伺服器端

import java.io.*;
import java.net.*;
public class Server
{
   public static void main(String args[])
{ 
     ServerSocket server=null;
     Socket you=null;
   DataInputStream in=null;
   DataOutputStream out=null;
  try
   {
      server=new ServerSocket(4331);
   }catch(IOException e)
   {
      System.out.println(e);
   }
    try{
       System.out.println("等待客戶呼叫");
      you=server.accept();
     out=new DataOutputStream(you.getOutputStream());
    in =new DataInputStream(you.getInputStream());
    while(true)
     {
       char c=in.readChar();
      System.out.println("伺服器收到："+c);
     out.writeChar((char)(c-32));
    Thread.sleep(500);
     }
    }
    catch(Exception e)
   {
      System.out.println("客戶已斷開"+e);
    }   
}   

}

客戶端

import java.io.*;
import java.net.*;
public class Client
{
   public static void main(String args[])
{ 
    
     Socket mysocket;
   DataInputStream in=null;
   DataOutputStream out=null;
  try
   {
      mysocket=new Socket("172.23.36.242",4331);
     out=new DataOutputStream(mysocket.getOutputStream());
       in =new DataInputStream(mysocket.getInputStream());
    char c='a';   
         while(true)
     {
       if(c>'z')
      c='a';
    out.writeChar(c);
   char s=in.readChar();
   System.out.println("客戶收到："+s);
 c++;
      Thread.sleep(500);    


}
   }catch(Exception e)
   {
      System.out.println(e);
   }
 
}   
}