public class LinkedList implements List, Deque { 
 Node first; 
 Node last; 
 int size; 
 
 public boolean add(E e) { 
    final Node l = last; 
    final Node newNode = new Node<>(l, e, null); 
    last = newNode; 
    if (l == null) 
      first = newNode; 
    else 
      l.next = newNode; 
    size++; 
    modCount++; 
    return true; 
  } 
 
 private static class Node { 
    E item; 
    Node next; 
    Node prev; 
 
    Node(Node prev, E element, Node next) { 
      this.item = element; 
      this.next = next; 
      this.prev = prev; 
    } 
  }  
} 

/**  
   * 递归，在反转当前节点之前先反转后续节点  
   */  
  public static Node reverse(Node head) {  
    if (null == head || null == head.getNextNode()) {  
      return head;  
    }  
    Node reversedHead = reverse(head.getNextNode());  
    head.getNextNode().setNextNode(head);  
    head.setNextNode(null);  
    return reversedHead;  
  }  
  
  /**  
   * 遍历，将当前节点的下一个节点缓存后更改当前节点指针  
   *  
   */  
  public static Node reverse2(Node head) {  
    if (null == head) {  
      return head;  
    }  
    Node pre = head;  
    Node cur = head.getNextNode();  
    Node next;  
    while (null != cur) {  
      next = cur.getNextNode();  
      cur.setNextNode(pre);  
      pre = cur;  
      cur = next;  
    }  
    //将原链表的头节点的下一个节点置为null，再将反转后的头节点赋给head    
    head.setNextNode(null);  
    head = pre;  
      
    return head;  
  }