sclass DefaultButtonBorder extends JPanel {
  JButton button;
  
  *(JButton *button) {
    super(new BorderLayout);
    setBorder(makeBorder());
    add(button);
    onEnabledChanged(button, -> setBorder(makeBorder()));
  }
  
  Border makeBorder() {
    ret BorderFactory.createLineBorder(main isEnabled(button) ? Color.black : Color.lightGray);
  }
}