gistfile1.txt

final String GROUP_ID = "my_group";
final String CHANNEL_ID = "my_channel";


//called in Application.onCreate()
private void init(){

if(Build.VERSION.SDK_INT >= 26)
			{
			    NotificationManager notificationManager = getSystemService(NotificationManager.class);


				notificationManager.createNotificationChannelGroup(new NotificationChannelGroup(GROUP_ID, getResources().getString(R.string.app_name)));
				NotificationChannel notificationChannel =
						new NotificationChannel(CHANNEL_ID, getResources().getString(R.string.app_name), NotificationManager.IMPORTANCE_LOW);
				notificationChannel.setLockscreenVisibility(NotificationCompat.VISIBILITY_SECRET);
				notificationChannel.setShowBadge(true);
				notificationChannel.setGroup(GROUP_ID);
				notificationManager.createNotificationChannel(notificationChannel);

		}
		
		
		
}


//on API<=25 notification doesnt shown in Statusbar, but visible in notifications list
private void secretNotification(){

               NotificationCompat.Builder notif = new NotificationCompat.Builder(
				this, CHANNEL_ID) //doesnt work on API26 without ChannelID
				.setContentTitle(
						this.getResources().getString(R.string.app_name))
				.setContentText(text)
				.setChannelId(CHANNEL_ID)
				.setGroup(GROUP_ID)
				.setAutoCancel(false)
				.setPriority(NotificationCompat.PRIORITY_MIN)
				.setVisibility(NotificationCompat.VISIBILITY_SECRET)				
				.setSmallIcon(R.drawable.icon);

		startForeground(NOTIFICATION_ID, notif.build());

}


//notification visible always
private void visibleNotification(){
            NotificationManagerCompat nMgr =
					NotificationManagerCompat.from(this);

			NotificationCompat.Builder notif = new NotificationCompat.Builder(this, CHANNEL_ID)//doesnt work on API26 without ChannelID
			        .setContentTitle(this.getResources().getString(R.string.title))
					.setChannelId(CHANNEL_ID)
					.setGroup(GROUP_ID)
			        .setContentText(this.getResources().getString(R.string.text))			       
			        .setSmallIcon(android.R.drawable.ic_dialog_alert);
			 nMgr.notify(NOTIFICATION_ID2, notif.build());
			

}