try {
                    double rikaz = Double.parseDouble(tFJmlRikaz.getString());
                    double nrikaz = Double.parseDouble(tFNisabRikaz.getString());
                    double zrikaz = 0;
                    zrikaz = rikaz * nrikaz;
                    tFZRikaz.setString(String.valueOf(zrikaz));
                } catch (NumberFormatException e) {
                    alert = new Alert("Error", "You should enter Username and Location", null, AlertType.ERROR);
                        alert.setTimeout(Alert.FOREVER);
                        myDisplay.setCurrent(alert);
                    e.printStackTrace();
                }

do wes ta tambahi ngene iki...
sing error ning myDisplay.setCurrent(alert);
opo goro2
aku kan gawene nganggo visualMidlet ning netbeans..
display ne bingung mungkin yo..