@Override
    public void actionPerformed(ActionEvent ae)
    {
        // WHICH BUTTON WAS PRESSED?
        String command = ae.getActionCommand();
        
        // CHANGE THE BACKGROUND IMAGE?
        if (command.equals(BG_IMAGE_COMMAND))
        {
            // UPDATE THE BACKGROUND IMAGE IF THE USER
            // DOESN'T BACK OUT
            String bgImage = selectImage();
            if (bgImage != null)
            {
                // GO AHEAD AND CHANGE IT
                 model.updateBackgroundImage(bgImage);
            }
        }
        // CHANGE THE START NODE IMAGE?
        else if (command.equals(START_IMAGE_COMMAND))
        {
            // UPDATE THE START IMAGE IF THE USER 
            // DOESN'T BACK OUT
            String startImage = selectImage();
            if (startImage != null)
            {
                // GO AHEAD AND CHANGE IT
                model.updateStartingLocationImage(startImage);
            }
        }
        // CHANGE THE DESTINATION NODE IMAGE?
        else if (command.equals(DEST_IMAGE_COMMAND))
        {
            // UPDATE THE DEST IMAGE IF THE USER
            // DOESN'T BACK OUT
            String destImage = selectImage();
            if (destImage != null)
            {
                // GO AHEAD AND CHANGE IT
                model.updateDestinationImage(destImage);
            }
        }
    }