ProGuard manual

Troubleshooting

While preparing a configuration for processing your code, you may bump into a few problems. The following sections discuss some common issues and solutions:

Problems while processing¶

ProGuard may print out some notes and non-fatal warnings:

Note: can't find dynamically referenced class ...

ProGuard can't find a class or interface that your code is accessing by means of introspection. You should consider adding the jar that contains this class.

Note: ... calls '(...)Class.forName(variable).newInstance()'

Your code uses reflection to dynamically create class instances, with a construct like "(MyClass)Class.forName(variable).newInstance()". Depending on your application, you may need to keep the mentioned classes with an option like "-keep class MyClass", or their implementations with an option like "-keep class * implements MyClass". You can switch off these notes by specifying the -dontnote option.

Note: ... accesses a field/method '...' dynamically

Your code uses reflection to find a fields or a method, with a construct like ".getField("myField")". Depending on your application, you may need to figure out where the mentioned class members are defined and keep them with an option like "-keep class MyClass { MyFieldType myField; }". Otherwise, ProGuard might remove or obfuscate the class members, since it can't know which ones they are exactly. It does list possible candidates, for your information. You can switch off these notes by specifying the -dontnote option.

Note: ... calls 'Class.get...', 'Field.get...', or 'Method.get...'

Your code uses reflection to access metadata from the code, with an invocation like "class.getAnnotations()". You then generally need to preserve optional class file attributes, which ProGuard removes by default. The attributes contain information about annotations, enclosing classes, enclosing methods, etc. In a summary in the log, ProGuard provides a suggested configuration, like -keepattributes *Annotation*. If you're sure the attributes are not necessary, you can switch off these notes by specifying the -dontnote option.

Note: the configuration refers to the unknown class '...'

Your configuration refers to the name of a class that is not present in the program jars or library jars. You should check whether the name is correct. Notably, you should make sure that you always specify fully-qualified names, not forgetting the package names.

Note: the configuration keeps the entry point '...', but not the descriptor class '...'

Your configuration contains a -keep option to preserve the given method (or field), but no -keep option for the given class that is an argument type or return type in the method's descriptor. You may then want to keep the class too. Otherwise, ProGuard will obfuscate its name, thus changing the method's signature. The method might then become unfindable as an entry point, e.g. if it is part of a public API. You can automatically keep such descriptor classes with the -keep option modifier includedescriptorclasses (-keep,includedescriptorclasses ...). You can switch off these notes by specifying the -dontnote option.

Note: the configuration explicitly specifies '...' to keep library class '...'

Your configuration contains a -keep option to preserve the given library class. However, you don't need to keep any library classes. ProGuard always leaves underlying libraries unchanged. You can switch off these notes by specifying the -dontnote option.

Note: the configuration doesn't specify which class members to keep for class '...'

Your configuration contains a -keepclassmembers/-keepclasseswithmembers option to preserve fields or methods in the given class, but it doesn't specify which fields or methods. This way, the option simply won't have any effect. You probably want to specify one or more fields or methods, as usual between curly braces. You can specify all fields or methods with a wildcard "*;". You should also consider if you just need the more common -keep option, which preserves all specified classes and class members. The overview of all keep options can help. You can switch off these notes by specifying the -dontnote option.

Note: the configuration specifies that none of the methods of class '...' have any side effects

Your configuration contains an option -assumenosideeffects to indicate that the specified methods don't have any side effects. However, the configuration tries to match all methods, by using a wildcard like "*;". This includes methods from java.lang.Object, such as wait() and notify(). Removing invocations of those methods will most likely break your application. You should list the methods without side effects more conservatively. You can switch off these notes by specifying the -dontnote option.

Note: duplicate definition of program/library class

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.

Warning: can't write resource ... Duplicate zip entry

Your input jars contain multiple resource files with the same name. ProGuard continues copying the resource files as usual, skipping any files with previously used names. Once more, 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. There is no option to switch off these warnings.

