Hi Pradeep,
In general render parameters are
private in nature and not available outside the portlet. Let's say you set a render parameter X in
action method of portlet A. When portlet A is rendered (after the execution of
action method), the
render method makes use of the render parameter X in someway that it affects the generated content. For instance, X could represent success/failure of the
action method. Now, you may want this render parameter X to be available to other portlets on the same portal page so that they can use it while generating their own content. To do so, you configure the parameter X as a 'public render parameter' in
portlet.xml file, making it available to other portlets also.
As render parameters can only be of type
String, their use is limited in inter-portlet communication. Events can carry payload (which could be a complex object), in some scenarios you'll find it more appropriate to use event-based IPC.
regards
ashish