package java.util;
import java.util.function.Consumer;
/**
* LinkedList基于链表实现
* 实现了List、Deque、Cloneable、Serializable接口
*/
public class LinkedList<E>
extends AbstractSequentialList<E>
implements List<E>, Deque<E>, Cloneable, java.io.Serializable
{
transient int size = 0;//list默认的长度
transient Node<E> first;//list第一个节点
transient Node<E> last;//list最后一个节点
public LinkedList() {
}
public LinkedList(Collection<? extends E> c) {
this();
addAll(c);
}
//在链表的开始连接一个节点
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++;//修改次数，用于快速失败机制
}
//在链表结尾连接一个节点
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++;
}
//在succ节点之前连接一个节点
void linkBefore(E e, Node<E> succ) {
// assert succ != null; 断言
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++;
}
//截取f.next节点到尾节点
//不过这个地方会断言f肯定是头节点，所以此方法是取消连接第一个节点，也即删除第一个节点
private E unlinkFirst(Node<E> f) {
// assert f == first && f != null;
final E element = f.item;
final Node<E> next = f.next;
f.item = null;
f.next = null; // help GC
first = next;
if (next == null)
last = null;
else
next.prev = null;
size--;
modCount++;
return element;
}
//取消连接最后一个节点(因为断言)
private E unlinkLast(Node<E> l) {
// assert l == last && l != null;
final E element = l.item;
final Node<E> prev = l.prev;
l.item = null;
l.prev = null; // help GC
last = prev;
if (prev == null)
first = null;
else
prev.next = null;
size--;
modCount++;
return element;
}
//删除一个非空节点x
E unlink(Node<E> x) {
// assert x != null;
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;
}
//得到第一个节点，如果第一个节点为null，会抛出NoSuchElementException
public E getFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return f.item;
}
//得到最后一个节点，如果最后一个节点为null，会抛出NoSuchElementException
public E getLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return l.item;
}
//得到第一个节点，如果第一个节点为null，会抛出NoSuchElementException
//与getFirst不同的是该方法会删除第一个节点
public E removeFirst() {
final Node<E> f = first;
if (f == null)
throw new NoSuchElementException();
return unlinkFirst(f);
}
//得到最后一个节点，如果最后一个节点为null，会抛出NoSuchElementException
//与getLast不同的是该方法会删除最后一个节点
public E removeLast() {
final Node<E> l = last;
if (l == null)
throw new NoSuchElementException();
return unlinkLast(l);
}
//向链表头节点连接一个新节点(由元素e决定)
public void addFirst(E e) {
linkFirst(e);
}
//向链表尾节点连接一个新节点(由元素e决定)
public void addLast(E e) {
linkLast(e);
}
//判断链表是否包含某一个元素o，会迭代所有元素
public boolean contains(Object o) {
return indexOf(o) != -1;
}
//得到链表长度，也即链表中元素的个数
public int size() {
return size;
}
//向链表中新增一个元素e，默认新增位置为尾端
public boolean add(E e) {
linkLast(e);
return true;
}
//通过迭代的方式去删除某一个元素，如果这个元素有重复，则只删除第一个元素(从头节点开始)
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;
}
//批量增加元素，默认增加到队尾
public boolean addAll(Collection<? extends E> c) {
return addAll(size, c);
}
//批量增加元素，增加到index位置之后，可能会抛出IndexOutOfBoundsException异常
public boolean addAll(int index, Collection<? extends E> c) {
checkPositionIndex(index);
Object[] a = c.toArray();
int numNew = a.length;
if (numNew == 0)//c中若没有元素的话，则会返回false
return false;
Node<E> pred, succ;//插入后c的首节点的前驱节点与尾节点的后驱节点
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;
}
//清除所有元素
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++;
}
//通过位置索引的到元素，头节点index=0
public E get(int index) {
checkElementIndex(index);
return node(index).item;
}
//在指定位置插入节点，会覆盖原位置的元素
public E set(int index, E element) {
checkElementIndex(index);
Node<E> x = node(index);
E oldVal = x.item;
x.item = element;
return oldVal;
}
//在指定位置插入节点，不会会覆盖原位置的元素
public void add(int index, E element) {
checkPositionIndex(index);
if (index == size)
linkLast(element);
else
linkBefore(element, node(index));
}
//清除位置index的元素
public E remove(int index) {
checkElementIndex(index);
return unlink(node(index));
}
//判断index是不是一个已存在元素的位置
private boolean isElementIndex(int index) {
return index >= 0 && index < size;
}
//判断index是不是迭代器或添加操作的有效位置的索引。
private boolean isPositionIndex(int index) {
return index >= 0 && index <= size;
}
private String outOfBoundsMsg(int index) {
return "Index: "+index+", Size: "+size;
}
private void checkElementIndex(int index) {
if (!isElementIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
private void checkPositionIndex(int index) {
if (!isPositionIndex(index))
throw new IndexOutOfBoundsException(outOfBoundsMsg(index));
}
//根据index返回节点，此处index断言isElementIndex
Node<E> node(int index) {
// assert isElementIndex(index);
if (index < (size >> 1)) {//并不是从头开始迭代到尾，而是根据判断止迭代一半
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;
}
}
//搜索操作
//返回o在链表中的位置，如果有多个，只返回第一个，从头节点开始
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;
}
//返回o在链表中的位置，如果有多个，只返回第一个，从尾节点开始
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;
}
// 队列操作
//查看队列的第一个元素，但不移除这个元素，并且不会抛出异常
public E peek() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
//得到第一个元素，如果为null，抛出NoSuchElementException异常
public E element() {
return getFirst();
}
//查看队列的第一个元素，会移除这个元素，不会抛出异常
