未在tomcat ubuntu中引用更新的servlet类

I am beginner to servlets. I am trying to create and run servlets using tomcat in ubuntu. I am facing a problem. I am able to call the servlet from the html file by adding an entries into web.xml. But when I change the java program a little and recompile and invoke the new servlet class, the html still seems to call the old one.I am beginner to servlets. I am trying to creat