Exception in the thread "main" java.lang.NoClassDe

[java4mls]

While in the process of adding comments to an already created (and running) class application, there was an error which will not permit the application to run that reads as follows: "Exception in the thread "main" java.lang.NoClassDefFoundError: Hello2" Please find the error for me, I have changed things and followed the instructions closely, but don't seem to be getting it. Thank you very much. I have pasted the text as in TextPad below:

//Filename Hello2.java
//Written by MLS
//Written on February 11, 2006
public class Hello2
/* This class demonstrates that use of the println() method to print the message Hello, world! */
{
public static void main(String[] args)
{
System.out.println("Hello, world!");
}
}