双向链表模拟

       /*
      public LinkedList() {}
      // linkeList: first=null last=null
      */

        // 构造一个空链表
        LinkedList linkedList = new LinkedList();
        // 添加第一个元素
        /*
            public boolean add(E e) {
                    linkLast(e);
                    return true;
                }
         */
        linkedList.add(1);
        /*
        //添加
            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++;
    }
         */
        // 添加第二个元素
        linkedList.add(2);
        System.out.println(linkedList);
        // 删除节点(默认第一个节点)
        /*
        //1
        public E remove() {
            return removeFirst();
         }
         //2
         public E remove() {
            return removeFirst();
          }
          //3
          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;
    }
         */
        linkedList.remove(); 

public class LinkedList_ {
    public static void main(String[] args) {
        // 模拟双向列表
        //创建三个节点
        Node rick = new Node("rick");
        Node gelnn = new Node("gelnn");
        Node lucy = new Node("lucy");
        // 连接三个节点形成双向链表
        rick.next = gelnn;
        gelnn.next = lucy;
        lucy.pre = gelnn;
        gelnn.pre = rick;
        // 创建头节点
        Node first = rick;
        Node last = lucy;
        //遍历
        while (true) {
            if (first == null) {
                break;
            }
            System.out.println(first);
            first = first.next;
        }
//       添加节点
        Node jack = new Node("jack");
        rick.next = jack;
        gelnn.pre = jack;
        jack.pre = rick;
        jack.next = gelnn;
        // 重置first指向头结点
        first = rick;
        System.out.println("添加后");
        while (true) {
            if (first == null) {
                break;
            }
            System.out.println(first);
            first = first.next;
        }
    }
}

// 表示双向列表的一个节点
class Node {

    private Object item; //存放数据的
    public Node next; // 指向下一个节点
    public Node pre;   //指向上一个节点

    public Node(Object name) {
        this.item = name;
    }

    @Override
    public String toString() {
        return "Node name=" + item;
    }

}