java - StringIndexout of range -

i got error: stringindex out of range: -1 error line string anemail = linefromfile.substring(s+1, e). can see im trying print part of line in input file doesn't work. can me explain why?

import java.io.*;  public class email13  {     static boolean isvalidemailcharacter(char c)     {         boolean result = false;         if((c>='a'&&c<='z')||(c>='a'&&c<='z')||(c>='0'&&c<='9')||(c=='.')||(c=='-')||(c=='+'))             result = true;         return result;     }      public static void main(string[] args) throws exception{     bufferedreader cin, fin;     cin = new bufferedreader(new inputstreamreader(system.in));     //description     system.out.println("programmer: minh nguyen");     system.out.println("description: program start final project.");     system.out.println();          string namein, nameout, dein, deout;     namein="";     nameout="";     dein = "filecontainingemails.txt";      system.out.print("enter input filename [default:" + dein + "]: ");     namein = cin.readline();      if(namein.compareto("")==0){         namein = dein;       deout = "copypastemyemails.txt";         system.out.print("enter output filename [default:" + deout + "]: ");         nameout = cin.readline();         if(nameout.compareto("")==0)           nameout = deout;     }     else if(namein.compareto("")>0){         deout = namein;         system.out.print("enter output filename [default:" + deout + "]: ");         nameout = cin.readline();         if(nameout.compareto("")==0)           nameout = namein;     }     fin = new bufferedreader(new filereader(namein));     //read input file     while(true)     {         if(!fin.ready()) break;         string linefromfile;         linefromfile = fin.readline();         int s, e, hasdot;          (int = 0; < linefromfile.length(); i++) // each char in string...                    {       if(linefromfile.charat(i)=='@')       {           for(s=i;s>-1;s--)           {               if(isvalidemailcharacter(linefromfile.charat(s))==false)                   for(e=1; e< linefromfile.length(); e++)                   {                       if(isvalidemailcharacter(linefromfile.charat(e))==false)                       {                           string anemail = linefromfile.substring(s+1, e);                           system.out.println(anemail);                           break;                       }                    }           }          }                                                                       }    }      fin.close();      printwriter fout;     fout = new printwriter(new filewriter(nameout));     fout.close();           }  } 

suppose line has 10 characters. i loop goes 0 9.

you have s loop, goes i 0.

and inside that, access `linefromfile.substring(s+1);

so when i 9, s loop starts @ 9, , try access index 9+1, index 10, outside of line.