Writing user define and in built method for android

I want to execute user define and in built method in Unity. I am clearly aware with call of object and class related method available in Java API.

Such as following type of code

AndroidJavaClass intentClass = new AndroidJavaClass("android.content.Intent"); AndroidJavaObject intentObject = new AndroidJavaObject("android.content.Intent"); intentObject.Call("setAction", intentClass.GetStatic("ACTION_SEND_MULTIPLE")); intentObject.Call("setType", "/"); intentObject.Call("putExtra", intentClass.GetStatic("EXTRA_SUBJECT"), "SUBJECT"); intentObject.Call("putExtra", intentClass.GetStatic("EXTRA_TEXT"), "This is my text to send."); intentObject.Call("putExtra", intentClass.GetStatic("EXTRA_STREAM"), new Uri(pathToImage).LocalPath);

Now I want to learn more about same type in concept. I want to write my custom method in android such as

 public static String getPath() {
 }

How to write this method code in Unity?

I want to use callback method in android such as

 @Override
 protected void onActivityResult(int arg0, int arg1, Intent arg2) {
         super.onActivityResult(arg0, arg1, arg2);
         
 }

Please give some suggestion in this.