Leetcode-Add Two Numbers

You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

Solution:

/**
 * 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) {
        if (l1==null) return l2;
        if (l2==null) return l1;

        ListNode preHead = new ListNode(0);
        ListNode end = preHead;
        int carry = 0;
        while (l1!=null || l2!=null){
            int val = carry;
            if (l1!=null) val += l1.val;
            if (l2!=null) val += l2.val;            
            carry = val/10;
            val = val%10;
            ListNode newNode = new ListNode(val);
            end.next = newNode;
            end = newNode;
            if (l1!=null) l1 = l1.next;
            if (l2!=null) l2 = l2.next;
        }
        if (carry!=0){
            ListNode newNode = new ListNode(carry);
            end.next = newNode;
        }


        return preHead.next;
        
    }
}