7062169: (coll) micro-optimize ArrayList.remove(Object)
Reviewed-by: martin, psandoz, igerasim
/*
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
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* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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*/
package java.util;
import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;
/**
* Resizable-array implementation of the {@code List} interface. Implements
* all optional list operations, and permits all elements, including
* {@code null}. In addition to implementing the {@code List} interface,
* this class provides methods to manipulate the size of the array that is
* used internally to store the list. (This class is roughly equivalent to
* {@code Vector}, except that it is unsynchronized.)
*
* <p>The {@code size}, {@code isEmpty}, {@code get}, {@code set},
* {@code iterator}, and {@code listIterator} operations run in constant
* time. The {@code add} operation runs in <i>amortized constant time</i>,
* that is, adding n elements requires O(n) time. All of the other operations
* run in linear time (roughly speaking). The constant factor is low compared
* to that for the {@code LinkedList} implementation.
*
* <p>Each {@code ArrayList} instance has a <i>capacity</i>. The capacity is
* the size of the array used to store the elements in the list. It is always
* at least as large as the list size. As elements are added to an ArrayList,
* its capacity grows automatically. The details of the growth policy are not
* specified beyond the fact that adding an element has constant amortized
* time cost.
*
* <p>An application can increase the capacity of an {@code ArrayList} instance
* before adding a large number of elements using the {@code ensureCapacity}
* operation. This may reduce the amount of incremental reallocation.
*
* <p><strong>Note that this implementation is not synchronized.</strong>
* If multiple threads access an {@code ArrayList} instance concurrently,
* and at least one of the threads modifies the list structurally, it
* <i>must</i> be synchronized externally. (A structural modification is
* any operation that adds or deletes one or more elements, or explicitly
* resizes the backing array; merely setting the value of an element is not
* a structural modification.) This is typically accomplished by
* synchronizing on some object that naturally encapsulates the list.
*
* If no such object exists, the list should be "wrapped" using the
* {@link Collections#synchronizedList Collections.synchronizedList}
* method. This is best done at creation time, to prevent accidental
* unsynchronized access to the list:<pre>
* List list = Collections.synchronizedList(new ArrayList(...));</pre>
*
* <p id="fail-fast">
* The iterators returned by this class's {@link #iterator() iterator} and
* {@link #listIterator(int) listIterator} methods are <em>fail-fast</em>:
* if the list is structurally modified at any time after the iterator is
* created, in any way except through the iterator's own
* {@link ListIterator#remove() remove} or
* {@link ListIterator#add(Object) add} methods, the iterator will throw a
* {@link ConcurrentModificationException}. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
* as it is, generally speaking, impossible to make any hard guarantees in the
* presence of unsynchronized concurrent modification. Fail-fast iterators
* throw {@code ConcurrentModificationException} on a best-effort basis.
* Therefore, it would be wrong to write a program that depended on this
* exception for its correctness: <i>the fail-fast behavior of iterators
* should be used only to detect bugs.</i>
*
* <p>This class is a member of the
* <a href="{@docRoot}/java/util/package-summary.html#CollectionsFramework">
* Java Collections Framework</a>.
*
* @param <E> the type of elements in this list
*
* @author Josh Bloch
* @author Neal Gafter
* @see Collection
* @see List
* @see LinkedList
* @see Vector
* @since 1.2
*/
public class ArrayList<E> extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
private static final long serialVersionUID = 8683452581122892189L;
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* Shared empty array instance used for empty instances.
*/
private static final Object[] EMPTY_ELEMENTDATA = {};
/**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access
/**
* The size of the ArrayList (the number of elements it contains).
*
* @serial
*/
private int size;
/**
* Constructs an empty list with the specified initial capacity.
