import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.fxml.FXMLLoader;
import javafx.stage.Stage;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.scene.control.Label;

public class App extends Application {
    public static void main(String[] args) {
        launch(args);
    }

    @Override
    public void start(Stage primaryStage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("app.fxml"));
        Scene scene1 = new Scene(root, 300, 250);
        primaryStage.setScene(scene1);
        primaryStage.show();
    }

    @FXML
    private Label celfelirat;

    @FXML
    protected void onClickMehetGomb(ActionEvent event) {
        celfelirat.setText("Működik");
    }
}