Java中将List＜String＞中的元素拼接成字符串，逗号隔开

List<String> costSubjectCodes = new ArrayList<>(); 
costSubjectCodes .add("张三"); 
costSubjectCodes .add("李四"); 
String costCodes = costSubjectCodes.stream().map(String::valueOf).collect(Collectors.joining(","));
System.out.println(costCodes );//输出 张三,李四