activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="16dp"
    android:orientation="vertical">

    <TextView
        android:id="@+id/textXML"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="This font was set via XML"
        android:textSize="30sp" />

    <TextView
        android:id="@+id/textCode"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="This font was set via code"
        android:textSize="30sp" />

    <Button
        android:id="@+id/changeFontButton"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Change font programmatically"
        android:layout_gravity="center_horizontal"/>

</LinearLayout>