OS時間の変更でJavaアプリが止まる

public class clsThread  implements Runnable{
  private Thread thr;
  private boolean flgThread = false;
  void threadOnOff(boolean sw) {
    if(sw){
      if(thr == null) {
        thr = new Thread(this);
        flgThread = true;
        thr.start();
      }
    } else {
      flgThread = false;
      thr = null;
    }
  }

  public void run(){
    while (flgThread) {
      try{
        thr.sleep(1000);
      }catch(Exception ex){}            
      System.out.println("Now Time = " + String.valueOf(System.currentTimeMillis()));
    }
  }
}

public class Frame1 extends Frame {
  //フレームのビルド
  public Frame1() {
    enableEvents(AWTEvent.WINDOW_EVENT_MASK);
    try {
      jbInit();
    }
    catch(Exception e) {
      e.printStackTrace();
    }
  }
  //コンポーネントの初期化
  private void jbInit() throws Exception  {
    this.setSize(new Dimension(236, 283));
    this.setTitle("TEST");
    this.addMouseListener(new Frame1_this_mouseAdapter(this));
    this.setLayout(null);
    this.setResizable(false);
    this.setVisible(false);
  }
  //ウィンドウが閉じられたときに終了するようにオーバーライド
  protected void processWindowEvent(WindowEvent e) {
    super.processWindowEvent(e);
    if (e.getID() == WindowEvent.WINDOW_CLOSING) {
      System.exit(0);
    }
  }
  void this_mouseClicked(MouseEvent e) {
    System.out.println("click");
  }
}

class Frame1_this_mouseAdapter extends java.awt.event.MouseAdapter {
  Frame1 adaptee;
  Frame1_this_mouseAdapter(Frame1 adaptee) {
    this.adaptee = adaptee;
  }
  public void mouseClicked(MouseEvent e) {
    adaptee.this_mouseClicked(e);
  }
}

  void this_mouseClicked(MouseEvent e) {
    System.out.println("click");
    Thread th = Thread.currentThread();
    th.dumpStack();
  }