Inheritance — Basics

Basic features of inheritance in Kotlin — closed by default, implicit inheritance of Any, with a quick note about the execution order of initializers

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THE CURRENT VERSION OF THIS ARTICLE IS PUBLISHED HERE.

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Tags: #FYI

This article is part of the Kotlin Primer, an opinionated guide to the Kotlin language, which is indented to help facilitate Kotlin adoption inside Java-centric organizations. It was originally written as an organizational learning resource for Etnetera a.s. and I would like to express my sincere gratitude for their support.

It is recommended to read the Introduction before moving on. Check out the Table of Contents for all articles.

Probably one of the most controversial design decision in the Kotlin language is the fact that classes (and class members) are closed by default. This means that to be able to extend a class (or override a class member), it must explicitly be marked using the open keyword. Classes (or class members) which are not marked in this way cannot be extended.