Is your JSP page named “HelloWorld.jsp” as well? If so, please do not name classes and JSP pages the same name, the reason is that there is currently a bug where during validation both are compiled to class files (ending up in 2 separate files with the same name that USE eachother) so likely the validator is thinking you mean your JSP page when you say “HelloWorld hw” which obviously is not what you wanted.
The reason this works in app servers is because they will prefix/suffix the JSP page with some constant string like “_jsp_page.java” when it is converted.