Array Index Out Of Bounds - Java Recursive Method

Question

I am writing a program with 3 different methods to practice recursion. I have successfully implemented one of three, but I am a little stuck on the second right now. This method attempts to count the number of "smiles" (:)) in a character array. I thought I had it written correctly but when I test it out I keep getting an ArrayIndexOutOfBoundsException, but I'm not sure why. My method is as follows:

public static int countSmiles(char[] letters, int index) {

    int smileCounter = 0;

    //If the array is less than 2 in length it cannot include ":)".
    if(letters.length < 2) {
        return 0;
    }

    //If there is a smile increment the counter.
    else if(letters[index] == ':') {
        if(letters[index+1] == ')') {
            smileCounter++;
        }
    }

    //Increment the index
    index++;

    //Recursive assignment
    smileCounter = countSmiles(letters, index);

    //Return number of smiles
    return smileCounter;

}

And the method I am testing with is as follows:

public static void main(String[] args) {

    char[] JavaCharArray = {'r', 's', 't', 'u', ':', ')', 'v'};
    System.out.println(countSmiles(JavaCharArray, 0));
}

From my code it doesn't seem that the index I am trying to access (0) is negative nor greater than the provided array. I really just don't understand.

Pointing in right direction: What is a debugger and how can it help me diagnose problems? — Andreas
– Andreas, Commented Jan 31, 2020 at 3:12
Hint: Your stop condition is letters.length < 2, but letters.length never changes, so it'll never be true. Perhaps you should include the changing value (index) in the stop condition, somehow. — Andreas
– Andreas, Commented Jan 31, 2020 at 3:13
FYI: Down-voted for not attempting to debug your own code before asking us to debug it for you. — Andreas
– Andreas, Commented Jan 31, 2020 at 3:15
Alright thank you for your help. I will be sure to debug in the future before coming here, I apologize. — Brandon Bischoff
– Brandon Bischoff, Commented Jan 31, 2020 at 3:16
"it doesn't seem that the index I am trying to access (0) is negative nor greater than the provided array" The error occurs when index = 7, i.e. equal to the length of the array.. — Andreas
– Andreas, Commented Jan 31, 2020 at 3:19

DiogoSantana · Accepted Answer · 2020-01-31 03:16:58Z

1

In a recursive method, you need a stop condition. Try:

...
if(letters.length < 2) {
    return 0;
}

if (index + 2 > letters.length) {
    return 0;
}
...

answered Jan 31, 2020 at 3:16

DiogoSantana

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3 Comments

Brandon Bischoff Over a year ago

I get that I was missing my base case now, but it is now just returning 0 every time

DiogoSantana Over a year ago

I guess now you need to debug.

Brandon Bischoff Over a year ago

It was a simple mistake: forgot to add the smileCounter value of each method call to the next. Can't thank you guys enough for your help!

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