Firebase Authentication | User Login using Firebase in Android

 Step 1 Login Activity.xml(Launcher)

<?xml version="1.0" encoding="utf-8"?>

<RelativeLayout 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"

    android:background="@drawable/gradient"

    android:gravity="center"

    android:padding="16dp"

    tools:context=".Login">

    <RelativeLayout

        android:layout_width="match_parent"

        android:layout_height="wrap_content"

        android:layout_gravity="center">

        <androidx.cardview.widget.CardView xmlns:Card_View="http://schemas.android.com/apk/res-auto"

            android:layout_width="match_parent"

            android:layout_height="350dp"

            android:layout_margin="5dp"

            android:padding="10dp"

            Card_View:cardCornerRadius="5dp"

            Card_View:cardElevation="5dp">

            <LinearLayout

                android:layout_width="match_parent"

                android:layout_height="wrap_content"

                android:layout_gravity="center"

                android:layout_margin="5dp"

                android:orientation="vertical">

                <com.google.android.material.textfield.TextInputLayout

                    android:id="@+id/emailError"

                    android:layout_width="match_parent"

                    android:layout_height="wrap_content"

                    android:layout_marginTop="5dp">

                    <EditText

                        android:id="@+id/email"

                        android:layout_width="match_parent"

                        android:layout_height="wrap_content"

                        android:layout_marginTop="10dp"

                        android:hint="@string/prompt_email"

                        android:inputType="textEmailAddress"

                        android:maxLines="1"

                        android:paddingStart="5dp"

                        android:singleLine="true" />

                </com.google.android.material.textfield.TextInputLayout>

                <com.google.android.material.textfield.TextInputLayout

                    android:id="@+id/passError"

                    android:layout_width="match_parent"

                    android:layout_height="wrap_content"

                    android:layout_marginTop="5dp"

                    app:passwordToggleEnabled="true">

                    <EditText

                        android:id="@+id/password"

                        android:layout_width="match_parent"

                        android:layout_height="wrap_content"

                        android:layout_marginTop="10dp"

                        android:hint="@string/prompt_password"

                        android:inputType="textPassword"

                        android:maxLines="1"

                        android:paddingStart="5dp"

                        android:singleLine="true" />

                </com.google.android.material.textfield.TextInputLayout>

                <Button

                    android:id="@+id/login"

                    android:layout_width="match_parent"

                    android:layout_height="50dp"

                    android:layout_margin="20dp"

                    android:background="@drawable/button_gradient"

                    android:text="@string/login"

                    android:textColor="@android:color/white"

                    android:textSize="16sp" />

                <TextView

                    android:id="@+id/register"

                    android:layout_width="match_parent"

                    android:layout_height="wrap_content"

                    android:layout_marginTop="5dp"

                    android:gravity="center"

                    android:text="@string/create_new"

                    android:textColor="@color/colorPrimary"

                    android:textSize="16sp" />

            </LinearLayout>

        </androidx.cardview.widget.CardView>

    </RelativeLayout>

    <ImageView

        android:id="@+id/profile"

        android:layout_width="100dp"

        android:layout_height="100dp"

        android:layout_centerHorizontal="true"

        android:layout_marginTop="-50dp"

        android:background="@drawable/round_background"

        android:padding="15dp"

        android:src="@drawable/profile" />

</RelativeLayout>

 Step 2 Login Activity.Java

package com.example.loginapp;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Patterns;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputLayout;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;

public class Login extends AppCompatActivity {

    EditText email1, password1;
    Button login;
    TextView register;
    boolean isEmailValid, isPasswordValid;
    TextInputLayout emailError, passError;

    private FirebaseAuth mAuth;

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

        mAuth = FirebaseAuth.getInstance();

        email1 = (EditText) findViewById(R.id.email);
        password1 = (EditText) findViewById(R.id.password);
        login = (Button) findViewById(R.id.login);
        register = (TextView) findViewById(R.id.register);
        emailError = (TextInputLayout) findViewById(R.id.emailError);
        passError = (TextInputLayout) findViewById(R.id.passError);

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

        register.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // redirect to RegisterActivity
                Intent intent = new Intent(getApplicationContext(), RegisterActivity.class);
                startActivity(intent);
            }
        });
    }

    public void SetValidation() {

        String email, password, name;
        email = email1.getText().toString();
        password = password1.getText().toString();




        // Check for a valid email address.
        if (email1.getText().toString().isEmpty()) {
            emailError.setError(getResources().getString(R.string.email_error));
            isEmailValid = false;
        } else if (!Patterns.EMAIL_ADDRESS.matcher(email1.getText().toString()).matches()) {
            emailError.setError(getResources().getString(R.string.error_invalid_email));
            isEmailValid = false;
        } else  {
            isEmailValid = true;
            emailError.setErrorEnabled(false);
        }

