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.
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.