Mushahid2521

public class MainActivity extends AppCompatActivity{

    final FragmentManager fragmentManager = getSupportFragmentManager();
    
    Fragment active_fragment;
    SongsFragment songs_fragment;
    ArtistsFragment artists_fragment;
    AlbumsFragment albums_fragment;

    @Override

Mushahid2521

public class MainActivity extends AppCompatActivity {

    final Fragment fragment1 = new HomeFragment();
    final Fragment fragment2 = new DashboardFragment();
    final Fragment fragment3 = new NotificationsFragment(); 
    final FragmentManager fm = getSupportFragmentManager();
    Fragment active = fragment1;

    @Override
    protected final void onCreate(@NonNull Bundle savedInstanceState) {

Mushahid2521

public class MainActivity extends AppCompatActivity {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);
    
    .....
    Songs songs_fragment = new SongsFragment()
    getSupportFragmentManager().beginTransaction().replace(R.id.container, songs_fragment).commit()
    .....
}