abstract override of implemented method?

[Jeroen de Wolf]

Mooh...

In one of the pre-assessment exams on the internet I stumbled across an explanation belonging to a certain question which stated that is possible to make an abstract override of an implemented method. I verified it and it is indeed possible to do that, but what's the use of it. I fail to see the logic of it.

Jeroen de Wolf

[Steven Bell]

I suppose if you want to make a 'family' of classes that have a common superclass, and you want the compiler to make sure you override a certain method because the inherited functionality isn't appropriate. I can't think of a real example where it would be useful, but why not.

[Mike Gershman]

Suppose there is family of classes with an abstract superclass. Suppose that the Object.equals() method is definitely wrong for this family but each class must define equality differently.
Putting "public abstract boolean equals(Object obj);" in the superclass forces each subclass to define an appropriate equals() method.