unable to instantiate activity component info, getting runtime exception and java.lang.nullpointer exception
<p>I am doing to develop an app that perform <strong>walkie talkie</strong> function over <strong>WiFi direct</strong>.
I create walkietalkiefunction activity that that record audio using <strong>media recorder thread</strong> class and send it to client using RTP socket(<strong>Sendersocket class</strong>).I tried to start this activity from fragment. I tried many times and I found the error (Runtime exception:Unable to in instantiate activity ComponentInfo{com.walkietakli2.android.mcomp/com.walkietakli2.android.mcomp.WalkieTalkieFunction}: java.lang.NullPointerException). so pls help me? I can't  solve it. do you have an idea how to fix this problem? </p>

<pre><code>03-09 08:40:09.361: E/AndroidRuntime(1301): FATAL EXCEPTION: main
03-09 08:40:09.361: E/AndroidRuntime(1301): java.lang.RuntimeException: Unable to instantiate activity componentInfo{com.walkietakli2.android.mcomp/com.walkietakli2.android.mcomp.WalkieTalkieFunction}: java.lang.NullPointerException
03-09 08:40:09.361: E/AndroidRuntime(1301):     at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.os.Handler.dispatchMessage(Handler.java:99)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.os.Looper.loop(Looper.java:137)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.ActivityThread.main(ActivityThread.java:5039)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at java.lang.reflect.Method.invokeNative(Native Method)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at java.lang.reflect.Method.invoke(Method.java:511)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at dalvik.system.NativeStart.main(Native Method)
03-09 08:40:09.361: E/AndroidRuntime(1301): Caused by: java.lang.NullPointerException
03-09 08:40:09.361: E/AndroidRuntime(1301):     at com.walkietakli2.android.mcomp.WalkieTalkieFunction.&lt;init&gt;(WalkieTalkieFunction.java:26)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at java.lang.Class.newInstanceImpl(Native Method)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at  java.lang.Class.newInstance(Class.java:1319)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
03-09 08:40:09.361: E/AndroidRuntime(1301):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
03-09 08:40:09.361: E/AndroidRuntime(1301):     ... 11 more
</code></pre>

<p>Here is code :
                package com.walkietakli2.android.mcomp;</p>

<pre><code>            import android.net.wifi.p2p.WifiP2pDevice;
            import android.net.wifi.p2p.WifiP2pInfo;
            import android.os.Bundle;
            import android.app.Activity;
            import android.content.Context;
            import android.database.Cursor;
            import android.view.Menu;
            import android.view.View;
            import android.widget.EditText;
            import android.widget.ImageButton;

            public class WalkieTalkieFunction extends Activity {

                private WifiP2pDevice device =null;
                private WifiP2pInfo info =null;
                private FreqManager frqman =new FreqManager();
                private DeviceListFragment dlf=null;
                //Context context =null;
                //Object sstmonitor =new Object();

                Object mrtmonitor=new Object();

                String host = info.groupOwnerAddress.getHostAddress();

                @Override
                protected void onCreate(Bundle savedInstanceState)    
    {
           super.onCreate(savedInstanceState);

            setContentView(R.layout.activity_walkie_talkie_function);


    ImageButton recorder1=(ImageButton)findViewById(R.id.recorderbtn);
    recorder1.setOnClickListener(new View.OnClickListener() {

                @Override
                public void onClick(View v) {


      SocketSenderThread sst =new SocketSenderThread(8988,device.deviceAddress, 
                                                  sstmonitor);

        EditText edtxt1= (EditText) findViewById (R.id.wtflbl1);

            if(frqman.isInSameGroup
                                     (dlf.getSelectedItemPosition()))
                      {
        MediaRecorderThread mrt =new MediaRecorderThread(host, 
                         mrtmonitor);
                                   mrt.run();
                        edtxt1.setText("now recording");
                                  // sst.init();
                                   //sst.run();
                                 }                          
                        }
                    });
                }

                @Override
           public boolean onCreateOptionsMenu(Menu menu) {

            getMenuInflater().inflate(R.menu.
            activity_walkie_talkie_function, menu);
                    return true;
                }

