try{
        Class.forName("com.mysql.jdbc.Driver");
        Connection c = DriverManager.getConnection(
          "jdbc:mysql://localhost/ventas2018","root","");

        Statement s = c.createStatement();
        ResultSet r = s.executeQuery(
                "select * from producto");

        DefaultTableModel model =
                (DefaultTableModel)jTable1.getModel();
        model.setNumRows(0);
        while (r.next()){
            String[] fila = { r.getString("codigo"),
                              r.getString("nombre"),
                              r.getString("precio")};
            model.addRow(fila);
        }

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