Why do some claim that Java's implementation of generics is bad?

Question

I\'ve occasionally heard that with generics, Java didn\'t get it right. (nearest reference, here)

Pardon my inexperience, but what would have made them better?

Answer 1

Java generics are compile-time only and are compiled into non-generic code. In C#, the actual compiled MSIL is generic. This has huge implications for performance because Java still casts during runtime. See here for more.