Swing/TitledSeparator のバックアップ(No.4)

private static JComponent makeTitledSeparator(
    final String title, final Color target,
    final int height, final int titlePosition) {
  return new JLabel() {
    @Override public Dimension getMaximumSize() {
      Dimension d = super.getPreferredSize();
      d.width = Short.MAX_VALUE;
      return d;
    }
    private Color color;
    @Override public void updateUI() {
      super.updateUI();
      color = null;
      setBorder(BorderFactory.createTitledBorder(
          BorderFactory.createMatteBorder(height, 0, 0, 0, new Icon() {
        private int width = -1;
        private Paint painter1, painter2;
        @Override public void paintIcon(Component c, Graphics g, int x, int y) {
          int w = c.getWidth();
          if(w!=width || painter1==null || painter2==null || color==null) {
            width = w;
            Point2D start = new Point2D.Float(0f, 0f);
            Point2D end   = new Point2D.Float((float)width, 0f);
            float[] dist  = {0.0f, 1.0f};
            color = getBackground();
            color = color==null ? UIManager.getColor("Panel.background") : color;
            Color tc = target==null ? color : target;
            painter1 = new LinearGradientPaint(start, end, dist, new Color[] {tc.darker(),   color});
            painter2 = new LinearGradientPaint(start, end, dist, new Color[] {tc.brighter(), color});
          }
          int h = getIconHeight()/2;
          Graphics2D g2  = (Graphics2D)g.create();
          g2.setPaint(painter1);
          g2.fillRect(x, y,   width, getIconHeight());
          g2.setPaint(painter2);
          g2.fillRect(x, y+h, width, getIconHeight()-h);
          g2.dispose();
        }
        @Override public int getIconWidth()  { return 200; } //dummy width
        @Override public int getIconHeight() { return height; }
      }), title, TitledBorder.DEFAULT_JUSTIFICATION, titlePosition));
      //System.out.println(getInsets());
    }
  };
}