[Java]JDK1.8 LinkedList源码剖析

类中共享的变量和常用方法

1. int size：存放LinkedList的元素个数
2. Node first：存放第一个节点
3. Node last：存放最后一个节点
4. private static class Node ：内部类，有三个属性：E item，Node next，Node prev

类的实现

1. 构造方法有两种：
   
   1. 默认构造方法public LinkedList()，实例化一个空的链表list
   2. 带参构造方法public LinkedList(Collection<? extends E> c)，添加集合c中的所有元素到新LinkedList中
2. getFirst()、getLast()：直接返回first变量和last变量的item
3. public E removeFirst()：使用private E unlinkFirst(Node<E> f)方法移除linkedList第一个节点元素

final E element = f.item;final Node<E> next = f.next;f.item = null;f.next = null; // help GCfirst = next;if (next == null)    last = null;else    next.prev = null;size--;modCount++;return element;

4.public E removeLast()：与removeFirst方法类似
5.public void addFirst(E e)：使用private void linkFirst(E e)方法将e插入到第一个元素

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++;

6.public void addLast(E e)：方法与addFirst方法类似
7.public boolean contains(Object o)：使用public int indexOf(Object o)方法来判断linkedList中是否包含o，遍历LinkedList，若找到则返回index，未找到则返回-1：

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;

8.public boolean add(E e)：使用void linkLast(E e)方法在linkedList末尾增加元素

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++;

9.public boolean remove(Object o)：移除指定元素节点：

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;

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;}

10.public boolean addAll(int index, Collection<? extends E> c)将集合c中的所有元素添加到linkedList中：

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;

11.public void clear()清空LinkedList：

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++;

12.Node<E> node(int index)找到指定下标的节点，先判断下标是在链表的前半段还是后半段，决定从后往前还是从前往后查找：

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;}

上述方法就是增删改查的基本方法，中间还有很多功能和上述方法相同，只是方法名不同的方法。

13.public Iterator<E> descendingIterator()：生成一个逆序迭代器

14.public Spliterator<E> spliterator()：生成一个并行迭代器，示例如下：

LinkedList<String> ll = new LinkedList<String>();ll.add("xzc");ll.add("qwe");Spliterator<String> iterator = ll.spliterator();iterator.forEachRemaining(ele -> System.out.print(ele));