ArrayList源码分析

*
 public class ArrayList<E> extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable

{
private static final long serialVersionUID = 8683452581122892189L;

/** Default initial capacity.
 */
private static final int DEFAULT_CAPACITY = 10;
/**
 * Shared empty array instance used for empty instances.
 */
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
 * Shared empty array instance used for default sized empty instances. We
 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
 * first element is added.
 */
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
 * The array buffer into which the elements of the ArrayList are stored.
 * The capacity of the ArrayList is the length of this array buffer. Any
 * empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
 * will be expanded to DEFAULT_CAPACITY when the first element is added.
 */
transient Object[] elementData; // non-private to simplify nested class access
/**
 * The size of the ArrayList (the number of elements it contains).
 *
 * @serial
 */
private int size;
/**
 * Constructs an empty list with the specified initial capacity.
 *
 * @param  initialCapacity  the initial capacity of the list
 * @throws IllegalArgumentException if the specified initial capacity
 *         is negative
 */
public ArrayList(int initialCapacity) {
    if (initialCapacity > 0) {
        this.elementData = new Object[initialCapacity];
    } else if (initialCapacity == 0) {
        this.elementData = EMPTY_ELEMENTDATA;
    } else {
        throw new IllegalArgumentException("Illegal Capacity: "+
                                           initialCapacity);
    }
}
/**
 * Constructs an empty list with an initial capacity of ten.
 */
public ArrayList() {
    this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
 * Constructs a list containing the elements of the specified
 * collection, in the order they are returned by the collection's
 * iterator.
 *
 * @param c the collection whose elements are to be placed into this list
 * @throws NullPointerException if the specified collection is null
 */
public ArrayList(Collection<? extends E> c) {
    elementData = c.toArray();
    if ((size = elementData.length) != 0) {
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, size, Object[].class);
    } else {
        // replace with empty array.
        this.elementData = EMPTY_ELEMENTDATA;
    }
}
/**
 * Trims the capacity of this <tt>ArrayList</tt> instance to be the
 * list's current size.  An application can use this operation to minimize
 * the storage of an <tt>ArrayList</tt> instance.
 */
public void trimToSize() {
    modCount++;
    if (size < elementData.length) {
        elementData = (size == 0)
          ? EMPTY_ELEMENTDATA
          : Arrays.copyOf(elementData, size);
    }
}
/**
 * Increases the capacity of this <tt>ArrayList</tt> instance, if
 * necessary, to ensure that it can hold at least the number of elements
 * specified by the minimum capacity argument.
 *
 * @param   minCapacity   the desired minimum capacity
 */
public void ensureCapacity(int minCapacity) {
    int minExpand = (elementData != DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
        // any size if not default element table
        ? 0
        // larger than default for default empty table. It's already
        // supposed to be at default size.
        : DEFAULT_CAPACITY;
    if (minCapacity > minExpand) {
        ensureExplicitCapacity(minCapacity);
    }
}
private static int calculateCapacity(Object[] elementData, int minCapacity) {
    if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
        return Math.max(DEFAULT_CAPACITY, minCapacity);
    }
    return minCapacity;
}
private void ensureCapacityInternal(int minCapacity) {
    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
private void ensureExplicitCapacity(int minCapacity) {
    modCount++;
    // overflow-conscious code
    if (minCapacity - elementData.length > 0)
        grow(minCapacity);
}
/**
 * The maximum size of array to allocate.
 * Some VMs reserve some header words in an array.
 * Attempts to allocate larger arrays may result in
 * OutOfMemoryError: Requested array size exceeds VM limit
 */
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
 * Increases the capacity to ensure that it can hold at least the
 * number of elements specified by the minimum capacity argument.
 *
 * @param minCapacity the desired minimum capacity
 */
private void grow(int minCapacity) {
    // overflow-conscious code
    int oldCapacity = elementData.length;
    int newCapacity = oldCapacity + (oldCapacity >> 1);
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;
    if (newCapacity - MAX_ARRAY_SIZE > 0)
        newCapacity = hugeCapacity(minCapacity);
    // minCapacity is usually close to size, so this is a win:
    elementData = Arrays.copyOf(elementData, newCapacity);
}
private static int hugeCapacity(int minCapacity) {
    if (minCapacity < 0) // overflow
        throw new OutOfMemoryError();
    return (minCapacity > MAX_ARRAY_SIZE) ?
