奇怪的readLine()

import java.net.URL;
import java.net.MalformedURLException;
import java.io.*;

 

class Test{
 public static void main(String args[]){
  URL root=null;
  URL url=null;
  String readstring;
  DataInputStream dis;
  try{
   root=new URL("http://localhost/");
   url=new URL(root,args[0]);
   
   dis=new DataInputStream(url.openStream());
   while ((readstring =dis.readLine())!=null){
    System.out.println(readstring);
   }
  
   System.out.println("***************** end of the file***********");
   dis.close();
  }catch(MalformedURLException e){
   System.out.println("MalformedURLException:"+e);
 }
  catch(IOException e){
   System.out.println("IOException:"+e);
  }
 }
}

 

 

 

运行后提示：

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 0
 at Test.main(Test.java:13)