JTable for employees in SQL table

I have been studying Java for 4 months and this project is what I came up with. I know I should make more classes and methods for quality but I am still learning. Please help to me if there is any simpler and cleaner ways to achieve the same results as this.

```
import java.awt.FlowLayout;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.event.ListSelectionEvent;
import javax.swing.table.DefaultTableModel;
import javax.swing.JTable;
import javax.swing.JLabel;
import java.awt.Font;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Vector;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;

public class GUI extends JDialog {

private JTextField txtID;
private JTextField txtName;
private JTextField txtDep;
private JTextField txtGender;
private JTextField txtPosition;
private JTextField txtSalary;
private JTable table;
ResultSet rs;
Connection conn;
Statement statement;

public GUI() throws SQLException {

setBounds(100, 100, 671, 448);
getContentPane().setLayout(null);
try {
// Set System L&F
UIManager.setLookAndFeel(
UIManager.getSystemLookAndFeelClassName());
} catch (UnsupportedLookAndFeelException | ClassNotFoundException | InstantiationException | IllegalAccessException ex) {
System.out.println(ex.getMessage());
}

table = new JTable();
JScrollPane scrollPane = new JScrollPane();
scrollPane.setBounds(10, 11, 635, 205);
getContentPane().add(scrollPane);

scrollPane.setViewportView(table);

String

Prefer composition over inheritance

Unless you want to modify the behavior of a class, don't inherit from it. You should have a field which is the JDialog and work with it.

Hungarian notation

With a good IDE, or with good naming, you don't have to add the type of in the variable name.

FlowLayout fl_buttonPane = new FlowLayout(FlowLayout.LEFT);

This could have been called buttonsLayout or something similar. Be clear with your name and take the time to choose name that matters. Re-read your code from bottom up, this can help sometimes to see where the names are troublesome.

Vector is a thing of the past

The Vector class should not been used anymore. Prefer the List interface with an implementation like ArrayList over it. See why I should not use Vector in Java for more information.

PreparedStatement

You should learned to use PreparedStatement in Java so that code that looks like this would become safer and cleaner :

String sql_stmt3 = "UPDATE employees SET full_name = '" + txtName.getText() + "'";
            sql_stmt3 += ",gender = '" + txtGender.getText() + "'";
            sql_stmt3 += ",department = '" + txtDep.getText() + "'";
            sql_stmt3 += ",position = '" + txtPosition.getText() + "'";
            sql_stmt3 += ",salary = '" + txtSalary.getText() + "'";
            sql_stmt3 += " WHERE employee_id = '" + txtID.getText() + "'";

One of the problem with creating a query by appending String is that your vulnerable to injection. By using PreparedStatement, you're negating a bit part of that issue, and you can re-use a preparedstatement too.

StackExchange Code Review Q#150835, answer score: 2