error while validatingjava.lang.NullPointerException

Question

I have the code once I am running it it just gave me error error while validatingjava.lang.NullPointerException

   public Login() {


    setTitle("Appoinment Booking System :: Login");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBackground(new Color(250, 250, 210));
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);

    JLabel userLabel = new JLabel("Username");

    JLabel passwordLabel = new JLabel("Password");

    userText = new JTextField();
    userText.setColumns(10);

    passwordText = new JPasswordField();

    JLabel lblLogin = new JLabel("Login ");

    JLabel lblNewLabel = new JLabel("Appoinment Booking Sytem");
    lblNewLabel.setFont(new Font("Tahoma", Font.PLAIN, 25));
    lblNewLabel.setForeground(new Color(32, 178, 170));

    JButton btnLogin = new JButton("Login");
    btnLogin.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {

            System.out.println("a");
            dao = new AppDao();
            //System.out.println("b");
            char[] tempPass = passwordText.getPassword();
            //System.out.println("c");
            String password=null;
            //System.out.println("D");
            password = String.copyValueOf(tempPass);
            //System.out.println("e");
            if(dao.verifyUser(userText.getText(), password))
            {
                dispose();
                System.out.println("f");
                 //JOptionPane.showMessageDialog(null, "You have logged in successfully","Success",
                 //        JOptionPane.INFORMATION_MESSAGE);
                 new Dashboard(userText.getText());
                 System.out.println("g");
                //this.setContentPane(dashboard);

            }
            else 
            {
                 JOptionPane.showMessageDialog(null, "You not  logged in successfully","Success",
                         JOptionPane.INFORMATION_MESSAGE);
                         System.out.println("h");
            }
        }
    });

Now I have the connector in other class in other class, I really stock to hot to solve this problem it , I have add two three different type of the connector it did not work < I have made some other tips as well to solve this problem as well but it does not work so I need any programmer attention to solve this problem

  Connection con;
  PreparedStatement pst;
  ResultSet rs;
  AppDao() {
    try {
        System.out.println("a");
        //MAKE SURE YOU KEEP THE mysql_connector.jar file in java/lib folder
        //ALSO SET THE CLASSPATH
        String MYSQL_DRIVER_CLASS_NAME = ("com.mysql.jdbc.Driver");
        System.out.println("b");
        String MYSQL_DB_CONNECTION_PATH = ("jdbc:mysql://localhost:90/booking_appointment");
        System.out.println("f");
        String MYSQL_DB_USERNAME = "root";
        System.out.println("f");
        String MYSQL_DB_PASSWORD = "cnwl";
        System.out.println("c");
    } catch (Exception e) {
        System.out.println(e);
    }
  }
  public Connection getConnection() {
    try {
        Class.forName("com.mysql.jdbc.Driver");
        con = DriverManager.getConnection("jdbc:mysql://localhost:90/booking_appointment", "root", "cnwl");
        return con;
    } catch (Exception e) {
        // TODO: handle exception
        e.printStackTrace();
        return null;
    }
  }