[
    {
        "a": "u",
        "b": "v"
    },
    {
        "a": "x",
        "b": "y"
    }
]

JSONArray jsonArray = new JSONArray(result);

for(int i=0; i<jsonArray.length(); i++) {

   JSONObject jsonObject = jsonArray.getJSONObject(i);
   //further processing here

}

JSONArray[0] is not a JSONObject.

["{"a":"u","b":"v"},{"a":"x","b":"y"}]"]