        // Check for a valid password.
        if (password1.getText().toString().isEmpty()) {
            passError.setError(getResources().getString(R.string.password_error));
            isPasswordValid = false;
        } else if (password1.getText().length() < 6) {
            passError.setError(getResources().getString(R.string.error_invalid_password));
            isPasswordValid = false;
        } else  {
            isPasswordValid = true;
            passError.setErrorEnabled(false);
        }

        if (isEmailValid && isPasswordValid) {
            Toast.makeText(getApplicationContext(), "Successfully", Toast.LENGTH_SHORT).show();

            mAuth.signInWithEmailAndPassword(email, password)
                    .addOnCompleteListener(
                            new OnCompleteListener<AuthResult>() {
                                @Override
                                public void onComplete(
                                        @NonNull Task<AuthResult> task)
                                {
                                    if (task.isSuccessful()) {
//                                        Toast.makeText(getApplicationContext(),
//                                                "Login successful!!",
//                                                Toast.LENGTH_LONG)
//                                                .show();

                                        // hide the progress bar
//                                        progressbar.setVisibility(View.GONE);

                                        // if sign-in is successful
                                        // intent to home activity
                                        Intent intent
                                                = new Intent(Login.this,
                                                MainActivity.class);
                                        startActivity(intent);
                                        finish();
                                    }

                                    else {

                                        // sign-in failed
                                        Toast.makeText(getApplicationContext(),
                                                "Login failed!!",
                                                Toast.LENGTH_LONG)
                                                .show();

                                        // hide the progress bar
//                                        progressbar.setVisibility(View.GONE);
                                    }
                                }
                            });
        }

    }
}

 Step 3 Register Activity.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView 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=".RegisterActivity"
    android:padding="16dp"
    android:background="@drawable/gradient"
    android:scrollbarThumbVertical="@null">



    <androidx.cardview.widget.CardView
        xmlns:Card_View="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="center"
        android:layout_margin="5dp"
        android:padding="10dp"
        Card_View:cardCornerRadius="5dp"
        Card_View:cardElevation="5dp">

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_gravity="center"
            android:layout_margin="5dp"
            android:orientation="vertical">

            <com.google.android.material.textfield.TextInputLayout
                android:id="@+id/nameError"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="5dp">

                <EditText
                    android:id="@+id/name"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:hint="@string/name"
                    android:inputType="textNoSuggestions"
                    android:maxLines="1"
                    android:paddingStart="5dp"
                    android:singleLine="true"/>

            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:id="@+id/emailError"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="5dp">

                <EditText
                    android:id="@+id/email"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:hint="@string/prompt_email"
                    android:inputType="textEmailAddress"
                    android:maxLines="1"
                    android:paddingStart="5dp"
                    android:singleLine="true"/>

            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:id="@+id/phoneError"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="5dp">

                <EditText
                    android:id="@+id/phone"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:hint="@string/phone_number"
                    android:maxLength="12"
                    android:inputType="number"
                    android:maxLines="1"
                    android:paddingStart="5dp"
                    android:singleLine="true"/>

            </com.google.android.material.textfield.TextInputLayout>

            <com.google.android.material.textfield.TextInputLayout
                android:id="@+id/passError"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                app:passwordToggleEnabled="true"
                android:layout_marginTop="5dp">

                <EditText
                    android:id="@+id/password"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:layout_marginTop="10dp"
                    android:hint="@string/prompt_password"
                    android:inputType="textPassword"
                    android:maxLines="1"
                    android:paddingStart="5dp"
                    android:singleLine="true"/>

            </com.google.android.material.textfield.TextInputLayout>

            <Button
                android:id="@+id/register"
                android:layout_width="match_parent"
                android:layout_height="50dp"
                android:layout_margin="20dp"
                android:background="@drawable/button_gradient"
                android:text="@string/register"
                android:textColor="@android:color/white"
                android:textSize="16sp"/>

            <TextView
                android:id="@+id/login"
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:layout_marginTop="5dp"
                android:layout_marginBottom="5dp"
                android:gravity="center"
                android:text="@string/not_register"
                android:textColor="@color/colorPrimary"
                android:textSize="16sp"/>

        </LinearLayout>
    </androidx.cardview.widget.CardView>


</ScrollView>

 Step 4 RegisterActivity.Java

package com.example.loginapp;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;

import android.content.Intent;
import android.os.Bundle;
import android.util.Patterns;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import com.google.android.gms.tasks.OnCompleteListener;
import com.google.android.gms.tasks.Task;
import com.google.android.material.textfield.TextInputLayout;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;

public class RegisterActivity extends AppCompatActivity {

    EditText name1, email1, phone1, password1;
    Button register;
    TextView login;
    boolean isNameValid, isEmailValid, isPhoneValid, isPasswordValid;
    TextInputLayout nameError, emailError, phoneError, passError;

    private FirebaseAuth mAuth;


