Java Cookbook: Problems and Solutions for Java Developers

Organization of This Book

Let’s go over the organization of this book. Each chapter consists of a handful of recipes, short sections that describe a problem and its solution, along with a code example. The code in each recipe is intended to be largely self-contained; feel free to borrow bits and pieces of any of it for use in your own projects. The code is distributed with a Berkeley-style copyright, just to discourage wholesale reproduction.

I start off Chapter 1, Getting Started: Compiling and Running Java, by describing some methods of compiling your program on different platforms, running them in different environments (browser, command line, windowed desktop), and debugging.

Chapter 2, Interacting with the Environment, moves from compiling and running your program to getting it to adapt to the surrounding countryside—the other programs that live in your computer.

The next few chapters deal with basic APIs. Chapter 3, Strings and Things, concentrates on one of the most basic but powerful data types in Java, showing you how to assemble, dissect, compare, and rearrange what you might otherwise think of as ordinary text. This chapter also covers the topic of internationalization/localization so that your programs can work as well in Akbar, Afghanistan, Algiers, Amsterdam, and Angleterre as they do in Alberta, Arkansas, and Alabama.

Chapter 4, Pattern Matching with Regular Expressions, teaches you how to use the powerful regular expressions technology from Unix in many string-matching and pattern-matching problem domains. Regex processing has been standard in Java for years, but if you don’t know how to use it, you may be reinventing the flat tire.

Chapter 5, Numbers, deals both with built-in numeric types such as int and double, as well as the corresponding API classes (Integer, Double, etc.) and the conversion and testing facilities they offer. There is also brief mention of the “big number” classes. Because Java programmers often need to deal in dates and times, both locally and internationally, Chapter 6, Dates and Times, covers this important topic.

The next few chapters cover data processing. As in most languages, arrays in Java are linear, indexed collections of similar objects, as discussed in Chapter 7, Structuring Data with Java. This chapter goes on to deal with the many Collections classes: powerful ways of storing quantities of objects in the java.util package, including use of Java Generics.

Despite some syntactic resemblance to procedural languages such as C, Java is at heart an Object-Oriented Programming (OOP) language, with some important Functional Programming (FP) constructs skilfully blended in. Chapter 8, Object-Oriented Techniques, discusses some of the key notions of OOP as it applies to Java, including the commonly overridden methods of java.lang.Object and the important issue of design patterns. Java is not, and never will be, a pure FP language. However, it is possible to use some aspects of FP, increasingly so with Java 8 and its support of lambda expressions (a.k.a. closures). This is discussed in Chapter 9, Functional Programming Techniques: Functional Interfaces, Streams, and Parallel Collections.

The next chapter deals with aspects of traditional input and output. Chapter 10, Input and Output: Reading, Writing, and Directory Tricks, details the rules for reading and writing files (don’t skip this if you think files are boring; you’ll need some of this information in later chapters). The chapter also shows you everything else about files—such as finding their size and last-modified time—and about reading and modifying directories, creating temporary files, and renaming files on disk.

Big data and data science have become a thing, and Java is right in there. Apache Hadoop, Apache Spark, and much more of the big data infrastructure is written in, and extensible with, Java, as described in Chapter 11, Data Science and R. The R programming language is popular with data scientists, statsticians, and other scientists. There are at least two reimplementations of R coded in Java, and Java can also be interfaced directly with the standard R implementation in both directions, so this chapter covers R as well.

Because Java was originally promulgated as the programming language for the internet, it’s only fair to spend some time on networking in Java. Chapter 12, Network Clients, covers the basics of network programming from the client side, focusing on sockets. Today so many applications need to access a web service, primarily RESTful web services, that this seemed to be necessary. I’ll then move to the server side in Chapter 13, Server-Side Java, wherein you’ll learn some server-side programming techniques.

One simple text-based representation for data interchange is JSON, the JavaScript object notation. Chapter 14, Processing JSON Data, describes the format and some of the many APIs that have emerged to deal with it.

Chapter 15, Packages and Packaging, shows how to create packages of classes that work together. This chapter also talks about deploying (a.k.a. distributing and installing) your software.

Chapter 16, Threaded Java, tells you how to write classes that appear to do more than one thing at a time and let you take advantage of powerful multiprocessor hardware.

Chapter 17, Reflection, or “A Class Named Class”, lets you in on such secrets as how to write API cross-reference documents mechanically and how web servers are able to load any old Servlet—never having seen that particular class before—and run it.

Sometimes you already have code written and working in another language that can do part of your work for you, or you want to use Java as part of a larger package. Chapter 18, Using Java with Other Languages, shows you how to run an external program (compiled or script) and also interact directly with native code in C/C++ or other languages.

There isn’t room in a book this size for everything I’d like to tell you about Java. The Afterword presents some closing thoughts and a link to my online summary of Java APIs that every Java developer should know about.

Finally, Appendix A, Java Then and Now, gives the storied history of Java in a release-by-release timeline, so whatever version of Java you learned, you can jump in here and get up to date quickly.

So many topics, and so few pages! Many topics do not recieve 100% coverage; I’ve tried to include the most important or most useful parts of each API. To go beyond, check the official javadoc pages for each package; many of these pages have some brief tutorial information on how the package is to be used.

Besides the parts of Java covered in this book, two other platform editions, Java ME and Java EE, have been standardized. Java Micro Edition (Java ME) is concerned with small devices such as handhelds, cell phones, and fax machines. At the other end of the size scale—large server machines—there’s Eclipse Jakarta EE, replacing the former Java EE, which in the last century was known as J2EE. Jakarta EE is concerned with building large, scalable, distributed applications. APIs that are part of Jakarta EE include Servlets, JavaServer Pages, JavaServer Faces, JavaMail, Enterprise JavaBeans (EJBs), Container and Dependency Injection (CDI), and Transactions. Jakarta EE packages normally begin with “javax” because they are not core packages. This book mentions but a few of these; there is also a Java EE 8 Cookbook by Elder Moraes (O’Reilly) that covers some of the Jakarta EE APIs, as well as an older Java Servlet & JSP Cookbook by Bruce Perry (O’Reilly).

This book doesn’t cover Java Micro Edition, Java ME. At all. But speaking of cell phones and mobile devices, you probably know that Android uses Java as its language. What should be comforting to Java developers is that Android also uses most of the core Java API, except for Swing and AWT, for which it provides Android-specific replacements. The Java developer who wants to learn Android may consider looking at my Android Cookbook (O’Reilly), or the book’s website.