The getLikes() method, as you pointed out, takes an Object ID and returns a list of users who have liked that object. To get the things that a user has liked, you should use getPagesLiked(). With no arguments, it gets a list of Page objects for the objects that the authenticated user has liked or you can pass in a user ID to get that user's likes.
In case it's unclear, the reason it returns a list of Page objects is because ultimately almost every object on Facebook is represented by a Page. So, when you "like" a television show, restaurant, or whatever, you're really liking the page that represents that object.
Spring Social Project Lead