JD-Gui Probably one of the most widely used tools for Java decompilation, as it is easy to use and provides a graphical user interface which allows to quickly open up and inspect a class file or JAR. You can find it over here.
Not open source, though, and no longer being maintained. Thus it’s not able to decompile Java features from version 8 and newer. The corresponding IntelliJ plugin is also no longer being maintained and not compatible with IntelliJ 2018.
FernFlower Very new and promising analytical Java decompiler (becoming an integral part of IntelliJ 14). Supports Java up to version 6 (annotations, generics, enum types).
Free, but notand open source. This one aims to decompile modern Java features, including Java 12 switch expressions, Java 8 lambdas (pre and post Java beta 103 changes), Java 7 String switches etc., though is itself written in Java 6.
Soot is a framework for analyzing and transforming Java and Android applications, originally developed by the Sable Research Group of McGill University. It’s not very commonly used “just” as a decompiler, as it also defines an intermediate byte code language.
Recaf
A Java Bytecode editor and reverse engineering tool aimed at being intuitive to use. It can present bytecode through multiple decompilers (CFR, FernFlower, Procyon) or in a table layout to allow displaying class elements that are indecipherable in standard decompilers. Recaf uses context-sensitive menus to interact with classes, methods, and fields, allowing users to search for use cases, rename items, and edit definitions in a disassembled format.
It supports jars, wars, classes, and extracting classes from running Java processes.
It is written completely in Java and is fully open source.
Konloch’s Bytecode Viewer
Enigma
A tool specifically geared for deobfuscation:
Originally used to deobfuscate Minecraft versions. Uses Procyon internally.
A more up to date fork can be found here
