If you use a Formatter object to write the values, you can change the numbers to characters using a %c tag in the format() method. I think it only works in a text file; Formatter is the opposite of Scanner, so it is a basic and simple text writing device. But it works and is easy to use.
BTW. You don't have hex values. You have a number 00....00 0100 0001, for example, which might represent 41 in hex, or 65 in decimal, or 101 in octal, or 'A' as a char. Or even 00....00 0100 0001 in any of the Java integer number primitive formats. You char type is only a number which is displayed as a character. So you can display the same number in all sorts of different format.