Design problem with Swing

Question

Hi all. I've run into some design problems when trying to create a Swing app.
I've got a non-graphical class that emulates a power supply unit. Let's call it PSUnit. I have to create a GUI for PSUnit.
Every class designed to build a full GUI app uses PSUnit in some way (changes its voltage, displays voltage, turns it on, turns it off, etc.)
Here's the catch. Suppose I've got a class:
public class BuildingBlock extends JPanel {
     // code includes a JTextBox displaying
     // the current PSUnit voltage.
}another class is created for setting the voltage:
public class AnotherBlock extends JPanel {
     // this class contains a JSpinner and
     // a button that retrieves the JSpinner value
     // and sets it as the current voltage of
     // PSUnit
}When the button in AnotherBlock is clicked, I must notify the BuildingBlock class that a PSUnit has changed its state so it can update it's values and display the correct data.
I've tried to do this a few times but failed miserably, so I'm hoping you guys could help me out.
Please note that both of the above classes have some additional code and it's not very pleasant to make one class an inner class of another. I should be able to create a "standalone" classes which, combined together, form a GUI for PSUnit.
Thanks.

Answer 1

Yes this is a common problem that many of us have when building UIs
Here's the question: In this instance, are these two classes really independant? Could they stand alone? Often when building a GUI, it's not even that easy to answer that question, but these leads to the two ways you can solve this
#1. Make them independent, and use listeners either using Observable / Observer or creating your own custom listeners. The advantage of this is smaller classes and more independence. The disadvantage is it's generally more complicated, especially at the design stage
#2 (what I'd probably recommend). Make 1 GUI class "MyPSFrame", then declare your panel classes as inner classes within that class. This way, everything goes into one spot, and everything is shareable. This also makes sense if you can't have 1 of the panels without the other.