ProGuard may terminate when it encounters parsing errors or I/O errors, or some more serious warnings:

Warning: can't find superclass or interface
Warning: can't find referenced class

A class in one of your program jars or library jars is referring to a class or interface that is missing from the input. The warning lists both the referencing class(es) and the missing referenced class(es). There can be a few reasons, with their own solutions:

1. If the missing class is referenced from your own code, you may have forgotten to specify an essential library. Just like when compiling all code from scratch, you must specify all libraries that the code is referencing, directly or indirectly. If the library should be processed and included in the output, you should specify it with -injars, otherwise you should specify it with -libraryjars. For example, if ProGuard complains that it can't find a java.lang class, you have to make sure that you are specifying the run-time library of your platform. For JSE, these are typically packaged in lib/rt.jar (vm.jar for IBM's JVM, and classes.jar in MacOS X) or as of Java 9, jmods/java.base.jmod.

2. If the missing class is referenced from a pre-compiled third-party library, and your original code runs fine without it, then the missing dependency doesn't seem to hurt. The cleanest solution is to filter out the referencing class or classes from the input, with a filter like "-injars myapplication.jar(!somepackage/SomeUnusedReferencingClass.class)". DexGuard will then skip this class entirely in the input, and it will not bump into the problem of its missing reference. However, you may then have to filter out other classes that are in turn referencing the removed class. In practice, this works best if you can filter out entire unused packages at once, with a wildcard filter like "-libraryjars mylibrary.jar(!someunusedpackage/**)".

3. If you don't feel like filtering out the problematic classes, you can try your luck with the -ignorewarnings option, or even the -dontwarn option. Only use these options if you really know what you're doing though.

Error: Can't find any super classes of ... (not even immediate super class ...)

Error: Can't find common super class of ... and ...

It seems like you tried to avoid the warnings from the previous paragraph by specifying -ignorewarnings or -dontwarn, but it didn't work out. ProGuard's optimization step and preverification step really need the missing classes to make sense of the code. Preferably, you would solve the problem by adding the missing library, as discussed. If you're sure the class that references the missing class isn't used either, you could also try filtering it out from the input, by adding a filter to the corresponding -injars option: "-injars myapplication.jar(!somepackage/SomeUnusedClass.class)". As a final solution, you could switch off optimization (-dontoptimize) and preverification (-dontpreverify).

Warning: can't find referenced field/method '...' in program class ...

A program class is referring to a field or a method that is missing from another program class. The warning lists both the referencing class and the missing referenced class member. Your compiled class files are most likely inconsistent. Possibly, some class file didn't get recompiled properly, or some class file was left behind after its source file was removed. Try removing all compiled class files and rebuilding your project.

Warning: can't find referenced field/method '...' in library class ...

A program class is referring to a field or a method that is missing from a library class. The warning lists both the referencing class and the missing referenced class member. Your compiled class files are inconsistent with the libraries. You may need to recompile the class files, or otherwise upgrade the libraries to consistent versions.

1. If there are unresolved references to class members in program classes, your compiled class files are most likely inconsistent. Possibly, some class file didn't get recompiled properly, or some class file was left behind after its source file was removed. Try removing all compiled class files and rebuilding your project.

2. If there are unresolved references to class members in library classes, your compiled class files are inconsistent with the libraries. You may need to recompile the class files, or otherwise upgrade the libraries to consistent versions.

Alternatively, you may get away with ignoring the inconsistency with the options -ignorewarnings or even -dontwarn.

Warning: can't find enclosing class/method

If there are unresolved references to classes that are defined inside methods in your input, once more, your compiled class files are most likely inconsistent. Possibly, some class file didn't get recompiled properly, or some class file was left behind after its source file was removed. Try removing all compiled class files and rebuilding your project.

Warning: library class ... depends on program class ...

If any of your library classes depend on your program classes, by extending, implementing or just referencing them, your processed code will generally be unusable. Program classes can depend on library classes, but not the other way around. Program classes are processed, while library classes always remain unchanged. It is therefore impossible to adapt references from library classes to program classes, for instance if the program classes are renamed. You should define a clean separation between program code (specified with -injars) and library code (specified with -libraryjars), and try again.

