SignIn in Firebase using Email and Google Account (Java)

 This is main_activity.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <EditText
        android:id="@+id/editTextTextPersonName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="108dp"
        android:ems="10"
        android:hint="Email"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/editTextTextPassword"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="24dp"
        android:ems="10"
        android:hint="password"
        android:inputType="textPassword"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextTextPersonName" />

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="Login"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextTextPassword" />

    <Button
        android:id="@+id/button2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginBottom="48dp"
        android:text="register"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.888"
        app:layout_constraintStart_toStartOf="parent" />

    <Button
        android:id="@+id/button5"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="google sign in"
        app:layout_constraintBottom_toTopOf="@+id/button2"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />
</androidx.constraintlayout.widget.ConstraintLayout>

This is Registerpage

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".registerPage">

    <EditText
        android:id="@+id/editTextTextPersonName2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="208dp"
        android:ems="10"
        android:hint="Email"
        android:inputType="textPersonName"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <EditText
        android:id="@+id/editTextTextPassword2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="8dp"
        android:ems="10"
        android:hint="password"
        android:inputType="textPassword"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.497"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextTextPersonName2" />

    <Button
        android:id="@+id/button3"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:text="register"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/editTextTextPassword2" />

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="login"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.919"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button3"
        app:layout_constraintVertical_bias="0.904" />
</androidx.constraintlayout.widget.ConstraintLayout>

This is Dashboard.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/emailFromFirebase"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".DashboardPage">

    <TextView
        android:id="@+id/textView"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Welcome to Dashboard."
        android:textAlignment="center"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.5"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/signOut"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="sign out"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/textView"
        app:layout_constraintVertical_bias="0.337" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        app:layout_constraintBottom_toTopOf="@+id/textView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.498"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.614" />
</androidx.constraintlayout.widget.ConstraintLayout>

This is MainActivity

package com.example.firebasewithemail;

import androidx.activity.result.ActivityResult;
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.example.firebasewithemail.Models.ViewModel;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInAccount;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.common.api.ApiException;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;

public class MainActivity extends AppCompatActivity {
    private Button loginBtn;
    private Button registerBtn;
    private Button googleSignIn;
    private EditText emailFeild;
    private EditText passFeild;

    private FirebaseAuth auth = FirebaseAuth.getInstance();

    private ViewModel viewModel;
    private GoogleSignInClient googleSignClient;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        loginBtn = findViewById(R.id.button);
        registerBtn = findViewById(R.id.button2);
        emailFeild = findViewById(R.id.editTextTextPersonName);
        passFeild = findViewById(R.id.editTextTextPassword);
        googleSignIn = findViewById(R.id.button5);

        viewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(getApplication())).get(ViewModel.class);

        loginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String email = emailFeild.getText().toString();
                String pass = passFeild.getText().toString();
                if (email.isEmpty() && pass.isEmpty()) {
                    Toast.makeText(getApplicationContext(), "Please enter your email and password", Toast.LENGTH_SHORT).show();
                } else {
                    viewModel.signInWithEmail(email, pass);
                    viewModel.user.observe(MainActivity.this, new Observer<FirebaseUser>() {
                        @Override
                        public void onChanged(FirebaseUser firebaseUser) {
                            if (firebaseUser != null) {
                                startActivity(new Intent(MainActivity.this, DashboardPage.class));
                            } else {
                                Toast.makeText(MainActivity.this, "These Credential is not match with our database.", Toast.LENGTH_LONG)
                                        .show();
                            }
                        }
                    });
                }
            }
        });

        registerBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(MainActivity.this, registerPage.class));
            }
        });

        googleSignIn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                        .requestIdToken(getString(R.string.default_web_client_id))
                        .requestEmail()
                        .build();
                googleSignClient = GoogleSignIn.getClient(MainActivity.this, gso);
                Intent intent = googleSignClient.getSignInIntent();
                launcher.launch(intent);
            }
        });

    }

    @Override
    protected void onStart() {
        super.onStart();
        if (FirebaseAuth.getInstance().getCurrentUser() != null){
            startActivity(new Intent(MainActivity.this, DashboardPage.class));
        }
    }

    ActivityResultLauncher<Intent> launcher = registerForActivityResult(new ActivityResultContracts.StartActivityForResult(), (ActivityResult result) -> {
        Task<GoogleSignInAccount> task = GoogleSignIn.getSignedInAccountFromIntent(result.getData());
        try {
            GoogleSignInAccount account = task.getResult(ApiException.class);
            viewModel.signWithGoogle(MainActivity.this, account.getIdToken());

        } catch (ApiException e) {
            Log.w("TAG", "Google sign in failed", e);
        }

            });

