.requireNonNull(operator);
        final int expectedModCount = modCount;
        final Object[] es = elementData;
        for (; modCount == expectedModCount && i < end; i++)
            es[i] = operator.apply(elementAt(es, i));
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }

    @Override
    @SuppressWarnings("unchecked")
    public void sort(Comparator<? super E> c) {
        final int expectedModCount = modCount;
        Arrays.sort((E[]) elementData, 0, size, c);
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
        modCount++;
    }

    void checkInvariants() {
        // assert size >= 0;
        // assert size == elementData.length || elementData[size] == null;
    }
}