We cnotinue from the previous article where we created a JAR file and placed it in Unity. The current setup includes a simple UI and a script attached to the UseJavaExample GameObject.

Below is the Unity API for calling Java code:

void Start()
{
    // Calling static methods
    AndroidJavaClass javaClass = new AndroidJavaClass("your.class.name");
    javaClass.CallStatic("MethodName");                    // void static method
    javaClass.CallStatic<string>("MethodName");            // static method with return value
    javaClass.CallStatic("MethodName", "parameter");      // void static method with parameter
    javaClass.CallStatic<int>("MethodName", "parameter"); // static method with return and parameter
    // Static fields
    javaClass.GetStatic<string>("FieldName");
    javaClass.SetStatic("FieldName", "newValue");

    // Calling instance methods
    AndroidJavaObject javaObject = new AndroidJavaObject("your.class.name");
    javaObject.Call("MethodName");                         // void instance method
    javaObject.Call<string>("MethodName");                 // instance method with return
    javaObject.Call("MethodName", "parameter");           // void instance method with parameter
    javaObject.Call<int>("MethodName", "parameter");     // instance method with return and parameter
    // Instance fields
    javaObject.Get<string>("FieldName");
    javaObject.Set("FieldName", "newValue");
}

Now we implement the code in UseJavaCodeExample.cs. The script references buttons, input fields, and a text display.

using UnityEngine;
using UnityEngine.UI;

public class UseJavaCodeExample : MonoBehaviour
{
    public Button[] buttons;
    public InputField[] textField;
    public Text infoText;

    private AndroidJavaClass javaClass = null;
    private AndroidJavaObject javaObject = null;

    void Start()
    {
        javaClass = new AndroidJavaClass("com.godshadow.test.Test");
        javaObject = new AndroidJavaObject("com.godshadow.test.Test");
        SetupButtonListeners();
    }

    private void SetupButtonListeners()
    {
        buttons[0].onClick.AddListener(SetLogStatic);
        buttons[1].onClick.AddListener(GetLogStatic);
        buttons[2].onClick.AddListener(SetLogFieldStatic);
        buttons[3].onClick.AddListener(GetLogFieldStatic);
        buttons[4].onClick.AddListener(SetNameInstance);
        buttons[5].onClick.AddListener(GetNameInstance);
        buttons[6].onClick.AddListener(SetNameFieldInstance);
        buttons[7].onClick.AddListener(GetNameFieldInstance);
    }

    private void SetLogStatic()
    {
        javaClass.CallStatic("SetLog", textField[0].text);
        infoText.text = "SetLogs: " + textField[0].text;
    }

    private void GetLogStatic()
    {
        string result = javaClass.CallStatic<string>("GetLog");
        infoText.text = "GetLogs: " + result;
    }

    private void SetLogFieldStatic()
    {
        javaClass.SetStatic("Logs", textField[0].text);
        infoText.text = "SetFieldLogs: " + textField[0].text;
    }

    private void GetLogFieldStatic()
    {
        string value = javaClass.GetStatic<string>("Logs");
        infoText.text = "GetFieldLogs: " + value;
    }

    private void SetNameInstance()
    {
        javaObject.Call("SetName", textField[1].text);
        infoText.text = "SetName: " + textField[1].text;
    }

    private void GetNameInstance()
    {
        string name = javaObject.Call<string>("GetName");
        infoText.text = "GetName: " + name;
    }

    private void SetNameFieldInstance()
    {
        javaObject.Set("Name", textField[1].text);
        infoText.text = "SetFieldName: " + textField[1].text;
    }

    private void GetNameFieldInstance()
    {
        string name = javaObject.Get<string>("Name");
        infoText.text = "GetFieldName: " + name;
    }
}

Important: This will only work when the applicasion is built and run on an Android device or emulator, not in the Unity Editor.