• They could be anything containing your Business Logic, Utils, Constants, Network Utils(Example: – Http call’s)
• We can make singleton class by our own by following  “Singleton Design Pattern”.
• We can also make use of “get_it” package which Flutter Favorite for registering instances globally with more advance concepts like Lazy Initialization, Depends On, with Different Scope and more...

getIt.registerSingleton<AlarmInventoryService>(AlarmInventoryService());