HFE page 426

[Sany Bel]

Question no. 4
Given the following container-manager unidirectional relationship
Foo(0-1) -> Bar(0-1)
And the object realtions:
f1 -> b1
f2 -> b2
What will be true after the following code runs ?
f2.setBar(f1.getBar());
A. f1.getBar() == null;
B. b2.getFoo() == null;
C. b1.getBar() == null;
D. None of the above
I got the answer right first time. A & B.
But when I thought about it again can we have b2.getFoo(). It is a "unidirectional" relationship and Foo has a field for Bar. Can Bar have a field for Foo too?

[Nathaniel Stoddard]

Sany,
The whole point of the question is to test your knowledge of what happens when you take members of one association and put it in another one. In this case, since it's a 1-to-1 association, taking b1 and associating it with f2 disassociates b2 from any f-object and disassociates f1 from any b-object.
So, f1.getBar() == null, f2.getBar() == b1. B-objects don't have any links to their associated f-object, so b2.getFoo() doesn't mean anything. B-objects also don't have any association with other B-objects, so b1.getBar() doesn't have any meaning either.
In the end, the answer is A. B and C are false because they would be syntactically invalid given the unidirectional nature and structure of the question. D is incorrect since A is correct. Therefore, only A is correct.

[Sany Bel]

Exactly!! That's my point. But the book says both A & B are correct. That is the reason I am confused. As I mentioned, when I looked at it the second time, I thought only A should be correct given the unidirectional nature of the relationship.

[Nathaniel Stoddard]

Sany,
Oh -- well in that case you're right.

[Leon Chen]

I think b2 should not have a getFoo() method.

[Vishwa Kumba]

http://www.oreilly.com/catalog/hfjejb/errata/hfjejb.unconfirmed
p:432, Q:4 error.

[Leon Chen]

Vishwa, that is unconfirmed.