Firebase Authentication signup,login, mail in android

Firebase Authentication

create email and password and send Verification mail to the user

email with firebase.

package com.example.bestnoteapp;

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

import android.content.Intent;
import android.os.Bundle;
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.snackbar.Snackbar;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class signup extends AppCompatActivity {
    EditText email,password;
    Button signupbtn,loginbtn;
    TextView Logintext;
    private FirebaseAuth mAuth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_signup);

        email = findViewById(R.id.signupemail);
        password = findViewById(R.id.signuppassword);
        loginbtn = findViewById(R.id.Login);
        signupbtn = findViewById(R.id.signup);
        Logintext = findViewById(R.id.Loginbtn);
        mAuth = FirebaseAuth.getInstance();



        loginbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(signup.this,MainActivity.class);
                startActivity(intent);
            }
        });

        Logintext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent intent = new Intent(signup.this,MainActivity.class);
                startActivity(intent);
            }
        });


        signupbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String mail = email.getText().toString().trim();
                String pass = password.getText().toString().trim();

                if(mail.isEmpty()){
                    Toast.makeText(getApplicationContext(), "Email is not Blank please enter email", Toast.LENGTH_SHORT).show();
                    Snackbar mysnackbar = Snackbar.make(loginbtn,"Email is not Blank",Snackbar.LENGTH_SHORT);
                    mysnackbar.setAction("undo", new View.OnClickListener() {
                        @Override
                        public void onClick(View view) {
                            mysnackbar.dismiss();
                        }
                    });
                    mysnackbar.show();
                }else if(pass.isEmpty()){
                    Toast.makeText(getApplicationContext(), "Password is not Blank", Toast.LENGTH_SHORT).show();
                }else if(pass.length() < 5){
                    Toast.makeText(signup.this, "Password char most be greater then 5", Toast.LENGTH_SHORT).show();
                }else{
//                    Intent intent = new Intent(signup.this,MainActivity.class);
//                    startActivity(intent);
                    mAuth.createUserWithEmailAndPassword(mail,pass).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                        @Override
                        public void onComplete(@NonNull Task<AuthResult> task) {
                            if(task.isSuccessful()){
                                Toast.makeText(getApplicationContext(), "successfully register", Toast.LENGTH_SHORT).show();
                                sendEmailVerification();
                            }else{
                                Toast.makeText(getApplicationContext(), "Failed to register", Toast.LENGTH_SHORT).show();
                            }
                        }
                    });

                }
                 }
        });



    }
    //send email verification
    private void sendEmailVerification(){
        FirebaseUser firebaseUser = mAuth.getCurrentUser();

        if(firebaseUser != null){
            firebaseUser.sendEmailVerification().addOnCompleteListener(new OnCompleteListener<Void>() {
                @Override
                public void onComplete(@NonNull Task<Void> task) {
                    Toast.makeText(getApplicationContext(), "verification email is send and Login again", Toast.LENGTH_SHORT).show();
                    mAuth.signOut();
                    finish();
                    startActivity(new Intent(signup.this,MainActivity.class));
                }
            });
        }
    }


}

SignIn with Email and Password

package com.example.bestnoteapp;

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

import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
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.firebase.auth.AuthResult;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;

public class MainActivity extends AppCompatActivity {
    EditText email,password;
    Button logins,signup;
    TextView forgotpassword;
    FirebaseAuth firebaseAuth;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        firebaseAuth = FirebaseAuth.getInstance();
        FirebaseUser firebaseUser = firebaseAuth.getCurrentUser();

        if(firebaseUser != null){
            startActivity(new Intent(getApplicationContext(),notesactivity.class));
        }

        // Write a message to the database
//        insert data into realtime database
//        FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
//        DatabaseReference databaseReference = firebaseDatabase.getReference();
//        databaseReference.child("user").child("userId").setValue(1);
//        databaseReference.child("user").child("name").setValue("krishna");

           FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
           DatabaseReference databaseReference = firebaseDatabase.getReference().child("Books");
//        databaseReference.child("user").child("email").setValue(email.getText().toString());
//        databaseReference.child("user").child("password").setValue(password.getText().toString());


        email = findViewById(R.id.login_email);
        password = findViewById(R.id.login_password);
        logins = findViewById(R.id.login_button);
        signup = findViewById(R.id.signupbtns);
        forgotpassword = findViewById(R.id.forgot_password);


        logins.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String emails = email.getText().toString().toString();
                String passwords = password.getText().toString().toString();
                if(emails.isEmpty() || passwords.isEmpty()){
                    Toast.makeText(MainActivity.this, "Email and password most be field", Toast.LENGTH_SHORT).show();
                }else{
//                    Intent intent = new Intent(MainActivity.this,forgot_password.class);
//                    startActivity(intent);
                     firebaseAuth.signInWithEmailAndPassword(emails,passwords).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                         @Override
                         public void onComplete(@NonNull Task<AuthResult> task) {
                             if(task.isSuccessful()){
                                 CheckMailVerified();
//                                 Toast.makeText(MainActivity.this, "you are Login", Toast.LENGTH_SHORT).show();
                             }else{
                                 Toast.makeText(MainActivity.this, "Please Enter a correct details", Toast.LENGTH_SHORT).show();
                             }
                         }
                     });
                }
                }
        });

