title: How to set a fragment as default fragment for BottomNavigation?
body: <p>I have a Bottom Navigation in my MainActivity.java with 3 fragments.
  I want to set one of my fragments as default to open automatically when app starts.
  how can i do that?
  this is my Main Activity.java:</p>
  
  <pre><code>public class MainActivity extends AppCompatActivity {
  private static final String TAG = MainActivity.class.getSimpleName();
  private BottomNavigationView bottomNavigation;
  private Fragment fragment;
  private android.support.v4.app.FragmentManager fragmentManager;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_main);
      bottomNavigation = (BottomNavigationView)findViewById(R.id.bottom_navigation);
      bottomNavigation.inflateMenu(R.menu.bottom_menu);
      fragmentManager = getSupportFragmentManager();
  
  
  
      bottomNavigation.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
          @Override
          public boolean onNavigationItemSelected(@NonNull MenuItem item) {
              Fragment selectedFragment = null;
              int id = item.getItemId();
              switch (id){
                  case R.id.intros:
                      fragment = new IntrosFragment();
                      break;
                  case R.id.menus:
                      fragment = new MenusFragment();
                      break;
                  case R.id.infos:
                      fragment = new InfosFragment();
                      break;
              }
              FragmentTransaction transaction = fragmentManager.beginTransaction();
              transaction.replace(R.id.main_container, fragment).commit();
              return true;
          }
      });
  
  
  }
  }
  </code></pre>
  
  <p>and this is one my fragment for example(they're all the same):</p>
  
  <pre><code>public class IntrosFragment extends Fragment {
  
  
  public IntrosFragment() {
  
  }
  
  @Override
  public View onCreateView(LayoutInflater inflater, ViewGroup container,
                           Bundle savedInstanceState) {
      View rootView = inflater.inflate(R.layout.fragment_intro, container, false);
      // Inflate the layout for this fragment
      TextView txt = (TextView) rootView.findViewById(R.id.introtv);
      Typeface font = Typeface.createFromAsset(getActivity().getAssets(), "fonts/naskh.ttf");
      txt.setTypeface(font);
  
      return rootView;
  }
  }
  </code></pre>
  
  <p>what should I do?</p>