The ArrayList is just a growable array and is presumably using an exponential growth strategy so it's equivalent to what several of the others are doing. You could indeed tell Java how big the ArrayList will grow in advance, but you could for example likewise do that with the Rust Vec by asking for Vec::with_capacity(num_tasks) instead of Vec::new().

Since this is amortized exponential growth it's likely making negligible difference, although it is good style to tell data structures what you know about their size early.

The Go approach doesn't appear to pay this penalty, it's just incrementing a (presumably atomic?) counter, although I have no idea where these tasks actually "live" until they decrement the counter again - but most of the others are likewise using a growable array.