trouble implementing counting sort for strings

I get this error when I attempt to sort it based off the second char in the string but it runs
fine when I use the first char

Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: Index -1 out of bounds for length 8
at StringCountSort.countingSort(StringCountSort.java:27)
at StringCountSort.main(StringCountSort.java:38)

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import java.util.Arrays;
public class StringCountSort{
public static void countingSort(String[] array, int size, int digit)
{
String[] result = new String[size+1];
int maximum = 122;
int[] count = new int[maximum + 1];
for (int i = 0; i < count.length; i++){
count[i] = 0;
}
for (int i = 0; i < size; i++){
count[array[i].charAt(digit)] +=1;
}
for (int i = 1; i < count.length; i++){
count[i] += count[i-1];
}
for (int i = size -1; i >= 0; i--){
result[count[array[i].charAt(digit)] - 1] = array[i];
count[array[i].charAt(0)]--;
}
for (int i = 0; i < size; i++) {
array[i] = result[i];
}
}
public static void main(String args[]){
String[] data = { "eg", "fa", "bz", "ch", "hv", "df", "ag" };
StringCountSort.countingSort(data, data.length, 1);
System.out.println("Sorted Array in Ascending Order: ");
System.out.println(Arrays.toString(data));
}
}

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line 28 result[count[array[i].charAt(digit)] - 1] = array[i]; 
line 37 StringCountSort.countingSort(data, data.length, 1); 

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Change

count[array[i].charAt(0)]--;

to

count[array[i].charAt(digit)]--;

This should do the trick.

I also suggest the following improvements:

1. You don't need to pass the length of array as an argument.
2. You don't need to set every int of count to 0;
3. maximum should be Character.MAX_VALUE, to support every possible character.

The finished function could look like this:

    public static void countingSort(String[] array, int digit) {
String[] result = new String[array.length];
int[] count = new int[Character.MAX_VALUE + 1];
for (int i = 0; i < array.length; i++){
count[array[i].charAt(digit)]++;
}
for (int i = 1; i < count.length; i++){
count[i] += count[i-1];
}
for (int i = array.length -1; i >= 0; i--){
result[count[array[i].charAt(digit)] - 1] = array[i];
count[array[i].charAt(digit)]--;
}
for (int i = 0; i < array.length; i++) {
array[i] = result[i];
}
}

Things that need to be changed are (if you want to sort the strings on the basis of first character)

1. count[array[i].charAt(digit)] +=1 to count[array[i].charAt(0)] +=1
2. result[count[array[i].charAt(digit)] - 1] = array[i]; count[array[i].charAt(0)]--; to result[--count[array[i].charAt(0)]] = array[i];

If you want to sort the string on the basis of the second character then simply change :

1. count[array[i].charAt(0)]--; to count[array[i].charAt(digit)]--;