Which of these accurately describes an interface?

An interface in object-oriented programming is a type that is used to specify a contract for classes. It defines a set of method signatures that any implementing class must fulfill. This means that an interface serves as a blueprint, defining "what" methods a class must implement without providing the actual logic or body of those methods. This characteristic of containing only method signatures without implementation is fundamental to the role of interfaces in promoting abstraction and decoupling in code design.

By adhering to this principle, implementing classes can provide their specific implementations of the defined methods, while clients of the interface can rely on the defined behaviors without needing to know the details of those implementations. Consequently, interfaces are pivotal in achieving polymorphism and enabling multiple classes to share common functionality while still being distinct entities.

The other choices describe characteristics that do not define an interface accurately. For instance, stating that an interface is a class that cannot be instantiated is misleading because an interface is not a class at all but a different construct focused on behavior rather than instantiation. The idea of multiple constructors applies to classes but not to interfaces, which do not possess any constructor implementations. Lastly, while interfaces can provide an alternative to inheritance concerning method implementations, they primarily function as a means of achieving multiple inheritance of behavior,