A Beginner's Guide to Scala, Object Orientation and Functional Programming

Description

Scala is now an established programming language developed by Martin Oderskey and his team at the EPFL. The name Scala is derived from Sca(lable) La(nguage). Scala is a multi-paradigm language, incorporating object oriented approaches with functional programming. Although some familiarity with standard computing concepts is assumed (such as the idea of compiling a program and executing this compiled from etc.) and with basic procedural language concepts (such as variables and allocation of values to these variables) the early chapters of the book do not assume any familiarity with object orientation nor with functional programming These chapters also step through other concepts with which the reader may not be familiar (such as list processing). From this background, the book provides a practical introduction to both object and functional approaches using Scala. These concepts are introduced through practical experience taking the reader beyond the level of the language syntax to the philosophy and practice of object oriented development and functional programming. Students and those actively involved in the software industry will find this comprehensive introduction to Scala invaluable. Contents 1 Introduction 1.1 Introduction 1.2 What Is Scala? 1.3 Why Scala? 1.4 Java to Scala Quick Comparison 1.5 Scala Versions 1.6 Is This Book for You? 1.7 Approach Taken by This Book 2 Elements of Object Orientation 2.1 Introduction 2.2 Terminology 2.3 Types of Hierarchy 2.4 The Move to Object Technology 2.5 Summary 2.6 Exercises 2.7 Further Reading 3 Why Object Orientation? 3.1 Introduction 3.2 The Procedural Approach 3.2.1 A Naked Data Structure 3.2.2 Procedures for the Data Structure 3.2.3 Packages 3.3 Does Object Orientation Do Better? 3.3.1 Packages Versus Classes 3.3.2 Inheritance 3.4 Summary 4 Constructing an Object-Oriented System 4.1 Introduction 4.2 The Application: Windscreen Wipe Simulation 4.3 Where Do We Start? 4.4 Identifying the Objects 4.5 Identifying the Services or Methods 4.6 Refining the Objects 4.7 Bringing It All Together 4.8 Where Is the Structure? 4.9 Summary 4.10 Exercises 4.11 Further Reading References 5 Functional Programming 5.1 Introduction 5.2 What Is Functional Programming? 5.3 Advantages to Functional Programming 5.4 Disadvantages of Functional Programming 5.5 Scala and Functional Programming 6 Scala Background 6.1 Introduction 6.2 The Class Person 6.3 Functional Programming 6.4 A Hybrid Language 7 A Little Scala 7.1 Introduction 7.2 The Scala Environment 7.3 The Scala Shell 7.4 The Scala IDE 7.4.1 Creating an IntelliJ Project 7.4.2 Inside IntelliJ 7.4.3 Creating a Module 7.5 Implementing the Object 7.6 Running the Application 7.6.1 Scala Interpreter Console 7.7 Scala Classpath 7.8 Compiling and Executing Scala 7.9 Memory Management 7.9.1 Why Have Automatic Memory Management? 7.9.2 Memory Management in Scala 7.9.3 When Is Garbage Collection Performed? 