There are two primary advantages of C over Java: 1) C allows you to write programs that directly access the computer's hardware. This is essential for certain tasks, things like device drivers (programs that adapt the operating system to various hardware devices - video adapters, NIC cards, etc) and bootstrap loaders (programs that load the operating system) are good examples. 2) C programs execute almost as efficiently as programs written in assembler/machine language. Since the C language (in most implementations) doesn't perform any runtime error checking and has no instantion/finalizer overhead it can be translated to near-optimal machine language.
