BottomNavigationView는 별도의 리스너가 존재하므로 그걸 사용하세요. 기존 코드를 재활용하면 아래와 같은 형태가 될 것 같네요.
bottomNavigationView.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
@Override
public boolean onNavigationItemSelected(@NonNull MenuItem item) {
onFragmentChanged (item.getItemId());
}
});
...
private void onFragmentChanged(int menuId) {
Fragment destnation;
switch (menuId) {
case R.id.main_fragment:
destnation = mainFragment
break;
case R.id.menu_fragment:
destnation = menuFragment
break;
default:
return;
}
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.container, destnation)
.commit();
}