Android : send message to server with ClientThread in java

i have this code that i am trying to send a message to the server . how can i send message to the server with this command

using this command:

clientThread.sendText(un + " " + user + " yes");

getting this error:

09-09 05:02:21.494: E/AndroidRuntime(1145): java.lang.NullPointerException
09-09 05:02:21.494: E/AndroidRuntime(1145):     at com.example.tictac.MenuActivity$ConnectThread.sendText(MenuActivity.java:373)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at com.example.tictac.MenuActivity$2.onClick(MenuActivity.java:176)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at com.android.internal.app.AlertController$ButtonHandler.handleMessage(AlertController.java:166)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at android.os.Handler.dispatchMessage(Handler.java:102)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at android.os.Looper.loop(Looper.java:137)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at android.app.ActivityThread.main(ActivityThread.java:4998)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at java.lang.reflect.Method.invokeNative(Native Method)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at java.lang.reflect.Method.invoke(Method.java:515)
09-09 05:02:21.494: E/AndroidRuntime(1145):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)

from this code:

public void connectUser() {
        clientThread = new ConnectThread();
        clientThread.start();

    }

    class ConnectThread extends Thread {
        InputStream input;
        OutputStream output;
        ObjectOutputStream oos;
        Socket s;

        public void sendText(String text) {
            try {
                oos.writeObject(text);

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

        public void run() {
            try {
                s = new Socket(HOST, PORT);
                output = s.getOutputStream();
                oos = new ObjectOutputStream(output);
                oos.writeObject("mmmmmmmmmmmm");

                isOnline = true;
                isConnected = true;

                new ListenThread(s).start();

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

what does the error mean? and how to fix it thanks