Julia is a realist in that she has a real grip on her humanity, and that of others. She obviously is against Big Brother and the system, and the reason for this is that she understands that there is validity to being a regular, free, loved and loving person. She is also a realist in that she uses every tool she needs to get what she wants, and in that see can see the weaknesses of others and use them to work them around the things she wants and needs.
She may be a cynic, though, if you think of her being an idealist and trying to live out some utopian goal that she wanted to create for herself, going against the "norm" of her society. However, I do not think there is more evidence to support cynicism than there is to support her realism.
In the context in which George Orwell's novel 1984 takes place, there is no real distinction between a realist and a cynic. So autocratic is the society Orwell depicts, and so dystopian, that any individual who accurately perceives the situation in which he or she exists can easily appear both a realist and a cynic, and Julia certainly qualifies. The episode in Chapter 10 when Winston more-or-less formally makes Julia's acquaintance illustrates the nature of Julia's character quite well. Inquiring of his new-found friend the origins of the chocolate she has shared with him, he receives the following reply:
'Black market,’ she said indifferently. ’Actually I am that sort of girl, to look at. I’m good at games. I was a troop-leader in the Spies. I do voluntary work three evenings a week for the Junior Anti-Sex League. Hours and hours I’ve spent pasting their bloody rot all over London. I always carry one end of a banner in the processions. I always Iook cheerful and I never shirk anything. Always yell with the crowd, that’s what I say. It’s the only way to be safe.’
Julia is very much a realist in her perception of the society in which she lives, and of the requirements of continuing to exist in that society with a modicum of privilege. She is, however, exceptionally cynical in her interpretation of the government's dictates and of the nature of that society. Under the circumstances in which she lives, Julia is both a realist and a cynic, as it would, for any citizen possessed of even a modicum of critical thought in the society depicted in 1984, be impossible to be otherwise.