x = last; x != null; x = x.prev) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
// 查找失败
return false;
}
/**
* Returns a list-iterator of the elements in this list (in proper
* sequence), starting at the specified position in the list.
* Obeys the general contract of {@code List.listIterator(int)}.
*
* The list-iterator is fail-fast: if the list is structurally
* modified at any time after the Iterator is created, in any way except
* through the list-iterator's own {@code remove} or {@code add}
* methods, the list-iterator will throw a
* {@code ConcurrentModificationException}. Thus, in the face of
* concurrent modification, the iterator fails quickly and cleanly, rather
* than risking arbitrary, non-deterministic behavior at an undetermined
* time in the future.
*
* @param index index of the first element to be returned from the
* list-iterator (by a call to {@code next})
* @return a ListIterator of the elements in this list (in proper
* sequence), starting at the specified position in the list
* @throws IndexOutOfBoundsException {@inheritDoc}
* @see List#listIterator(int)
*/
public ListIterator listIterator(int index) {
checkPositionIndex(index);
return new ListItr(index);
}
private class ListItr implements ListIterator {
private Node lastReturned;
private Node next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int index) {
// assert isPositionIndex(index);
next = (index == size) ? null : node(index);
nextIndex = index;
}
public boolean hasNext() {
return nextIndex < size;
}
public E next() {
checkForComodification();
if (!hasNext())
throw new NoSuchElementException();
lastReturned = next;
next = next.next;
nextIndex++;
return lastReturned.item;
}
public boolean hasPrevious() {
return nextIndex > 0;
}
public E previous() {
checkForComodification();
if (!hasPrevious())
throw new NoSuchElementException();
lastReturned = next = (next == null) ? last : next.prev;
nextIndex--;
return lastReturned.item;
}
public int nextIndex() {
return nextIndex;
}
public int previousIndex() {
return nextIndex - 1;
}
public void remove() {
checkForComodification();
if (lastReturned == null)
throw new IllegalStateException();
Node lastNext = lastReturned.next;
unlink(lastReturned);
if (next == lastReturned)
next = lastNext;
else
nextIndex--;
lastReturned = null;
expectedModCount++;
}
public void set(E e) {
if (lastReturned == null)
throw new IllegalStateException();
checkForComodification();
lastReturned.item = e;
}
public void add(E e) {
checkForComodification();
lastReturned = null;
if (next == null)
linkLast(e);
else
linkBefore(e, next);
nextIndex++;
expectedModCount++;
}
public void forEachRemaining(Consumer action) {
Objects.requireNonNull(action);
while (modCount == expectedModCount && nextIndex < size) {
action.accept(next.item);
lastReturned = next;
next = next.next;
nextIndex++;
}
checkForComodification();
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
/**
* 节点的数据结构，包含前后节点的引用和当前节点
*
* @param
*/
private static class Node {
// 存储的元素
E item;
// 后继结点
Node next;
// 前驱结点
Node prev;
// 前驱结点、存储的元素和后继结点作为参数的构造方法
Node(Node prev, E element, Node next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
/**
* 返回迭代器
*
* @since 1.6
*/
public Iterator descendingIterator() {
return new DescendingIterator();
}
/**
* 因为采用链表实现，所以迭代器很简单
*/
private class DescendingIterator implements Iterator {
private final ListItr itr = new ListItr(size());
public boolean hasNext() {
return itr.hasPrevious();
}
public E next() {
return itr.previous();
}
public void remove() {
itr.remove();
}
}
/**
* 父类克隆方法
*/
@SuppressWarnings("unchecked")
private LinkedList superClone() {
try {
return (LinkedList) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
}
/**
* 克隆，浅拷贝
*
* @return a shallow copy of this {@code LinkedList} instance
*/
public Object clone() {
LinkedList clone = superClone();
// 链表初始化
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
// 插入结点
for (Node x = first; x != null; x = x.next)
clone.add(x.item);
// 返回克隆后的对象引用
return clone;
}
/**
* Returns an array containing all of the elements in this list
* in proper sequence (from first to last element).
*
*
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.
*
*
This method acts as bridge between array-based and collection-based
* APIs.
*
* @return an array containing all of the elements in this list
* in proper sequence
*/
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Node x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}
/**
* 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.
*
*
If the list fits in the specified array with room to spare (i.e.,
* the array has more elements than the list), the element in the array
* immediately following the end of the list is set to {@code null}.
