You must read JSR specifications if you have any such type of query.
I have copied and pasted the description of function registerAlarm:
public static long registerAlarm(String midlet,
Register a time to launch the specified application. The PushRegistry supports one outstanding wake up time per MIDlet in the current suite. An application is expected to use a TimerTask for notification of time based events while the application is running.
If a wakeup time is already registered, the previous value will be returned, otherwise a zero is returned the first time the alarm is registered.
midlet - class name of the MIDlet within the current running MIDlet suite to be launched, when the alarm time has been reached. The named MIDlet MUST be registered in the descriptor file or the jar file manifest with a MIDlet-<n> record. This parameter has the same semantics as the MIDletClassName in the Push registration attribute defined above in the class description.
time - time at which the MIDlet is to be executed in the format returned by Date.getTime()
the time at which the most recent execution of this MIDlet was scheduled to occur, in the format returned by Date.getTime()
ConnectionNotFoundException - if the runtime system does not support alarm based application launch
ClassNotFoundException - if the MIDlet class name can not be found in the current MIDlet suite or if this class is not included in any of the MIDlet-<n> records in the descriptor file or the jar file manifest or if the midlet argument is null
SecurityException - if the MIDlet does not have permission to register an alarm
Date.getTime(), Timer, TimerTask