Java: StringIndexOutOfBoundsException when using .charAt() in for-loop

Question

thank you in advance for reading about my problem.

I am making a Hangman game where I want to print out a hidden version of the current word, but I would like to update it when a correct letter is guessed (on the right spot, too). I've been looking around StackOverflow but I just can't seem to find an explaination that I understand. If someone could help me, that would be great. :D

I'll post the for-loop that this is about. I can post more of the code if you might need it. The answerInput and guessInputString are both read from the console earlier in my code using a br.readLine() method.

for (int i = 0; i < inputAnswer.length(); i++) {

    char inputAnswerChar = inputAnswer.charAt(i);

    char guessInputChar =guessInputString.charAt(i);

    if (inputAnswerChar == guessInputChar) {

        replacementString.replace(replacementString.charAt(i), inputAnswerChar);
    }

}

Thank you for any help that you can give me!

Answer 1

Your code is assuming that guessInputString and replacementString both have at least as many characters as inputAnswer , which is obviously wrong to assume, since your loop only guarantees that the i 'th character exists for the inputAnswer String.

BTW, replacementString.replace(replacementString.charAt(i), inputAnswerChar) has no effect, since it cannot change the String it is executed for (since String s are immutable). You must assign the new String returned by this method back to replacementString :

replacementString = replacementString.replace(replacementString.charAt(i), inputAnswerChar)