UDP Server

import java.net.*;
class Server
{
    Server()
    {
        try
        {
            byte           buf[]  = new byte[200];
            DatagramPacket rDP    = new DatagramPacket(buf,200);
            
            DatagramSocket socket = new DatagramSocket(9000);
            for(int i=0;i<10;i++)
            {
                socket.receive(rDP);
                String str = PacketToString(rDP);
                System.out.println("from Client:"+str);
                //根据收到的信，来找到发信人，发信地址、发信名字
                InetAddress ip  = rDP.getAddress();
                int         port= rDP.getPort();
                
                Thread.sleep(1000);
                String info = "一物降一物";
                DatagramPacket sendPacket=StringToPacket(ip,port,info);
                socket.send(sendPacket);
                
                
            }
        }
        catch(Exception e)
        {
            System.out.println(e.getMessage());
            e.printStackTrace();
        }
    }
    
    public static void main(String s[])
    {
        new Server();
    }
    
    
    DatagramPacket StringToPacket(InetAddress ip,int port,String message)
    {
        int    length = message.length();
        byte   buf[]  = new byte[length];
        buf           = message.getBytes();
        DatagramPacket  dp = new DatagramPacket(buf,0,buf.length,ip,port);
        return dp; 
    }
    
    
    String PacketToString(DatagramPacket dp)
    {
        int  length = dp.getLength();
        byte buf[]  = new byte[length];
        buf         = dp.getData();
        String str  = new String(buf,0,length);
        return str;
    }
}