        Integer.MAX_VALUE :
        MAX_ARRAY_SIZE;
}
/**
 * Returns the number of elements in this list.
 *
 * @return the number of elements in this list
 */
public int size() {
    return size;
}
/**
 * Returns <tt>true</tt> if this list contains no elements.
 *
 * @return <tt>true</tt> if this list contains no elements
 */
public boolean isEmpty() {
    return size == 0;
}
/**
 * Returns <tt>true</tt> if this list contains the specified element.
 * More formally, returns <tt>true</tt> if and only if this list contains
 * at least one element <tt>e</tt> such that
 * <tt>(o==null ? e==null : o.equals(e))</tt>.
 *
 * @param o element whose presence in this list is to be tested
 * @return <tt>true</tt> if this list contains the specified element
 */
public boolean contains(Object o) {
    return indexOf(o) >= 0;
}
/**
 * Returns the index of the first occurrence of the specified element
 * in this list, or -1 if this list does not contain the element.
 * More formally, returns the lowest index <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 */
public int indexOf(Object o) {
    if (o == null) {
        for (int i = 0; i < size; i++)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = 0; i < size; i++)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}
/**
 * Returns the index of the last occurrence of the specified element
 * in this list, or -1 if this list does not contain the element.
 * More formally, returns the highest index <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
 * or -1 if there is no such index.
 */
public int lastIndexOf(Object o) {
    if (o == null) {
        for (int i = size-1; i >= 0; i--)
            if (elementData[i]==null)
                return i;
    } else {
        for (int i = size-1; i >= 0; i--)
            if (o.equals(elementData[i]))
                return i;
    }
    return -1;
}
/**
 * Returns a shallow copy of this <tt>ArrayList</tt> instance.  (The
 * elements themselves are not copied.)
 *
 * @return a clone of this <tt>ArrayList</tt> instance
 */
public Object clone() {
    try {
        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
 * <tt>null</tt>.  (This is useful in determining the length of the
 * list <i>only</i> if the caller knows that the list does not contain
 * any null elements.)
 *
 * @param a the array into which the elements of the list are to
 *          be stored, if it is big enough; otherwise, a new array of the
 *          same runtime type is allocated for this purpose.
 * @return an array containing the elements of the list
 * @throws ArrayStoreException if the runtime type of the specified array
 *         is not a supertype of the runtime type of every element in
 *         this list
 * @throws NullPointerException if the specified array is null
 */
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
    if (a.length < size)
        // Make a new array of a's runtime type, but my contents:
        return (T[]) Arrays.copyOf(elementData, size, a.getClass());
    System.arraycopy(elementData, 0, a, 0, size);
    if (a.length > size)
        a[size] = null;
    return a;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
E elementData(int index) {
    return (E) elementData[index];
}
/**
 * Returns the element at the specified position in this list.
 *
 * @param  index index of the element to return
 * @return the element at the specified position in this list
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public E get(int index) {
    rangeCheck(index);
    return elementData(index);
}
/**
 * Replaces the element at the specified position in this list with
 * the specified element.
 *
 * @param index index of the element to replace
 * @param element element to be stored at the specified position
 * @return the element previously at the specified position
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public E set(int index, E element) {
    rangeCheck(index);
    E oldValue = elementData(index);
    elementData[index] = element;
    return oldValue;
}
/**
 * Appends the specified element to the end of this list.
 *
 * @param e element to be appended to this list
 * @return <tt>true</tt> (as specified by {@link Collection#add})
 */
public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    elementData[size++] = e;
    return true;
}
/**
 * Inserts the specified element at the specified position in this
 * list. Shifts the element currently at that position (if any) and
 * any subsequent elements to the right (adds one to their indices).
 *
 * @param index index at which the specified element is to be inserted
 * @param element element to be inserted
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public void add(int index, E element) {
    rangeCheckForAdd(index);
    ensureCapacityInternal(size + 1);  // Increments modCount!!
    System.arraycopy(elementData, index, elementData, index + 1,
                     size - index);
    elementData[index] = element;
    size++;
}
/**
 * Removes the element at the specified position in this list.
 * Shifts any subsequent elements to the left (subtracts one from their
 * indices).
