MainActivity.java (CalenderView)

public class MainActivity extends AppCompatActivity implements OnDateSelectedListener, OnMonthChangedListener {

    private static final DateFormat FORMATTER = SimpleDateFormat.getDateInstance();

    @Bind(R.id.calendarView)
    MaterialCalendarView widget;

    @Bind(R.id.textView)
    TextView textView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ButterKnife.bind(this);

        widget.setOnDateChangedListener(this);
        widget.setOnMonthChangedListener(this);

        //Setup initial text
        textView.setText(getSelectedDatesString());
    }

    @Override
    public void onDateSelected(@NonNull MaterialCalendarView widget, @Nullable CalendarDay date, boolean selected) {
        textView.setText(getSelectedDatesString());
        Toast.makeText(getApplicationContext(),""+getSelectedDatesString(),Toast.LENGTH_LONG).show();
    }

    @Override
    public void onMonthChanged(MaterialCalendarView widget, CalendarDay date) {
        //noinspection ConstantConditions
        getSupportActionBar().setTitle(FORMATTER.format(date.getDate()));
    }

    private String getSelectedDatesString() {
        CalendarDay date = widget.getSelectedDate();
        if (date == null) {
            return "No Selection";
        }
        return FORMATTER.format(date.getDate());
    }
}