visalig

Firebase userRef= new Firebase(USERS_LOCATION);
userRef.child(userId).addListenerForSingleValueEvent(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot snapshot) {
        if (snapshot.getValue() !== null) {
            //user exists, do something
        } else {
            //user does not exist, do something else
        }
    }