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). (Use --help to list arguments).

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/