Echoserver

 Client.java  
 import java.io.*;  
 import java.net.*;  
 public class Client {  
     public static void main(String[] args) {  
     try {  
       Socket s = new Socket("Localhost", 9999);  
       BufferedReader r = new BufferedReader(new InputStreamReader(s.getInputStream()));  
       PrintWriter w = new PrintWriter(s.getOutputStream(), true);  
       BufferedReader con = new BufferedReader(new InputStreamReader(System.in));  
       String line;  
       do {  
         line = r.readLine();  
         if( line != null )  
           System.out.println(line);  
         line = con.readLine();  
         w.println(line);  
       }  
       while ( !line.trim().equals("bye") );  
     }  
     catch (Exception err) {  
       System.err.println(err);  
     }  
   }  
 }  
 Server.java  
 import java.io.*;  
 import java.net.*;  
 public class Server {  
   private ServerSocket server;    
   public Server(int portnum) {  
     try{  
       server = new ServerSocket(portnum);  
     }  
     catch (Exception err) {  
       System.out.println(err);  
     }  
   }  
   public void serve() {  
     try {  
       while (true) {  
         Socket client = server.accept();            
         BufferedReader r = new BufferedReader(new InputStreamReader(client.getInputStream()));  
         PrintWriter w = new PrintWriter(client.getOutputStream(), true);  
         w.println("Welcome to the Java EchoServer. Type 'bye' to close.");  
         String line;  
         do {  
           line = r.readLine();  
           if( line != null )  
           w.println("Got: "+ line);  
         }  
         while ( !line.trim().equals("bye") );  
         client.close();  
       }  
     }  
     catch (Exception err) {  
       System.err.println(err);  
     }  
   }  
   public static void main(String[] args){  
     Server s = new Server(9999);  
     s.serve();  
   }    
 }  
 Output  
 Welcome to the Java EchoServer. Type 'bye' to close.  
 hi  
 Got: hi  
 whats up  
 Got: whats up  
 f9  
 Got: f9