前言
- {@link java.util.ArrayList}的线程安全变体，其中所有可变操作（{@code add}，{@code set}等）都通过对基础数组进行全新复制来实现。
- 通常这样做的成本太高，但是在遍历操作的数量远远超过变异的情况下，它可能比替代方法更有效，并且在您无法或不想同步遍历而又需要防止并发线程之间的干扰时很有用。
- “快照”样式的迭代器方法在创建迭代器时使用对数组状态的引用。
- 此数组在迭代器的生命周期内永不更改，因此不会发生干扰，并且保证迭代器不会抛出{@code ConcurrentModificationException}。
- 自创建迭代器以来，该迭代器将不会反映对列表的添加，删除或更改。
- 不支持对迭代器本身进行元素更改操作（{@code remove}，{@code set}和{@code add}）。
- 这些方法抛出{@code UnsupportedOperationException}。
- 允许所有元素，包括{@code null}。
- 内存一致性影响：与其他并发集合一样，在将对象放入{@code CopyOnWriteArrayList}发生或访问或删除之后发生的操作之前，线程中的操作来自另一个线程中{@code CopyOnWriteArrayList}的元素的元素。
- 此类是Java集合框架的成员。
源码
package java.util.concurrent;
public class CopyOnWriteArrayList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
private static final long serialVersionUID = 8673264195747942595L;
/** The lock protecting all mutators */
final transient ReentrantLock lock = new ReentrantLock();
/** The array, accessed only via getArray/setArray. */
private transient volatile Object[] array;
/**
* Gets the array. Non-private so as to also be accessible
* from CopyOnWriteArraySet class.
*/
final Object[] getArray() {
return array;
}
/**
* Sets the array.
*/
final void setArray(Object[] a) {
array = a;
}
/**
* Creates an empty list.
*/
public CopyOnWriteArrayList() {
setArray(new Object[0]);
}
/**
* 创建一个列表，该列表包含指定集合的元素，其顺序由集合的迭代器返回。
*/
public CopyOnWriteArrayList(Collection<? extends E> c) {
Object[] elements;
if (c.getClass() == CopyOnWriteArrayList.class)
elements = ((CopyOnWriteArrayList<?>)c).getArray();
else {
elements = c.toArray();
// c.toArray might (incorrectly) not return Object[] (see 6260652)
if (elements.getClass() != Object[].class)
elements = Arrays.copyOf(elements, elements.length, Object[].class);
}
setArray(elements);
}
/**
* 创建一个保存给定数组副本的列表。
*/
public CopyOnWriteArrayList(E[] toCopyIn) {
setArray(Arrays.copyOf(toCopyIn, toCopyIn.length, Object[].class));
}
/**
* 返回此列表中的元素数。
*/
public int size() {
return getArray().length;
}
/**
* Returns {@code true} if this list contains no elements.
*
* @return {@code true} if this list contains no elements
*/
public boolean isEmpty() {
return size() == 0;
}
/**
* Tests for equality, coping with nulls.
