LoginWindow loginWindow = new LoginWindow();

public class LoginWindow {

private JFrame frame;
private JTextField tf_Username;
private JPasswordField pf_Password;
private MainWindow mainWindow = new MainWindow();
private Connection connect = null;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                LoginWindow window = new LoginWindow();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}
public LoginWindow() {
    initialize();
    connect = SQLite.connectDb();
}

public void initialize() {
    frame = (new JFrame());
    frame.setTitle("Member Login");
    frame.getContentPane().setBackground(Color.GRAY);
    frame.setBounds(100, 100, 350, 200);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(null);
    frame.setResizable(false);

    JLabel lbl_Username = new JLabel("Username:");
    lbl_Username.setBounds(50, 71, 80, 14);
    frame.getContentPane().add(lbl_Username);

    JLabel lbl_Password = new JLabel("Password:");
    lbl_Password.setBounds(50, 96, 80, 14);
    frame.getContentPane().add(lbl_Password);

    pf_Password = new JPasswordField();
    pf_Password.addKeyListener(new KeyAdapter() {
        @Override
        public void keyTyped(KeyEvent e) {
            if(e.getKeyChar()==KeyEvent.VK_ENTER){
                login();
            }
        }
    });
    pf_Password.setBounds(119, 96, 160, 20);
    frame.getContentPane().add(pf_Password);

    JLabel lbl_LoginImage = new JLabel("");
    Image img = new ImageIcon(this.getClass().getResource("/Login.png")).getImage();
    lbl_LoginImage.setIcon(new ImageIcon(img));
    lbl_LoginImage.setBounds(65, 11, 214, 35);
    frame.getContentPane().add(lbl_LoginImage);

    tf_Username = new JTextField();
    tf_Username.setBounds(119, 68, 160, 20);
    frame.getContentPane().add(tf_Username);
    tf_Username.setColumns(10);

    JButton btn_Login = new JButton(" Login");
    Image imgBtn = new ImageIcon(this.getClass().getResource("/Button.png")).getImage();
    btn_Login.setIcon(new ImageIcon(imgBtn));
    btn_Login.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            login();
        }
    });
    btn_Login.setBounds(235, 127, 89, 23);
    frame.getContentPane().add(btn_Login);

}
public void login(){
    PreparedStatement preparedStatement = null;
    ResultSet result = null;
    try{

        preparedStatement = connect.prepareStatement("select * from Admins where Username=? and Password=?");
        preparedStatement.setString(1, tf_Username.getText());
        preparedStatement.setString(2, String.valueOf(pf_Password.getPassword()));
        result = preparedStatement.executeQuery();
        int cnt = 0;
        while(result.next()){
            cnt++;
        }
        if(cnt == 1){
            frame.dispose();
            mainWindow.setVisible(true);


        }
        else if(cnt > 1){
            JOptionPane.showMessageDialog(null, "Duplicate Username and Password!");
        }
        else{
            JOptionPane.showMessageDialog(null, "Username or Password is incorrect!");
        }
    }catch(Exception c){
        JOptionPane.showMessageDialog(null, c);
    }
    finally{
        try {
            result.close();
            preparedStatement.close();
        } catch (SQLException b) {
        }
    }
}

public class MainWindow extends JFrame {

private JPanel contentPane;
private Connection connect = null;

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                MainWindow frame = new MainWindow();
                frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

public MainWindow() {
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setBounds(100, 100, 450, 300);
    contentPane = new JPanel();
    contentPane.setBackground(Color.GRAY);
    contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
    setContentPane(contentPane);
    contentPane.setLayout(null);

    JLabel lbl_Welcome = new JLabel("Hello, ");
    lbl_Welcome.setBounds(10, 11, 216, 14);
    contentPane.add(lbl_Welcome);
}

public String getFullName(){
    connect = SQLite.connectDb();
    PreparedStatement preparedStatement = null;
    ResultSet result = null;

    try {
        preparedStatement = connect.prepareStatement("select * from Admins where Username=?");
        result = preparedStatement.executeQuery();;
        String name = result.getString("Name");
        String surname = result.getString("Surname");
        String fullname = name + "" + surname;
        return fullname;
    }catch (SQLException e) {
        JOptionPane.showMessageDialog(null, e);
        return null;
    }
    finally{
        try {
            result.close();
            preparedStatement.close();
        }catch (SQLException b) {
            JOptionPane.showMessageDialog(null, b);
        }
    }
}

public String getFullName(){
    connect = SQLite.connectDb();
    PreparedStatement preparedStatement = null;
    ResultSet result = null;

    try {
        preparedStatement = connect.prepareStatement("select * from Admins where Username=?");
        result = preparedStatement.executeQuery();;
        String name = result.getString("Name");
        String surname = result.getString("Surname");
        String fullname = name + "" + surname;
        return fullname;
    }catch (SQLException e) {
        JOptionPane.showMessageDialog(null, e);
        return null;
    }
    finally{
        try {
            result.close();
            preparedStatement.close();
        }catch (SQLException b) {
            JOptionPane.showMessageDialog(null, b);
        }
    }
}