Software development today is embracing functional programming (FP), whether it's for writing concurrent programs or for managing Big Data. Where does that leave Java developers? This concise book offers a pragmatic, approachable introduction to FP for Java developers or anyone who uses an object-oriented language. Dean Wampler, Java expert and author of Programming Scala (O'Reilly), shows you how to apply FP principles such as immutability, avoidance of side-effects, and higher-order functions to your Java code. Each chapter provides exercises to help you practice what you've learned. Once you grasp the benefits of functional programming, you'll discover that it improves all of the code you write. * Learn basic FP principles and apply them to object-oriented programming * Discover how FP is more concise and modular than OOP * Get useful FP lessons for your Java type design - such as avoiding nulls * Design data structures and algorithms using functional programming principles * Write concurrent programs using the Actor model and software transactional memory * Use functional libraries and frameworks for Java - and learn where to go next to deepen your functional programming skills