public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
transient int size = 0;
* 第一个节点
*/
transient Node<E> first;
* 最后一个节点
*/
transient Node<E> last;
* 构造一个空的LinkedList
*/
public LinkedList() {
}
* 添加指定的元素集合到该集合的最后，添加的顺序就是指定集合遍历的顺序。
* 如果有其他线程的方法修改了入参，对这个方法没有影响
*/
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
* Links e as first element.
*/
private void linkFirst(E e) {
final Node<E> f = first;
final Node<E> newNode = new Node<>(null, e, f);
first = newNode;
if (f == null)
last = newNode;
else
f.prev = newNode;
size++;
modCount++;
}
* 添加元素e到最后
*/
void linkLast(E e) {
final Node<E> l = last;
final Node<E> newNode = new Node<>(l, e, null);
last = newNode;
if (l == null)
first = newNode;
else
l.next = newNode;
size++;
modCount++;
}
* Inserts element e before non-null Node succ.
* 在一个元素前面添加元素
*/
void linkBefore(E e, Node<E> succ) {
final Node<E> pred = succ.prev;
final Node<E> newNode = new Node<>(pred, e, succ);
succ.prev = newNode;
if (pred == null)
first = newNode;
else
pred.next = newNode;
size++;
modCount++;
}
* Unlinks non-null first node f.
*/
private E unlinkFirst(Node<E> f) {
final E element = f.item;
final Node<E> next = f.next;
f.item = null;
f.next = null;
first = next;
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
* 将最后一个元素的前一个元素设置为last，并设置移除元素的item为空，prev为空
*/
private E unlinkLast(Node<E> l) {
final E element = l.item;
final Node<E> prev = l.prev;
l.item = null;
l.prev = null;
last = prev;
if (prev == null)
first = null;
else
prev.next = null;
size--;
modCount++;
return element;
}
* 修改被移除节点的前一个节点的next指向移除节点的next
* 修改被移除节点的后一个节点的prev指向为被移除节点的prev
* 将移除节点的x.item、x.next和x.prev都置为空
*/
E unlink(Node<E> x) {
final E element = x.item;
final Node<E> next = x.next;
final Node<E> prev = x.prev;
if (prev == null) {
first = next;
} else {
prev.next = next;
x.prev = null;
}
if (next == null) {
last = prev;
} else {
next.prev = prev;
x.next = null;
}
x.item = null;
size--;
modCount++;
return element;
}
* 返回第一个元素
*/
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
* 返回最后一个元素
*/
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
* 移除第一个元素，并返回
*/
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
* 移除该集合的最后一个元素并返回移除元素
*/
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
* 在该集合开始位置添加元素
*/
public void addFirst(E e) {
linkFirst(e);
}
* 添加指定的元素到该集合的最后
* 该方法等同于add方法
*/
public void addLast(E e) {
linkLast(e);
}
* 如果链表中包含指定的元素，则返回true
*/
public boolean contains(Object o) {
return indexOf(o) != -1;
}
* 返回该集合的元素个数
*/
public int size() {
return size;
}
* 添加指定的元素到该集合的最后
* 这个方法和addLast等效
*/
public boolean add(E e) {
linkLast(e);
return true;
}
* 从当前集合中移除第一个配置入参的数据，从第一个元素依次遍历。移除成功返回true
*/
public boolean remove(Object o) {
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
* 添加指定的元素集合到该集合的最后，添加的顺序就是指定集合遍历的顺序。
* 如果有其他线程的方法修改了入参，对这个方法没有影响
*/
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
* 添加指定的元素集合到该集合的指定位置，添加的顺序就是指定集合遍历的顺序。
* 有可能需要修改索引位置的元素
* 如果有其他线程的方法修改了入参，对这个方法没有影响
*/
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)
return false;
Node<E> pred, succ;
if (index == size) {
succ = null;
pred = last;
} else {
succ = node(index);
pred = succ.prev;
}
for (Object o : a) {
@SuppressWarnings("unchecked") E e = (E) o;
Node<E> newNode = new Node<>(pred, e, null);
if (pred == null)
first = newNode;
else
pred.next = newNode;
pred = newNode;
}
if (succ == null) {
last = pred;
} else {
pred.next = succ;
succ.prev = pred;
}
size += numNew;
modCount++;
return true;
}
* 清空该集合
*/
public void clear() {
for (Node<E> x = first; x != null; ) {
Node<E> next = x.next;
x.item = null;
x.next = null;
x.prev = null;
x = next;
}
first = last = null;
size = 0;
modCount++;
}
* 返回指定index的元素
*/
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
* 替换参数指定位置的元素为参数指定的值，并返回被替换的值
*/
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
* 在该集合中添加指定的元素到指定的位置
* 有可能需要修改索引位置的元素
*/
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
* 移除指定index位置的元素
*/
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
* 校验参数index是否在集合的正常范围内
*/
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
* 校验参数index是否在集合的正常范围内
*/
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
* Returns the (non-null) Node at the specified element index.
