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Learn Kotlin Programming

By : Stephen Samuel, Stefan Bocutiu

Learn Kotlin Programming

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

Preface

Who this book is for

What this book covers

To get the most out of this book

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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 runtime

The REPL

Kotlin for scripting

Kotlin with Gradle

Kotlin with Maven

IntelliJ and Kotlin

Eclipse and Kotlin

Mixing Kotlin and Java in a project

Summary

Kotlin Basics

Kotlin Basics

val and var

Type inference

Basic types in Kotlin

Comments

Packages

Imports

String templates

Ranges

Loops

Exception handling

Instantiating classes

Referential equality and structural equality

This expression

Visibility modifiers

Control flow as expressions

The null syntax

The when expression

Type hierarchy

Code contracts

Summary

Object-Oriented Programming in Kotlin

Object-Oriented Programming in Kotlin

Classes

Interfaces

Inheritance

Visibility modifiers

Abstract classes

Interface or abstract classes

Polymorphism

Overriding rules

Inheritance versus composition

Class delegation

Sealed classes

Summary

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

Operators

Function literals

Tail recursive functions

Varargs

Standard library functions

Generic functions

Pure functions

Java from Kotlin

Kotlin from Java

Summary

Higher-Order Functions and Functional Programming

Higher-Order Functions and Functional Programming

Higher-order functions

Closures

Anonymous functions

Function references

Function-literal receivers

Functions in the JVM

Function composition

Inline functions

Currying and partial application

Memoization

Type alias

Either

Custom DSLs

Validation and error accumulation

Summary

Properties

Properties

Why use properties?

Overriding getters and setters

Visibility

Late initialization

Delegated properties

Lazy initializations

Lateinit versus lazy

Observables

A non-null property delegate

Properties or methods?

Summary

Null Safety, Reflection, and Annotations

Null Safety, Reflection, and Annotations

Nullable types

Smart cast

Safe null access

Elvis operator

Safe casting

Optional

Reflection

Constructors

Objects and companions

Useful KClass properties

Reflective functions and properties

Annotations

Standard annotations

Runtime annotation discovery

Summary

Generics

Generics

Parameterized functions

Parameterized types

Bounded polymorphism

Type variance

Nothing type

Type projection

Type erasure

Type reification

Recursive type bounds

Algebraic data types

Summary

Data Classes

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

Limitations

Summary

Collections

Collections

Class hierarchy

Arrays

Lists

Maps

Sets

Read-only views

Indexed access

Sequences

Summary

Testing in Kotlin

Testing in Kotlin

Getting started

Choosing a spec

Matchers

Inspectors

Interceptors

Project config

Property testing

Table-driven testing

Tags, conditions, and config

Summary

Microservices with Kotlin

Microservices with Kotlin

Definition

Drawbacks

Why microservices?

Lagom

Defining services

Implementing a Lagom service

Summary

Section 3: Advanced Concepts in Kotlin

Section 3: Advanced Concepts in Kotlin

Concurrency

Concurrency

Threads

Deadlocks and livelocks

Executors

Race conditions

Summary

Coroutines

Coroutines

Suspending functions

Coroutine builders

Structured concurrency

Jobs

Context and scope

Cancellation and failure

Async

Coroutine dispatchers

Error handling

Summary

Application of Coroutines

Application of Coroutines

Channels

select expression

Debugging coroutines

Coroutines in action

Summary

Kotlin Serialization

Kotlin Serialization

Setup

Json serialization and deserialization

How it works

Protobuf serialization and deserialization

Annotations

Rules

Summary

Other Books You May Enjoy

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Type erasure

Kotlin is designed primarily as a language for the Java Virtual Machine (JVM), and when the JVM was first designed, generics were not included as a feature. Over time, it became apparent that this was a major flaw of the language, and so, in Java 1.5 (or Java SDK 5), released in 2004, generics were added as a feature to the compiler.

However, because of a desire to stay backward compatible with previous versions of Java, the designers of Java decided that generics would be implemented using a technique called erasure. Erasure is the name given to the process by which the compiler removes type parameters during compilation.

In Java, a class defined as List<T> in the source code would be compiled simply as List, or List<Object>, if you like. This poses problems, some of which have already been introduced:

Functions with the same names and same erased parameters...

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