nilai_course.child(keys).addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                    if(dataSnapshot.exists()){
                        for(DataSnapshot nilaiHasil : dataSnapshot.getChildren()){

                            String nilaiHasilKey = nilaiHasil.getKey();
                            for(DataSnapshot nilaiHasil2: nilaiHasil.getChildren())
                            {
                             String keyUid = nilaiHasil2.getKey();
                             String score =  nilaiHasil2.getValue.toString();
                            }

                            nilai_key.add(nilaiHasilKey);

                            //here i want to store the last value like 100,100 etc


                            keterangan_nilai.child(keys).child(nilaiHasilKey).addValueEventListener(new ValueEventListener() {
                                @Override
                                public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                                    NilaiMatakuliah nilai = dataSnapshot.getValue(NilaiMatakuliah.class);
                                    listNilai.add(nilai);
                                    progressBar_nilai.setVisibility(View.GONE);

                                    mAdapter.notifyDataSetChanged();


                                }

                                @Override
                                public void onCancelled(@NonNull DatabaseError databaseError) {

                                }
                            });
                        }
                    }else{
                        //tidak ada nilai
                    }