Raoul-Gabriel Urma - Java 8 in Action: Lambdas, Streams, and functional-style programming

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To our parents

Back in 1998 when I was eight years old, I picked up my first book on computingon JavaScript and HTML. Little did I know that opening that book would transform my life by exposing me to programming languages and the amazing things I could do with them. I was hooked. Every so often I still find a new programming language feature that revives this excitement because it enables me to write clearer, more concise code in half the time. I hope that the new ideas in Java 8, incorporated from functional programming and explored in this book, inspire you in the same way.

So, you may wonder, how did this book come about?

Well, back in 2011, Brian Goetz (the Java Language Architect at Oracle) was sharing various proposals to add lambda expressions to Java, with the aim of getting the community involved. These rekindled my excitement, and I started to evangelize the ideas, organizing Java 8 workshops at various developer conferences and giving lectures to students at the University of Cambridge.

By April 2013, word had spread, and our publisher at Manning emailed asking whether I was interested in writing a book about lambdas in Java 8. At the time I was a humble second-year PhD candidate, and that seemed to be a bad idea because it would interfere with my thesis submission schedule. On the other hand, carpe diem; I thought writing a short book shouldnt be too much work, right? (It was only later that I realized I was utterly wrong!) So I sought advice from my PhD supervisor, Professor Alan Mycroft, who, it turned out, was ready to support me in this adventure (even offering to help in such non-PhD workIm forever in his debt). A few days later we met fellow Java 8 evangelist Mario Fusco, who had vast professional experience and had become well known for his talks on functional programming at major developer conferences.

We quickly realized that by combining our energy and diverse backgrounds we could deliver, not just a short book on Java 8 lambdas, but instead a book that, we hope, the Java community will still be reading in five or ten years. We had a unique opportunity to discuss in depth many topics that will benefit Java programmers and open doors to a new universe of ideas: functional programming.

NowJuly 2014, 15 months later, after many long nights, endless edits, and an unforgettable experienceyou have our work in your hands and we hope you will enjoy it!

R AOUL -G ABRIEL U RMA
U NIVERSITY OF C AMBRIDGE

This book would not have been possible without the support of many amazing people:

• Personal friends and people who provided valuable reviews and suggestions on a volunteer basis: Richard Walker, Jan Saganowski, Brian Goetz, Stuart Marks, Cem Redif, Paul Sandoz, Stephen Colebourne, igo Mediavilla, Allahbaksh Asadullah, Tomasz Nurkiewicz, and Michael Mller
• Our Manning Early Access Program (MEAP) readers who posted comments in the Author Online forum
• The reviewers from the development process who provided helpful feedback: Antonio Magnaghi, Brent Stains, Franziska Meyer, Furkan Kamachi, Jason Lee, Jrn Dinkla, Lochana Menikarachchi, Mayur Patil, Nikolaos Kaintantzis, Simone Bordet, Steve Rogers, Will Hayworth, and William Wheeler
• Susan Conant, our development editor at Manning, who was very patient in answering all our questions and concerns, provided detailed feedback for each of our draft chapters, and supported us in all possible ways
• Ivan Todorovi and Jean-Franois Morin, who provided a thorough technical proofread of the manuscript shortly before it went to production; and Al Scherer, who provided technical expertise during development

R AOUL -G ABRIEL U RMA

First and foremost, Id like to thank my parents for their endless love and support in my life. This little dream of writing a book has now come true! Next, I would like to express my eternal gratitude to Alan Mycroft, my PhD supervisor and coauthor, for his trust and support. Id also like to thank my coauthor Mario Fusco for sharing this fun journey. Finally, Id like to thank friends who have provided mentorship, useful advice, and encouragement in my life: Sophia Drossopoulou, Aidan Roche, Warris Bokhari, Alex Buckley, Martijn Verburg, Tomas Petricek, and Tian Zhao. You guys rock!

M ARIO F USCO

Id like to especially thank my wife, Marilena, whose boundless patience allowed me to stay focused on the book, and our daughter, Sofia, because the infinite chaos she can produce allowed me to get creatively distracted from the book. As youll discover reading the book, Sofia also taught us, like only a two-year-old baby girl can, the difference between internal and external iteration. Id like to also thank Raoul-Gabriel Urma and Alan Mycroft, with whom I shared the (big) joys and the (small) pains of this writing experience.

A LAN M YCROFT

Id like to thank my wife, Hilary, and the rest of my family for enduring the many hours that just a bit more work to do on the book consumed. I also thank my colleagues and students over the years for teaching me how to teach, Mario and Raoul for being such efficient coauthors, and particularly Raoul for his skill at being so pleasantly demanding when requiring the next bit of text by Friday.

Put simply, the new features in Java 8 are the biggest change to Java in the 18 years since Java 1.0 was released. Nothing has been taken away, so all your existing Java code continues to workbut the new features provide powerful new idioms and design patterns to help you write clearer, more concise code. At first you might think (as with all new features), Why are they changing my language again? But then, after a bit of practice, comes the revelation that youve just used the features to write shorter, clearer code in half the time you expectedand you realize you could never go back to old Java again.