Inheritances

[AlbaLed]

There are two types of inheritances, interface inheritance and implmentation inheritance. Define their differences. Define their advantages and disadvantages?

 

 

[wood]

 

[*]Interface inheritance models "is-a'' relationships. This means that a derived class can perform all actions the base class can perform. The derived class may add further methods; however, it cannot remove methods. The derived class may alter the how actions are done. Interface inheritance creates subtype - supertype relations.

 

[*]Implementation inheritance makes the (non-private) methods of the base class available for the derived class. In C++ the implementation is automatically inherited whenever the interface is inherited; pure implementation inheritance is also possible using a private base class. This is a "uses'' relationship. It is a rarely used technique.

 

From this link

[AlbaLed]

Interface inheritances could detrement performance if they are the only form of inheritance supported. While implementation inheritances have a more serious flaw, suppose we change the superclass, and delete a variable used by all the subclasses then when the programs are compiled a nice-not-easy-to-find error is created.

Solution ?? Simple, support both, let the programmer do the decision.

 

One more

Are subclasses subtypes ?

[wood]

Nope... Check this out.

 

 

[AlbaLed]

"Nevertheless, we note that most existing object-oriented programming languages do identify type and class as well as subtype and subclass. That is, a class is identified with the type of objects it generates, while only subclasses generate subtypes",

 

Quote from your link.

[AlbaLed]

wood any thoughts on this??

[wood]

As mentioned at the beginning of the paragraph, there's a clear theoretical difference between subclasses and subtypes. However, some languages might just treat the concepts as one and the same, providing what inheritance and subtyping capabilities it supports. Did I misunderstand anything?

 

[AlbaLed]

In order to be a subtype, the methods of the subclass must satisfy the superclass's specifications. That is if a correct "is-a" relationship holds that's when a subclass can be called a subtype. Subclasses can be subtypes if they are well behaved, for example if you subclass a class called PlanarShape which provides Area() and make a Cube where Area() returns volume, there is no subtyping because a Cube "is not a" (not "is-a")PlanarShape. check this link out it seems good

http://6170.lcs.mit.edu/www-archive/Old-2001-Spring/recitations/recitation4.html

[Vinay]

well thr r so many different concepts regarding inheritance lying thr but basic remains tht supertype-subtype one.

 

the thing is tht ETS cannot provide us questions tht can have multiple definations like inheritance,parameter passing etc. though if they refer to these topics I think they will definately focus on things tht r very general or otherwise a question can become ambiguous.

 

The best thing tht they do is tht they define wht they r talking abt in questions so you know wht they r talking abt. this is evident frm the practice test.

[wood]

Thanks for the link AlbaLed.. now it seems clear.

 

Yeah Vinay.. I agree with you. Sometimes we go a little overboard in a discussion, however, that doesn't hurt us much. We will never forget about the subject now.

 

Wood