How do I fix this error?

public class MainActivity extends ActionBarActivity {

    public static final String TAG = MainActivity.class.getSimpleName();
    private CurrentWeather mCurrentWeather;

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

        String apiKey = "***my_API_key****";
        double apiLat = 37.8267;
        double apiLong = -122.423;
        String forecastURL = "https://api.forecast.io/forecast/" + apiKey + "/" + apiLat + "," + apiLong;
        if (isNetworkOnline()) {
            OkHttpClient client = new OkHttpClient();
            Request request = new Request.Builder().url(forecastURL).build();
            Call call = client.newCall(request);
            call.enqueue(new Callback() {
                @Override
                public void onFailure(Request request, IOException e) {

                }

                @Override
                public void onResponse(Response response) throws IOException {
                    try {
                        String JsonData = response.body().toString();
                        Log.v(TAG, response.body().string());
                        if (response.isSuccessful()) {
                            mCurrentWeather = getCurrentDetails(JsonData);
                        } else {
                            alertUserAboutError();
                        }
                    } catch (IOException | JSONException e) {
                        Log.e(TAG, "Caught exception: ", e);
                    }
                }
            });
        } else {
            Toast.makeText(this, getString(R.string.network_not_available), Toast.LENGTH_LONG).show();
        }
        Log.d(TAG, "Main UI code is running.");
    }

    private CurrentWeather getCurrentDetails(String jsonData) throws JSONException {
        // getting the first JSON object in the json formatted link.
        JSONObject forecast = new JSONObject(jsonData);
        String timeZone = forecast.getString("timezone");

        // getting the second JSON object in the json format by looking for the
        // keyword "currently"
        JSONObject currently = forecast.getJSONObject("currently");
        CurrentWeather currentWeather = new CurrentWeather();
        currentWeather.setHumidity(currently.getDouble("humidity"));
        currentWeather.setIcon(currently.getString("icon"));
        currentWeather.setPrecipChance(currently.getDouble("precipProbability"));
        currentWeather.setSummary(currently.getString("summary"));
        currentWeather.setTemperature(currently.getDouble("temperature"));
        currentWeather.setTime(currently.getLong("time"));
        currentWeather.setTimeZone(timeZone);
        // Displaying the formatted time from seconds to the format we
        // specified.
        Toast.makeText(MainActivity.this, currentWeather.getFormattedTime(), Toast.LENGTH_LONG).show();
        return currentWeather;
    }

    private boolean isNetworkOnline() {
        ConnectivityManager manager = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
        NetworkInfo networkInfo = manager.getActiveNetworkInfo();
        if (networkInfo != null && networkInfo.isConnected()) {
            return true;
        } else {
            return false;
        }
    }
}