//check email already exist or not.
    firebaseAuth.fetchSignInMethodsForEmail(email)
            .addOnCompleteListener(new OnCompleteListener() {
                @Override
                public void onComplete(@NonNull Task task) {

                    boolean isNewUser = task.getResult().getSignInMethods().isEmpty();

                    if (isNewUser) {
                        Log.e("TAG", "Is New User!");
                    } else {
                        Log.e("TAG", "Is Old User!");
                    }

                }
            });