title: getting java.lang.StringIndexOutOfBoundsException error
body: <p>while i am doing a simple cipher program. i was encounter this error</p>
  
  <pre><code>Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1
  at java.lang.String.charAt(Unknown Source)
  at Caesar.main(Caesar.java:27)
  </code></pre>
  
  <p>well, i am not quite clear on what is the cause. i require some help from some veteran here @@ below are my code.</p>
  
  <pre><code>import java.util.Scanner;
  import java.io.FileReader;
  import java.io.IOException;
  import java.io.PrintWriter;
  
  public class Caesar {
  
      public static void main(String[] args){
           String from = "abcdefghijklmnopqrstuvwxyz";
           String to   = "feathrzyxwvusqponmlkjigdcb";
              Scanner console = new Scanner(System.in);
              System.out.print("Input file: ");
              String inputFileName = console.next();
              System.out.print("Output file: ");
          String outputFileName = console.next();
  
          try{ 
              FileReader reader = new FileReader("C:/"+inputFileName+".txt");
              Scanner in = new Scanner(reader);
              PrintWriter out = new PrintWriter("C:/"+outputFileName+".txt");
  
                  while (in.hasNextLine()){
                      String line = in.nextLine();
                      String outPutText = "";
                      for (int i = 0; i &lt; line.length(); i++){
                          char c = to.charAt(from.indexOf(line.charAt(i)));
                          outPutText += c;
                      }
                      System.out.println("Plaintext: " + line);
                      System.out.println("Ciphertext: " + outPutText);
                      out.println(outPutText);         
                  }
                  System.out.println("Processing file complete");
                  out.close();
          }
          catch (IOException exception){ 
              System.out.println("Error processing file:" + exception);
          }
  }
  }
  </code></pre>