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

        Statement s = c.createStatement();
        String sql =
          "update producto set nombre='%2', precio='%3' where codigo='%1'";
        sql = sql.replace("%1",jTextField1.getText());
        sql = sql.replace("%2",jTextField2.getText());
        sql = sql.replace("%3",jTextField3.getText());
        s.execute(sql);

        jButton1ActionPerformed(null);

        javax.swing.JOptionPane.showMessageDialog(null, sql);
      } catch(Exception e){
        e.printStackTrace();
      }