/*
* Copyright 2000-2012 JetBrains s.r.o.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.intellij.util.containers;
import com.intellij.util.ArrayUtil;
import com.intellij.util.ArrayUtilRt;
import com.intellij.util.concurrency.AtomicFieldUpdater;
import org.jetbrains.annotations.NotNull;
import org.jetbrains.annotations.Nullable;
import java.util.*;
/**
* This class is a
* - lock-free (CAS instead of ReentrantLock)
* - less-memory (no lock field)
* - less-garbage (does not create Object[0] arrays)
* - non-cloneable, non-serializable, no-subList-method variant of {@link java.util.concurrent.CopyOnWriteArrayList}.
* It generally is faster than COWAL in case of low write-contention.
* (Note that it is not advisable to use COWAL in high write-contention code anyway, consider using {@link ConcurrentHashMap}) instead)
*/
class LockFreeCopyOnWriteArrayList<E> implements List<E>, RandomAccess {
@SuppressWarnings("FieldMayBeFinal")
private volatile Object[] array;
LockFreeCopyOnWriteArrayList() {
array = ArrayUtil.EMPTY_OBJECT_ARRAY;
}
LockFreeCopyOnWriteArrayList(@NotNull Collection<? extends E> c) {
array = c.isEmpty() ? ArrayUtil.EMPTY_OBJECT_ARRAY : c.toArray();
}
@NotNull
Object[] getArray() {
return array;
}
private static final AtomicFieldUpdater<LockFreeCopyOnWriteArrayList, Object[]> ARRAY_UPDATER
= AtomicFieldUpdater.forFieldOfType(LockFreeCopyOnWriteArrayList.class, Object[].class);
private boolean replaceArray(@NotNull Object[] oldArray, @NotNull Object[] newArray) {
return ARRAY_UPDATER.compareAndSet(this, oldArray, newArray);
}
/**
* Returns the number of elements in this list.
*
* @return the number of elements in this list
*/
@Override
public int size() {
return array.length;
}
/**
* Returns <tt>true</tt> if this list contains no elements.
*
* @return <tt>true</tt> if this list contains no elements
*/
@Override
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, @NotNull 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, @NotNull 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
*/
@Override
public boolean contains(Object o) {
Object[] elements = array;
return indexOf(o, elements, 0, elements.length) >= 0;
}
/**
* {@inheritDoc}
*/
@Override
public int indexOf(Object o) {
Object[] elements = array;
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(E e, int index) {
Object[] elements = array;
return indexOf(e, elements, index, elements.length);
}
/**
* {@inheritDoc}
*/
@Override
public int lastIndexOf(Object o) {
Object[] elements = array;
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(E e, int index) {
Object[] elements = array;
return lastIndexOf(e, elements, index);
}
/**
* Returns an array containing all of the elements in this list
* in proper sequence (from first to last element).
* <p/>
* <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/>
* <p>This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all the elements in this list
*/
@NotNull
@Override
public Object[] toArray() {
Object[] elements = array;
if (elements.length == 0) return ArrayUtilRt.EMPTY_OBJECT_ARRAY;
return Arrays.copyOf(elements, elements.length, Object[].class);
}
/**
* 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/>
* <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/>
* <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/>
* <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>:
* <p/>
* <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
*/
@NotNull
@Override
@SuppressWarnings("unchecked")
public <T> T[] toArray(@NotNull T[] a) {
Object[] elements = array;
int len = elements.length;
if (a.length < len) {
return (T[])Arrays.copyOf(elements, len, a.getClass());
}
System.arraycopy(elements, 0, a, 0, len);
if (a.length > len) {
a[len] = null;
}
return a;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
private E get(@NotNull Object[] a, int index) {
return (E)a[index];
}
/**
* {@inheritDoc}
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public E get(int index) {
return get(array, index);
}
/**
* Replaces the element at the specified position in this list with the
* specified element.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@Override
public E set(int index, E element) {
E oldValue;
Object[] elements;
Object[] newElements;
do {
elements = array;
oldValue = get(elements, index);
if (oldValue == element) {
// Not quite a no-op; ensures volatile write semantics
newElements = elements;
}
else {
newElements = createArraySet(elements, index, element);
}
} while(!replaceArray(elements, newElements));
return oldValue;
}
@NotNull
private static Object[] createArraySet(@NotNull Object[] elements, int index, Object element) {
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len, Object[].class);
newElements[index] = element;
return newElements;
}
/**
* Appends the specified element to the end of this list.
