public class MainActivity extends AppCompatActivity implements BottomNavigatorView.OnBottomNavigatorViewItemClickListener {

    private static final int DEFAULT_POSITION = 0;

    private FragmentNavigator mNavigator;

    // a simple custom bottom navigation view
    private BottomNavigatorView bottomNavigatorView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        mNavigator = new FragmentNavigator(getSupportFragmentManager(), new FragmentAdapter(), R.id.container);
        // set default tab position
        mNavigator.setDefaultPosition(DEFAULT_POSITION);
        mNavigator.onCreate(savedInstanceState);

        bottomNavigatorView = (BottomNavigatorView) findViewById(R.id.bottomNavigatorView);
        bottomNavigatorView.setOnBottomNavigatorViewItemClickListener(this);

        setCurrentTab(mNavigator.getCurrentPosition());
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        mNavigator.onSaveInstanceState(outState);
    }

    @Override
    public void onBottomNavigatorViewItemClick(int position, View view) {
        setCurrentTab(position);
    }

    private void setCurrentTab(int position) {
        mNavigator.showFragment(position);
        bottomNavigatorView.select(position);
    }
}

public class FragmentAdapter implements FragmentNavigatorAdapter {

    private static final String TABS[] = {"Chats", "Contacts", "Circle", "Me"};

    @Override
    public Fragment onCreateFragment(int position) {
        return MainFragment.newInstance(TABS[position]);
    }

    @Override
    public String getTag(int position) {
        // an simple unique tag
        return MainFragment.TAG + TABS[position];
    }

    @Override
    public int getCount() {
        return TABS.length;
    }
}