Need help finding index of char in a string

[chocolate-glaze]

Hi!
I'm trying to write a method that finds the index of a specified occurrence of a character in a given string using recursion. I've managed to count the number of times a character occurs in the string, but can't figure out how to find the index of a particular character using recursion.

Any help would be greatly appreciated. Here is my code so far:

public static int nthIndexOf (int n, char ch, String str) {
		if (str == null || str.equals("") || n <= 0) {
			return -1;
		}
		
		int restOfString = nthIndexOf(n,ch,str.substring(1));
		if (ch == str.charAt(0)) {
			restOfString++;
		}
		
	/*	if (n != (restOfString + 1)) {
			restOfString = nthIndexOf(n,ch,str.substring(1));
		}*/
		
		return restOfString;
	}