*
* @param e element to be appended to this list
* @return <tt>true</tt> (as specified by {@link java.util.Collection#add})
*/
@Override
public boolean add(E e) {
while (true) {
Object[] elements = array;
Object[] newElements = createArrayAdd(elements, e);
if (replaceArray(elements, newElements)) break;
}
return true;
}
@NotNull
private Object[] createArrayAdd(@NotNull Object[] elements, E e) {
int len = elements.length;
Object[] newElements = new Object[len + 1];
if (len != 0) {
System.arraycopy(elements, 0, newElements, 0, len);
}
newElements[len] = e;
return newElements;
}
/**
* 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}
*/
@Override
public void add(int index, E element) {
while (true) {
Object[] elements = array;
Object[] newElements = createArrayAdd(elements, index, element);
if (replaceArray(elements, newElements)) break;
}
}
@NotNull
private Object[] createArrayAdd(@NotNull Object[] elements, int index, E element) {
int len = elements.length;
if (index > len || index < 0) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + len);
}
int numMoved = len - index;
Object[] newElements = new Object[len + 1];
if (index != 0) {
System.arraycopy(elements, 0, newElements, 0, index);
}
if (numMoved != 0) {
System.arraycopy(elements, index, newElements, index + 1, numMoved);
}
newElements[index] = element;
return 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}
*/
@Override
public E remove(int index) {
E oldValue;
while (true) {
Object[] elements = array;
Object[] newElements = createArrayRemove(elements, index);
if (replaceArray(elements, newElements)) {
oldValue = get(elements, index);
break;
}
}
return oldValue;
}
@NotNull
private static Object[] createArrayRemove(@NotNull Object[] elements, int index) {
int len = elements.length;
int numMoved = len - index - 1;
Object[] newElements = len == 1 ? ArrayUtilRt.EMPTY_OBJECT_ARRAY : new Object[len - 1];
if (index != 0) {
System.arraycopy(elements, 0, newElements, 0, index);
}
if (numMoved != 0) {
System.arraycopy(elements, index + 1, newElements, index, numMoved);
}
return newElements;
}
/**
* 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
*/
@Override
public boolean remove(Object o) {
while (true) {
Object[] elements = array;
Object[] newElements = createArrayRemove(elements, o);
if (newElements == null) {
return false;
}
if (replaceArray(elements, newElements)) return true;
}
}
// null means not found
@Nullable
private static Object[] createArrayRemove(@NotNull Object[] elements, Object o) {
int len = elements.length;
if (len == 0) {
return null;
}
// Copy while searching for element to remove
// This wins in the normal case of element being present
int newLen = len - 1;
Object[] newElements = newLen == 0 ? ArrayUtilRt.EMPTY_OBJECT_ARRAY : new Object[newLen];
int i;
for (i = newLen; i != 0; --i) {
Object element = elements[i];
if (eq(o, element)) {
// found one; copy remaining and exit
System.arraycopy(elements, 0, newElements, 0, i);
break;
}
newElements[i-1] = element;
}
// special handling for last cell
if (i == 0 && !eq(o, elements[0])) {
return null;
}
return newElements;
}
/**
* 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
* ({@code{fromIndex < 0 || toIndex > size() || toIndex < fromIndex})
*/
private void removeRange(int fromIndex, int toIndex) {
Object[] elements;
Object[] newElements;
do {
elements = array;
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) {
newElements = Arrays.copyOf(elements, newlen, Object[].class);
}
else {
newElements = new Object[newlen];
System.arraycopy(elements, 0, newElements, 0, fromIndex);
System.arraycopy(elements, toIndex, newElements, fromIndex, numMoved);
}
}
while (!replaceArray(elements, 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 boolean addIfAbsent(E e) {
Object[] elements;
Object[] newElements;
do {
// Copy while checking if already present.
