IntelliJ IDEA 2021.1 Help

Get started with Kotlin

Before you start working with Kotlin, make sure that the plugin is enabled. The plugin is bundled with IntelliJ IDEA and is activated by default. If the plugin is not activated, enable it on the Plugins page of the Settings/Preferences dialog Ctrl+Alt+S as described in Manage plugins.

IntelliJ IDEA provides first-class support for Kotlin. It includes Kotlin-specific project templates, coding assistance, refactorings, debugging, analysis tools and so on. Most of the Java tools are available for Kotlin, so, for example, if you know how to use Java debugger or refactorings, your experience will be enough to use these in Kotlin. In this topic, you will find the instructions to get started with Kotlin in IntelliJ IDEA.

Create a Kotlin project

  1. From the main menu, select File | New | Project.

  2. In the left-hand menu, select Kotlin.

  3. Select the project template. The template defines the project structure, dependencies... The following project templates are available:

    • Application (JVM): backend application with Kotlin/JVM.

    • Console Application: console application with Kotlin/JVM. Use it for prototyping or testing purposes.

    • Mobile Application: mobile applications for iOS and Android with Kotlin Multiplatform Mobile, which supports sharing common code between platforms.

    • Mobile Library: library that supports sharing code between iOS and Android.

    • Application (Multiplatform): applications for different platforms that support sharing common code.

    • Library: library for sharing common code among different platforms.

    • Native Application: application with Kotlin/Native that works as a standalone application under a specific platform.

    • Full-stack Web Application: full-fledged web application using Kotlin/JS for the frontend and Kotlin/JVM for the backend.

    • Frontend Application: frontend application with Kotlin/JS and non-Kotlin backend. If you use Kotlin for backend, the better option is Full-stack Web Application.

  4. Select the build system that you are going to use in the project.

    Kotlin new project gradleg
  5. Specify the JDK that will be used in the project (version 1.8 or later is recommended). The JDK:

    • is essential for projects built with IntelliJ IDEA build system.

    • used for coding assistance in projects built with Gradle and Maven

    If you don't have a JDK installed, you can download it right in the dialog.

  6. Specify group id, artifact name and version of the primary artifact. Not applicable for IntelliJ build system.

  7. If you chose IntelliJ as the build system, specify the Kotlin Runtime library that will be used in the project.

  8. Click Next to proceed to configuring the module structure. For detailed information, see New Project Wizard reference.

Mix Java and Kotlin in one project

You can call Java code from Kotlin and vice versa. This enables you to gradually transition a project to Kotlin or use both languages in parallel, for example, by using Kotlin for testing an existing Java codebase.

In order to start using Kotlin in your project, make sure that the Kotlin plugin is enabled and the Kotlin dependency is added to your project.

Add Kotlin dependency to an existing JVM project

  • If your project uses IntelliJ IDEA build tool, create a Kotlin file. When a notification appears stating that Kotlin is not configured for the project, click Configure, then select if you want to use Kotlin with Java or JavaScript.

    Kotlin configurator
  • For other build tools, follow the steps in:

Convert Java to Kotlin

IntelliJ IDEA allows you to automatically convert your Java code to Kotlin. The resulting code is not supposed to be perfect, however, it may be helpful in some situations.

If you are not satisfied with the result of conversion, you can roll it back with Ctrl+Z.

  1. Paste Java code in a Kotlin file. In the dialog that appears, click Yes

  2. With a Java file open in the editor, go to main menu and select Code | Convert Java File to Kotlin File or press Ctrl+Alt+Shift+K.

Last modified: 25 March 2021