Which type of method can be included in an interface?

An interface in ABAP cannot include static methods, private methods, or protected methods, as these do not align with the fundamental purpose and nature of an interface. An interface is designed to define a contract that must be implemented by any class that adheres to it, primarily focusing on instance methods.

In the context of object-oriented programming, instance methods in interfaces are accessible to any class that implements the interface, allowing for polymorphism and adherence to a specific functionality outlined by the interface. Therefore, the correct type of method that can be included in an interface is indeed instance methods, making them the primary focus within an interface structure. This allows various classes to implement these methods in their own way while conforming to the same defined contract, promoting code reusability and flexibility in design.