Callback methods

[A Kumar]

Hi,

Whats the difference between callback methods and methods?

Regards

[Peter Chase]

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.

[A Kumar]

but what exactly does it mean when someone writes..

"callback methods such as .."

They could as well write it as

methods...

Whats the special significance.....?

[Pratibha Malhotra]

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.

java.io.Serializable 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

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

[A Kumar]

Thanks Pratibha!!!