Help on SwingUtilities

Hi All,
I'm a newbie in java programming
I've a problem:
I'm using Java(TM) 2 SDK, Standard Edition Version 1.4.2 because the
libraries comm.jar works good (in the latest version is non true).
In this version SwingWorker does not work very well.
I'm creating a Swing Interface that have to refresh every time that a
file was modified, I know that i've to use SwingUtilities.invokeLater()
but i dont know how and where i've to put it

This is a part of the code:

Principal (Main Class)
Class1 (Graphic Interface)
Class2 (Check if a File was modified)
Class3 (Find a String in that File)

//***PSEUDO CODE ***
public class Principal {
  public static void main(String[] args) {

    final Class1 mov = new Class1();
    final Class2 FWT = new Class2();
    SwingUtilities.invokeLater(new Runnable() {
      public void run() {
        mov.jTextField1.setText(FWT.misura_letta);
      }
    });
  }
}

public class Class1 extends JPanel {

    JTextField jTextField1;
    Class1(){
        jTextField1 = new javax.swing.JTextField();
        JPanel Panel2 = new JPanel();
        Panel2.add(jTextField1);
        JFrame f = new JFrame("Graphics");
        f.getContentPane().add(Panel2);
        f.pack();
        f.setVisible(true);
    }
}

class Class2 implements Runnable {
   Thread readThread;
   public String misura_letta ="";

   public Class2(){

    readThread = new Thread(this);
    readThread.start();

   }
 public void run() {
  try {
    Thread.sleep(20000);
    TimerTask task = new FileWatcher( new
File("DaSerialeAll_prova.txt") ) {
      protected void onChange( File file ) {
        System.out.println( "File "+ file.getName() +" have change !"
);
        Class3 CTDF = new Class3();
        misura_letta = CTDF.str;
    System.out.println("misura letta: " +misura_letta);
      }
    };

    java.util.Timer timer = new java.util.Timer();
    timer.schedule( task , new Date(), 10 );

  } catch (InterruptedException e) {}
 }
}

public class Class3 {
  String str ="";
  public Class3 () {
  // (...) Read the File and find a string that i want to put in the
graphical interface
  str = str.trim();

  }
}
//*** end PSEUDO CODE ***

Thanks to all
Sal