Should capturing parentheses affect a separate negative lookahead?

Question

I am using Java. I have the following text:

"hyst and hy"

Why (hy)(?![a-z]) returns two "hy"s. The idea is to match any "hy" that is not followed by any character between a-z.

If I do hy(?![a-z]) (hy without parentheses) it works (finds only the second "hy") but I don't understand why if I use parentheses (hy) in the RegEx it matches the first "hy" in hyst

Answer 1

When you use a capture group you obtain two results, the first is the whole pattern and the second the capture group. The first hy has never been matched.

If you remove the parenthesis, you obtain only that match the whole pattern.