Modern Java introduces major enhancements that impact the core Java technologies and APIs at the heart of the Java platform. Many old Java idioms are no longer needed, and new features and programming paradigms can make you far more effective. However, navigating these changes can be challenging. Core Java for the Impatient, Fourth Edition, is a complete yet concise guide that reflects all changes through Java SE 21, Oracle's latest Long-Term Support (LTS) release. Written by Cay S. Horstmann--author of the classic two-volume Core Java--this indispensable tutorial offers a faster, easier pathway for learning modern Java. Horstmann covers everything working developers need to know, including the powerful concepts of lambda expressions and streams, modern constructs such as records and sealed classes, and sophisticated concurrent programming techniques. Given the size and scope of Java 21, there's plenty to cover, but it's presented in small chunks organized for quick access and easy understanding, with plenty of practical insights and sample code to help you quickly apply all that's new. 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.