activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.taufan.materialdesigntheme.MainActivity">

    <include
        android:id="@+id/toolbar"
        layout="@layout/toolbar"/>

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/toolbar"
        android:text="Hello World!\nIni aplikasi material design :)" />
</RelativeLayout>