public class Collection extends AppCompatActivity {

    TextView ttl, tgat, tsch;
    Button btnshw, btngt;
    Spinner sping;
    DatabaseReference d2ref;

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

        tgat = (TextView) findViewById(R.id.texigat);
        tsch = (TextView) findViewById(R.id.texisch);
        //tcls = (TextView) findViewById(R.id.texiclass);
        ttl = (TextView) findViewById(R.id.texirs);
        btnshw = (Button) findViewById(R.id.bshow);
        btngt = (Button) findViewById(R.id.bgat);
        sping = (Spinner) findViewById(R.id.spingat);

        btnshw.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                d2ref = FirebaseDatabase.getInstance().getReference().child("2018-19").child("Gat No 14")
                        .child("School no 109").child("Standard 2nd");
                d2ref.addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                        String rs = dataSnapshot.child("Rupees").getValue().toString();
                        ttl.setText(rs);
                    }

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

                    }
                });
            }
        });

        btngt.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
        d2ref = FirebaseDatabase.getInstance().getReference().child("2018-19");
        ValueEventListener eventListener = new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                final List<String> gatno = new ArrayList<String>();

                for (DataSnapshot dsnap : dataSnapshot.child("Gat No 14").getChildren()) {
                    String gat = dsnap.getKey();
                    gatno.add(gat);
                }
                ArrayAdapter<String> adapter = new ArrayAdapter<String>(Collection.this, android.R.layout.simple_spinner_item);
                adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
                sping.setAdapter(adapter);

                /*I wasn't able to get the value in 1st spinner so I didn't
                 wrote program for second spinner*/
            }

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

            }
        };
        d2ref.addListenerForSingleValueEvent(eventListener);
            }
        });
    }
}