Programming Scala

Prepared exclusively for sam kaplan What Readers Are Saying About Programming Scala This books speaks directly to developers faced with the real and hard problems of concurrency. It offers clear solutions for building actors on the JVM. John Heintz Principal, Gist Labs Venkat introduces (Java) developers to programming Scala in an easy- to-follow, pragmatic style. This book covers Scala from basics to concurrency, one of the most critical and most difficult topics in programming today. Venkat gets to the meat without any fluff, and I highly recommend this book to get you up to speed on Scala quickly. Scott Leberknight Chief architect, Near Infinity Corporation Once again Venkat has made learning easy and fun. With his conver- sational style, this book allows developers to quickly learn the Scala language, its uniqueness, and how it can be best utilized in a multi- language environment. Ian Roughley Consultant, Down & Around, Inc. Multicore processors demand that developers have a solid grounding in the functional programming concepts found at the core of Scala. Venkat provides a great guide to get you started with this exciting new language. Nathaniel T. Schutta Author, speaker, teacher A pleasure to read! A great introduction to Scala for the experienced Java developer! This book teaches the “Scala way” of programming from a Java, object-oriented perspective. Very thorough yet concise. Albert Scherer Software architect, Follett Higher Education Group, Inc. Download at Boykma.Com Prepared exclusively for sam kaplan Concurrency is the next giant challenge we must face as developers, and traditional imperative languages make it too hard. Scala is a functional language on the JVM that offers easy multithreading, concise syntax, and seamless Java interop. This book guides Java developers through the important capabilities and nuances of Scala, show- ing why so much interest is bubbling around this new language. Neal Ford Software architect/meme wrangler, ThoughtWorks, Inc. Programming Scala is concise, easy to read, and thorough...one of the best introductions to Scala currently available. It’s a must-read for the programmer who wants to stay relevant as we enter the era of ubiqui- tous multicore processing. This is one of the books that I will go back to, time and again, in the coming years. Arild Shirazi Senior software developer, CodeSherpas, Inc. Download at Boykma.Com Prepared exclusively for sam kaplan Download at Boykma.Com Prepared exclusively for sam kaplan Programming Scala Tackle Multicore Complexity on the JVM Venkat Subramaniam The Pragmatic Bookshelf Raleigh, North Carolina Dallas, Texas Download at Boykma.Com Prepared exclusively for sam kaplan Many of the designations used by manufacturers and sellers to distinguish their products are claimed as trademarks. Where those designations appear in this book, and The Pragmatic Programmers, LLC was aware of a trademark claim, the designations have been printed in initial capital letters or in all capitals. The Pragmatic Starter Kit, The Pragmatic Programmer, Pragmatic Programming, Pragmatic Bookshelf and the linking g device are trademarks of The Pragmatic Programmers, LLC. Every precaution was taken in the preparation of this book. However, the publisher assumes no responsibility for errors or omissions, or for damages that may result from the use of information (including program listings) contained herein. Our Pragmatic courses, workshops, and other products can help you and your team create better software and have more fun. For more information, as well as the latest Pragmatic titles, please visit us at http://www.pragprog.com Copyright © 2008 Venkat Subramaniam. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmit- ted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. ISBN-10: 1-934356-31-X ISBN-13: 978-1-934356-31-9 Printed on acid-free paper. P1.0 printing, June 2009 Version: 2009-7-7 Download at Boykma.Com Prepared exclusively for sam kaplan Contents 1 Introduction 11 1.1 Why Scala? .......................... 11 1.2 What’s Scala? ........................ 14 1.3 Functional Programming .................. 19 1.4 What’s in This Book? .................... 22 1.5 Who Is This Book For? ................... 24 1.6 Acknowledgments ...................... 24 2 Getting Started 26 2.1 Downloading Scala ..................... 26 2.2 Installing Scala ....................... 27 2.3 Take Scala for a Ride .................... 28 2.4 Scala on the Command Line ................ 30 2.5 Running Scala Code as a Script .............. 31 2.6 Scala from an IDE ...................... 32 2.7 Compiling Scala ....................... 32 3 Getting Up to Speed in Scala 34 3.1 Scala as Concise Java ................... 