import java.awt.*;
import java.awt.event.*;
import java.time.LocalTime;

import javax.swing.*;


class Klokke {

    private static JLabel klokkeslett = new JLabel(naa());


    private static String naa(){
        //Henter den lokale tiden naa paa format "12:34:56"
        LocalTime t = LocalTime.now();
        return String.format("%02d:%02d:%02d", 
            t.getHour(), t.getMinute(), t.getSecond());
    }

    public static void main(String[] args) {
        JFrame vindu = new JFrame("Klokke");
        vindu.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JPanel panel = new JPanel();
        vindu.add(panel);

        klokkeslett.setFont(new Font("sans serif", Font.PLAIN, 100));
        panel.add(klokkeslett);

        vindu.pack();
        vindu.setVisible(true);

        class SekundTeller implements Runnable {
            public void run(){
                boolean fortsett = true;
                while(fortsett){ // kjorer hele tiden
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                        fortsett = false;
                    }
                    klokkeslett.setText(naa()); // nytt kall på naa
                }
            }
        }

        new Thread(new SekundTeller()).start();
    }
}