As described in PSARC/2003/321, the Multiple JRE support is intended
to be backported to the tail of appropriate release series. At a
minimum, this must include the 1.4.2 family (others were optional
based upon business need - no such need has yet be cited).
It is very significant that the critically important 1.4.2 family
is the only Java release family which won't function as the final
target of a JRE release specification. This is because a bug was
introduced in the support of the 32/64 bit version switching flags
which causes the launcher executable to not properly recognize
itself on Solaris and Linux.