reverse-linked-list Java code

Reverse a linked list from position m to n. Do it in-place and in one-pass.
For example:
Given1->2->3->4->5->NULL, m = 2 and n = 4,
return1->4->3->2->5->NULL.
Note:
Given m, n satisfy the following condition:
1 ≤ m ≤ n ≤ length of list.

/** * Definition for singly-linked list. * public class ListNode { *     int val; *     ListNode next; *     ListNode(int x) { *         val = x; *         next = null; *     } * } */public class Solution {    public ListNode reverseBetween(ListNode head, int m, int n) {        ListNode dummy = new ListNode(0);        dummy.next = head;        ListNode preStart = dummy;        ListNode start = head;        for (int i = 1; i < m; i ++ ) {            preStart = start;            start = start.next;        }        // reverse        for (int i = 0; i < n - m; i ++ ) {            ListNode temp = start.next;            start.next = temp.next;            temp.next = preStart.next;            preStart.next = temp;        }        return dummy.next;    }}