question: public String toString ( final String sep ) { if ( isEmpty ( ) ) { return StringUtilities . EMPTY ; } else { final StringBuilder buffer = new StringBuilder ( ) ; buffer . append ( head ) ; for ( ImmutableList < A > l = tail ; l . nonEmpty ( ) ; l = l . tail ) { buffer . append ( sep ) ; buffer . append ( l . head ) ; } return buffer . toString ( ) ; } }
target:  Form a string listing all elements with given separator character.