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Best practices for calling Java/Kotlin code

Learn about the best practices for calling Java/Kotlin code from C# scripts.
Read time 2 minutesLast updated 7 days ago
Learn about the best practices for calling Java and Kotlin plug-in code from C# scripts to improve performance of your application.

Minimize JNI calls

Using the Java Native Interface (JNI), through either the high-level or low-level C# API is resource intensive and can be slow. To improve performance, and also code clarity, it's best practice to keep the number of JNI calls low.
To avoid unnecessary JNI calls, the high-level C# API caches the ID of each Java method that you call. This means that subsequent calls to the same method aren't as resource intensive as the first call. The calls don't need to be during the same frame or even from the same 
AndroidJavaObject
/
AndroidJavaClass
instance. If you use the low-level API and want this performance benefit, you must manually cache method ID. Otherwise, it's best practice to use the high-level API.
Note
Unity maintains the cache until the application closes. This includes while the application is in the background.

Manage garbage collection

It's best practice to wrap any instance of 
AndroidJavaObject
or 
AndroidJavaClass
with a 
using
statement to ensure Unity destroys them as soon as possible. If you don't use 
using
, Unity's garbage collector will still release all created instances, but you lose control over when this happens.
The following code example demonstrates how to use 
using
statements to access the system language in an optimal way:
using UnityEngine;public class LocaleExample : MonoBehaviour{    void Start()    {        using (AndroidJavaClass cls = new AndroidJavaClass("java.util.Locale"))        using (AndroidJavaObject locale = cls.CallStatic<AndroidJavaObject>("getDefault"))        {            if (locale != null)            {                Debug.Log("current lang = " + locale.Call<string>("getDisplayLanguage"));            }        }    }}

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