It also could be specified through xml:

<TextView
    android:layout_height="wrap_content"
    android:layout_width="wrap_content"
    android:requiresFadingEdge="vertical"
    android:fadingEdgeLength="24dp" />

By the way, fading edge could be used for ScrollView and other scrollable views as well.

Here is example: https://stackoverflow.com/a/16726054/7699617