 *
 * @param index the index of the element to be removed
 * @return the element that was removed from the list
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public E remove(int index) {
    rangeCheck(index);
    modCount++;
    E oldValue = elementData(index);
    int numMoved = size - index - 1;
    if (numMoved > 0)
        System.arraycopy(elementData, index+1, elementData, index,
                         numMoved);
    elementData[--size] = null; // clear to let GC do its work
    return oldValue;
}
/**
 * Removes the first occurrence of the specified element from this list,
 * if it is present.  If the list does not contain the element, it is
 * unchanged.  More formally, removes the element with the lowest index
 * <tt>i</tt> such that
 * <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
 * (if such an element exists).  Returns <tt>true</tt> if this list
 * contained the specified element (or equivalently, if this list
 * changed as a result of the call).
 *
 * @param o element to be removed from this list, if present
 * @return <tt>true</tt> if this list contained the specified element
 */
public boolean remove(Object o) {
    if (o == null) {
        for (int index = 0; index < size; index++)
            if (elementData[index] == null) {
                fastRemove(index);
                return true;
            }
    } else {
        for (int index = 0; index < size; index++)
            if (o.equals(elementData[index])) {
                fastRemove(index);
                return true;
            }
    }
    return false;
}
/*
 * Private remove method that skips bounds checking and does not
 * return the value removed.
 */
private void fastRemove(int index) {
    modCount++;
    int numMoved = size - index - 1;
    if (numMoved > 0)
        System.arraycopy(elementData, index+1, elementData, index,
                         numMoved);
    elementData[--size] = null; // clear to let GC do its work
}
/**
 * Removes all of the elements from this list.  The list will
 * be empty after this call returns.
 */
public void clear() {
    modCount++;
    // clear to let GC do its work
    for (int i = 0; i < size; i++)
        elementData[i] = null;
    size = 0;
}
/**
 * Appends all of the elements in the specified collection to the end of
 * this list, in the order that they are returned by the
 * specified collection's Iterator.  The behavior of this operation is
 * undefined if the specified collection is modified while the operation
 * is in progress.  (This implies that the behavior of this call is
 * undefined if the specified collection is this list, and this
 * list is nonempty.)
 *
 * @param c collection containing elements to be added to this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws NullPointerException if the specified collection is null
 */
public boolean addAll(Collection<? extends E> c) {
    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew);  // Increments modCount
    System.arraycopy(a, 0, elementData, size, numNew);
    size += numNew;
    return numNew != 0;
}
/**
 * Inserts all of the elements in the specified collection into this
 * list, starting at the specified position.  Shifts the element
 * currently at that position (if any) and any subsequent elements to
 * the right (increases their indices).  The new elements will appear
 * in the list in the order that they are returned by the
 * specified collection's iterator.
 *
 * @param index index at which to insert the first element from the
 *              specified collection
 * @param c collection containing elements to be added to this list
 * @return <tt>true</tt> if this list changed as a result of the call
 * @throws IndexOutOfBoundsException {@inheritDoc}
 * @throws NullPointerException if the specified collection is null
 */
public boolean addAll(int index, Collection<? extends E> c) {
    rangeCheckForAdd(index);
    Object[] a = c.toArray();
    int numNew = a.length;
    ensureCapacityInternal(size + numNew);  // Increments modCount
    int numMoved = size - index;
    if (numMoved > 0)
        System.arraycopy(elementData, index, elementData, index + numNew,
                         numMoved);
    System.arraycopy(a, 0, elementData, index, numNew);
    size += numNew;
    return numNew != 0;
}
/**
 * Removes from this list all of the elements whose index is between
 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
 * Shifts any succeeding elements to the left (reduces their index).
 * This call shortens the list by {@code (toIndex - fromIndex)} elements.
 * (If {@code toIndex==fromIndex}, this operation has no effect.)
 *
 * @throws IndexOutOfBoundsException if {@code fromIndex} or
 *         {@code toIndex} is out of range
 *         ({@code fromIndex < 0 ||
 *          fromIndex >= size() ||
 *          toIndex > size() ||
 *          toIndex < fromIndex})
 */
protected void removeRange(int fromIndex, int toIndex) {
    modCount++;
    int numMoved = size - toIndex;
    System.arraycopy(elementData, toIndex, elementData, fromIndex,
                     numMoved);
    // clear to let GC do its work
    int newSize = size - (toIndex-fromIndex);
    for (int i = newSize; i < size; i++) {
        elementData[i] = null;
    }
    size = newSize;
}
/**
 * Checks if the given index is in range.  If not, throws an appropriate
 * runtime exception.  This method does *not* check if the index is
 * negative: It is always used immediately prior to an array access,
 * which throws an ArrayIndexOutOfBoundsException if index is negative.