Warning: class file ... unexpectedly contains class ...

The given class file contains a definition for the given class, but the directory name of the file doesn't correspond to the package name of the class. ProGuard will accept the class definition, but the current implementation will not write out the processed version. Please make sure your input classes are packaged correctly. Notably, class files that are in the WEB-INF/classes directory in a war should be packaged in a jar and put in the WEB-INF/lib directory. If you don't mind these classes not being written to the output, you can specify the -ignorewarnings option, or even the -dontwarn option.

Warning: ... is not being kept as ..., but remapped to ...

There is a conflict between a -keep option and the mapping file specified with an -applymapping option, in the obfuscation step. The given class name or class member name can't be kept by its original name, as specified in the configuration, but it has to be mapped to the other given name, as specified in the mapping file. You should adapt your configuration or your mapping file to remove the conflict. Alternatively, if you're sure the renaming won't hurt, you can specify the -ignorewarnings option, or even the -dontwarn option.

Warning: field/method ... can't be mapped to ...

There is a conflict between some new program code and the mapping file specified with an -applymapping option, in the obfuscation step. The given class member can't be mapped to the given name, because it would conflict with another class member that is already being mapped to the same name. This can happen if you are performing incremental obfuscation, applying an obfuscation mapping file from an initial obfuscation step. For instance, some new class may have been added that extends two existing classes, introducing a conflict in the name space of its class members. If you're sure the class member receiving another name than the one specified won't hurt, you can specify the -ignorewarnings option, or even the -dontwarn option. Note that you should always use the -useuniqueclassmembernames option in the initial obfuscation step, in order to reduce the risk of conflicts.

Error: Unsupported class version number

You are trying to process class files compiled for a recent version of Java that your copy of ProGuard doesn't support yet. You should check on-line if there is a more recent release.

Error: You have to specify -keep options

You either forgot to specify -keep options, or you mistyped the class names. ProGuard has to know exactly what you want to keep: an application, an applet, a servlet, a midlet,..., or any combination of these. Without the proper seed specifications, ProGuard would shrink, optimize, or obfuscate all class files away.

Error: Expecting class path separator ';' before 'Files\Java\...' (in Windows)

If the path of your run-time jar contains spaces, like in "Program Files", you have to enclose it with single or double quotes, as explained in the section on file names. This is actually true for all file names containing special characters, on all platforms.

Error: Can't read [.../lib/rt.jar] (No such file or directory)

In MacOS X, the run-time classes may be in a different place than on most other platforms. You'll then have to adapt your configuration, replacing the path <java.home>/lib/rt.jar by <java.home>/../Classes/classes.jar.

As of Java 9, the runtime classes are packaged in <java.home>/jmods/java.base.jmod and other modules next to it.

Error: Can't read ...

ProGuard can't read the specified file or directory. Double-check that the name is correct in your configuration, that the file is readable, and that it is not corrupt. An additional message "Unexpected end of ZLIB input stream" suggests that the file is truncated. You should then make sure that the file is complete on disk when ProGuard starts (asynchronous copying? unflushed buffer or cache?), and that it is not somehow overwritten by ProGuard's own output.

Error: Can't write ...

ProGuard can't write the specified file or directory. Double-check that the name is correct in your configuration and that the file is writable.

Internal problem starting the ProGuard GUI (Cannot write XdndAware property) (in Linux)

In Linux, at least with Java 6, the GUI may not start properly, due to Sun Bug #7027598. The work-around at this time is to specify the JVM option -DsuppressSwingDropSupport=true when running the GUI.

Should ProGuard crash while processing your application:

OutOfMemoryError

You can try increasing the heap size of the Java virtual machine, with the usual -Xmx option:

• In Java, specify the option as an argument to the JVM: java -Xmx1024m
• In Ant, set the environment variable ANT_OPTS=-Xmx1024m
• In Gradle, set the environment variable GRADLE_OPTS=-Xmx1024m
• In Maven, set the environment variable MAVEN_OPTS=-Xmx1024m
• In Eclipse, add the line -Xmx1024m to the file eclipse.ini inside your Eclipse install.

