Java developers often use decompilers to aid reverse engineering and obfuscators to prevent it. Decompilers translate low-level class files to Java source and can produce "good" output. Obfuscators transform class files into semantically-equivalent versions that are either: (1) difficult to decompile, or (2) decompilable, but result in "hardto- understand" Java source.

We present a set of metrics developed to quantify the effectiveness of decompilers and obfuscators. The metrics include some selective size and counting metrics and an expression complexity metric. We have applied these metrics to evaluate a collection of decompilers and obfuscators. By quantitatively comparing original Java source against decompiled and obfuscated code respectively, we show which decompilers produce "good" code and whether obfuscations result in "hard-to-understand" code.