What is Java written in?

Sun actually has multiple JVMs. The HotSpot JVM is written largely in C++, because HotSpot is heavily based on the Animorphic Smalltalk VM which is written in C++.

More interesting than HotSpot is IMHO the Maxine Research VM, which is written (almost) completely in Java.

Strictly speaking, C++ (the JVM code does make use of C++ OO facilities).

You can find out for yourself at: http://www.sun.com/software/opensource/java/.

C.

Sun's not a Java shop; it's a C shop. That's what Solaris is written in.