question: public static boolean isHex ( String str ) { if ( str == null || str . length ( ) == 0 ) return false ; for ( int i = str . length ( ) - 1 ; i >= 0 ; i -- ) { char c = str . charAt ( i ) ; if ( ! ( c >= '0' && c <= '9' ) ) { c = Character . toLowerCase ( c ) ; if ( ! ( c == 'a' || c == 'b' || c == 'c' || c == 'd' || c == 'e' || c == 'f' ) ) return false ; } } return true ; }
target:  tests if String value is Hex Value