*
* @param initialCapacity the initial capacity of the list
* @throws IllegalArgumentException if the specified initial capacity
* is negative
*/
public ArrayList(int initialCapacity) {
if (initialCapacity > 0) {
this.elementData = new Object[initialCapacity];
} else if (initialCapacity == 0) {
this.elementData = EMPTY_ELEMENTDATA;
} else {
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
}
}
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* Constructs a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection whose elements are to be placed into this list
* @throws NullPointerException if the specified collection is null
*/
public ArrayList(Collection<? extends E> c) {
elementData = c.toArray();
if ((size = elementData.length) != 0) {
// defend against c.toArray (incorrectly) not returning Object[]
// (see e.g. https://bugs.openjdk.java.net/browse/JDK-6260652)
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, size, Object[].class);
} else {
// replace with empty array.
this.elementData = EMPTY_ELEMENTDATA;
}
}
/**
* Trims the capacity of this {@code ArrayList} instance to be the
* list's current size. An application can use this operation to minimize
* the storage of an {@code ArrayList} instance.
*/
public void trimToSize() {
modCount++;
if (size < elementData.length) {
elementData = (size == 0)
? EMPTY_ELEMENTDATA
: Arrays.copyOf(elementData, size);
}
}
/**
* Increases the capacity of this {@code ArrayList} instance, if
* necessary, to ensure that it can hold at least the number of elements
* specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
public void ensureCapacity(int minCapacity) {
if (minCapacity > elementData.length
&& !(elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
&& minCapacity <= DEFAULT_CAPACITY)) {
modCount++;
grow(minCapacity);
}
}
/**
* The maximum size of array to allocate (unless necessary).
* Some VMs reserve some header words in an array.
* Attempts to allocate larger arrays may result in
* OutOfMemoryError: Requested array size exceeds VM limit
*/
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
/**
* Increases the capacity to ensure that it can hold at least the
* number of elements specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
* @throws OutOfMemoryError if minCapacity is less than zero
*/
private Object[] grow(int minCapacity) {
return elementData = Arrays.copyOf(elementData,
newCapacity(minCapacity));
}
private Object[] grow() {
return grow(size + 1);
}
/**
* Returns a capacity at least as large as the given minimum capacity.
* Returns the current capacity increased by 50% if that suffices.
* Will not return a capacity greater than MAX_ARRAY_SIZE unless
* the given minimum capacity is greater than MAX_ARRAY_SIZE.
*
* @param minCapacity the desired minimum capacity
* @throws OutOfMemoryError if minCapacity is less than zero
*/
private int newCapacity(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity <= 0) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA)
return Math.max(DEFAULT_CAPACITY, minCapacity);
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return minCapacity;
}
return (newCapacity - MAX_ARRAY_SIZE <= 0)
? newCapacity
: hugeCapacity(minCapacity);
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE)
? Integer.MAX_VALUE
: MAX_ARRAY_SIZE;
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return size;
}
/**
* Returns {@code true} if this list contains no elements.
*
* @return {@code true} if this list contains no elements
*/
public boolean isEmpty() {
return size == 0;
}
/**
* Returns {@code true} if this list contains the specified element.
* More formally, returns {@code true} if and only if this list contains
* at least one element {@code e} such that
* {@code Objects.equals(o, e)}.
*
* @param o element whose presence in this list is to be tested
* @return {@code true} if this list contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o) >= 0;
}
/**
* Returns the index of the first occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the lowest index {@code i} such that
* {@code Objects.equals(o, get(i))},
* or -1 if there is no such index.
*/
public int indexOf(Object o) {
if (o == null) {
for (int i = 0; i < size; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = 0; i < size; i++)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Returns the index of the last occurrence of the specified element
* in this list, or -1 if this list does not contain the element.
* More formally, returns the highest index {@code i} such that
* {@code Objects.equals(o, get(i))},
* or -1 if there is no such index.
*/
public int lastIndexOf(Object o) {
if (o == null) {
for (int i = size-1; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
for (int i = size-1; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
/**
* Returns a shallow copy of this {@code ArrayList} instance. (The
* elements themselves are not copied.)
*
* @return a clone of this {@code ArrayList} instance
*/
public Object clone() {
try {
ArrayList<?> v = (ArrayList<?>) super.clone();
v.elementData = Arrays.copyOf(elementData, size);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError(e);
}
}
/**
* Returns an array containing all of the elements in this list
* in proper sequence (from first to last element).
