fragmentManager
                .beginTransaction()
                .replace(R.id.fl_container, new FragmentA())
                .commit();
  fragmentManager
                .beginTransaction()
                .replace(R.id.fl_container, new FragmentB())
                .addToBackStack(null)
                .commit();
  fragmentManager
                .beginTransaction()
                .replace(R.id.fl_container, new FragmentC())
                .addToBackStack(null)
                .commit();

Fragment fragment = fragmentManager.findFragmentById(R.id.fl_container);
        if (fragment instanceof IRootFragment) {
            if (fragmentManager.getBackStackEntryCount() > 0) {
                getSupportFragmentManager().popBackStack(
                fragmentManager.getBackStackEntryAt(0).getId(),
             FragmentManager.POP_BACK_STACK_INCLUSIVE);
            }
            super.onBackPressed();
        } else {
            fragmentManager.popBackStackImmediate();
        }