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

        mAuth = FirebaseAuth.getInstance();

        name1 = (EditText) findViewById(R.id.name);
        email1 = (EditText) findViewById(R.id.email);
        phone1 = (EditText) findViewById(R.id.phone);
        password1 = (EditText) findViewById(R.id.password);
        login = (TextView) findViewById(R.id.login);
        register = (Button) findViewById(R.id.register);
        nameError = (TextInputLayout) findViewById(R.id.nameError);
        emailError = (TextInputLayout) findViewById(R.id.emailError);
        phoneError = (TextInputLayout) findViewById(R.id.phoneError);
        passError = (TextInputLayout) findViewById(R.id.passError);

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

        login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // redirect to LoginActivity
                Intent intent = new Intent(getApplicationContext(), Login.class);
                startActivity(intent);
            }
        });
    }

    public void SetValidation() {

        String email, password, name;
        int phone;
        email = email1.getText().toString();
        password = password1.getText().toString();
        name = name1.getText().toString();


        // Check for a valid name.
        if (name1.getText().toString().isEmpty()) {
            nameError.setError(getResources().getString(R.string.name_error));
            isNameValid = false;
        } else {
            isNameValid = true;
            nameError.setErrorEnabled(false);
        }

        // Check for a valid email address.
        if (email1.getText().toString().isEmpty()) {
            emailError.setError(getResources().getString(R.string.email_error));
            isEmailValid = false;
        } else if (!Patterns.EMAIL_ADDRESS.matcher(email1.getText().toString()).matches()) {
            emailError.setError(getResources().getString(R.string.error_invalid_email));
            isEmailValid = false;
        } else {
            isEmailValid = true;
            emailError.setErrorEnabled(false);
        }

        // Check for a valid phone number.
        if (phone1.getText().toString().isEmpty()) {
            phoneError.setError(getResources().getString(R.string.phone_error));
            isPhoneValid = false;
        } else {
            isPhoneValid = true;
            phoneError.setErrorEnabled(false);
        }

        // Check for a valid password.
        if (password1.getText().toString().isEmpty()) {
            passError.setError(getResources().getString(R.string.password_error));
            isPasswordValid = false;
        } else if (password1.getText().length() < 6) {
            passError.setError(getResources().getString(R.string.error_invalid_password));
            isPasswordValid = false;
        } else {
            isPasswordValid = true;
            passError.setErrorEnabled(false);
        }

        if (isNameValid && isEmailValid && isPhoneValid && isPasswordValid) {
            Toast.makeText(getApplicationContext(), "Successfully", Toast.LENGTH_SHORT).show();


            mAuth
                    .createUserWithEmailAndPassword(email, password)
                    .addOnCompleteListener(new OnCompleteListener<AuthResult>() {

                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {
                            if (task.isSuccessful()) {
//                                Toast.makeText(getApplicationContext(),
//                                        "Registration successful!",
//                                        Toast.LENGTH_LONG)
//                                        .show();

                                // hide the progress bar


                                // if the user created intent to login activity
                                Intent intent
                                        = new Intent(RegisterActivity.this, Login.class);
                                startActivity(intent);
                                finish();
                            } else {

                                // Registration failed
                                Toast.makeText(
                                        getApplicationContext(),
                                        "Registration failed!!"
                                                + " Please try again later",
                                        Toast.LENGTH_LONG)
                                        .show();

                                // hide the progress bar

                            }
                        }
                    });


        }


    }
}

 Step 5 Add In Your String

<resources>
    <string name="app_name">LoginApp</string>
    <string name="prompt_email">Email</string>
    <string name="prompt_password">Password</string>
    <string name="login">Login</string>
    <string name="create_new">Click here for register</string>
    <string name="not_register">Not Register?</string>
    <string name="name">Name</string>
    <string name="phone_number">Phone Number</string>
    <string name="register">Register</string>
    <string name="name_error">Please enter your name</string>
    <string name="phone_error">Please enter your phone number</string>
    <string name="email_error">Please enter your email address</string>
    <string name="error_invalid_email">This email address is invalid</string>
    <string name="password_error">Please enter a password</string>
    <string name="error_invalid_password">Please enter a minimum password of 6 characters</string>
</resources>

 Step 6 Dependencies 

implementation platform('com.google.firebase:firebase-bom:29.0.3')
implementation 'com.google.firebase:firebase-auth'