Linked List Add Forward

/**
You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.

You may assume the two numbers do not contain any leading zero, except the number 0 itself.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 8 -> 0 -> 7
*/
class LinkedListAdditionForward {
    public int carry=0;
    public ListNode newHead = null;

    public ListNode addTwoNumbers(ListNode h1, ListNode h2){
        int len1 = getLength(h1);
        int len2 = getLength(h2);
        if(len1>len2){
            int diff = len1-len2;
            while(diff>0){
                ListNode n = new ListNode(0);
                n.next = h2;
                h2=n;
                diff--;
            }
        }
        if(len1<len2){
            int diff = len2-len1;
            while(diff>0){
                ListNode n = new ListNode(0);
                n.next = h1;
                h1=n;
                diff--;
            }
        }
        ListNode newHead = addRecursion(h1, h2);
        if(carry!=0){
            ListNode n = new ListNode(1);
            n.next = newHead;
            newHead = n;
        }
        return newHead;
    }
    public ListNode addRecursion(ListNode h1, ListNode h2){
        if(h1==null && h2==null){
            return null;
        }
        addRecursion(h1.next, h2.next);
        int a = h1.val + h2.val + carry;
        carry=0;
        if(a>9){
            carry =1;
            a = a%10;
        }
        ListNode n = new ListNode(a);
        if(newHead==null){
            newHead =n;
        }else{
            n.next = newHead;
            newHead = n;
        }
        return newHead;
    }
    public int getLength(ListNode head){
        int len=0;
        while(head!=null){
            len++;
            head = head.next;
        }
        return len;
    }
}