It's often not possible to consider rewriting a project in an entirely new programming language, and therefore, it becomes important for languages to work well together. Java developers that want to take advantage of Kotlin features might want to introduce Kotlin in isolated parts of their code base. As mentioned in the previous section, because Kotlin is well integrated with existing JVM tooling, adding Kotlin to an existing Java project is quick and easy when using IntelliJ or Android Studio.

In this section, we'll walk through how to add Kotlin to an existing IntelliJ project. This will demonstrate how you can start using Kotlin today, even if you're not working on a brand-new project.