*/
private static boolean eq(Object o1, Object o2) {
return (o1 == null) ? o2 == null : o1.equals(o2);
}
/**
* 静态版本的indexOf，允许重复调用而无需每次都重新获取数组。
*/
private static int indexOf(Object o, Object[] elements,
int index, int fence) {
if (o == null) {
for (int i = index; i < fence; i++)
if (elements[i] == null)
return i;
} else {
for (int i = index; i < fence; i++)
if (o.equals(elements[i]))
return i;
}
return -1;
}
/**
* lastIndexOf的静态版本。
*/
private static int lastIndexOf(Object o, Object[] elements, int index) {
if (o == null) {
for (int i = index; i >= 0; i--)
if (elements[i] == null)
return i;
} else {
for (int i = index; i >= 0; i--)
if (o.equals(elements[i]))
return i;
}
return -1;
}
/**
* 如果此列表包含指定的元素，则返回{@code true}。
* 更正式地说，当且仅当此列表包含至少一个元素{@code e}时，才返回{@code true}（o == null？e == null：o.equals（e））。
*/
public boolean contains(Object o) {
Object[] elements = getArray();
return indexOf(o, elements, 0, elements.length) >= 0;
}
/**
* {@inheritDoc}
*/
public int indexOf(Object o) {
Object[] elements = getArray();
return indexOf(o, elements, 0, elements.length);
}
/**
* 返回指定元素在此列表中首次出现的索引，从{@code index}开始向前搜索；如果未找到该元素，则返回-1。
* 更正式地，返回最低索引{@code i}，使得（i> = index &&（e == null？get（i）== null：e.equals（get（i））））;或者如果-1没有这样的索引。
*
*/
public int indexOf(E e, int index) {
Object[] elements = getArray();
return indexOf(e, elements, index, elements.length);
}
/**
* {@inheritDoc}
*/
public int lastIndexOf(Object o) {
Object[] elements = getArray();
return lastIndexOf(o, elements, elements.length - 1);
}
/**
* 返回此列表中指定元素最后一次出现的索引，从{@code index}向后搜索，如果找不到该元素，则返回-1。
* 更正式地，返回最高索引{@code i}使得（i <= index &&（e == null？get（i）== null：e.equals（get（i））））或-1没有这样的索引。
*
*/
public int lastIndexOf(E e, int index) {
Object[] elements = getArray();
return lastIndexOf(e, elements, index);
}
/**
* 返回此列表的浅表副本。 （元素本身不会被复制。）
*
* @return a clone of this list
*/
public Object clone() {
try {
@SuppressWarnings("unchecked")
CopyOnWriteArrayList<E> clone =
(CopyOnWriteArrayList<E>) super.clone();
clone.resetLock();
return clone;
} catch (CloneNotSupportedException e) {
throw new InternalError();
}
}
/**
* 以正确的顺序（从第一个元素到最后一个元素）返回一个包含此列表中所有元素的数组。
* 返回的数组将是“安全的”，因为此列表不保留对其的引用。
* （换句话说，此方法必须分配一个新数组）。
* 因此，调用者可以自由修改返回的数组。
* 此方法充当基于数组的API和基于集合的API之间的桥梁。
*/
public Object[] toArray() {
Object[] elements = getArray();
return Arrays.copyOf(elements, elements.length);
}
/**
* 返回一个数组，该数组按适当顺序（从第一个元素到最后一个元素）包含此列表中的所有元素；返回数组的运行时类型是指定数组的运行时类型。
* 如果列表适合指定的数组，则将其返回。
* 否则，将使用指定数组的运行时类型和此列表的大小分配一个新数组。
* 如果此列表适合指定的数组并有剩余空间（即，数组中的元素多于此列表），则紧接列表末尾的数组中的元素将设置为{@code null}。
* （仅当调用者知道此列表不包含任何null元素时，此方法才可用于确定此列表的长度。
* ）像{@link
* 基于的API。
* 此外，此方法允许对输出数组的运行时类型进行精确控制，并且在某些情况下可以用于节省分配成本。
* 假设{@code x}是已知仅包含字符串的列表。
* 以下代码可用于将列表转储到新分配的{@code String}数组中：{@code String [] y = x.toArray（new String [0]）;}请注意，{@ code toArray（new Object [0]）}的功能与{@code toArray（）}相同。
*/
@SuppressWarnings("unchecked")
public <T> T[] toArray(T a[]) {
Object[] elements = getArray();
int len = elements.length;
if (a.length < len)
return (T[]) Arrays.copyOf(elements, len, a.getClass());
else {
System.arraycopy(elements, 0, a, 0, len);
if (a.length > len)
a[len] = null;
return a;
}
}
// Positional Access Operations
@SuppressWarnings("unchecked")
private E get(Object[] a, int index) {
return (E) a[index];
}
/**
* {@inheritDoc}
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E get(int index) {
return get(getArray(), index);
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E set(int index, E element) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
E oldValue = get(elements, index);
if (oldValue != element) {
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len);
newElements[index] = element;
setArray(newElements);
} else {
// Not quite a no-op; ensures volatile write semantics
setArray(elements);
}
return oldValue;
} finally {
lock.unlock();
}
}
/**
* 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
*/
public boolean add(E e) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len + 1);
newElements[len] = e;
setArray(newElements);
return true;
} finally {
lock.unlock();
}
}
/**
* 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).
