java单链表操作

class ListNode{    int val ;    ListNode next = null ;    public ListNode(int val)    {        this.val = val;    }}class LinkList{       ListNode first  ;    int p = 0 ;    //链表添加结点    public void add(ListNode node,int index)    {          ListNode cur = first ;          ListNode pre = first ;        while(true)         {            if(p == index)            {                pre.next = node;                node.next = cur ;            }             pre = cur ;            cur = cur.next;            p++ ;         }    }    //反转链表    public void reverseList(ListNode first)    {        ListNode cur = null;        ListNode pre = null;        while(first != null)        {   cur = first.next;            first.next = pre;            pre = first ;            first = cur;        }    }}