In my experience NASDAQ's system is both a stellar example of law-latency Java and, due to its rarity, a demonstration of the apparent difficulty. Every other trading system I have seen implemented in Java has suffered noticably from poor memory management (too much GC-related variance). I would expect that Nasdaq approaches their trading software much more like an embedded system, at which point the engineering discipline and mastery of the playform matters much more than the language.

Also as mentioned elsewhere in the thread, trading systems don't suffer from frequent cold restarts, so hotspot work amortizes extremely well. So Java is much more optimal there than e.g. a command line tool.