This section looks at asynchronous event handling: e.g., responding to button clicks.
It uses that as an excuse to examine four options that will be seen again with GUI widget event handling, array sorting, and multithreaded programming: separate classes, interfaces, named inner classes, and anonymous inner classes. It also gives a brief preview of Java 8 lambdas, which are covered detail later.
See http://courses.coreservlets.com/Course-Materials/java.html for the complete tutorial series (Programming with Java 8) and associated code. That site also lets you download PDF files of each lecture for saving or printing, and includes exercises and exercise solutions for each of the topics.