Fontサイズをコンポーネントの幅に応じて変更する

private final Font font = new Font(Font.MONOSPACED, Font.PLAIN, 12);
private final JTextPane editor = new JTextPane() {
  private float font_size = 0f;
  @Override public void doLayout() {
    Insets i = getInsets();
    float f = .08f * (getWidth() - i.left - i.right);
    if (Math.abs(font_size - f) > 1.0e-1) {
      setFont(font.deriveFont(f));
      font_size = f;
    }
    super.doLayout();
  }
};