How does thinkphp inherit its own Action?

How does thinkphp inherit its own ActionGlobalAction. class. phpPHPcodeclassGlobalActionextendsAction {publicfunction_initialize () {}} IndexAction. class. phpPHPcodeclassIndexActio thinkphp inherit its own Action?
GlobalAction. class. php

PHP code

  Class GlobalAction extends Action {public function _ initialize (){}}

IndexAction. class. php

PHP code

  Class IndexAction extends GlobalAction {}

An error is reported when I write the result so that GlobalAction is not found.

------ Solution --------------------
Before class IndexAction extends GlobalAction, GlobalAction. class. php must be loaded in. Otherwise, an error is returned.
------ Solution --------------------
Include (/index. php/lib/GlobalAction. class. php)