34 3.2 Scala Classes for Java Primitives ............. 37 3.3 Tuples and Multiple Assignments ............. 38 3.4 Strings and Multiline Raw Strings ............ 40 3.5 Sensible Defaults ...................... 41 3.6 Operator Overloading .................... 43 3.7 Scala Surprises for the Java Eyes ............. 45 4 Classes in Scala 53 4.1 Creating Classes ....................... 53 4.2 Defining Fields, Methods, and Constructors . 54 4.3 Extending a Class ...................... 57 4.4 Singleton Object ....................... 58 4.5 Stand-Alone and Companion Objects .......... 60 4.6 static in Scala ........................ 61 Download at Boykma.Com Prepared exclusively for sam kaplan CONTENTS 8 5 Sensible Typing 63 5.1 Collections and Type Inference .............. 64 5.2 The Any Type ........................ 66 5.3 More About Nothing ..................... 67 5.4 Option Type ......................... 68 5.5 Method Return Type Inference .............. 69 5.6 Passing Variable Arguments (Varargs) .......... 70 5.7 Variance of Parameterized Type .............. 71 6 Function Values and Closures 75 6.1 Moving from Normal to Higher-Order Functions . 75 6.2 Function Values ....................... 76 6.3 Function Values with Multiple Parameters . 78 6.4 Currying ........................... 80 6.5 Reusing Function Values .................. 81 6.6 Positional Notation for Parameters ............ 83 6.7 Execute Around Method Pattern ............. 84 6.8 Partially Applied Functions ................ 87 6.9 Closures ........................... 88 7 Traits and Type Conversions 91 7.1 Traits ............................. 91 7.2 Selective Mixins ....................... 94 7.3 Decorating with Traits ................... 95 7.4 Method Late Binding in Traits ............... 97 7.5 Implicit Type Conversions ................. 99 8 Using Collections 103 8.1 Common Scala Collections ................. 103 8.2 UsingaSet .......................... 104 8.3 Using a Map ......................... 106 8.4 UsingaList ......................... 108 8.5 The for Expression ..................... 113 9 Pattern Matching and Regular Expressions 116 9.1 Matching Literals and Constants ............. 116 9.2 Matching a Wildcard .................... 117 9.3 Matching Tuples and Lists ................. 118 9.4 Matching with Types and Guards ............. 119 9.5 Pattern Variables and Constants in case Expressions . 120 9.6 Pattern Matching XML Fragments ............ 121 9.7 Matching Using case Classes ............... 121 Download at Boykma.Com Report erratum Prepared exclusively for sam kaplan this copy is (P1.0 printing, June 2009) CONTENTS 9 9.8 Matching Using Extractors ................. 124 9.9 Regular Expressions .................... 128 9.10 Regular Expressions as Extractors ............ 129 10 Concurrent Programming 131 10.1 Promote Immutability .................... 131 10.2 Concurrency Using Actor .................. 133 10.3 Message Passing ....................... 137 10.4 The Actor Class ....................... 139 10.5 The actor Method ...................... 141 10.6 receive and receiveWithin Methods ............ 144 10.7 react and reactWithin Methods .............. 146 10.8 loop and loopWhile ..................... 151 10.9 Controlling Thread of Execution ............. 153 10.10 Choosing Among the Receive Methods .......... 154 11 Intermixing with Java 156 11.1 Using Scala Classes in Scala ............... 156 11.2 Using Java Classes in Scala ................ 159 11.3 Using Scala Classes in Java ................ 161 11.4 Extending Classes ...................... 165 12 Unit Testing with Scala 167 12.1 Using JUnit ......................... 167 12.2 Using ScalaTest ....................... 169 12.3 Start with a Canary Test .................. 169 12.4 Using Runner ........................ 170 12.5 Asserts ............................ 172 12.6 Exception Tests ....................... 174 12.7 Sharing Code Between Tests ................ 176 12.8 Functional Style with FunSuite .............. 178 12.9 Running ScalaTests Using JUnit ............. 179 13 Exception Handling 183 13.1 Exception Handling ..................... 183 13.2 Mind the Catch Order ................... 186 14 Using Scala 187 14.1 The Net Asset Application ................. 187 14.2 Getting Users’ Input .................... 187 14.3 Reading and Writing Files ................. 188 14.4 XML as a First-Class Citizen ................ 190 Download at Boykma.Com Report erratum Prepared exclusively for sam kaplan this copy is (P1.0 printing, June 2009) CONTENTS 10 14.5 Reading and Writing XML ................. 193 14.6 Getting Stock Prices from the Web ............ 196 14.7 Making

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