Add Two Numbers

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        // Start typing your Java solution below
        // DO NOT write main() function
        int val = l1.val + l2.val;
        ListNode ret = new ListNode(val % 10);
        ListNode lastnode = ret;
        while(l1.next != null || l2.next !=null){
            int newval = 0;
            if (l1.next != null){
                l1 = l1.next;
                newval += l1.val;
            }
            if (l2.next != null){
                l2 = l2.next;
                newval += l2.val;
            }
            if (val > 9) newval ++;
           
            if (lastnode == ret){
                ret.next = new ListNode(newval % 10);
                lastnode = ret.next;
            }
            else {
                lastnode.next = new ListNode(newval % 10);
                lastnode = lastnode.next;
            }
           
            val = newval;
        }
       
        if (val > 9){
            lastnode.next = new ListNode(1);
            lastnode = lastnode.next;
        }
       
        lastnode.next = null;
       
        return ret;
    }
}