"To the best of our knowledge, the presented embedded Java system is the smallest Java system available. The Leros processor consumes less than 5% of the logic cells of the smallest FPGA from Altera and the Muvium compiler produces a JVM, including the Java application, that can execute in a few KB ROM and less than 1 KB RAM. The Leros processor is available in open-source and the Leros port of Muvium is freely available."
http://www.jopdesign.com/doc/lerosjvm.pdf
http://www.jopdesign.com/publications.html