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

    bottomNavigationView=(BottomNavigationView)findViewById(R.id.bottomNavigationView);
    bottomNavigationView.setOnNavigationItemSelectedListener(navigationItemSelectedListener);

    getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,new FragmentHome()).commit();
}

private BottomNavigationView.OnNavigationItemSelectedListener navigationItemSelectedListener=
        new BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
                Fragment selectedFragment=null;

                switch (menuItem.getItemId())
                {
                    case R.id.nav_home:
                        selectedFragment=new FragmentHome();
                        break;
                    case R.id.nav_graph:
                        selectedFragment=new FragmentGraph();
                        break;
                    case R.id.nav_calendar:
                        selectedFragment=new FragmentCalendar();
                        break;
                }
                getSupportFragmentManager().beginTransaction().replace(R.id.fragment_container,selectedFragment).commit();

                return true;
            }
        };