Add two number represented by Linked Lists - Algorithms and Problem SolvingAlgorithms and Problem Solving

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: (9 -> 9 -> 7) + (4 -> 3 -> 7)
Output: 1 -> 5 -> 3 -> 3

public class ListNode {
	      int val;
	      ListNode next;
	      ListNode(int x) { val = x; }
	  }
    
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
        ListNode result = null;
        ListNode tail = null;
        int carry = 0;
        while(l1 != null || l2 != null){
            int a = (l1 != null) ? l1.val : 0;
            int b = (l2 != null) ? l2.val : 0;
            
            int sum = (a+b)+carry;
            carry = sum/10;
            ListNode node = new ListNode(sum%10);
            if(result == null){
                result = node;
                tail = node;
            }
            else{
                tail.next = node;
                tail=node;
            }
            
            l1 = l1 != null ? l1.next : l1;
            l2 = l2 != null ? l2.next : l2;
        }
        
        if(carry == 1){
            ListNode node = new ListNode(1);
            tail.next = node;
        }
        
        return result;
    }