I build fairly high-performance Java code. And get hit with three major gotchas which prevent it from approaching C code.

- There's no way to do array access without null pointer and index checks each and every time.

- Generics with basic types, and their unfortunate embedding into syntax (like the new for() syntax), are awful. Boxing and unboxing incur a ludicrously high penalty, and generics push coders away from using arrays. Unlike in C++, generics have been the enemy of performance.

- Poor quality collections classes (ArrayList and HashMap are notoriously bad)

Sure there's a few other things like pointer walking etc. in C, and Java's poor floating point, but the big three above are the killers.