In a bid to ease the adoption of its Kotlin programming language by Java developers, JetBrains has introduced a Java to Kotlin converter extension for Microsoft’s Visual Studio Code editor. Long established as an alternative to Java, Kotlin is widely used in Java spaces such as Android mobile application development.

Introduced February 19, the Java to Kotlin converter extension is downloadable from the Visual Studio Marketplace. Developers using it can convert individual Java files into Kotlin code with a context menu action, reducing the manual effort of migrating legacy codebases or switching languages in the middle of a project. The extension uses the same underlying engine used in JetBrains IDEs and draws on large language models (LLMs) to provide idiomatic conversion suggestions, providing one-click, review-before-you-commit Java to Kotlin migration inside VS Code, according to JetBrains.

Developers can expect a reliable conversion that respects Kotlin idioms and syntax requirements, Alina Dolgikh, Kotlin product manager at JetBrains, said. The extension was developed out of recognition that many developers use VS Code for a variety of projects and tasks, even if JetBrains’s IntelliJ Idea IDE remains the premier IDE for Kotlin, she said.

The Java to Kotlin converter extension gives the following settings to VS Code:

• j2k.provider: The LLM backend to use for the Java to Kotlin conversion. Default: GitHub Copilot.
• j2k.model: The model tag to use with the selected provider. Default: codellama:instruct.
• j2k.ollama.baseUrl: The base URL of the target instance, when the provider selected is Ollama.
• j2k.openRouter.baseUrl: The base URL of the target instance, when the provider selected is OpenRouter.
• j2k.apiKey: The API key to use with the selected provider (stored in VS Code Secrets).