Mega Code Archive
Copy On Write ArrayList
<![CDATA[
/*
* Written by Doug Lea with assistance from members of JCP JSR-166
* Expert Group. Adapted and released, under explicit permission,
* from JDK ArrayList.java which carries the following copyright:
*
* Copyright 1997 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
import java.util.AbstractList;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;
import java.util.NoSuchElementException;
import java.util.RandomAccess;
/**
* A thread-safe variant of {@link java.util.ArrayList} in which all mutative
* operations (<tt>add</tt>, <tt>set</tt>, and so on) are implemented by
* making a fresh copy of the underlying array.
*
* <p> This is ordinarily too costly, but may be <em>more</em> efficient
* than alternatives when traversal operations vastly outnumber
* mutations, and is useful when you cannot or don't want to
* synchronize traversals, yet need to preclude interference among
* concurrent threads. The "snapshot" style iterator method uses a
* reference to the state of the array at the point that the iterator
* was created. This array never changes during the lifetime of the
* iterator, so interference is impossible and the iterator is
* guaranteed not to throw <tt>ConcurrentModificationException</tt>.
* The iterator will not reflect additions, removals, or changes to
* the list since the iterator was created. Element-changing
* operations on iterators themselves (<tt>remove</tt>, <tt>set</tt>, and
* <tt>add</tt>) are not supported. These methods throw
* <tt>UnsupportedOperationException</tt>.
*
* <p>All elements are permitted, including <tt>null</tt>.
*
* <p>This class is a member of the
* <a href="{@docRoot}/../guide/collections/index.html">
* Java Collections Framework</a>.
*
* @since 1.5
* @author Doug Lea
*/
public class CopyOnWriteArrayList
implements List, RandomAccess, Cloneable, java.io.Serializable {
private static final long serialVersionUID = 8673264195747942595L;
/** The array, accessed only via getArray/setArray. */
private volatile transient Object[] array;
/**
* This has been made public to support more efficient iteration.
* <strong>DO NOT MODIFY this array upon getting it</strong>.
* Otherwise you risk wreaking havoc on your list. In fact, if you are
* not the author of this comment, you probably shouldn't use it at all.
* @return this lists internal array
*/
public Object[] getArray() { return array; }
void setArray(Object[] a) { array = a; }
/**
* Creates an empty list.
*/
public CopyOnWriteArrayList() {
setArray(new Object[0]);
}
/**
* Creates a list containing the elements of the specified
* collection, in the order they are returned by the collection's
* iterator.
*
* @param c the collection of initially held elements
* @throws NullPointerException if the specified collection is null
*/
public CopyOnWriteArrayList(Collection c) {
Object[] elements = new Object[c.size()];
int size = 0;
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
elements[size++] = e;
}
setArray(elements);
}
/**
* Creates a list holding a copy of the given array.
*
* @param toCopyIn the array (a copy of this array is used as the
* internal array)
* @throws NullPointerException if the specified array is null
*/
public CopyOnWriteArrayList(Object[] toCopyIn) {
copyIn(toCopyIn, 0, toCopyIn.length);
}
/**
* Replaces the held array with a copy of the <tt>n</tt> elements
* of the provided array, starting at position <tt>first</tt>. To
* copy an entire array, call with arguments (array, 0,
* array.length).
* @param toCopyIn the array. A copy of the indicated elements of
* this array is used as the internal array.
* @param first The index of first position of the array to
* start copying from.
* @param n the number of elements to copy. This will be the new size of
* the list.
*/
private void copyIn(Object[] toCopyIn, int first, int n) {
int limit = first + n;
if (limit > toCopyIn.length)
throw new IndexOutOfBoundsException();
Object[] newElements = copyOfRange(toCopyIn, first, limit,
Object[].class);
synchronized (this) { setArray(newElements); }
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
public int size() {
return getArray().length;
}
/**
* 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;
}
/**
* Test for equality, coping with nulls.
*/
private static boolean eq(Object o1, Object o2) {
return (o1 == null ? o2 == null : o1.equals(o2));
}
/**
* static version of indexOf, to allow repeated calls without
* needing to re-acquire array each time.
* @param o element to search for
* @param elements the array
* @param index first index to search
* @param fence one past last index to search
* @return index of element, or -1 if absent
*/
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;
}
/**
* static version of lastIndexOf.
