Swing/MouseOverPainter のバックアップ(No.4)

class HighlightCursorTextArea extends JTextArea {
  public HighlightCursorTextArea() {
    super();
    setOpaque(false);
    RollOverListener rol = new RollOverListener();
    addMouseMotionListener(rol);
    addMouseListener(rol);
  }
  private final Color linecolor = new Color(250,250,220);
  @Override protected void paintComponent(Graphics g) {
    Graphics2D g2 = (Graphics2D)g;
    Insets i = getInsets();
    int h = g2.getFontMetrics().getHeight();
    int y = rollOverRowIndex*h+i.top;
    g2.setPaint(linecolor);
    g2.fillRect(i.left, y, getSize().width-i.left-i.right, h);
    super.paintComponent(g);
  }
  private int rollOverRowIndex = -1;
  private class RollOverListener extends MouseInputAdapter {
    @Override public void mouseExited(MouseEvent e) {
      rollOverRowIndex = -1;
      repaint();
    }
    @Override public void mouseMoved(MouseEvent e) {
      int row = getLineAtPoint(e.getPoint());
      if(row != rollOverRowIndex) {
        rollOverRowIndex = row;
        repaint();
      }
    }
    @Override public int getLineAtPoint(Point pt) {
      Element root = getDocument().getDefaultRootElement();
      return root.getElementIndex(viewToModel(pt));
    }
  }
}