Avoid Redundant Parameters for Generics in Java

Question

I'm creating a helper class for my JavaFX application as follows:

public class ViewHelper<T extends Parent, U extends Controller> {
    private static final String FXML_EXTENSION = ".fxml";
    private final Class<? extends Controller> clazz;
    private FXMLLoader loader;
    private T t;

    public ViewHelper(Class<? extends Controller> clazz) throws IOException {
        this.clazz = clazz;
        this.load();
    }

    private void load() throws IOException {
        this.loader = new FXMLLoader(fxmlUrl());
        this.t = this.loader.load();
    }

    private URL fxmlUrl() {
        return clazz.getResource(clazz.getSimpleName() + FXML_EXTENSION);
    }

    public T component() {
        return t;
    }

    public U controller() {
        return loader.getController();
    }
}

The usage is:

var viewHelper = new ViewHelper<BorderPane, MainController>(MainController.class);
BorderPane borderPane = viewHelper.component();
MainController mainController = viewHelper.controller();

It actually works and achieves what I want. However, it irritates me to see I have to pass MainController twice when at all times they are the same. No instance that they are not the same. How can I avoid one of them during instance creation of ViewHelper ?

Instead of:

var viewHelper = new ViewHelper<BorderPane, MainController>(MainController.class);

I would prefer something like:

var viewHelper = new ViewHelper<BorderPane>(MainController.class);

or:

var viewHelper = new ViewHelper<BorderPane, MainController>();

Thanks for any help.

Answer 1

You can add a static method to be called instead of the constructor.

public static <T extends Parent, U extends Controller> ViewHelper<T, U> of(Class<T> componentType, Class<U> controllerType) throws IOException {
    return new ViewHelper<T, U>(controllerType);
}

You then call it like this:

var viewHelper = ViewHelper.of(BorderPane.class, MainController.class);