* @param o element to search for
* @param elements the array
* @param index first index to search
* @return index of element, or -1 if absent
*/
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;
}
/**
* 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) {
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);
}
/**
* Returns the index of the first occurrence of the specified element in
* this list, searching forwards from <tt>index</tt>, or returns -1 if
* the element is not found.
* More formally, returns the lowest index <tt>i</tt> such that
* <tt>(i >= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param e element to search for
* @param index index to start searching from
* @return the index of the first occurrence of the element in
* this list at position <tt>index</tt> or later in the list;
* <tt>-1</tt> if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is negative
*/
public int indexOf(Object 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);
}
/**
* Returns the index of the last occurrence of the specified element in
* this list, searching backwards from <tt>index</tt>, or returns -1 if
* the element is not found.
* More formally, returns the highest index <tt>i</tt> such that
* <tt>(i <= index && (e==null ? get(i)==null : e.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param e element to search for
* @param index index to start searching backwards from
* @return the index of the last occurrence of the element at position
* less than or equal to <tt>index</tt> in this list;
* -1 if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is greater
* than or equal to the current size of this list
*/
public int lastIndexOf(Object e, int index) {
Object[] elements = getArray();
return lastIndexOf(e, elements, index);
}
/**
* Returns a shallow copy of this list. (The elements themselves
* are not copied.)
*
* @return a clone of this list
*/
public Object clone() {
try {
return super.clone();
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError();
}
}
/**
* 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 the elements in this list
*/
public Object[] toArray() {
Object[] elements = getArray();
return copyOf(elements, elements.length);
}
/**
* 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 this list fits in the specified array with room to spare
* (i.e., the array has more elements than this list), the element in
* the array immediately following the end of the list is set to
* <tt>null</tt>. (This is useful in determining the length of this
* list <i>only</i> if the caller knows that this list does not contain
* any null elements.)
*
* <p>Like the {@link #toArray()} method, this method acts as bridge between
* array-based and collection-based APIs. Further, this method allows
* precise control over the runtime type of the output array, and may,
* under certain circumstances, be used to save allocation costs.
*
* <p>Suppose <tt>x</tt> is a list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of <tt>String</tt>:
*
* <pre>
* String[] y = x.toArray(new String[0]);</pre>
*
* Note that <tt>toArray(new Object[0])</tt> is identical in function to
* <tt>toArray()</tt>.
*
* @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 all the elements in this 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
*/
public Object[] toArray(Object a[]) {
Object[] elements = getArray();
int len = elements.length;
if (a.length < len)
return 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
/**
* {@inheritDoc}
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public Object get(int index) {
return (getArray()[index]);
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized Object set(int index, Object element) {
Object[] elements = getArray();
int len = elements.length;
Object oldValue = elements[index];
if (oldValue != element) {
Object[] newElements = copyOf(elements, len);
newElements[index] = element;
setArray(newElements);
}
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 per the spec for {@link Collection#add})
*/
public boolean add(Object e) {
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = copyOf(elements, len + 1);
newElements[len] = e;
setArray(newElements);
}
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).
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public synchronized void add(int index, Object element) {
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 = 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);
}
/**
* 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 synchronized Object remove(int index) {
Object[] elements = getArray();
int len = elements.length;
Object oldValue = elements[index];
int numMoved = len - index - 1;
if (numMoved == 0)
setArray(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;
}
/**
* 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
* <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 synchronized boolean remove(Object o) {
Object[] elements = getArray();
int len = elements.length;
if (len != 0) {
// Copy while searching for element to remove
// This wins in the normal case of element being present
int newlen = len - 1;
Object[] newElements = new Object[newlen];
for (int i = 0; i < newlen; ++i) {
if (eq(o, elements[i])) {
// found one; copy remaining and exit
for (int k = i + 1; k < len; ++k)
newElements[k-1] = elements[k];
setArray(newElements);
return true;
} else
newElements[i] = elements[i];
}
// special handling for last cell
if (eq(o, elements[newlen])) {
setArray(newElements);
return true;
}
}
return false;
}
/**
* Removes from this list all of the elements whose index is between
* <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.
* Shifts any succeeding elements to the left (reduces their index).
* This call shortens the list by <tt>(toIndex - fromIndex)</tt> elements.
* (If <tt>toIndex==fromIndex</tt>, 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 (fromIndex < 0 || fromIndex >= size() || toIndex
* > size() || toIndex < fromIndex)
*/
private synchronized void removeRange(int fromIndex, int toIndex) {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || fromIndex >= len ||
toIndex > len || toIndex < fromIndex)
throw new IndexOutOfBoundsException();
int newlen = len - (toIndex - fromIndex);
int numMoved = len - toIndex;
if (numMoved == 0)
setArray(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);
}
}
/**
* Append the element if not present.
