Compile from command line

[AdelJava]

Dear All,
Hope every one is fine.
I'm really struggling with compiling java from command line.

first, I set the classpath , this is good!
but the problem I have in my program is :

I have this package in the program:

import weka.core.*;
The problem when I do the following
javac programname.java
I received : package weka.core.* does not exist!

I do not know why. could any one help please?

Adel,