The HotSpot JVM is mainly written in C++, but there are a few places where C code is used.

It should be noted that for most programming languages, it is highly likely that the compiler and other code used for most if not all programming languages are written in C. If you're using Java, you're using C code. If you're using Perl, you're using C code. If you're using Python, you're using C code. And so on.