如果单击底部导航项，如何转换到活动而不是片段？

setContentView(R.layout.activity_main);
        fm.beginTransaction().add(R.id.main_container,fragment3).hide(fragment3).commit();
        fm.beginTransaction().add(R.id.main_container,fragment2).hide(fragment2).commit();
        fm.beginTransaction().add(R.id.main_container,fragment1).commit();        //this is fragment

        //this is implementing fragment  
        final BottomNavigationView bottomNavigationView = findViewById(R.id.nav_bawah);
        bottomNavigationView.setSelectedItemId(R.id.navigation_dashboard);
        bottomNavigationView.setOnNavigationItemSelectedListener(new 
        BottomNavigationView.OnNavigationItemSelectedListener() {
            @Override
            public boolean onNavigationItemSelected( MenuItem item) {

                switch (item.getItemId()) {

                    case R.id.navigation_dashboard:

                        fm.beginTransaction().hide(active).show(fragment1).commit();
                        active=fragment1;

                        break;
                    case R.id.navigation_challange:

                        fm.beginTransaction().hide(active).show(fragment2).commit();
                        active=fragment2;

                        break;

                    case R.id.navigation_chat:

                        fm.beginTransaction().hide(active).show(fragment3).commit();
                        active = fragment3;

                        break;

                }
                return true;

            }
        });