question: @ Parallel @ Realtime ( limit = LINEAR ) public E reduce ( BinaryOperator < E > operator ) { Iterator < E > itr = iterator ( ) ; if ( ! itr . hasNext ( ) ) return null ; E accumulator = itr . next ( ) ; while ( itr . hasNext ( ) ) accumulator = operator . apply ( accumulator , itr . next ( ) ) ; return accumulator ; }
target:  Performs a reduction by applying the specified operator over the elements of this collection.