load jar file of class dynamically

package com.example.sposedtest;

import java.io.File;
import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.widget.Button;
import dalvik.system.DexClassLoader;

public class MainActivity extends Activity {

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);

  Button btn = (Button) findViewById(R.id.button1);
  btn.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    // de.robv.android.xposed.XposedBridge.
    load_class();
   }
  });

  Button btn2 = (Button) findViewById(R.id.Button2);
  btn2.setOnClickListener(new View.OnClickListener() {
   @Override
   public void onClick(View v) {
    // TODO Auto-generated method stub
    // de.robv.android.xposed.XposedBridge.
    click_button();
   }
  });
 }

 private static native void click_button();

 private void load_class() {
  final File optimizedDexPath = getDir("dex", Context.MODE_PRIVATE);
  Log.d("DEXLOADER", " dexInternalStoragePath.exists = "
    + optimizedDexPath.toString());
  Log.d("DEXLOADER", " dexInternalStoragePath.exists = "
    + optimizedDexPath.exists());
  if (!optimizedDexPath.exists()) {
   try {
    optimizedDexPath.createNewFile();
   } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }

  DexClassLoader loader = new DexClassLoader("/data/MainActivity.jar",
    optimizedDexPath.getAbsolutePath(), null, getClassLoader());
  Class<?> clazz;
  try {
   clazz = loader.loadClass("com.example.test.MainActivity");
   Object obj = clazz.newInstance();
   Method m = clazz.getMethod("sayHello");
   m.invoke(obj);
   Log.d("DEXLOADER", "m = " + m);
  } catch ( Exception e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
   // TODO Auto-generated catch block
  }
  // dog.sayHello();
 }

 public void sayHello() {
   Log.d("DEXLOADER", ">>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>helloooooooooooooooooooooo ");
 }

 @Override
 public boolean onCreateOptionsMenu(Menu menu) {
  // Inflate the menu; this adds items to the action bar if it is present.
  getMenuInflater().inflate(R.menu.main, menu);
  return true;
 }
}