问基本的服务器和客户端交互- Java

EN

    public class Server 
    {
    public static void main(String[] args) 
    {
    ServerSocket ss;
    try {
    ss=new ServerSocket(2018);
    Socket s=ss.accept();
    System.out.println("connected...");
    Handler h =new Handler(s);
    Thread t=new Thread(h);
    t.start();
    }catch(IOException ex)
    {
    ex.printStackTrace();
    }

//client handler.

    public Handler(Socket s) 
        {
            cs=s;
        }

        @Override
        public void run() 
        {

            try 
            {
            pw=new PrintWriter(cs.getOutputStream());
            sc=new Scanner(cs.getInputStream());
            pw.write("SERVER SAYS:Hello");
            pw.flush();
            System.out.println(sc.nextLine());

            }catch(IOException e)
            {
                e.printStackTrace();
            }
        //then the client.

         public class Client {
        public static void main(String[] args) 
        {
            Socket s;
            PrintWriter pw;
            Scanner sc;

            try {
            s=new Socket("localhost",2018);
            pw=new PrintWriter(s.getOutputStream());
            sc=new Scanner(s.getInputStream());
            pw.write("HELLO");
            pw.flush();
            String msg=sc.nextLine();
            System.out.println(msg);
            }catch(IOException e)
            {
            e.printStackTrace();
            }