Difference Between Abstract Classes and Interfaces in Kotlin

9 min readApr 25

Abstract classes and interfaces are two powerful tools in Kotlin that help developers define contracts for classes that inherit from them. In this blog, we’ll explore those differences and learn when to use each one.

Imagine you want to build a car factory. To do that, you need to make sure that every car that comes out of your factory meets certain standards, such as having four wheels, an engine, and a steering wheel. But you don’t want to build every car yourself, so you’ll need to hire some workers to help you.

Now, think of abstract classes and interfaces as the contracts you give to your workers. An abstract class is like a blueprint for building a specific type of car, with some parts already built in. For example, you might have a blueprint for a sports car, with the engine and steering wheel already included, but with spaces left for the workers to add their own design to the exterior. So, each worker can use this blueprint to build their own version of a sports car, but they still have the flexibility to make their own design choices.

On the other hand, an interface is like a checklist that each worker has to follow, no matter what kind of car they’re building. So, instead of providing a blueprint for a specific type of car, you give each worker a list of requirements that every car they build must meet, such as having four wheels and an engine. This allows for greater flexibility in your car factory, since each worker can build their own version of a car as long as it meets the requirements on the checklist.

Abstract classes provide more specific details about the parts that need to be included in a car, while interfaces provide a more general set of requirements that every car must meet.

Abstract classes are more rigid in terms of the blueprint that needs to be followed, while interfaces are more flexible in terms of allowing for different designs as long as they meet the requirements.

What is an Abstract Class?

An abstract class is a class that cannot be instantiated, but can be inherited by other classes.

Abstract classes can contain both abstract and non-abstract methods with implementation details.


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