Using Observable/Observer

[V Bose]

The interface java.util.Observer has a method

 void update(Observable o, Object arg) 

This is called when a state change occurs in the Observable.
I came across this
Sun Tutorial, but am still unclear as to how do you pass the entire state information using just one Object variable.

Has anyone come across a similar situation...?

Thanks

[Ernest Friedman-Hill]

Object is the ultimate superclass of all other classes; therefore you can pass anything at all: a String describing the change, a special class you've defined for this purpose, an array of Lists of Maps full of interesting data... anything.

[V Bose]

Originally posted by Ernest Friedman-Hill:
Object is the ultimate superclass of all other classes; therefore you can pass anything at all: a String describing the change, a special class you've defined for this purpose, an array of Lists of Maps full of interesting data... anything.

You are right. I was thinking about implementation specific issues, such as if one were to pass a List of states that changed, then the Observer would have to parse the list and figure out what changed etc...a little more expensive than I had thought initially...

Thanks

[Ken Blair]

Originally posted by V Bose:


You are right. I was thinking about implementation specific issues, such as if one were to pass a List of states that changed, then the Observer would have to parse the list and figure out what changed etc...a little more expensive than I had thought initially...

Thanks

Which is a good reason to create your own implementation of Observer to suit your needs. You don't have to use java.util.Observer or java.util.Observable to do so.

[Stan James]

Note the other form of this method that leaves the arbitrary object off. Then I think we'd expect the observer to call the observable and ask what changed or just get all the latest state.