LinkedList源码分析

数据结构（LinkedList是双向循环链表）

1. 构造方法

/**
     * Constructs an empty list.//构造一个空的列表
     */
public LinkedList() {
        header.next = header.previous = header;
}

private transient Entry<E> header = new Entry<E>(null, null, null);

Entry(E element, Entry<E> next, Entry<E> previous) {//节点的构造函数
        this.element = element;  //元素的值
        this.next = next;             //后驱
        this.previous = previous;  //前驱
    }
}

2. 函数add

/**
     * Appends the specified element to the end of this list.
     *
     * <p>This method is equivalent to {@link #addLast}.
     *
     * @param e element to be appended to this list
     * @return <tt>true</tt> (as specified by {@link Collection#add})
     */

public boolean add(E e) {
    addBefore(e, header);
        return true;
}

private Entry<E> addBefore(E e, Entry<E> entry) {
    Entry<E> newEntry = new Entry<E>(e, entry, entry.previous); //创建一个新的节点
    newEntry.previous.next = newEntry;  //新的节点的前面一个元素的后驱是自己
    newEntry.next.previous = newEntry;  //新的节点的后面一个元素的前驱是自己
    size++;
    modCount++;
    return newEntry;
 }