A short comparison of an abstract class and interface in Java.
| Abstract Classes | Interfaces |
|---|---|
| abstract class can have static, final or static final variable with any access specifier | interface can have only static final (constant) variable i.e. by default |
| abstract class can extend from a class or from an abstract class | interface can extend only from an interface |
| in abstract class keyword ‘abstract’ is mandatory to declare a method as an abstract | in an interface keyword ‘abstract’ is optional to declare a method as an abstract |
| abstract class can have both abstract and concrete methods | interface can have only abstract methods |
| abstract class can have protected , public and public abstract methods | interface can have only public abstract methods i.e. by default |
| a class can extend only one abstract class | a class can implement any number of interfaces |
| abstract class can extend only one class or one abstract class at a time | interface can extend any number of interfaces at a time |