Nested child fragments for bottom navigation view in Java

MyFragment.java

    public class MyFragment
            extends Fragment {
    
        public MyFragment() {
            super(R.layout.my_fragment);
        }
    
        private int selectedIndex = 0;
    
        private FirstFragment firstFragment;
        private SecondFragment secondFragment;
        private ThirdFragment thirdFragment;
    
        private MyFragmentBinding binding = null;
    
        private List<Fragment> getFragments() {
            return new ArrayList<Fragment>() {{
                add(firstFragment);
                add(secondFragment);
                add(thirdFragment);
            }};
        }
    
        private List<TextView> getTabs() {
            return new ArrayList<TextView>() {{
                add(binding.buttonFirstTab);
                add(binding.buttonSecondTab);
                add(binding.buttonThirdTab);
            }};
        }
    
        private FragmentTransaction selectFragment(FragmentTransaction fragmentTransaction, int selectedIndex) {
            List<Fragment> fragments = getFragments();
            FragmentTransaction ft = fragmentTransaction;
            for(int index = 0; index < fragments.size(); index++) {
                Fragment fragment = fragments.get(index);
                if(index == selectedIndex) {
                    ft = ft.attach(fragment);
                } else {
                    ft = ft.detach(fragment);
                }
            }
    
            return ft;
        }
    
        public void selectFragment(int indexToSelect) {
            this.selectedIndex = indexToSelect;
    
            setupTabSelectedState(indexToSelect);
    
            FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction();
            fragmentTransaction = selectFragment(fragmentTransaction, indexToSelect);
            fragmentTransaction.commit();
        }
    
        private void setupTabSelectedState(int selectedIndex) {
            List<TextView> tabs = getTabs();
    
            for(int index = 0; index < tabs.size(); index++) {
                TextView tab = tabs.get(index);
    
                if(index == selectedIndex) {                
                    tab.setTextColor(ContextCompat.getColor(requireContext(), R.color.tab_selected));
                } else {
                    tab.setTextColor(ContextCompat.getColor(requireContext(), R.color.tab_unselected));
                }
            }
        }
    
        @Override
        public void onCreate(@Nullable Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
    
            if(savedInstanceState == null) {
                firstFragment = new FirstFragment();
                secondFragment = new SecondFragment();
                thirdFragment = new ThirdFragment();
    
                FragmentTransaction fragmentTransaction = getChildFragmentManager().beginTransaction()
                        .add(R.id.container, firstFragment, "firstFragment")
                        .add(R.id.container, secondFragment, "secondFragment")
                        .add(R.id.container, thirdFragment, "thirdFragment");
    
                fragmentTransaction = selectFragment(fragmentTransaction, selectedIndex);
    
                fragmentTransaction.commit();
            } else {
                selectedIndex = savedInstanceState.getInt("selectedIndex", 0);
    
                firstFragment = (FirstFragment) getChildFragmentManager().findFragmentByTag("firstFragment");
                secondFragment = (SecondFragment) getChildFragmentManager().findFragmentByTag("secondFragment");
                thirdFragment = (ThirdFragment) getChildFragmentManager().findFragmentByTag("thirdFragment");
            }
        }
    
        @Override
        public void onViewCreated(View view, @Nullable Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
    
            binding = MyFragmentBinding.bind(view);
    
            setupTabSelectedState(selectedIndex);
    
            List<TextView> tabs = getTabs();
    
            for(int index = 0; index < tabs.size(); index++) {
                TextView tab = tabs.get(index);
                final int i = index;
                tab.setOnClickListener(v -> {
                    selectFragment(i);
                });
            }
        }
    
        @Override
        public void onSaveInstanceState(@NonNull Bundle outState) {
            super.onSaveInstanceState(outState);
            outState.putInt("selectedIndex", selectedIndex);
        }

        @Override
        public void onDestroyView() {
            super.onDestroyView();
            binding = null;
        } 
    }