learning android ...why there is class within a class

Question

I am coming form php background and am trying to learn android. I saw this in a sample code that I am looking at where there is class defination within a class. How does that even work? can someone explain that to me? You can see that LongOperation class is defined within RestfulServices class.

public class RestFulWebservice extends Activity {


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.rest_ful_webservice);  

        final Button GetServerData = (Button) findViewById(R.id.GetServerData);

        GetServerData.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View arg0) {

                // WebServer Request URL
                String serverURL = "http://androidexample.com/media/webservice/JsonReturn.php";

                // Use AsyncTask execute Method To Prevent ANR Problem
                new LongOperation().execute(serverURL);
            }
        });    

    }


    // Class with extends AsyncTask class
    private class LongOperation  extends AsyncTask<String, Void, Void> {

        // Required initialization

        private final HttpClient Client = new DefaultHttpClient();
        private String Content;
        private String Error = null;
        private ProgressDialog Dialog = new ProgressDialog(RestFulWebservice.this);
        String data =""; 
        TextView uiUpdate = (TextView) findViewById(R.id.output);
        TextView jsonParsed = (TextView) findViewById(R.id.jsonParsed);
        int sizeData = 0;  
        EditText serverText = (EditText) findViewById(R.id.serverText);


        protected void onPreExecute() {
            // NOTE: You can call UI Element here.

            //Start Progress Dialog (Message)

            Dialog.setMessage("Please wait..");
            Dialog.show();

            try{
                // Set Request parameter
                data +="&" + URLEncoder.encode("data", "UTF-8") + "="+serverText.getText();

            } catch (UnsupportedEncodingException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            } 

        }

        // Call after onPreExecute method
        protected Void doInBackground(String... urls) {

            /************ Make Post Call To Web Server ***********/
            BufferedReader reader=null;

                 // Send data 
                try
                { 

                   // Defined URL  where to send data
                   URL url = new URL(urls[0]);

                  // Send POST data request

                  URLConnection conn = url.openConnection(); 
                  conn.setDoOutput(true); 
                  OutputStreamWriter wr = new OutputStreamWriter(conn.getOutputStream()); 
                  wr.write( data ); 
                  wr.flush(); 

                  // Get the server response 

                  reader = new BufferedReader(new InputStreamReader(conn.getInputStream()));
                  StringBuilder sb = new StringBuilder();
                  String line = null;

                    // Read Server Response
                    while((line = reader.readLine()) != null)
                        {
                               // Append server response in string
                               sb.append(line + "\n");
                        }

                    // Append Server Response To Content String 
                   Content = sb.toString();
                }
                catch(Exception ex)
                {
                    Error = ex.getMessage();
                }
                finally
                {
                    try
                    {

                        reader.close();
                    }

                    catch(Exception ex) {}
                }

            /*****************************************************/
            return null;
        }

        protected void onPostExecute(Void unused) {
            // NOTE: You can call UI Element here.

            // Close progress dialog
            Dialog.dismiss();

            if (Error != null) {

                uiUpdate.setText("Output : "+Error);

            } else {

                // Show Response Json On Screen (activity)
                uiUpdate.setText( Content );

             /****************** Start Parse Response JSON Data *************/

                String OutputData = "";
                JSONObject jsonResponse;

                try {

                     /****** Creates a new JSONObject with name/value mappings from the JSON string. ********/
                     jsonResponse = new JSONObject(Content);

                     /***** Returns the value mapped by name if it exists and is a JSONArray. ***/
                     /*******  Returns null otherwise.  *******/
                     JSONArray jsonMainNode = jsonResponse.optJSONArray("Android");

                     /*********** Process each JSON Node ************/

                     int lengthJsonArr = jsonMainNode.length();  

                     for(int i=0; i < lengthJsonArr; i++) 
                     {
                         /****** Get Object for each JSON node.***********/
                         JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);

                         /******* Fetch node values **********/
                         String name       = jsonChildNode.optString("name").toString();
                         String number     = jsonChildNode.optString("number").toString();
                         String date_added = jsonChildNode.optString("date_added").toString();


                         OutputData += " Name           : "+ name +" \n "
                                     + "Number      : "+ number +" \n "
                                     + "Time                : "+ date_added +" \n " 
                                     +"--------------------------------------------------\n";

                         //Log.i("JSON parse", song_name);
                    }
                 /****************** End Parse Response JSON Data *************/     

                     //Show Parsed Output on screen (activity)
                     jsonParsed.setText( OutputData );


                 } catch (JSONException e) {

                     e.printStackTrace();
                 }


             }
        }

    }

}

Answer 1

That is allowed in Java. It is very likely that LongOperation is not needed outside of the scope of RestfulServices. Because of that, the developer may chose to nest LongOperation inside RestfulServices.

Answer 2

Java syntax allows this construct. It is called an inner class. http://docs.oracle.com/javase/tutorial/java/javaOO/innerclasses.html

Inner classes are one particular kind of nested classes. http://docs.oracle.com/javase/tutorial/java/javaOO/nested.html