AndroidBullOfficial

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
        android:shape="rectangle">

        <solid
            android:color="@android:color/white">
        </solid>

        <corners
            android:bottomLeftRadius="@dimen/_25sdp"

AndroidBullOfficial

<?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"
    android:background="@android:color/white"
    tools:context=".SignUp">

AndroidBullOfficial

package com.arslan6015.demodatabase;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;

import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;

AndroidBullOfficial

// Read from the database
myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
        // This method is called once with the initial value and again
        // whenever data at this location is updated.
        String value = dataSnapshot.getValue(String.class);
        Log.d(TAG, "Value is: " + value);
    }

AndroidBullOfficial

FirebaseDatabase database = FirebaseDatabase.getInstance();
//you can also use .child() to get the same results
DatabaseReference myRef = database.getReference("message").child("java").child("user");   

myRef.setValue("Hello, Worldd!");

AndroidBullOfficial

// Write a message to the database
FirebaseDatabase database = FirebaseDatabase.getInstance();
DatabaseReference myRef = database.getReference("message/java/user");       //set path to get the multiple dropdown nodes

myRef.setValue("Hello, World!");

AndroidBullOfficial

// Write a message to the database
FirebaseDatabase database = FirebaseDatabase.getInstance();             // Get the database instance and store into object
DatabaseReference myRef = database.getReference("message");             // getReference() get the refrence if the refrence is already creted... if refrence is not created then it will create a new refrence here

myRef.setValue("Hello, World!");              // assign value to the particular refrence.

AndroidBullOfficial

// Validates timestamp is not a future value
{
 “rules”: {
 “posts”: {
 “$uid”: {
 “timestamp”: { 
 “.validate”: “newData.val() <= now” 
 }
 }
 }

AndroidBullOfficial

// Checks presence of child attributes
{
 “rules”: {
 “posts”: {
 “$uid”: {
 “.validate”: “newData.hasChildren([‘username’, ‘timestamp’])”
 }
 }
 }
}

AndroidBullOfficial

// Validates string datatype and length range
{
 “rules”: {
 “posts”: {
 “$uid”: {
 “.validate”: “newData.isString() 
 && newData.val().length > 0
 && newData.val().length <= 140”
 }
 }