Most people always have the following problem when run their java programs under linux box:
Exception in thread "main" java.lang.NoClassDefFoundError: *.java
Even though these programs  really have no problem at all.
Here are some solutions for you:
1) Check your syntax that you are trying to run the java class and make sure it should be like this (assume the class file is foo.class):
java  foo      instead of    java  foo.class

2) Make sure your classpath contain the special path ".", actually this is most likely where the problem come from. 
You can try to run your program as follows.

java -cp .  foo   or
java  -classpath  .  foo

If it works, then you are suppose to add "." to you classpath.
For example:
export CLASSPATH=.:$JAVA_HOME/lib:JAVA_HOME/jre/lib

3) Check it out if you compiled the java file without specifying the package that import in your file.

What if all these works are done, but your still got the same problem?
Well, in this case, you've got to have a look at your souce code......

Good luck!