Alexander Zakharov

import javafx.fxml.Initializable;

public class MainController implements Initializable {

    // ...

    @FXML
    public void initialize(URL location, ResourceBundle resources) {

       // ...

    }

// ...

}

public class AddFormController extends MainController {

    // ...

    @Override
    public void initialize(URL location, ResourceBundle resources) {
        super.initialize(location, resources);

        // ...

    }

    // ...

}