action

@Override
    public void actionPerformed(ActionEvent e) {

        if (e.getSource() == btnSave) {

            try {
                int gTT = Integer.parseInt(txtTT.getText());
                int gTR = Integer.parseInt(txtTR.getText());
                String gName = txtName.getText();
                int gPhone = Integer.parseInt(txtPhone.getText());
                String gLab = cboLab.getSelectedItem().toString();

                String gRB = "";
                if (rbDJTMK.isSelected()) {
                    gRB = rbDJTMK.getActionCommand();
                } else if (rbDJPA.isSelected()) {
                    gRB = rbDJPA.getActionCommand();
                }

                JOptionPane.showMessageDialog(null, "Time taken : " + gTT + "\nTime returned : " + gTR
                        + "\nLecturer name : " + gName + "\nPhone number : " + gPhone
                        + "\nLaboratory : " + gLab + "\nDepartment : " + gRB);

                Class.forName("com.mysql.jdbc.Driver");
                conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/semester4", "root", "");
                stmt = conn.createStatement();
                stmt.executeUpdate("insert into laboratory values(" + gTT + "," + gTR + ",'" + gName + "'," + gPhone + ",'" + gLab + "','" + gRB + "')");

            } catch (Exception exc) {
                System.err.println("Got an exception! ");
                System.err.println(exc.getMessage());
            }

        }

        else if (e.getSource() == btnDisplay) {

            try {

                JOptionPane.showMessageDialog(null, "Load data from database ...");


                ResultSet rs = stmt.executeQuery("select * from laboratory");
                while (rs.next());

                int gdTT = rs.getInt("TIME_TAKEN");
                int gdTR = rs.getInt("TIME_RETURNED");
                String gdName = rs.getString("LECTURER_NAME");
                int gdPhone = rs.getInt("PHONE_NUMBER");
                String gdLab = rs.getString("LABORATORY");
                String gdDep = rs.getString("DEPARTMENT");

                DefaultTableModel model = new DefaultTableModel();
                JTable table = new JTable(model);
                JScrollPane scrollPane = new JScrollPane();

                model.addRow(new Object [] {gdTT, gdTR, gdName, gdPhone, gdLab, gdDep});
                table.setModel(model);
                scrollPane = new JScrollPane(table);
                scrollPane.setBounds(130,120,400,150);
                add(scrollPane);

            } catch (Exception exc2) {
                exc2.printStackTrace();
            }
        }

        else if (e.getSource() == btnClose) {
            int close = JOptionPane.showConfirmDialog(null, "Do you want to close this program ?", "Exit", JOptionPane.YES_NO_OPTION);
            if (close == JOptionPane.YES_OPTION) {
                System.exit(0);
            } else if (close == JOptionPane.NO_OPTION) {
                setDefaultCloseOperation(JFrame.DO_NOTHING_ON_CLOSE);
            }
        }

    }