View Full Version : I think I screwed up my JDK

March 26th, 2007, 02:13 AM
Hi all.

I am somewhat new to linux but quite familiar with computers. I need some help resolving a problem that I think is caused by incompatible Java versions.

I'm running Ubuntu 6.10 and recently tried to install the sun JDK 6.

I wrote a quick test app and this is what happened:

Exception in thread "main" java.lang.UnsupportedClassVersionError: Bad version number in .class file
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java :620)
at java.security.SecureClassLoader.defineClass(Secure ClassLoader.java:124)
at java.net.URLClassLoader.defineClass(URLClassLoader .java:260)
at java.net.URLClassLoader.access$100(URLClassLoader. java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java: 195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.j ava:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:3 06)
at sun.misc.Launcher$AppClassLoader.loadClass(Launche r.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:2 51)
at java.lang.ClassLoader.loadClassInternal(ClassLoade r.java:319)

The test app is just a basic 'hello world' type of program and compiles and runs on my windows machines.

What I've found is that it seems that the JRE itself wasn't upgraded to 1.6 when I installed the JDK. The reason I believe this is true is this:

ashercim@command:~/Projects$ java -version
java version "1.5.0_08"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_08-b03)
Java HotSpot(TM) Client VM (build 1.5.0_08-b03, mixed mode, sharing)
ashercim@command:~/Projects$ javac -version
javac 1.6.0

I can't seem to uninstall or update Java at all on this machine. I installed java originally using the instructions at sun's website for their self extracting .bin file.

My question specifically is this:
Am I correct that this program won't run because it is being compiled with a later version of the compiler than the JRE?

Will uninstalling and reinstalling java solve this problem?

If it will, how can I force java to be completely uninstalled?
(It doesn't show up in Add/Remove Programs)

Thanks in advance to anyone who can help.

March 26th, 2007, 03:45 AM
Try this to make sure your system is pointed to the current verision

sudo update-alternatives --config java

March 26th, 2007, 05:38 AM

That did the trick.

I wish I asked you guys 2 days ago. LOL

March 26th, 2007, 10:29 AM
Glad to help.

Ramses de Norre
March 26th, 2007, 02:23 PM
This will set all java-related programs to java 6:

sudo update-java-alternatives -s java-6-sun