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public void add(int index, E element) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+len);
Object[] newElements;
int numMoved = len - index;
if (numMoved == 0)
newElements = Arrays.copyOf(elements, len + 1);
else {
newElements = new Object[len + 1];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index, newElements, index + 1,
numMoved);
}
newElements[index] = element;
setArray(newElements);
} finally {
lock.unlock();
}
}
/**
* Removes the element at the specified position in this list.
* Shifts any subsequent elements to the left (subtracts one from their
* indices). Returns the element that was removed from the list.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public E remove(int index) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
E oldValue = get(elements, index);
int numMoved = len - index - 1;
if (numMoved == 0)
setArray(Arrays.copyOf(elements, len - 1));
else {
Object[] newElements = new Object[len - 1];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index + 1, newElements, index,
numMoved);
setArray(newElements);
}
return oldValue;
} finally {
lock.unlock();
}
}
/**
* Removes the first occurrence of the specified element from this list,
* if it is present. If this list does not contain the element, it is
* unchanged. More formally, removes the element with the lowest index
* {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>
* (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) {
Object[] snapshot = getArray();
int index = indexOf(o, snapshot, 0, snapshot.length);
return (index < 0) ? false : remove(o, snapshot, index);
}
/**
* A version of remove(Object) using the strong hint that given
* recent snapshot contains o at the given index.
*/
private boolean remove(Object o, Object[] snapshot, int index) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] current = getArray();
int len = current.length;
if (snapshot != current) findIndex: {
int prefix = Math.min(index, len);
for (int i = 0; i < prefix; i++) {
if (current[i] != snapshot[i] && eq(o, current[i])) {
index = i;
break findIndex;
}
}
if (index >= len)
return false;
if (current[index] == o)
break findIndex;
index = indexOf(o, current, index, len);
if (index < 0)
return false;
}
Object[] newElements = new Object[len - 1];
System.arraycopy(current, 0, newElements, 0, index);
System.arraycopy(current, index + 1,
newElements, index,
len - index - 1);
setArray(newElements);
return true;
} finally {
lock.unlock();
}
}
/**
* 从此列表中删除索引在{@code fromIndex}（包括）和{@code toIndex}（不包括）之间的所有元素。
* 将所有后续元素向左移动（减少其索引）。
* 此调用通过{@code（toIndex-fromIndex）}元素来缩短列表。
* （如果{@code toIndex == fromIndex}，则此操作无效。
* ）
* 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.)
*
* @param fromIndex index of first element to be removed
* @param toIndex index after last element to be removed
* @throws IndexOutOfBoundsException if fromIndex or toIndex out of range
* ({@code fromIndex < 0 || toIndex > size() || toIndex < fromIndex})
*/
void removeRange(int fromIndex, int toIndex) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || toIndex > len || toIndex < fromIndex)
throw new IndexOutOfBoundsException();
int newlen = len - (toIndex - fromIndex);
int numMoved = len - toIndex;
if (numMoved == 0)
setArray(Arrays.copyOf(elements, newlen));
else {
Object[] newElements = new Object[newlen];
System.arraycopy(elements, 0, newElements, 0, fromIndex);
System.arraycopy(elements, toIndex, newElements,
fromIndex, numMoved);
setArray(newElements);
}
} finally {
lock.unlock();
}
}
/**
* Appends the element, if not present.
*
* @param e element to be added to this list, if absent
* @return {@code true} if the element was added
*/
public boolean addIfAbsent(E e) {
Object[] snapshot = getArray();
return indexOf(e, snapshot, 0, snapshot.length) >= 0 ? false :
addIfAbsent(e, snapshot);
}
/**
* A version of addIfAbsent using the strong hint that given
* recent snapshot does not contain e.
*/
private boolean addIfAbsent(E e, Object[] snapshot) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] current = getArray();
int len = current.length;
if (snapshot != current) {
// Optimize for lost race to another addXXX operation
int common = Math.min(snapshot.length, len);
for (int i = 0; i < common; i++)
if (current[i] != snapshot[i] && eq(e, current[i]))
return false;
if (indexOf(e, current, common, len) >= 0)
return false;
}
Object[] newElements = Arrays.copyOf(current, len + 1);
newElements[len] = e;
setArray(newElements);
return true;
} finally {
lock.unlock();
}
}
/**
* Returns {@code true} if this list contains all of the elements of the
* specified collection.
