ProGuard is a free Java class file shrinker, optimizer, and
obfuscator. It can detect and remove unused classes, fields,
methods, and attributes. It can then optimize bytecode and
remove unused instructions. Finally, it can rename the
remaining classes, fields, and methods using short
meaningless names. The resulting jars are smaller and harder
to reverse-engineer.

WWW: https://www.guardsquare.com/en/products/proguard