java将list转为逗号隔开字符串，将逗号连接的字符串转成字符数组，​将逗号分隔的字符串转换为List​（Java逗号分隔-字符串与数组相互转换）

List<String> testList = new ArrayList<>();
testList.add("test1");
testList.add("test2");
testList.add("test3");
 
String newStr = testList.stream().collect(Collectors.joining(","));
System.out.println(newStr);

String str = "aa,bb,cc";
String[] strList = str.split(",");
 
for(int i=0;i<strList.length;i++){
	System.out.println(strList[i]);
}

String str = "a,b,c";
List<String> resultList = Arrays.asList(str.split(","));
System.out.println(resultList);

String str="ab cd efg";
char[] a=str.toCharArray();
System.out.println(Arrays.toString(a));