Java Decompilers Compared

The object of a Java decompiler is to convert Java class files into Java source code. In the chaotic world of software development there are many reasons, legitimate and otherwise, to wish for such a tool. Decompilers can save the day when you have the binary for your own code, but have misplaced or otherwise lost the corresponding source code. On the other hand, decompilers are the prized components of any good software piracy kit. Most often, however, decompilers help programmers clarify poor documentation (one decompiled function is worth a thousand words) or provide a means for creating not-yet-written documentation. When was the last time you thought the documentation for any software was complete and correct?
In any case, the transparent and information-rich structure of Java class files -- a feature that makes Java's dynamic linking much better than previous models -- also makes such tools particularly easy to build. In fact, there is an arms race brewing between decompilers and so-called obfuscators, which profess to provide Java code some measure of protection from decompilers. In essence, obfuscators remove all non-essential symbolic information from your class files and, optionally, replace it with fake symbolic information designed to confuse the decompiler. Crema, the companion obfuscator to the Mocha decompiler, was examined in detail in the December issue of JavaWorld. (See the Resources section at the end of this column for a link to this article and to several obfuscator products.)