Alphabetical order of what? Fiction books? In Dewey, fiction pretty much all goes in the same place--800s, sorted maybe language and national origin; stuff is otherwise probably only sorted by author's last name or the main entry otherwise. Most libraries I've seen using Dewey don't even bother to use the DDC on the fiction stuff, because there's no point--and they separate from the rest of the fiction (mystery, romance, western, graphic novels, etc) because genre readers like that. It saves a lot of hunting. DDC doesn't have any kind of genre provision. Neither does the Library of Congress Classification. The closest you're likely to get is the use of LOC Subject Headings, which have a little bit of provision for genre, but it's frankly overkill to use them.
Classification is all about organizing the non-fiction, which constitutes the bulk of most published material, including what's held in most libraries. Trust me, when you come looking for, say, books on Java, you'll be glad they're not interfiled with every other book in the collection, alphabetical under the author's name.