Multiple Alarms not working

this is code for multiple ALARMS but its not working. Thanx in advance

Intent intentAlarm = new Intent(MainActivity.this,AlarmReceiver.class); final int _id = (int) System.currentTimeMillis();

PendingIntent intent = PendingIntent.getBroadcast(this, _id, intentAlarm, PendingIntent.FLAG_UPDATE_CURRENT); //r3 is value entered by use in milliseconds (for example if users enters 15000 then alarm should fire after 15 seconds)

long r4=r3+new GregorianCalendar().getTimeInMillis(); AlarmManager alarmManager=(AlarmManager) getSystemService(Context.ALARM_SERVICE); alarmManager.set(AlarmManager.RTC_WAKEUP,r4, intent);