question: @ CheckReturnValue @ Nonnull public static String join ( @ Nonnull Collection < String > s , @ Nonnull String delimiter ) { StringBuilder buffer = new StringBuilder ( ) ; Iterator < String > iter = s . iterator ( ) ; while ( iter . hasNext ( ) ) { buffer . append ( iter . next ( ) ) ; if ( iter . hasNext ( ) ) { buffer . append ( delimiter ) ; } } return buffer . toString ( ) ; }
target:  Join a collection of strings, separated by a delimiter