private void btn_loginActionPerformed(java.awt.event.ActionEvent evt) {
                rs =db.querySelectAll(" users "," username=' "+txt_username.getText()
                            +"' and password='"+ txt_password.getText()+"'");
                    //System.out.println("La requête est bien passée");

            try {

                while(rs.next()){
                    username1 =rs.getString("username");
                        password1 =rs.getString("password");
                         hak = rs.getString("type");

                }
            }catch (SQLException ex){
                Logger.getLogger(Login.class.getName()).log(Level.SEVERE,null, ex);
            }
            if((username1 == null) && (password1 == null)){
                JOptionPane.showMessageDialog(this,"le nom utilisateur ou le mot de pass est incorrect");

            }else {
                if (hak.equals("directeur")){
                    Principale h = new Principale();
                    h.setVisible(true);
                    this.dispose();
                }else{
                    Cachier k = new Cachier();
                    k.setVisible(true);
                    this.dispose();
                }


        }
}                                         `