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);
		});
	}
}