Book Image

Learn Java with Projects

By : Dr. Seán Kennedy, Maaike van Putten
5 (3)
Book Image

Learn Java with Projects

5 (3)
By: Dr. Seán Kennedy, Maaike van Putten

Overview of this book

Learn Java with Projects stands out in the world of Java guides; while some books skim the surface and others get lost in too much detail, this one finds a nice middle ground. You’ll begin by exploring the fundamentals of Java, from its primitive data types through to loops and arrays. Next, you’ll move on to object-oriented programming (OOP), where you’ll get to grips with key topics such as classes, objects, encapsulation, inheritance, polymorphism, interfaces, and more. The chapters are designed in a way that focuses on topics that really matter in real-life work situations. No extra fluff here, so that you get more time to spend on the basics and form a solid foundation. As you make progress, you’ll learn advanced topics including generics, collections, lambda expressions, streams and concurrency. This book doesn't just talk about theory—it shows you how things work with little projects, which eventually add up to one big project that brings it all together. By the end of this Java book, you’ll have sound practical knowledge of Java and a helpful guide to walk you through the important parts of Java.
Table of Contents (22 chapters)
1
Part 1: Java Fundamentals
9
Part 2: Object-Oriented Programming
15
Part 3: Advanced Topics

Exploring sealed interfaces

In Chapter 9, we learned that sealed classes enable us to scope our inheritance hierarchy by specifying which classes can subtype our class. We used both the sealed and permits keywords as a pair to do this. Once a class has been sealed, each subclass of that class must be sealed, non-sealed, or final – that is, we continue the sealed hierarchy (sealed), end the sealed hierarchy (non-sealed), or end the hierarchy altogether (final).

It is also possible to seal interfaces. We will use the example from Chapter 9 with some small changes. Firstly, Figure 10.11 shows the relevant UML diagram, which will help explain the code:

Figure 10.11 – Sealed interface UML diagram

Figure 10.11 – Sealed interface UML diagram

In this figure, we have an interface, indicated by <<interface>>, called Driveable. In UML, to specify that a class implements an interface, the <<realize>> keyword is used (plus the dashed line with an arrow referring to the...