add one ll java

import java.util.Scanner;

/**
 * Created by MOHIT on 24-01-2018.
 */

class node{

    public int element;
    public node link;

    //constructor that accepts only element
    node(int element) {
        this.element = element;
        this.link = null;
    }

    //constructor that accepts both link and element
    node(int element, node link){
        this.element = element;
        this.link = link;
    }

    //method to update the element
    void updateData(int element){
        this.element = element;
    }

    //method to update or setup link
    void updateLink(node link){
        this.link = link;
    }

    //method to get the element from the node
    int getElement(){
        return this.element;
    }

    //method to get the next node
    node getNextNode(){
        return this.link;
    }
}

class LL {

    Scanner sc = new Scanner(System.in);
    node head;

    void insertAtStart(int number){

        node newNode = new node(number);

        if(head == null){
            head = newNode;
        } else {
            newNode.updateLink(head);
        }
        head = newNode;

        return;
    }

    void insertAtEnd(int element){
        if(head == null){
            this.insertAtStart(element);
            return;
        }
        node current = this.head;
        while(current.getNextNode() != null){
            current = current.getNextNode();
        }

        node newNode = new node(element);
        current.updateLink(newNode);
        return;
    }

    void display(){
        node current = this.head;

        while(current!= null){
            System.out.print(current.getElement());
            if(current.getNextNode() != null){
                System.out.print("-->");
            }
            current = current.getNextNode();
        }
    }

    // function to reverse k starting nodes from the linked list
    // function to reverse linked list
    void reverse(){
        if(this.head == null){
            return;
        }

        node nextNode = null;
        node prev = null;
        node current = this.head;
        while(current != null){
            nextNode = current.getNextNode();
            current.updateLink(prev);
            prev = current;
            current = nextNode;
        }
        this.head = prev;
    }

    void addOne(){
        this.reverse();
        addingOneUtil();
        this.reverse();
    }

    // adding one to linked list
    private void addingOneUtil(){
        int carry = 1;
        int sum = 0;
        node start = this.head;
        while(start != null && carry != 0){
            sum = start.getElement() + carry;
            start.updateData(sum % 10);
            carry = sum / 10;
            start = start.getNextNode();
        }
        if(carry != 0){
            this.insertAtEnd(carry);
        }
    }
}
public class LinkedList {
    public static void main(String arg[]) {
        System.out.println("Program to add one to a number represented by Linked List.");

        LL l1 = new LL();
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.insertAtEnd(9);
        l1.display();

        System.out.println("\nNumber after adding one is : ");
        l1.addOne();
        l1.display();
    }
}