android set toolbar transparent programmatically

1<?xml version="1.0" encoding="utf-8"?>
2<androidx.constraintlayout.widget.ConstraintLayout
3   xmlns:android="http://schemas.android.com/apk/res/android"
4   xmlns:app="http://schemas.android.com/apk/res-auto"
5   xmlns:tools="http://schemas.android.com/tools"
6   android:layout_width="match_parent"
7   android:layout_height="match_parent"
8   tools:context=".MainActivity"
9   android:background="#222222">
10   <TextView
11      android:layout_width="wrap_content"
12      android:layout_height="wrap_content"
13      android:text="Hello World!"
14      app:layout_constraintBottom_toBottomOf="parent"
15      app:layout_constraintLeft_toLeftOf="parent"
16      app:layout_constraintRight_toRightOf="parent"
17      app:layout_constraintTop_toTopOf="parent" />
18</androidx.constraintlayout.widget.ConstraintLayout>