How to cast loaded class from external apk into interface class

//Interface class -> packaged to myinterface.jar

package com.example.my_interface;
import com.example.my_interface.point;

pubic abstract class MyInterface{
    publib Object obj;  
    public abstract Point newPoint(Point p);
}    

//--- and other class ----

package com.example.my_interface.point;
public abstract class Point{
    public int x;
    public int y;   
}

//Project 1 - included myinterface.jar and packaged to classA.apk

package com.testing.classa;
import com.example.my_interface.point;

public class ClsA extends MyInterface{  

    @Override
    public Point newPoint(Point p){
        Point newP;
        newP.x = p.x + 1;
        newP.y = p.y + 1;

        return newP;
    }
}

//Main project // Included myinterface.jar // From this class (ClassB), i want to call "newPoint" method from "ClsA" in classA.apk file.

package com.testing;
import com.example.my_interface.point;

public class ClsB{

    Point p1;
    p1.x = 2;
    p1.y = 3;

    Point newP;

    String apkfilePath = '/data/data/com.testing/files/apps/classA.apk';
    final File optimizedDexOutputPath = cnt.getDir("outdex", Context.MODE_PRIVATE);

    DexClassLoader dLoader = new DexClassLoader(apkfilePath,
                    optimizedDexOutputPath.getAbsolutePath(),
                    null, ClassLoader.getSystemClassLoader().getParent());

    try{
        Class<?> loadedClass = dLoader.loadClass("com.testing.classa.ClsA");
        Object obj = (Object) loadedClass.newInstance();   // (*)

        Method m = loadedClass.getDeclaredMethod("newPoint", Point.class);
        m.setAccessible(true);

        newP = (Point) m.invoke(obj, p1);                   //(**)

    }catch(Exception ex){
        ex.printStackTrace();
    }

    Log.d("NewPoint x",Integer.toString(newP.x));
    Log.d("NewPoint y",Integer.toString(newP.xy));
}

Question 1. At (*): I can not cast "obj" returned after instance to MyInterface class, like:

Object obj = (Object) loadedClass.newInstance();
MyInterface mi = (MyInterface) obj;

-> Error:

Can not cast com.testing.classa.ClsA to com.example.my_interface.MyInterface`

Why not? while in com.testing.classa.ClsA had extends MyInterface ?

Question 2. At (**): ERROR,

java.lang.IllegalArgumentException: argument 1 should have type com.example.my_interface.point, got com.example.my_interface.point

I think in main class had interface myinterface.jar, and on classA.apk had myinterface.jar too, and them can not talk together. What's solution for this problem?

p/s: I searched on google, has someone suggest remove common lib from .apk (here myinterface.jar), but, if removing it that will be can not build because errors.

Help me, thanks.