You can also reduce the amount of memory that ProGuard needs by removing unnecessary library jars from your configuration, or by filtering out unused library packages and classes.

StackOverflowError

This error might occur when processing a large code base on Windows (surprisingly, not so easily on Linux). In theory, increasing the stack size of the Java virtual machine (with the usual -Xss option) should help too. In practice however, the -Xss setting doesn't have any effect on the main thread, due to Sun Bug #4362291. As a result, this solution will only work when running ProGuard in a different thread, e.g. from its GUI.

Unexpected error

ProGuard has encountered an unexpected condition, typically in the optimization step. It may or may not recover. You should be able to avoid it using the -dontoptimize option. In any case, please report the problem, preferably with the simplest example that causes ProGuard to crash.

Otherwise...

Maybe your class files are corrupt. See if recompiling them and trying again helps. If not, please report the problem, preferably with the simplest example that causes ProGuard to crash.

Unexpected observations after processing¶

If ProGuard seems to run fine, but your processed code doesn't look right, there might be a couple of reasons:

Disappearing classes

If you are working on Windows and it looks like some classes have disappeared from your output, you should make sure you're not writing your output class files to a directory (or unpacking the output jar). On platforms with case-insensitive file systems, such as Windows, unpacking tools often let class files with similar lower-case and upper-case names overwrite each other. If you really can't switch to a different operating system, you could consider using ProGuard's -dontusemixedcaseclassnames option. Also, you should make sure your class files are in directories that correspond to their package names. ProGuard will read misplaced class files, but it will currently not write their processed versions. Notably, class files that are in the WEB-INF/classes directory in a war should be packaged in a jar and put in the WEB-INF/lib directory.

Classes or class members not being kept

If ProGuard is not keeping the right classes or class members, make sure you are using fully qualified class names. If the package name of some class is missing, ProGuard won't match the elements that you might be expecting. It may help to double-check for typos too. You can use the -printseeds option to see which elements are being kept exactly.

If you are using marker interfaces to keep other classes, the marker interfaces themselves are probably being removed in the shrinking step. You should therefore always explicitly keep any marker interfaces, with an option like "-keep interface MyMarkerInterface".

Similarly, if you are keeping classes based on annotations, you may have to avoid that the annotation classes themselves are removed in the shrinking step. You should package the annotation classes as a library, or explicitly keep them in your program code with an option like "-keep @interface *".

Class names not being obfuscated

If the names of some classes in your obfuscated code aren't obfuscated, you should first check all your configuration files. Chances are that some -keep option is preserving the original names. These options may be hiding in your own configuration files or in configuration files from libraries.

Field names not being obfuscated

If the names of some fields in your obfuscated code aren't obfuscated, this may be due to -keep options preserving the original names, for the sake of libraries like GSON. Such libraries perform reflection on the fields. If the names were obfuscated, the resulting JSON strings would come out obfuscated as well, which generally breaks persistence of the data or communication with servers.

Method names not being obfuscated

If the names of some methods in your obfuscated code aren't obfuscated, this is most likely because they extend or implement method names in the underlying runtime libraries. Since the runtime libraries are not obfuscated, any corresponding names in the application code can't be obfuscated either, since they must remain consistent.

Variable names not being obfuscated

If the names of the local variables and parameters in your obfuscated code don't look obfuscated, because they suspiciously resemble the names of their types, it's probably because the decompiler that you are using is coming up with those names. ProGuard's obfuscation step does remove the original names entirely, unless you explicitly keep the LocalVariableTable or LocalVariableTypeTable attributes.

Problems while preverifying for Java Micro Edition¶

If ProGuard seems to run fine, but the external preverifier subsequently produces errors, it's usually for a single reason:

InvalidClassException, class loading error, or verification error

If you get any such message from the preverifier, you are probably working on a platform with a case-insensitive file system, such as Windows. The preverify tool always unpacks the jars, so class files with similar lower-case and upper-case names overwrite each other. You can use ProGuard's -dontusemixedcaseclassnames option to work around this problem. If the above doesn't help, there is probably a bug in the optimization step of ProGuard. Make sure you are using the latest version. You should be able to work around the problem by using the -dontoptimize option. You can check the bug database to see if it is a known problem (often with a fix). Otherwise, please report it, preferably with the simplest example on which you can find ProGuard to fail.

