Try Procyon to get a better view of the code.
https://bitbucket.org/mstrobel/procy...a%20Decompiler
It can output the jar file as raw (which you see now), as an AST, or as Java.
(IIRC, JBE uses the Procyon library internally)
Another one which is suppose to be good is CFR:
http://www.benf.org/other/cfr/
But I haven't used it (yet) myself.
The cvm on your Kindle (since at least firmware 5.6.x) is a Java8 vm, but I don't think there is a lot of J8 features used in the code (yet).