Common Annotations in Kotlin

Introduction

Common Annotations 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.

Kotlin and Java provide built-in annotations such as Deprecated and Suppress. 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

• Kotlin and Java provide built-in annotations such as Deprecated and Suppress.
• JvmStatic, JvmOverloads and JvmField help Java interop.
• Frameworks add validation and serialization annotations.

Syntax

@Suppress("UNUSED_VARIABLE")

Common Annotations in Kotlin Example Program in Kotlin

@Suppress("UNUSED_VARIABLE")
fun main(args: Array<String>) {
    val unused = 10
    println("Common annotations example")
}

Sample Output

Common annotations example

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. val unused = 10 assigns or updates a value used later in the program.

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

4. Kotlin and Java provide built-in annotations such as Deprecated and Suppress.

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: kotlin and Java provide built-in annotations such as Deprecated and Suppress.
• 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

• Kotlin and Java provide built-in annotations such as Deprecated and Suppress.
• JvmStatic, JvmOverloads and JvmField help Java interop.
• Frameworks add validation and serialization 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.