public void initialize(){
    User user = new User();
    user.addUser();
}

public void addUser() {
    User newUser = new User();
    UserDAO uDAO = new UserDAO();
    uDAO.createUser(newUser);
}

package Server;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.io.IOException;
import java.nio.file.FileSystems;
import java.nio.file.Path;
import java.util.ArrayList;
import java.util.Scanner;

public class UserDAO implements UserDAOInterface {

    private static final String User_File = "users.txt";
    private File dataFile;

    public UserDAO() {
        Path dPath = FileSystems.getDefault().getPath("src/MainMenu",User_File);
        dataFile = new File(dPath.toString());
    }

    public ArrayList<User> getAllUsers() {
        Scanner sc;
        String record = null;
        String[] fields;
        ArrayList<User> users = new ArrayList<User>();

        try {
            sc = new Scanner(dataFile);
            while (sc.hasNextLine()) {
                record = sc.nextLine();
                fields = record.split(";");
                String username = fields[0];
                String password = fields[1];
                User u = new User();
                users.add(u);
            }
        } catch (FileNotFoundException e) {
            System.out.println("No record found!");
            //e.printStackTrace();
        }
        return users;
    }

    public User getUser(String username) {
        ArrayList<User> users = getAllUsers();
        User user = null;
        for (User u: users) {
            if (u.getUsername().equals(username)) {
                user = u;
                break;
            }
        }
        return user;
    }

    public boolean createUser(User user) {
        boolean existing = false;
        ArrayList<User> users = getAllUsers();
        for (User u: users) {
            if (u.getUsername().equals(user.getUsername())) {
                existing = true;
                break;
            }
        }
        if (!existing) {
            users.add(user);
            synToFile(users);
        }
        return !existing;
    }

    public void updateUser(User user) {
        ArrayList<User> users = getAllUsers();
        for (int i = 0; i < users.size(); i++) {
            User u = users.get(i);
            if (u.getUsername().equals(user.getUsername())){
                 users.set(i, user);
            }
        }
        synToFile(users);
    }

    public void deleteUser(User user) {
        ArrayList<User> users = getAllUsers();
        User delUser = null;
        for (User u: users) {
            if (user.getUsername().equals(u.getUsername())){
                delUser = u;
                break;
            }
        }
        if (delUser != null) {
            users.remove(delUser);
            synToFile(users);
        }
    }

    public void synToFile(ArrayList<User> userList) {
        if (userList == null) {
            return;
        }

        try {
            FileWriter out = new FileWriter(dataFile);
            for (User u: userList) {
                out.append(u.toString() + "n");
        }
        }catch (IOException e) {
            e.printStackTrace();
        }
    }
}