e se você usar o getSelectedIndex() ?
vai retornar o valor em inteiro do item selecionando começando a contar de zero, e retorna -1 se não houver item selecionado... =]
getSelectedIndex
public int getSelectedIndex()
Returns the first item in the list that matches the given item. The result is not always defined if the JComboBox allows selected items that are not in the list. Returns -1 if there is no selected item or if the user specified an item which is not in the list.
Returns:
an integer specifying the currently selected list item, where 0 specifies the first item in the list; or -1 if no item is selected or if the currently selected item is not in the list