question: private static int charToNibble ( char c ) { if ( c > 'f' ) { throw new IllegalArgumentException ( "Invalid hex character: " + c ) ; } int nibble = hexCodes [ c ] ; if ( nibble < 0 ) { throw new IllegalArgumentException ( "Invalid hex character: " + c ) ; } return nibble ; }
target:  Convert a single hex character to its corresponding hex value using pre-calculated translation table.