Project structure and build basics in Kotlin - Mini Project: Build & Apply

Project structure and build basics

📖 Scenario: You are starting a simple Kotlin project to understand how to organize files and build a program.

🎯 Goal: You will create a basic Kotlin project with a main function, add a configuration variable, write a simple function, and print the result.

📋 What You'll Learn

Create a Kotlin file with a main function

Add a configuration variable inside the main function

Write a function that uses the configuration variable

Print the output of the function

💡 Why This Matters

🌍 Real World

Understanding project structure and build basics helps you start any Kotlin application clearly and organized.

💼 Career

Knowing how to set up main functions, variables, and functions is essential for Kotlin developers building apps or backend services.

1

Create the main function

Create a Kotlin main function with no parameters and inside it declare a variable projectName set to the string "MyKotlinProject".

Kotlin

fun main() {
    // Your code here
}

Hint

Use fun main() { } to create the main function and inside it declare val projectName = "MyKotlinProject".

2

Add a configuration variable

Inside the main function, add a variable called version and set it to the string "1.0".

Kotlin

fun main() {
    val projectName = "MyKotlinProject"
    // Your code here
}

Hint

Declare val version = "1.0" inside the main function below projectName.

3

Write a function to show project info

Write a function called showProjectInfo that takes two parameters: name and version, both strings. The function should return a string formatted as "Project: {name}, Version: {version}". Call this function inside main using the variables projectName and version, and store the result in a variable called info.

Kotlin

fun main() {
    val projectName = "MyKotlinProject"
    val version = "1.0"
    // Your code here
}

// Your function here

Hint

Define fun showProjectInfo(name: String, version: String): String returning the formatted string. Then call it inside main and assign to info.

4

Print the project info

Add a println statement inside the main function to print the variable info.

Kotlin

fun main() {
    val projectName = "MyKotlinProject"
    val version = "1.0"
    val info = showProjectInfo(projectName, version)
    // Your code here
}

fun showProjectInfo(name: String, version: String): String {
    return "Project: $name, Version: $version"
}

Hint

Use println(info) inside main to display the project info.

Practice

1. Which folder in a typical Kotlin project contains the main source code files?

easy

A. resources/main

B. src/test/kotlin

C. build/libs

D. src/main/kotlin

Solution

1. Step 1: Understand standard Kotlin project folders

   The src/main/kotlin folder is where the main Kotlin source files are placed.

2. Step 2: Differentiate from other folders

   src/test/kotlin is for test code, build/libs is for compiled output, and resources/main is for resource files.

3. Final Answer:

   src/main/kotlin -> Option D

4. Quick Check:

   Main source code folder = src/main/kotlin [OK]

Hint: Main code is always under src/main/kotlin folder [OK]

Common Mistakes:

• Confusing test folder with main source folder
• Thinking build output folders contain source code
• Mixing resource folders with source code folders

2. Which file is commonly used to define build instructions in a Kotlin project using Gradle?

easy

A. settings.gradle

B. build.gradle.kts

C. gradle.properties

D. manifest.xml

Solution

1. Step 1: Identify Gradle build script files

   Gradle uses build.gradle.kts (Kotlin DSL) or build.gradle (Groovy DSL) to define build instructions.

2. Step 2: Differentiate from other Gradle-related files

   settings.gradle configures multi-project builds, gradle.properties holds properties, and manifest.xml is unrelated.

3. Final Answer:

   build.gradle.kts -> Option B

4. Quick Check:

   Build instructions file = build.gradle.kts [OK]

Hint: Build scripts are named build.gradle.kts for Kotlin DSL [OK]

Common Mistakes:

• Confusing settings.gradle with build.gradle.kts
• Thinking gradle.properties contains build logic
• Mixing XML files with Gradle scripts

3. Given this Gradle build snippet, what will be the output directory for compiled Kotlin classes?

kotlin {
    jvmToolchain(17)
}

tasks.withType(org.jetbrains.kotlin.gradle.tasks.KotlinCompile).configureEach {
    kotlinOptions.jvmTarget = "17"
}

medium

A. build/classes/kotlin/main

B. src/main/kotlin

C. build/libs

D. out/production

Solution

1. Step 1: Understand Gradle default output folders

   By default, Kotlin compiled classes go to build/classes/kotlin/main for the main source set.

2. Step 2: Differentiate source and output folders

   src/main/kotlin is source code, build/libs holds packaged jars, and out/production is not standard for Gradle Kotlin projects.

3. Final Answer:

   build/classes/kotlin/main -> Option A

4. Quick Check:

   Compiled classes output = build/classes/kotlin/main [OK]

Hint: Compiled classes go under build/classes/kotlin/main by default [OK]

Common Mistakes:

• Confusing source folder with output folder
• Thinking build/libs holds class files instead of jars
• Assuming non-standard output folders

4. You see this error when running Gradle: Could not find method kotlin() for arguments. What is the likely cause?

medium

A. The Kotlin plugin is not applied in build.gradle.kts

B. The source folder is missing

C. The JVM target version is invalid

D. The Gradle wrapper is outdated

Solution

1. Step 1: Understand the error message context

   The error means Gradle does not recognize the kotlin {} block, usually because the Kotlin plugin is missing.

2. Step 2: Check common causes

   Missing plugins { kotlin("jvm") version "x.y.z" } causes this error. Source folder or JVM target issues cause different errors. Outdated Gradle wrapper usually causes version incompatibility errors.

3. Final Answer:

   The Kotlin plugin is not applied in build.gradle.kts -> Option A

4. Quick Check:

   Missing Kotlin plugin causes kotlin() method error [OK]

Hint: Check if Kotlin plugin is applied when kotlin() method errors occur [OK]

Common Mistakes:

• Assuming source folder missing causes this error
• Blaming JVM target version without checking plugin
• Ignoring plugin application in build script

5. You want to add a new resource folder to your Kotlin project for configuration files. Where should you place it to follow standard Gradle project structure?

hard

A. src/resources/main

B. resources/config

C. src/main/resources

D. config/resources

Solution

1. Step 1: Recall standard resource folder location

   Gradle expects resource files in src/main/resources to include them in the build output.

2. Step 2: Differentiate from incorrect folder structures

   Folders like resources/config, src/resources/main, or config/resources are not standard and won't be automatically included.

3. Final Answer:

   src/main/resources -> Option C

4. Quick Check:

   Resource files go under src/main/resources [OK]

Hint: Put resource files in src/main/resources for Gradle to find them [OK]

Common Mistakes:

• Placing resources outside src/main folder
• Using non-standard folder names
• Not including resources in build output