File APIs for Java Developers
Manipulate DOC, XLS, PPT, PDF and many others from your application.
The moose likes Beginning Java and the fly likes Callback methods Big Moose Saloon
  Search | Java FAQ | Recent Topics | Flagged Topics | Hot Topics | Zero Replies
Register / Login
JavaRanch » Java Forums » Java » Beginning Java
Bookmark "Callback methods" Watch "Callback methods" New topic

Callback methods

A Kumar
Ranch Hand

Joined: Jul 04, 2004
Posts: 980

Whats the difference between callback methods and methods?

Peter Chase
Ranch Hand

Joined: Oct 30, 2001
Posts: 1970
Callback methods are methods. So, it makes no sense to speak of a difference between them.

A callback method is an ordinary Java method. The only thing special about them is how you intend them to be used. You can't enforce that a method is only used for callbacks.

Betty Rubble? Well, I would go with Betty... but I'd be thinking of Wilma.
A Kumar
Ranch Hand

Joined: Jul 04, 2004
Posts: 980
but what exactly does it mean when someone writes..

"callback methods such as .."

They could as well write it as


Whats the special significance.....?
Pratibha Malhotra
Ranch Hand

Joined: Dec 21, 2003
Posts: 199
Callback is comman mechanism in C.

It is used to pass a object to a method as an argument. Method inturn can invoke other methods associated with the Object passed to it as an argument.

Callback technique is essentialy used in scenarios where user wants to
invoke different methods without leeting client know which method of which class is being invoked.

Java use interfaces for callbacks mechanism. In this case, a method holds an interface reference in its argument list and then invokes a method in the interface. Interface is one such example from Java API.

Now the million dollar Question - Why on this Planet do we want a callback?
When we pass a parameter, method being invoked gets the information (ie parameter value etc). What is returned is a result primitive or Object which provides only meager flow of info. Callback mechanism however allows a two-way communication channel between caller and callee.

Visitor Pattern is a classic example to demonstrate how Callback technique should ideally be used

[ September 28, 2006: Message edited by: Pratibha Malhotra ]

~ Pratibha Malhotra<br /> <br />Sun Certified Java Programmer<br />SCEA 1.4 (In Progress)<br />~~~~~~~~~~~~~~~~~~~~~~~~~~~<br />"Many of life's failures are people who did not realize how close they were to success when they gave up!!"
A Kumar
Ranch Hand

Joined: Jul 04, 2004
Posts: 980
Thanks Pratibha!!!
I agree. Here's the link:
subject: Callback methods
jQuery in Action, 3rd edition