Difference between Interface and Abstract Class.

 

	Interface	Abstract Class
1	If we don’t know about the 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	Inside interface every method is always public and abstract whether we are declaring or not. Hence interface is also considered as 100% pure Abstract class.	Every method present in Abstract class need not be public and Abstract. In addition to abstract methods we can take concrete methods also.
3	We can’t declare interface method with the following modifiers. Publicàprivate, protected Abstract->final, static, synchronized, native, strictfp	There are no restrictions on Abstract class method modifiers.
4	Every variable present inside interface is always public, static and final.	The variable present inside Abstract class need not be public static and final.
5	For interface variable, we must 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.
6	Inside interface we can’t declare instance and static blocks, otherwise we will get compile error.	Inside Abstract class we can declare instance and static blocks.
7	Insider interface we can’t declare constructors.	Inside Abstract class we can declare constructor, which will be executed at the time of child object creation.