*
* @param e element to be added to this list, if absent
* @return <tt>true</tt> if the element was added
*/
public synchronized boolean addIfAbsent(Object e) {
// Copy while checking if already present.
// This wins in the most common case where it is not present
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = new Object[len + 1];
for (int i = 0; i < len; ++i) {
if (eq(e, elements[i]))
return false; // exit, throwing away copy
else
newElements[i] = elements[i];
}
newElements[len] = e;
setArray(newElements);
return true;
}
/**
* Returns <tt>true</tt> if this list contains all of the elements of the
* specified collection.
*
* @param c collection to be checked for containment in this list
* @return <tt>true</tt> if this list contains all of the elements of the
* specified collection
* @throws NullPointerException if the specified collection is null
* @see #contains(Object)
*/
public boolean containsAll(Collection c) {
Object[] elements = getArray();
int len = elements.length;
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
if (indexOf(e, elements, 0, len) < 0)
return false;
}
return true;
}
/**
* 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 <tt>true</tt> 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 (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
*/
public synchronized boolean removeAll(Collection c) {
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(copyOfRange(temp, 0, newlen, Object[].class));
return true;
}
}
return 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 <tt>true</tt> 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 (optional)
* @throws NullPointerException if this list contains a null element and the
* specified collection does not permit null elements (optional),
* or if the specified collection is null
* @see #remove(Object)
*/
public synchronized boolean retainAll(Collection c) {
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(copyOfRange(temp, 0, newlen, Object[].class));
return true;
}
}
return false;
}
/**
* Appends all of the elements in the specified collection that
* are not already contained in this list, to the end of
* this list, in the order that they are returned by the
* specified collection's iterator.
*
* @param c collection containing elements to be added to this list
* @return the number of elements added
* @throws NullPointerException if the specified collection is null
* @see #addIfAbsent(Object)
*/
public int addAllAbsent(Collection c) {
int numNew = c.size();
if (numNew == 0)
return 0;
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] temp = new Object[numNew];
int added = 0;
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
if (indexOf(e, elements, 0, len) < 0 &&
indexOf(e, temp, 0, added) < 0)
temp[added++] = e;
}
if (added != 0) {
Object[] newElements = new Object[len + added];
System.arraycopy(elements, 0, newElements, 0, len);
System.arraycopy(temp, 0, newElements, len, added);
setArray(newElements);
}
return added;
}
}
/**
* Removes all of the elements from this list.
* The list will be empty after this call returns.
*/
public synchronized void clear() {
setArray(new Object[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.
*
* @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
* @see #add(Object)
*/
public boolean addAll(Collection c) {
int numNew = c.size();
if (numNew == 0)
return false;
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
Object[] newElements = new Object[len + numNew];
System.arraycopy(elements, 0, newElements, 0, len);
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
newElements[len++] = e;
}
setArray(newElements);
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 this 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
* @see #add(int,Object)
*/
public boolean addAll(int index, Collection c) {
int numNew = c.size();
synchronized (this) {
Object[] elements = getArray();
int len = elements.length;
if (index > len || index < 0)
throw new IndexOutOfBoundsException("Index: " + index +
", Size: "+ len);
if (numNew == 0)
return false;
int numMoved = len - index;
Object[] newElements;
if (numMoved == 0)
newElements = copyOf(elements, len + numNew);
else {
newElements = new Object[len + numNew];
System.arraycopy(elements, 0, newElements, 0, index);
System.arraycopy(elements, index,
newElements, index + numNew,
numMoved);
}
for (Iterator itr = c.iterator(); itr.hasNext(); ) {
Object e = itr.next();
newElements[index++] = e;
}
setArray(newElements);
return true;
}
}
/**
* Save the state of the list to a stream (i.e., serialize it).
*
* @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.
* @param s the stream
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException{
// Write out element count, and any hidden stuff
s.defaultWriteObject();
Object[] elements = getArray();
int len = elements.length;
// Write out array length
s.writeInt(len);
// Write out all elements in the proper order.
for (int i = 0; i < len; i++)
s.writeObject(elements[i]);
}
/**
* Reconstitute the list from a stream (i.e., deserialize it).
* @param s the stream
*/
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in size, and any hidden stuff
s.defaultReadObject();
// Read in array length and allocate array
int len = s.readInt();
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);
}
/**
* Returns a string representation of this list, containing
* the String representation of each element.
