여기다 물어볼게 아니고 파이어베이스 문서를 보셔야죠
https://firebase.google.com/docs/database/android/start/
myRef.addValueEventListener(new ValueEventListener() {
@Override
public void onDataChange(DataSnapshot dataSnapshot) {
// This method is called once with the initial value and again
// whenever data at this location is updated.
String value = dataSnapshot.getValue(String.class);
Log.d(TAG, "Value is: " + value);
}
@Override
public void onCancelled(DatabaseError error) {
// Failed to read value
Log.w(TAG, "Failed to read value.", error.toException());
}
});