* 返回指定index的Node
*/
Node<E> node(int index) {
if (index < (size >> 1)) {
Node<E> x = first;
for (int i = 0; i < index; i++)
x = x.next;
return x;
} else {
Node<E> x = last;
for (int i = size - 1; i > index; i--)
x = x.prev;
return x;
}
}
* 从链表的开始处循环比较指定的元素，如果存在循环到index的值，如果不存在则返回-1
*/
public int indexOf(Object o) {
int index = 0;
if (o == null) {
for (Node<E> x = first; x != null; x = x.next) {
if (x.item == null)
return index;
index++;
}
} else {
for (Node<E> x = first; x != null; x = x.next) {
if (o.equals(x.item))
return index;
index++;
}
}
return -1;
}
* 从后往前查找
*/
public int lastIndexOf(Object o) {
int index = size;
if (o == null) {
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (x.item == null)
return index;
}
} else {
for (Node<E> x = last; x != null; x = x.prev) {
index--;
if (o.equals(x.item))
return index;
}
}
return -1;
}
* 返回第一个元素，不会移除该元素
*/
public E peek() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
* 返回第一个元素
*/
public E element() {
return getFirst();
}
* 返回第一个元素并移除它，如果集合为空则返回null
* @since 1.5
*/
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
* 移除该集合的第一个元素，并返回
*/
public E remove() {
return removeFirst();
}
* 添加指定的元素到集合的末尾
* @since 1.5
*/
public boolean offer(E e) {
return add(e);
}
* 在集合的最前面添加一个元素
* @since 1.6
*/
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
* 在集合的最后面添加一个元素
* @since 1.6
*/
public boolean offerLast(E e) {
addLast(e);
return true;
}
* 返回第一个元素，如果该集合是空的则返回null。
* 不会移除该元素
* @since 1.6
*/
public E peekFirst() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
* 返回最后一个元素，如果该集合是空的则返回null。
* 不会移除该元素
* @since 1.6
*/
public E peekLast() {
final Node<E> l = last;
return (l == null) ? null : l.item;
}
* 返回第一个元素并移除它，如果集合为空则返回null
* @since 1.6
*/
public E pollFirst() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
* 返回最后一个元素并移除它，如果集合为空则返回null
* @since 1.6
*/
public E pollLast() {
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
* 和方法addFirst()相同
* @since 1.6
*/
public void push(E e) {
addFirst(e);
}
* 和方法removeFirst()相同
* @since 1.6
*/
public E pop() {
return removeFirst();
}
* 移除第一个匹配入参元素，从头依次遍历。如果没有匹配的则不会改变该元素
*/
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
* 移除该集合中最后一个配置入参元素，从尾到头依次循环。如果集合中没有则集合不会改变
* 移除成功返回true
*/
public boolean removeLastOccurrence(Object o) {
if (o == null) {
for (Node<E> x = last; x != null; x = x.prev) {
if (x.item == null) {
unlink(x);
return true;
}
}
} else {
for (Node<E> x = last; x != null; x = x.prev) {
if (o.equals(x.item)) {
unlink(x);
return true;
}
}
}
return false;
}
* 返回一个list的迭代器，该迭代器包含集合中从指定位置开始到结束的所有元素。
* 该list迭代器是快速失败的，已经创建的迭代器在任何时候结构被修改，比如执行了add或remove方法，将会抛出
* ConcurrentModificationException异常
*/
public ListIterator<E> listIterator(int index) {
checkPositionIndex(index);
return new ListItr(index);
}
private class ListItr implements ListIterator<E> {
private Node<E> lastReturned;
private Node<E> next;
private int nextIndex;
private int expectedModCount = modCount;
