public static String join(Collection<String> collection, String separator) {
        if (collection == null) {
            return null;
        }
        return join(collection.toArray(new String[collection.size()]), separator, 0, collection.size());
    }
public static String join ( Collection < String > collection , String separator ) { if ( collection == null ) { return null ; } return join ( collection . toArray ( new String [ collection . size ( ) ] ) , separator , 0 , collection . size ( ) ) ; }
Join a collection of Strings

@param collection strings to join
@param separator  the separator to insert between the strings
@return a string made of the strings in collection separated by separator