About Question enthuware.ocajp.i.v7.2.877 :

[Russtam]

I think its also need to add calculateArea() call to constructor, because after constructing instance data will left inconsistent.

[Hiar85]

I think its also need to add calculateArea() call to constructor, because after constructing instance data will left inconsistent.

I agree

[admin]

That would be required if the question were asking you about the invariant i.e. area must be consistent with the length. As of now the question is only about encapsulation.
I have updated the constructor to update area as well in any case.

thank you for your feedback!
Paul.