*
* <p>The returned array will be "safe" in that no references to it are
* maintained by this list. (In other words, this method must allocate
* a new array). The caller is thus free to modify the returned array.
*
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list in
* proper sequence
*/
public Object[] toArray() {
return Arrays.copyOf(elementData, size);
}
/**
* Returns an array containing all of the elements in this list in proper
* sequence (from first to last element); the runtime type of the returned
* array is that of the specified array. If the list fits in the
* specified array, it is returned therein. Otherwise, a new array is
* allocated with the runtime type of the specified array and the size of
* this list.
*
* <p>If the list fits in the specified array with room to spare
* (i.e., the array has more elements than the list), the element in
* the array immediately following the end of the collection is set to
* {@code null}. (This is useful in determining the length of the
* list <i>only</i> if the caller knows that the list does not contain
* any null elements.)
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T[] a) {
if (a.length < size)
// Make a new array of a's runtime type, but my contents:
return (T[]) Arrays.copyOf(elementData, size, a.getClass());
System.arraycopy(elementData, 0, a, 0, size);
if (a.length > size)
a[size] = null;
return a;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
@SuppressWarnings("unchecked")
static <E> E elementAt(Object[] es, int index) {
return (E) es[index];
}
/**
* Returns the element at the specified position in this list.
*
* @param index index of the element to return
* @return the element at the specified position in this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {
Objects.checkIndex(index, size);
return elementData(index);
}
/**
* Replaces the element at the specified position in this list with
* the specified element.
*
* @param index index of the element to replace
* @param element element to be stored at the specified position
* @return the element previously at the specified position
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E set(int index, E element) {
Objects.checkIndex(index, size);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
/**
* This helper method split out from add(E) to keep method
* bytecode size under 35 (the -XX:MaxInlineSize default value),
* which helps when add(E) is called in a C1-compiled loop.
*/
private void add(E e, Object[] elementData, int s) {
if (s == elementData.length)
elementData = grow();
elementData[s] = e;
size = s + 1;
}
/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return {@code true} (as specified by {@link Collection#add})
*/
public boolean add(E e) {
modCount++;
add(e, elementData, size);
return true;
}
/**
* Inserts the specified element at the specified position in this
* list. Shifts the element currently at that position (if any) and
* any subsequent elements to the right (adds one to their indices).
*
* @param index index at which the specified element is to be inserted
* @param element element to be inserted
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public void add(int index, E element) {
rangeCheckForAdd(index);
modCount++;
final int s;
Object[] elementData;
if ((s = size) == (elementData = this.elementData).length)
elementData = grow();
System.arraycopy(elementData, index,
elementData, index + 1,
s - index);
elementData[index] = element;
size = s + 1;
}
/**
* Removes the element at the specified position in this list.
* 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;
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If the list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* {@code i} such that
* {@code Objects.equals(o, get(i))}
* (if such an element exists). Returns {@code true} if this list
* contained the specified element (or equivalently, if this list
* changed as a result of the call).
*
* @param o element to be removed from this list, if present
* @return {@code true} if this list contained the specified element
*/
public boolean remove(Object o) {
final Object[] es = elementData;
final int size = this.size;
int i = 0;
found: {
if (o == null) {
for (; i < size; i++)
if (es[i] == null)
break found;
} else {
for (; i < size; i++)
if (o.equals(es[i]))
break found;
}
return false;
}
fastRemove(es, i);
return true;
}
/**
* Private remove method that skips bounds checking and does not
* return the value removed.
*/
private void fastRemove(Object[] es, int i) {
modCount++;
final int newSize;
if ((newSize = size - 1) > i)
System.arraycopy(es, i + 1, es, i, newSize - i);
es[size = newSize] = null;
}
/**
* Removes all of the elements from this list. The list will
* be empty after this call returns.
