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

Explaining Optionals

An Optional can be thought of as a container that may or may not be empty. As per the API, the container “may or may not contain a non-null value”. An Optional is primarily used as a method return type where there is a real need to represent “no result” and when returning null could cause errors. Before Java 8, programmers would return null but now, since Java 8, we can return an empty Optional instead. This has several advantages:

  • Reduces the risk of NullPointerExceptions
  • By using Optional as the return type, the API can now clearly state that there may not be a value returned
  • The Optional API facilitates the functional programming style

As well as Optional<T>, there are Optionals for the primitive types also; namely: OptionalInt, OptionalDouble and OptionalLong. We will examine them later.

Let us first look at how to create Optionals.

Creating Optionals

The API provides several static methods for...