Honestly banning Java books is doing any future programmers a service. j/k
But they ban books on all kinds of things, like Buddhism, which I've seen attributed to a fear that prisoners will teleport themselves out of prison or something.
I knew two CO's, both pitiable folk who couldn't pass the police test, so as unsurprising as it should be, prison book policies never cease to surprise me in their unrelenting stupidity.
I always picture that warden from that movie who said something like "the only book you need is the Bible, son"