Interactor / use case class design?

I've heard that an interactor / use case class should only have one method which is the execute() method as it was discussed here and implemented here. But I found an example where the interactor class has more than one methods here. Which one is better? And as far as I know, the interactor classes aren't that necessary. So if I remove the interactor classes, should the presenter has all models it needs such as DatabaseManager and SharedPreferencesManager as its instance variable? Or there should be "one big interactor" as it was implemented here?