Thanks, that's very clear and helps.
"Craig R. McClanahan" wrote:
> Rueda P wrote:
>
> > I have tried declaring counter using <%! %> .
> >
> > What I found is that when this jsp, containing the counter, is accessed,
> > counter increment.
> >
> > So, my assumption is that the variable declared withing <%! %> is
> > declared as static global variable.
> >
>
> You might want to look at the JSP Specification, available at:
>
> http://java.sun.com/products/jsp/download.html
>
> for a definitive description of what these directives mean, and what they do.
>
> >
> > Is this correct????
> >
>
> No, but it amounts to almost the same thing in a JSP environment.
>
> Consider a JSP page with these contents (among other things):
>
> <%! int a = 0; %>
> <% int b = 0; %>
>
> If you look at the source code of the servlet that is generated for this page, you
> will find the following:
>
> public class xxxxx extends yyyyy {
>
> int a = 0;
>
> public void _jspService(ServletRequest request,
> ServletResponse response) throws ServletException, IOException {
>
> int b = 0;
>
> }
>
> }
>
> In other words, a variable declared inside "<%! %>" becomes an *instance* variable
> in the generated servlet class, while the "<% %>" variable becomes a *local*
> variable inside the servlet's service method.
>
> So what's the difference? The "a" variable is shared among all users of this
> particular page, so modifications made to it are visible to everyone. The "b"
> variable is reinitialized on each request, and it is not shared between requests --
> each simultaneous request is running on a separate thread, with a separate stack
> that contains all of the local variables.
>
> How is an instance variable different from a static variable? Well, there is one
> copy of an *instance* variable for each *instance* of the enclosing class, while
> with statics there is a single copy of the variable for an entire class loader (for
> servlets and JSPs, that really means for an entire web application).
>
> The reason that instance variables and static variables have almost the same effect
> in JSPs and servlets is that the servlet container guarantees that there will be
> only one instance of the class (unless you implement SingleThreadModel, but that's
> a different discussion). Since all users share the same instance of the JSP page,
> there is little practical difference between statics and instance variables in JSP
> pages and servlets. However, they are substantially different in general Java
> programming, where you might have many instances of a particular class.
>
> >
> > Rueda
> >
>
> Craig McClanahan
>
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