This chapter introduced you to Java's concept of interfaces. Interfaces are defined much the same way as classes, but with the interface keyword. Other differences are that all methods are public and abstract by default. You can define attributes to interfaces, but they must be static and final.
The big difference between classes and interfaces comes in how you use them. This chapter dedicated a lot of space to help you make this differentiation.
The next chapter will introduce you to Java's implementation of exception handling.