Property Overriding in Kotlin

Introduction

Property Overriding 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.

Properties can also be overridden in subclasses. 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

• Properties can also be overridden in subclasses.
• Parent property must be open and child property must use override.
• Overridden properties follow the same rules as functions.

Syntax

open val type = "Base"

Property Overriding in Kotlin Example Program in Kotlin

open class Device {
    open val type = "Device"
}
class Phone : Device() {
    override val type = "Phone"
}

fun main(args: Array<String>) {
    println(Phone().type)
}

Sample Output

Phone

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. open val type = "Device" assigns or updates a value used later in the program.

3. override val type = "Phone" assigns or updates a value used later in the program.

4. The println(Phone().type) statement writes a line to the console — this produces part of the sample output below.

5. Properties can also be overridden in subclasses.

6. 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: properties can also be overridden in subclasses.
• 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

• Properties can also be overridden in subclasses.
• Parent property must be open and child property must use override.
• Overridden properties follow the same rules as functions.
• 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.