Realism and Minimalism: The Sun Also Rises is definitely a "realistic novel" (take a look at the Bedford Guide, page 330.) Hemingway uses concrete details, colloquial speech, and heavy characterization through dialogue, in order to present a realistic view of the world. Hemingway's style has been called "minimalist," and he is famous for perfecting a simple, concise, concrete prose (enhanced by ironic understatement and underscored by emotional tension) that many writers have imitated ever since. He was heavily influenced by Ezra Pound's "imagist" movement. Imagist writing (see Bedford, page 169) demands "direct treatment of the 'thing'" and "the use of absolutely no word that does not contribute to the total design."
Hemingway's Characters: Hemingway's heroes tend to be "tough" characters who face the senselessness of "modern" society with courage and honesty. They can look brutality and death (even the apparent absence of God) in the face and either fight it with a primitive passion (think of the bullfighters) or accept it stoically, if cynically (think of Jake Barnes). Hemingway's heroes don't run away from the violent, hopeless society they see around them. In The Sun Also Rises Hemingway seems to sharply contrast strong, passionate characters like Jake and Pedro Romero with the insecure, self-pitying Robert Cohn. Brett Ashley, though tough minded and cynical, might actually be in a category of her own. Let's see what happens.