pushkarajthorat

I dont understand why we need to implement same interface through the herarchie of class

example :

gives compilation error : Duplicate interface a for the type c


but

is working fine

__________________
[Pushkaraj]


Imagination is more important than knowledge – Albert Einstein

titaniumdecoy

Get rid of the ",a" in the first snippet.

pushkarajthorat

OK i think I have to make it more clear

Is there any good reason where we need to implement the interface in a class which is already implemented in some of its superclasses...

If you are giving the reason as, "if we have to change the functionality", then we could simply override function insted.

and if reason is, "If we have to get a reference of interface pointing the class object" then its already implementing the interface in superclass.

but I want to know that what we get extra if we implement the interaface, in subclass.

__________________
[Pushkaraj]


Imagination is more important than knowledge – Albert Einstein

titaniumdecoy

If a class implements interface I, its subclasses also implement interface I. It makes no difference whether these classes explicitly implement interface I.

physicist

in short, you get nothing extra. might as well not specify em

msi_333

As you know ,interfaces are with no any implementation , we often make the implementation of it in subclass rather than super class .Because it will be needed only in this subclass for example
if we have a super class X and two sub classes Y & Z, now if we implement the interface in X both Y ,Z will also inherit it ,But it will be not a good OOP design if class Y need this interface and class Z don't.So in this case to make it more simple we make the implementation in the subclass Y only and this will decrease the lines of code and make it easier to understand, .So it is a design trick and depends on your software engineering
work! . I hope what i wrote is useful to you my friend and good luck .

__________________
Don't walk in front of me, I may not follow.
Don't walk behind me, I may not lead.
Just walk beside me and be my friend

pegasus001

But will it work if you specify some methods in the interface a??? Because you have to implement two times the same methods, and it doesn't concern overloading. I don't see why you would do that.

__________________
You never test the depth of a river with both feet.
The believer is happy. The doubter is wise.
Free speech carries with it some freedom to listen.
The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

titaniumdecoy

Actually, it does concern overloading, and you do not have to implement the same methods more than once.

Imagine a non-abstract class A which implements interface I. As class A is not abstract, it must provide an implementation for any methods declared in I.

Now imagine class B extends class A. Class B need not implement any of the methods declared in interface I as the implementations for those methods are inherited from its superclass A.

However, if class B does provide implementations for some or all of the methods declared in I, those methods will take precedence over those defined in class A. In other words, when a method is called on an object, the VM looks for a definition first in that class, then in its superclass, and continues up the class hierarchy until an implementation is found.

I recommend this problem from my CS AP class in high school. It covers all of this and may be easier to understand.

pegasus001

It all makes sense now.

__________________
You never test the depth of a river with both feet.
The believer is happy. The doubter is wise.
Free speech carries with it some freedom to listen.
The next generation will always surpass the previous one. It`s one of the never ending cycles of life.

lectricpharaoh

To answer the OPs question, I think the reason that the implementation of an interface is made explicit when it's already implicit (due to a superclass implementing it) is to make things more clear. It is a good design idea, as it makes it easier for the programmer to determine if a given interface is implemented by a particular class (no need to check the hierarchy of classes). Functionally, though, it makes no difference.

__________________
And once again, Probability proves itself willing to sneak into a back alley and service Drama as would a copper-piece harlot.
- Vaarsuvius, Order of the Stick