About Question com.enthuware.ets.scjp.v6.2.759 :

[ETS User]

The instructions on this question are less than helpful.

[ETS User]

It should be obvious that you have to provide a correct implementation of hashCode that meets the contracts of both equals and hashCode. It should be an automatic response to check for this.

The rule of thumb is that if a member is used in hashCode, it must be used in equals. The opposite is not true, however, as we see in this question.

[aitorbk]

I fully agree with the reply: if you use a member not used in equals, you are breaking the contract:if they are equal they should have the same hashcode, and if you use interests, they would be "equal" but with a different hashcode!!