public interface ExampleModel {
    Observable<String> getResponse(String request);
}

public interface ExampleView {
    Observable<String> changeText();
    void showResponse(String response);
}

public interface ExamplePresenter {
    void onCreate();
}

public class ExamplePresenerImpl implementation ExamplePresenter {
    private ExampleView view;
    private Model model;

    private Subscription subscription;

    public ExamplePresenterImpl(ExampleView view) {
        this.view = view;
	this.model = new RetrofitAdapter.Builder(ExampleModel.class).addUrl(...).build();
    }

    public void onCreate() {
        subscription = view
                           .changeText()
                           .flatMap(query -> model.getResponse(query))
                           .subscribe(response -> view.showResponse(response));
	}

    public void onDestroy() {
        subscription.unsubscribe();
    }
}

public class ExampleActivity extends Activity implementation ExampleView {
    private EditText editText;
    private TextView textView;
    private ExamplePresenter presenter;

    public void onCreate(...) {
        this.editText = (EditText) findViewById(...);
	this.textView = (TextView) findViewById(...);

	presenter = new ExamplePresenterImpl(this);
	presenter.onCreate();
    }

    public void onDestroy() {
        presenter.onDestroy();
    }

    @Override
    public Observable<String> changeText() {
        return ObservableWidge.text(editText);
    }

    @Override
    void showResponse(String response) {
        textView.setText(response);
    }
}