If you are an active trader and consider Java, eventually you will be interested by JQuantLib http://www.jquantlib.org/
In a nutshell, it is an open source library for quantitative finance, written in 100% Java, which aims to ‘port’ QuantLib from C++ to Java,
keeping exaclty the same API (as much as possible) and performing very closely to the C++ implementation (QuantLib).