7.9.4 Checking the Available Memory 8 Scala Building Blocks 8.1 Introduction 8.2 Apps and Applications 8.3 The Basics of the Language 8.3.1 Some Terminology 8.3.2 The Message Passing Mechanism 8.3.3 The Statement Terminator 9 Scala Classes 9.1 Introduction 9.2 Classes 9.2.1 Class Definitions 9.2.2 Developing a Class Definition 9.2.3 Classes and Messages 9.2.4 Instances and Instance Variables 9.2.5 Classes and Inheritance 9.2.5.1 An Example of Inheritance 9.2.5.2 The Yo-Yo Problem 9.2.6 Instance Creation 9.2.7 Constructors 9.2.8 Auxiliary Constructors 9.2.9 Class Initialisation Behaviour 9.2.10 Review of Classes and Constructors 9.3 Case Classes 9.3.1 A Sample Class 10 Scala Methods 10.1 Introduction 10.2 Method Definitions 10.2.1 Method Parameters 10.2.2 Comments 10.2.3 The Local Variables Section 10.2.4 The Statements Section 10.2.5 The Return Operator 10.2.6 An Example Method 10.2.7 Overriding toString 10.2.8 Defining Property Methods 10.3 Named Parameters 11 Packages and Encapsulation 11.1 Introduction 11.2 Packages 11.2.1 Declaring a Package 11.2.2 Additional Package Definitions Options 11.2.2.1 Package Per File 11.2.2.2 Chain Package Definitions 11.2.2.3 Nested Package Definitions 11.2.3 An Example Package 11.2.4 Accessing Package Elements 11.2.5 An Example of Using a Package 11.3 Import Options 11.4 Additional Import Features 11.5 Package Objects 11.6 Key Scala Packages 11.7 Default Imports 11.8 Encapsulation 11.8.1 Scala Visibility Modifiers 11.8.2 Private Modified 11.8.3 Protected Modifier 12 Building a Class 12.1 Introduction 12.2 Create a New Module 12.3 Create a New Package 12.4 Create a New Class 12.5 Defining the Class 12.6 Adding Behaviour 12.7 Test Application 12.8 Override Tostring 12.9 Extras 13 Classes, Inheritance and Abstraction 13.1 Introduction 13.1.1 What Are Classes for? 13.2 Inheritance Between Types 13.3 Inheritance Between Classes 13.3.1 The Role of a Subclass 13.3.2 Capabilities of Classes 13.3.3 Overriding Behaviour 13.3.4 Protected Members 13.4 Restricting a Subclass 13.5 Abstract Classes 13.6 The Super Keyword 13.7 Scala Type Hierarchy 13.8 Polymorphism 14 Objects and Instances 14.1 Introduction 14.2 Singleton Objects 14.3 Companion Objects 14.3.1 Companion Object Behaviour 14.3.2 A Object or an Instance 15 Value Classes 15.1 Introduction 15.2 Value Classes 15.3 Simple Value Type Example 15.4 Additional Value Class Concepts 15.5 Negating Value Classes 16 Scala Constructs 16.1 Introduction 16.2 Numbers and Numeric Operators 16.2.1 Numeric Values 16.2.2 Arithmetic Operators 16.3 Characters and Strings 16.3.1 Characters 16.3.2 Strings 16.4 Assignments 16.5 Variables 16.5.1 Temporary Variables 16.5.2 Pseudo-Variables 16.5.3 Variable Scope 16.5.4 Option, Some and None 16.5.5 Boolean Values 16.5.6 Literals 16.6 Messages and Message Selectors 16.6.1 Invoking Methods 16.6.2 Precedence 16.7 Summary 17 Control and Iteration 17.1 Introduction 17.2 Control Structures 17.2.1 The if Statement 17.2.2 If Returns a Value 17.3 Iteration 17.3.1 For Loops 17.3.2 For Until 17.3.3 For Loop with a Filter 17.3.4 Longhand for Loop 17.3.5 For-Yield Loop 17.3.6 While Loops 17.3.7 Do Loops 17.3.8 An Example of Loops 17.4 Equality 17.5 Recursion 17.5.1 The Match Expression 18 Traits 18.1 Introduction 18.2 What Are Traits? 18.3 Defining a Trait 18.4 Using a Trait 18.5 Abstract Trait Members 18.6 Dynamic Binding of Traits 18.7 Sealed Traits 18.8 Marker Traits 18.9 Trait Dependencies 18.10 To Trait or not to Trait 19 Further Traits 19.1 Introduction 19.2 Stackable Modifications 19.3 Fat Versus Thin Traits 19.4 Universal Traits 19.5 Traits for a Data Type 19.6 Single Abstract Method (SAM) Traits 20 Arrays 20.1 Introduction 20.2 Arrays 20.2.1 Arrays of Objects 20.2.2 Ragged Arrays 20.3 Creating Square Arrays 20.4 Looping Through Arrays 20.5 The Main Method Revisited 21 Tuples 21.1 Introduction 