How to scan all wireless networks around through code in android?

Scan for wireless networks in the current area: 

public class WifiTester extends Activity {
  TextView mainText;
  WifiManager mainWifi;
  WifiReceiver receiverWifi;
  List<ScanResult> wifiList;
  StringBuilder sb = new StringBuilder();
  
  public void onCreate(Bundle savedInstanceState) {
   super.onCreate(savedInstanceState);
   setContentView(R.layout.main);
   mainText = (TextView) findViewById(R.id.mainText);
   mainWifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
   receiverWifi = new WifiReceiver();
   registerReceiver(receiverWifi, new IntentFilter(
      WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
   mainWifi.startScan();
   mainText.setText("\nStarting Scan...\n");
  }

  public boolean onCreateOptionsMenu(Menu menu) {
    menu.add(0, 0, 0, "Refresh");
    return super.onCreateOptionsMenu(menu);
  }

  public boolean onMenuItemSelected(int featureId, MenuItem item) {
    mainWifi.startScan();
    mainText.setText("Starting Scan");
    return super.onMenuItemSelected(featureId, item);
  }

  protected void onPause() {
    unregisterReceiver(receiverWifi);
    super.onPause();
  }

  protected void onResume() {
    registerReceiver(receiverWifi, new IntentFilter(
       WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
    super.onResume();
  }
  
  class WifiReceiver extends BroadcastReceiver {
    public void onReceive(Context c, Intent intent) {
    sb = new StringBuilder();
    wifiList = mainWifi.getScanResults();
    for(int i = 0; i < wifiList.size(); i++){
      sb.append(new Integer(i+1).toString() + ".");
      sb.append((wifiList.get(i)).toString());
      sb.append("\n");
    }
    mainText.setText(sb);
    }
  }
}