Lost VB Programmer needs help

Question

Hi,
I have created a JFrame with a JSplitPane and placed a JTree in the left side of the SplitPane. I made a class that populates the tree with a tree of options. When the user clicks the tree I want he right pane to change. The treemenu was an event listner that is working fine.
The problem is the left pane is in a separate .java file called TreeMenu. On the JFrame I simply create a new instance of it and it populates the tree for me.
As a VB programmer I would declare my TreeMenu to have an event such as MenuChanged("Selected Help"). The JFrame would see the message and call the right pane to update.
How do I do this in Java? My problem occurs when I move code out to a separate class. If everything was done frm the one frame then I would be fine, but i want to modularise the application.
Please help.
Aaran

Answer 1

Here's a bit of code that may help you with your modularity issues.
File: Switchboard.java
interface Switchboard {
    void operator(TreeData identity);
}File: CallMaker.java
import java.awt.event.*;
public class CallMaker implements TreeSelectionListener {
    private TreeData identity;
    private Switchboard destination;
    CallMaker( TreeData id, Switchboard swbd ) {
        identity = id;
        destination = swbd;
    public void valueChanged( TreeSelectionEvent e ) {
        destination.operator( identity );
}For what you're trying to do I would suggest the following:
1)Declare the Tree Populator to implement the Switchboard interface.
2)put the code that populates the table into the operator method, or
simply call the class/method that populates the tree from the
operator method.
3)Use an instance of the CallMaker class as a Listener on your tree.
It should work something like this:
public class PanePopulator implements Switchboard;
//Other code and whatnot...
   public void operator(TreeData td) {
      //Decide how to populate the right pane
      //based on the TreeData.  Call other classes/methods.
}In a separate file...
public class TreeSide {
   JTree tree = new JTree();
   //initialize the tree.
   TreeData treeInfo = new TreeData();
   PanePopulator rightPane = new PanePopulator();
   tree.addTreeSelectionListener(new CallMaker(treeInfo, rightPane));
   treeInfo = (TreeData)theCurrentTreeSelection;
}as long as treeInfo contains the data you need to populate the right pane, you'll be fine.
When a selection is made the CallMaker instance calls: rightPane.operator(treeInfo);
This provides your rightPane instance with the information it needs to populate the rightPane.