}

This is RegisterActivity

package com.example.firebasewithemail;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import com.example.firebasewithemail.Models.ViewModel;
import com.google.firebase.auth.FirebaseUser;

public class registerPage extends AppCompatActivity {

    private Button registerBtn;
    private Button loginBtn;
    private EditText emailFeild;
    private EditText passFeild;

    private ViewModel viewModel;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register_page);

        loginBtn = findViewById(R.id.button4);
        registerBtn = findViewById(R.id.button3);
        emailFeild = findViewById(R.id.editTextTextPersonName2);
        passFeild = findViewById(R.id.editTextTextPassword2);

        viewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(getApplication())).get(ViewModel.class);

        registerBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String email = emailFeild.getText().toString();
                String pass = passFeild.getText().toString();
                if (email.isEmpty() && pass.isEmpty()) {
                    Toast.makeText(getApplicationContext(), "Please enter your email and password", Toast.LENGTH_SHORT).show();
                } else {
                    viewModel.signUpWithEmail(registerPage.this, email, pass);
                }
            }
        });

        loginBtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                finish();
            }
        });

    }
}

This is DashboardActivity

package com.example.firebasewithemail;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.Observer;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import com.example.firebasewithemail.Models.ViewModel;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class DashboardPage extends AppCompatActivity {
    private final FirebaseAuth auth = FirebaseAuth.getInstance();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_dashboard_page);

        TextView showEmail = findViewById(R.id.textView2);

        String email = auth.getCurrentUser().getEmail();

        showEmail.setText(email);

        Toast.makeText(getApplicationContext(), "You Successfully log in.", Toast
                .LENGTH_LONG)
                .show();

        Button signOut = findViewById(R.id.signOut);
        signOut.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                auth.signOut();
                finish();
            }
        });

    }
}

This is Repository class

package com.example.firebasewithemail.Models;

import android.content.Context;
import android.content.Intent;
import android.widget.Toast;

import androidx.activity.result.ActivityResultLauncher;
import androidx.annotation.NonNull;
import androidx.lifecycle.MutableLiveData;

import com.example.firebasewithemail.DashboardPage;
import com.example.firebasewithemail.R;
import com.google.android.gms.auth.api.signin.GoogleSignIn;
import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.android.gms.auth.api.signin.GoogleSignInOptions;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.OnFailureListener;
import com.google.android.gms.tasks.Task;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.auth.GoogleAuthProvider;
import com.google.firebase.firestore.FirebaseFirestore;

import java.util.HashMap;
import java.util.Map;


public class FireRepo {
    private FirebaseAuth auth = FirebaseAuth.getInstance();
    private FirebaseFirestore db = FirebaseFirestore.getInstance();

    MutableLiveData<FirebaseUser> signUpWithEmail(String email, String pass) {
        MutableLiveData<FirebaseUser> user = new MutableLiveData<>();
        auth.signInWithEmailAndPassword(email, pass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                user.setValue(auth.getCurrentUser());
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {

            }
        });
        return user;
    }


    void signUpWithEmail(Context context, String email, String pass) {
        auth.createUserWithEmailAndPassword(email, pass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                addingUserToFirebase(task.getResult().getUser().getEmail());
                Toast.makeText(context, "You successfully register.", Toast.LENGTH_LONG)
                        .show();
            }
        }).addOnFailureListener(new OnFailureListener() {
            @Override
            public void onFailure(@NonNull Exception e) {
                Toast.makeText(context, "Something Went Wrong.", Toast.LENGTH_LONG)
                        .show();
            }
        });
    }


    void signInWithGoogle(Context context, String idToken) {
        AuthCredential credential = GoogleAuthProvider.getCredential(idToken, null);
        auth.signInWithCredential(credential).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                addingUserToFirebase(task.getResult().getUser().getEmail());
                context.startActivity(new Intent(context, DashboardPage.class));
            }
        });
    }

    void addingUserToFirebase(String email) {
        Map<String, String> data = new HashMap<>();
        data.put("Email", email);
        db.collection("Users")
                .add(data);
    }

}

This is ViewModel

package com.example.firebasewithemail.Models;

import android.app.Application;
import android.content.Context;
import android.view.View;

import androidx.annotation.NonNull;
import androidx.lifecycle.AndroidViewModel;
import androidx.lifecycle.MutableLiveData;

import com.google.android.gms.auth.api.signin.GoogleSignInClient;
import com.google.firebase.auth.FirebaseUser;

public class ViewModel extends AndroidViewModel {
    public MutableLiveData<FirebaseUser> user;
    FireRepo repository = new FireRepo();
    public ViewModel(Application application) {
        super(application);
    }

    public void signInWithEmail(String email, String pass) {
        user = repository.signUpWithEmail(email, pass);
    }

    public void signUpWithEmail(Context context, String email, String pass) {
        repository.signUpWithEmail(context, email, pass);
    }

    public void signWithGoogle(Context context, String idToken) {
        repository.signInWithGoogle(context, idToken);
    }

}

This simple app is for signing in firbase using email, password and Google singIn method both.