如何替换ViewPager中的片段和更改工具栏

// 创建FragmentPagerAdapter的子类
public class MyPagerAdapter extends FragmentPagerAdapter {
    private List<Fragment> fragmentList;

    public MyPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
        super(fm);
        this.fragmentList = fragments;
    }

    @Override
    public Fragment getItem(int position) {
        return fragmentList.get(position);
    }

    @Override
    public int getCount() {
        return fragmentList.size();
    }
}

// 在Activity或Fragment中使用ViewPager
ViewPager viewPager = findViewById(R.id.viewPager);
List<Fragment> fragments = new ArrayList<>();
fragments.add(new Fragment1());
fragments.add(new Fragment2());
fragments.add(new Fragment3());

MyPagerAdapter pagerAdapter = new MyPagerAdapter(getSupportFragmentManager(), fragments);
viewPager.setAdapter(pagerAdapter);

// 替换ViewPager中的片段
fragments.set(1, new NewFragment());
pagerAdapter.notifyDataSetChanged();

// 更改工具栏
Toolbar toolbar = findViewById(R.id.toolbar);
setSupportActionBar(toolbar);