What is the most common programming language used by quant firms?
C++
Is Java a good enough substitute for C++? Interpreters are substantially faster than they used to be, and financial applications don’t really need to interact with the hardware directly (as far as I can tell). Or is it worth learning C++ anyway.
When you join these firms, do they already have these programs in place? So all you do is maintenance, or do they expect you to make some jazzy models?
Quant stuff can be written in Java, but the problem is that all of the existing code is in C/C++. There aren’t many 3rd party libraries for quant available in Java either, so you’d either have to build a lot of stuff yourself, or use JNI to make Java talk to C++ libraries.
Got it! That makes a lot of sense to me now. Nothing wrong with Java, except that the industry standardized on C++ when Java was still in digital diapers, and no one wants to rewrite all that code, or have to have people be required to know JNI. Well… I got this C++ book right here… 
Make sure you get a SAS book next to that C++ book as well, and if you really want to be complete, make sure to go over Matlab as well.