tmflores
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How to troubleshoot a Java exeption error for java.lan.ClassFormatError: Unknown constant tag 0 in class file
When I try starting a particular Java based program that was recently upgraded, it gives me an error which says: An exception occured in the JVM. Detail - java.lang.ClassFormatError
JavaError.jpg
JavaError.jpg
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ASKER
nm I found it. now, would it be possible to replace that particular .class file with a known good one?
If you obtain a clean JRE, and unpack the JAR where all the runtime classes are stored in (typically rt.jar), you'll get a clean copy of the FetcherInfo class. The first thing I would do then is to do a binary compare of the two files. If the two are identical, then you're probably dealing with a bytecode modification issue AFTER the clean FetcherInfo gets loaded into the JVM... so basically looking at externally stored classes is not going to get your anywhere.
If the binary diff does give you a difference, could you please post the first 16 bytes of both files. The header contains .class file version information, and you may have an issue there too.
If the binary diff does give you a difference, could you please post the first 16 bytes of both files. The header contains .class file version information, and you may have an issue there too.
ASKER
the effected FetcherInfo.class will not open. when I try to decompile it I get the attached error so I can't (or don't know how to) compare the binary of each FetcherInfo.class.
Any suggestions?
FetcherInfo-decompile-error.doc
Any suggestions?
FetcherInfo-decompile-error.doc
OK, for now, I would concentrate on seeing a hexdump diff of the two files. Forget the buggy decompiler that you used. So a) produce hexdumps of the two files, then b) use a diff program to produce a diff output.
Like I said, the very first you need to establish is whether the two files are identical or not. If they differ, then it's a question of "what differs" ?
HTH
Like I said, the very first you need to establish is whether the two files are identical or not. If they differ, then it's a question of "what differs" ?
HTH
ASKER
I was able to get the error to go away by just replacing the entire rt.jar file with a known good. Thank you for your assistance.
ASKER