Note that it is no longer necessary to use an external preverifier. With the -microedition option, ProGuard will preverify the class files for Java Micro Edition.

Problems at run-time¶

If ProGuard runs fine, but your processed application doesn't work, there might be several reasons:

Stack traces without class names or line numbers

If your stack traces don't contain any class names or lines numbers, even though you are keeping the proper attributes, make sure this debugging information is present in your compiled code to start with. Notably the Ant javac task has debugging information switched off by default.

NoClassDefFoundError

Your class path is probably incorrect. It should at least contain all library jars and, of course, your processed program jar.

ClassNotFoundException

Your code is probably calling Class.forName, trying to create the missing class dynamically. ProGuard can only detect constant name arguments, like Class.forName("com.example.MyClass"). For variable name arguments like Class.forName(someClass), you have to keep all possible classes using the appropriate -keep option, e.g. "-keep class com.example.MyClass" or "-keep class * implements com.example.MyInterface". While setting up your configuration, you can specify the option -addconfigurationdebugging to help track down these cases at run-time and let the instrumented code suggest settings for them.

NoSuchFieldException

Your code is probably calling something like myClass.getField, trying to find some field dynamically. Since ProGuard can't always detect this automatically, you have to keep the missing field using the appropriate -keep option, e.g. "-keepclassmembers class com.example.MyClass { int myField; }". While setting up your configuration, you can specify the option -addconfigurationdebugging to help track down these cases at run-time and let the instrumented code suggest settings for them.

NoSuchMethodException

Your code is probably calling something like myClass.getMethod, trying to find some method dynamically. Since ProGuard can't always detect this automatically, you have to keep the missing method using the appropriate -keep option, e.g. "-keepclassmembers class com.example.MyClass { void myMethod(); }". While setting up your configuration, you can specify the option -addconfigurationdebugging to help track down these cases at run-time and let the instrumented code suggest settings for them. More specifically, if the method reported as missing is values or valueOf, you probably have to keep some methods related to enumerations.

MissingResourceException or NullPointerException

Your processed code may be unable to find some resource files. ProGuard simply copies resource files over from the input jars to the output jars. Their names and contents remain unchanged, unless you specify the options -adaptresourcefilenames and/or -adaptresourcefilecontents. Furthermore, directory entries in jar files aren't copied, unless you specify the option -keepdirectories. Note that Sun advises against calling Class.getResource() for directories (Sun Bug #4761949](http://bugs.sun.com/view_bug.do?bug_id=4761949)).

Disappearing annotations

By default, the obfuscation step removes all annotations. If your application relies on annotations to function properly, you should explicitly keep them with -keepattributes *Annotation*.

Invalid or corrupt jarfile

You are probably starting your application with the java option -jar instead of the option -classpath. The java virtual machine returns with this error message if your jar doesn't contain a manifest file (META-INF/MANIFEST.MF), if the manifest file doesn't specify a main class (Main-Class: ...), or if the jar doesn't contain this main class. You should then make sure that the input jar contains a valid manifest file to start with, that this manifest file is the one that is copied (the first manifest file that is encountered), and that the main class is kept in your configuration,

InvalidJarIndexException: Invalid index

At least one of your processed jar files contains an index file META-INF/INDEX.LIST, listing all class files in the jar. ProGuard by default copies files like these unchanged. ProGuard may however remove or rename classes, thus invalidating the file. You should filter the index file out of the input (-injars in.jar(!META-INF/INDEX.LIST)) or update the file after having applied ProGuard (jar -i out.jar).

InvalidClassException, class loading error, or verification error (in Java Micro Edition)

If you get such an error in Java Micro Edition, you may have forgotten to specify the -microedition option, so the processed class files are preverified properly.

