Difference : Interface and Abstract class

              This is most common question in the interview room. Many of interviewee are confused or find them-self trapped while answering this question. Following are the basic  difference between the abstract and interface

Interface	Abstract Class
If we don't know anything about implementation, just we have requirement specification then we should go for interface	If we are talking about implementation but not completely (Partial implementation) then we should go for Abstract class
Inside Interface every method is always public and abstract, whether we are declaring or not. Hence interface is also considered as 100% Abstract class	Every method present in Abstract class need not be public and abstract. In addition to abstract methods we can take concrete method also
Every variable present inside interface is always public, static and final whether we are declaring or not	The variable present inside Abstract class need not be public, static and final
We can't declare interface variables with the modifiers : private, protected, transient and volatile	There are no restrictions on Abstract class variable modifiers
For interface variables compulsory we should perform initialization at the time of declaration otherwise we will get compile time error	For Abstract class variables it is not required to perform initialization at the time of declaration
Inside interface we can't declare instance and static block. Otherwise we will get compile time error.	Inide Abstract class we can declare instance and static block
Inside interface we can't declare constructors.	Inside Abstract class we can declare constructor, which will be executed at the time of child objectcreation.
We implements interface.	We extends abstract class