Java has seen many changes since its initial release in 1996. The classic book, Core Java, covers, in meticulous detail, not just the language but all core libraries and a multitude of changes between versions, spanning two volumes and over 2,000 pages. However, if you just want to be productive with modern Java, there is a much faster, easier pathway for learning the language and core libraries. In this book, I don’t retrace history and don’t dwell on features of past versions. I show you the good parts of Java as it exists today, so you can put your knowledge to work quickly.

As with my previous "Impatient" books, I quickly cut to the chase, showing you what you need to know to solve a programming problem without lecturing about the superiority of one paradigm over another. I also present the information in small chunks, organized so that you can quickly retrieve it when needed.

Assuming you are proficient in some other programming language, such as Python, C++, JavaScript, Swift, PHP, or Ruby, with this book you will learn how to become a competent Java programmer. I cover all aspects of Java that a developer needs to know today, including the powerful concepts of lambda expressions and streams, as well as modern constructs such as records and pattern matching.

This book is fully updated to Java 21. It uses modern features and does not dwell on historical or obsolete constructs. Preview features that may make it to the language in the future are not covered either.

A key reason to use Java is to tackle concurrent programming. With parallel algorithms and threadsafe data structures readily available in the Java library, the way application programmers should handle concurrent programming has completely changed. I provide fresh coverage, showing you how to use the powerful library features instead of error-prone low-level constructs.

Traditionally, books on Java have focused on user interface programming, but nowadays, few developers produce user interfaces on desktop computers. You will be able to use this book effectively without being distracted by lengthy GUI code.

Finally, this book is written for application programmers, not for a college course and not for systems wizards. The book covers issues that application programmers need to wrestle with, such as logging and working with files, but you won’t learn how to implement a linked list by hand or how to write a web server.

I hope you enjoy this rapid-fire introduction into modern Java, and I hope it will make your work with Java productive and enjoyable.

If you find errors or have suggestions for improvement, please visit http://horstmann.com/javaimpatient/bugs.html¹ and leave a comment.