question: public static String join ( String separator , List < ? > elements ) { if ( elements == null || elements . size ( ) == 0 ) { return "" ; } StringBuilder sb = new StringBuilder ( elements . size ( ) * 3 ) ; int i = 0 ; for ( Object elem : elements ) { if ( separator . length ( ) > 0 && i ++ > 0 ) { sb . append ( separator ) ; } sb . append ( format ( elem ) ) ; } return sb . toString ( ) ; }
target:  Returns a string containing all elements concatenated by a specified separator.