This applies to any language with static types. Or that allows code to be separated in multiple files, for that matter.
In Haskell, I can literally ask the editor to list me all functions that operate on type X. Even in C written with a modicum of coding discipline, 90% of the functions relevant to type X will be defined in X.h, wherein 100% of the functions in X.h are relevant to type X. (And the 10% of functions relevant to type X that aren't in X.h? Well, in Java, they also wouldn't be part of class X anyway.)
