Java.lang.NoClassDefFound

Question

Can anyone point me in the right direction with this error;
Exception in Thread "main" java.lang.NoClassDefFoundError: app2
where app2 is the name of my application. My application contains 3 classes. app2 is the main class which is constructed by the main method. app2 calls the next class, which calls the third. the application was working before and i can't find what i changed.
I'd really appreciate it if some one could give me an idea what this error means and any possinle causes.
Thanks

Answer 1

I'm kinda new too, so hopefully in trying to answer people, I'll discover that I too am wrong, and will be corrected, and will learn in the process.
Anyhow, depending on what O/S ya run, ya have to set the classpath in different ways. I use a .bat file that I run in dos when I first open dos. I edit the bat file to have the classpath set to whatever I need. I have multiple bat files and I use the one for the project that I'm currently working on.
a dot means the current class, otherwise you can just just put in the path to the directory, and you can have multiple things set, separating them by a semicolon.
so like a bat file like so:
PATH=C:\WINDOWS;C:\WINDOWS\COMMAND;C:\;c:\jdk1.3.0_02\bin
SET CLASSPATH=.;C:\JavaProjects
cd c:\JavaProjects
Add directories ya wanna use w/semicolons separating them, then give it all a go once again.
Or you can download jbuilder or somesuch and just hit the compile button.
If I'm wrong about anything, I hope someone will tell me, I wanna know if I am.