Java actually doesn't have generics. It has syntactic sugar for generics, but they are so horribly broken they can't be fixed.

For example, because the generics are just sugar for casts, you can't specialize them. Because you can't specialize them, you have to put behavior in the "wrong place". Take for example a hash map from Double -> T. Because IEEE floats don't actually form an equivalence class (NaN != NaN), they don't make great keys to a hash table (if you put NaN in, you can't get it out). But, rather than specializing the hash table for floats to give special NaN handling, Java had to make Double(NaN) == Double(NaN), so when they're boxed, they do form an equivalence class.

And if that were the only inconsistent behavior in primitives versus their boxed counterparts, that would be great...

EDIT: To those who downvote, would you discuss your objections? I understand that I may come off a bit caustic, but having been burned by the myriad correctness issues in Java, it's hard not to. These aren't abstract problems that don't come up in practice -- for a public example, look at what Paul Phillips has to say about the JVM and standard libraries.