Question

Ive got a few instances of subclasses of View (like ImageView, ViewGroup, TextView, etc) , which i have them all implement two methods a() and b() and they all have to run the same init() method which is long and does the same for all of them.
how should i design my architecture to enhance code reusability in that case?

if it was C++ i could multi inherite from view and a new abstract class that runs init() on time of creation and have abstarct methods a() and b(), how is it acheived in Java?

maybe there’s some way to acheive it using some kind of a decorator?

Answer 1

If I understand you correctly, you can create an abstract class AbstractView that extends View and implements your common init() method. AbstractView should declare the abstract methods a() and b(), but leave the implementations to the subclasses.

public abstract class AbstractView extends View {
    public void init() {
        // common init implementation here
    }

    public abstract void a();
    public abstract void b();
}

Since you’re trying to add behavior to a group of existing subclasses (ImageView, ViewGroup, TextView, etc.), you probably do need to create a wrapper for each subclass (MyImageView, MyViewGroup, MyTextView, etc.). Each of these subclasses would extend AbstractView and implement their own a() and b() methods, but inherit the common init() method (along with all of the methods implemented in the View class. You can then create delegate methods for the exising behavior in ImageView, ViewGroup, TextView, etc. that you need to keep unchanged.

public class MyImageView extends AbstractView {

    private ImageView wrappedImageView;

    public MyImageView(Context context) {
        wrappedImageView = new ImageView(context);
    }

    // TODO: Implement other constructor wrappers

    final void clearColorFilter() {
        wrappedImageView.clearColorFilter();
    }

    // TODO: Implement other method wrappers

    @Override
    public void a() {
        // specific implementation here
    }

    @Override
    public void b() {
        // specific implementation here
    }
}