Is possible to call a Unity3D function from a Java Android Class?

You can do something like this in Java once you have integrated with eclipse using the SendMessage function.

 public class myawesomeanroidapp extends UnityPlayerActivity
 {

 /** Called when the activity is first created. */
 
 @Override
 public void onCreate(Bundle savedInstanceState) 
 {
     super.onCreate(savedInstanceState);
 }

 public void SendMessageToUnity()
 {
     UnityPlayer.UnitySendMessage("Main Camera","foo",Integer.toString(fooint));
 }

}

See this page under example 3 of the Android section. You do it very similarly to how you do it on iOS except that you have to create a JavaObject.