An interface is a programming construct that defines a contract for classes or objects. It specifies a set of methods, properties, and events that a class or object must implement. Interfaces provide a way to achieve abstraction and polymorphism by defining a common set of behaviors that multiple classes can adhere to, regardless of their specific implementations.
An interface specifies what a class or object or function should do (i.e. its behavior) without dictating how it should do it. This promotes code modularity and separation of concerns.
An interface typically contains a signature (i.e. a method name, return types, and parameter list) but do not provide method bodies. Classes that implement an interface must supply concrete implementations for the methods defined in the interface.
Interfaces facilitate polymorphism, allowing objects of different classes to be treated uniformly if they implement the same interface. This enables dynamic binding and enhances flexibility and extensibility in software design.
Interfaces are useful in testing because they allow you to create mock objects or stubs that implement the same interface as the real objects they replace. This simplifies testing and isolates components.
In many programming languages, classes can implement multiple interfaces, allowing them to inherit behaviors from multiple sources. This is often seen as a solution to the "diamond problem" that arises with multiple inheritance of classes.