- Abstract classes can have constants, members, method stubs and defined methods.
- Methods and members of an abstract class can be defined with any visibility.
- A child class can only extend a single abstract (or any other) class.
- A child class can define abstract methods with the same or less restrictive visibility.
- Abstract class can have both abstract and concrete methods.
- In abstract class keyword ‘abstract’ is mandatory to declare a method as an abstract.
- Abstract class can have static, final or static final variable with any access specifier.
- Interfaces can only have consts and methods stubs.
- All methods of an interface must be defined as public.
- An interface can extend or a class can implement multiple other interfaces.
- A class implementing an interface must define the methods with the exact same visibility.
- Interface can have only abstract methods.
- In an interface keyword ‘abstract’ is optional to declare a method as an abstract
- Interface can have only static final (constant) variable i.e. by default.