@SuppressWarnings("unchecked") public <T extends SubSystem>T addSystemIfAbsent(Class<?> systemApi,T system){
  SubSystem oldService=_systemMap.putIfAbsent(systemApi,system);
  if (oldService != null) {
    return (T)oldService;
  }
  _pendingStart.add(system);
  if (_lifecycle.isActive()) {
    startSystems();
  }
  return null;
}

@ SuppressWarnings ( "unchecked" ) public < T extends SubSystem > T addSystemIfAbsent ( Class < ? > systemApi , T system ) { SubSystem oldService = _systemMap . putIfAbsent ( systemApi , system ) ; if ( oldService != null ) { return ( T ) oldService ; } _pendingStart . add ( system ) ; if ( _lifecycle . isActive ( ) ) { startSystems ( ) ; } return null ; }
adds a new system .
