ublic class Authentication extends AppCompatActivity implements View.OnClickListener {

private FirebaseAuth mAuth;
private FirebaseAuth.AuthStateListener mAuthStateListener;

private EditText ETemail;
private EditText ETpassword;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_authentication);

mAuth = FirebaseAuth.getInstance();

mAuthStateListener = new FirebaseAuth.AuthStateListener() {
@Override
public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
FirebaseUser user = firebaseAuth.getCurrentUser();

if (user != null) {
//Если пользователь авторизовался
} else {

}

}
};
ETemail = (EditText) findViewById(R.id.et_email);
ETpassword = (EditText) findViewById(R.id.et_password);

findViewById(R.id.btn_sign_in).setOnClickListener(this);
findViewById(R.id.btn_registration).setOnClickListener(this);
}

@Override
public void onClick(View view) {
if(view.getId() == R.id.btn_sign_in)
{
signIn(ETemail.getText().toString(),ETpassword.getText().toString());
}else if(view.getId() == R.id.btn_registration){

createAccount(ETemail.getText().toString(),ETpassword.getText().toString());
}
}
private void createAccount (String email , String password)
{
mAuth.createUserWithEmailAndPassword(email,password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if(task.isSuccessful()){
Toast.makeText(Authentication.this,"Регистрация успешна",Toast.LENGTH_SHORT).show();
}
if(!task.isSuccessful()){
Toast.makeText(Authentication.this,"Регистрация провалена",Toast.LENGTH_SHORT).show();
}
}
});
{
}
}
private void signIn(String email,String password)
{
mAuth.signInWithEmailAndPassword(email, password).addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
@Override
public void onComplete(@NonNull Task<AuthResult> task) {
if(task.isSuccessful()){
Toast.makeText(Authentication.this,"Авторизация успешна",Toast.LENGTH_SHORT).show();
}
if(!task.isSuccessful()){
Toast.makeText(Authentication.this,"Авторизация провалена",Toast.LENGTH_SHORT).show();
}
}
});
}
}