Course Content
KOTLIN Tutorial
About Lesson

Abstract Classes and Interfaces

In the world of Kotlin programming, abstract classes play a crucial role in building robust and scalable applications. An abstract class is a class that cannot be instantiated and is typically used as a base class for other classes. In this post, we’ll delve into the concept of abstract classes in Kotlin, exploring their features and how they contribute to building flexible software solutions.

What is an Abstract Class?

An abstract class in Kotlin is declared using the abstract keyword. Unlike regular classes, you cannot create an instance of an abstract class. Instead, it serves as a blueprint for other classes, providing a common structure and behavior. Abstract classes can contain both abstract and non-abstract members.

Declaring Abstract Members

Abstract classes often include abstract members, which are methods without a body. These members must be implemented by the subclasses that extend the abstract class. This mechanism ensures that the subclasses adhere to a specific contract defined by the abstract class.

Implementing Abstract Classes

To use an abstract class in Kotlin, you need to create a subclass that inherits from the abstract class using the : symbol. The subclass must provide implementations for all the abstract members defined in the abstract class. This process enforces a level of consistency and structure in your codebase.

Exploring Interfaces in Kotlin

In addition to abstract classes, Kotlin supports interfaces, which provide another way to achieve abstraction and define contracts. Interfaces in Kotlin can include both abstract and non-abstract members, similar to abstract classes.

Defining Interfaces

An interface is declared using the interface keyword in Kotlin. It contains a set of method signatures, properties, and other members that the implementing classes must provide. Interfaces support multiple inheritances, allowing a class to implement multiple interfaces.

Implementing Interfaces

When a class implements an interface, it must provide concrete implementations for all the methods declared in that interface. This ensures that the class adheres to the contract specified by the interface. Kotlin’s concise syntax makes it straightforward to implement interfaces and achieve code reuse through multiple inheritance.

Abstract Classes vs. Interfaces

While both abstract classes and interfaces enable abstraction in Kotlin, they serve different purposes. Abstract classes provide a common base for subclasses to inherit and can contain both abstract and non-abstract members. On the other hand, interfaces define contracts that classes can implement, supporting multiple inheritances.

When to Use Abstract Classes or Interfaces

Choosing between abstract classes and interfaces depends on the specific requirements of your application. If you need a base class with some common functionality and want to share code among subclasses, abstract classes are a suitable choice. If you aim to define contracts and achieve multiple inheritances, interfaces are the preferred option.