Java Observer and Observable not working properly between applications

Question

I have an application with a main JFrame that contains a default list model. I want that if I modify something on these records, the second running application is automatically updated.

So far I have a MainController class which implements the listener and overwrites the update method:

public class MainController implements ActionListener, Observer {
  public void update(Observable o, Object o1) {}
}

and a simple class that extends Observable

public class Comanda extends Observable{}

My problem is that if I delete one record from the first application, the second list doesn't update. The program is deleting the record from the text file but is not updating the default list model. Same problem with edit or add.

I tried adding "reloadList()" in the update method, but that doesn't work. Ideas?

It'd be useful if you show your code for starting the notification of observers. (Observer/Observable really should have been deprecated in 1.1. I also would use anonymous inner classes rather than having a single class do multiple tasks.) — Tom Hawtin - tackline
@rhose87: "...to update the second running application" [sic]... You are running two different Java applications and expect the action that are happening in one application to be notified in the other!? — TacticalCoder

DaveJohnston DaveJohnston · Accepted Answer · 2012-01-16T00:21:55

Have you called addObserver on Comanda and added the MainController as an Observer? Also, when the change occurs are you calling setChanged and notifyObservers?

Looking at the code you have posted I can see that you have not wired the Observer and Observable Objects together. As I said, you have to call addObserver on your Observable object, then within your Observable Object, whenever a change is made you need to call setChanged then notifyObservers. Only when notifyObservers is called will the update method of any Observers that have been added be called.

You said in your question that when you delete one record the list doesn't update, which makes me think that Comanda is probably not the Object that you want to Observe. Whichever Object it is that holds the List of records is the one that should be the Observable.

Have a look at this for some more information on the Observer/Observable pattern.

Java Observer and Observable not working properly between applications

2 Answers