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

Understanding abstract classes

In Chapter 9, we covered the abstract keyword. Let’s review some key points that we discussed. An abstract method is exactly that – it is abstract. It has no code. It doesn’t even have curly braces – {}. This is typically a design decision. The class containing the abstract method wants subclasses to provide the code. This means that the class itself is “incomplete” and therefore any class defining an abstract method must itself be abstract. Any subclass of the abstract class must either override the abstract method or declare that it too is abstract. The compiler will complain otherwise.

However, the inverse is not the case – an abstract class need not have any abstract methods at all. Again, this is a design decision. Since the class is marked as abstract, it is considered “incomplete” (even though it may contain code for all the methods). This prevents objects based on abstract classes...