Operating maintenance on Services via a scheduler Conception and implementation issue

This is the Service abstract class (I don't want to force the user to redefine terminate and initialize):

package schedule;

public abstract class Service {


    public abstract String getReferer ();


    public static void terminate () {

    }

    public static void initialize() {

    }
}

I'm making a Scheduler to operate treatment on a whole set of Services it has stored.

Scheduler is a Service, and it is an observer, and every Service is a Singleton.

Without talking about Singletons (I have already seen StackOverFlow mad over these, but I need a pool of classes with single controlled access) is it a bad idea to try to store types ? In that way, i could make something like

Set<Class<? extends Service>> servicePool; // defined in the ctor as a TreeSet

public static void initialize () {
    if (instance == null)
        throw new CustomException("Ill-initialised Scheduler");
    for (<? extends Service> S : instance.servicePool)
        S.initialize(); // static function called on S as a class.
}

Would that be a bad thing ? and Why ? Else, How to do it ? Maybe I shouldn't put initialize (and terminate) static in Scheduler, but it would mean to either stop it from being a Service (which is wrong, semantically) or to make initialize instance-dependant, which would lose all the interest of this Service thing.

Moreover, I will likely run lots of dead code (for the Services which didn't (for instance) redefined terminate (). Is there a way to test if (function is redefeined) then run function ?