Help running Java apps in Mac OS 10.1.3

Question

I'm currently taking an intro course to Java and I've been using the OS 10.1.3 Unix Shell to compile and run my assignments, using the "javac" command to compile my classes and the "java" command to run them. It's been working fine until a few days ago when every class I started to compile from that day on wouldn't run. The previous classes I've compiled run fine, however if I re-compile them and attempt to run them I incur the same problem.
I get this error :
Exception in thread "main" java.lang.NoClassDefFoundError:
followed by the classname.
The best I can figure is that I've accidently changed some option in the java system, but now I have no idea as to how to change it back. I've asked my CS professor what to do but ofcoarse he's a PC user and when he hears Mac he just replies "I don't know about Macs" eventhough I've tried telling him that OS X is unix based. Anyways, if there are any well informed Mac OS 10.1.3 users out there, please help me so that I can resume my CS assignments on my Mac.
Thanks,
Craig

Answer 1

1. Are you certain that you have all of your java files compiled
and that their class files are in your classpath? Did you import
the class TestWeeklyEmployee in your java file that has your
main method? Do all of your class filenames have the same
name (minus the .java or .class) as the class in the file?All of the java files needed to run the class are in the same directory, and they all have the correct names, You see I'm able to run my programs perfectly on other machines, infact I have to test them in the computer labs before I turn them in. So I know that my probrem isn't a syntax error.
2. when you start the terminal, type the following:
echo $CLASSPATH
and make sure that the output it gives has the . [dot] that you
added via the .cshrc file at the end or that only a dot gets
displayed. If it does not have your dot in the output, then you will
have to use the -classpath option to the java runtime binary to
tell it where your classes are located.I tried typing echo $CLASSPATH but I got this error message:
CLASSPATH: Undefined variable.
And I had directly copied the code you wrote into my .cshrc file.
3. When you try to run your java program, are you sure that you > are in the directory where all of the class files are located? use
the "ls" command to see if your class files are in the current
directory. (you may want to search the web for a UNIX tutorial or
a UNIX for beginners type of article so that you can feel more
comfortable using the Terminal application)Yes all of my classes are in the same directory and yes I'm in the correct directory when compiling and attempting to run my programs.
4. Assuming that 3 is true: If you run your program using the
"java -classpath . MyClassWithAMainMethod" do you still get an
error? If you do, then I am pretty sure that you have neglected to
import a class that your main method is trying to instantiate or
that you have not compiled the source of the class in question >
(or both).All classes are imported correctly and yes I have compiled the class. As I said it works fine when I compile and run on other machines, just not mine.
Are you trying to install the developer tools from the developer
cds? If you are and you have since updated your OS to 10.1.x,
then I would not expect project builder to work. The same thing
happened to me when I upgraded to 10.1.x. Sounds like you
may need to install the latest developer tools which can be
downloaded for free from the Apple Developer Connection site
(http://www.apple.com/developer). Installing the latest developer
tools should get things right for you.The developer tools that I'm attemping to run are not from the CD, they're the current downloadable version from apple developer. I've contacted apple developer support with my problem with project builder, but they blew me off.
So now that we've eliminated these possibilities, any other ideas?
Thanks,
Craig