// This wins in the most common case where it is not present
elements = array;
int len = elements.length;
newElements = new Object[len + 1];
for (int i = 0; i < len; ++i) {
if (eq(e, elements[i])) {
return false; // exit, throwing away copy
}
newElements[i] = elements[i];
}
newElements[len] = e;
}
while (!replaceArray(elements, 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)
*/
@Override
public boolean containsAll(@NotNull Collection<?> c) {
Object[] elements = array;
int len = elements.length;
for (Object e : c) {
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
* (<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 #remove(Object)
*/
@Override
public boolean removeAll(@NotNull Collection<?> c) {
while (true) {
Object[] elements = array;
Object[] newElements = createArrayRemoveAll(elements, c);
if (newElements == null) return false;
if (replaceArray(elements, newElements)) return true;
}
}
// null means not found
@Nullable
private static Object[] createArrayRemoveAll(@NotNull Object[] elements, @NotNull Collection<?> c) {
int len = elements.length;
if (len == 0) {
return null;
}
// temp array holds those elements we know we want to keep
int newLen = 0;
Object[] temp = new Object[len];
for (Object element : elements) {
if (!c.contains(element)) {
temp[newLen++] = element;
}
}
if (newLen == len) {
return null;
}
return Arrays.copyOf(temp, newLen, Object[].class);
}
/**
* 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
* (<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 #remove(Object)
*/
@Override
public boolean retainAll(@NotNull Collection<?> c) {
while (true) {
Object[] elements = array;
Object[] newElements = createArrayRetainAll(elements, c);
if (newElements == null) return false;
if (replaceArray(elements, newElements)) return true;
}
}
@Nullable
private static Object[] createArrayRetainAll(@NotNull Object[] elements, @NotNull Collection<?> c) {
int len = elements.length;
if (len == 0) {
return null;
}
// temp array holds those elements we know we want to keep
int newlen = 0;
Object[] temp = new Object[len];
for (Object element : elements) {
if (c.contains(element)) {
temp[newlen++] = element;
}
}
if (newlen == len) {
return null;
}
return Arrays.copyOf(temp, newlen, Object[].class);
}
/**
* 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(@NotNull Collection<? extends E> c) {
Object[] cs = c.toArray();
if (cs.length == 0) {
return 0;
}
Object[] uniq = new Object[cs.length];
Object[] elements;
Object[] newElements;
int added;
do {
elements = array;
int len = elements.length;
added = 0;
for (Object e : cs) { // scan for duplicates
if (indexOf(e, elements, 0, len) < 0 &&
indexOf(e, uniq, 0, added) < 0) {
uniq[added++] = e;
}
}
if (added == 0) {
return 0;
}
newElements = Arrays.copyOf(elements, len + added, Object[].class);
System.arraycopy(uniq, 0, newElements, len, added);
}
while (!replaceArray(elements, newElements));
return added;
}
/**
* Removes all of the elements from this list.
* The list will be empty after this call returns.
*/
@Override
public void clear() {
array = ArrayUtilRt.EMPTY_OBJECT_ARRAY;
}
/**
* 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)
*/
@Override
public boolean addAll(@NotNull Collection<? extends E> c) {
Object[] cs = c.toArray();
if (cs.length == 0) {
return false;
}
while (true) {
Object[] elements = array;
Object[] newElements = createArrayAddAll(elements, cs);
if (replaceArray(elements, newElements)) return true;
}
}
@NotNull
private static Object[] createArrayAddAll(@NotNull Object[] elements, @NotNull Object[] cs) {
int len = elements.length;
Object[] newElements = Arrays.copyOf(elements, len + cs.length, Object[].class);
System.arraycopy(cs, 0, newElements, len, cs.length);
return newElements;
}
/**
* 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)
*/
@Override
public boolean addAll(int index, @NotNull Collection<? extends E> c) {
Object[] cs = c.toArray();
if (cs.length == 0) {
return false;
}
while (true) {
Object[] elements = array;
Object[] newElements = createArrayAddAll(elements, index, cs);
if (replaceArray(elements, newElements)) break;
}
return true;
}
@NotNull
private static Object[] createArrayAddAll(@NotNull Object[] elements, int index, @NotNull Object[] cs) {
int len = elements.length;
if (index > len || index < 0) {
throw new IndexOutOfBoundsException("Index: " + index + ", Size: " + len);
}
int numMoved = len - index;
Object[] newElements;
if (numMoved == 0) {
newElements = Arrays.copyOf(elements, len + cs.length, Object[].class);
}
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);
return newElements;
}
/**
* Returns a string representation of this list. The string
* representation consists of the string representations of the list's
* elements in the order they are returned by its iterator, enclosed in
* square brackets (<tt>"[]"</tt>). Adjacent elements are separated by
* the characters <tt>", "</tt> (comma and space). Elements are
* converted to strings as by {@link String#valueOf(Object)}.
