How to display my Firebase Database with this array down below?

Question

What to pass in getVerticalData() down below I want to display the DB in getVerticalData.get(0); What to pass there to display the Database ?

How to display my Firebase Database with this array down below?

private ArrayList<Object> objects = new ArrayList<();
MainAdapter adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);


    RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recycler_View);
    adapter = new MainAdapter(this, getObject());
    recyclerView.setAdapter(adapter);
    recyclerView.setLayoutManager(newLinearLayoutManager(this));
}

private ArrayList <Object> getObject() {

    objects.add(getVerticalData().get(0));
    objects.add(getHorizontalData().get(0));
    objects.add(getVerticalData2().get(0));
    return objects;
}

Here I would like to display the data from FB DB.

public static ArrayList<SingleVertical> getVerticalData() {
    final ArrayList<SingleVertical> singleVerticals = new ArrayList<>();

   /* DatabaseReference db = FirebaseDatabase.getInstance().getReference("test");
    db.addChildEventListener(new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            SingleVertical post = dataSnapshot.getValue(SingleVertical.class);
            singleVerticals.add(post);
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    }); */

    singleVerticals.add(new SingleVertical("Charlie Chaplin", "Sir Charles Spencer \"Charlie\" Chaplin, KBE was an English comic actor,....", R.mipmap.ic_launcher));
    singleVerticals.add(new SingleVertical("Mr.Bean", "Mr. Bean is a British sitcom created by Rowan Atkinson and Richard Curtis, and starring Atkinson as the title character.", R.mipmap.ic_launcher_round));
    singleVerticals.add(new SingleVertical("Jim Carrey", "James Eugene \"Jim\" Carrey is a Canadian-American actor, comedian, impressionist, screenwriter...", R.mipmap.ic_launcher));
    return singleVerticals;
}

public static ArrayList<SingleVertical> getVerticalData2() {
    ArrayList<SingleVertical> singleVerticals = new ArrayList<>();
    singleVerticals.add(new SingleVertical("Charlie Chaplin", "Sir Charles Spencer \"Charlie\" Chaplin, KBE was an English comic actor,....", R.mipmap.ic_launcher));
    singleVerticals.add(new SingleVertical("Mr.Bean", "Mr. Bean is a British sitcom created by Rowan Atkinson and Richard Curtis, and starring Atkinson as the title character.", R.mipmap.ic_launcher_round));
    singleVerticals.add(new SingleVertical("Jim Carrey", "James Eugene \"Jim\" Carrey is a Canadian-American actor, comedian, impressionist, screenwriter...", R.mipmap.ic_launcher));
    return singleVerticals;
}


public static ArrayList<SingleHorizontal> getHorizontalData() {
    ArrayList<SingleHorizontal> singleHorizontals = new ArrayList<>();
    singleHorizontals.add(new SingleHorizontal(R.mipmap.ic_launcher, "Charlie Chaplin", "Sir Charles Spencer \"Charlie\" Chaplin, KBE was an English comic actor,....", "2010/2/1"));
    singleHorizontals.add(new SingleHorizontal(R.mipmap.ic_launcher_round, "Mr.Bean", "Mr. Bean is a British sitcom created by Rowan Atkinson and Richard Curtis, and starring Atkinson as the title character.", "2010/2/1"));
    singleHorizontals.add(new SingleHorizontal(_launcher, "Jim Carrey", "James Eugene \"Jim\" Carrey is a Canadian-American actor, comedian, impressionist, screenwriter...", "2010/2/1"));
    return singleHorizontals;
}

I cannot figure out what parameter I should pass to getVertical();