Hi,

I'm working on a program for a class assignment and ran into a problem.  The program is essentially finished, I just need to add one additional feature to it.  The program is split up into two classes: one that handles creating the GUI (MortgageDisplay) and the other that performs calculations and manipulates the GUI (MortgageCalc).  What I want to do is add a listener that will tell me when text has been entered into a JTextField.

The program is a simple mortgage calculator.  I have two ways for the user to enter information.  They can either choose between three pre-selected mortgage terms from a JComboBox or type in the terms (rate and number of years) for the mortgage.  What I want to accomplish is to deactivate the combo box when text is entered into either of the term text fields (txtRate and txtYears).

The Java documentation says this about adding a text listener for a JTextCompent:

DocumentListener myListener = ??;
JTextField myArea = ??;
myArea.getDocument().addDocumentListener(myListener);

This doesn't make any sense because DocumentListener is an Interface and cannot be instantiated.  The compiler gives an error if you try.  Even if it did work, I do not think it would work correctly.  Because the program is separated into two classes, all of the other action listeners are setup like this:

calculate.addActionListener (calculations);  //'calculations' is an object of type MortgageCalc that links the listeners defined in MortgageDisplay class. 'calculate' is a JButton.

The above code for the DocumentListener might work for a single class, but probably not across two classes.  I've tried several variations with no success.

I did try an ActionListener, but that didn't work either.  This is what I did:

//In the MortgageDisplay class

txtRate.addActionListener (calculations);
txtYears.addActionListener (calculations);

//In the MortgageCalc class

public void actionPerformed (ActionEvent e) {

   if (e.getSource ( ) == txtRate) {
       userInterface.comboSelectTerms.setEnabled (false); //'userInterface' is an object of type MortgageDisplay
    }

   if (e.getSource ( ) == txtYears) {
       userInterface.comboSelectTerms.setEnabled (false);
   }
}

I figured that the keypress events would be caught when the user typed into the textboxes, but I was wrong.  The only listener defined in JTextField is ActionLister (i.e. addActionListener).  The other listeners (such as key listeners) are defined in the awt.  AFAIK, you can't implement an awt event listener on a JComponent.  Any recommendations or links to additional info?