What is Reflection in Kotlin: Explanation and Examples

In Kotlin, reflection is a feature that lets a program inspect and modify its own structure at runtime, such as classes, functions, and properties. It allows you to access information about objects and call functions dynamically using kotlin.reflect APIs.

How It Works

Reflection in Kotlin works like a mirror that lets your program look at itself while running. Imagine you have a toolbox, but instead of just using the tools, you can also check what tools are inside, what they do, and even change them if needed. This is what reflection allows your code to do with classes, functions, and properties.

Under the hood, Kotlin provides a special set of tools in the kotlin.reflect package. These tools let you ask questions like "What functions does this class have?", "What is the name of this property?", or "Can I call this method dynamically?". This is very useful when you don’t know everything about the objects your program will handle until it runs.

Example

This example shows how to use reflection to get the name of a class and call a function dynamically.

kotlin

import kotlin.reflect.full.*

class Person(val name: String) {
    fun greet() = "Hello, my name is $name"
}

fun main() {
    val person = Person("Alice")
    val kClass = person::class

    println("Class name: ${kClass.simpleName}")

    val greetFunction = kClass.members.find { it.name == "greet" }
    val greeting = greetFunction?.call(person)

    println(greeting)
}

Output

Class name: Person
Hello, my name is Alice

When to Use

Reflection is useful when you need to work with code that is not fully known at compile time. For example, it helps in frameworks that automatically map data to objects, like serialization libraries or dependency injection tools. It also allows creating flexible code that can adapt to different classes or call methods dynamically.

However, reflection can slow down your program and make it harder to understand, so use it only when necessary, such as in testing, debugging, or building libraries that require dynamic behavior.

Key Points

• Reflection lets Kotlin programs inspect and modify their own structure at runtime.
• It uses the kotlin.reflect package to access class and function information.
• Reflection is powerful but can reduce performance and code clarity.
• Common uses include frameworks, testing, and dynamic method calls.

Key Takeaways

Reflection allows Kotlin code to examine and interact with its own structure during execution.

Use the kotlin.reflect package to access class names, properties, and functions dynamically.

Reflection is helpful for frameworks and dynamic programming but can impact performance.

Avoid overusing reflection to keep code simple and efficient.