Programming Kotlin

Creating Interfaces and Abstract Classes

Object-oriented programming is programming with hierarchies of abstractions—complex applications typically have multiple interfaces, abstract classes, and implementation classes. We heavily rely on interfaces to specify behavior of abstractions and use abstract classes to reuse implementations. So learning about interfaces and abstract classes is a good starting point for learning about building object-oriented hierarchies.

In recent years interfaces have dramatically evolved in Java. In the past, interfaces were permitted to carry only method declarations and no implementation: they could tell a lot about what’s possible, but never did anything—kinda like my boss. In recent versions of Java, interfaces ...