Similarities and Difference b/w Interface and Abstract class

Similarities b/w Interface and Abstract class:
1. We can't create a object of both Interface and Abstract class.
2. We create object of the class who inherit either abstract class of interface.
3. abstract methods are contained in both interface and abstract classes.

Differences b/w Abstract class and interface:

S.No	Interface	Abstract Class
1	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
2	Every method is always public and abstract whether we are declaring or not. Hence interface is 100% abstract class	Every method present in Abstract class need not be public and abstract. And Abstract class is having abstract methods as well as concrete methods also
3	Every variable is always public,static and final whether we are declaring or not	There is no restriction here
4	For interface variables compulsory we should perform initialization at the time of declaration otherwise we would get Compile time error	For Abstract class variables its not required to perform initialization at the time of declaration
5	It supports Multiple Inheritance	By extending abstract class you can not extend another class because Java does not support multiple inheritance
6	we cannot create constructor	we can create constructor
7*	when you add a new method in existing interface it breaks all its implementation and you need to provide an implementation in all clients which is not good.	By using abstract class you can provide default implementation in super class.