Perhaps you give the answer to this question in your book but I don't have it (yet). So I am just nosy and interested to learn why you decided to use Java in your book as the programming language and not C++. I don't want to start a thread regarding the never ending discussion about which programming language is right. There are pros and cons for and against any language.
Just a few words about my background:
I am using C++ and xlwplus for the function development in Excel.
Further, the second tool I am using for model development and testing is Quantrix (http://www.quantrix.com/). This tool is fully written in Java/Eclipse. If I need to add a new function to Quantrix I can use Eclipse, Java and the Quantrix API to do this.
Third, there are policies and regulations by universities and companies. I have to use Excel/VBA at my day job to be compatible with my colleagues.
I am looking forward to your reply!