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

public class Receive extends Frame implements Runnable,ActionListener
{ 
  int port;                                        
  InetAddress group=null;                          
  MulticastSocket socket=null;                     
  Button 開始接收,停止接收;   
  TextArea 顯示正在接收內容,顯示已接收的內容;  
  Thread thread;                                   
  boolean 停止=false;
  public Receive()
   { 
     super("定時接收信息");
     thread=new Thread(this);
     開始接收=new Button("開始接收");
     停止接收=new Button("停止接收");
     停止接收.addActionListener(this); 
     開始接收.addActionListener(this); 
     顯示正在接收內容=new TextArea(10,10);
     顯示正在接收內容.setForeground(Color.blue); 
     顯示已接收的內容=new TextArea(10,10);
     Panel north=new Panel();
     north.add(開始接收);
     north.add(停止接收);
     add(north,BorderLayout.NORTH);
     Panel center=new Panel();
     center.setLayout(new GridLayout(1,2)); 
     center.add(顯示正在接收內容);
     center.add(顯示已接收的內容);
     add(center,BorderLayout.CENTER);
     validate();
     port=5000;                                       
     try{
         group=InetAddress.getByName("239.255.0.0");  
         socket=new MulticastSocket(port);            
         socket.joinGroup(group);           
                                            
       }
    catch(Exception e)
       {
       } 
   setBounds(100,50,360,380);   
   setVisible(true);
   addWindowListener(new WindowAdapter()
                     { public void windowClosing(WindowEvent e)
                       { System.exit(0);
      	               }
      	             });
                            
   }
  public void actionPerformed(ActionEvent e)
   {
    if(e.getSource()==開始接收)
      {
        開始接收.setBackground(Color.blue);
        停止接收.setBackground(Color.gray);
        if(!(thread.isAlive()))
           {
             thread=new Thread(this);
           }
        try
           {
             thread.start(); 
             停止=false;        
           }
        catch(Exception ee)
           {
           }
      }
    if(e.getSource()==停止接收)
      {
        開始接收.setBackground(Color.gray);
        停止接收.setBackground(Color.blue);
        thread.interrupt(); 
        停止=true; 
      }
   }

  public void run()
  {
   
    while(true)   
    {  
       byte data[]=new byte[8192];
       DatagramPacket packet=null;
       packet=new DatagramPacket(data,data.length,group,port);  
       try
           {  
             socket.receive(packet);
             String message=new String(packet.getData(),0,packet.getLength());
             顯示正在接收內容.setText("正在接收的內容:\n"+message);
             顯示已接收的內容.append(message+"\n");
           }
      catch(Exception e)
           {
           }
      if(停止==true)
           {
             break;
           } 
    } 
  }
 
 public static void main(String args[])
 { 
    new Receive();
 }
}