How to use simply adapterViewPager.getRegisteredFragment(number)

Hi masters I need some help My fundemantal Project source codes is here http://ift.tt/1R9ohgz A

You can download working zipped project file.

In the FirstFragment class , Button1 works fine with below codes very good

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////// View but1 = (View) getActivity().findViewById(R.id.button1);

    // //////////
    but1.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {

            pager.setCurrentItem(pager.getCurrentItem() + 2);

        }
    });

//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

but Button 3 not run with below codes

    View but3 = (View) getActivity().findViewById(R.id.button3);

    // //////////
    but3.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {


            MyPagerAdapter adapterViewPager = ((MyPagerAdapter)pager.getAdapter());


            //pager.setCurrentItem(pager.getCurrentItem() + 2);

            adapterViewPager.getRegisteredFragment(2;



        }
    });

//////////////////////////////

In my orginal project I created MANY Fragments class and different layouts, I want to use adapterViewPager.getRegisteredFragment

I want help for adapterViewPager.getRegisteredFragment(..);