* (This is useful in determining the length of the list only if
* the caller knows that the list does not contain any null elements.)
*
*
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.
*
*
Suppose {@code x} is a list known to contain only strings.
* The following code can be used to dump the list into a newly
* allocated array of {@code String}:
*
*
* String[] y = x.toArray(new String[0]);
*
* Note that {@code toArray(new Object[0])} is identical in function to
* {@code toArray()}.
*
* @param a the array into which the elements of the list are to
* be stored, if it is big enough; otherwise, a new array of the
* same runtime type is allocated for this purpose.
* @return an array containing the elements of the list
* @throws ArrayStoreException if the runtime type of the specified array
* is not a supertype of the runtime type of every element in
* this list
* @throws NullPointerException if the specified array is null
*/
@SuppressWarnings("unchecked")
public T[] toArray(T[] a) {
if (a.length < size)
a = (T[]) java.lang.reflect.Array.newInstance(
a.getClass().getComponentType(), size);
int i = 0;
Object[] result = a;
for (Node x = first; x != null; x = x.next)
result[i++] = x.item;
if (a.length > size)
a[size] = null;
return a;
}
private static final long serialVersionUID = 876323262645176354L;
/**
* 序列化
*/
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// 默认序列化
s.defaultWriteObject();
// 写入元素数量
s.writeInt(size);
// 遍历链表，写入所有元素
for (Node x = first; x != null; x = x.next)
s.writeObject(x.item);
}
/**
* 反序列化
*/
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// 默认反序列化
s.defaultReadObject();
// 读取元素数量
int size = s.readInt();
// 遍历链表，读取所有元素并尾部插入
for (int i = 0; i < size; i++)
linkLast((E) s.readObject());
}
/**
* Creates a late-binding
* and fail-fast {@link Spliterator} over the elements in this
* list.
*
*
The {@code Spliterator} reports {@link Spliterator#SIZED} and
* {@link Spliterator#ORDERED}. Overriding implementations should document
* the reporting of additional characteristic values.
*
* @return a {@code Spliterator} over the elements in this list
* @implNote The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}
* and implements {@code trySplit} to permit limited parallelism..
* @since 1.8
*/
@Override
public Spliterator spliterator() {
return new LLSpliterator(this, -1, 0);
}
/**
* A customized variant of Spliterators.IteratorSpliterator
*/
static final class LLSpliterator implements Spliterator {
static final int BATCH_UNIT = 1 << 10; // batch array size increment
static final int MAX_BATCH = 1 << 25; // max batch array size;
final LinkedList list; // null OK unless traversed
Node current; // current node; null until initialized
int est; // size estimate; -1 until first needed
int expectedModCount; // initialized when est set
int batch; // batch size for splits
LLSpliterator(LinkedList list, int est, int expectedModCount) {
this.list = list;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getEst() {
int s; // force initialization
final LinkedList lst;
if ((s = est) < 0) {
if ((lst = list) == null)
s = est = 0;
else {
expectedModCount = lst.modCount;
current = lst.first;
s = est = lst.size;
}
}
return s;
}
public long estimateSize() {
return (long) getEst();
}
public Spliterator trySplit() {
Node p;
int s = getEst();
if (s > 1 && (p = current) != null) {
int n = batch + BATCH_UNIT;
if (n > s)
n = s;
if (n > MAX_BATCH)
n = MAX_BATCH;
Object[] a = new Object[n];
int j = 0;
do {
a[j++] = p.item;
} while ((p = p.next) != null && j < n);
current = p;
batch = j;
est = s - j;
return Spliterators.spliterator(a, 0, j, Spliterator.ORDERED);
}
return null;
}
public void forEachRemaining(Consumer action) {
Node p;
int n;
if (action == null) throw new NullPointerException();
if ((n = getEst()) > 0 && (p = current) != null) {
current = null;
est = 0;
do {
E e = p.item;
p = p.next;
action.accept(e);
} while (p != null && --n > 0);
}
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
}
public boolean tryAdvance(Consumer action) {
Node p;
if (action == null) throw new NullPointerException();
if (getEst() > 0 && (p = current) != null) {
--est;
E e = p.item;
current = p.next;
action.accept(e);
if (list.modCount != expectedModCount)
throw new ConcurrentModificationException();
return true;
}
return false;
}
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
}