A package-info class contains annotated package and annotation type. These classes are compiled using JDK 6 compiler with target 1.5. JDK 5 fails to load the generated package-info with the following error:

Exception in thread "main" java.lang.ClassFormatError: Illegal class modifiers in class pack/package-info: 0x1600
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
        at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
        at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
        at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
        at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
        at java.security.AccessController.doPrivileged(Native Method)
        at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
        at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
        at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(Class.java:242)
        at java.lang.Package.getPackageInfo(Package.java:350)
        at java.lang.Package.getDeclaredAnnotations(Package.java:375)
        at pack.Main.main(Main.java:26)

It seems that the problem is that the JDK 6 compiler target 1.5 adds "synthetic" and "abstract" attributes for the package-info classes that JDK 5 runtime doesn't understand.

Package-info, annotation type and Main class java source files are attached. As well as the output of the Jcoder tool for package-info classes compiled by different compilers.

Related information: 
       JVMS 3ed spec update: http://ccc.sfbay/6232928
       CRs: 6313196, 6232928

If this is a compiler bug, please reassign it to the java/compiler category.
Posted Date : 2007-05-04 12:41:40.0

Compile with JDK 5

This is an accomodation for a compiler bug.  It is possible that there are people out there that are using an non-updated JDK6 which will generate code that JDK5 runtime won't recognize.
Posted Date : 2007-06-27 02:00:00.0

I'm not sure what "non-updated JDK6" means, but this bug is present when compiling with JDK6u1 (build 1.6.0_01-b06) - which is the latest one listed - and running on JDK5u12 (build 1.5.0_12-b04) - which is also the latest one listed.

This bug is still present with classes compiled with JDK6u3 running under JDK5u14.

I developed a fix for this at https://fix1600.dev.java.net/

The maven fix at https://fix1600.dev.java.net/ is awesome, great workaround!  Thanks!

Can someone put "fix1600" back on server "http://download.java.net/maven/2/org/jvnet/" ?
The server was down earlier this week, and now seems to be running on a Nov2007-backup that is missing "fix1600".

It seems this is fixed in some update release, don't know in which one, but seems to work at least in u10, and probably in u7 too.