private static void addChangeEntry(InOut in, AddressBook book)
   {
      String name = in.nextLine("Enter name: ");
      String key = in.nextLine("Enter key: ");
      String value = in.nextLine("Enter value: ");
      String oldValue = book.put(name, key, value);
      if (oldValue == null)
         in.message("Entry added");
      else
         in.message("Entry updated");
   }