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

Question

I am getting this error when I include an opensource library that I had to compile from source. Now, all the suggestions on the web indicate that the code was compiled in o

Answer 1

Did you compile with Eclipse? It uses a different compiler (not javac). That should not result in this error (if everything is configured properly), but you can try to compile it with javac instead.

If that fixed the problem, try to see if Eclipse has some incorrect compiler settings. Specifically have it target Java 5.

Answer 2

Also check any jar files in your project that have been compiled for a higher version of Java. If these are your own libraries, you can fix this by changing the target version attribute to javac

<javac destdir="${classes.dir}"
            debug="on" classpathref="project.classpath" target="1.6">

Answer 3

I've learned that error messages like this are usually right. When it couldn't POSSIBLY (in your mind) be what the error being reported says, you go hunting for a problem in another area...only to find out hours later that the original error message was indeed right.

Since you're using Eclipse, I think Thilo has it right The most likely reason you are getting this message is because one of your projects is compiling 1.6 classes. It doesn't matter if you only have a 1.5 JRE on the system, because Eclipse has its own compiler (not javac), and only needs a 1.5 JRE to compile 1.6 classes. It may be weird, and a setting needs to be unchecked to allow this, but I just managed to do it.

For the project in question, check the Project Properties (usually Alt+Enter), Java Compiler section. Here's an image of a project configured to compile 1.6, but with only a 1.5 JRE.

Answer 4

Have you tried doing a full "clean" and then rebuild in Eclipse (Project->Clean...)?

Are you able to compile and run with "javac" and "java" straight from the command line? Does that work properly?

If you right click on your project, go to "Properties" and then go to "Java Build Path", are there any suspicious entries under any of the tabs? This is essentially your CLASSPATH.

In the Eclipse preferences, you may also want to double check the "Installed JREs" section in the "Java" section and make sure it matches what you think it should.

You definitely have either a stale .class file laying around somewhere or you're getting a compile-time/run-time mismatch in the versions of Java you're using.

Answer 5

Deleting the project specific settings files (Eclipse workspace/project folder/.settings/) from the project folder also will do. Obviously, we need to do a project clean and build after deleting.

Answer 6

changing the project to use java 1.7: For this to work follow those steps :

• Change Compiler Compliance Level
• Change your projects JRE/JDK to something of the same level(1.7 in my case)
• Do the same change in all the projects referenced by your project
• Change your run/debug configuration to use the JRE/JDK (or of the same level)

Not working?

• delete projects Bin directory
• Clean
• reBuild

Still not working?

in your project's directory: edit .settings/org.eclipse.jdt.core.prefs > make sure your target level is applied

Good Luck!