How to create simple daily notification system in Android API 29?

Question

As the title says, how to do it? I was looking for help in documentation and YouTube tutorials but it didn't help me at all.

What I want to have in my application is to let user schedule a daily notification to receive. For example if one sets 9am, then everyday at 9am phone notifies about something.

The best option would be to save current state of switch which tells if user wants to get notifications or not.

Right now, everything is taken from https://www.tutorialspoint.com/how-to-create-everyday-notifications-at-certain-time-in-android.

NotificationActivity.java

public class NotificationActivity extends AppCompatActivity {
    public static final String NOTIFICATION_CHANNEL_ID = "10001" ;
    private final static String default_notification_channel_id = "default" ;
    Button btnDate;
    final Calendar myCalendar = Calendar.getInstance () ;
    @Override
    protected void onCreate (Bundle savedInstanceState) {
        super .onCreate(savedInstanceState) ;
        setContentView(R.layout.activity_notification) ;
        btnDate = findViewById(R.id.btnDate) ;
    }
    private void scheduleNotification (Notification notification , long delay) {
        Intent notificationIntent = new Intent( this, NotificationReceiver.class ) ;
        notificationIntent.putExtra(NotificationReceiver.NOTIFICATION_ID , 1 ) ;
        notificationIntent.putExtra(NotificationReceiver.NOTIFICATION, notification) ;
        PendingIntent pendingIntent = PendingIntent. getBroadcast ( this, 0 , notificationIntent , PendingIntent. FLAG_UPDATE_CURRENT ) ;
        AlarmManager alarmManager = (AlarmManager) getSystemService(Context. ALARM_SERVICE ) ;
        assert alarmManager != null;
        alarmManager.set(AlarmManager. ELAPSED_REALTIME_WAKEUP , delay , pendingIntent) ;
    }
    private Notification getNotification (String content) {
        NotificationCompat.Builder builder = new NotificationCompat.Builder( this, default_notification_channel_id ) ;
        builder.setContentTitle( "Scheduled Notification" ) ;
        builder.setContentText(content) ;
        builder.setSmallIcon(R.drawable. ic_launcher_foreground ) ;
        builder.setAutoCancel( true ) ;
        builder.setChannelId( NOTIFICATION_CHANNEL_ID ) ;
        return builder.build() ;
    }
    DatePickerDialog.OnDateSetListener date = new DatePickerDialog.OnDateSetListener() {
        @Override
        public void onDateSet (DatePicker view , int year , int monthOfYear , int dayOfMonth) {
            myCalendar .set(Calendar. YEAR , year) ;
            myCalendar .set(Calendar. MONTH , monthOfYear) ;
            myCalendar .set(Calendar. DAY_OF_MONTH , dayOfMonth) ;
            updateLabel() ;
        }
    } ;
    public void setDate (View view) {
        new DatePickerDialog(NotificationActivity.this, date ,
                myCalendar .get(Calendar. YEAR ) ,
                myCalendar .get(Calendar. MONTH ) ,
                myCalendar .get(Calendar. DAY_OF_MONTH )
        ).show() ;
    }
    private void updateLabel () {
        String myFormat = "dd/MM/yy" ; //In which you need put here
        SimpleDateFormat sdf = new SimpleDateFormat(myFormat , Locale. getDefault ()) ;
        Date date = myCalendar .getTime() ;
        btnDate .setText(sdf.format(date)) ;
        scheduleNotification(getNotification( btnDate .getText().toString()) , date.getTime()) ;
    }
}

NotificationReceiver.java

import static com.pracainzynierska.inzynierka.SettingsActivity.NOTIFICATION_CHANNEL_ID ;
public class NotificationReceiver extends BroadcastReceiver {
    public static String NOTIFICATION_ID = "notification-id" ;
    public static String NOTIFICATION = "notification";
    public void onReceive (Context context , Intent intent) {
        NotificationManager notificationManager = (NotificationManager) context.getSystemService(Context. NOTIFICATION_SERVICE ) ;
        Notification notification = intent.getParcelableExtra( NOTIFICATION ) ;
        if (android.os.Build.VERSION. SDK_INT >= android.os.Build.VERSION_CODES. O ) {
            int importance = NotificationManager. IMPORTANCE_HIGH ;
            NotificationChannel notificationChannel = new NotificationChannel( NOTIFICATION_CHANNEL_ID , "NOTIFICATION_CHANNEL_NAME" , importance) ;
            assert notificationManager != null;
            notificationManager.createNotificationChannel(notificationChannel) ;
        }
        int id = intent.getIntExtra( NOTIFICATION_ID , 0 ) ;
        assert notificationManager != null;
        notificationManager.notify(id , notification) ;
    }
}

SettingsActivity (only part of saving switch state)

notificationSwitch = findViewById(R.id.NotificationSwitch);
        notificationSwitch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(SettingsActivity.this, NotificationActivity.class);
                startActivity(intent);
                SharedPreferences.Editor editor = getSharedPreferences(NicknameTextView.getText().toString(),MODE_PRIVATE).edit();
                editor.putBoolean("notification_status",notificationSwitch.isChecked());
                editor.commit();
            }
        });

I'm trying to save switch state by SharedPreferences cause my app is only local.