Override property types in child classes in java android

Question

I'm trying to implement my app with the MVP (Model-View-Presenter) pattern in Android but I'm facing a problem. I want to have an abstract base presenter with a view class property that is of a generic type ViewInterface but when creating a real presenter I'd like this property to be of the type RealPresenterView and if possible without needing to override the same function in all presenters.

As I probably didn't explain myself properly here's a bit of code to illustrate the case, first the base presenter:

abstract public class BasePresenter { protected ViewInterface view; protected ViewInterface getView() { return view; } }

then the real presenter

public class RealPresenter { protected RealPresenterView view; // ... view.methodOnlyExistingInRealPresenterView(); }

I wanted to be able to use the view in RealPresenter as RealPresenterView without needing to add much code in the class. Is that possible?

I've read about class templates but I haven't seen how to implement in this case without adding functions in every presenter.

n00dl3 · Accepted Answer · 2017-04-07 08:45:36Z

You can use generics :

BasePresenter

abstract public class BasePresenter<T extends ViewInterface> { protected T view; protected T getView() { return view; } }

RealPresenter

public class RealPresenter extends BasePresenter<RealPresenterView> { }

Note that I didn't code in java for some time, but I think that's ok.

mmm could be that <T implements ViewInterface> is <T extends ViewInterface>, this syntax gives me an error but if I change that looks like it works

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