import java.awt.*;
import javax.swing.*;

public class Denko extends JPanel implements Runnable {
  private JLabel label;
  private volatile Thread thread = null;
  private String msg = "0123456789ABCDEF ";

  public Denko() {
    label = new JLabel(msg);
    add(label);
    JButton startBtn = new JButton("start");
    startBtn.addActionListener(e -> startThread());
    JButton stopBtn = new JButton("stop");
    stopBtn.addActionListener(e -> stopThread());
    setLayout(new FlowLayout());
    add(startBtn); add(stopBtn);
    startThread();
  }

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

  private void stopThread() {
    thread = null;
  }
  
  public void run() {
    Thread thisThread = Thread.currentThread();
    for (int i = 0; thread == thisThread; i = (i + 1) % msg.length()) {
      String str = msg.substring(i) + msg.substring(0, i);
      SwingUtilities.invokeLater(() -> label.setText(str));
      try {
        Thread.sleep(100); // 100 ミリ秒お休み
      } catch (InterruptedException e) {}
    }
  }

  public static void main(String[] args) {
    SwingUtilities.invokeLater(() -> {
      JFrame frame = new JFrame("電光掲示板");
      frame.add(new Denko());
      frame.pack();
      frame.setVisible(true);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    });
  }
}