Book Image

Learn Kotlin Programming - Second Edition

By : Stephen Samuel, Stefan Bocutiu

Book Image

Learn Kotlin Programming - Second Edition

By: Stephen Samuel, Stefan Bocutiu

Overview of this book

Kotlin is a general-purpose programming language used for developing cross-platform applications. Complete with a comprehensive introduction and projects covering the full set of Kotlin programming features, this book will take you through the fundamentals of Kotlin and get you up to speed in no time. Learn Kotlin Programming covers the installation, tools, and how to write basic programs in Kotlin. You'll learn how to implement object-oriented programming in Kotlin and easily reuse your program or parts of it. The book explains DSL construction, serialization, null safety aspects, and type parameterization to help you build robust apps. You'll learn how to destructure expressions and write your own. You'll then get to grips with building scalable apps by exploring advanced topics such as testing, concurrency, microservices, coroutines, and Kotlin DSL builders. Furthermore, you'll be introduced to the kotlinx.serialization framework, which is used to persist objects in JSON, Protobuf, and other formats. By the end of this book, you'll be well versed with all the new features in Kotlin and will be able to build robust applications skillfully.

Preface

Who this book is for

What this book covers

To get the most out of this book

Free Chapter

Section 1: Fundamental Concepts in Kotlin

Section 1: Fundamental Concepts in Kotlin

Getting Started with Kotlin

Getting Started with Kotlin

Technical requirements

Using the command line to compile and run Kotlin code

Kotlin for scripting

Kotlin with Gradle

Kotlin with Maven

IntelliJ and Kotlin

Eclipse and Kotlin

Mixing Kotlin and Java in a project

Kotlin Basics

Basic types in Kotlin

String templates

Exception handling

Instantiating classes

Referential equality and structural equality

This expression

Visibility modifiers

Control flow as expressions

The null syntax

The when expression

Object-Oriented Programming in Kotlin

Object-Oriented Programming in Kotlin

Visibility modifiers

Abstract classes

Interface or abstract classes

Overriding rules

Inheritance versus composition

Class delegation

Section 2: Practical Concepts in Kotlin

Section 2: Practical Concepts in Kotlin

Functions in Kotlin

Functions in Kotlin

Defining functions

Single expression functions

Member functions

Local functions

Top-level functions

Named parameters

Default parameters

Extension functions

Function literals

Tail recursive functions

Standard library functions

Generic functions

Java from Kotlin

Kotlin from Java

Higher-Order Functions and Functional Programming

Higher-Order Functions and Functional Programming

Higher-order functions

Anonymous functions

Function references

Function-literal receivers

Functions in the JVM

Function composition

Inline functions

Currying and partial application

Validation and error accumulation

Properties

Why use properties?

Overriding getters and setters

Late initialization

Delegated properties

Lazy initializations

Lateinit versus lazy

A non-null property delegate

Properties or methods?

Null Safety, Reflection, and Annotations

Null Safety, Reflection, and Annotations

Safe null access

Objects and companions

Useful KClass properties

Reflective functions and properties

Standard annotations

Runtime annotation discovery

Generics

Parameterized functions

Parameterized types

Bounded polymorphism

Type projection

Type reification

Recursive type bounds

Algebraic data types

Data Classes

Introduction to data classes

Automatic creation of getters and setters

The copy method

toString out of the box

The hashCode and equals methods generated for you

Destructed declarations

Destructing types

Data class definition rules

Collections

Class hierarchy

Read-only views

Testing in Kotlin

Testing in Kotlin

Getting started

Choosing a spec

Property testing

Table-driven testing

Tags, conditions, and config

Microservices with Kotlin

Microservices with Kotlin

Why microservices?

Defining services

Implementing a Lagom service

Section 3: Advanced Concepts in Kotlin

Section 3: Advanced Concepts in Kotlin

Concurrency

Deadlocks and livelocks

Race conditions

Coroutines

Suspending functions

Coroutine builders

Structured concurrency

Context and scope

Cancellation and failure

Coroutine dispatchers

Application of Coroutines

Application of Coroutines

select expression

Debugging coroutines

Coroutines in action

Kotlin Serialization

Kotlin Serialization

Json serialization and deserialization

Protobuf serialization and deserialization

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Null Safety, Reflection, and Annotations

The dreaded null pointer exception is a familiar sight to anyone who has been a Java developer for any length of time. It is caused by a failure to handle null references correctly. Avoiding these errors has been the subject of many different ideas in many different programming languages. In this chapter, we'll review Kotlin's approach to null safety. Speaking at QCon, a conference organized by the developer blogging site InfoQ, Tony Hoare, the creator of the null pointer, referred to nulls as his billion-dollar mistake.

There are several different approaches to solving this so-called billion-dollar mistake.

In C, it was common for code that referenced a null pointer to simply crash. Java improved on this by having a NullPointerException that would not crash the JVM but could be handled by a try/catch block; however, the onus...