First create a Timer like this

private Timer timer;
    private TimerTask timerTask;
    public void startTimer() {
        timer = new Timer();
        timerTask = new TimerTask() {
            public void run() {
                // Add your code
            }
        };
        timer.schedule(timerTask, 1000, 1000); //
    }

Also you need to stop your timer.
So

 public void stoptimertask() {
        if (timer != null) {
            timer.cancel();
            timer = null;
        }
    }

Call StartTimer and StopTimer in OnStartCommand() and onDestroy() respectively. Add these lines in onDestroy()

Intent broadcastIntent = new Intent();
        broadcastIntent.setAction("restartservice");
        broadcastIntent.setClass(this, Restarter.class);
        this.sendBroadcast(broadcastIntent);

it can be handled in multiple ways, you have not stopped your timer

Note:- posting code in Kotlin

1)

override fun onDestroy() {
   counter.cancel()
}

2. in your activity

override fun onResume() {
    super.onResume()
    val notificationManager = getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager
     notificationManager.cancelAll()
}

I’m developing a countdown app, and currently trying to show a notification when you exit the app while the countdown is running. Correspondingly, I want the notification to disappear when the user returns to the app.

So far I’ve managed to make it work for a simple notification with static text, do the following: in MainActivity.java, in onStop(), I create an intent and initiate the service with startService(intent). Symmetrically, in onStart() I run stopService(intent) so that when you return to the app the service gets canceled. This works like a charm, the notification appears and disappears when it must.

The next step has been trying to make the notification show a text that varies (it will say “X minutes remaining”). According to the info out there, to update an existing notification you have to create a new one, give it the same ID as the existing one, and call .notify of a NotificationManager. When I do this the notification indeed gets updated correctly (the text changes as expected), BUT: now, returning to the main activity does not cancel the notification. The icon stays up there and doesn’t get interrupted.

I’ve been trying to solve this for hours and hours. I’ve also tried hacks like sending signals via shared preferences to tell the service to stop, but for some reason, it seems to completely ignore the command stopself() too.

Does anybody have a suggestion of what could be the cause? Any help would be greatly appreciated. Here is the relevant code:

MainActivity.java:

    @Override
protected void onStart() {
    super.onStart();

    Intent serviceIntent = new Intent(getBaseContext(), CounterService.class);
    stopService(serviceIntent);

}

protected void onStop() {
    super.onStop();
    Intent serviceIntent = new Intent(getBaseContext(), CounterService.class);
    startService(serviceIntent);

}

CounterService.java:

public class CounterService extends Service {
Notification notification;
NotificationManager notificator;
Intent intentNoti;
CountDownTimer counter;
@Nullable
@Override
public IBinder onBind(Intent intent) {
    return null;
}

@Override
public void onCreate() {
    super.onCreate();
}

@Override
public int onStartCommand(Intent intent, int flags, int startId) {

intentNoti = new Intent(this, MainActivity.class);
final PendingIntent pending = PendingIntent.getActivity(this, 0, intentNoti, 0);

final Bitmap icon = BitmapFactory.decodeResource(getResources(),
            R.drawable.common_full_open_on_phone);

//Countdown
counter = new CountDownTimer (30000, 1000) {

        public void onTick(long millisUntilFinished) {
           String time = String.valueOf(System.currentTimeMillis());

            notification = new Notification.Builder(CounterService.this)
                    .setContentTitle("Name")
                    .setContentText(time)
                    .setSmallIcon(R.drawable.icon_start)
                    .setLargeIcon(Bitmap.createScaledBitmap(icon, 128, 128, false))
                    .setContentIntent(pending)
                    .setOngoing(true).build();

            notificator = (NotificationManager) getSystemService(Context.NOTIFICATION_SERVICE);
            notificator.notify(1001, notification);


        }

        public void onFinish() {
        }

    }.start();
    return START_STICKY;
  }
 @Override
    public void onDestroy() {
        super.onDestroy();
        counter.cancel();
    }
}