21.2 Tuples 21.3 Tuple Characteristics 21.4 Tuple Classes 21.5 Creating a Tuple 21.6 Working with Tuples 21.7 Iterating Over a Tuple 21.8 Element Extraction 22 Functional Programming in Scala 22.1 Introduction 22.2 Scala as a Functional Language 22.3 Defining Scala Functions 22.4 Class, Objects, Methods and Functions 22.5 Lifting a Method 22.6 Single Abstract Method Traits 22.7 Closure 22.8 Referential Transparency 23 Higher-Order Functions 23.1 Introduction 23.2 Higher-Order Function Concepts 23.3 Scala Higher-Order Functions 23.4 Using Higher-Order Functions 23.5 Higher-Order Functions in Scala Collections 24 Partially Applied Functions and Currying 24.1 Introduction 24.2 Partially Applied Functions 24.3 Currying 24.3.1 Introduction to Currying 24.3.2 Defining Multiple Parameter List Functions 24.3.3 Using Curried Functions 24.3.4 Building Domain-Specific Languages 25 Scala Collections Framework 25.1 Introduction 25.2 What Are Collections? 25.3 Scala Collections 25.3.1 Package Scala.Collection 25.3.2 Common Seq Behaviour 25.3.3 Common Set Behaviour 25.3.4 Common Map Behaviour 26 Immutable Lists and Maps 26.1 Introduction 26.2 The Immutable List Collection 26.2.1 List Creation 26.2.2 List Concatenation 26.2.3 List Operations 26.2.4 List Processing 26.2.5 Further List Processing 26.2.6 Pattern Matching 26.2.7 Converting to a List 26.2.8 Lists of User Defined Types 26.3 The Immutable Map Type 27 Immutable and Mutable Collection Packages 27.1 Introduction 27.2 Package Scala.Collection.Immutable 27.2.1 Sequences 27.2.2 Sets 27.2.3 Maps 27.3 Package Scala.Collection.Mutable 27.3.1 ArrayBuffer 27.3.2 ListBuffer 27.3.3 LinkedList 27.3.4 Stack 27.3.5 HashMap 27.4 Generic Collections 27.5 Summary 28 Type Parameterisation 28.1 Introduction 28.2 The Set Class 28.3 Adding Type Parameterisation 28.3.1 The MyQueue Mutable Class 28.3.2 The Immutable Queue Class 28.4 Variance 28.5 Lower and Upper Bounds 28.6 Combining Variance and Bounds 29 Further Language Constructs 29.1 Introduction 29.2 Implicit Conversions 29.3 Implicit Parameters 29.4 Implicit Objects 29.5 Implicit Classes 29.6 Scala Annotations 29.7 Type Declarations 29.8 Enumerations 29.9 Lazy Evaluation 30 Exception Handling 30.1 Introduction 30.2 What Is an Exception? 30.3 What Is Exception Handling? 30.4 Throwing an Exception 30.5 Catching an Exception 30.6 Try Block Returns a Value 30.7 Defining an Exception 30.8 A More Functional Approach 30.9 The Try Type 31 Akka Actors 31.1 Introduction 31.2 The Actor Model 31.3 Some Terminology 31.4 Scala Threads 31.5 Akka Scala Actor Library 31.6 Concurrent Hello World 31.7 Concurrent Actors 31.8 The Akka Actor API 31.9 Actor Lifecycle 31.10 Akka Configuration 31.11 Actor DSL 32 Further Akka Actors 32.1 Introduction 32.2 Generating a Result from an Actor 32.3 Futures 32.4 Dispatchers 32.5 Actor Hierarchies 32.6 Actor Supervision 32.7 Good Practices 33 Scala and JDBC Database Access 33.1 Introduction 33.2 Why JDBC? 33.3 What Is JDBC? 33.4 Working with JDBC 33.5 The Database Driver 33.6 Registering Drivers 33.7 Setting Up MySQL 33.8 Setting Up the Database 33.8.1 Starting/Stopping/Connecting to MySQL 33.9 Creating a Database 33.9.1 Adding a User 33.9.2 Selecting to Work with a Database 33.9.3 Creating a Table 33.9.4 Adding Data to a Table 33.10 Opening a Connection 33.11 Inserting into a Table 33.12 Obtaining Data from a Database 33.13 Update an Existing Row 33.14 Deleting from a Table 33.15 