The ninth part of the course material focuses on two essential concepts of object oriented programming, namely inheritance and interfaces. You will learn to create classes that inherit another classes, and also classes that implement one or more interfaces. You are also going to notice that an object can be represented by any of its actual types.
The table of contents above lists the topics of the ninth part of the course. The ninth part has been designed to cover the ninth week of the course. You should reserve well above 10 hours for each part of the course, depending on previous experience with computers. If you've tried programming before, you might advance faster in the beginning.