JavaLinkedList源码深入分析

 //可以看出node是一个双链表结构
    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;
        }
    }

 //尾插
    void linkLast(E e) {
        //保存的链表的尾部节点
        final Node<E> l = last;
        //新的节点的前一个node指向链表的最后一个,next 为null
        final Node<E> newNode = newNode < E > (l, e, null);
        last = newNode;
        if (l == null)//如果最后一个节点为null，说明链表是空的
            first = newNode;
        else//如果不为null，last的next节点指向新的节点
            l.next = newNode;
        size++;
        modCount++;
    }

  public void add(int index, E element) {
        if (index == size)//新插入节点刚好在链表尾部
            linkLast(element);
        else
            linkBefore(element, node(index));
    }
    Node<E> node(int index) {
        //如果index小于链表的一半，则头部遍历
        if (index < (size >> 1)) {
            Node<E> x = first;
            for (int i = 0; i < index; i++)
                x = x.next;
            return x;
        } else { //如果index大于链表的一半，则尾部遍历
            Node<E> x = last;
            for (int i = size - 1; i > index; i--)
                x = x.prev;
            return x;
        }
    }

  void linkBefore(E e, Node<E> succ) {
        // assert succ != null;
        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++;
    }

public E get(int index) {
        checkElementIndex(index);
        return node(index).item;
    }
	public E set(int index, E element) {
        checkElementIndex(index);
        Node<E> x = node(index);
        E oldVal = x.item;
        x.item = element;
        return oldVal;
    }

 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;
    }

 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;
    }