import java.io.*;
import java.net.*;
 
public class MyServer {
    public static void main(String args[]) {
 
        ServerSocket echoServer = null;
        String line;
        DataInputStream is;
        PrintStream os;
        Socket clientSocket = null;
 
// Try to open a server socket on port 9999
       try {
           echoServer = new ServerSocket(9999);
        }
        catch (IOException e) {
           System.out.println(e);
        }   
// Create a socket object from the ServerSocket to listen and accept 
// connections.
// Open input and output streams
 
try {
           clientSocket = echoServer.accept();
           is = new DataInputStream(clientSocket.getInputStream());
           os = new PrintStream(clientSocket.getOutputStream());
 
// As long as we receive data, echo that data back to the client.
 
           while (true) {
             line = is.readLine();
             os.println(line); 
           }
        }   
catch (IOException e) {
           System.out.println(e);
        }
    }
}
 
 
 
[b] Client code [/b]
import java.io.*;
import java.net.*;
 
public class MyClient {
    public static void main(String[] args) {
 
        Socket smtpSocket = null;  
        DataOutputStream os = null;
        DataInputStream is = null;
 
        try {
            smtpSocket = new Socket("hostname", 25);
            os = new DataOutputStream(smtpSocket.getOutputStream());
            is = new DataInputStream(smtpSocket.getInputStream());
        } catch (UnknownHostException e) {
            System.err.println("Don't know about host: hostname");
        } catch (IOException e) {
            System.err.println("Couldn't get I/O for the connection to: hostname");
        }
 
	if (smtpSocket != null && os != null && is != null) {
            try {
 
				os.writeBytes("HELO\n"); 
				os.close();
                is.close();
                smtpSocket.close();   
            } catch (UnknownHostException e) {
                System.err.println("Trying to connect to unknown host: " + e);
            } catch (IOException e) {
                System.err.println("IOException:  " + e);
            }
        }
    }           
}

/*  SimpleClient.java
*  @author Charles Bell
*  @version December 15, 2000
*  email: charles@quantumhyperspace.com
*/
 
import java.io.*;
import java.net.*;
 
/**  Connects to a SimpleServer which is listening on port 8189
*/
public class SimpleClient{
 
  String serverurl = "127.0.0.1";
  int serverport = 8189;
 
  /**  Instantiates an instance of the SimpleClient class and initilaizes it.
  */
  public static void main(String[] args){
    SimpleClient simpleclient = new SimpleClient();
    simpleclient.init();
  }
 
  /**  Connects to the SimpleServer on port 8189 and sends a few demo lines
  *  to the server, and reads, displays the server reply,
  *  then issues a Bye command signaling the server to quit.
  */
  public void init(){
    Socket socket = null;    
    try{
      System.out.println("Connecting to " + serverurl + " on port " + serverport);
      socket = new Socket(serverurl,serverport);
      //Set socket timeout for 10000 milliseconds or 10 seconds just 
      //in case the host can't be reached
      socket.setSoTimeout(10000);
      System.out.println("Connected.");
      
      InputStreamReader inputstreamreader = new InputStreamReader(socket.getInputStream());
      BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
      //establish an printwriter using the output streamof the socket object
      //and set auto flush on    
      PrintWriter printwriter = new PrintWriter(socket.getOutputStream(),true);
      printwriter.println("Hey howze it going today!");
      printwriter.println("This is some anonymous user on the client side.");
      printwriter.println("Let's see what happens when I type this.");
      printwriter.println("Oh well, I've had enough.");
      printwriter.println("Bye");
      String lineread = "";
      while ((lineread = bufferedreader.readLine()) != null){
        System.out.println("Received from Server: " + lineread);
      }
      System.out.println("Closing connection.");
      bufferedreader.close();
      inputstreamreader.close();
      printwriter.close();
      socket.close();
      System.exit(0);
 
    }catch(UnknownHostException unhe){
      System.out.println("UnknownHostException: " + unhe.getMessage());
    }catch(InterruptedIOException intioe){
      System.out.println("Timeout while attempting to establish socket connection.");
    }catch(IOException ioe){
      System.out.println("IOException: " + ioe.getMessage());
    }finally{
      try{
        socket.close();
      }catch(IOException ioe){
        System.out.println("IOException: " + ioe.getMessage());
      }
    }
  }
}

/*  SimpleServer.java
*  @author Charles Bell
*  @version December 15, 2000
*  email: charles@quantumhyperspace.com
*/
 
import java.io.*;
import java.net.*;
import java.util.*;
 
/**  When started allows one client to connect. It listens on port 8189.
*  It returns whatever a connected client sends.
*  It shuts down when the client sends a Bye line.
*
*/
public class SimpleServer{
 
  /**  Instantiates an instance of the SimpleServer class and initilaizes it.
  */
  public static void main(String[] args){
    SimpleServer simpleserver = new SimpleServer();
    simpleserver.init();
  }
 
  /**  Sets up a ServerSocket and listens on port 8189.
  */
  public void init(){
    ServerSocket serversocket = null;
    Socket socket = null;
    try{
      //establish a server socket monitoring port 8189 
      //port 8189 is not used by any services
      serversocket = new ServerSocket(8189);
      System.out.println("Listening at 127.0.0.1 on port 8189");
 
      //wait indefinitely until a client connects to the socket
      socket = serversocket.accept();
 
      //set up communications for sending and receiving lines of text data
      //establish a bufferedreaderr from the input stream provided by the socket object
      InputStreamReader inputstreamreader = new InputStreamReader(socket.getInputStream());
      BufferedReader bufferedreader = new BufferedReader(inputstreamreader);
 
      //establish an printwriter using the output streamof the socket object
      //and set auto flush on    
      PrintWriter printwriter = new PrintWriter(socket.getOutputStream(),true);
 
      //for binary data use
      // DataInputStream and DataOutputStream
 
      //for serialized objects use
      // ObjectInputStream and ObjectOutputStream
 
      String datetimestring = (Calendar.getInstance()).getTime().toString();
      printwriter.println("You connected to the Simple Server at " + datetimestring);
      printwriter.println("Send Bye to disconnect.");
 
      String lineread = "";
      boolean done = false;
      while (((lineread = bufferedreader.readLine()) != null) && (!done)){
        System.out.println("Received from Client: " + lineread);
        printwriter.println("You sent: " + lineread);
        if (lineread.compareToIgnoreCase("Bye") == 0) done = true;
      }
      System.out.println("Closing connection.");
      bufferedreader.close();
      inputstreamreader.close();
      printwriter.close();
      socket.close();
    }catch(UnknownHostException unhe){
      System.out.println("UnknownHostException: " + unhe.getMessage());
    }catch(InterruptedIOException intioe){
      System.out.println("Timeout while attempting to establish socket connection.");
    }catch(IOException ioe){
      System.out.println("IOException: " + ioe.getMessage());
    }finally{
      try{
        socket.close();
        serversocket.close();
      }catch(IOException ioe){
        System.out.println("IOException: " + ioe.getMessage());
      }
    }
  }
}