 */
private void rangeCheck(int index) {
    if (index >= size)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
 * A version of rangeCheck used by add and addAll.
 */
private void rangeCheckForAdd(int index) {
    if (index > size || index < 0)
        throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
 * Constructs an IndexOutOfBoundsException detail message.
 * Of the many possible refactorings of the error handling code,
 * this "outlining" performs best with both server and client VMs.
 */
private String outOfBoundsMsg(int index) {
    return "Index: "+index+", Size: "+size;
}
/**
 * Removes from this list all of its elements that are contained in the
 * specified collection.
 *
 * @param c collection containing elements to be removed from this list
 * @return {@code true} if this list changed as a result of the call
 * @throws ClassCastException if the class of an element of this list
 *         is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this list contains a null element and the
 *         specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 *         or if the specified collection is null
 * @see Collection#contains(Object)
 */
public boolean removeAll(Collection<?> c) {
    Objects.requireNonNull(c);
    return batchRemove(c, false);
}
/**
 * Retains only the elements in this list that are contained in the
 * specified collection.  In other words, removes from this list all
 * of its elements that are not contained in the specified collection.
 *
 * @param c collection containing elements to be retained in this list
 * @return {@code true} if this list changed as a result of the call
 * @throws ClassCastException if the class of an element of this list
 *         is incompatible with the specified collection
 * (<a href="Collection.html#optional-restrictions">optional</a>)
 * @throws NullPointerException if this list contains a null element and the
 *         specified collection does not permit null elements
 * (<a href="Collection.html#optional-restrictions">optional</a>),
 *         or if the specified collection is null
 * @see Collection#contains(Object)
 */
public boolean retainAll(Collection<?> c) {
    Objects.requireNonNull(c);
    return batchRemove(c, true);
}
private boolean batchRemove(Collection<?> c, boolean complement) {
    final Object[] elementData = this.elementData;
    int r = 0, w = 0;
    boolean modified = false;
    try {
        for (; r < size; r++)
            if (c.contains(elementData[r]) == complement)
                elementData[w++] = elementData[r];
    } finally {
        // Preserve behavioral compatibility with AbstractCollection,
        // even if c.contains() throws.
        if (r != size) {
            System.arraycopy(elementData, r,
                             elementData, w,
                             size - r);
            w += size - r;
        }
        if (w != size) {
            // clear to let GC do its work
            for (int i = w; i < size; i++)
                elementData[i] = null;
            modCount += size - w;
            size = w;
            modified = true;
        }
    }
    return modified;
}
/**
 * Save the state of the <tt>ArrayList</tt> instance to a stream (that
 * is, serialize it).
 *
 * @serialData The length of the array backing the <tt>ArrayList</tt>
 *             instance is emitted (int), followed by all of its elements
 *             (each an <tt>Object</tt>) in the proper order.
 */
private void writeObject(java.io.ObjectOutputStream s)
    throws java.io.IOException{
    // Write out element count, and any hidden stuff
    int expectedModCount = modCount;
    s.defaultWriteObject();
    // Write out size as capacity for behavioural 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();
    }
}
/**
 * Reconstitute the <tt>ArrayList</tt> instance from a stream (that is,
 * deserialize it).
 */
private void readObject(java.io.ObjectInputStream s)
    throws java.io.IOException, ClassNotFoundException {
    elementData = EMPTY_ELEMENTDATA;
    // Read in size, and any hidden stuff
    s.defaultReadObject();
    // Read in capacity
    s.readInt(); // ignored
    if (size > 0) {
        // be like clone(), allocate array based upon size not capacity
        int capacity = calculateCapacity(elementData, size);
        SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, capacity);
        ensureCapacityInternal(size);
        Object[] a = elementData;
        // Read in all elements in the proper order.
        for (int i=0; i<size; i++) {
            a[i] = s.readObject();
        }
    }
}
/**
 * Returns a list iterator over the elements in this list (in proper
 * sequence), starting at the specified position in the list.
