calling java method from unity c#

Hello everyone, Can anyone tell me how to call java methods from unity c#. I tried the following but its not working for me.

In Unity :

 void OnGUI () {
     string somestring;
     AndroidJavaClass jc= new AndroidJavaClass("com.example.pluginsample.MainActivity");
     AndroidJavaObject jo = jc.GetStatic<AndroidJavaObject>("instance");
     somestring = jo.Call<string>("Foo");
     GUI.Label (new Rect (20, 20, 100, 20), somestring);
 }
 

In Java Class:

 public String Foo()
 {
     return "Hello";        
 }