StringJoiner in java 8:- StringJoiner is used to construct a sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.
Prior to adding something to the StringJoiner, its sj.toString() method will, by default, return prefix + suffix. However, if the setEmptyValue method is called, the emptyValue supplied will be returned instead. This can be used, for example, when creating a string using set notation to indicate an empty set, i.e. "{}", where the prefix is "{", the suffix is "}" and nothing has been added to the StringJoiner.
