Creating class hierarchies to abstract and specialize behavior

In the previous chapters, we have been creating classes in Java 9 to generate blueprints for real-life objects. We declared classes and then we created instances of these classes in JShell. Now it is time to take advantage of many of the most advanced features of object-oriented programming included in Java 9 and start designing a hierarchy of classes instead of working with isolated classes. First, we will design all the classes that we need based on the requirements, and then we will use the features available in Java 9 to code the designed classes.

We worked with classes to represent virtual creatures. Now, let's imagine that we have to develop a complex Web Service that requires us to work with dozens of types of virtual animal. Many of these virtual animals will be similar to pets and domestic animals in the first stage of the project. The requirements specify that our Web Service will start working with the following four...