Exception while connecting android application with web service
<p>This coding i got from here. I get error in log cat view like the one i mentioned after the coding.. please provide me some suggestion to clear this..</p>

<pre><code>package com.example.firstws;



import android.app.Activity;
import android.os.Bundle;
import android.widget.TextView;
import org.ksoap2.SoapEnvelope;
import org.ksoap2.serialization.SoapObject;
import org.ksoap2.serialization.SoapPrimitive;
import org.ksoap2.serialization.SoapSerializationEnvelope;
import org.ksoap2.transport.AndroidHttpTransport;

public class Firstws extends Activity {
    /** Called when the activity is first created. */
    private static final String SOAP_ACTION="http://tempuri.org/CelsiusToFarenheit";
    private static final String METHOD_NAME="CelsiusToFarenheit";
    private static final String NAMESPACE="http://tempuri.org/";
    private static final String URL="http://www.w3schools.com/webservices/tempconvert.asmx";
    TextView tv=(TextView)findViewById(R.id.textView1);
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        SoapObject Request=new SoapObject(NAMESPACE,METHOD_NAME);
        Request.addProperty("Celsius","32");
        SoapSerializationEnvelope soapEnvelope=new SoapSerializationEnvelope(SoapEnvelope.VER11);
        soapEnvelope.dotNet=true;
        soapEnvelope.setOutputSoapObject(Request);
        AndroidHttpTransport aht=new AndroidHttpTransport(URL);
        try
        {
            aht.call(SOAP_ACTION, soapEnvelope);
            SoapPrimitive resultString=(SoapPrimitive)soapEnvelope.getResponse();
            tv.setText("Status:"+resultString);
        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
        }

    }
</code></pre>

<p>Error:</p>

<pre><code>java.lang.runtime exception: unable to instantiate the activity componentinfo{com.example.firstws/com.example.firstws.Firstws}: java.lang.NullpointerException
</code></pre>
