Chapter 1, Getting Started with Kotlin, covers how to install Kotlin, the Jetbrains Intellij IDEA, and the Gradle build system. Once the setup of the tool chain is complete, the chapter shows how to write your first Kotlin program.

Chapter 2, Kotlin Basics, dives head first into the basics of Kotlin, including the basic types, basic syntax, and program control flow structures such as if statements, for loops, and while loops. The chapter concludes with Kotlin-specific additions such as when expressions and type inference.

Chapter 3, Object-Oriented Code in Kotlin, focuses on the object-orientated aspects of the language. It introduces classes, interfaces, objects and the relationship between them, subtypes, and polymorphism.

Chapter 4, Functions in Kotlin, shows that functions, also known as procedures or methods, are the basic building blocks of any language. This chapter covers the syntax for functions, including the Kotlin enhancements such as named parameters, default parameters, and function literals.

Chapter 5, Higher Order Functions and Functional Programming, focuses on the functional programming side of Kotlin, including closures--also known as lambdas--and function references. It further covers functional programming techniques such as partial application, function composition, and error accumulation.

Chapter 6, Properties, explains that properties work hand in hand with object-orientated programming to expose values on a class or object. This chapter covers how properties work, how the user can best make use of them, and also how they are represented in the bytecode.

Chapter 7, Null Safety, Reflection, and Annotations, explains that null safety is one of the main features that Kotlin provides, and the first part of this chapter covers in depth the whys and hows of null safety in Kotlin. The second part of the chapter introduces reflection--run time introspection of code--and how it can be used for meta programming with annotations.

Chapter 8, Generics, explains that generics, or parameterized types, are a key component of any advanced type system, and the type system in Kotlin is substantially more advanced than that available in Java. This chapter covers variance, the type system including the Nothing type, and algebraic data types.

Chapter 9, Data Classes, shows that immutability and boiler-plate free domain classes are a current hot topic, due to the way they facilitate more robust code and simplify concurrent programming. Kotlin has many features focused on this area, which it calls data classes.

Chapter 10, Collections, explains that collections are one of the most commonly used aspects of any standard library, and Java collections are no different. This chapter describes the enhancements that Kotlin has made to the JDK collections, including functional operations such as map, fold, and filter.

Chapter 11, Testing in Kotlin, explains that one of the gateways into any new language is using it as a language for writing test code. This chapter shows how the exciting test framework KotlinTest can be used to write expressive, human-readable tests, with much more power than the standard jUnit tests allow.

Chapter 12, Microservices in Kotlin, shows that microservices have come to dominate server-side architecture in recent years, and Kotlin is an excellent choice for writing such services. This chapter introduces the Lagom microservice framework and shows how it can be used to great effect with Kotlin.

Chapter 13, Concurrency, explains that as multi-core aware programs are becoming more and more important in server-side platforms, This chapter is focused on a solid introduction to concurrent programming techniques that are vital in modern development, including threads, concurrency primitives, and futures.

This book requires a computer running MacOS, Linux, or Windows, capable of running the latest versions of Java. It is recommended that the machine has enough memory to run a recent version of Jetbrains' Intellij IDEA.

This book is aimed those who have little or no Kotlin experience and wish to learn the language quickly. The focus of the book is on server-side development in Kotlin and would be best suited to a developer who is currently a server-side developer or who wishes to learn. No prior knowledge of functional or object-orientated programming is required, but knowledge of some other programming language is recommended.

Some chapters contain brief sections comparing Java implementations to their Kotlin cousins, but these pages can be skipped by those who have no prior Java knowledge.

In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.

Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "When using a data class, you get a copy method out of the box."

A block of code is set as follows:

    public class Sensor { 
      private final String id; 
      private final double value; 
      public Sensor(String id, double value) { 
        this.id = id;
        this.value = value; 
      }

When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:

    public class Sensor { 
      private final String id; 
      private final double value; 
      public Sensor(String id, double value) { 
        this.id = id;
        this.value = value; 
      }

Any command-line input or output is written as follows:

$ sdk install gradle 3.0

New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "In IntelliJ, choose Code | Generate."

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To send us general feedback, simply e-mail [email protected], and mention the book's title in the subject of your message.

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