NavigationDrawer and snippets

Good day! I make an application on android, I decided to take the interface with NavigationDrawer and fragments. That is, there are several tabs in the driver; when pressed, a specific fragment should be loaded into the container. However, when you press a button, the application crashes. What could be the problem?

Mainactivity.java:

 public class MainActivity extends AppCompatActivity { DefaultFragment frag1; SettingsFragment frag2; StatisticFragment frag3; HeroesFragment frag4; FragmentTransaction ftrans; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); frag1 = new DefaultFragment(); frag2 = new SettingsFragment(); frag3 = new StatisticFragment(); ftrans = getSupportFragmentManager().beginTransaction(); ftrans.add(R.id.fragment_container, frag1); ftrans.commit(); Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar); setSupportActionBar(toolbar); //navdrawer new DrawerBuilder().withActivity(this); PrimaryDrawerItem item1 = new PrimaryDrawerItem().withIdentifier(1).withName(R.string.drawer_item_stat);//первый объект в дравере (Статистика) SecondaryDrawerItem item2 = new SecondaryDrawerItem().withIdentifier(2).withName(R.string.drawer_item_settings);//второй(Настройки) SecondaryDrawerItem item3 = new SecondaryDrawerItem().withIdentifier(3).withName(R.string.drawer_item_heroes);//третий(Герои) Drawer result = new DrawerBuilder() .withActivity(this) .withToolbar(toolbar) .addDrawerItems( item1, item2, item3) .withOnDrawerItemClickListener(new Drawer.OnDrawerItemClickListener() { @Override public boolean onItemClick(View view, int position, IDrawerItem drawerItem) { ftrans = getSupportFragmentManager().beginTransaction(); switch ((int) drawerItem.getIdentifier()) { case 1: ftrans.replace(R.id.fragment_container, frag3); case 2: ftrans.replace(R.id.fragment_container, frag2); case 3: ftrans.replace(R.id.fragment_container, frag4); } ftrans.commit(); return true; } }).build(); } }`