*/
public void clear() {
modCount++;
final Object[] es = elementData;
for (int to = size, i = size = 0; i < to; i++)
es[i] = null;
}
/**
* Appends all of the elements in the specified collection to the end of
* this list, in the order that they are returned by the
* specified collection's Iterator. The behavior of this operation is
* undefined if the specified collection is modified while the operation
* is in progress. (This implies that the behavior of this call is
* undefined if the specified collection is this list, and this
* list is nonempty.)
*
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(Collection<? extends E> c) {
Object[] a = c.toArray();
modCount++;
int numNew = a.length;
if (numNew == 0)
return false;
Object[] elementData;
final int s;
if (numNew > (elementData = this.elementData).length - (s = size))
elementData = grow(s + numNew);
System.arraycopy(a, 0, elementData, s, numNew);
size = s + numNew;
return true;
}
/**
* Inserts all of the elements in the specified collection into this
* list, starting at the specified position. Shifts the element
* currently at that position (if any) and any subsequent elements to
* the right (increases their indices). The new elements will appear
* in the list in the order that they are returned by the
* specified collection's iterator.
*
* @param index index at which to insert the first element from the
* specified collection
* @param c collection containing elements to be added to this list
* @return {@code true} if this list changed as a result of the call
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws NullPointerException if the specified collection is null
*/
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
Object[] a = c.toArray();
modCount++;
int numNew = a.length;
if (numNew == 0)
return false;
Object[] elementData;
final int s;
if (numNew > (elementData = this.elementData).length - (s = size))
elementData = grow(s + numNew);
int numMoved = s - index;
if (numMoved > 0)
System.arraycopy(elementData, index,
elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
size = s + numNew;
return true;
}
/**
* Removes from this list all of the elements whose index is between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by {@code (toIndex - fromIndex)} elements.
* (If {@code toIndex==fromIndex}, this operation has no effect.)
*
* @throws IndexOutOfBoundsException if {@code fromIndex} or
* {@code toIndex} is out of range
* ({@code fromIndex < 0 ||
* toIndex > size() ||
* toIndex < fromIndex})
*/
protected void removeRange(int fromIndex, int toIndex) {
if (fromIndex > toIndex) {
throw new IndexOutOfBoundsException(
outOfBoundsMsg(fromIndex, toIndex));
}
modCount++;
shiftTailOverGap(elementData, fromIndex, toIndex);
}
/** Erases the gap from lo to hi, by sliding down following elements. */
private void shiftTailOverGap(Object[] es, int lo, int hi) {
System.arraycopy(es, hi, es, lo, size - hi);
for (int to = size, i = (size -= hi - lo); i < to; i++)
es[i] = null;
}
/**
* A version of rangeCheck used by add and addAll.
*/
private void rangeCheckForAdd(int index) {
if (index > size || index < 0)
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
/**
* Constructs an IndexOutOfBoundsException detail message.
* Of the many possible refactorings of the error handling code,
* this "outlining" performs best with both server and client VMs.
*/
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
/**
* A version used in checking (fromIndex > toIndex) condition
*/
private static String outOfBoundsMsg(int fromIndex, int toIndex) {
return "From Index: " + fromIndex + " > To Index: " + toIndex;
}
/**
* Removes from this list all of its elements that are contained in the
* specified collection.
*
* @param c collection containing elements to be removed from this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean removeAll(Collection<?> c) {
return batchRemove(c, false, 0, size);
}
/**
* Retains only the elements in this list that are contained in the
* specified collection. In other words, removes from this list all
* of its elements that are not contained in the specified collection.
*
* @param c collection containing elements to be retained in this list
* @return {@code true} if this list changed as a result of the call
* @throws ClassCastException if the class of an element of this list
* is incompatible with the specified collection
* (<a href="Collection.html#optional-restrictions">optional</a>)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements
* (<a href="Collection.html#optional-restrictions">optional</a>),
* or if the specified collection is null
* @see Collection#contains(Object)
*/
public boolean retainAll(Collection<?> c) {
return batchRemove(c, true, 0, size);
}
boolean batchRemove(Collection<?> c, boolean complement,
final int from, final int end) {
Objects.requireNonNull(c);
final Object[] es = elementData;
int r;
// Optimize for initial run of survivors
for (r = from;; r++) {
if (r == end)
return false;
if (c.contains(es[r]) != complement)
break;
}
int w = r++;
try {
for (Object e; r < end; r++)
if (c.contains(e = es[r]) == complement)
es[w++] = e;
} catch (Throwable ex) {
// Preserve behavioral compatibility with AbstractCollection,
// even if c.contains() throws.
