简单来说:
“key”:“value” --> 此时value为String
“key":0 --> 此时value为int
“key”:{“k1”:“v1”} --> 此时value为JSONObject
“key”:[v] --> 此时value为JSONArray
以下举例数据结构：

{
    "error": 0,
    "status": "success",
    "results": [
        {
            "currentCity": "青岛",
            "index": [
                {
                    "title": "穿衣",
                    "zs": "较冷",
                    "tipt": "穿衣指数",
                    "des": "建议着厚外套加毛衣等服装。年老体弱者宜着大衣、呢外套加羊毛衫。"
                },
                {
                    "title": "紫外线强度",
                    "zs": "中等",
                    "tipt": "紫外线强度指数",
                    "des": "属中等强度紫外线辐射天气，外出时建议涂擦SPF高于15、PA+的防晒护肤品，戴帽子、太阳镜。"
                }
            ]

        }
    ]
}

解析代码：

public class Test {

public static void main(String[] args) {

    String s = "{\"error\":0,\"status\":\"success\",\"results\":[{\"currentCity\":\"青岛\",\"index\":[{\"title\":\"穿衣\",\"zs\":\"较冷\",\"tipt\":\"穿衣指数\",\"des\":\"建议着厚外套加毛衣等服装。年老体弱者宜着大衣、呢外套加羊毛衫。\"},{\"title\":\"紫外线强度\",\"zs\":\"最弱\",\"tipt\":\"紫外线强度指数\",\"des\":\"属弱紫外线辐射天气，无需特别防护。若长期在户外，建议涂擦SPF在8-12之间的防晒护肤品。\"}],}]}";

    JSONObject jsonObject = JSONObject.fromObject(s);

    //提取出error为 0
    int error = jsonObject.getInt("error");
    System.out.println("error:" + error);

    //提取出status为 success
    String status = jsonObject.getString("status");
    System.out.println("status:" + status);    

    //注意：results中的内容带有中括号[]，所以要转化为JSONArray类型的对象
    JSONArray result = jsonObject.getJSONArray("results");

    for (int i = 0; i < result.size(); i++) {
        //提取出currentCity为 青岛
        String currentCity = result.getJSONObject(i).getString("currentCity");
        System.out.println("currentCity:" + currentCity);

        //注意：index中的内容带有中括号[]，所以要转化为JSONArray类型的对象
        JSONArray index = result.getJSONObject(i).getJSONArray("index");

        for (int j = 0; j < index.size(); j++) {
            String title = index.getJSONObject(j).getString("title");
            System.out.println("title:" + title);
            String zs = index.getJSONObject(j).getString("zs");
            System.out.println("zs:" + zs);
            String tipt = index.getJSONObject(j).getString("tipt");
            System.out.println("tipt:" + tipt);
            String des = index.getJSONObject(j).getString("des");
            System.out.println("des:" + des);
        }
    }
}
}