Java code obfuscation related In the Android project

Hello, I recently encountered a problem. Android applications are compiled with confusion, sometimes there is a problem of variable duplicate names in the same domain (abnormal display at runtime).The problem disappears after a recompilation.
My question is why variables with different names appear duplicate names after code confusion? How to solve it? How to avoid similar problems in the future? Thank you very much.

Hi @jackkong1222,

Did you by any chance had the opportunity to look at ProGuard’s Troubleshooting guide? This issue is documented under “Note: duplicate definition of program/library class”, available on this page: ProGuard Manual: Troubleshooting | Guardsquare

From the manual;

Your program jars or library jars contain multiple definitions of the listed classes. ProGuard continues processing as usual, only considering the first definitions. The warning may be an indication of some problem though, so it’s advisable to remove the duplicates. A convenient way to do so is by specifying filters on the input jars or library jars. You can switch off these notes by specifying the -dontnote option.

The standard Android build process automatically specifies the input jars for you. There may not be an easy way to filter them to remove these notes. You could remove the duplicate classes manually from your libraries. You should never explicitly specify the input jars yourself (with -injars or -libraryjars ), since you’ll then get duplicate definitions. You should also not add libraries to your application that are already part of the Android run-time (notably org.w3c.dom , org.xml.sax , org.xmlpull.v1 , org.apache.commons.logging.Log , org.apache.http , and org.json ). They are possibly inconsistent, and the run-time libraries would get precedence anyway.

Please let me know if anything is not clear or should this not be relevant to your question.

Kind regards,

Jonas

Thank you very much. Maybe because I didn’t describe it clearly, it seems that you didn’t understand my problem.

I define several variables in a class, for example: "public int ID; public int msg;”, However, after compiling, through the dex2jar and jd-gui decompilation, it is found that these two variables become “public int ID;”, And the application runs abnormally; Recompile again, the variable is no longer the same name, and the application runs normally.

My question is: why does the problem of variable duplicate name occasionally occur after confusion, and how to avoid it?

Hi @jackkong1222,

Can you please check your mapping.txt file generated by ProGuard to verify if these variables (or other parts of code) were assigned the same (obfuscated) name by ProGuard? If not, this seems more like a bug in either dex2jar or jd-gui.

Kind regards,

Jonas

So far, it has only happened once,The mapping.txt file was not output before, and the mapping.txt file was output later, The results are as follows:

// The first time:(in Mapping.txt):
int id → id
int cellX → nv
int msg → nx

//The second time:(in Mapping.txt):
int id → id
int cellX → ex
int msg → ez

The variable id is always id, so it is reasonable to suspect that the variable MSG is also confused with id when there is a problem. It should not be the problem of dex2jar or JD GUI. After all, the application displays an exception. Recompile once, and the application interface displays normally without any code changes.

My question is: Whether configuring “-useuniqueclassmembernames” can solve the problem, or whether there are other suggestions to ensure that the same problem will not occur in the future.

Kind regards,
Jack