// Controller.java
public class Controller {
    @FXML
    public MenuButton sendBtn;


    @FXML
    public void initialize(){
    }
}

//Main.java
public class Main extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception{
        Parent root = FXMLLoader.load(getClass().getResource("sample.fxml"));
        primaryStage.setTitle("title");
        primaryStage.setScene(new Scene(root, 350, 400));
        primaryStage.show();
    }


    public static void main(String[] args)
    {

        launch(args);

     // sendBtn.setText("new !"); ??

    }
}