About Question enthuware.ocpjp.i.v11.2.868 :

[Deleted User 6318]

In the exam, you may get a question that says "100 characters", in that case, ensureCapacity() may not be a valid option.

And then what would be valid way?
I see there is even no such simple field in StringBuilder nor AbstractStringBuilder as capacity, it's somehow not that clearly for me calculated...

[admin]

There is no way to ensure the capacity at exactly 100 (or any specific number). The point is to read the problem statement carefully.