What is the theme of Salinger's The Catcher in the Rye?

A theme of a work of literature is the message the author would like to convey. Most pieces of literature—especially novels—have multiple themes. When stating the theme of a novel, it is important that you can support that theme with details from the text. I will briefly go over some possible themes for The Catcher in the Rye.
Alienation from society: Holden constantly pushes people away. He has a hard time understanding people and fitting in with society. He calls most people “phonies” for behaving in ways that he does not believe are completely genuine, which is ironic because he has a penchant for lying. When he meets with Sally Hayes, he criticizes her for liking certain movies. He says of the movie they are going to see:

I didn't much want to see it, but I knew old Sally, the queen of the phonies, would start drooling all over the place when I told her I had tickets for that, because the Lunts were in it and all. She liked shows that are supposed to be very sophisticated and dry and all, with the Lunts and all. I don't.

Holden goes on to say that he doesn’t like most actors because they are fake. His inability to understand and enjoy the things most people around him enjoy makes it difficult for him to fit in. He's so hard on people for being "phony" or conforming with society that he manages to constantly push people away.
Loss of innocence: Throughout the novel, Holden is preoccupied with preserving the innocence of children, especially his younger sister, Phoebe. This is where the novel gets its title. When Pheobe asks Holden what he wants to be when he grows up, he responds:

I keep picturing all these little kids playing some game in this big field of rye and all. Thousands of little kids, and nobody's around--nobody big, I mean--except me. And I'm standing on the edge of some crazy cliff. What I have to do, I have to catch everybody if they start to go over the cliff--I mean if they're running and they don't look where they're going I have to come out from somewhere and catch them. That's all I'd do all day. I'd just be the catcher in the rye and all. I know it's crazy, but that's the only thing I'd really like to be. I know it's crazy.

His desire to be the “catcher in the rye” symbolizes his desire to protect childhood innocence and keep young people away from harm.
The search for human connection: Ironically, though Holden pushes people away, he spends much of the novel searching for a real human connection. He mentions wanting to call up various people, especially his old friend, Jane, just so that he can interact with someone he understands. When he is looking for his sister, Phoebe, in the park, he comes across a girl whose ice skate he helps tighten. He even tries to spend more time with her, showing his desperation to talk to someone he doesn't see as "phony":

I asked her if she'd care to have a hot chocolate or something with me, but she said no, thank you. She said she had to meet her friend. Kids always have to meet their friend. That kills me.

He doesn’t see that it is odd that he, a teenager, would ask a little kid to go for hot chocolate with him, but it’s because his intentions are innocent. He simply wants to connect.