Bytecode Viewer is a Java Bytecode Viewer, GUI FernFlower Java Decompiler, GUI Jar-Jar, Hex Viewer, Code Searcher, Debugger and more.
It's written completely in Java, and it's open sourced. It's currently being maintained and developed by Konloch.

Code from various projects has been used, including but not limited to:
J-RET by WaterWolf
JHexPane by Sam Koivu
JSynaxPane by Ayman Al
Commons IO by Apache
ASM by OW2

Features:
Java Decompiler - It uses a modified version of FernFlower.
Bytecode Decompiler - A modified version of J-RET's.
Hex Viewer - Powered by JHexPane.
Each Decompiler/Viewer is toggleable.
Fully Featured Search System.
A Plugin System With Built In Plugins. (Show All Strings, Malicious Code Scanner, String Decrypters, etc)
Recent Files.
And more! Give it a try for yourself!

Are you a Java Reverse Engineer? Do you want to learn?
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http://the.bytecode.club