How to implement an Adnroid plugin with events

Hi,
I use some Bluetooth Android plugin. It consist from “bluetooth.jar” library and two C# scripts: the first one just calls methods from library, the second script contains callback methods for android events. For example:

    public class BluetoothEventListener : MonoBehaviour {

      void FoundDeviceEvent(string Device)
      {
       //todo
      }
    }

Could anybody explain to me how it’s work? In other words, how call from java code some methods in Unity’s script (C# or JavaScript)?

Use the UnityPlayer.UnitySendMessage method as described in the notes below the code of Example 3:

…and detailed in the iOS implementation: