What do I need to do after I change a .java file?#

• Tomcat starts, but wikipages are not loaded -> update Tomcat-Context... this happens when mvn installing while tomcat is running...
• What is an plugin, what is an extension, what is an extension point (http://d3webwiki.informatik.uni-wuerzburg.de/Wiki.jsp?page=Plugins%20and%20Extensions)
• What is the Scope of an extension