*
* @param c collection to be checked for containment in this list
* @return {@code true} if this list contains all of the elements of the
* specified collection
* @throws NullPointerException if the specified collection is null
* @see
*/
public boolean containsAll(Collection<?> c) {
Object[] elements = getArray();
int len = elements.length;
for (Object e : c) {
if (indexOf(e, elements, 0, len) < 0)
return false;
}
return true;
}
/**
* 从此列表中删除指定集合中包含的所有其元素。由于需要内部临时阵列，因此在此类中此操作特别昂贵。
* Removes from this list all of its elements that are contained in
* the specified collection. This is a particularly expensive operation
* in this class because of the need for an internal temporary array.
*
* @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
*/
public boolean removeAll(Collection<?> c) {
if (c == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// temp array holds those elements we know we want to keep
int newlen = 0;
Object[] temp = new Object[len];
for (int i = 0; i < len; ++i) {
Object element = elements[i];
if (!c.contains(element))
temp[newlen++] = element;
}
if (newlen != len) {
setArray(Arrays.copyOf(temp, newlen));
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
/**
* 仅保留此列表中包含在指定集合中的元素。
* 换句话说，从该列表中删除所有未包含在指定集合中的元素。
*
* 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
*/
public boolean retainAll(Collection<?> c) {
if (c == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// temp array holds those elements we know we want to keep
int newlen = 0;
Object[] temp = new Object[len];
for (int i = 0; i < len; ++i) {
Object element = elements[i];
if (c.contains(element))
temp[newlen++] = element;
}
if (newlen != len) {
setArray(Arrays.copyOf(temp, newlen));
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
/**
* 按指定集合的迭代器返回的顺序，将指定集合中尚未包含在此列表中的所有元素追加到此列表的末尾。
*/
public int addAllAbsent(Collection<? extends E> c) {
Object[] cs = c.toArray();
if (cs.length == 0)
return 0;
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
int added = 0;
// uniquify and compact elements in cs
for (int i = 0; i < cs.length; ++i) {
Object e = cs[i];
if (indexOf(e, elements, 0, len) < 0 &&
indexOf(e, cs, 0, added) < 0)
cs[added++] = e;
}
if (added > 0) {
Object[] newElements = Arrays.copyOf(elements, len + added);
System.arraycopy(cs, 0, newElements, len, added);
setArray(newElements);
}
return added;
} finally {
lock.unlock();
}
}
/**
* Removes all of the elements from this list.
* The list will be empty after this call returns.
*/
public void clear() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
setArray(new Object[0]);
} finally {
lock.unlock();
}
}
/**
* 按照指定集合的迭代器返回的顺序，将指定集合中的所有元素追加到此列表的末尾。
*/
public boolean addAll(Collection<? extends E> c) {
Object[] cs = (c.getClass() == CopyOnWriteArrayList.class) ?
