J2SDK 1.3.1's version string is:
/usr/local/java/jdk1.3.1/solsparc/bin/java -version
java version "1.3.1-rc1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-rc1-b18)
Java HotSpot(TM) Client VM (build 1.3.1rc1-b18, mixed mode)

Note HotSpot version string doesn't have a "-" between "1.3.1" and "rc1", but J2SE version string does have it.