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).