The concept reverse engineering led to the invention of decompilers in the world of softwares and programming. Decompilers in java is mainly used to covert the compiled object code back to source. Decompilers often help programmers by helping them to recover the lost code from the compiled binaries. Decompilation of java code or any code from some other languages need to undergo some steps like disassembly, program analysis, code analysis, structure rebuilding and code generation depending on the language or type of the code. But nowadays, decompilers are mainly used for software piracy and is used to steal copyrighted code rather than for legitimate use. We will discuss some of the best known decompilers for Java in this post.

There are lot of commercial as well as open source decompilers are available for Java. But here we are going to look at some of the best known ones.

Commercial decompilers

1. DejaVu
2. WingDis
3. SourceTec Java Decompiler
4. Class Craker
5. Source Again

Open source decompilers

1. Jad - is a c++ based java compiler and doesnt need JRE for its functioning and the decompiler supports batch conversion.

2. DJ Java Decompiler - one of the famous disassembler which often creates correct code with 100% accuracy.

3. JODE - mix of decompiler and optimiser.

4. JReversePro - completely written in java and produces java object based code. Its has got facility to inspect constant pool constants.

Apart from these compilers there are few Eclipse plugins to do the job from your workspace. The well known java decompiler plugin for eclipse is JadClipse. I have found one very good article regarding decompilation and obfuscation with IBM, How to lock down your Java code (or open up someone else’s) . Not always and Not everycode can be decompiled or reverse engineered. There are lot of commercial as well as open source obfuscators and code morphing tools available to protect the source code.