The answer
The variable 'i' is the anchor point in the haystack. The variable 'j' is the offset. Adding them together allows the inner loop to scan forward in the haystack.
Nested Loops in Brute-Force String Matching
Why do we check haystack.charAt(i + j)?
More FAQs in Nested Loops in Brute-Force String Matching
It is an algorithm designed to find if a smaller string (needle) exists completely contiguous within a larger string (haystack).
The outer loop iterates through the haystack to set a starting point. The inner loop iterates through the needle to check if all characters match from that starting point.
This is a crucial boundary optimization. If the remaining characters in the haystack are fewer than the needle's length, it is physically impossible to find a match.
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