Java loop over Json array?

In your code the element dataArray is an array of JSON objects, not a JSON object itself. The elements A, B, and C are part of the JSON objects inside the dataArray JSON array.

You need to iterate over the array

public static void main(String[] args) throws Exception {
    String jsonStr = "{         \"dataArray\": [{              \"A\": \"a\",                \"B\": \"b\",               \"C\": \"c\"            }, {                \"A\": \"a1\",              \"B\": \"b2\",              \"C\": \"c3\"           }]      }";

    JSONObject jsonObj = new JSONObject(jsonStr);

    JSONArray c = jsonObj.getJSONArray("dataArray");
    for (int i = 0 ; i < c.length(); i++) {
        JSONObject obj = c.getJSONObject(i);
        String A = obj.getString("A");
        String B = obj.getString("B");
        String C = obj.getString("C");
        System.out.println(A + " " + B + " " + C);
    }
}

prints

a b c
a1 b2 c3

I don't know where msg is coming from in your code snippet.

Java Docs to the rescue:

You can use http://www.json.org/javadoc/org/json/JSONObject.html#getJSONArray(java.lang.String) instead

JSONArray dataArray= sync_reponse.getJSONArray("dataArray");

for(int n = 0; n < dataArray.length(); n++)
{
    JSONObject object = dataArray.getJSONObject(n);
    // do some stuff....
}