I am wondering whether Object is superclasses of “loose” abstract classes as well, i.e. the abstract classes that do not extend other abstract classes. I don’t see this mattering much in effect. But how is the “formal” wording on this one when putting things all together.
The following support and contradict the Q in the subject line the way i see it:
Supporting (“Yes” to Q above): i.) A concrete class can inherit from an abstract one, ii.) every class is a descendant of Object, and iii.) every class (except Object) has exactly one superclass. If Object weren’t a superclass to abstract classes,
then (iii) should necessarily be violated for the special case of Object— “a class can have two superclasses iff one of them is Object and the other is an abstract one.”
Contradicting (“No” to Q): An abstract class cannot be sub to a concrete one, and Object is concrete. But then, this too can be phrased as “for the special case of Object class.”
Is it more on one side than the other, or is it merely something like “a bit of both– exceptional for the Object class”. thanks in advance.
Note: i read the discussions on
Why java.lang.Object is not abstract?.
Correcting my obvious mistake in the original message above:
Abstract classes can apparently inherit from concrete ones. That makes Object their superclass as well.
The think I think you are confused about is that it is legal for an abstract class to inherit a Concrete class. It’s fairly rare, but it can happen. This question shows quite a few examples of such.