The Server (that which presents your classes to those interested in your classes) has to know where your classes are.

When you develop on your private machine, you are the one that is being "served" the applet. So you may "point" to your local class directory/folder (i.e. set the classpath to your local directory). When you put this on a web server, you must "inform" that server how to find your classes as well. So you have to know where your web server looks for certain files (in this case, the class files), so that it can "serve" the public (whoever is your audience--intranet/internet).

You can tailor this in an html page using a relative or absolute url that says where the applet class is.

<HTML><HEAD><TITLE> A Simple Program </TITLE></HEAD><BODY>
Here is the output of my program:
<APPLET CODE="HelloWorld.class" WIDTH=150 HEIGHT=25></APPLET></BODY></HTML>