How do I use ProGuard?

Question

I was trying to learn how to use ProGuard, and it is no way as easy as I thought. At first I found a simple Java code to try it, a simple two class Swing calculator.

The code can be found by following that link, but I found it too verbose to post the it here. Anyway, it is a plain application with entry point on Calc.main(), there are no packages.

Then I compiled both sources with:

$ javac *.java

and created the .jar file (because it seems ProGuard only work with jars):

$ jar cvef Calc calc.jar *.class
added manifest
adding: Calc.class(in = 3869) (out= 2126)(deflated 45%)
adding: Calc$ClearListener.class(in = 468) (out= 327)(deflated 30%)
adding: CalcLogic.class(in = 1004) (out= 515)(deflated 48%)
adding: Calc$NumListener.class(in = 1005) (out= 598)(deflated 40%)
adding: Calc$OpListener.class(in = 1788) (out= 1005)(deflated 43%)

Wrote the ProGuard file named obfuscate.pro:

-injars       calc.jar
-outjars      calc_obf.jar
-libraryjars  <java.home>/lib/rt.jar

-keep public class Calc extends javax.swing.JFrame {
public static void main(java.lang.String[]);
}

And finally run ProGuard:

$ ~/progs/proguard/proguard4.8/bin/proguard.sh @obfuscate.pro
ProGuard, version 4.8
Reading program jar [/home/lucas/tmp/calc.jar]
Reading library jar [/usr/lib/jvm/java-7-openjdk-i386/jre/lib/rt.jar]
Error: The output jar is empty. Did you specify the proper '-keep' options?

Well, obviously didn't work. I got tired of messing with ProGruard parameters, specially with that -keep options, with no success. All I found in the docs related to my problem could not help me. Then I am resorting to you... What is wrong? How to do it right?

Answer 1

I got it to work using the following configuration file:

-injars       calc.jar
-outjars      calc_obf.jar
-libraryjars  <java.home>/lib/rt.jar
-keep class Calc {
  public static void main(java.lang.String[]);
}

Most notably, I ditched the public in front of class Calc.