public class Main {
    @Test
    public void main() {
   // write your code here
        int sum=0;
        for(int i=0;i<5;i++){
            sum+=i;
        }
        System.out.print(sum);
    }

    public void JSONTest(){
        String str="{\"errCode\":\"0\",\"id\":\"10\"}";
        System.out.print(str);
    }
    @Test
    public void setFastJson(){


        JSONObject root =new JSONObject();//导入的包的形式是阿里巴巴地
        root.put("errCode",1);
        root.put("errMsg","调用接口成功");
        JSONArray dateArr = new JSONArray();
        JSONObject rootZhangchao = new JSONObject();
        rootZhangchao.put("userName","张超");
        rootZhangchao.put("position","java开发");
        rootZhangchao.put("webAddress","www.itmayiedu.com");
        dateArr.add(rootZhangchao);
        root.put("date",dateArr);

        System.out.print(root.toJSONString());
    }
    @Test
    public void mapJson(){
        Map<String,Object> root = new HashMap<>();
        root.put("errCode",1);
        root.put("errMsg","调用接口成功");
        List<Map<String, Object>> userList = new ArrayList<>();
        Map<String, Object> rootzhangchao = new HashMap<>();
        rootzhangchao.put("id",1);
        rootzhangchao.put("userName","张超");
        rootzhangchao.put("position","java开发");
        rootzhangchao.put("webAdrress","www.itmayiedu.com");

        userList.add(rootzhangchao);
       root.put("date", userList);
        System.out.print(root.toString());

    }
    @Test
    public void entityJson(){
        Entity entity = new Entity();
        entity.setErrCode("0");
        entity.setErrMsg("调用接口成功");
        List<User> userList = new ArrayList<>();
        User user = new User();
        user.setId(1);
        user.setUserName("张超");
        user.setPosition("java软件开发");
        user.setWebAdrress("www.itmayiedu.com");
        userList.add(user);
        entity.setDate(userList);
        System.out.print(entity.toString());
    }
}

注：导入的包，只供测试使用：