php - Retrive data from database to java

I have a problem to view a date that I receive from my database. Let me explain what I'm doing. I have a database where there is a table called rate1 which is formed from a single column called value which it contains double numbers. My intent is to take all the data in this column, do the average and return it in my java code. I wanto to display the average in a TextView. My problem is that I do not see anything on the TextView. Can anyone tell me where I'm wrong, and if can he give me solutions to my mistakes? Now I add the code: This is the Average.java:

import android.app.ProgressDialog;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;

import android.widget.TextView;
import android.widget.Toast;

import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

public class Average extends AppCompatActivity {

private TextView textViewResult;

private ProgressDialog loading;

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

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

    loading = ProgressDialog.show(this,"Please wait...","Fetching...",false,false);

    String url = Config.DATA_URL.toString().trim();

    StringRequest stringRequest = new StringRequest(url, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            loading.dismiss();
            showJSON(response);
        }
    },
            new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    Toast.makeText(Average.this,error.getMessage().toString(),Toast.LENGTH_LONG).show();
                }
            });

    RequestQueue requestQueue = Volley.newRequestQueue(this);
    requestQueue.add(stringRequest);
}

private void showJSON(String response){
    String name="";
    try {
        JSONObject jsonObject = new JSONObject(response);
        JSONArray result = jsonObject.getJSONArray(Config.JSON_ARRAY);
        JSONObject collegeData = result.getJSONObject(0);
        name = collegeData.getString(Config.KEY_NAME);
    } catch (JSONException e) {
        e.printStackTrace();
    }
    textViewResult.setText("Name:\t"+name);
 }

}
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This is the Config.java:

public class Config {
public static final String DATA_URL = "https://lbstudios.000webhostapp.com/Average.php";
public static final String KEY_NAME = "value";
public static final String JSON_ARRAY = "result";
}
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And this is Average.php:

<?php
  $connect = mysqli_connect("********", "********", "********", "*******");
$response = mysqli_query($connect, 'SELECT AVG(value) AS average FROM rate1');
$result = array();
if ($response) {

/* fetch associative array */
while ($row = mysqli_fetch_assoc($response)) {
    $result[] = $row;
}

/* free result set */
mysqli_free_result($result);
}
echo json_encode($result);
?>
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