public E poll() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//查看队列的第一个元素，会移除这个元素，会抛出NoSuchElementException异常
public E remove() {
return removeFirst();
}
//向队列中插入一个元素，默认尾部
public boolean offer(E e) {
return add(e);
}
//双端队列操作
//向队列头部中插入一个元素
public boolean offerFirst(E e) {
addFirst(e);
return true;
}
//向队列中插入一个元素，默认尾部，与offer(E e)一致
public boolean offerLast(E e) {
addLast(e);
return true;
}
//从头部查看一个元素，不删除，且不抛出异常
public E peekFirst() {
final Node<E> f = first;
return (f == null) ? null : f.item;
}
//从尾部查看一个元素，不删除，且不抛出异常
public E peekLast() {
final Node<E> l = last;
return (l == null) ? null : l.item;
}
//从头部查看一个元素，并删除，不抛出异常
public E pollFirst() {
final Node<E> f = first;
return (f == null) ? null : unlinkFirst(f);
}
//从尾部查看一个元素，并删除，不抛出异常
public E pollLast() {
final Node<E> l = last;
return (l == null) ? null : unlinkLast(l);
}
//栈操作
//压栈
public void push(E e) {
addFirst(e);
}
//出栈，若没有元素会抛出异常
public E pop() {
return removeFirst();
}
//删除第一个出现的元素o
public boolean removeFirstOccurrence(Object o) {
return remove(o);
}
//删除最后一个出现的元素o
public boolean removeLastOccurrence(Object o) {
if (o == null) {//很聪明的从后往前遍历
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;
}
//迭代器
//双端链表迭代器
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) {
// 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;
}
//删除的是上一个元素
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++;
}
//设置上一个元素的值为e，会覆盖
public void set(E e) {
if (lastReturned == null)
throw new IllegalStateException();
checkForComodification();
lastReturned.item = e;
}
//上一个元素后插入一个的值为e的元素，不会覆盖
public void add(E e) {
checkForComodification();
lastReturned = null;
if (next == null)
linkLast(e);
else
linkBefore(e, next);
nextIndex++;
expectedModCount++;
}
//foreach 迭代剩余的元素，并使用Consumer影响
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();//审查快速失败
}
final void checkForComodification() {
if (modCount != expectedModCount)
throw new ConcurrentModificationException();
}
}
//链表中的实体类--节点
private static class Node<E> {
E item;//元素
Node<E> next;//前驱
Node<E> prev;//后驱
Node(Node<E> prev, E element, Node<E> next) {
this.item = element;
this.next = next;
this.prev = prev;
}
}
//单向的迭代器，只需往后不许往前
public Iterator<E> descendingIterator() {
return new DescendingIterator();
}
//单向迭代器
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);
}
}
//浅复制链表
public Object clone() {
LinkedList<E> clone = superClone();
// Put clone into "virgin" state
clone.first = clone.last = null;
clone.size = 0;
clone.modCount = 0;
// Initialize clone with our elements
for (Node<E> x = first; x != null; x = x.next)
clone.add(x.item);
return clone;
}
//toArray返回一个Object[]
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;
}
//toArray返回特定类型的数据
@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;//此处用引用逻辑实现赋值的，可以避免强制转换，只能说太6了
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;
//往一个流中写当前对象
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
// Write out any hidden serialization magic
s.defaultWriteObject();
// Write out size
s.writeInt(size);
// Write out all elements in the proper order.
for (Node<E> x = first; x != null; x = x.next)
s.writeObject(x.item);
}
//往一个流中读当前对象
@SuppressWarnings("unchecked")
private void readObject(java.io.ObjectInputStream s)
throws java.io.IOException, ClassNotFoundException {
// Read in any hidden serialization magic
s.defaultReadObject();
// Read in size
int size = s.readInt();
// Read in all elements in the proper order.
for (int i = 0; i < size; i++)
linkLast((E)s.readObject());
}
//可分裂的迭代器，用于并行计算
@Override
public Spliterator<E> spliterator() {
return new LLSpliterator<E>(this, -1, 0);
}
/** A customized variant of Spliterators.IteratorSpliterator */
static final class LLSpliterator<E> implements Spliterator<E> {
static final int BATCH_UNIT = 1 << 10; // batch array size increment 1024
static final int MAX_BATCH = 1 << 25; // max batch array size; 33554432
final LinkedList<E> list; // null OK unless traversed
Node<E> current; // 当前节点 默认为null
int est; // size的估计值，默认为-1
int expectedModCount; // 预期的修改数量，用于快速失败
int batch; // batch size for splits
LLSpliterator(LinkedList<E> list, int est, int expectedModCount) {
this.list = list;
this.est = est;
this.expectedModCount = expectedModCount;
}
final int getEst() {
int s; // force initialization
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;
}
//得到size估计值
public long estimateSize() { return (long) getEst(); }
//这就是为Spliterator专门设计的方法，区分与普通的Iterator，该方法会把当前元素划分一部分出去创建一个新的Spliterator作为返回，
//两个Spliterator变会并行执行，如果元素个数小到无法划分则返回null
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();
}
//tryAdvance就是顺序处理每个元素，类似Iterator，如果还有元素要处理，则返回true，否则返回false
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;
}
//其实就是表示该Spliterator有哪些特性，用于可以更好控制和优化Spliterator的使用
public int characteristics() {
return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
}
}
}
