Swing/TranslucentScrollBar のバックアップ(No.1)

public JComponent makeTranslucentScrollBar(JScrollPane scrollPane) {
  scrollPane.setComponentZOrder(scrollPane.getVerticalScrollBar(), 0);
  scrollPane.setComponentZOrder(scrollPane.getViewport(), 1);
  scrollPane.getVerticalScrollBar().setOpaque(false);

  scrollPane.setLayout(new ScrollPaneLayout() {
    @Override public void layoutContainer(Container parent) {
      JScrollPane scrollPane = (JScrollPane)parent;

      Rectangle availR = scrollPane.getBounds();
      availR.x = availR.y = 0;

      Insets insets = parent.getInsets();
      availR.x = insets.left;
      availR.y = insets.top;
      availR.width  -= insets.left + insets.right;
      availR.height -= insets.top  + insets.bottom;

      Rectangle vsbR = new Rectangle();
      vsbR.width  = 12;
      vsbR.height = availR.height;
      vsbR.x = availR.x + availR.width - vsbR.width;
      vsbR.y = availR.y;

      if(viewport != null) {
        viewport.setBounds(availR);
      }
      if(vsb != null) {
        vsb.setVisible(true);
        vsb.setBounds(vsbR);
      }
    }
  });
  scrollPane.getVerticalScrollBar().setUI(new BasicScrollBarUI() {
    private final Dimension d = new Dimension();
    @Override protected JButton createDecreaseButton(int orientation) {
      return new JButton() {
        @Override public Dimension getPreferredSize() {
          return d;
        }
      };
    }
    @Override protected JButton createIncreaseButton(int orientation) {
      return new JButton() {
        @Override public Dimension getPreferredSize() {
          return d;
        }
      };
    }
    @Override protected void paintTrack(Graphics g, JComponent c, Rectangle r) {}
    private final Color defaultColor  = new Color(220,100,100,100);
    private final Color draggingColor = new Color(200,100,100,100);
    private final Color rolloverColor = new Color(255,120,100,100);
    @Override protected void paintThumb(Graphics g, JComponent c, Rectangle r) {
      Graphics2D g2 = (Graphics2D)g.create();
      g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                          RenderingHints.VALUE_ANTIALIAS_ON);
      Color color = null;
      JScrollBar sb = (JScrollBar)c;
      if(!sb.isEnabled() || r.width>r.height) {
        return;
      }else if(isDragging) {
        color = draggingColor;
      }else if(isThumbRollover()) {
        color = rolloverColor;
      }else{
        color = defaultColor;
      }
      g2.setPaint(color);
      g2.fillRect(r.x,r.y,r.width-1,r.height-1);
      g2.setPaint(Color.WHITE);
      g2.drawRect(r.x,r.y,r.width-1,r.height-1);
      g2.dispose();
    }
    @Override protected void setThumbBounds(int x, int y, int width, int height) {
      super.setThumbBounds(x, y, width, height);
      //scrollbar.repaint(x, 0, width, scrollbar.getHeight());
      scrollbar.repaint();
    }
  });
  return scrollPane;
}