question: public final Frequency frequency ( ) { final int length = Math . abs ( this . length ) ; if ( length == 0 ) return Frequency . NoFrequency ; switch ( units ) { case Years : if ( length == 1 ) return Frequency . Annual ; else return Frequency . OtherFrequency ; case Months : if ( 12 % length == 0 && length <= 12 ) return Frequency . valueOf ( 12 / length ) ; else return Frequency . OtherFrequency ; case Weeks : if ( length == 1 ) return Frequency . Weekly ; else if ( length == 2 ) return Frequency . Biweekly ; else if ( length == 4 ) return Frequency . EveryFourthWeek ; else return Frequency . OtherFrequency ; case Days : if ( length == 1 ) return Frequency . Daily ; else return Frequency . OtherFrequency ; default : throw new LibraryException ( UNKNOWN_TIME_UNIT ) ; } }
target:  To get at Frequency represented by the period