CFR will decompile modern Java features - up to and including much of Java
9, 10, 12 and beyond, but is written entirely in Java 6, so will work
anywhere!

It'll even make a decent go of turning class files from other JVM langauges
(like Kotlin) back into Java!

To use, simply run the specific version jar, with the class name(s) you
want to decompile (either as a path to a class file, or as a fully
qualified classname on your classpath).

Alternately, to decompile an entire jar, simply provide the jar path,
and if you want to emit files (which you probably do!)
add --outputdir /tmp/putithere.

WWW: https://www.benf.org/other/cfr/