C#

using UnityEngine;

public class TestPlugin : MonoBehaviour
{
    const string pluginName = "com.cw.unity.MyPlugin";
    static AndroidJavaClass _pluginClass;
    static AndroidJavaObject _pluginInstance;

    public static AndroidJavaClass PluginClass
    {
        get
        {
            if (_pluginClass == null)
            {
                _pluginClass = new AndroidJavaClass(pluginName);
            }

            return _pluginClass;
        }
    }

    public static AndroidJavaObject PluginInstance
    {
        get
        {
            if (_pluginInstance == null)
            {
                _pluginInstance = PluginClass.CallStatic<AndroidJavaObject>("getInstance");
            }

            return _pluginInstance;
        }
    }

    private void Start()
    {
        Debug.LogFormat("Start");
        Debug.LogFormat("{0}", PluginClass);
        Debug.LogFormat("{1}", PluginInstance);
        //Debug.LogFormat("Start {0}", GetElapsedTime());
    }

    float elapsedTime = 0;

    private void Update()
    {
        elapsedTime += Time.deltaTime;

        if (elapsedTime >= 5)
        {
            elapsedTime -= 5;
            Debug.LogFormat("Tick {0}", GetElapsedTime());
        }
    }

    double GetElapsedTime()
    {
        if (Application.platform == RuntimePlatform.Android)
        {
            return PluginInstance.Call<double>("getElapsedTime");
        }

        Debug.LogWarning("Wrong platform!");
        return 0;
    }
}