Hi everyone:
  Try fewest word: from Java Turotial->Custom Networking->All About
Sockets->Reading from and Writing to a socket, the following program:
import java.io.*;
import java.net.*;

public class EchoClient {
   public static void main(String[] args) throws IOException {

       Socket echoSocket = null;
       PrintWriter out = null;
       BufferedReader in = null;

       try {
           echoSocket = new Socket("taranis", 7);
           out = new PrintWriter(echoSocket.getOutputStream(), true);
           in = new BufferedReader(new InputStreamReader(
                                       echoSocket.getInputStream()));
       } catch (UnknownHostException e) {
           System.err.println("Don't know about host: taranis.");
           System.exit(1);
       } catch (IOException e) {
           System.err.println("Couldn't get I/O for "
                              + "the connection to: taranis.");
           System.exit(1);
       }

    BufferedReader stdIn = new BufferedReader(
                                  new InputStreamReader(System.in));
    String userInput;

    while ((userInput = stdIn.readLine()) != null) {
       out.println(userInput);
       System.out.println("echo: " + in.readLine());
    }

    out.close();
    in.close();
    stdIn.close();
    echoSocket.close();
   }
}

But it says "Don't know about host: taranis". If I change it to my
computer's name, it says "Couldn't get I/O for the connection to:
taranis.";
So how can I open echo service on a computer? Thanks.