How to Update Data Without Button

Question

I need a help how to update data through the website in android application. I have fetched the data through a website, but I have no any idea or example for changing the data automatically.

The Data Change On Restarting Application Or Onclick Through. Please tell Me How to update data automatically.

MainActivity.java

package com.example.exampleproject;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.JsonObjectRequest;
import com.android.volley.toolbox.Volley;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity {
RequestQueue requestQueue;
String showUrl = "http://wap2mob.net/rand.php";
TextView example;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
requestQueue = Volley.newRequestQueue(getApplicationContext());
example = (TextView) findViewById(R.id.example);
JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.POST,
showUrl, null, new Response.Listener<JSONObject>() {
@Override
public void onResponse(JSONObject response) {
System.out.println(response.toString());
try {
JSONArray success = response.getJSONArray("success");
for (int i = 0; i < success.length(); i++) {
JSONObject succes = success.getJSONObject(i);
example.setText(succes.getString("random"));
}
} catch (JSONException e) {
e.printStackTrace();
}
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
System.out.append(error.getMessage());
}
});
requestQueue.add(jsonObjectRequest);
}
}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.exampleproject.MainActivity" >

    <TextView
        android:id="@+id/example"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_centerVertical="true"
        android:text="TextView" />

</RelativeLayout>

See OutPut