question: public StateSet complement ( StateSet set ) { if ( set == null ) return null ; StateSet result = new StateSet ( ) ; result . bits = new long [ set . bits . length ] ; int i ; int m = Math . min ( bits . length , set . bits . length ) ; for ( i = 0 ; i < m ; i ++ ) { result . bits [ i ] = ~ bits [ i ] & set . bits [ i ] ; } if ( bits . length < set . bits . length ) System . arraycopy ( set . bits , m , result . bits , m , result . bits . length - m ) ; if ( DEBUG ) Out . dump ( "Complement of " + this + Out . NL + "and " + set + Out . NL + " is :" + result ) ; return result ; }
target:  Returns the set of elements that contained are in the specified set but are not contained in this set.