Create a Java or Kotlin source plug-in

This page explains how to indicate to Unity to create a plug-inA set of code created outside of Unity that creates functionality in Unity. There are two kinds of plug-ins you can use in Unity: Managed plug-ins (managed .NET assemblies created with tools like Visual Studio) and Native plug-ins (platform-specific native code libraries). More info
See in Glossary from a Java (.java) or Kotlin (.kt) source file.

1. In the Assets folder, place your Java (.java) or Kotlin (.kt) source file.
   Tip: It’s best practice to create a sub-folder to contain your Java and Kotlin source files.
2. Select the source file and view it in the InspectorA Unity window that displays information about the currently selected GameObject, asset or project settings, allowing you to inspect and edit the values. More info
   See in Glossary window.
3. In the Inspector, under the Select Platforms for plugin section, enable Android.
4. Select Apply.

Note: You can place the source files in any folder in your Project, except in special use locations such as StreamingAssets. If you place files in these locations, the Unity Editor doesn’t display the plug-in inspector.

Edit Java or Kotlin files in an exported Android Studio project

By default when you export a Unity project for Android, Unity copies any Java/Kotlin files over to the Android Studio project. If you edit these files in Android Studio, the changes are not reflected in the original files in the Unity project. If you export the Unity project again, the export process will overwrite your changes in Android Studio.

To resolve this, Unity provides the Symlink Sources Build Setting. If you select this Build Setting, Unity creates a symbolic link in the Android Studio project to Java/Kotlin files in the Unity project, instead of copying files over. This means that if you edit the files from Android Studio, the edit affects the files in the original Unity project.

Additional resource

• Call Java and Kotlin plug-in code from C# scripts