need advice using swing jfilechooser

hi
I created a gui app in which I have two jfilechooser widgets ,one to
select a file and other to select a different directory.I want the
selected filename and selected directory name to be displayed in a
textarea.If no selection is made ,i want to display an error message
instead.
I coded like this

class MyView extends JFrame {
    private JFileChooser filechooser;
    private JFileChooser dirchooser;
    private JTextArea resultfield;
   ...//and many jpanels to contain these widgets above
     //and ok,quit buttons
   public MyView(MyModel model){
    super("top frame");
    model=model;
        createAndAddAllWidgets();
       }
   public void createAndAddAllWidgets(){
   ...
   filechooser=new JFileChooser("Select imagefile");
   ...
   dirchooser=new JFileChooser();
   dirchooser.setFileSelectionMode(JFileChooser.DIRECTORIES_ONLY);
   ...
   //similarly adds textarea and needed ok, quit buttons
   }
   public String getSelectedFile(){
   //?
   }
   public String getSelectedFolder(){
   //?
   }
  public void displayMessage(String msg){
    resultfield.setText(msg);
   }
   public void addOKButtonListener(ActionListener okl){
    okbtn.addActionListener(okl);
   }
   public void addQuitButtonListener(ActionListener qbl){
    quitbtn.addActionListener(qbl);
   }

}//end of MyView class

class MyController{
    private MyModel model;
    private MyView view;
    public MyController(MyModel m,MyView v ){
        model=m;
        view=v;
        view.addOKButtonListener(new OKButtonListener());
        view.addQuitButtonListener(new QuitButtonListener());
    }
        class OKButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
         String fileselection=view.getSelectedFile();
         String folderselection=view.getSelectedFolder();

         String result=model.processSelections(fileselection,
folderselection);
         view.displayResult(result);
        }
    }//end inner class
    class QuitButtonListener implements ActionListener {
        public void actionPerformed(ActionEvent e) {
         view.dispose();
        }
    }//end inner class
}//end of MyController class

class MyModel{
    public String processSelections(String filename,String foldername){
        String result="you selected file:"+filename+" you selected
folder:"+foldername;
        return result;
    }
}//end of MyModel class

What I couldn't figure out was how to code the logic in MyView's
getSelectedFile(),getSelectedFolder() methods..
I can get the selected file name string as ,

filechooser.getSelectedFile().getPath() and
the selected folder name as
dirchooser.getSelectedFile().getPath()

But,how should I deal with the situation when no file is selected or
no folder is selected?Should I return an empty string from the method ?
How can I display an error message if both happen at the same time?
I need to display the result from MyModel's processSelections() if
selections are made.I am not sure how I should do this.Should I define
a new Exception for these empty selection cases? or should I create
StringBuffer and append messages into it, and use it when I call
MyView's displayMessage() ?
If anyone can help me here ,it would be nice.
thanks,
jim