 * The specified index indicates the first element that would be
 * returned by an initial call to {@link ListIterator#next next}.
 * An initial call to {@link ListIterator#previous previous} would
 * return the element with the specified index minus one.
 *
 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 */
public ListIterator<E> listIterator(int index) {
    if (index < 0 || index > size)
        throw new IndexOutOfBoundsException("Index: "+index);
    return new ListItr(index);
}
/**
 * Returns a list iterator over the elements in this list (in proper
 * sequence).
 *
 * <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
 *
 * @see #listIterator(int)
 */
public ListIterator<E> listIterator() {
    return new ListItr(0);
}
/**
 * Returns an iterator over the elements in this list in proper sequence.
 *
 * <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
 *
 * @return an iterator over the elements in this list in proper sequence
 */
public Iterator<E> iterator() {
    return new Itr();
}
/**
 * An optimized version of AbstractList.Itr
 */
private class Itr implements Iterator<E> {
    int cursor;       // index of next element to return
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;
    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
    @SuppressWarnings("unchecked")
    public void forEachRemaining(Consumer<? super E> consumer) {
        Objects.requireNonNull(consumer);
        final int size = ArrayList.this.size;
        int i = cursor;
        if (i >= size) {
            return;
        }
        final Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length) {
            throw new ConcurrentModificationException();
        }
        while (i != size && modCount == expectedModCount) {
            consumer.accept((E) elementData[i++]);
        }
        // update once at end of iteration to reduce heap write traffic
        cursor = i;
        lastRet = i - 1;
        checkForComodification();
    }
    final void checkForComodification() {
        if (modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}
/**
 * An optimized version of AbstractList.ListItr
 */
private class ListItr extends Itr implements ListIterator<E> {
    ListItr(int index) {
        super();
        cursor = index;
    }
    public boolean hasPrevious() {
        return cursor != 0;
    }
    public int nextIndex() {
        return cursor;
    }
    public int previousIndex() {
        return cursor - 1;
    }
    @SuppressWarnings("unchecked")
    public E previous() {
        checkForComodification();
        int i = cursor - 1;
        if (i < 0)
            throw new NoSuchElementException();
        Object[] elementData = ArrayList.this.elementData;
        if (i >= elementData.length)
            throw new ConcurrentModificationException();
        cursor = i;
        return (E) elementData[lastRet = i];
    }
    public void set(E e) {
        if (lastRet < 0)
            throw new IllegalStateException();
        checkForComodification();
        try {
            ArrayList.this.set(lastRet, e);
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }
    public void add(E e) {
        checkForComodification();
        try {
            int i = cursor;
            ArrayList.this.add(i, e);
            cursor = i + 1;
            lastRet = -1;
            expectedModCount = modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }
}
/**
 * Returns a view of the portion of this list between the specified
 * {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.  (If
 * {@code fromIndex} and {@code toIndex} are equal, the returned list is
 * empty.)  The returned list is backed by this list, so non-structural
 * changes in the returned list are reflected in this list, and vice-versa.
 * The returned list supports all of the optional list operations.
 *
 * <p>This method eliminates the need for explicit range operations (of
 * the sort that commonly exist for arrays).  Any operation that expects
 * a list can be used as a range operation by passing a subList view
 * instead of a whole list.  For example, the following idiom
 * removes a range of elements from a list:
 * <pre>
 *      list.subList(from, to).clear();
 * </pre>
 * Similar idioms may be constructed for {@link #indexOf(Object)} and
 * {@link #lastIndexOf(Object)}, and all of the algorithms in the
 * {@link Collections} class can be applied to a subList.
 *
 * <p>The semantics of the list returned by this method become undefined if
 * the backing list (i.e., this list) is <i>structurally modified</i> in
 * any way other than via the returned list.  (Structural modifications are
 * those that change the size of this list, or otherwise perturb it in such
 * a fashion that iterations in progress may yield incorrect results.)
