shreyas Kulkarni

Can anyone please tell me what are the advantages of using Null object pattern? I tried to search too. I used it in my doubly linked list as first and last node(head and tail) but I am not able to figure out its use.
Thanks

If you implement any interface for your class like
class x implements yourInterface
then you have to write every abstract method you have in that interface. So you can force to override all those methods by using interface.

We can achieve multiple inheritance means, we can implement as many interfaces as we want but in java, we can extend only 1 class.. So sometimes its advisable to use interface instead of abstract class dependng on your design.

Yes, we cant write any code in methods of interface. Just declaration. The concrete class that implements interface has to write all the methods.
Hope you find it useful.

Ya but I guess that also will not be the only reason, because its quite understandable when I said him(interviewer)its for validating data. so we can validate means eg: not allowing users to set value to null. I am not saying what you said is wrong but is there anything else with this?

Not sure whether I am writting at correct place or Not:-

Can anyone answer me, Why data members are private when we can access them through getter/setters?. why we dont make it public then?

-I gave answer like, if you want to validate your data, like adding some condition kinda, you can do it by adding just that code in getter and it will reflect everywhere but if it is public we have to change code everywhere..
And same for setter we can have validation like not greater or less than this etc....
But interviewer was still not happy...
Any other addition to my answer?