((CopyOnWriteArrayList<?>)c).getArray() : c.toArray();
if (cs.length == 0)
return false;
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (len == 0 && cs.getClass() == Object[].class)
setArray(cs);
else {
Object[] newElements = Arrays.copyOf(elements, len + cs.length);
System.arraycopy(cs, 0, newElements, len, cs.length);
setArray(newElements);
}
return true;
} finally {
lock.unlock();
}
}
/**
* 从指定位置开始，将指定集合中的所有元素插入此列表。
* 将当前位于该位置的元素（如果有）和任何后续元素右移（增加其索引）。
* 新元素将按照指定集合的迭代器返回的顺序显示在此列表中。
*
*/
public boolean addAll(int index, Collection<? extends E> c) {
Object[] cs = c.toArray();
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+len);
if (cs.length == 0)
return false;
int numMoved = len - index;
Object[] newElements;
if (numMoved == 0)
newElements = Arrays.copyOf(elements, len + cs.length);
else {
newElements = new Object[len + cs.length];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index,
newElements, index + cs.length,
numMoved);
}
System.arraycopy(cs, 0, newElements, index, cs.length);
setArray(newElements);
return true;
} finally {
lock.unlock();
}
}
public void forEach(Consumer<? super E> action) {
if (action == null) throw new NullPointerException();
Object[] elements = getArray();
int len = elements.length;
for (int i = 0; i < len; ++i) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
action.accept(e);
}
}
public boolean removeIf(Predicate<? super E> filter) {
if (filter == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
int newlen = 0;
Object[] temp = new Object[len];
for (int i = 0; i < len; ++i) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
if (!filter.test(e))
temp[newlen++] = e;
}
if (newlen != len) {
setArray(Arrays.copyOf(temp, newlen));
return true;
}
}
return false;
} finally {
lock.unlock();
}
}
public void replaceAll(UnaryOperator<E> operator) {
if (operator == null) throw new NullPointerException();
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len);
for (int i = 0; i < len; ++i) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
newElements[i] = operator.apply(e);
}
setArray(newElements);
} finally {
lock.unlock();
}
}
public void sort(Comparator<? super E> c) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
Object[] newElements = Arrays.copyOf(elements, elements.length);
@SuppressWarnings("unchecked") E[] es = (E[])newElements;
Arrays.sort(es, c);
setArray(newElements);
} finally {
lock.unlock();
}
}
/**
* Saves this list 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 list is emitted
* (int), followed by all of its elements (each an Object)
* in the proper order.
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
s.defaultWriteObject();
Object[] elements = getArray();
// Write out array length
s.writeInt(elements.length);
// Write out all elements in the proper order.
for (Object element : elements)
s.writeObject(element);
}
/**
* Reconstitutes this list 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 {
s.defaultReadObject();
// bind to new lock
resetLock();
// Read in array length and allocate array
int len = s.readInt();
SharedSecrets.getJavaOISAccess().checkArray(s, Object[].class, len);
Object[] elements = new Object[len];
// Read in all elements in the proper order.
for (int i = 0; i < len; i++)
elements[i] = s.readObject();
setArray(elements);
}
/**
* 返回此列表的字符串表示形式。
* 字符串表示形式由列表的元素的字符串表示形式组成，其顺序由列表的迭代器返回，并括在方括号（{@code“ []”}）中。
* 相邻元素由字符{@code“，”}（逗号和空格）分隔。
* 元素通过{@link String＃valueOf（Object）}转换为字符串。
*/
public String toString() {
return Arrays.toString(getArray());
}
/**
* 比较指定对象与此列表是否相等。
* 如果指定的对象与此对象相同，或者它也是一个{@link List}以及{@linkplain List＃iterator（）迭代器}在指定对象上返回的元素序列，则返回{@code true} list与迭代器在此列表上返回的序列相同。
* 如果两个序列的长度相同并且序列中相同位置的相应元素相等，则认为这两个序列相同。
* 如果{@code（e1 == null？e2 == null：e1.equals（e2））}，则两个元素{@code e1}和{@code e2}被视为相等。
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
List<?> list = (List<?>)(o);
Iterator<?> it = list.iterator();
Object[] elements = getArray();
int len = elements.length;
for (int i = 0; i < len; ++i)
if (!it.hasNext() || !eq(elements[i], it.next()))
return false;
if (it.hasNext())
return false;
return true;
}
/**
* Returns the hash code value for this list.
*
* <p>This implementation uses the definition in {@link List
*
* @return the hash code value for this list
*/
public int hashCode() {
int hashCode = 1;
Object[] elements = getArray();
int len = elements.length;
for (int i = 0; i < len; ++i) {
Object obj = elements[i];
hashCode = 31*hashCode + (obj==null ? 0 : obj.hashCode());
}
return hashCode;
}
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does <em>NOT</em> support the
* {@code remove} method.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator<E> iterator() {
return new COWIterator<E>(getArray(), 0);
}
/**
* {@inheritDoc}
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does <em>NOT</em> support the
* {@code remove}, {@code set} or {@code add} methods.
