Here's a simple counter app consisting of only a TextView and a Button. When the Button is pressed the counter (TextView

public class MainActivity extends AppCompatActivity implements MainActivityView {
    TextView counter;
    Button button;
    MainActivityPresenter presenter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        presenter = new MainActivityPresenter(this);

        counter = (TextView) findViewById(R.id.textView);
        button = (Button) findViewById(R.id.button);
        button.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                int count = Integer.parseInt(counter.getText().toString());
                presenter.updateCounterTextView(count + "");
            }
        });
    }

    @Override
    public void changeTextViewText(String text) {
        counter.setText(text);
    }
}

public interface MainActivityView {
   void changeTextViewText(String text);
}

public class MainActivityPresenter {
  MainActivityView newView;

 public MainActivityPresenter(MainActivityView view) {
        newView = view;
    } // MainActivityPresenter()

  public void updateCounterTextView(String text){
        newView.changeTextViewText(text);
    }
}