System.arraycopy(es, r, es, w, end - r);
w += end - r;
throw ex;
} finally {
modCount += end - w;
shiftTailOverGap(es, w, end);
}
return true;
}
/**
* Saves the state of the {@code ArrayList} instance to a stream
* (that is, serializes it).
*
* @param s the stream
* @throws java.io.IOException if an I/O error occurs
* @serialData The length of the array backing the {@code ArrayList}
* instance is emitted (int), followed by all of its elements
* (each an {@code Object}) in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// Write out element count, and any hidden stuff
int expectedModCount = modCount;
s.defaultWriteObject();
// Write out size as capacity for behavioral compatibility with clone()
s.writeInt(size);
// Write out all elements in the proper order.
for (int i=0; i<size; i++) {
s.writeObject(elementData[i]);
}
if (modCount != expectedModCount) {
throw new ConcurrentModificationException();
}
}
/**
* Reconstitutes the {@code ArrayList} instance from a stream (that is,
* deserializes it).
* @param s the stream
* @throws ClassNotFoundException if the class of a serialized object
* could not be found
* @throws java.io.IOException if an I/O error occurs
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in capacity
s.readInt(); // ignored
if (size > 0) {
// like clone(), allocate array based upon size not capacity
Object[] elements = new Object[size];
// Read in all elements in the proper order.
for (int i = 0; i < size; i++) {
elements[i] = s.readObject();
}
elementData = elements;
} else if (size == 0) {
elementData = EMPTY_ELEMENTDATA;
} else {
throw new java.io.InvalidObjectException("Invalid size: " + size);
}
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence), starting at the specified position in the list.
* The specified index indicates the first element that would be
* returned by an initial call to {@link ListIterator#next next}.
* An initial call to {@link ListIterator#previous previous} would
* return the element with the specified index minus one.
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator<E> listIterator(int index) {
rangeCheckForAdd(index);
return new ListItr(index);
}
/**
* Returns a list iterator over the elements in this list (in proper
* sequence).
*
* <p>The returned list iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @see #listIterator(int)
*/
public ListIterator<E> listIterator() {
return new ListItr(0);
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator() {
return new Itr();
}
/**
* An optimized version of AbstractList.Itr
*/
private class Itr implements Iterator<E> {
int cursor; // index of next element to return
int lastRet = -1; // index of last element returned; -1 if no such
int expectedModCount = modCount;
// prevent creating a synthetic constructor
Itr() {}
public boolean hasNext() {
return cursor != size;
}
@SuppressWarnings("unchecked")
public E next() {
checkForComodification();
int i = cursor;
if (i >= size)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1;
return (E) elementData[lastRet = i];
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.remove(lastRet);
cursor = lastRet;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
final int size = ArrayList.this.size;
int i = cursor;
if (i < size) {
final Object[] es = elementData;
if (i >= es.length)
throw new ConcurrentModificationException();
for (; i < size && modCount == expectedModCount; i++)
action.accept(elementAt(es, i));
// update once at end to reduce heap write traffic
cursor = i;
lastRet = i - 1;
checkForComodification();
}
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* An optimized version of AbstractList.ListItr
*/
private class ListItr extends Itr implements ListIterator<E> {
ListItr(int index) {
super();
cursor = index;
}
public boolean hasPrevious() {
return cursor != 0;
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
@SuppressWarnings("unchecked")
public E previous() {
checkForComodification();
int i = cursor - 1;
if (i < 0)
throw new NoSuchElementException();
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i;
return (E) elementData[lastRet = i];
}
public void set(E e) {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.set(lastRet, e);
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
public void add(E e) {
checkForComodification();
try {
int i = cursor;
ArrayList.this.add(i, e);
cursor = i + 1;
lastRet = -1;
expectedModCount = modCount;
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
}
/**
* Returns a view of the portion of this list between the specified
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive. (If
* {@code fromIndex} and {@code toIndex} are equal, the returned list is
* empty.) The returned list is backed by this list, so non-structural
* changes in the returned list are reflected in this list, and vice-versa.
