public RadioBoxList<V> addListener(Listener listener) {
        if(listener != null && !listeners.contains(listener)) {
            listeners.add(listener);
        }
        return this;
    }
public RadioBoxList < V > addListener ( Listener listener ) { if ( listener != null && ! listeners . contains ( listener ) ) { listeners . add ( listener ) ; } return this ; }
Adds a new listener to the {@code RadioBoxList} that will be called on certain user actions
@param listener Listener to attach to this {@code RadioBoxList}
@return Itself