### Question:
StringPartMethod { public static String join(CharSequence delimiter, CharSequence... elements) { Objects.requireNonNull(delimiter); Objects.requireNonNull(elements); StringJoiner joiner = new StringJoiner(delimiter); for (CharSequence cs: elements) { joiner.add(cs); } return joiner.toString(); }  static String join(CharSequence delimiter, CharSequence... elements); static String join(CharSequence delimiter,
                              Iterable<? extends CharSequence> elements);  }### Answer:
@Test @DisplayName("java 8 新增方法") void join() { String var = "123123"; var = String.join(":", "a","b","c"); log.info("-*--*--*--*- var: {} -*--*--*--*--",var); }
@Test void join1() { String var = "123123"; List<CharSequence> charSequences = Arrays.asList("a","b","c"); var = String.join("-",charSequences); log.info("-*--*--*--*- var: {} -*--*--*--*--",var); }