First, thanks for the reply.
It is a really simple program, Hello World.

public class HelloWorldApp
{
   public static void main (String arg[]){
       System.out.println("Hello World");
    }
}

Actually, i ran other programs too.  I was able to compile all the
programs , and, in this particular case, the command i used is
java HelloWorldApp(.class).
I used both with class and without class.  I got the same following
message.

Exception in thread "main" java.lang.NoClassDefFoundError:
HelloWorldApp(/class)

I was able to compile and run in the Linux machine at the University.
So, seems like problem is in my laptop envirionment.
Thank you very much.