 *
 * @throws IndexOutOfBoundsException {@inheritDoc}
 * @throws IllegalArgumentException {@inheritDoc}
 */
public List<E> subList(int fromIndex, int toIndex) {
    subListRangeCheck(fromIndex, toIndex, size);
    return new SubList(this, 0, fromIndex, toIndex);
}
static void subListRangeCheck(int fromIndex, int toIndex, int size) {
    if (fromIndex < 0)
        throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
    if (toIndex > size)
        throw new IndexOutOfBoundsException("toIndex = " + toIndex);
    if (fromIndex > toIndex)
        throw new IllegalArgumentException("fromIndex(" + fromIndex +
                                           ") > toIndex(" + toIndex + ")");
}
private class SubList extends AbstractList<E> implements RandomAccess {
    private final AbstractList<E> parent;
    private final int parentOffset;
    private final int offset;
    int size;
    SubList(AbstractList<E> parent,
            int offset, int fromIndex, int toIndex) {
        this.parent = parent;
        this.parentOffset = fromIndex;
        this.offset = offset + fromIndex;
        this.size = toIndex - fromIndex;
        this.modCount = ArrayList.this.modCount;
    }
    public E set(int index, E e) {
        rangeCheck(index);
        checkForComodification();
        E oldValue = ArrayList.this.elementData(offset + index);
        ArrayList.this.elementData[offset + index] = e;
        return oldValue;
    }
    public E get(int index) {
        rangeCheck(index);
        checkForComodification();
        return ArrayList.this.elementData(offset + index);
    }
    public int size() {
        checkForComodification();
        return this.size;
    }
    public void add(int index, E e) {
        rangeCheckForAdd(index);
        checkForComodification();
        parent.add(parentOffset + index, e);
        this.modCount = parent.modCount;
        this.size++;
    }
    public E remove(int index) {
        rangeCheck(index);
        checkForComodification();
        E result = parent.remove(parentOffset + index);
        this.modCount = parent.modCount;
        this.size--;
        return result;
    }
    protected void removeRange(int fromIndex, int toIndex) {
        checkForComodification();
        parent.removeRange(parentOffset + fromIndex,
                           parentOffset + toIndex);
        this.modCount = parent.modCount;
        this.size -= toIndex - fromIndex;
    }
    public boolean addAll(Collection<? extends E> c) {
        return addAll(this.size, c);
    }
    public boolean addAll(int index, Collection<? extends E> c) {
        rangeCheckForAdd(index);
        int cSize = c.size();
        if (cSize==0)
            return false;
        checkForComodification();
        parent.addAll(parentOffset + index, c);
        this.modCount = parent.modCount;
        this.size += cSize;
        return true;
    }
    public Iterator<E> iterator() {
        return listIterator();
    }
    public ListIterator<E> listIterator(final int index) {
        checkForComodification();
        rangeCheckForAdd(index);
        final int offset = this.offset;
        return new ListIterator<E>() {
            int cursor = index;
            int lastRet = -1;
            int expectedModCount = ArrayList.this.modCount;
            public boolean hasNext() {
                return cursor != SubList.this.size;
            }
            @SuppressWarnings("unchecked")
            public E next() {
                checkForComodification();
                int i = cursor;
                if (i >= SubList.this.size)
                    throw new NoSuchElementException();
                Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length)
                    throw new ConcurrentModificationException();
                cursor = i + 1;
                return (E) elementData[offset + (lastRet = i)];
            }
            public boolean hasPrevious() {
                return cursor != 0;
            }
            @SuppressWarnings("unchecked")
            public E previous() {
                checkForComodification();
                int i = cursor - 1;
                if (i < 0)
                    throw new NoSuchElementException();
                Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length)
                    throw new ConcurrentModificationException();
                cursor = i;
                return (E) elementData[offset + (lastRet = i)];
            }
            @SuppressWarnings("unchecked")
            public void forEachRemaining(Consumer<? super E> consumer) {
                Objects.requireNonNull(consumer);
                final int size = SubList.this.size;
                int i = cursor;
                if (i >= size) {
                    return;
                }
                final Object[] elementData = ArrayList.this.elementData;
                if (offset + i >= elementData.length) {
                    throw new ConcurrentModificationException();
                }
                while (i != size && modCount == expectedModCount) {
                    consumer.accept((E) elementData[offset + (i++)]);
                }
                // update once at end of iteration to reduce heap write traffic
                lastRet = cursor = i;
                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 = ArrayList.this.modCount;
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }
            public void set(E e) {
                if (lastRet < 0)
                    throw new IllegalStateException();
                checkForComodification();
                try {
