This is the last of three sections that cover OOP in Java. It discusses abstract classes, interfaces, @Override, visibility modifiers, and enums in detail. It also briefly discusses JavaDoc options and the classpath.
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.