if(dataModel instanceof MutableComboBoxModel) {
if (dataModel instanceof MutableComboBoxModel)
  public void addItem(Object element)  {  	if(dataModel instanceof MutableComboBoxModel) {    ((MutableComboBoxModel) dataModel).addElement(element);  	} else {  		throw new RuntimeException("Unable to add the item because the data model it is not an instance of MutableComboBoxModel.");  	}  }