title: android app not able to run and shows following error
body: <p>i am getting error in connecting to local host kindly help my code is</p>
  
  <pre><code>  public class MainActivity extends Activity implements OnClickListener{
  /** Called when the activity is first created. */
    TextView resultView;
     HttpClient client;
     JSONObject json;
  String Dat;
  Button btn;
  InputStream is=null;
  EditText name,roll_no;
  String result="";
  StringBuilder sb=null;
  JSONArray jArray;
  @Override
  public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      resultView = (TextView) findViewById(R.id.tv1);
      submit();
      btn.setOnClickListener(this);
  
  }
  public void onClick(View v){
  parse();
  
  }
  private String submit() {
       ArrayList&lt;NameValuePair&gt; nameValuePairs = new ArrayList&lt;NameValuePair&gt;();
          //http post
          try{
               HttpClient httpclient = new DefaultHttpClient();
               HttpPost httppost = new HttpPost("http://10.0.2.2:8081/onlineres/login");
               httppost.setEntity(new UrlEncodedFormEntity(nameValuePairs));
               HttpResponse response = httpclient.execute(httppost);
               HttpEntity entity = response.getEntity();
               is = entity.getContent();
               }catch(Exception e){
                   Log.e("log_tag", "Error in http connection"+e.toString());
              }
          try{
                BufferedReader reader = new BufferedReader(new InputStreamReader(is,"iso-8859-1"),8);
                 sb = new StringBuilder();
                 sb.append(reader.readLine() + "\n");
  
                 String line="0";
                 while ((line = reader.readLine()) != null) {
                                sb.append(line + "\n");
                  }
                  is.close();
                  result=sb.toString();
                  }catch(Exception e){
                        Log.e("log_tag", "Error converting result "+e.toString());
                  }
      return result;
    }
      public void parse(){
      String roll,name;
      try{
            jArray  = new JSONArray(result);
            JSONObject json_data=null;
            for(int i=0;i&lt;jArray.length();i++){
                   json_data = jArray.getJSONObject(i);
                   name=json_data.getString("Name");
                   roll =json_data.getString("Roll_no");
               }
            }
            catch(JSONException e1){
                Toast.makeText(getBaseContext(), "No City Found"     ,Toast.LENGTH_LONG).show();
            } catch (ParseException e1) {
                  e1.printStackTrace();
          }
  }
  }
  </code></pre>
  
  <p><strong>and logcat is</strong></p>
  
  <pre><code>   07-20 21:23:02.776: I/System.out(306): debugger has settled (1441)
      07-20 21:23:31.564: D/AndroidRuntime(306): Shutting down VM
      07-20 21:23:31.564: W/dalvikvm(306): threadid=1: thread exiting with uncaught exception     (group=0x4001d800)
      07-20 21:23:31.653: E/AndroidRuntime(306): FATAL EXCEPTION: main
      07-20 21:23:31.653: E/AndroidRuntime(306): java.lang.RuntimeException: Unable to start     activity ComponentInfo{com.example.prac/com.example.prac.MainActivity}:     java.lang.NullPointerException
      07-20 21:23:31.653: E/AndroidRuntime(306):  at     android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at     android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at     android.app.ActivityThread.access$2300(ActivityThread.java:125)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at     android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at android.os.Handler.dispatchMessage(Handler.java:99)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at android.os.Looper.loop(Looper.java:123)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at     android.app.ActivityThread.main(ActivityThread.java:4627)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at java.lang.reflect.Method.invokeNative(Native Method)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at java.lang.reflect.Method.invoke(Method.java:521)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
      07-20 21:23:31.653: E/AndroidRuntime(306):  at dalvik.system.NativeStart.main(Native Method)
     07-20 21:23:31.653: E/AndroidRuntime(306): Caused by: java.lang.NullPointerException
      07-20 21:23:31.653: E/AndroidRuntime(306):  at com.example.prac.MainActivity.onCreate(MainActivity.java:53)
     07-20 21:23:31.653: E/AndroidRuntime(306):   at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
     07-20 21:23:31.653: E/AndroidRuntime(306):   at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
     07-20 21:23:31.653: E/AndroidRuntime(306):   ... 11 more
  </code></pre>
  
  <p>kindly help me out in this</p>