Composite design process - help!

Question

Can anybody offer some guidance (any guidance). I have created several classes that I need to have communicate with each other. Therefore I created one called sessionData to kind of keep track of which class is doing what but it is not working. I get errors all over the place. Currently I have a JDesktopPane which has internal frames. Some of these internalframes call and make more internal frames. (as it is right now, they are created inside the new Internalframe) I need them to be created in the JDesktopPane instead. That is why I have the sessionData class. Any ideas? or point me to some code that already works. Or just answer, how do I instantiate ea. session in ea class?

Answer 1

I don't know if you want to use a session object. Session objects are an example of the Visitor pattern and have there advantages and disadvantages. Most of Swing uses an event notification process which is an example of the Observer pattern. You may want to read the sections in the design patterns book (Erich Gamma, et al) before deciding which will better serve your application. Most Swing apps I have worked on have used events.
You mentioned that you wanted your sessionData object to keep track of which class was doing what. That is kind of web programmers trick brought about because you have to keep track of what is happening on the client so you can respond appropriately. In Swing (or any other fat client), you can just wait for an event to happen and then deal with it appropriately. Much cleaner and elegant. Events are more object-oriented also because each class is more self contained. Your class doesn't care what someone else is doing, it only cares when someone sends an event to it.
As for your problem with JDesktopPane:
I don't understand what you are getting at. You have a JDesktopPane and you add a JInternalFrame to it, correct? Then something happens and you need to create a new JInternalFrame. You should add the second internal frame to the desktop pane not the first internal frame.
Here is a little example of what I am talking about. Say you have a little app that is opening files up and displaying them in a JInternalFrame. You might create an interface called FileListener that looks like this:
public interface FileListener {
  public void openFile(FileEvent fileEvent);
}The class which holds your JDesktopPane would then implement that interface and would create a new internal frame and add it to the desktop pane everytime the openFile method was called.
The FileEvent code would look like this:
public class FileEvent extends EventObject {
  private File file;
  public FileEvent(Object source, File file) {
    super(source);
    this.file = file;
  public File getFile() {
    return file;
}Then there are the classes that actually generate the FileEvent. For instance OpenAction might popup a JFileChooser and then fire an event so that a FileListener can open the File. Here are a couple of methods that might be in your OpenAction:
private List listeners = new LinkedList();
public void addFileListener(FileListener listener) {
  listeners.add(listener);
public void removeFileListener(FileListener listener) {
  listeners.remove(listener);
private void fireFileEvent(File file) {
  FileEvent event = new FileEvent(this, file);
  Iterator iterator = listeners.iterator();
  while (iterator.hasNext()) {
    ((FileListener)iterator.next()).openFile(event);
}When the JFileChooser returns with the selected file you can simply call fireFileEvent() and pass in the File as an argument. This will broadcast the event to everyone listening.
Lastly you register the class that is holding your JDesktopPane as a listener to OpenAction by calling the registerFileListener() method and you should see a new JInternal frame popup with the contents of the file that your JFileChooser selects.
Hope that helps,
-Phil