Add Two Numbers in Linked List

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:
Basic implementation question.
Tips: use a dummy head, which is the previous list node of the head.

public class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode dummy = new ListNode(0);
        ListNode tail = dummy;
        int carry = 0;
        while(l1 != null || l2 != null){
            int x = 0;
            int y = 0;
            if(l1 != null){
                x = l1.val;
                l1 = l1.next;
            }
            if(l2 != null){
                y = l2.val;
                l2 = l2.next;
            }
            int s = x + y + carry;
            ListNode node = new ListNode(s % 10);
            tail.next = node;
            tail = node;
            carry = s / 10;
        }
        if(carry == 1){
            ListNode node = new ListNode(carry);
            tail.next = node;
        }
        return dummy.next;
    }
}