While I've seen many people recommend Java (and I agree with them), I think you can learn both. But it depends on how much time you got. I recommend you first learn Java. Then python will be easy to learn, and focus mainly on modules for graphs. The reason why I recommend to learn both is because python is much better and easier to code about statistical analysis. But again do this only if you have time to just learn them.

If your project doesn't have anything to do with statistics and data analysis (I'm pretty sure you do though), learn only java. Also if you are wondering why I never mentioned JavaScript (JS), it's because i really don't recommend it. JS is much harder to learn and requires a lot of lines of code to do simple things.