The Java Tutorial goes on to list bullets for when an abstract class should be considered and for when an interface should be considered. Unsurprisingly, these are derived from the previously ...

The abstract modifier and nonpublic constructor of the Displayable class force developers to use its concrete subclasses in the LCDUI, which do contain the rendering logic.

The functional consumer interface is a key part of the Java Streams API. Here is a simple Consumer interface example to show you how to use this Java component.