Retrieving the Selected Button in a Group 
When you ask a button group for the currently selected button, it returns the selected button's model (rather than the selected button itself). Fortunately, the button group maintains the list of buttons and so you can iterate over this list looking for one with the same model. 

 
 static AbstractButton getSelection(ButtonGroup group) {
     // The next two lines should be in one line.
     for (Enumeration e=group.getElements();
        e.hasMoreElements(); ) {
         // The next two lines should be in one line.
         AbstractButton b = 
           (AbstractButton)e.nextElement();
         if (b.getModel() == group.getSelection()) {
             return b;
         }
     }
     return null;
 }