what is the use of Activator.java in CQ?

Symptoms
A change was made to a component by an author. The page needs to be refreshed in order to immediately reflect the change. Is there a way to automate this such that the author does not need to refresh the page?

Resolution
The cq:listeners [cq:EditListenersConfig] is used to refresh the HTML page after a certain action is performed on a component. The cq:listeners node should be located as shown:

/component-name [cq:Component]
/cq:editConfig [cq:editConfig]
/cq:listeners [cq:EditListenersConfig]

NOTE: Text in the "[]" is the nodetype. Text after "/" is the node name -- should be extact name except for the "component-name".

The following properties are associated with cq:listeners node are:

• aftercreate
• afterdelete
• afteredit
• afterinsert
• aftermove

afterremove There are three possible values that can be assigned to the properties above -- either "REFRESH_SELF", "REFRESH_PARENT", "REFRESH_PAGE".

So, if you want your text component to cause a page refresh after each edit, you would create the following structure:

...
/mytextcomponent [cq:Component]
/cq:editConfig [cq:editConfig]
/cq:listeners [cq:EditListenersConfig]
- afteredit {REFRESH_PAGE} <= property {value}
mytextcomponent.jsp <= code

Reference:
http://helpx.adobe.com/experience-manager/kb/RefreshPageWhenModifyDialog.html