FireStore

public class MainActivity extends AppCompatActivity {

    private static final String NAME_KEY = "Name";
    private static final String EMAIL_KEY = "Email";
    private static final String PHONE_KEY = "Phone";

FirebaseFirestore db;
    TextView textDisplay;

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
      db = FirebaseFirestore.getInstance();
        textDisplay = findViewById(R.id.textDisplay);
    }
}