* The returned list supports all of the optional list operations.
*
* <p>This method eliminates the need for explicit range operations (of
* the sort that commonly exist for arrays). Any operation that expects
* a list can be used as a range operation by passing a subList view
* instead of a whole list. For example, the following idiom
* removes a range of elements from a list:
* <pre>
* list.subList(from, to).clear();
* </pre>
* Similar idioms may be constructed for {@link #indexOf(Object)} and
* {@link #lastIndexOf(Object)}, and all of the algorithms in the
* {@link Collections} class can be applied to a subList.
*
* <p>The semantics of the list returned by this method become undefined if
* the backing list (i.e., this list) is <i>structurally modified</i> in
* any way other than via the returned list. (Structural modifications are
* those that change the size of this list, or otherwise perturb it in such
* a fashion that iterations in progress may yield incorrect results.)
*
* @throws IndexOutOfBoundsException {@inheritDoc}
* @throws IllegalArgumentException {@inheritDoc}
*/
public List<E> subList(int fromIndex, int toIndex) {
subListRangeCheck(fromIndex, toIndex, size);
return new SubList<>(this, fromIndex, toIndex);
}
private static class SubList<E> extends AbstractList<E> implements RandomAccess {
private final ArrayList<E> root;
private final SubList<E> parent;
private final int offset;
private int size;
/**
* Constructs a sublist of an arbitrary ArrayList.
*/
public SubList(ArrayList<E> root, int fromIndex, int toIndex) {
this.root = root;
this.parent = null;
this.offset = fromIndex;
this.size = toIndex - fromIndex;
this.modCount = root.modCount;
}
/**
* Constructs a sublist of another SubList.
*/
private SubList(SubList<E> parent, int fromIndex, int toIndex) {
this.root = parent.root;
this.parent = parent;
this.offset = parent.offset + fromIndex;
this.size = toIndex - fromIndex;
this.modCount = root.modCount;
}
public E set(int index, E element) {
Objects.checkIndex(index, size);
checkForComodification();
E oldValue = root.elementData(offset + index);
root.elementData[offset + index] = element;
return oldValue;
}
public E get(int index) {
Objects.checkIndex(index, size);
checkForComodification();
return root.elementData(offset + index);
}
public int size() {
checkForComodification();
return size;
}
public void add(int index, E element) {
rangeCheckForAdd(index);
checkForComodification();
root.add(offset + index, element);
updateSizeAndModCount(1);
}
public E remove(int index) {
Objects.checkIndex(index, size);
checkForComodification();
E result = root.remove(offset + index);
updateSizeAndModCount(-1);
return result;
}
protected void removeRange(int fromIndex, int toIndex) {
checkForComodification();
root.removeRange(offset + fromIndex, offset + toIndex);
updateSizeAndModCount(fromIndex - toIndex);
}
public boolean addAll(Collection<? extends E> c) {
return addAll(this.size, c);
}
public boolean addAll(int index, Collection<? extends E> c) {
rangeCheckForAdd(index);
int cSize = c.size();
if (cSize==0)
return false;
checkForComodification();
root.addAll(offset + index, c);
updateSizeAndModCount(cSize);
return true;
}
public 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 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 = root.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 && 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 = root.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 = root.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}
*/
@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 <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 */
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. */
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}
*/
@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).
*/
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();
expectedModCount++;
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) {
Objects.requireNonNull(operator);
final int expectedModCount = modCount;
final Object[] es = elementData;
final int size = this.size;
for (int i = 0; modCount == expectedModCount && i < size; i++)
es[i] = operator.apply(elementAt(es, 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++;
}
void checkInvariants() {
// assert size >= 0;
// assert size == elementData.length || elementData[size] == null;
}
}