What is the difference between an Interface and an Abstract class ?

Interface  v/s  Abstract class

• All methods in an interface are implicitly abstract
• Abstract class may contain both abstract and non-abstract methods.

• A class may implement a number of Interfaces
• Abstract class can extend only one abstract class

• In order for a class to implement an interface, it must implement all its declared methods. However, a class may not implement all declared methods of an abstract class. Though, in this case, the sub-class must also be declared as abstract.
• Abstract classes can implement interfaces without even providing the implementation of interface methods.

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• Variables declared in a Java interface is by default final.

• An abstract class may contain non-final variables.

• Members of a Java interface are public by default.
• A member of an abstract class can either be private, protected or public.