@Override
public void onBackPressed() {
    CustomerFrag cf = (CustomerFrag)getSupportFragmentManager().findFragmentByTag("Customer");
    if (cf != null)
        FragmentTransaction ft = getFragmentManager().beginTransaction();
        Fragment frag = new CustomerFrag();
        ft.replace(R.id.fl, frag);
        ft.addToBackStack("back");
        ft.commit();
    else
        super.onBackPressed();
}