SingleFragmentActivity

public abstract class SingleFragmentActivity extends AppCompatActivity {
    public abstract Fragment createFragment();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_fragment);
        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = createFragment();

     //   if (fragment==null) {
      //      fragment = createFragment();
        fm.beginTransaction().
                replace(R.id.fragment, fragment)
                .commit();


      //   }


    }
}