Package Declaration in Kotlin

Introduction

Package Declaration is a fundamental concept every Kotlin developer should understand. Packages group related classes and functions into namespaces, keep large codebases organized, and control visibility with import statements.

A package groups related classes and functions. 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

• A package groups related classes and functions.
• The package statement must be the first line in a Kotlin file (except comments).
• Package names usually follow reverse domain notation.

Syntax

package com.example.demo

Package Declaration in Kotlin Example Program in Kotlin

// File: Demo.kt
package com.example.demo

fun greet() = "Hello from package"

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

Sample Output

Hello from package

When to use

Use packages to separate features (networking, UI, data) and avoid name clashes between similarly named classes.

How it works

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

2. Comment: File: Demo.kt\npackage com.example.demo\n\nfun greet() = "Hello from package"\n\nfun main(args: Array<String>) {\n println(greet())\n} — documents intent for readers.

3. A package groups related classes and functions.

4. 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: a package groups related classes and functions.
• 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

• A package groups related classes and functions.
• The package statement must be the first line in a Kotlin file (except comments).
• Package names usually follow reverse domain notation.
• 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.