大家帮我看看程序 谢谢大家
程序功能：在文本框中输入完整的url，按start，url会加到上面的列表中去，然后会开始扫描那个网页，找到有超文本链接的，就把它们都加到列表中，直到结束为止

问题   就是   Visit功能不能实现   ：
网页中运行的时候会出现这样的提示呢：Errorjava.security.AccessControlException:access   denied(java.net.SocketPermission   (网址):80   connect,resolve)  

import   java.awt.*;
import   java.awt.List;
import   java.applet.*;
import   java.net.*;
import   java.io.*;
import   java.util.*;
public   class   CrawLerApplet   extends   Applet   implements   Runnable
{    
        private   TextField   urlField=new   TextField(30);
private   List   links=new   List(10,false);
private   URL   u=null;
private   Thread   runner=null;
private   int   n=0;
public   void   init()
{
setLayout(new   BorderLayout());
Panel   p=new   Panel();
p.setLayout(new   FlowLayout());
p.add(urlField);
p.add(new   Button( "Start "));
p.add(new   Button( "Visit "));

add( "South ",p);
add( "Center ",links);
}
public   boolean   action(Event   evt,Object   arg)
{
if(arg.equals( "Visit "))
{
visit(links.getSelectedItem());
}
else   if(arg.equals( "Start "))
{
String   s=urlField.getText();
if(s.length()> 0)
{
add(s);
urlField.setText( " ");
if(runner==null)
{
runner=new   Thread(this);
runner.setPriority(Thread.MIN_PRIORITY);
runner.start();
}
}
}
else   return   super.action(evt,arg);
return   true;
}
public   void   visit(String   s)
{
if(s==null)   return;
try
{
AppletContext   context=getAppletContext();
u=new   URL(s);
context.showDocument(u, "Webpage ");
}
catch(Exception   e)
{
showStatus( "Error "+e);
}
}
void   add(String   s)
{
int   i;
for(i=0;i <links.countItems();i++)
if(links.getItem(i).equals(s))   return;
links.addItem(s);
repaint();
}
public   void   search(String   s)
{
if(s==null)   return;
try
{
AppletContext   context=getAppletContext();
u=new   URL(s);
showStatus( "Opening "+s);
InputStream   input=u.openStream();
showStatus( "Opened "+s);
Searcher   search=new   Searcher(input);
String   name;
while((name=search.nextURL())!=null)
add(name);
input.close();
showStatus( "Done ");
}
catch(Exception   e)
{
showStatus( "Error "+e);
}
}
public   void   run()
{
while(n <links.countItems())
{
String   s=links.getItem(n);
n++;
search(s);
runner.yield();
}
}
public   void   stop()
{
if((runner!=null)&&runner.isAlive())
runner.suspend();
}
public   void   start()
{
if(runner!=null&&runner.isAlive())
runner.resume();
}
public   void   destroy()
{
if(runner!=null&&runner.isAlive())
runner.resume();