                    ArrayList.this.set(offset + lastRet, e);
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }
            public void add(E e) {
                checkForComodification();
                try {
                    int i = cursor;
                    SubList.this.add(i, e);
                    cursor = i + 1;
                    lastRet = -1;
                    expectedModCount = ArrayList.this.modCount;
                } catch (IndexOutOfBoundsException ex) {
                    throw new ConcurrentModificationException();
                }
            }
            final void checkForComodification() {
                if (expectedModCount != ArrayList.this.modCount)
                    throw new ConcurrentModificationException();
            }
        };
    }
    public List<E> subList(int fromIndex, int toIndex) {
        subListRangeCheck(fromIndex, toIndex, size);
        return new SubList(this, offset, fromIndex, toIndex);
    }
    private void rangeCheck(int index) {
        if (index < 0 || index >= this.size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > this.size)
            throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
    }
    private String outOfBoundsMsg(int index) {
        return "Index: "+index+", Size: "+this.size;
    }
    private void checkForComodification() {
        if (ArrayList.this.modCount != this.modCount)
            throw new ConcurrentModificationException();
    }
    public Spliterator<E> spliterator() {
        checkForComodification();
        return new ArrayListSpliterator<E>(ArrayList.this, offset,
                                           offset + this.size, this.modCount);
    }
}
@Override
public void forEach(Consumer<? super E> action) {
    Objects.requireNonNull(action);
    final int expectedModCount = modCount;
    @SuppressWarnings("unchecked")
    final E[] elementData = (E[]) this.elementData;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        action.accept(elementData[i]);
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
}
/**
 * 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<>(this, 0, -1, 0);
}
/** Index-based split-by-two, lazily initialized Spliterator */
static final class ArrayListSpliterator<E> 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 final ArrayList<E> list;
    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
    /** Create new spliterator covering the given  range */
    ArrayListSpliterator(ArrayList<E> list, int origin, int fence,
                         int expectedModCount) {
        this.list = list; // OK if null unless traversed
        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)
        ArrayList<E> lst;
        if ((hi = fence) < 0) {
            if ((lst = list) == null)
                hi = fence = 0;
            else {
                expectedModCount = lst.modCount;
                hi = fence = lst.size;
            }
        }
        return hi;
    }
    public ArrayListSpliterator<E> trySplit() {
        int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
        return (lo >= mid) ? null : // divide range in half unless too small
            new ArrayListSpliterator<E>(list, 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)list.elementData[i];
            action.accept(e);
            if (list.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
        ArrayList<E> lst; Object[] a;
        if (action == null)
            throw new NullPointerException();
        if ((lst = list) != null && (a = lst.elementData) != null) {
            if ((hi = fence) < 0) {
                mc = lst.modCount;
                hi = lst.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 (long) (getFence() - index);
    }
    public int characteristics() {
        return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
    }
}
@Override
public boolean removeIf(Predicate<? super E> filter) {
    Objects.requireNonNull(filter);
    // figure out which elements are to be removed
    // any exception thrown from the filter predicate at this stage
    // will leave the collection unmodified
    int removeCount = 0;
    final BitSet removeSet = new BitSet(size);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        @SuppressWarnings("unchecked")
        final E element = (E) elementData[i];
        if (filter.test(element)) {
            removeSet.set(i);
            removeCount++;
        }
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
    // shift surviving elements left over the spaces left by removed elements
    final boolean anyToRemove = removeCount > 0;
    if (anyToRemove) {
        final int newSize = size - removeCount;
        for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
            i = removeSet.nextClearBit(i);
            elementData[j] = elementData[i];
        }
        for (int k=newSize; k < size; k++) {
            elementData[k] = null;  // Let gc do its work
        }
        this.size = newSize;
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
        modCount++;
    }
    return anyToRemove;
}
@Override
@SuppressWarnings("unchecked")
public void replaceAll(UnaryOperator<E> operator) {
    Objects.requireNonNull(operator);
    final int expectedModCount = modCount;
    final int size = this.size;
    for (int i=0; modCount == expectedModCount && i < size; i++) {
        elementData[i] = operator.apply((E) elementData[i]);
    }
    if (modCount != expectedModCount) {
        throw new ConcurrentModificationException();
    }
    modCount++;
}
@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++;
}