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

// InternalFrame.titleFont
// InternalFrame.titleButtonHeight
// InternalFrame.titleButtonWidth
// InternalFrame.titlePaneHeight
String key = "InternalFrame.titlePaneHeight";
int height = UIManager.getLookAndFeelDefaults().getInt(key);
SpinnerNumberModel model = new SpinnerNumberModel(height, 0, 50, 1);
model.addChangeListener(e -> {
  int v = model.getNumber().intValue();
  UIManager.put(key, v);
  // UIManager.put("InternalFrame.titleButtonWidth", v);
  // UIManager.put("InternalFrame.titleButtonHeight", v);
  SwingUtilities.updateComponentTreeUI(desktop);
});
JSpinner spinner = new JSpinner(model) {
  @Override public void updateUI() {
    super.updateUI();
    int h = UIManager.getLookAndFeelDefaults().getInt(key);
    UIManager.put(key, h);
    model.setValue(h);
    SwingUtilities.updateComponentTreeUI(desktop);
  }
};