是程序本身有bug，还是java本身语句或者方法有bug呢？

lb_sean_he

最近看一本书，里面有个例子，关于网络编程方面的，如下：

1、服务端DatagramServer1 ：

import java.io.*;
import java.net.*;
import java.util.*;
/**
* <p>Title: </p>
*
* <p>Description: </p>
*
* <p>Copyright: Copyright (c) 2017</p>
*
* <p>Company: </p>
*
* @author not attributable
* @version 1.0
*/
public class DatagramServer1 extends Thread{
    DatagramSocket socket;
    DatagramPacket packet;
    int client;
    public DatagramServer1(DatagramSocket socket,DatagramPacket packet,int client) {
        this.socket = socket;
        this.packet = packet;
        this.client = client;
        this.start();
    }
    public void run(){
        try {
            byte[] received = packet.getData();
            System.out.println("Received from clinet = "+client+" "+new String(received));
            String response = "You are client"+client;
            byte[] buf = received;
            InetAddress address = packet.getAddress();
            int port = packet.getPort();
            packet = new DatagramPacket(buf,buf.length,address,port);
            socket.send(packet);
        } catch (IOException ex) {
            ex.printStackTrace();
        }
    }
    public static void main(String[] args)throws Exception{
        DatagramSocket socket = new DatagramSocket(4444);
        System.out.println("Server Started");
        byte[] buf = new byte[200];
        int i = 1;
        try {
            while(true){
              DatagramPacket packet = new DatagramPacket(buf,buf.length);
              System.out.println("Waiting for client = "+i);
              socket.receive(packet);
              new DatagramServer1(socket,packet,i);
              i++;
            }
        } catch (Exception ex) {
            ex.printStackTrace();
        }finally{
            socket.close();
        }
    }
}

2、客户端


import java.io.*;
import java.net.*;
import java.util.*;

/**
* <p>Title: </p>
*
* <p>Description: </p>
*
* <p>Copyright: Copyright (c) 2017</p>
*
* <p>Company: </p>
*
* @author not attributable
* @version 1.0
*/
public class DatagramClient {
    public DatagramClient() {
    }
    public static void main(String[] args) throws IOException{
        if(args.length!=2){
            System.out.println("Usage:"+"java DatagramClient <hostname> <message>");
            return;
        }
        DatagramSocket socket = new DatagramSocket();
        System.out.println("My message="+args[1]);
        byte[] buf = new byte[200];
        buf = args[1].getBytes();
        InetAddress address = InetAddress.getByName(args[0]);
        DatagramPacket packet = new DatagramPacket(buf,buf.length,address,4444);
        socket.send(packet);
        packet = new DatagramPacket(buf,buf.length);
        socket.receive(packet);
        String received = new String(packet.getData());
        System.out.println("The server returns my message:"+received);
        socket.close();
    }
}

问题在于：
比如：java DatagramClient hostName abc（hostName为主机名）
      客户机第一次向服务器输出了3个字符abc，服务器、客户机均显示正常
      第二次：java DatagramClient hostName 12，客户机真诚，但服务器显示12c

      服务器程序好像没有清除调似的！！？
      相关语句：byte[] received = packet.getData();
            System.out.println("Received from clinet = "+client+" "+new String(received));

如题，本人初学不久，对这个问题深感迷惑，请教大虾～谢谢！！

landddd

应该是服务器端的问题,应该在发送之后清空buf

lb_sean_he

应该和buf没有关系吧？显示错误的是new String(received)这里，每new一个DatagramServer1  （new DatagramServer1(socket,packet,i);） 也就意味着里面有一个局部变量received，默认值应该就为空了啊？

landddd

Server端的main方法中,将byte[] buf=new byte[200]
下移到 while(true)里面就应该没问题了

lb_sean_he

谢谢！