void set(int i) {
			previous = i > 0 ? chars.charAt(i - 1) : -1;
			current = chars.charAt(i);
			next = i + 1 < chars.length() ? chars.charAt(i + 1) : -1;
			index = i + 1;
		}
Joins the given CSV {@code columns}, using the given separator and
quote character.

@param columns the CSV columns to join
@return the joined CSV columns
jenetics.ext/src/main/java/io/jenetics/ext/util/CsvSupport.java