Can you find the problem in this code?

Question

I've searching some examples of the using of JTable on this forum.
So I've used a code found here.
But nothing happens, the JFrame doesn't appear on screen.
I'm sure my database "CLIENTES" exists inside the db folder. And also there's data inside "CLIENTES" table.
So, where is the problem then?
Thanks.
import java.io.*;
import java.sql.*;
import java.util.*;
import javax.swing.*;
import javax.swing.table.*;
public class TelaPrincipal extends JFrame {
   public TelaPrincipal() {
        Vector columnNames = new Vector();
        Vector data = new Vector();
        try {
           //  Connect to the Database
           String driver = "org.hsqldb.jdbcDriver";
           String url = "jdbc:hsqldb:file:./db/CLIENTES";
           String userId = "sa";
           String password = "";
           Class.forName(driver);
           Connection connection = DriverManager.getConnection(url, userId, password);
           //  Read data from a table
           String sql = "SELECT * FROM CLIENTES";
           Statement stmt = connection.createStatement();
           ResultSet rs = stmt.executeQuery(sql);
           ResultSetMetaData md = rs.getMetaData();
           int columns = md.getColumnCount();
           //  Get column names
           for (int i = 1; i <= columns; i++){
              columnNames.addElement( md.getColumnName(i) );
           //  Get row data
           while (rs.next()) {
              Vector row = new Vector(columns);
              for (int i = 1; i <= columns; i++) {
                 row.addElement(rs.getObject(i));
              data.addElement(row);
           rs.close();
           stmt.close();
        catch(ClassNotFoundException cnfe) {
           cnfe.printStackTrace();
        catch(SQLException sqle) {
          sqle.printStackTrace(); 
        //  Create table with database data
        JTable table = new JTable(data, columnNames);
        JScrollPane scrollPane = new JScrollPane( table );
        getContentPane().add(scrollPane);
    public static void main(String[] args) {
       TelaPrincipal tp = new TelaPrincipal();
       tp.setDefaultCloseOperation(EXIT_ON_CLOSE);
       tp.pack();
       tp.setVisible(true);
}

Answer 1

the jdbc driver is not on the classpath?