how do I fix a "string index out of bounds" error

[Keith Tremorin]

What am I doing wrong. I have been looking over this code for hours and Im sure its a simple fix.

import java.util.Scanner;
 
public class TremorinKeithA2Q1 {
 
public static void main(String[] args) {
 
  Scanner kbd = new Scanner(System.in);
 
  String esparanto;
  int len =0;
  char lastLetter;
    System.out.println("Please enter a word in Esperanto");
    esparanto = kbd.next();
 
    while (!esparanto.equals("cesi")) {
    len = esparanto.length();
    lastLetter =  esparanto.charAt(len);
    System.out.println(lastLetter);
 
    if(lastLetter == 'a') {
        System.out.println("That number is an adjective");
    }if(lastLetter == 'e'){
        System.out.println("That number is an adverb");
    }
 
 
 
 
 
}
}
}
 

I can compile it but when I run it I get:

Please enter a word in Esperanto
konkopa
Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String ind
ex out of range: 7
at java.lang.String.charAt(String.java:686)
at TremorinKeithA2Q1.main(TremorinKeithA2Q1.java:17)
Press any key to continue . . .

[Nepomuk]

The problem is with the line

lastLetter =  esparanto.charAt(len);

The characters are numbered from 0 to len - 1, so if you change it to

lastLetter =  esparanto.charAt(len - 1);

it should work as intended.

Greetings,
Nepomuk