*/
public String toString() {
Object[] elements = getArray();
int maxIndex = elements.length - 1;
StringBuffer buf = new StringBuffer();
buf.append("[");
for (int i = 0; i <= maxIndex; i++) {
buf.append(String.valueOf(elements[i]));
if (i < maxIndex)
buf.append(", ");
}
buf.append("]");
return buf.toString();
}
/**
* Compares the specified object with this list for equality.
* Returns true if and only if the specified object is also a {@link
* List}, both lists have the same size, and all corresponding pairs
* of elements in the two lists are <em>equal</em>. (Two elements
* <tt>e1</tt> and <tt>e2</tt> are <em>equal</em> if <tt>(e1==null ?
* e2==null : e1.equals(e2))</tt>.) In other words, two lists are
* defined to be equal if they contain the same elements in the same
* order.
*
* @param o the object to be compared for equality with this list
* @return <tt>true</tt> if the specified object is equal to this list
*/
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof List))
return false;
List l2 = (List)(o);
if (size() != l2.size())
return false;
ListIterator e1 = listIterator();
ListIterator e2 = l2.listIterator();
while (e1.hasNext()) {
if (!eq(e1.next(), e2.next()))
return false;
}
return true;
}
/**
* Returns the hash code value for this list.
*
* <p>This implementation uses the definition in {@link List#hashCode}.
*
* @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
* <tt>remove</tt> method.
*
* @return an iterator over the elements in this list in proper sequence
*/
public Iterator iterator() {
return new COWIterator(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
* <tt>remove</tt>, <tt>set</tt> or <tt>add</tt> methods.
*/
public ListIterator listIterator() {
return new COWIterator(getArray(), 0);
}
/**
* {@inheritDoc}
*
* <p>The list iterator returned by this implementation will throw an
* <tt>UnsupportedOperationException</tt> in its <tt>remove</tt>,
* <tt>set</tt> and <tt>add</tt> methods.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
public ListIterator listIterator(final int index) {
Object[] elements = getArray();
int len = elements.length;
if (index < 0 || index > len)
throw new IndexOutOfBoundsException("Index: " + index);
return new COWIterator(getArray(), index);
}
private static class COWIterator implements ListIterator {
/** 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;
}
public Object next() {
try {
return (snapshot[cursor++]);
} catch (IndexOutOfBoundsException ex) {
throw new NoSuchElementException();
}
}
public Object previous() {
try {
return (snapshot[--cursor]);
} catch (IndexOutOfBoundsException e) {
throw new NoSuchElementException();
}
}
public int nextIndex() {
return cursor;
}
public int previousIndex() {
return cursor - 1;
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; <tt>remove</tt>
* is not supported by this iterator.
*/
public void remove() {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; <tt>set</tt>
* is not supported by this iterator.
*/
public void set(Object e) {
throw new UnsupportedOperationException();
}
/**
* Not supported. Always throws UnsupportedOperationException.
* @throws UnsupportedOperationException always; <tt>add</tt>
* is not supported by this iterator.
*/
public void add(Object e) {
throw new UnsupportedOperationException();
}
}
/**
* Returns a view of the portion of this list between
* <tt>fromIndex</tt>, inclusive, and <tt>toIndex</tt>, exclusive.
* The returned list is backed by this list, so changes in the
* returned list are reflected in this list, and vice-versa.
* While mutative operations are supported, they are probably not
* very useful for CopyOnWriteArrayLists.
*
* <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 the list, or otherwise perturb it in such a fashion
* that iterations in progress may yield incorrect results.)
*
* @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 synchronized List subList(int fromIndex, int toIndex) {
Object[] elements = getArray();
int len = elements.length;
if (fromIndex < 0 || toIndex > len || fromIndex > toIndex)
throw new IndexOutOfBoundsException();
return new COWSubList(this, fromIndex, toIndex);
}
/**
* Sublist for CopyOnWriteArrayList.
* This class extends AbstractList merely for convenience, to
* avoid having to define addAll, etc. This doesn't hurt, but
* is wasteful. This class does not need or use modCount
* mechanics in AbstractList, but does need to check for
* concurrent modification using similar mechanics. On each
* operation, the array that we expect the backing list to use
* is checked and updated. Since we do this for all of the
* base operations invoked by those defined in AbstractList,
* all is well. While inefficient, this is not worth
* improving. The kinds of list operations inherited from
* AbstractList are already so slow on COW sublists that
* adding a bit more space/time doesn't seem even noticeable.
