FXML Controllers are not set in stone; you can add methods to them and use them to transfer information.

Consider the following example for the FirstDocument.fxml we used earlier in this chapter:

public class SmartController implements Initializable {
    
    public void setText(String newText) {
        textField.setText(newText);
    }

    @FXML
    private Button button;

    @FXML
    private TextField textField;
    
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        button.setText("hello");
    } 
}

Now, we can work with the FXML variables from other classes, as in the following example, from Application:

FXMLLoader loader = new FXMLLoader(getClass().getResource("FirstDocument.fxml"));
HBox root = loader.load();
loader.<SmartController>getController().setText("Text from App");