title: String index out of range -8
body: <p>I don't absolutely see a reason why the index is out of range. 
  the start is from the letters <code>atg</code> in the string <code>ataaactatgttttaaatgt</code> and ends with <code>taa</code>. What am I missing here?</p>
  
  <p>Edit: This is the line right here       </p>
  
  <p><code>String subStr1 = dna.substring(start,stop1);</code></p>
  
  <pre><code>/**
  
   *
   * @author Duke Software Team 
   */
  import edu.duke.*;
  import java.io.*;
  
  public class TagFinder2 {
  
  
    public String findProtein(String dna) {
      int start = dna.indexOf("atg");
  
      int stop1 = dna.indexOf("tag", start+3);
      int stop2 = dna.indexOf("tga",start+3);
      int stop3 = dna.indexOf("taa",start+3);
  
  
      String subStr1 = dna.substring(start,stop1);
      String subStr2 = dna.substring(start,stop2);
      String subStr3 = dna.substring(start,stop3);
  
      String result;
  
      if( subStr1.length() % 3 ==0 ){
        return subStr1;
      } else if (subStr2.length()%3==0){
        return subStr2;
      } else if (subStr3.length()%3 == 0) {
        return subStr3;
      } else {
  
        return "";
      }
    }
  
    private void stopCodon(String gene){
      //This prints out the last 3 characters of the gene
  
      String stopCodon = gene.substring(gene.length() - 3);
      System.out.println(stopCodon);
    }
  
    public void testing() {
      String a = "ataaactatgttttaaatgt";
      String b = "acatgataacctaag";
      String c = "AATGCTAGTTTAAATCTGA";
  
      String result = findProtein(a);
  
      stopCodon(result);
  
    }
    //public String stopCodon(String dna){
    //   return 
    //  }
  
  
  }
  </code></pre>