4
\$\begingroup\$

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 dbURl = "jdbc:mysql://localhost:3306/employees";
        try {
            conn = DriverManager.getConnection(dbURl, "root", "1234");
            if (conn != null) {
                System.out.println("Connected");

                String s1 = "SELECT * FROM employees";
                statement = conn.createStatement();

                rs = statement.executeQuery(s1);

                table.setModel(buildTableModel(rs));
                table.setBounds(10, 11, 634, 216);

            }

        } catch (Exception ex) {
            System.out.println(ex.getMessage());
        }

        table.getSelectionModel().addListSelectionListener((ListSelectionEvent event) -> {
            try {

                if (table.getSelectedRow() >= 0) {
                    Object employee_id = table.getValueAt(table.getSelectedRow(), 0);
                    Object full_name = table.getValueAt(table.getSelectedRow(), 1);
                    Object gender = table.getValueAt(table.getSelectedRow(), 2);
                    Object department = table.getValueAt(table.getSelectedRow(), 3);
                    Object position = table.getValueAt(table.getSelectedRow(), 4);
                    Object salary = table.getValueAt(table.getSelectedRow(), 5);

                    txtID.setText(employee_id.toString());
                    txtName.setText(full_name.toString());
                    txtGender.setText(gender.toString());
                    txtDep.setText(department.toString());
                    txtPosition.setText(position.toString());
                    txtSalary.setText(salary.toString());
                }
            } catch (Exception ex) {
                System.out.println(ex.getMessage());
            }
        });

        JPanel buttonPane = new JPanel();
        buttonPane.setBounds(0, 376, 655, 33);
        FlowLayout fl_buttonPane = new FlowLayout(FlowLayout.LEFT);
        fl_buttonPane.setHgap(10);
        buttonPane.setLayout(fl_buttonPane);
        getContentPane().add(buttonPane);

        JButton btnAdd = new JButton("ADD");
        btnAdd.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                String sql_stmt = "INSERT INTO employees (full_name,gender,department,position,salary)";
                sql_stmt += " VALUES ('" + txtName.getText() + "','" + txtGender.getText() + "','" + txtDep.getText()
                        + "','" + txtPosition.getText() + "','" + txtSalary.getText() + "')";

                try {

                    statement.executeUpdate(sql_stmt);
                    rs = statement.executeQuery("select * from employees");
                    table.setModel(buildTableModel(rs));

                } catch (SQLException e) {
                    System.out.println(e.getMessage());
                }

                clearInputBoxes();
            }
        });
        buttonPane.add(btnAdd);

        JButton btnUpdate = new JButton("UPDATE");
        btnUpdate.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
                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() + "'";

                try {

                    statement.executeUpdate(sql_stmt3);
                    rs = statement.executeQuery("select * from employees");
                    table.setModel(buildTableModel(rs));

                } catch (SQLException e) {
                    System.out.println(e.getMessage());
                }

                clearInputBoxes();
            }
        });
        btnUpdate.setActionCommand("OK");
        buttonPane.add(btnUpdate);
        getRootPane().setDefaultButton(btnUpdate);

        JButton btnDel = new JButton("DELETE");
        btnDel.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {

                String sql_stmt2 = "DELETE FROM employees WHERE employee_id = '" + txtID.getText() + "'";
                try {

                    statement.executeUpdate(sql_stmt2);
                    rs = statement.executeQuery("select * from employees");
                    table.setModel(buildTableModel(rs));

                } catch (SQLException e) {
                    System.out.println(e.getMessage());
                }

                clearInputBoxes();
            }

        });

        btnDel.setActionCommand("Cancel");
        buttonPane.add(btnDel);

        JLabel lblID = new JLabel("ID");
        lblID.setFont(new Font("Verdana", Font.BOLD, 14));
        lblID.setBounds(26, 237, 79, 23);
        getContentPane().add(lblID);

        JLabel lblFullname = new JLabel("Fullname");
        lblFullname.setFont(new Font("Verdana", Font.BOLD, 14));
        lblFullname.setBounds(26, 271, 79, 23);
        getContentPane().add(lblFullname);

        JLabel lblGender = new JLabel("Gender");
        lblGender.setFont(new Font("Verdana", Font.BOLD, 14));
        lblGender.setBounds(340, 237, 79, 23);
        getContentPane().add(lblGender);

        JLabel lblPosition = new JLabel("Position");
        lblPosition.setFont(new Font("Verdana", Font.BOLD, 14));
        lblPosition.setBounds(340, 271, 79, 23);
        getContentPane().add(lblPosition);

        JLabel lblDep = new JLabel("DEP");
        lblDep.setFont(new Font("Verdana", Font.BOLD, 14));
        lblDep.setBounds(26, 305, 79, 23);
        getContentPane().add(lblDep);

        JLabel lblSalary = new JLabel("Salary");
        lblSalary.setFont(new Font("Verdana", Font.BOLD, 14));
        lblSalary.setBounds(340, 305, 79, 23);
        getContentPane().add(lblSalary);

        txtID = new JTextField();
        txtID.setBounds(115, 240, 215, 20);
        getContentPane().add(txtID);
        txtID.setColumns(10);

        txtName = new JTextField();
        txtName.setColumns(10);
        txtName.setBounds(115, 274, 215, 20);
        getContentPane().add(txtName);

        txtDep = new JTextField();
        txtDep.setColumns(10);
        txtDep.setBounds(115, 308, 215, 20);
        getContentPane().add(txtDep);

        txtGender = new JTextField();
        txtGender.setColumns(10);
        txtGender.setBounds(429, 240, 107, 20);
        getContentPane().add(txtGender);

        txtPosition = new JTextField();
        txtPosition.setColumns(10);
        txtPosition.setBounds(429, 274, 215, 20);
        getContentPane().add(txtPosition);

        txtSalary = new JTextField();
        txtSalary.setColumns(10);
        txtSalary.setBounds(429, 308, 215, 20);
        getContentPane().add(txtSalary);

    }

    public static DefaultTableModel buildTableModel(ResultSet rs) throws SQLException {

        ResultSetMetaData metaData = rs.getMetaData();

        // names of columns
        Vector<String> columnNames = new Vector<String>();

        int columnCount = metaData.getColumnCount();

        for (int column = 1; column <= columnCount; column++) {
            columnNames.add(metaData.getColumnName(column));

        }

        // data of the table
        Vector<Vector<Object>> data = new Vector<Vector<Object>>();

        while (rs.next()) {

            Vector<Object> vector = new Vector<Object>();

            for (int columnIndex = 1; columnIndex <= columnCount; columnIndex++) {
                vector.add(rs.getObject(columnIndex));
            }
            data.add(vector);
        }

        return new DefaultTableModel(data, columnNames);

    }

    private void clearInputBoxes() {
        txtID.setText("");
        txtName.setText("");
        txtGender.setText("");
        txtDep.setText("");
        txtPosition.setText("");
        txtSalary.setText("");
    }

    public static void main(String[] args) throws Exception {
        GUI g = new GUI();
        g.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
        g.setVisible(true);
    }
}
\$\endgroup\$
2
\$\begingroup\$

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.

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.