I'm not an expert in HFT either, but know personally someone who's developing HFT apps in C++. I guess if your profit depends on milliseconds and lower, there's

I'm not an expert in HFT either, but know personally someone who's developing HFT apps in C++. I guess if your profit depends on milliseconds and lower, there's no point in taking chances with Java. But Java is of course huge in all kind of financial apps, including settlement of HFT deals (eg. not on a critical code path).