Annotation Targets in Kotlin

Introduction

Annotation Targets is a fundamental concept every Kotlin developer should understand. Annotations attach metadata to declarations. Frameworks like Spring, Retrofit, and Room read them to configure behaviour at compile or runtime.

Use @Target to specify where annotation can be applied. 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

• Use @Target to specify where annotation can be applied.
• Kotlin supports FIELD, PROPERTY, FUNCTION, CLASS and more.
• Correct targets avoid misuse of annotations.

Syntax

@Target(AnnotationTarget.FUNCTION)

Annotation Targets in Kotlin Example Program in Kotlin

@Target(AnnotationTarget.FUNCTION)
annotation class TestOnly

@TestOnly
fun demo() = "test function"

fun main(args: Array<String>) {
    println(demo())
}

Sample Output

test function

When to use

Use annotations to declare framework configuration declaratively instead of wiring everything manually.

How it works

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

2. fun demo() = "test function" assigns or updates a value used later in the program.

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

4. Use @Target to specify where annotation can be applied.

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: use @Target to specify where annotation can be applied.
• 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

• Use @Target to specify where annotation can be applied.
• Kotlin supports FIELD, PROPERTY, FUNCTION, CLASS and more.
• Correct targets avoid misuse of annotations.
• 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.