Elegant way to handle Keyboard Input in JavaFX

Question

I am currently working on a calculator in JavaFX and right now trying to implement keyboard input support.

For this I am trying to implement an EventHandler in the main

Answer 1

If you refactor the handler methods so they just determine the value they represent, then call another method, e.g.:

@FXML
private void handleDigitAction(ActionEvent event) {

    String digit = ((Button) event.getSource()).getText();
    handleDigit(digit) ;
}

public void handleDigit(String digit) {
    if (state == State.FIRST || state == State.SECOND) {
        oldText = displayField.getText();
    } else {
        oldText = "";
    }

    if ("0".equals(oldText) /*|| "0.0".equals(oldText)*/) {
        displayField.setText(digit);
    } else {
        displayField.setText(oldText + digit);
    }

    if (state == State.EQUALED || state == State.FIRST) {
        oldValue = Double.parseDouble(displayField.getText());
        state = State.FIRST;
    } else {
        newValue = Double.parseDouble(displayField.getText());
        state = State.SECOND;
    }
}

then you can call the new method as needed:

@Override
public void start(Stage stage) throws Exception {
    FXMLLoader loader = new FXMLLoader(getClass().getResource("FXMLDocument.fxml"));
    Parent root = loader.load();
    FXMLDocumentController controller = loader.getController();

    Scene scene_main = new Scene(root);

    stage.setScene(scene_main);
    stage.show();

    scene_main.setOnKeyPressed(new EventHandler() {
        @Override
        public void handle(KeyEvent keyEvent) {

            switch (keyEvent.getCode()) {
                case DIGIT1:
                    controller.handleDigit("1");
                    break ;
                case DIGIT2:
                    controller.handleDigit("2");
                    break ;
                case DIGIT3:
                    controller.handleDigit("3");
                    break ;
                case DIGIT4:
                    controller.handleDigit("4");
                    break ;
                case DIGIT5:
                    controller.handleDigit("5");
                    break ;
                case DIGIT6:
                    controller.handleDigit("6");
                    break ;
                case DIGIT7:
                    controller.handleDigit("7");
                    break ;
                case DIGIT8:
                    controller.handleDigit("8");
                    break ;
                case DIGIT9:
                    controller.handleDigit("9");
                    break ;

            }
        }
    }
    );
}

and so on.