*/
public ListIterator<E> listIterator() {
return new COWIterator<E>(getArray(), 0);
}
/**
* {@inheritDoc}
*
* <p>The returned iterator provides a snapshot of the state of the list
* when the iterator was constructed. No synchronization is needed while
* traversing the iterator. The iterator does <em>NOT</em> support the
* {@code remove}, {@code set} or {@code add} methods.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator<E> listIterator(int index) {
Object[] elements = getArray();
int len = elements.length;
if (index < 0 || index > len)
throw new IndexOutOfBoundsException("Index: "+index);
return new COWIterator<E>(elements, index);
}
/**
* Returns a {@link Spliterator} over the elements in this list.
*
* <p>The {@code Spliterator} reports {@link Spliterator
* {@link Spliterator
* {@link Spliterator
*
* <p>The spliterator provides a snapshot of the state of the list
* when the spliterator was constructed. No synchronization is needed while
* operating on the spliterator.
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
public Spliterator<E> spliterator() {
return Spliterators.spliterator
(getArray(), Spliterator.IMMUTABLE | Spliterator.ORDERED);
}
static final class COWIterator<E> implements ListIterator<E> {
/** Snapshot of the array */
private final Object[] snapshot;
/** Index of element to be returned by subsequent call to next. */
private int cursor;
private COWIterator(Object[] elements, int initialCursor) {
cursor = initialCursor;
snapshot = elements;
}
public boolean hasNext() {
return cursor < snapshot.length;
}
public boolean hasPrevious() {
return cursor > 0;
}
@SuppressWarnings("unchecked")
public E next() {
if (! hasNext())
throw new NoSuchElementException();
return (E) snapshot[cursor++];
}
@SuppressWarnings("unchecked")
public E previous() {
if (! hasPrevious())
throw new NoSuchElementException();
return (E) snapshot[--cursor];
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor-1;
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code remove}
* is not supported by this iterator.
*/
public void remove() {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code set}
* is not supported by this iterator.
*/
public void set(E e) {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; {@code add}
* is not supported by this iterator.
*/
public void add(E e) {
throw new UnsupportedOperationException();
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
Object[] elements = snapshot;
final int size = elements.length;
for (int i = cursor; i < size; i++) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
action.accept(e);
}
cursor = size;
}
}
/**
* Returns a view of the portion of this list between
* {@code fromIndex}, inclusive, and {@code toIndex}, exclusive.
* The returned list is backed by this list, so changes in the
* returned list are reflected in this list.
*
* <p>The semantics of the list returned by this method become
* undefined if the backing list (i.e., this list) is modified in
* any way other than via the returned list.
*
* @param fromIndex low endpoint (inclusive) of the subList
* @param toIndex high endpoint (exclusive) of the subList
* @return a view of the specified range within this list
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public List<E> subList(int fromIndex, int toIndex) {
final ReentrantLock lock = this.lock;
lock.lock();
try {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || toIndex > len || fromIndex > toIndex)
throw new IndexOutOfBoundsException();
return new COWSubList<E>(this, fromIndex, toIndex);
} finally {
lock.unlock();
}
}
/**
* CopyOnWriteArrayList的子列表。
* 此类仅出于方便起见扩展了AbstractList，以避免必须定义addAll等。
* 这没有什么坏处，但是很浪费。
* 该类不需要或不使用AbstractList中的modCount机制，但是需要使用类似的机制检查并发修改。
* 在每个操作上，都会检查并更新我们希望后备列表使用的阵列。
* 由于我们对AbstractList中定义的所有基本操作都执行了此操作，因此一切都很好。
* 尽管效率低下，但这不值得改善。
* 从AbstractList继承的列表操作种类在COW子列表上已经非常慢，以至于增加一点空间/时间似乎都不引人注意。
*/
private static class COWSubList<E>
extends AbstractList<E>
implements RandomAccess
{
private final CopyOnWriteArrayList<E> l;
private final int offset;
private int size;
private Object[] expectedArray;
COWSubList(CopyOnWriteArrayList<E> list,
int fromIndex, int toIndex) {
l = list;
expectedArray = l.getArray();
offset = fromIndex;
size = toIndex - fromIndex;
}
private void checkForComodification() {
