An interface is a lot like an abstract class. It too can have abstract functions, and any class that declares that it implements the interface needs to have an implementation of those abstract functions (or be an abstract class).

To declare that a class implements an interface, just add it after the superclass in a comma-delimited list. Since interfaces are not classes and do not have constructors, you just use the bare interface name, without () after it.

You can learn more about this in:

• the documentation
• Elements of Kotlin