a)for Future, we can provide extra services in Abstract 
Class ,these futures can able to access   all of its  
Clients. And also it supports reusability.
  suppose the implementer need not provide implementation 
for all the methods.
 
Where as in Interface we don’t have this future(reusability 
and extra servicess).
               each implementer need to provide 
implementation for all the methods and 
also                  we cont provide extra services in 
future.The interface should be constant.


b)Interface can support multiple  inheritance where as 
abstract class does not.