java servlets in web application

I may sound a little childish but i am bit confu开发者_高级运维sed over a very basic thing

I am using tomcat server. I wrote two servlets to include in my web application and saved them in the classes folder under the tomcat directory...the point I am wondering about is I didn't compiled the two classes and simply placed the .java files in it....still my application was running successfully..... how come this is possible?? does it has some sort of inbuild compiler or is it something else....

Tomcat has a feature called Client Deployer that allows you to do this, but as mentioned, this will only run on that Tomcat instance