Chapter 1. Starting the Journey
In this chapter, we’ll give you an introduction to the concepts and principles of this book. A good way of summarizing the overall approach is Practices and Principles over Technology. There are already many books about specific technologies, and we aren’t seeking to add to that enormous pile. That isn’t to say that the detailed knowledge that is specific to a given language, framework, or library isn’t useful. It’s just that it has a shorter shelf-life than general practices and principles that apply over longer periods of time and across different languages and frameworks. That’s where this book can help you.
Themes
Throughout the book we’ve used a project-based structure to aid learning. It’s worth thinking about the different themes that run through the chapters, how they link up together, and why we chose them. Following are the four different themes that weave through the chapters.
Java Features
Structuring code with classes and interfaces is discussed in Chapter 2. We move onto exceptions and packages in Chapter 3. You will also get a short overview of lambda expressions in Chapter 3. Then local variable type inferences and switch expressions are explained in Chapter 5, and finally lambda expressions and method references are covered in detail in Chapter 7. Java language features are important because so many software projects are written in Java, so it’s useful language to know the workings of it. Many of these language features are useful in other programming languages as well, such as C#, C++, Ruby, or Python. Even though those languages have differences, understanding the how to use a class and core OOP concepts will be valuable across different languages.
Software Design and Architecture
Throughout the book a series of design patterns are introduced that help provide you with common solutions to common problems that developers encounter. These are important to know because even though it may seem like every software project is different and comes with its own set of problems, in practice many of these have been encountered before. Understanding common problems and solutions that have been solved by developers keeps you from reinventing the wheel in a new software project and enables you to deliver software faster and more reliably.
The higher-level concepts of coupling and cohesion are introduced early on the book in Chapter 2. The Notification pattern is introduced in Chapter 3. How to design a user-friendly Fluent API and the Builder pattern are introduced in Chapter 5. We look at the big-picture concepts of event-driven and hexagonal architectures in Chapter 6 and the Repository pattern in Chapter 7. Finally, you’re also introduced to functional programming in Chapter 7.
SOLID
We cover all the SOLID principles throughout various chapters. These are a set of principles designed to help make software easier to maintain. While we like to think of writing software as the fun part, if the software that you write is successful it will need to evolve, grow, and be maintained. Trying to make the software as easy to maintain as possible helps this evolution, maintenance, and long-term addition of features. The SOLID principles and the chapters where we will discuss them are:
Testing
Writing reliable code that can be easily evolved over time is really important. Automated tests are key to this. As the software that you write scales in size it becomes increasingly hard to manually test different possible cases. You need to automate your testing processes to avoid the days of human effort it would take to test your software without it.
You learn about the basics of writing tests in Chapters 2 and 4. This is extended to test-driven development, or TDD, in Chapter 5. In Chapter 6 we cover the use of test doubles, including mocks and stubs.
Chapter Summary
Here’s the outline of the chapters.
- Chapter 2, The Bank Statements Analyzer
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You’ll write a program to analyze bank statements in order to help people understand their finances better. This will help you to learn more about core object-oriented design techniques such as Single Responsibility Principle (SRP), coupling, and cohesion.
- Chapter 3, Extending the Bank Statements Analyzer
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In this chapter you learn how to extend the code from Chapter 2, adding more features, using the Strategy Design pattern, the Open/Closed Principle, and how to model failures using exceptions.
- Chapter 4, The Document Management System
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In this chapter we help a successful doctor manage her patient records better. This introduces concepts such as inheritance within software design, the Liskov Substitution Principle, and tradeoffs between composition and inheritance. You will also learn how to write more reliable software with automated test code.
- Chapter 5, The Business Rules Engine
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You’ll learn about building a core business rules engine—a way of defining business logic that is flexible and easy to maintain. This chapter introduces the topics of test-driven development, developing a Fluent API, and the Interface Segregation Principle.
- Chapter 6, Twootr
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Twootr is a messaging platform that enables people to broadcast short messages to other users who follow them. This chapter builds out the core of a simple Twootr system. You’ll learn how to think outside-in—to go from requirements through to the core of your application. You’ll also learn how to use test doubles to isolate and test interactions from different components within your codebase.
- Chapter 7, Extending Twootr
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The final project-based chapter in the book extends the Twootr implementation from the previous chapter. It explains the Dependency Inversion Principle and introduces bigger picture architectural choices such as event-driven and hexagonal architectures. This chapter can help you extend your knowledge of automated testing by covering test doubles, such as stubs and mocks, and also functional programming techniques.
- Chapter 8, Conclusion
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This final concluding chapter revisits the major themes and concepts of the book and offers additional resources as you continue in your programming career.
Iterating on You
As a software developer you may well approach projects in an iterative fashion. That’s to say, slice off the highest priority week or two’s worth of work items, implement them, and then use the feedback in order to decide on the next set of items. We’ve found that it’s often worth evaluating the progress of your own skills in the same way.
At the end of every chapter there is a brief “Iterating on You” section with a few suggestions on how you improve upon on the learning from the chapter in your own time.
Now that you know what you can expect from this book, let’s get to work!