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java.lang.UnsupportedClassVersionError: Bad version number in .class file

java.lang.UnsupportedClassVersionError: Bad version number in .class file
[at java.lang.ClassLoader.defineClass1(Native Method)]
is an error that you may face in running a compiled java class file.

So as you can see from the stack trace, a class has not been loaded. But which class? The problem is this error message does not show the name of the failed .class, isn't it?

No, it is not.
This error is caused when you compile a .java file with one version of JDK and running the .class file with a different version of JVM.

Confused? You may say; same version is not required to compile and run.

Yes, that is true. But you can not run .class files that are compiled with a newer version than the JVM.

javac (compile) - version: X
java  (run)     - version: Y
If X is newer than Y; then you may face this issue at runtime.

Now you know how to solve this issue, isn't it?


  1. I tried 2 run some class files on java 1.5 I received from a friend and faced this error. Thanks for pointing the solution.

  2. It's crystal clear explanation. bunch of thanks Kamal.

  3. Thanks Kamal! Your post helped me.

  4. Dear Friend im facing the same problem but as u explaned i dont know how to use these commands plz help

  5. Hello friend,

    Please check the versions of javac and java on your computer and post them here, then we'll create the required commands.

  6. Wow cool
    I can fix my problem by you posted

  7. how is it that i remember being able to issue a "javac -version" before that worked, but now i can't figure out how to check my compiler version?

    java -version (always works)
    javac -version (now never works)


  8. java version "1.6.0_12"
    Java(TM) SE Runtime Environment (build 1.6.0_12-b04)
    Java HotSpot(TM) Client VM (build 11.2-b01, mixed mode, sharing)

    javac 1.6.0_12

    I got the versions as above, but still getting this error. I have tried compiling it with or without -cp option, but it is still failing to run. I am able to get this to work from another workstation. Can you please help?

  9. im facing the same problem but when i installed 1.5 it didnt showed any error but at run time it is showing the error
    and java -version is showing 1.3.1 version

  10. i installed latest 1.6 jvm and jre. javac -version is showing 1.6 but java -version is still showing 1.3 may be older version is not unistalled properly. help me

  11. Hi Satyam,

    Best thing to resolve this would be, first remove all jre/jdk installations. (Better not to install two different versions on one machine.)

    Then check for versions of both. That way you will be able to resolve this issue.

  12. I am getting this error for groovy 1.6.0.

    java.lang.UnsupportedClassVersionError: org/codehaus/groovy/tools/GroovyStarter (Unsupported major.minor version 49.0)

    and my java -version is java version "1.6.0_11"

    Any thoughts?

  13. I think 49.0 => Java 1.5 ... are you sure all were recompiled?
    Doesn't it identify the bad class file?

  14. I got the same exception and I solved it
    java.lang.UnsupportedClassVersionError: Bad version number in .class file
    [at java.lang.ClassLoader.defineClass1(Native Method)]

    I was using JDK 1.5
    I was trying to connect from eclipse using "postgresql-8.3-603.jdbc4.jar"
    this driver. This jdbc driver.

    After the error message i went to
    and found a compatibility list like this
    * JDK 1.1 - JDBC 1. Note that with the 8.0 release JDBC 1 support has been removed, so look to update your JDK when you update your server.
    * JDK 1.2, 1.3 - JDBC 2.
    * JDK 1.3 + J2EE - JDBC 2 EE. This contains additional support for javax.sql classes.
    * JDK 1.4, 1.5 - JDBC 3. This contains support for SSL and javax.sql, but does not require J2EE as it has been added to the J2SE release.
    * JDK 1.6 - JDBC4. Support for JDBC4 methods is limited. The driver builds, but the majority of new methods are stubbed out.

    So i used "postgresql-8.3-604.jdbc3.jar" instead of jdbc4.

    And then my connection was found by eclipse ran without any problem

  15. thanks for the tips.

  16. I have the same problem. But i have java version 1.5.0_21 and jvm is the same but in eclipse when i start tomcat this error happens.

    Any idea?

    I have check everything related to java so all is pointing to this version

    Thanks in advance

  17. // Tomcat and java version 1.5.0_21

    Can you try starting Tomcat without the projects that you have deployed there? Then you will be able to locate the web application that causes this error.

  18. Loud and clear..Thank you

  19. If you get this in ECLIPSE. Look at the javac compliance under Windows->Preferences->Java->Compiler and make sure its the same as Eclipse's default JRE version.

    This was driving me nuts - until I saw my Eclipse JRE was 1.5 and this setting was at 1.6!!!!

  20. thank you for the post I find it usefull.
    I find that a few days before I had installed Zend Studio on Windows 7, while replacing my JRE becoz Zend studio does't work well on this window and currently this is the one way to get it work well on Win7.

