static variables and methods in servlet

is there any harm in defining public static variables and methods in a Servlet and calling them from some other class or servlet or jsp files.
[ September 29, 2006: Message edited by: hasaN khaN ]

Servlets are also class � hence your can create static variables and methods in Servlets and access from other Servlets / Classes.

But the harm is that Servlet are not meant for that. They have defined role to be play in J2EE framework. Let your Servlets to do what it can do within the define boundary of role.

Defining static variables and method is crossing the boundary.

First, static variables and static methods are two different topics.

Unless you have a real good reason to use them and you really know what you're doing, I'd avoid using static variables in web apps. Doing so can lead to some confusing behavior.
[ September 29, 2006: Message edited by: Ben Souther ]

Ben is correct in that read/write static variables aren't well-suited to the web app environment. Final static variables used to defiend constants are a different matter though, and should be used to define constant values rather than hard-coding literals throughout the code.

You must be careful of that class or instance variables in servlets for thread safe.
Container maybe send mutiple request to one servlet instance,so servlet (jsp also)is in multiple threads enviroment.