[java]数组声明引发聊天室小程序无法运行

     这是一段经典的聊天室实现代码，通过DatagramSocket和DatagramPacket来发送和接受数据，使用的是UDP网络协议，程序出错的原因是声明的字符型数组 byte []buf ;在后面不可以使用，提示找不到字符，我输入buf.也并没有参数提示。奇怪，不得其解！

程序清单 Chat.java

import java.awt.*;
import java.awt.event.*;
import java.net.*;

/** *//**
 * 一个小型聊天室的实现
 */
 
 public class Chat
 ...{
     Frame f = new Frame("我的聊天室");
     TextField tfIP = new TextField(15); //15为行列
     List ls = new List(6);
     DatagramSocket ds;
     /**//*由于DatagramSocket的构造函数可能抛出异常，我们程序需要用try...catch扑获异常
      *所以不能直接在这里调用DatagramSocket的构函对ds进行初始化，我们需要将ds的初始化放在Chat
      *类里面去初始化
      */
      public Chat()
      ...{
          try
          ...{
              ds = new DatagramSocket(3000);
          }
          catch(Exception e)...{};
          
          new Thread(new Runnable()
          ...{
              public void run()
              ...{
                  byte [] buf = new byte[1024];
                  DatagramPacket dp1 = new DatagramPacket(buf,1024);
                  while(true)
                  ...{
                      try
                      ...{
                         ds.receive(dp1);
                         String strRecv = new String(buf,dp1.getLength())+" from "+
                             dp1.getAddress().getHostAddress();
                         ls.add(strRecv,0);
                      }
                      catch(Exception e)
                      ...{
                          e.printStackTrace();
                      }
                  }
              }
          }
          ).start();
      }
     
     public static void main(String[] args)
     ...{
         Chat chat = new Chat();
         chat.init();
     }
     
     public void init()
     ...{
         f.setSize(400,400);
         f.add(ls);
         
         Panel panel = new Panel();
         panel.setLayout(new BorderLayout());
         panel.add("East",tfIP); //添加组件
         TextField tfData = new TextField(20);
         f.add("South",tfData);
         f.setVisible(true);
         f.setResizable(false); //限制用户改变窗口大小
         
         //增加关闭窗口的事件处理代码
         f.addWindowListener(new WindowAdapter()
         ...{
             public void windowClosing(WindowEvent e)
             ...{
                 ds.close(); //关闭socket
                 f.setVisible(false);
                 f.dispose();
                 System.exit(0); //退出系统
             }
         });
         
         //增加在文本框输入值按下回车键的响应代码
         tfData.addActionListener(new ActionListener()
             ...{
                 public void actionPerformed(ActionEvent e)
                 ...{
                     //取出文本中的字符,并将其转换成字符数组
                     byte buf[];
                     buf = e.getActionCommand().getBytes();
                     //程序错误处，编译提示无法找到符号 buf
                     DatagramPacket dp = new DatagramPacket(buf,buf.length,
                         InetAddress.getAllByName(tfIP.getText()),3000);
                     try
                     ...{
                         ds.send(dp);
                     }
                     catch(Exception ex) //这里用ex代替e，因为e已经被使用了
                     ...{
                         ex.printStackTrace(); 
                     }
                     //清空发送数据后的文本框
                     ((TextField)e.getSource()).setText("");
                 }
             });
     }
 }