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

ImageIcon icon = new ImageIcon(getClass().getResource("test.png"));

Component beforeCanvas = new JComponent() {
  @Override protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    int iw = icon.getIconWidth();
    int ih = icon.getIconHeight();
    g.drawImage(icon.getImage(), 0, 0, iw, ih, this);
  }
};
split.setLeftComponent(beforeCanvas);

Component afterCanvas = new JComponent() {
  @Override protected void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2 = (Graphics2D) g.create();
    int iw = icon.getIconWidth();
    int ih = icon.getIconHeight();
    if (check.isSelected()) {
      g2.setColor(getBackground());
      g2.setXORMode(Color.BLUE);
    } else {
      g2.setPaintMode();
    }
    Point pt = getLocation();
    Insets ins = split.getBorder().getBorderInsets(split);
    g2.translate(-pt.x + ins.left, 0);
    g2.drawImage(icon.getImage(), 0, 0, iw, ih, this);
    g2.dispose();
  }
};
split.setRightComponent(afterCanvas);