Java code is pre-compiled to “bytecode” which can be run by Java virtual machines (i.e. similar to the Python interpreter). When you make the Java VM run some Java app, it will very likely recompile the bytecode to native code to be run on your computer (one of the reasons why Java apps usually take 5-10 seconds to start up). Technically, it is supposed to cache these compiled versions so that your app doesn’t do that everytime, but in reality things really don’t work that way (cache gets cleared out after running other Java apps).
Another point to note is the memory usage of Java apps. By being “managed code” (i.e. the Java VM is used to run apps), most apps will take up more ram than they are actually using, which has downsides as well as a few benefits in limited cases. The benefit is that creating heaps of new stuff quickly won’t take quite as long, but the downside is that the rest of the time, these apps tend to be memory hogs.
Another caveat to be aware of regarding managed code: I have worked with a few Java-based apps in the past where the managed memory management (i.e. instead of the programmer explicitly having to free memory, the VM tries to figure out when to free it - a process known as Garbage Collection) would cause some usability problems. The Garbage Collector back then was pretty yucky, and would cause the application to freeze for up to 10 seconds at a time, at inconvenient intervals while it “freed” unused memory and probably did some other tricks.
Personally, I hate Java. I used to hate it more than I currently do, however, having worked with it a bit, I give it a bit more leeway in a few aspects. A major sore point regarding its syntax is that it is like a castrated C++, trying to be a bit more newbie friendly but at the same time doing away with some useful constructs and introducing some inconsistencies.
Anyways, back on topic.
I applaud these latest efforts at implementing Blender in another language if it’s just as an academic exercise. Finally someone who has actually taken the effort of making what looks to be a partially functional port instead of sitting on the sidelines flame-blasting about “why d0n’t u rewrit3 d entir think in an0thr lagnuange” type rants.
Having said that, I second theeth’s comments. As a private tinkering exercise, good on you. But as far as making an official (or otherwise) port of Blender to another language by the development team goes, there is no interest at all.