怎么会有这种问题呀

Question

上面的代码相当于
class RButton extends JRadioButton
{ 
 protected void fireActionPerformed(ActionEvent event)
            {
               try
               {
                  textField.setText("No exception");
                  super.fireActionPerformed(event);
               }
               catch (Exception exception)
               {
                  textField.setText(exception.toString());
               }
            }
}
private void addRadioButton(String s, ActionListener listener)
   {  
      RButton button = new RButton(s, false);
       button.addActionListener(listener);
      add(button);
      group.add(button);
   }
其实就是继承