Inheritance Basics in Kotlin

Introduction

Inheritance Basics is a fundamental concept every Kotlin developer should understand. Inheritance models is-a relationships and enables code reuse. Kotlin classes are final by default, so you opt in to subclassing deliberately.

Inheritance allows a child class to reuse properties and functions of a parent class. In this tutorial you will learn the syntax, walk through a complete example program, study the sample output, and review best practices so you can apply the concept confidently in your own projects.

Definition

• Inheritance allows a child class to reuse properties and functions of a parent class.
• Kotlin classes are final by default; use open to allow inheritance.
• A subclass can extend only one superclass.

Syntax

open class Parent
class Child : Parent()

Inheritance Basics in Kotlin Example Program in Kotlin

open class Animal(val name: String) {
    open fun speak() = println("$name makes a sound")
}

class Dog(name: String) : Animal(name) {
    override fun speak() = println("$name barks")
}

fun main(args: Array<String>) {
    Dog("Bruno").speak()
}

Sample Output

Bruno barks

When to use

Use inheritance when a subclass truly is-a parent type and shares an interface, not just to reuse a few helper methods.

How it works

1. The program starts with a main function — the entry point that runs when you execute the file.

2. The println("$name makes a sound") statement writes a line to the console — this produces part of the sample output below.

3. The println("$name barks") statement writes a line to the console — this produces part of the sample output below.

4. Inheritance allows a child class to reuse properties and functions of a parent class.

5. Run the program in IntelliJ IDEA, Android Studio, or with the Kotlin command-line compiler (kotlinc / kotlin). Compare your console output with the sample output shown below.

Best Practices

• Understand the core idea: inheritance allows a child class to reuse properties and functions of a parent class.
• Prefer readable names and small functions so examples map directly to real projects.
• Run and modify the example — change values and observe how the output changes.

Common Mistakes

• Skipping the example and only reading the definition — hands-on practice cements the concept.
• Copying syntax without understanding nullable vs non-nullable types or scope rules.
• Ignoring compiler warnings that often point to safer alternatives.

Key Points

• Inheritance allows a child class to reuse properties and functions of a parent class.
• Kotlin classes are final by default; use open to allow inheritance.
• A subclass can extend only one superclass.
• Test the example locally and verify the output matches the sample.
• Experiment by changing input values to see how behaviour changes.

Notes

• Semicolons at the end of statements are optional in Kotlin.