android studio using tabbed for changing fragment and toolbar

I used switch for create tabbed and Fragment to change pages by tabbed on. now I want to have statement to say if user click one for example position 0 like chats Fragment my toolbar changes .

what i don't know is that how can i put a if statement on my result class SectionsPagerAdapter tabbed to change my toolbars that i created befor . I did some if statement on my mViewPager or mTabLayout but didn't worked.

My Activity for SectionsPagerAdapter :

     class SectionsPagerAdapter extends FragmentPagerAdapter{
            public SectionsPagerAdapter(FragmentManager fm) {
                super( fm );
            }

        @Override
        public Fragment getItem(int position) {

            switch (position) {
                case 0:
                    ChatsFragment chatsFragment = new ChatsFragment();
                    return chatsFragment;

                case 1:
                    ViewFragment viewFragment = new ViewFragment();
                    return viewFragment;

                case 2:
                    AccountFragment accountFragment = new AccountFragment();
                    return accountFragment;


                    default:
                        return null;



            }
        }
   @Override
    public int getCount() {
        return 3;
    }

    public CharSequence getPageTitle(int position){
        switch (position){

            case 0:
                return "Chats";

            case 1:
                return "View";

            case 2:
                return "Account";

            default:
                    return null;

        }

    }
}

My Code in Mainpage:

mViewPager=(ViewPager)findViewById( R.id.main_tabPager );
mSectionPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager() );
        mViewPager.setAdapter( mSectionPagerAdapter );
        mTabLayout =(TabLayout) findViewById( R.id.main_tabs );
        mTabLayout.setupWithViewPager( mViewPager );