A strange problem in Tomcat Servlet

Question

I am a starter in programming servlet.
I am running servlet under Tomcat 5.5.
I test the HelloWorld servlet. It works well and shows "Hello World".
But when I change the code to out.println("Hello World!!!"), and re-compile, the output remain the same.
Then I shut down the Tomcat and restart. The output becomes Hello World!!!.
What's the reason? The servlet engine only read the same class once?
How can I change it?
Thanks

Answer 1

With class files, I've noticed that sometimes changes to the code aren't displayed, you have to restart tomcat.
But if you're just displaying text, that should go in a jsp. In a jsp, changes are usually displayed when you reload the page (unless the browser caches the page). And the code is also cleaner to look at, without out.println's everywhere.
If you're using eclipse as your programming environment, then it should automatically do a "hot code replace" (which does fail in some cases, like if you add a method, so you have to be careful). If the changes are minor, you can do exactly what you're looking--modify a class, save it, and the class file gets changed without having to restart tomcat, and the recompilation is automatic which is great.