            }

enter code here
        package com.walkietakli2.android.mcomp;

        import java.io.File;
        import java.io.FileInputStream;
        import java.io.FileNotFoundException;
        import java.io.IOException;
        import java.io.InputStream;
        import java.net.DatagramSocket;
        import java.net.InetAddress;
        import java.net.SocketException;
        import java.net.UnknownHostException;

        import android.os.Environment;
        import android.util.Log;


        public class SocketSenderThread implements Runnable{

     public SocketSenderThread(int dport,
        String daddr, Object ssMonitor) {
    super();        
    this.daddr = daddr;
    this.dport = dport;
    ss_monitor = ssMonitor;


    init();
    }

   private void init()
   {
    DatagramSocket src_socket = null;
    try {
         src_socket = new DatagramSocket();         

 Log.i(TAG, "init: dest addr"+InetAddress.getByName(daddr)+" port: "+dport);
 rtp_socket = new RtpSocket(src_socket,   InetAddress.getByName(daddr),dport);
    } 
    catch (UnknownHostException e) {            
        e.printStackTrace();
    }
    catch (SocketException e) {
        Log.i(TAG, "Socket cannot be opened");
        e.printStackTrace();
    }
}

private InputStream audio_input;
private String daddr;
private int dport;


private static final String TAG = "WalkieTalkieEngine";

public static boolean all_files_sent = true;

RtpSocket rtp_socket = null;

Object ss_monitor = new Object();

@Override
public void run() {
    int sample_rate = 8000;
    int sample_size = 1;
    int frame_size = Constants.PKT_SIZE;
    int payload_type = 0;       
    boolean running = true;
    int last_file_sent = 0;
    int num_files = 0;

    int frame_rate = sample_rate/(frame_size/sample_size);



    while(running)
    {
        if(all_files_sent)
        {
            synchronized(ss_monitor)
            {
                try{
                    Log.i(TAG, "Waiting for notif");
                    ss_monitor.wait();
                }
                catch(InterruptedException e){}
                num_files = MediaRecorderThread.max_file_num;
            }
            Log.i(TAG, "Got Notif");
        }

        // create # of streams and set that to audio_input
        for (int i = last_file_sent; i &lt; num_files; i++) 
        {
            String path = null;
            try {
                Integer file_num = new Integer(i+1);
            path =Environment.getExternalStorageState().
               toString()+file_num.toString()+".3gp";
                audio_input = new FileInputStream(path);
                payload_type = i+1;
            } catch (FileNotFoundException e2) {                    
                e2.printStackTrace();
            }

            if (audio_input==null) 
                return;

            Log.e(TAG, "Trying to to send RTP packet from File"+path);

            byte[] buffer=new byte[frame_size+12];
            RtpPacket rtp_packet=new RtpPacket(buffer,0);
            rtp_packet.setPayloadType(payload_type);      
            int seqn=0;
            long time=0;
            long byte_rate=frame_rate*frame_size;

            boolean reading=true;

            Log.i(TAG, "Reading blocks of "+(buffer.length-12)+" bytes");
            while(reading)
            {
                int num=0;
                try {
                num = audio_input.read(buffer,12,buffer.length-12);
                } catch (IOException e1) {
                    e1.printStackTrace();
                }
                Log.i(TAG, "Number of blocks read: "+num);
                if(num &gt; 0)
                {
                    rtp_packet.setSequenceNumber(seqn++);
                       rtp_packet.setTimestamp(time);
                       rtp_packet.setPayloadLength(num);



                       try {
                        rtp_socket.send(rtp_packet);
            Log.i(TAG, "Sent packet of size: "+rtp_packet.getLength());
                    } catch (IOException e) {
                        Log.i(TAG, "Send failure");
                        e.printStackTrace();
                    }

                       long frame_time=(num*1000)/byte_rate;
                       time+=frame_time;

                 try {  Thread.sleep(frame_time);  } catch (Exception e) {}
                }
                else
                {
                    reading=false;
                    Log.i(TAG, "Error reading from InputStream");
                }
            }//end while reading
        File fileToDelete =new File(path);
            fileToDelete.delete();
            last_file_sent++;
        } // end-for

        all_files_sent =  true;
    } // end-while running
    }

        }
</code></pre>
