calendar application with messages

I'm having a deadlock here, I'm setting up a screen for my app, where it has a calendar, where the dates appear, and when I touch the date it appears the notes that another user made, but he wanted to know how he would do those notes, if I would do via database with the firebase or if I would do it directly in the app, and how exactly would it do that?

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;

import com.applandeo.materialcalendarview.CalendarView;
import com.applandeo.materialcalendarview.EventDay;
import com.applandeo.materialcalendarview.exceptions.OutOfDateRangeException;
import com.applandeo.materialcalendarview.listeners.OnDayClickListener;
import com.applandeo.materialcalendarview.utils.DateUtils;
import com.projeto.ensinodigital.ensinodigital.R;

import java.util.ArrayList;
import java.util.Calendar;
import java.util.List;
import java.util.Random;


public class AgendaActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_agenda);

        List<EventDay> events = new ArrayList<>();

        Calendar calendar = Calendar.getInstance();
        events.add(new EventDay(calendar, R.drawable.common_google_signin_btn_icon_dark));

        Calendar calendar1 = Calendar.getInstance();
        calendar1.add(Calendar.DAY_OF_MONTH, 2);
        events.add(new EventDay(calendar1, R.drawable.common_google_signin_btn_icon_dark));

        Calendar calendar2 = Calendar.getInstance();
        calendar2.add(Calendar.DAY_OF_MONTH, 5);
        events.add(new EventDay(calendar2, R.drawable.common_google_signin_btn_icon_dark));

        CalendarView calendarView = (CalendarView) findViewById(R.id.calendarView);

        Calendar min = Calendar.getInstance();
        min.add(Calendar.MONTH, -2);

        Calendar max = Calendar.getInstance();
        max.add(Calendar.MONTH, 2);

        calendarView.setMinimumDate(min);
        calendarView.setMaximumDate(max);

        calendarView.setEvents(events);

        calendarView.setDisabledDays(getDisabledDays());

        calendarView.setOnDayClickListener(new OnDayClickListener() {
            @Override
            public void onDayClick(EventDay eventDay) {
                Toast.makeText(getApplicationContext(), eventDay.getCalendar().getTime().toString() + " " + eventDay.isEnabled(),
                        Toast.LENGTH_LONG).show();

            }
        });

        Button setDateButton = (Button) findViewById(R.id.setDateButton);

        setDateButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                  //problema ta aqui, fica vermelho e ainda não consigo terminar //pq fala algo sobre variable calendario view is accessed from within inner class
                   calendarView.setDate(getRandomCalendar());
                } catch (OutOfDateRangeException exception) {
                    exception.printStackTrace();

                    Toast.makeText(getApplicationContext(),
                            "Date is out of range",
                            Toast.LENGTH_LONG).show();
                }
            }
        });
    }

    private List<Calendar> getDisabledDays() {
        Calendar firstDisabled = DateUtils.getCalendar();
        firstDisabled.add(Calendar.DAY_OF_MONTH, 2);

        Calendar secondDisabled = DateUtils.getCalendar();
        secondDisabled.add(Calendar.DAY_OF_MONTH, 1);

        Calendar thirdDisabled = DateUtils.getCalendar();
        thirdDisabled.add(Calendar.DAY_OF_MONTH, 18);

        List<Calendar> calendars = new ArrayList<>();
        calendars.add(firstDisabled);
        calendars.add(secondDisabled);
        calendars.add(thirdDisabled);
        return calendars;
    }

    private Calendar getRandomCalendar() {
        Random random = new Random();

        Calendar calendar = Calendar.getInstance();
        calendar.add(Calendar.MONTH, random.nextInt(99));

        return calendar;
    }
}