package com.elsebazaar.bottlecollections;

public class User {
    public String name;
    public String email;


    public String password;

    public User(){
    }

    public User(String name, String email, String password){
        this.name = name;
        this.email = email;
        this.password = password;
    }

    public String getName() {
        return name;
    }

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

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }


}

 FirebaseDatabase firebaseDatabase = FirebaseDatabase.getInstance();
 DatabaseReference databaseReference = firebaseDatabase.getReference();//databasereference

String uid = currentUser.getUid();
DatabaseReference userRef = databaseReference.child("users");//Create child node reference
userRef.child(uid).setValue(user);//Insert value to child node

package com.elsebazaar.bottlecollections;

import android.content.Intent;
import android.graphics.Color;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ProgressBar;
import android.widget.TextView;

import androidx.annotation.NonNull;

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;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;

public class Register extends MainActivity {

    private FirebaseDatabase firebaseDatabase;
    private DatabaseReference databaseReference;
    private FirebaseAuth mAuth;
    private User user;

    ProgressBar progressBar;
    EditText mName, mEmail, mPassword, mConfirmPassword;

    Button btnregister;
    TextView txtalreadyamember;
    Snackbar snackbar;
    String emailPattern = "[a-zA-Z0-9._-]+@[a-z]+\\.+[a-z]+";

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

        progressBar = findViewById(R.id.progressBar);

        mName = findViewById(R.id.ettxtName);
        mEmail = findViewById(R.id.ettxtEmail);
        mPassword = findViewById(R.id.ettxtPassword);
        mConfirmPassword = findViewById(R.id.ettxtConfirmPassword);
        btnregister = findViewById(R.id.btnRegister);
        txtalreadyamember = findViewById(R.id.txtAlreadyAMember);

        mAuth = FirebaseAuth.getInstance();

        //initListeners();
        btnregister.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String name = mName.getText().toString().trim();
                String email = mEmail.getText().toString().trim();
                String password = mPassword.getText().toString().trim();
                String confirmpassword = mConfirmPassword.getText().toString().trim();

                //check whether name is empty or not
                if(TextUtils.isEmpty(name)){
                    mName.setError("Name is required");
                    return;
                }

                //check whether email address is empty or not
                if(TextUtils.isEmpty(email)){
                    mEmail.setError("Email Address is required");
                    return;
                }

                //check email address pattern is correct or not
                //if (isEmailValid(email))

                if (!email.matches(emailPattern)){
                    mEmail.setError("Email Address is invalid");
                    return;
                }

                //check whether password is empty or not
                if(TextUtils.isEmpty(password)){
                    mPassword.setError(" Password is required");
                    return;
                }

                //check whether password is less than 6 characters?
                if(password.length() < 6){
                    mPassword.setError("Password must be >= 6 characters");
                    return;
                }

                //check whether password and confirm password are match or not
                if(!password.equals(confirmpassword)){
                    mConfirmPassword.setError("Password does not match");
                    return;
                }

                //Make progress bar visible
                progressBar.setVisibility(View.VISIBLE);

                //User Method call
                user = new User (name, email, password);

                //create user by calling registerUser function
                registerUser(email, password);

                //Call function to empty All EditText
                emptyInputEditText();
            }
        });
    }

    private void registerUser(String email, String password) {
        //Register the user in firebase
        mAuth.createUserWithEmailAndPassword(email,password).addOnCompleteListener(new OnCompleteListener<AuthResult>() {
            @Override
            public void onComplete(@NonNull Task<AuthResult> task) {
                if (task.isSuccessful()){

                    FirebaseUser user = mAuth.getCurrentUser();
                    updateUI(user);

                    //display snackbar with green background
                    View view = findViewById(android.R.id.content);
                    String message = "Account Created Successfully";
                    int duration = Snackbar.LENGTH_LONG;

                    snackbar = Snackbar.make(view, message, duration)
                            .setAction("Action", null);
                    View sbView = snackbar.getView();
                    sbView.setBackgroundColor(Color.GREEN);
                    snackbar.show();

                    //Toast.makeText(Register.this,"Account Created",Toast.LENGTH_SHORT).show();
                    startActivity(new Intent(getApplicationContext(), Home.class));

                }
                else{
                    //display snackbar with red background
                    View view = findViewById(android.R.id.content);
                    String message = "Email ID already exits";
                    int duration = Snackbar.LENGTH_LONG;

                    snackbar = Snackbar.make(view, message, duration)
                            .setAction("Action", null);
                    View sbView = snackbar.getView();
                    sbView.setBackgroundColor(Color.RED);
                    snackbar.show();

                    //Toast.makeText(Register.this,"Error Occured" + task.getException(),Toast.LENGTH_SHORT).show();*/
                   // updateUI(null);
                    progressBar.setVisibility(View.INVISIBLE);
                }
            }
        });
    }


    /**
     * This method is to empty all input edit text
     */
    private void emptyInputEditText() {
        mName.setText(null);
        mEmail.setText(null);
        mPassword.setText(null);
        mConfirmPassword.setText(null);
    }

    public void onStart(){
        super.onStart();
        //check if user is signed in and update UI accordingly
        FirebaseUser currentUser = mAuth.getCurrentUser();
        updateUI(currentUser);
    }


    private void updateUI(FirebaseUser currentUser) {
        if (user != null) {
            firebaseDatabase = FirebaseDatabase.getInstance();
            databaseReference = firebaseDatabase.getReference();//databasereference

            String uid = currentUser.getUid();
            DatabaseReference userRef = databaseReference.child("users");//Create child node reference
            userRef.child(uid).setValue(user);//Insert value to child node
        }
    }

    public void enabled(View view) {
        Intent intent = new Intent(Register.this, MainActivity.class);
        startActivity(intent);
        finish();
    }
}

That's it. Run your program and see the result.