*
* @return a string representation of this list
*/
@NotNull
public String toString() {
return Arrays.toString(array);
}
/**
* Compares the specified object with this list for equality.
* Returns {@code true} if the specified object is the same object
* as this object, or if it is also a {@link java.util.List} and the sequence
* of elements returned by an {@linkplain java.util.List#iterator() iterator}
* over the specified list is the same as the sequence returned by
* an iterator over this list. The two sequences are considered to
* be the same if they have the same length and corresponding
* elements at the same position in the sequence are <em>equal</em>.
* Two elements {@code e1} and {@code e2} are considered
* <em>equal</em> if {@code (e1==null ? e2==null : e1.equals(e2))}.
*
* @param o the object to be compared for equality with this list
* @return {@code true} 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<?> list = (List<?>)o;
Iterator<?> it = list.iterator();
for (Object element : array) {
if (!it.hasNext() || !eq(element, it.next())) {
return false;
}
}
return !it.hasNext();
}
/**
* Returns the hash code value for this list.
* <p/>
* <p>This implementation uses the definition in {@link java.util.List#hashCode}.
*
* @return the hash code value for this list
*/
public int hashCode() {
int hashCode = 1;
for (Object obj : array) {
hashCode = 31 * hashCode + (obj == null ? 0 : obj.hashCode());
}
return hashCode;
}
/**
* Returns an iterator over the elements in this list in proper sequence.
* <p/>
* <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
*/
@NotNull
@Override
public Iterator<E> iterator() {
Object[] elements = array;
if (elements.length == 0) return EmptyIterator.getInstance();
return new COWIterator<E>(elements, 0);
}
/**
* {@inheritDoc}
* <p/>
* <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.
*/
@NotNull
@Override
public ListIterator<E> listIterator() {
return listIterator(0);
}
/**
* {@inheritDoc}
* <p/>
* <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.
*
* @throws IndexOutOfBoundsException {@inheritDoc}
*/
@NotNull
@Override
public ListIterator<E> listIterator(final int index) {
Object[] elements = array;
int len = elements.length;
if (index < 0 || index > len) {
throw new IndexOutOfBoundsException("Index: " + index);
}
return elements.length == 0 ? EmptyListIterator.<E>getInstance() : new COWIterator<E>(elements, index);
}
private static 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(@NotNull Object[] elements, int initialCursor) {
cursor = initialCursor;
snapshot = elements;
}
@Override
public boolean hasNext() {
return cursor < snapshot.length;
}
@Override
public boolean hasPrevious() {
return cursor > 0;
}
@Override
@SuppressWarnings("unchecked")
public E next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return (E)snapshot[cursor++];
}
@Override
@SuppressWarnings("unchecked")
public E previous() {
if (!hasPrevious()) {
throw new NoSuchElementException();
}
return (E)snapshot[--cursor];
}
@Override
public int nextIndex() {
return cursor;
}
@Override
public int previousIndex() {
return cursor - 1;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
@Override
public void set(E e) {
throw new UnsupportedOperationException();
}
@Override
public void add(E e) {
throw new UnsupportedOperationException();
}
}
@NotNull
@Override
public List<E> subList(int fromIndex, int toIndex) {
throw new UnsupportedOperationException();
}
}