Creating a Table 33.16 Stored Procedures 33.17 JDBC Data Sources 33.18 Connection Pooling 33.19 JDBC Metadata 33.19.1 DatabaseMetaData 33.19.2 ResultSetMetaData 34 Scala Style Database Access 34.1 Introduction 34.2 Slick 34.3 Querulus 34.4 Squeryl 34.5 O/R Broker 35 Slick: Functional Relational Mapping for Scala 35.1 Introduction 35.2 Obtaining Slick 35.3 Connecting to a Database 35.4 Mapping Tables to Scala Types 35.5 Table Query Interface 35.6 Creating Tables 35.7 Inserting Data 35.8 Composing Database I/O Actions 35.9 Example Setting Up a Database 35.10 Querying for Data 35.11 Updating, Upserting and Deleting Data 36 Testing 36.1 Introduction 36.2 Types of Testing 36.3 What Should Be Tested? 36.4 Types of Testing 36.4.1 Unit Testing 36.4.2 Integration Testing 36.4.3 System Testing 36.4.4 Installation Testing 36.4.5 Smoke Tests 36.5 Automating Testing 37 Scala Testing 37.1 Introduction 37.2 Scala Runtime Test Facilities 37.2.1 Validation Checks 37.2.2 Using Require and Assert 37.3 Test Libraries in Scala 37.3.1 ScalaTest 37.3.2 Spec 37.3.3 ScalaCheck 37.4 Scalatest Testing Framework 37.4.1 Setting up Your Scala Project 37.4.2 ScalaTest and JUnit 37.4.2.1 The package 37.4.2.2 RunWith Annotation 37.4.2.3 Naming Conventions 37.4.3 Scala Test and Functional Test Suites 37.5 Scalatest and Feature Tests 37.6 Test-Driven Development 37.6.1 The TDD Cycle 37.6.2 Test Complexity 37.6.3 Refactoring 38 Play Framework 38.1 Introduction 38.2 Introduction to Play 38.2.1 Working with a Web Application 38.2.2 How Play Changes the Stack 38.3 Starting with Play 38.3.1 Download and Install Play 38.3.2 Using a Play Starter Project 38.3.3 Starting the Application 38.4 Examining the Structure of the Application 38.5 Editing the Application 38.5.1 Working with Your IDE 38.5.2 Importing into IntelliJ 38.5.3 Working with the Application 38.6 Model–View–Controller 38.7 Exploring the Play Application 39 RESTful Services 39.1 Introduction 39.2 RESTful Services 39.3 A RESTful API 39.4 Creating the RESTful Web Application 39.5 JavaScript and jQuery 39.6 The jQuery Client 39.6.1 Obtaining jQuery 39.6.2 Adding jQuery to the Application 40 Scalaz 40.1 Introduction 40.2 Obtaining Scalaz 40.3 Scalaz Overview 40.4 Some Useful Typeclasses 40.4.1 Equals Typeclass 40.4.2 Order Typeclass 40.5 Standard Class Extensions 40.5.1 Extensions to Option 40.5.2 Boolean Extensions 40.5.3 Extensions to List 40.5.4 Extensions for Map 40.5.5 Extensions to String 40.6 The Other Either 40.7 Tagging 41 GUIs in Scala Swing 41.1 Introduction 41.2 Windows as Objects 41.3 Windows in Scala 41.4 Scala Swing 41.5 Scala Swing Packages 41.6 Swing Scala Worked Examples 41.6.1 Simple Hello World UI 41.6.2 Panels and UI Layout 41.6.3 Working with a BorderPanel 41.6.4 Working with a BoxPanel 41.6.5 Displaying a Table 42 User Input in Scala Swing 42.1 Introduction 42.2 Handling User Input 42.2.1 Scala Swing Actions 42.2.2 Working with Menus 42.3 A Simple GUI Example 43 Scala Build Tools 43.1 Introduction 43.2 Why We Need a Build Tool 43.3 Maven 43.3.1 Maven Repositories 43.3.2 The Maven POM 43.3.3 Scala and Maven 43.3.4 Maven Lifecycle Commands 43.4 SBT 43.4.1 Creating an SBT Project 43.4.2 SBT Lifecycle Commands 44 Scala & Java Interoperability 44.1 Introduction 44.2 A Simple Example 44.3 Inheritance 44.4 Issues 44.4.1 Scala Objects 44.4.2 Companion Modules 44.4.3 Traits 44.5 Functions 44.6 Collection Classes 44.7 Implementing a Java Interface