Java Applet flackert

public class Example extends Applet {

	public void init() {
		// Hintergrundfarbe einstellen
		setBackground(Color.WHITE);

		// Panel, welches die Uhr zeichnet, erzeugen und einfügen
		final ClockPanel cPanel = new ClockPanel();
		add(cPanel);
		
		// Applet auf die korrekte Größe skalieren
		setSize(cPanel.getPreferredSize());

		// Neuen Thread starten, der jede Sekunde versucht neu zu zeichnen
		new Thread() {

			public void run() {
				while (true) {
					try {
						sleep(1000);
					} catch (InterruptedException e) {}

					cPanel.repaint();
				}
			};
		}.start();
	}
}

public class ClockPanel extends JPanel {

	// ===================================================================
	// {[> Attributes
	// ==============
	private GregorianCalendar calendar = new GregorianCalendar();
	private BufferedImage offscreenImage;



	// ===================================================================
	// {[> Initializers and Constructors
	// =================================
	public ClockPanel() {
		setPreferredSize(new Dimension(400, 400));
	}



	// ===================================================================
	// {[> Private Methods
	// ===================
	private void paintClockBorder(Graphics2D g, int center, int radius) {
		g.setColor(Color.BLACK);

		int x1, y1, x2, y2;

		for (int i = 0; i < 12; i++) {
			x1 = center + (int) ((radius - 15) * Math.cos(Math.toRadians(30 * i)));
			y1 = center + (int) ((radius - 15) * Math.sin(Math.toRadians(30 * i)));
			x2 = center + (int) (radius * Math.cos(Math.toRadians(30 * i)));
			y2 = center + (int) (radius * Math.sin(Math.toRadians(30 * i)));
			g.drawLine(x1, y1, x2, y2);
		}

		for (int i = 0; i < 60; i++) {
			x1 = center + (int) ((radius - 2) * Math.cos(Math.toRadians(6 * i)));
			y1 = center + (int) ((radius - 2) * Math.sin(Math.toRadians(6 * i)));
			x2 = center + (int) (radius * Math.cos(Math.toRadians(6 * i)));
			y2 = center + (int) (radius * Math.sin(Math.toRadians(6 * i)));
			g.drawLine(x1, y1, x2, y2);
		}
	}

	private void paintClockCenterDot(Graphics2D g, int center, int size) {
		g.setColor(Color.BLACK);
		g.fillArc(center - size / 2, center - size / 2, size, size, 0, 360);
	}

	private void paintClockDate(Graphics2D g, int center, int xOffset, int yOffset, String text) {
		int textWidth = g.getFontMetrics(g.getFont()).stringWidth(text);
		int textHeight = (int) g.getFont().getLineMetrics(text, g.getFontRenderContext()).getHeight();

		g.drawString(text, xOffset + center - textWidth / 2, yOffset + center + textHeight / 2);
	}

	private void paintClockHands(Graphics2D g, int center, int radius, int hours, int minutes, int seconds) {
		int x, y;

		g.setColor(Color.BLACK);
		x = center + (int) (radius * 0.5 * Math.cos(Math.toRadians(hours % 12 * 30 + minutes / 2.0 - 90)));
		y = center + (int) (radius * 0.5 * Math.sin(Math.toRadians(hours % 12 * 30 + minutes / 2.0 - 90)));
		g.drawLine(center, center, x, y);

		x = center + (int) (radius * 0.65 * Math.cos(Math.toRadians(minutes * 6 - 90)));
		y = center + (int) (radius * 0.65 * Math.sin(Math.toRadians(minutes * 6 - 90)));
		g.drawLine(center, center, x, y);

		g.setColor(Color.RED);
		x = center + (int) (radius * 0.8 * Math.cos(Math.toRadians(seconds * 6 - 90)));
		y = center + (int) (radius * 0.8 * Math.sin(Math.toRadians(seconds * 6 - 90)));
		g.drawLine(center, center, x, y);
	}

	private void paintClockTimeDigital(Graphics2D g, int center, int xOffset, int yOffset, String text) {
		int textWidth = g.getFontMetrics(g.getFont()).stringWidth(text);
		int textHeight = (int) g.getFont().getLineMetrics(text, g.getFontRenderContext()).getHeight();

		g.drawString(text, xOffset + center - textWidth / 2, yOffset + center + textHeight / 2);
	}



	// ===================================================================
	// {[> Public Methods
	// ==================
	public void paint(Graphics g) {
		// Sicherstellen, dass das Offscreen-Image existiert und die korrekte Größe hat!
		final int width = getWidth(), height = getHeight();
		if (offscreenImage == null || offscreenImage.getWidth() != width || offscreenImage.getHeight() != height) {
			offscreenImage = new BufferedImage(width, height, BufferedImage.TYPE_INT_ARGB);
		}
		Graphics2D g2d = offscreenImage.createGraphics();

		// Erstmal alles löschen (mit der Hintergrundfarbe des beinhaltenden Containers überschreiben)
		g2d.setColor(getParent().getBackground());
		g2d.fillRect(0, 0, width, height);

		// Antialiasing aktivieren
		g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

		// Paar Variablen initialisieren und Uhrzeit bestimmen
		final int center = width / 2;
		final int radius = center - 15;

		calendar.setTimeInMillis(System.currentTimeMillis());
		final int hours = calendar.get(Calendar.HOUR_OF_DAY);
		final int minutes = calendar.get(Calendar.MINUTE);
		final int seconds = calendar.get(Calendar.SECOND);

		final int year = calendar.get(Calendar.YEAR);
		final int month = calendar.get(Calendar.MONTH) + 1;
		final int day = calendar.get(Calendar.DAY_OF_MONTH);

		// Die einzelnen Elemente der Uhr zeichnen
		paintClockBorder(g2d, center, radius);
		paintClockCenterDot(g2d, center, 6);
		paintClockHands(g2d, center, radius, hours, minutes, seconds);
		g2d.setColor(Color.BLUE);
		g2d.setFont(g.getFont().deriveFont(24f));
		paintClockDate(g2d, center, 0, -100, String.format("%02d.%02d.%04d", day, month, year));
		paintClockTimeDigital(g2d, center, 0, 100, String.format("%02d:%02d:%02d", hours, minutes, seconds));

		// Aufräumen
		g2d.dispose();

		// Den Inhalt des OffscreenImage in einem Rutsch zeichnen lassen
		g.drawImage(offscreenImage, 0, 0, null);
	}
}