question: public static String join ( String separator , List < String > strings ) { StringBuilder sb = new StringBuilder ( ) ; for ( Iterator < String > iter = strings . iterator ( ) ; iter . hasNext ( ) ; ) { String s = iter . next ( ) ; sb . append ( s ) ; if ( iter . hasNext ( ) ) sb . append ( separator ) ; } return sb . toString ( ) ; }
target:  Reverse of String.split. Glues together the strings and inserts the separator between each consecutive pair.