Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -1 when trying to find a palindrome

Issue

I am trying to make a program that sees if a word is a palindrome or not. However, I am getting the above error. When I run the program it puts together the word backwards, up until there are no more letters left. That is when I get the error.

// Programmer: Your name
// Class, Section and Term: ...
// Purpose: Find the average of a list of integer numbers. The list is ended with a sentiel value SENTINEL.
// Topic: while-loop
// Import the Scanner Class for input operations.

      import java.util.Scanner;

      public class SimpleProgram {

      public static void main(String[] args) {

      // Create the Scanner object, scnr, to perform input operations.

      Scanner scnr = new Scanner(System.in);

      // Declare the identifiers
      String reverse;
      reverse = "";
      int index;
      int number;         
      String letter;     
      final String end = "Stop";

  
   System.out.println("Please type a word:");
   letter = scnr.next();
      index = letter.length() + 0;

      
       while (!letter.equals(reverse) || (index >= 0)) {
        //  while (letter.equals(reverse.length() + 0));
         
            index--;
         
        
      
     // index = letter.length()-1 - index--;
      // index + 1;
     // System.out.println(index.CharAt(index--));
   
      reverse = reverse + letter.charAt(index);
      System.out.println(reverse);
      
          
      }
   if (letter.equals(reverse)) {
      System.out.println(letter + " is a palindrome!");
   }
  
   else {
      System.out.println(letter + " is not a palindrome, spelt backwards it is: " + reverse);
   
   }
   scnr.close();
   }
   
}

Solution

You need just the change the while condition look at my edition it's works !!

public static void main(String[] args) {

        // Create the Scanner object, scnr, to perform input operations.

        Scanner scnr = new Scanner(System.in);

        // Declare the identifiers
        String reverse;
        reverse = "";
        int index;
        int number;         
        String letter;     
        final String end = "Stop";

        System.out.println("Please type a word:");
        letter = scnr.next();
        index = letter.length() - 1;


        while (!letter.equals(reverse) && (index >= 0)) {
            //  while (letter.equals(reverse.length() + 0));
  
            // index = letter.length()-1 - index--;
            // index + 1;
            // System.out.println(index.CharAt(index--));

            reverse = reverse + letter.charAt(index);
            System.out.println(reverse);
            index--;


        }
        if (letter.equals(reverse)) {
            System.out.println(letter + " is a palindrome!");
        }

        else {
            System.out.println(letter + " is not a palindrome, spelt backwards it is: " + reverse);

        }
        scnr.close();

result :

olaalo is a palindrome!

Answered By - Med Elgarnaoui