What is the theme in High Fidelity by Nick Hornby?

Hiding behind one's hobby is a theme in this book. Rob's hobby is music. He owns a record shop, regularly goes to gigs, and has an enormous record collection. Along with his colleagues Rob and Dick, his hobby has become an obsession. Together they send people away from the shop if they think he or she does not have a good taste in music, make compilation tapes corresponding to their moods, and spend most of their working day thinking up top five lists. Music has consumed Rob's life for so long he has begun to define his life by lists and references to popular culture. In Rob's world, his girlfriend is pretty in a Sheena Easton pre-Hollywood makeover kind of way and Bruce Springsteen singing about revisiting his old flames sounds like a good idea.