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


Pres Brawner
Ranch Hand

Joined: Jan 18, 2001
Posts: 92
I was reading in our Just Java book (around page 211) about Interfaces. Included in that discussion was a mention about "Callbacks". Unfortunately, they use the word "callback" in the definition.
I don't get it.
What's called back? Back from what?
The example shows a method that takes a runnable. Then there is an object that implements runnable. Finally there is an instantiation of the object. The method gets called passing the object to it.
I understand that the run method is indirectly called when you run the method.
Why is that a call back?
Thanks for any clues on this.
paul wheaton

Joined: Dec 14, 1998
Posts: 20972

The idea of a callback is that you have pass an object to a method and that method invokes methods on that class when an event occurs.
Usually, this will be some sort of listener.
I'll create an object that implements a listener interface. Then I'll pass that object to a listener method. When the appropriate event happens, a method in my listener is called.

permaculture Wood Burning Stoves 2.0 - 4-DVD set
Pres Brawner
Ranch Hand

Joined: Jan 18, 2001
Posts: 92
Thanks Paul.
So this is what is done with Swing, right? Event listening?
Then the "Back" part is back to object's method when the triggering event occurs.
Am I getting this?
I agree. Here's the link:
subject: callbacks
It's not a secret anymore!