if (l.getArray() != expectedArray)
throw new ConcurrentModificationException();
}
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: "+index+
",Size: "+size);
}
public E set(int index, E element) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
rangeCheck(index);
checkForComodification();
E x = l.set(index+offset, element);
expectedArray = l.getArray();
return x;
} finally {
lock.unlock();
}
}
public E get(int index) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
rangeCheck(index);
checkForComodification();
return l.get(index+offset);
} finally {
lock.unlock();
}
}
public int size() {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
return size;
} finally {
lock.unlock();
}
}
public void add(int index, E element) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
if (index < 0 || index > size)
throw new IndexOutOfBoundsException();
l.add(index+offset, element);
expectedArray = l.getArray();
size++;
} finally {
lock.unlock();
}
}
public void clear() {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
l.removeRange(offset, offset+size);
expectedArray = l.getArray();
size = 0;
} finally {
lock.unlock();
}
}
public E remove(int index) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
rangeCheck(index);
checkForComodification();
E result = l.remove(index+offset);
expectedArray = l.getArray();
size--;
return result;
} finally {
lock.unlock();
}
}
public boolean remove(Object o) {
int index = indexOf(o);
if (index == -1)
return false;
remove(index);
return true;
}
public Iterator<E> iterator() {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
return new COWSubListIterator<E>(l, 0, offset, size);
} finally {
lock.unlock();
}
}
public ListIterator<E> listIterator(int index) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
if (index < 0 || index > size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
return new COWSubListIterator<E>(l, index, offset, size);
} finally {
lock.unlock();
}
}
public List<E> subList(int fromIndex, int toIndex) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
checkForComodification();
if (fromIndex < 0 || toIndex > size || fromIndex > toIndex)
throw new IndexOutOfBoundsException();
return new COWSubList<E>(l, fromIndex + offset,
toIndex + offset);
} finally {
lock.unlock();
}
}
public void forEach(Consumer<? super E> action) {
if (action == null) throw new NullPointerException();
int lo = offset;
int hi = offset + size;
Object[] a = expectedArray;
if (l.getArray() != a)
throw new ConcurrentModificationException();
if (lo < 0 || hi > a.length)
throw new IndexOutOfBoundsException();
for (int i = lo; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) a[i];
action.accept(e);
}
}
public void replaceAll(UnaryOperator<E> operator) {
if (operator == null) throw new NullPointerException();
final ReentrantLock lock = l.lock;
lock.lock();
try {
int lo = offset;
int hi = offset + size;
Object[] elements = expectedArray;
if (l.getArray() != elements)
throw new ConcurrentModificationException();
int len = elements.length;
if (lo < 0 || hi > len)
throw new IndexOutOfBoundsException();
Object[] newElements = Arrays.copyOf(elements, len);
for (int i = lo; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
newElements[i] = operator.apply(e);
}
l.setArray(expectedArray = newElements);
} finally {
lock.unlock();
}
}
public void sort(Comparator<? super E> c) {
final ReentrantLock lock = l.lock;
lock.lock();
try {
int lo = offset;
int hi = offset + size;
Object[] elements = expectedArray;
if (l.getArray() != elements)
throw new ConcurrentModificationException();
int len = elements.length;
if (lo < 0 || hi > len)
throw new IndexOutOfBoundsException();
Object[] newElements = Arrays.copyOf(elements, len);
@SuppressWarnings("unchecked") E[] es = (E[])newElements;
Arrays.sort(es, lo, hi, c);
l.setArray(expectedArray = newElements);
} finally {
lock.unlock();
}
}
public boolean removeAll(Collection<?> c) {
if (c == null) throw new NullPointerException();
boolean removed = false;
final ReentrantLock lock = l.lock;
lock.lock();
try {
int n = size;
if (n > 0) {
int lo = offset;
int hi = offset + n;
Object[] elements = expectedArray;
if (l.getArray() != elements)
throw new ConcurrentModificationException();
int len = elements.length;
if (lo < 0 || hi > len)
throw new IndexOutOfBoundsException();
