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

class FocusOwnerCaret extends DefaultCaret {
  private static final Color COLOR = Color.GRAY.brighter();
  private static final HighlightPainter NO_FOCUS_PAINTER = new DefaultHighlightPainter(COLOR);

  @Override public void focusLost(FocusEvent e) {
    super.focusLost(e);
    updateSelectionHighlightPainter();
  }

  @Override public void focusGained(FocusEvent e) {
    super.focusGained(e);
    updateSelectionHighlightPainter();
  }

  private void updateSelectionHighlightPainter() {
    setSelectionVisible(false); // removeHighlight
    setSelectionVisible(true); // addHighlight
  }

  @Override protected Highlighter.HighlightPainter getSelectionPainter() {
    JTextComponent c = getComponent();
    Container w = c.getTopLevelAncestor();
    // boolean isFocused = w instanceof Window && ((Window) w).isFocused();
    boolean isActive = w instanceof Window && ((Window) w).isActive();
    return c.hasFocus() && isActive ? super.getSelectionPainter() : NO_FOCUS_PAINTER;
    // https://ateraimemo.com/Swing/CaretSelectionHighlight.html
    // return c.hasFocus() ? super.getSelectionPainter() : NO_FOCUS_PAINTER;
  }
}