*/
private static class COWSubList extends AbstractList {
private final CopyOnWriteArrayList l;
private final int offset;
private int size;
private Object[] expectedArray;
// only call this holding l's lock
private COWSubList(CopyOnWriteArrayList list,
int fromIndex, int toIndex) {
l = list;
expectedArray = l.getArray();
offset = fromIndex;
size = toIndex - fromIndex;
}
// only call this holding l's lock
private void checkForComodification() {
if (l.getArray() != expectedArray)
throw new ConcurrentModificationException();
}
// only call this holding l's lock
private void rangeCheck(int index) {
if (index < 0 || index >= size)
throw new IndexOutOfBoundsException("Index: " + index +
",Size: " + size);
}
public Object set(int index, Object element) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
Object x = l.set(index + offset, element);
expectedArray = l.getArray();
return x;
}
}
public Object get(int index) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
return l.get(index + offset);
}
}
public int size() {
synchronized (l) {
checkForComodification();
return size;
}
}
public void add(int index, Object element) {
synchronized (l) {
checkForComodification();
if (index<0 || index>size)
throw new IndexOutOfBoundsException();
l.add(index + offset, element);
expectedArray = l.getArray();
size++;
}
}
public void clear() {
synchronized (l) {
checkForComodification();
l.removeRange(offset, offset+size);
expectedArray = l.getArray();
size = 0;
}
}
public Object remove(int index) {
synchronized (l) {
rangeCheck(index);
checkForComodification();
Object result = l.remove(index + offset);
expectedArray = l.getArray();
size--;
return result;
}
}
public Iterator iterator() {
synchronized (l) {
checkForComodification();
return new COWSubListIterator(l, 0, offset, size);
}
}
public ListIterator listIterator(final int index) {
synchronized (l) {
checkForComodification();
if (index<0 || index>size)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+size);
return new COWSubListIterator(l, index, offset, size);
}
}
public List subList(int fromIndex, int toIndex) {
synchronized (l) {
checkForComodification();
if (fromIndex<0 || toIndex>size)
throw new IndexOutOfBoundsException();
return new COWSubList(l, fromIndex + offset,
toIndex + offset);
}
}
}
private static class COWSubListIterator implements ListIterator {
private final ListIterator i;
private final int offset;
private final int size;
private COWSubListIterator(List l, int index, int offset,
int size) {
this.offset = offset;
this.size = size;
i = l.listIterator(index + offset);
}
public boolean hasNext() {
return nextIndex() < size;
}
public Object next() {
if (hasNext())
return i.next();
else
throw new NoSuchElementException();
}
public boolean hasPrevious() {
return previousIndex() >= 0;
}
public Object previous() {
if (hasPrevious())
return i.previous();
else
throw new NoSuchElementException();
}
public int nextIndex() {
return i.nextIndex() - offset;
}
public int previousIndex() {
return i.previousIndex() - offset;
}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(Object e) {
throw new UnsupportedOperationException();
}
public void add(Object e) {
throw new UnsupportedOperationException();
}
}
// // Support for resetting lock while deserializing
// private static final Unsafe unsafe = Unsafe.getUnsafe();
// private static final long lockOffset;
// static {
// try {
// lockOffset = unsafe.objectFieldOffset
// (CopyOnWriteArrayList.class.getDeclaredField("lock"));
// } catch (Exception ex) { throw new Error(ex); }
// }
// private void resetLock() {
// unsafe.putObjectVolatile(this, lockOffset, new ReentrantLock());
// }
//
// Temporary emulations of anticipated new j.u.Arrays functions
private static Object[] copyOfRange(Object[] original, int from, int to,
Class newType) {
int newLength = to - from;
if (newLength < 0)
throw new IllegalArgumentException(from + " > " + to);
Object[] copy = (Object[]) java.lang.reflect.Array.newInstance
(newType.getComponentType(), newLength);
System.arraycopy(original, from, copy, 0,
Math.min(original.length - from, newLength));
return copy;
}
private static Object[] copyOf(Object[] original, int newLength,
Class newType) {
Object[] copy = (Object[]) java.lang.reflect.Array.newInstance
(newType.getComponentType(), newLength);
System.arraycopy(original, 0, copy, 0,
Math.min(original.length, newLength));
return copy;
}
private static Object[] copyOf(Object[] original, int newLength) {
return copyOf(original, newLength, original.getClass());
}
}
]]>