import java.io.*;import java.net.*;public class HelloServer{public static void main(String args[]) throws IOException    {        ServerSocket serverSocket = null;        PrintWriter out = null;try{            serverSocket = new ServerSocket(9999);        }catch(IOException e)        {            System.err.println("Counld not listen on port:9999");            System.exit(1);        }        Socket clientSocket = null;try{            clientSocket = serverSocket.accept();        }catch(IOException e)        {            System.err.println("Accept failed");            System.exit(1);        }        out = new PrintWriter(clientSocket.getOutputStream(),true);        out.println("hello world!");        clientSocket.close();        serverSocket.close();    }}

import java.io.*;import java.net.*;public class HelloClient{public static void main(String args[]) throws IOException    {        Socket helloSocket = null;        BufferedReader in  = null;try{            helloSocket = new Socket("172.20.223.73",9999);            in = new BufferedReader(new InputStreamReader(helloSocket.getInputStream()));        }catch(UnknownHostException e){            System.err.println("Don't know about host:localhost!");            System.exit(1);        }catch(IOException e)        {            System.err.println("Couldn't get I/O for the connection");            System.exit(1);        }        System.out.println(in.readLine());        in.close();        helloSocket.close();    }}