According to my knowledge, Textchat can be implemented either thru pushing or polling technology.

polling tech - (In case of applet is on front end) Let us assume on client side an applet always polls the server every few seconds(based on settings) to retrieve the messages for that client.
 
(In case of jsp in on front end) jsp page which shows the messages that is refereshing every 4 or 5 sec - I mean it is also requesting the server and retrieving the messages stored in any object pertained to that client.

But, I heard that pushing technology is good for implementing the textchat? What and How?
Can any one explain ?
Thanks in advance,
UV