import java.awt.Font;
import java.util.Date;

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Digitaluhr extends JPanel implements Runnable {

private static final long serialVersionUID = 1L;

private JLabel label;

private Date date;

private Font font = new Font("Verdana", Font.PLAIN, 20);

private Thread thread;

public Digitaluhr() {
    label = new JLabel();
    label.setFont(font);
    this.add(label);
    start();
}

private void gibDate() {
    label.setText(date.toString());
}

public void start() {
    if (thread == null) {
        thread = new Thread(this);
        thread.start();
    }
}

public void run() {

    while (true) {
        date = new Date();
        gibDate();
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
                e.printStackTrace();
        }
    }
}

public static void main(String[] args) {
    Digitaluhr c = new Digitaluhr();
    JFrame f = new JFrame();
    f.add(c);
    f.setSize(350, 60);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.setVisible(true);
}
}