Modern application development for the Android platform is almost unthinkable without the use of a programming language Kotlin. Officially supported by Google, this tool offers developers a concise syntax, improved code security, and full compatibility with existing Java libraries. However, beginners often find it difficult to initially set up a development environment, especially if they are installing Android Studio from scratch or working on a legacy project.
The process of integrating this language into your workflow can range from simply checking a box in the project creation wizard to manually editing build configuration files. Understanding how to properly enable Kotlin syntax support is a fundamental skill for any mobile developer. In this article we will analyze in detail all stages of connection, from creating a new project to migrating old code.
Creating a new project with Kotlin support
The easiest and most reliable way to get started with this language - create a new project where support will be enabled by default. When running Android Studio version of Arctic Fox or later, the system automatically prompts you to select a programming language during the initialization stage. You need to select the option Kotlin in the drop-down menu when creating Empty Activity or any other template.
If you are using an older version of the development environment, the process may require additional attention. In the New Project Wizard window, be sure to make sure that the checkbox Include Kotlin support is active. Ignoring this step will result in the project being built entirely in Java, and you will have to manually make changes to the build files later, which increases the risk of compatibility errors.
Once you click the button Finish, the development environment will automatically generate the necessary dependencies in the file build.gradle. You will see that the main activity file will have the extension .kt instead of the usual .java. This is a clear sign that the compiler is configured correctly and is ready to process code in the new language.
When creating a project, always select the latest stable version of the Android SDK to avoid problems with outdated APIs in Kotlin code.
Manual activation in an existing project
Situations when you need to add language support into an already running project written in Java are quite common. To do this, open the root file build.gradle (Project level) of your application. You need to add the Kotlin compiler plugin to the block buildscript . Without this step, the build system simply will not understand how to process files with the extension .kt.
Next you should go to the modular file build.gradle (Module: app). Here you need to add a dependency to the language standard library. The connection syntax is as follows: you need to add a line implementation "org.jetbrains.kotlin:kotlin-stdlib:$kotlin_version" to the section dependencies. Make sure that the library version matches the plugin version specified in the root file.
After making changes to the configuration files, be sure to synchronize the project. Click the button Sync Nowthat appears at the top of the editor, or select the item File → Sync Project with Gradle Files in the main menu. This process will download all the necessary artifacts from the repositories and set up the internal structure of the project.
☑️ Kotlin Connection Checklist
Converting Java code to Kotlin
One of the main advantages of the ecosystem is the possibility of seamless migration of legacy code. You don't have to rewrite old classes manually; built-in tools Android Studio will do this for you. To run the converter, open any Java file in an editor, right-click and select Convert Java File to Kotlin File.
from the context menu. The automatic converter does an impressive job of translating Java's imperative style into the more functional Kotlin style. It replaces cumbersome constructs with concise expressions, removes semicolons, and converts getters/setters into properties. However, the result is not always perfect: sometimes manual tuning is required, especially if the source code used complex design patterns or specific annotations.
kt, but they can coexist with Java files in the same project. The compiler will easily process mixed code, allowing you to call Kotlin methods from Java and vice versa. This makes it possible to migrate gradually, file by file, without stopping the development of new functions.
⚠️ Attention: After mass conversion, be sure to check the logic for working with null safety. The converter can add operators
!!(unsafe cast), which can cause the application to crash if the value is null.
What to do if the conversion was completed with errors?
If the automatic converter could not process the file, try splitting it into smaller parts or perform the conversion manually, copying method logic by method. Also check if the code contains obsolete libraries that are incompatible with the new syntax.
Configuring the compiler and versions
The correct operation of the project directly depends on the consistency of the versions of the plugin and the standard library. The file gradle.properties often defines a variable kotlin_versionthat is used in all modules of the project. Changing this variable in one place allows you to update the language throughout the application at once, which is extremely convenient when supporting large projects.
When using the Gradle build system version 7.0 and higher, as well as Android Studio Chipmunk and newer, it is recommended to use the plugin org.jetbrains.kotlin.android instead of the old one kotlin-android. The new plugin provides better build performance and more accurate integration with profiling tools. Switching to a new plugin requires minimal changes in the build scripts.
Below is a table of correspondence between Android Studio versions, the Gradle plugin and the recommended Kotlin version for stable operation:
| Android Studio version | Gradle plugin version | Version Kotlin | Support status |
|---|---|---|---|
| Hedgehog (2023.1.1) | 8.1.0+ | 1.9.0+ | Stable |
| Giraffe (2022.3.1) | 8.0.0+ | 1.8.0+ | Stable |
| Electric Eel (2022.1.1) | 7.4.0+ | 1.7.0+ | Supported |
| Arctic Fox (2020.3.1) | 7.0.0+ | 1.5.0+ | Outdated |
Always keep the Kotlin plugin version and version of the stdlib library synchronized to avoid compilation errors like “Module was compiled with an incompatible version.”
Solving common compilation errors
Even with proper configuration, developers may encounter errors related to Gradle caching or dependency conflicts. A common problem is an error Unresolved referencewhen the IDE does not see standard Kotlin classes. In most cases, this can be solved by clearing the cache: select from the menu File → Invalidate Caches / Restart and confirm the action.
Another common situation is a conflict between library versions. If your project uses third-party libraries that themselves depend on Kotlin, there may be duplicate classes in the classpath. To solve this problem, use the command ./gradlew dependencies in the terminal to visualize the dependency tree and find conflicting versions.
Sometimes the error occurs due to incorrect configuration of source sets. Make sure that the folder src/main/kotlin is correctly recognized as a source code directory. In modern versions of Android Studio this happens automatically, but in older projects you may need to explicitly specify the path in the assembly file.
⚠️ Attention: The Android Studio interface and menu item names may vary slightly depending on the installed version and operating system. Always check the official JetBrains documentation if you can't find what you're looking for.
Use the keyboard shortcut Ctrl+Shift+A (Cmd+Shift+A on Mac) to quickly find any setting or action in Android Studio by entering the name of the plugin or command.
Optimizing APK size when using Kotlin
One of the concerns of developers when switching to a new language is the increase in the size of the final application file. The Kotlin standard library does add some weight to the APK, especially if the project uses a lot of functions from the library. However, modern compression tools make it possible to minimize this impact to imperceptible amounts.
To reduce the size of the application, be sure to enable the mechanism ProGuard or R8 in the build settings of the release version. These tools remove unused code and optimize bytecode, which is critical for Kotlin projects. Activation is done by setting the parameter minifyEnabled true in the block buildTypes of the file build.gradle.
In addition, starting with certain versions of the compiler, it became possible to include the Kotlin library directly in Android runtime (if the OS version allows it), which could theoretically eliminate the need to embed the library in each APK. However, in practice, using R8 is the most effective and universal optimization method.
Does Kotlin affect the speed of the application?
No, Kotlin code compiles to the same Java bytecode, so runtime performance is identical. In some cases, Kotlin can be even faster by using inline functions that eliminate the overhead of creating wrapper objects.
Is it possible to use Kotlin in old Eclipse projects?
Technically it is possible with complex manual configuration, but it is highly not recommended. The Kotlin ecosystem is tailored for Gradle and Android Studio. For old Eclipse projects, the best solution would be to migrate the project itself to Android Studio.
Do I need to install a separate Kotlin plugin for Android Studio?
In modern versions of Android Studio, the Kotlin plugin is already built in by default. Separate installation is required only for very old versions of the IDE (before version 3.0), which are no longer supported by Google.