Re: I'm annoyed

From:

Lew <com.lewscanon@lew>

Newsgroups:

comp.lang.java.programmer

Date:

Thu, 31 Jul 2008 01:38:14 -0400

Message-ID:

<P_WdnfCC1qtb0gzVnZ2dnUVZ_uGdnZ2d@comcast.com>

Mike Schilling wrote:

I have some Java code that analyzes Java code using reflection. It
loads classes using ClassLoader.loadClass() (catching the
ClassNotFoundException if they're missing) and then uses reflection to
gather data about them. I started up what should have been a long run
before I left work, and later this evening remoted in to find that it
had died almost immediately.

Why? It appears that trying to load class AaaBbb but finding class
Aaabbb whose name differs only in case (quite easy to do on a
case-insensitive file system), instead of throwing a
ClassNotFoundException, throws a NoClassDefFoundError (that's right,
Error.) This was not caught, and caused the program to exit. This is
not documented behavior. It's not hard to fix (catch Throwable
instead of the expected ClassNotFoundException), but the result is
that something which should have completd overnight might or might not
be done by tomorrow morning.

NoClassDefFoundError is the standard response by the JVM when the desired
class, in this case AaaBbb, is not present at run time.

The problem is that the reflective code didn't catch that the class was
missing. So it passed on to the JVM the request to go ahead and load the
class. That's why it was an Error, not an Exception. It's an Error when the
situation is so tangled that the JVM cannot fix it. Thus you experienced the
correct behavior.

In this case I infer that you were running under Windows, and the OS lied to
the JVM about the availability of the class, precluding the Exception and
forcing the Error.

--
Lew