int newSize = 0;
Object[] temp = new Object[n];
for (int i = lo; i < hi; ++i) {
Object element = elements[i];
if (!c.contains(element))
temp[newSize++] = element;
}
if (newSize != n) {
Object[] newElements = new Object[len - n + newSize];
System.arraycopy(elements, 0, newElements, 0, lo);
System.arraycopy(temp, 0, newElements, lo, newSize);
System.arraycopy(elements, hi, newElements,
lo + newSize, len - hi);
size = newSize;
removed = true;
l.setArray(expectedArray = newElements);
}
}
} finally {
lock.unlock();
}
return removed;
}
public boolean retainAll(Collection<?> c) {
if (c == null) throw new NullPointerException();
boolean removed = false;
final ReentrantLock lock = l.lock;
lock.lock();
try {
int n = size;
if (n > 0) {
int lo = offset;
int hi = offset + n;
Object[] elements = expectedArray;
if (l.getArray() != elements)
throw new ConcurrentModificationException();
int len = elements.length;
if (lo < 0 || hi > len)
throw new IndexOutOfBoundsException();
int newSize = 0;
Object[] temp = new Object[n];
for (int i = lo; i < hi; ++i) {
Object element = elements[i];
if (c.contains(element))
temp[newSize++] = element;
}
if (newSize != n) {
Object[] newElements = new Object[len - n + newSize];
System.arraycopy(elements, 0, newElements, 0, lo);
System.arraycopy(temp, 0, newElements, lo, newSize);
System.arraycopy(elements, hi, newElements,
lo + newSize, len - hi);
size = newSize;
removed = true;
l.setArray(expectedArray = newElements);
}
}
} finally {
lock.unlock();
}
return removed;
}
public boolean removeIf(Predicate<? super E> filter) {
if (filter == null) throw new NullPointerException();
boolean removed = false;
final ReentrantLock lock = l.lock;
lock.lock();
try {
int n = size;
if (n > 0) {
int lo = offset;
int hi = offset + n;
Object[] elements = expectedArray;
if (l.getArray() != elements)
throw new ConcurrentModificationException();
int len = elements.length;
if (lo < 0 || hi > len)
throw new IndexOutOfBoundsException();
int newSize = 0;
Object[] temp = new Object[n];
for (int i = lo; i < hi; ++i) {
@SuppressWarnings("unchecked") E e = (E) elements[i];
if (!filter.test(e))
temp[newSize++] = e;
}
if (newSize != n) {
Object[] newElements = new Object[len - n + newSize];
System.arraycopy(elements, 0, newElements, 0, lo);
System.arraycopy(temp, 0, newElements, lo, newSize);
System.arraycopy(elements, hi, newElements,
lo + newSize, len - hi);
size = newSize;
removed = true;
l.setArray(expectedArray = newElements);
}
}
} finally {
lock.unlock();
}
return removed;
}
public Spliterator<E> spliterator() {
int lo = offset;
int hi = offset + size;
Object[] a = expectedArray;
if (l.getArray() != a)
throw new ConcurrentModificationException();
if (lo < 0 || hi > a.length)
throw new IndexOutOfBoundsException();
return Spliterators.spliterator
(a, lo, hi, Spliterator.IMMUTABLE | Spliterator.ORDERED);
}
}
private static class COWSubListIterator<E> implements ListIterator<E> {
private final ListIterator<E> it;
private final int offset;
private final int size;
COWSubListIterator(List<E> l, int index, int offset, int size) {
this.offset = offset;
this.size = size;
it = l.listIterator(index+offset);
}
public boolean hasNext() {
return nextIndex() < size;
}
public E next() {
if (hasNext())
return it.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public E previous() {
if (hasPrevious())
return it.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return it.nextIndex() - offset;
}
public int previousIndex() {
return it.previousIndex() - offset;
}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(E e) {
throw new UnsupportedOperationException();
}
public void add(E e) {
throw new UnsupportedOperationException();
}
@Override
public void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
int s = size;
ListIterator<E> i = it;
while (nextIndex() < s) {
action.accept(i.next());
}
}
}
// Support for resetting lock while deserializing
private void resetLock() {
UNSAFE.putObjectVolatile(this, lockOffset, new ReentrantLock());
}
private static final sun.misc.Unsafe UNSAFE;
private static final long lockOffset;
static {
try {
UNSAFE = sun.misc.Unsafe.getUnsafe();
Class<?> k = CopyOnWriteArrayList.class;
lockOffset = UNSAFE.objectFieldOffset
(k.getDeclaredField("lock"));
} catch (Exception e) {
throw new Error(e);
}
}
}
