How to find a Needle in a Haystack in Java without using any library functions of String class. String class is modified so that we can only use charAt(index) which returns '$' if index is out of bound. We are not even allowed to use .length etc . What would be the brute force and optimal way to solve this problem.

public int findNeedle(String haystack, String needle){
}

For Example:   
Haystack:  "applepieorange"
Needle: "apple"  
should return 0 

Thanks