Project structure and build basics in Kotlin - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the purpose of the src/main/kotlin directory in a Kotlin project?

It holds the main Kotlin source code files that make up the application logic.

beginner

What file typically defines the build configuration in a Kotlin project using Gradle?

The build.gradle.kts file defines dependencies, plugins, and build tasks.

beginner

Why do Kotlin projects often have a src/test/kotlin directory?

It contains test code to verify that the main application code works correctly.

intermediate

What is the role of the gradlew script in a Kotlin project?

It runs Gradle tasks using the project's specified Gradle version, ensuring consistent builds.

beginner

What does the dependencies block in build.gradle.kts do?

It lists libraries and tools the project needs to compile and run.

Where should you put your Kotlin source files in a standard Gradle project?

A src/main/kotlin

B src/resources

C build/libs

D src/test/resources

The main Kotlin source files go in src/main/kotlin.

Which file controls the build process in a Kotlin Gradle project?

A build.gradle.kts

B settings.gradle

C gradlew.bat

D README.md

build.gradle.kts defines the build configuration.

What is the purpose of the src/test/kotlin folder?

A To store resource files

B To store compiled classes

C To store test code

D To store build scripts

src/test/kotlin holds test source files.

What does the Gradle wrapper (gradlew) ensure?

A Faster compilation

B Consistent Gradle version across machines

C Automatic code formatting

D Running tests only

Gradle wrapper ensures the same Gradle version is used everywhere.

In build.gradle.kts, where do you specify external libraries?

A repositories block

B plugins block

C tasks block

D dependencies block

The dependencies block lists external libraries.

Describe the typical folder structure of a Kotlin project using Gradle and explain the purpose of each main folder.

Think about where your code, tests, and build settings live.

Explain how the Gradle build system works in a Kotlin project and why the Gradle wrapper is useful.

Focus on build configuration and consistent environment.

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