I want to return data from doInBackground method and compair with other string in other method :  what i do in this code for comparing retrieved data from server to other string, please tell me changes.

ArrayList<HashMap<String, String>> matchStudentsList = new ArrayList<HashMap<String, String>>();


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.third_sem);
        present = (Button) findViewById(R.id.button2);

        bt= BluetoothAdapter.getDefaultAdapter();

        // Call Async task to get the match fixture
        new GetFixture().execute();

    }
    private class GetFixture extends AsyncTask<String, Void, String> {
        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }
        @Override
        protected String doInBackground(String... arg0) {
            ServiceHandler serviceClient = new ServiceHandler();
            Log.d("url: ", "> " + URL_Students);
            String json = serviceClient.makeServiceCall(URL_Students,ServiceHandler.GET);
            // print the json response in the log
            Log.d("Get match fixture response: ", "> " + json);
            if (json != null) {
                try {
                    Log.d("try", "in the try");
                    JSONObject jsonObj = new JSONObject(json);
                    Log.d("jsonObject", "new json Object");
                    // Getting JSON Array node
                    matchRecords = jsonObj.getJSONArray(TAG_Table);
                    Log.d("json aray", "user point array");
                    int len = matchRecords.length();
                    Log.d("len", "get array length");
                    for (int i = 0; i <len; i++) {
                        JSONObject c = matchRecords.getJSONObject(i);
                        String RollNo = c.getString(TAG_Roll_No);
                        Log.d("RollNo", RollNo);
                        String FirstName = c.getString(TAG_First_Name);
                        Log.d("FirstName", FirstName);
                        String LastName = c.getString(TAG_Last_Name);
                        Log.d("LastName", LastName);
                        //  hashmap for single match
                        HashMap<String, String> matchFixture = new HashMap<String, String>();
                        // adding each child node to HashMap key => value
                        matchFixture.put(TAG_Roll_No, RollNo);
                        matchFixture.put(TAG_First_Name, FirstName);
                        matchFixture.put(TAG_Last_Name, LastName);
                        matchStudentsList.add(matchFixture);


                    }



                }
                catch (JSONException e) {
                    Log.d("catch", "in the catch");
                    e.printStackTrace();
                }
            } else {
                Log.e("JSON Data", "Didn't receive any data from server!");
            }
            return null;
        }




        @Override
        protected void onPostExecute(String result) {
            super.onPostExecute(result);




             ListAdapter adapter = new SimpleAdapter(
                        ThirdSem.this, matchStudentsList,
                        R.layout.list_checkitem, new String[]{TAG_Roll_No, TAG_First_Name, TAG_Last_Name, TAG_BAddress}
                        , new int[]{R.id.RollNo, R.id.FirstName, R.id.LastName }

            );
                setListAdapter(adapter);

        }


    }



}
it will be very very helpful for me please, thanx in advance whose can solve it