My tools were formerly written in Java, but I finally (phew) converted all of them to another, executable, programming language. I think it was a terrible design choice to make them in Java for multiple reasons, but back then it was the only programming I could use for modern PCs that had file I/O.
Now I am very glad I learnt to use C and the bases of C++ correctly (trust me it's no simple task, especially C++) but it's worth it as the languages are compilable. There is also other issues with Java other than the lack of compilability (yes, gcj is supposed to compile Java programs into native executable files but I never got them working).
Usage of the JVM is not easy and is confusing for novices who are already new to the command line. I can't count how many complaints I got because of this. And I have to admit that even for myself it was hard to use my own tools because of that, I had to look up how to invoke the JVM properly every time, so it annoyed me just as much as other users (I made the tools first for my own personal usage, and then I share them so that they can be useful for others too).
The syntax for Java can be horrible whenever you need something *not* to be object oriented, which turns out to be pretty often. It encourages you to write unstructured programs. And you have to use the "new" keyboard all the time. The language is based on the lack of memory management, thus on the fact that you will constantly waste memory that will be garbage collected later, which can potentially be source of inefficiency.
For all those reason I'd advice against Java for new designs
However, I have to admit that OO is much easier to understand and apply in Java than in C++. Don't learn OO with C++, just learn another OO language and then learn how to apply it to C++.
PS : Oh, to answer your question, download my tools, and you might find an archive with the "old" java version in them. You are free to study them in any way, just don't hope to get any support for those versions, they are officially deprecated.