public static void main(String[] args) {
List<String> list1 = new ArrayList<>();
list1.add("a");
list1.add("b");
list1.add("c");
//转换 String.join(",",list1);
System.out.println(String.join(",",list1));
//输出结果 a,b,c
List<Integer> list2 = new ArrayList<>();
list2.add(0);
list2.add(1);
list2.add(2);
//转换 Joiner.on(",").join(list2);
System.out.println(Joiner.on(",").join(list2));
//输出结果 0,1,2
}