The JAR you're trying to use has most likely been obfuscated, probably for the purpose of preventing what you're trying to do. Some Java obfuscators change the package, class, method, and variable names to violate the JLS but still be valid compiled bytecode; that appears to be exactly what has been done to this JAR. It will be very difficult to make sense of the de-compiled code in that case.
JARs that are obfuscated usually leave just their public API un-obfuscated for your code to use; everything else is scrambled to prevent you from de-compiling it and/or using it directly.