Wait a sec, that's not infrastructure there running in individual trading departments. Major transactional backbones in banking almost all run on Java/Unix as I understand.
For the really mission-critical systems there's more COBOL, C++ and even VAX Basic (I'm not kidding) than there is Java, and there's a lot of mainframe and VMS too, and weird Unixes like Dynix. A lot of it is stuff that people outside the industry will never even see anymore.
One project I worked on in fixed income was C++ based, it could handle a few hundred trades per second on modest kit. When I left I think the J2EE rewrite was up to 6 trades per minute...
Thanks for the insights! Yes, my friend's dad in Munich used to program the main software handling Hypo-Vereinsbank's transactions and it was all in COBOL (a previous programmer had introduced a small rounding error, which resulted in havoc... good story).
Very interesting to see this diversity of systems.
Transactional backbones run COBOL, not Java. Only the inter-system interfaces uses Java and other "new" languages. However, most of them run on Unix...as in, versions of Unix that are older than the internet.
