Code examples: Call Java/Kotlin code from C# scripts

Unity provides high-level APIs such as AndroidJavaObject, AndroidJavaClass, and AndroidJavaProxy that allow you to interact with Java/Kotlin code from C# scriptsA piece of code that allows you to create your own Components, trigger game events, modify Component properties over time and respond to user input in any way you like. More info
See in Glossary.

The following code examples demonstrate how to use these APIs.

Example 1: Get the hash code for a Java string

The following code example creates an instance of java.lang.String initialized with a string, and retrieves the hash value for that string.

using UnityEngine;
public class JavaExamples
{
    public static int GetJavaStringHashCode(string text)
    {
        using (AndroidJavaObject jo = new AndroidJavaObject("java.lang.String", text))
        {
            int hash = jo.Call<int>("hashCode");
            return hash;
        }
    }
}

This example:

1. Creates an AndroidJavaObject that represents a java.lang.String.
2. The AndroidJavaObject constructor takes at least one parameter, which is the name of the class to construct an instance of. Any parameters after the class name are for the constructor call on the object, in this case the text parameter from GetJavaStringHashCode.
3. Calls hashCode() to get the hash code of the string. This call uses the int generic type parameter for Call because hashCode() returns the hash code as an integer.

Note: You can’t use dotted notation to instantiate a nested Java class. You must use the $ separator to instantiate inner classes. For example, Use android.view.ViewGroup$LayoutParams or android/view/ViewGroup$LayoutParams, where the LayoutParams class is nested in the ViewGroup class.

Example 2: Retrieve the application’s cache directory

The following code example shows how to retrieve the cache directory for the current application in C# without using plug-insA 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.

using UnityEngine;

public class JavaExamples
{
    public static string GetApplicationCacheDirectory()
    {
       using (AndroidJavaClass unityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer"))
        using (AndroidJavaObject currentActivity = unityPlayer.GetStatic<AndroidJavaObject>("currentActivity"))
        using (AndroidJavaObject javaFile = currentActivity.Call<AndroidJavaObject>("getCacheDir"))
        {
            string cacheDirectory = javaFile.Call<string>("getCanonicalPath");
            return cacheDirectory;
        }
    }
}

This example:

1. Creates an AndroidJavaClass to represent com.unity3d.player.UnityPlayer. It’s best practice to use AndroidJavaClass instead of AndroidJavaObject to access static members.
2. Creates an AndroidJavaObject to represent the current activity, which is a static member of com.unity3d.player.UnityPlayer.
3. Calls getCacheDir() on the Activity object, which returns a File object that represents the cache directory.
4. Calls getCanonicalPath() on the File object can to get the cache directory as a string.

Note: This example is for reference purposes. Instead, to access the application’s cache and file directory use the Application.temporaryCachePath and Application.persistentDataPath APIs.

Example 3: Pass data from Java to Unity

The following code example shows how to pass data from Java to Unity using UnitySendMessage.

using UnityEngine;

public class JavaExamples : MonoBehaviour
{

    private void Start()
    {
        AndroidJNIHelper.debug = true;
        using (AndroidJavaClass jc = new AndroidJavaClass("com.unity3d.player.UnityPlayer"))
        {
            jc.CallStatic("UnitySendMessage", "My GameObject", "JavaMessage", "NewMessage");
        }
    }

    private void JavaMessage(string message)
    {
        Debug.Log("message from java: " + message);
    }
}

This example:

1. Creates an AndroidJavaClass to represent com.unity3d.player.UnityPlayer.
2. Calls the staticUnitySendMessage method that is a member of com.unity3d.player.UnityPlayer.

Although you call UnitySendMessage from within Unity, it uses Java to relay the message, which then calls back to the native/Unity code to deliver it to the GameObjectThe fundamental object in Unity scenes, which can represent characters, props, scenery, cameras, waypoints, and more. A GameObject’s functionality is defined by the Components attached to it. More info
See in Glossary named My GameObject which has an attached script that contains a method called JavaMessage.

Additional resources

• Supported data types for Java/Kotlin and C# code
• Best practices for calling Java/Kotlin code
• Example: Create and use Kotlin source plug-in