        signup.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,signup.class);
                startActivity(intent);
            }
        });

        forgotpassword.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(MainActivity.this,forgot_password.class);
                startActivity(intent);
            }
        });
    }

    private void CheckMailVerified(){
        FirebaseUser currentUser = firebaseAuth.getCurrentUser();
        if(currentUser.isEmailVerified() == true){
            Toast.makeText(getApplicationContext(), "Logged In", Toast.LENGTH_SHORT).show();
            finish();
            startActivity(new Intent(MainActivity.this,signup.class));
        }else{
            Toast.makeText(getApplicationContext(), "Verified your mail first", Toast.LENGTH_SHORT).show();
            firebaseAuth.signOut();
            startActivity(new Intent(MainActivity.this,notesactivity.class));
        }
    }

}

Forgot Password

package com.example.bestnoteapp;

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

import android.content.Intent;
import android.os.Bundle;
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.firebase.auth.FirebaseAuth;

public class forgot_password extends AppCompatActivity {

    EditText email;
    Button recover;
    TextView gobacktoLogin;
    FirebaseAuth firebaseAuth;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_forgot_password);
        email  = findViewById(R.id.email);
        recover  = findViewById(R.id.recover);
        gobacktoLogin  = findViewById(R.id.gobacktoLogin);
        firebaseAuth = FirebaseAuth.getInstance();


        
        recover.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                String emailtext = email.getText().toString().trim();
                if(emailtext.isEmpty()){
                Toast.makeText(forgot_password.this, "Email Can't be blank", Toast.LENGTH_SHORT).show();
                 }else{
                    FirebaseAuth.getInstance().sendPasswordResetEmail(emailtext)
                            .addOnCompleteListener(new OnCompleteListener<Void>() {
                                @Override
                                public void onComplete(@NonNull Task<Void> task) {
                                    if (task.isSuccessful()) {
                                        Toast.makeText(forgot_password.this, "your password is Forgot successfully", Toast.LENGTH_SHORT).show();
                                        finish();
                                        Intent intent = new Intent(forgot_password.this,signup.class);
                                        startActivity(intent);
                                    }else{
                                        Toast.makeText(forgot_password.this, "Email is wrong,Account doesn't Exist", Toast.LENGTH_SHORT).show();
                                    }
                                }
                            });


                }
              }
        });
        gobacktoLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent intent = new Intent(forgot_password.this, MainActivity.class);
                startActivity(intent);
            }
        });
    }
}

How to insert data into firebase database:

 First create a java class file inside the class create constructor, Geter and setter.

package com.example.androidtutorial;

public class student {
    String name;
    String desc;
    String Address;

    public student(String name, String desc, String address) {
        this.name = name;
        this.desc = desc;
        this.Address = address;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDesc() {
        return desc;
    }

    public void setDesc(String desc) {
        this.desc = desc;
    }

    public String getAddress() {
        return Address;
    }

    public void setAddress(String address) {
        this.Address = address;
    }
}

inside mainpage: call the constructor

    private void Submitdata(){
        submit.setOnClickListener(v->{
            String yname = name.getText().toString();
            String yaddress = address.getText().toString();
            String ydesc = desc.getText().toString();

            if(yname.isEmpty() || yaddress.isEmpty() || ydesc.isEmpty()){
                Toast.makeText(this, "All Field are available", Toast.LENGTH_SHORT).show();
            }else{
            Intent intent = new Intent(this,GetuserDataIntent.class);
            intent.putExtra("name",yname);
            intent.putExtra("address",yaddress);
            intent.putExtra("desc",ydesc);
            intent.putExtra("image",R.drawable.ic_launcher_background);

            startActivity(intent);
            Toast.makeText(this, "submit data", Toast.LENGTH_SHORT).show();

            student = firebaseDatabase.getReference().child("student");
//            creating a constructor and set value 
            student data = new student(yname,ydesc,yaddress);
            student.push().setValue(data);
            }
            });
    }

Insert only one data in firbase Realtime database

 private void insertdata(){
    DatabaseReference name = firebaseDatabase.getReference("UserData").child("UserId").child("name");
    DatabaseReference desc = firebaseDatabase.getReference("UserData").child("UserId").child("desc");
    DatabaseReference address = firebaseDatabase.getReference("UserData").child("UserId").child("address");
    name.setValue("Krishna");
    desc.setValue("Hello world");
    address.setValue("Walling 13");
 }