这段代码有什么问题

Question

 try 
             { 
           process =runtime.exec("ping "+ip[0]+" -n 1"); 
           is = process.getInputStream(); 
           isr=new InputStreamReader(is); 
            br =new BufferedReader(isr); 
            out.println("<pre>"); 
              while( (line = br.readLine()) != null ) 
               { 
               
                if(line.lastIndexOf( "回复")!=-1){ 
               
               String   time; 
            time=line.substring(line.lastIndexOf( "来自")+4,line.lastIndexOf( "TTL")-16/*若要仅得到数值，此处加上   -3   */); 
            out.println(time); 
            out.println(line); 
             
          
     
             } 
          out.println("</pre>"); 
            is.close(); 
            isr.close(); 
      br.close(); 
           }
           
           
           }//end of try
                catch(IOException e ) 
                { 
                   out.println(e); 
                   runtime.exit(1); 
                     } 其实关于subString的用法有错吗?