ListItr(int 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<E> 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<? super E> 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();
}
}
private static class Node<E> {
E item;
Node<E> next;
Node<E> prev;
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
* 将LinkedList转换成Iterator
* @since 1.6
*/
public Iterator<E> descendingIterator() {
return new DescendingIterator();
}
* Adapter to provide descending iterators via ListItr.previous
*/
private class DescendingIterator implements Iterator<E> {
private final ListItr itr = new ListItr(size());
public boolean hasNext() {
return itr.hasPrevious();
}
public E next() {
return itr.previous();
}
public void remove() {
itr.remove();
}
}
@SuppressWarnings("unchecked")
private LinkedList<E> superClone() {
try {
return (LinkedList<E>) super.clone();
} catch (CloneNotSupportedException e) {
throw new InternalError(e);
}
}
* 返回一个浅拷贝对象
*/
public Object clone() {
LinkedList<E> clone = superClone();
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
for (Node<E> x = first; x != null; x = x.next)
clone.add(x.item);
return clone;
}
* 返回一个数组包含这个集合的所有元素，集合中元素的顺序就是集合中从第一个到最后一个的顺序
* 该数组是新创建的，和该集合没有任何关系
*
*/
public Object[] toArray() {
Object[] result = new Object[size];
int i = 0;
for (Node<E> x = first; x != null; x = x.next)
result[i++] = x.item;
return result;
}
* 返回一个数组包含这个集合的所有元素，集合中元素的顺序就是集合中从第一个到最后一个的顺序。返回的数组类型就是参数指定的类型
* 如果指定数组的length小于集合的size将会创建出一个新的数组，创建出来的数组大小和集合size相同。
* 如果指定数组的length大于等于集合size，将替换指定数组的从0开始到集合size的元素，并将size位置的数组元素置为null
* 注意该方法可能会返回一个新的数组，也可能沿用原来的数组
*/
@SuppressWarnings("unchecked")
public <T> 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<E> 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;
* Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
* and <em>fail-fast</em> {@link Spliterator} over the elements in this
* list.
*
* <p>The {@code Spliterator} reports {@link Spliterator#SIZED} and
* {@link Spliterator#ORDERED}. Overriding implementations should document
* the reporting of additional characteristic values.
*
* @implNote
* The {@code Spliterator} additionally reports {@link Spliterator#SUBSIZED}
* and implements {@code trySplit} to permit limited parallelism..
*
* @return a {@code Spliterator} over the elements in this list
* @since 1.8
*/
@Override
public Spliterator<E> spliterator() {
return new LLSpliterator<E>(this, -1, 0);
}
static final class LLSpliterator<E> implements Spliterator<E> {
static final int BATCH_UNIT = 1 << 10;
static final int MAX_BATCH = 1 << 25;
final LinkedList<E> list;
Node<E> current;
int est;
int expectedModCount;
int batch;
LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {
this.list = list;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getEst() {
int s;
final LinkedList<E> 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<E> trySplit() {
Node<E> 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<? super E> action) {
Node<E> 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<? super E> action) {
Node<E> 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;
}
}
}
