Setting up game object in constructor

NativeCalculations.cs

using System;
using System.Runtime.InteropServices;
using UnityEngine;

namespace Plugins.NativeCalculations
{
    ...

    public static class NativeCalculations
    {
        // Game object is created to receive async messages
        private const string GAME_OBJECT_NAME = "PluginBridge";
        private static GameObject gameObject;
        
        ...

        static NativeCalculations()
        {

            // Create Game Object to allow sending messages from Java or Objective C to Unity
            gameObject = new GameObject();

            // Object name must match UnitySendMessage call in Java or Objective C
            gameObject.name = GAME_OBJECT_NAME;

            // Attach this class to allow for handling of callbacks from Java or Objective C
            gameObject.AddComponent<NativeCalculationsCallbackHandler>();

            // Do not destroy when loading a new scene
            UnityEngine.Object.DontDestroyOnLoad(gameObject);

            // Initialize Plugin
            switch (Application.platform)
            {
                case RuntimePlatform.Android:
                    var androidJavaUnityPlayer = new AndroidJavaClass("com.unity3d.player.UnityPlayer");

                    // Current activity does not change for Unity
                    var currentActivity = androidJavaUnityPlayer.GetStatic<AndroidJavaObject>("currentActivity");

                    // Initialize native Java object
                    androidJavaNativeCalculation = new AndroidJavaObject(JAVA_OBJECT_NAME, currentActivity);
                    break;

                case RuntimePlatform.IPhonePlayer:
                    // No initialization needed
                    break;

                default:
                    throw new PlatformNotSupportedException();
            }
        }
        
        ...

        /*
         * -----------------------------
         * Native Async Callback Handler
         * -----------------------------
         */

        private class NativeCalculationsCallbackHandler : MonoBehaviour
        {
            private void HandleException(string exception)
            {
                throw new Exception(exception);
            }

            private void HandleAsyncCalculation(string calculationResultsJSON)
            {
                var calculationResults = JsonUtility.FromJson<CalculationResults>(calculationResultsJSON);
                handleAsyncCalculation?.Invoke(calculationResults);
            }
        }
    }
}