Recyclerview not showing data.Something is missing in my code - android-recyclerview

Question

I am beginner in Android.
This is My Java file. I just want to show data is recycler view, but when i open it on emulator my app crashes.Help me to find out the fault in my code.
private RecyclerView rview;
private MyAdapter adapter;
private ArrayList<Student> list;
private DatabaseReference reference;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_check_record);
reference = FirebaseDatabase.getInstance().getReference("Student");
rview = findViewById(R.id.recyclerview);
list = new ArrayList<>();
rview.setHasFixedSize(true);
rview.setLayoutManager(new LinearLayoutManager(this));
rview.addItemDecoration(new DividerItemDecoration(rview.getContext(),
DividerItemDecoration.VERTICAL));
adapter = new MyAdapter(this, list);
rview.setAdapter(adapter);
reference.addListenerForSingleValueEvent(listener);
}
ValueEventListener listener = new ValueEventListener() {
#Override
public void onDataChange(#NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()){
list.clear();
for (DataSnapshot snapshot:dataSnapshot.getChildren()){
Student s =dataSnapshot.getValue(Student.class);
list.add(s);
}
adapter.notifyDataSetChanged();
}
else {
Toast.makeText(CheckRecordActivity.this, "No Record Found", Toast.LENGTH_SHORT).show();
}
}
#Override
public void onCancelled(#NonNull DatabaseError databaseError) {
Toast.makeText(CheckRecordActivity.this, databaseError.toString(), Toast.LENGTH_SHORT).show();
}
};
}

Answer 1

Set recyclerview manager on this way:-
final LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity(), LinearLayoutManager.VERTICAL, false);
rv.setLayoutManager(layoutManager);
You have to check 4 things,
you have to not initialize your firebase instance on your Application class like(FirebaseApp.initializeApp(this))
Check DatabaseReference refrence is null or not
DataSnapshot value is return or not
Check array value is null or not
if there four value is null,so app can be crash.