php - JSON Android Error- Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference

My app is crashing and the log is showing this error:

Attempt to invoke virtual method 'java.lang.String org.json.JSONObject.getString(java.lang.String)' on a null object reference on the line where I do:

ab = jobj.getString("title");

I'm a noob to Android development. Please help!

public class MainActivity extends ActionBarActivity {

JSONObject jobj = null;

ClientServerInterface clientServerInterface = new ClientServerInterface();
TextView textView;
String ab = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    textView = (TextView) findViewById(R.id.textView);

    new RetrieveData().execute();
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}


@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.action_settings)
    {

        return true;
    }

    return super.onOptionsItemSelected(item);
}

class RetrieveData extends AsyncTask
{
    protected String doInBackground(String... arg0) {
        jobj = clientServerInterface.makeHttpRequest("http://**.***.***.**/printresult.php");

        try {
            ab = jobj.getString("title");
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return ab;
    }

    protected void onPostExecute(String ab){
        textView.setText(ab);

    }
}
}

Here's the other file:

public class ClientServerInterface {

static InputStream is = null;

static JSONObject jobj = null;
static String json = "";


public ClientServerInterface(){
}
public JSONObject makeHttpRequest(String url){
    DefaultHttpClient httpclient = new DefaultHttpClient();
    HttpPost httppost = new HttpPost(url);
    try{

        HttpResponse httpresponse = httpclient.execute(httppost);
        HttpEntity httpentity = httpresponse.getEntity();
        is = httpentity.getContent();
    }catch (ClientProtocolException e){
        e.printStackTrace();
    }catch (IOException e){
        e.printStackTrace();
    }

    try{

        BufferedReader reader = new BufferedReader(new InputStreamReader(is, "iso-8859-1"), 8);
        StringBuilder sb = new StringBuilder();
        String line = null;
        try{
            while((line = reader.readLine())!= null){
                sb.append(line+"\n");
            }
            is.close();
            json = sb.toString();
            try{

                jobj = new JSONObject(json);
            }catch (JSONException e){
                e.printStackTrace();
            }
        }catch(IOException e){
            e.printStackTrace();
        }
    }catch (UnsupportedEncodingException e){
        e.printStackTrace();
    }

    return jobj;
}
}

Maybe it is in my php file?

require_once('connection.php');


$qry = "SELECT * FROM eventdetails";
$result = mysql_query($qry);
$rows = array();
while($r = mysql_fetch_assoc($result)){
$rows[] = $r;
}
echo json_encode($rows);
mysql_close();
?>

I'm really stumped. Please help!

Answer

The error, as user1023110 pointed out, happens because the constructor is throwing an exception. In this case, I was giving the constructor a JSONArray and it giving the error that it could not be converted to JSONObject. First, I added this to the top of my ClientServerInterface class:

static JSONArray jarr = null;

Then, I added these two lines:

jarr = new JSONArray(json);
jobj = jarr.getJSONObject(0);

where I previously had this:

jobj = new JSONObject(json);

The method now returns the first JSONObject of the JSONArray.

Thanks to all your help!