  21. Thank U very much dude.. Ur explantion was very clear..

  22. The problem is that versions of compilation (javac) and run (java) must be the same, but not necessarily in your PC. The JDBC connection is to be compatible with our PC.
    So the solution is to find the appropriate JDBC.

  23. Of course the error message should tell me the class. In my case I have both Java 1.5 set in the Eclipse project, and the settings show that 1.5 class files are being built. I also am running with JDK1.5. Without telling me the class in error, there is no way I can trouble shoot.

  24. Sofia BertoliniMarch 26, 2010 8:48 AM

    Hi all!!!

    Is it possible to have version X and version Y such that Y=X and still get this?:

    Error compiling the report java source!
    java.lang.UnsupportedClassVersionError: Bad version number in .class file     at java.lang.ClassLoader.defineClass1(Native Method)     at java.lang.ClassLoader.defineClass(
    ... and so on....

    Trying to compile a jasper report on iReport 3.7.1 (netbeans platform)...

    Any guess?

    Grazie mille!!

    Mac OSX v. 10.5.8 Intel
    Java(TM) SE Runtime Environment (build 1.6.0_17-b04-248-9M3125)
    sofiad:~ sofi$ javac -version
    javac 1.6.0_17

  25. // 27

    Hi Sofia,

    This error message is only there when this version conflict occurs.

    Even though you are using 1.6.0_17 jdk & jre; you may be using some other jar files that were generated with classes generated with a newer version of Java. So you can check Java versions used for them as well?

  26. Hello,

    Running from the command line (Windows XP) I have,
    Java as: java version "1.4.2_03"
    Javac as: javac 1.6.0_11

    This is causing a conflict. I can't find the older version of the JRE in the Windows Control Panel to remove it I can only see Java 6 Update 11 and the JDK SE Update 11. I can't find any reference to the older java on the Java console in the Windows Control Panel either.

    When I'm using NetBeans, everything is working correctly as it is pointing to right folders.

    My PATH is C:\Program Files\Java\jdk1.6.0_11\bin

    How do I remove the older version?

  27. Well this error is due to the compiler version and JRE version are different.

    If you are interested, You can easily reproduce it in Eclipse

    Install jdk1.5 and Jdk1.6 in your system.

    Create a simple java project in eclipse

    Set the compiler version to 1.6 through menu->Windows-Preference->Compiler to 1.6

    the select the project and change the buildpath jre to 1.5. (check eclipse help)

    Try to run the program.

    You get the this error!!!

  28. Thanks for the solution.

  29. Thanks for solving my problem.

  30. Thanks... my eclipse was using a different version. Problem solved.

  31. Thanks Kamal this post helped me...
    I was running an ANT build with javac version 1.6_0 update 21
    < javac srcdir="src/main/test" destdir="target/classes" classpathref="compile.classpath" />

    The classes were getting deployed to Apache Tomcat 6.0.26 container...I think Apache Tomcat still requires version 1.5...when I added my ant script above following two conditions it redeployed worked for me. Here is the updated antscript line:
    < javac srcdir="src/main/test" destdir="target/classes" classpathref="compile.classpath" source="1.5" target="1.5" />

  32. a big thank you

  33. i have same problem i have jdk1.5 with mac osx and jvm 1.6 in eclipse n i cant found the sollll of this problem plz anybody suggest me but i have to do.........

  34. Wow, thank you, very nice and clear explanation. Refering to Eclipse (in my case) specifically, you have to go preferences->java->installed JREs an then check which you prefer.

  35. this problem will be arised bcoz of jdk and jre are not the same version.

  36. how to do 4x4 tiles with red n blue color using method start() it can changed into other color in JAVA lang?

  37. I have deleted/reloaded Java 25 times. Get the same error: java.lang.ClassFormatError:Truncated class file???

  38. Crisp and clear mate , i hav resolved the problem in short time thanks for the post.

  39. Thanks for article...solved the problem

  40. Hi,

    I have a question that if I compile and build (war and ear files) with 1.6.0_22 and my weblogic server is running on 1.6.0_11, then will it work?

    Both are using java 1.6 but server has 1.6 with updates 11 and in my system I have Java 1.6 with update 22.

    Please put your suggestions.

    Thanks in advance !!!!


  41. Thanks very much...That was the best explanation i got on net.
    3 Cheers!....

  42. Combining class files into a JAR file to make standalone program?

  43. I would like to have an exclusive Mother Board Troubleshooting Book with detailed depictions and steps?

  44. I am having prolems loading some pages due to a java error. How can I fix the problem?

  45. I am having prolems loading some pages due to a java error. How can I fix the problem?

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