I don't know where you got C++ from.
In any case, I assume they stayed with Java as their entire code base was Java with the exception of what ever they program their FPGAs with.
Re:A JVM Does That? (2011) [pdf]
by TickleSteve on Friday July 08, 2016 @01:52AM
(#12053770)
FPGA's are typically used for the real-time front-end in systems like this....
...Which means that the Java side wasn't doing anything particularly quick or real-time.
The Java side was the 'easy&slow' side.... hence they could use Java.
Yeah, I concur with what the other guy says. There is no way they were using Java for the HFT side.
C++ doesn't improve on I/O (including cache misses).
Even better than using C++? Something sounds off.