IntelliJ IDEA 2023.1 Help

Tutorial: Create your first Kotlin application

In this tutorial, you will learn how to:

  • Create a Kotlin project.

  • Write code using the basic coding assistance features.

  • Run your code from IntelliJ IDEA.

  • Build and package the application.

  • Run the packaged application.

You can choose to build your app with one of the four supported build tools.

Create a new project

In IntelliJ IDEA, a project helps you organize everything that is necessary for developing your application in a single unit.

  1. On the Welcome screen, click New Project. Otherwise, from the main menu, select File | New | Project.

  2. From the list on the left, select New Project.

  3. Name your new project and change its location if necessary.

  4. Select the Create Git repository checkbox to place the new project under version control.

    You will be able to do it later at any time.

  5. From the Language list, select Kotlin.

  6. Select the Gradle IntelliJ Maven build system.

  7. Choose the Groovy Kotlin language for the build script.

  8. From the JDK list, select the JDK that you want to use in your project.

    If the JDK is installed on your computer, but not defined in the IDE, select Add JDK and specify the path to the JDK home directory.

    If you don't have the necessary JDK on your computer, select Download JDK.

  9. Enable the Add sample code option to create a file with a sample Hello World! application.

    New Kotlin project with the Gradle build system with Kotlin DSL
    New Kotlin project with the Gradle build system with Groovy DSL
    New Kotlin project with the IntelliJ build system
    New Kotlin project with the Maven build system

  10. Click Create.

Write code

Source code is the central part of your project. In source code, you define what your application will be doing. Real projects may be very big and contain hundreds of thousands lines of code. In this tutorial we are going to start with a simple three-line application that asks the user their name and greets them.

  1. In the Project tool window on the left, expand the node named after your project and open the /src/main/kotlin/main.kt file.

    src/main/kotlin/main.kt in the Project tool window
    src/main/kotlin/main.kt in the Project tool window
    src/main/kotlin/main.kt in the Project tool window
    src/main/kotlin/main.kt in the Project tool window

  2. The file only contains the main() function with print statements. This function is the entry point of your program.

    Replace the Hello World! sample with the following code snippet:

    fun main(args: Array<String>) { println("What is your name?") }

  3. Now that the program asks users for input, provide them with a way to give it. Also, the program needs to store the input somewhere.

    Move the caret to the next line and type val name = rl. IntelliJ IDEA will suggest to convert rl to readln(). Hit Enter to accept the suggestion.

    Code completion in action

  4. Move the caret to the next line, type sout, and hit Enter.

    Live templates in action

  5. Place the caret inside the parentheses of the println statement and type "Hello, $". Press Control+Space to invoke code completion and select the name variable from the list.

    Code completion in action

Now we have a working code that reads the username from the console, stores it in a read-only variable, and outputs a greeting using the stored value.

Run code from IntelliJ IDEA

Let's verify that our program works as expected.

IntelliJ IDEA allows you to run applications right from the editor. You don't need to worry about the technical aspect because IntelliJ IDEA automatically does all the necessary preparations behind the scenes.

  • Click the Run icon in the gutter and select Run 'MainKt' or press Control+Shift+F10.

    The Run option in the menu

When the program has started, the Run tool window opens, where you can review the output and interact with the program.

The output of the program in the Console tab

Package as JAR

At this point, you know how to write code and run it from IntelliJ IDEA, which is convenient in the development process. However, this is not the way the users are supposed to run applications. For the users to run it on their computers, we are going to build and package the application as a jar file.

Building the app includes the following steps:

  • Compiling the sources – in this step, you translate the code you've just written into JVM bytecode. The compiled sources have the .class extension.

  • Bundling the dependencies – for the application to function correctly, we need to provide the libraries it depends on. The only required library for this project is Kotlin runtime, but still, it needs to be included. Otherwise, the users will have to provide it themselves every time they run the program, which is not very convenient.

Both the compiled sources and the dependencies end up in the resulting .jar file. The result of the build process such as .jar file is called an artifact.

  1. Open the build.gradle.kts build.gradle script.

    The Build Gradle script in the project structure
    The Build Gradle script in the project structure

  2. In the build script, add the following task definition:

    tasks.jar { manifest { attributes["Main-Class"] = "MainKt" } configurations["compileClasspath"].forEach { file: File -> from(zipTree(file.absoluteFile)) } duplicatesStrategy = DuplicatesStrategy.INCLUDE }
    tasks.jar { manifest { attributes 'Main-Class': 'MainKt' } from { configurations.compile.collect { it.isDirectory() ? it : zipTree(it) } } }

    The manifest section specifies the entry point of the program, and the rest tells the build tool to recursively scan the project for dependencies and include them in the build.

  3. When the definition is added to the build file, press Control+Shift+O or click Reimport All Projects in the Gradle tool window to import the changes.

  4. In the right-hand sidebar, open Gradle and run the jar task (Tasks | build | jar). If the sidebar is not present, go to View | Appearance and toggle the Tool Window Bars menu item.

    Kotlin Tutorial Gradle Jar

The resulting JAR appears in the build/libs directory.

The resulting JAR in the out directory viewed using the Project Tool Window

  1. Go to File | Project Structure Control+Alt+Shift+S and open the Artifacts tab.

  2. Click Add the Plus icon, then JAR, then From modules with dependencies.

    Adding new artifact in the Project Structure dialog

  3. In the Main Class field, click the Browse button, and select Main.kt as the main class.

    Specify the absolute path to /src/main/resources as the manifest directory, for example: /Users/me.user/IdeaProjects/greeting/src/main/resources

    The Select Main Class dialog

  4. Click OK in the Create JAR from Modules dialog.

    The Create JAR from Modules dialog
    The Create JAR from Modules dialog

  5. Click OK in the Project Structure dialog.

  6. From the main menu, select Build | Build Artifacts, then click Build.

    The Build option in the Build Artifact menu

The resulting JAR appears in the out/artifacts directory.

The resulting JAR in the out directory viewed using the Project Tool Window

Run the JAR

Run from IntelliJ IDEA

  • In the Project tool window, right-click the .jar file and select Run.

    This is a quick way to run a .jar file from IntelliJ IDEA.

Run from CLI

  • Open the terminal and from the containing folder, run:

    java -jar consoleApp.jar java -jar greeting.jar java -jar greeting-1.0-SNAPSHOT.jar

    This is how the users of your application would run it.

Last modified: 19 April 2023
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