Error: No Such Field or Method, Error verifying method (in a Java Micro Edition emulator)

If you get such a message in a Motorola or Sony Ericsson phone emulator, it's because these emulators don't like packageless classes and/or overloaded fields and methods. You can work around it by not using the options -repackageclasses '' and -overloadaggressively.

Failing midlets (on a Java Micro Edition device)

If your midlet runs in an emulator and on some devices, but not on some other devices, this is probably due to a bug in the latter devices. For some older Motorola and Nokia phones, you might try specifying the -useuniqueclassmembernames option. It avoids overloading class member names, which triggers a bug in their java virtual machine. You might also try using the -dontusemixedcaseclassnames option. Even if the midlet has been properly processed and then preverified on a case-sensitive file system, the device itself might not like the mixed-case class names. Notably, the Nokia N-Gage emulator works fine, but the actual device seems to exhibit this problem.

Disappearing loops

If your code contains empty busy-waiting loops, ProGuard's optimization step may remove them. More specifically, this happens if a loop continuously checks the value of a non-volatile field that is changed in a different thread. The specifications of the Java Virtual Machine require that you always mark fields that are accessed across different threads without further synchronization as volatile. If this is not possible for some reason, you'll have to switch off optimization using the -dontoptimize option.

SecurityException: SHA1 digest error

You may have forgotten to sign your program jar after having processed it with ProGuard.

ClassCastException: class not an enum
IllegalArgumentException: class not an enum type

You should make sure you're preserving the special methods of enumeration types, which the run-time environment calls by introspection. The required options are shown in the examples.

ArrayStoreException: sun.reflect.annotation.EnumConstantNotPresentExceptionProxy

You are probably processing annotations involving enumerations. Again, you should make sure you're preserving the special methods of the enumeration type, as shown in the examples.

IllegalArgumentException: methods with same signature but incompatible return types

You are probably running some code that has been obfuscated with the -overloadaggressively option. The class java.lang.reflect.Proxy can't handle classes that contain methods with the same names and signatures, but different return types. Its method newProxyInstance then throws this exception. You can avoid the problem by not using the option.

CompilerError: duplicate addition

You are probably compiling or running some code that has been obfuscated with the -overloadaggressively option. This option triggers a bug in sun.tools.java.MethodSet.add in Sun's JDK 1.2.2, which is used for (dynamic) compilation. You should then avoid this option.

ClassFormatError: repetitive field name/signature

You are probably processing some code that has been obfuscated before with the -overloadaggressively option. You should then use the same option again in the second processing round.

ClassFormatError: Invalid index in LocalVariableTable in class file

If you are keeping the LocalVariableTable or LocalVariableTypeTable attributes, ProGuard's optimizing step is sometimes unable to update them consistently. You should then let the obfuscation step remove these attributes or disable the optimization step.

NullPointerException: create returned null (Dagger)
IllegalStateException: Module adapter for class ... could not be loaded. Please ensure that code generation was run for this module.
IllegalStateException: Could not load class ... needed for binding members/...

Dagger 1 relies on reflection to combine annotated base classes and their corresponding generated classes. DexGuard's default configuration already preserves the generated classes, but you still preserve the annotated base classes in your project-specific configuration. This is explained in some more detail in the Dagger example.

NoSuchMethodError or AbstractMethodError

You should make sure you're not writing your output class files to a directory on a platform with a case-insensitive file system, such as Windows. Please refer to the section about disappearing classes for details.

Furthermore, you should check whether you have specified your program jars and library jars properly. Program classes can refer to library classes, but not the other way around.

If all of this seems ok, perhaps there's a bug in ProGuard (gasp!). If so, please report it, preferably with the simplest example on which you can find ProGuard to fail.

VerifyError

Verification errors when executing a program are almost certainly the result of a bug in the optimization step of ProGuard. Make sure you are using the latest version. You should be able to work around the problem by using the -dontoptimize option. You can check the bug database to see if it is a known problem (often with a fix). Otherwise, please report it, preferably with the simplest example on which ProGuard fails.