java8語法糖List，List，String之間互轉

public class Test {
    public static void main(String[] args) {
        List<Integer> integerList = new ArrayList<>();
        integerList.add(1);
        integerList.add(2);
        integerList.add(3);
        // List<Integer> 轉爲 List<String>
        List<String> stringList = integerList.stream().map(String::valueOf).collect(Collectors.toList());
        System.out.println("List<Integer> 轉爲 List<String>=====>" + stringList);

        //List<String> 轉爲 String 以逗號分隔
        String str = String.join(",", stringList);
        System.out.println("List<String> 轉爲 String 以逗號分隔====>" + str);

        //List<String> 轉爲 List<Integer>
        List<Integer> integerList1 = stringList.stream().map(Integer::valueOf).collect(Collectors.toList());
        System.out.println("List<String> 轉爲 List<Integer>====>" + integerList1);
    }
}

打印結果：

List<Integer> 轉爲 List<String>=====>[1, 2, 3]
List<String> 轉爲 String 以逗號分隔====>1,2,3
List<String> 轉爲 List<Integer>====>[1, 2, 3]