Book Image

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria
Book Image

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Overview of this book

The Android team has announced first-class support for Kotlin 1.1. This acts as an added boost to the language and more and more developers are now looking at Kotlin for their application development. This recipe-based book will be your guide to learning the Kotlin programming language. The recipes in this book build from simple language concepts to more complex applications of the language. After the fundamentals of the language, you will learn how to apply the object-oriented programming features of Kotlin 1.1. Programming with Lambdas will show you how to use the functional power of Kotlin. This book has recipes that will get you started with Android programming with Kotlin 1.1, providing quick solutions to common problems encountered during Android app development. You will also be taken through recipes that will teach you microservice and concurrent programming with Kotlin. Going forward, you will learn to test and secure your applications with Kotlin. Finally, this book supplies recipes that will help you migrate your Java code to Kotlin and will help ensure that it's interoperable with Java.

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Table of Contents (21 chapters)
Title Page
Title Page
Copyright and Credits
Copyright and Credits
Packt Upsell
Packt Upsell
Contributors
Contributors
Preface
Preface
Free Chapter
1
Installation and Working with Environment
Installation and Working with Environment
Introduction
Creating Kotlin Android project
How to use Gradle to run Kotlin code
How to run a Kotlin compiled class
How to build a self-executable JAR with Gradle and Kotlin
Reading console input in Kotlin
Converting Java code to Kotlin and vice versa
How to write an idiomatic logger in Kotlin
Escaping for Java identifiers that are keywords in Kotlin
Disambiguating using the "as" keyword to locally rename the clashing entity
Doing bit manipulations in Kotlin
Parsing String to Long, Double, or Int
Using String templates in Kotlin
2
Control Flow
Control Flow
Introduction
Assigning result to an expression using the if keyword
Using range with the when expression
Using when with custom objects
Using try–catch as an expression
How to write a swap function in Kotlin using the also function
How to throw a custom exception in Kotlin
How to make a multiconditional loop in Kotlin
3
Classes and Objects
Classes and Objects
Introduction
Initializing body of constructor
Converting one data type into another
How to type check an object
How to work with an abstract class in Kotlin
How to iterate over a class's properties in Kotlin
How to work with inline properties
How to work with nested class
Getting class in Kotlin
Working with delegated properties
Working with enums
4
Functions
Functions
Introduction
Specifying default values in functions
Using named arguments in functions
Creating the RecyclerView Adapter in Kotlin
Creating getter setters in Kotlin
Passing variable arguments to a function
Passing a function as a parameter to another
Declaring a static function
Using the use keyword in Kotlin
Working with closures
Function literals with receivers
Working with anonymous functions
5
Object-Oriented Programming
Object-Oriented Programming
Introduction
Working with interfaces in Kotlin
How to implement complicated interfaces with multiple overridden methods in Kotlin
How to extend a class in Kotlin (Inheritance and Extension functions)
How to work with Generics in Kotlin
How to implement polymorphism in Kotlin
Restricting class hierarchies
6
Collections Framework
Collections Framework
Introduction
How to merge two collections
Splitting original collection into pair of collections
Sorting a list by specified comparator
Sorting in descending order
Parsing a JSON response using Gson
How to filter and map using lambda expressions
How to sort a list of objects and keep null objects at the end
How to implement a lazy list in Kotlin
How to pad a string in Kotlin
How to flatten an array or map
How to sort collection by multiple fields in Kotlin
How to use limit in Kotlin list
How to create a 2D array in Kotlin
How to skip the first "n" entries in Kotlin
7
Handling File Operations in Kotlin
Handling File Operations in Kotlin
Introduction
Reading from files using InputReader
Reading all lines in a file using InputReader
Reading line by line using InputReader
Reading from files using BufferedReader
Reading all lines in a file using BufferedReader
Reading line by line using bufferedReader
Reading string and JSON over network
8
Anko Commons and Extension Function
Anko Commons and Extension Function
Introduction
Setting up Anko with Gradle
Extending Android framework using extension function
Using extensions as properties
Using intents with Anko
Making a call intent using Anko
Sending a text intent using Anko
Browsing the web browser using Anko
Sharing some text using intents in Anko
Sending an email using Anko
Creating Android dialogs with Anko
Showing an alert dialog with a list of text items
Using Anko in Views
Logging using Anko
Handling dimensions with Anko
Version checking on Android
9
Anko Layouts
Anko Layouts
Introduction
Setting up Anko library for Anko layouts in Gradle
Creating user-interface programmatically
Working with the old code of XML layouts
Using the provided AnkoComponent interface
Setting theme for Android views in Anko
Setting layout parameters for Anko views
Adding listeners to Anko views
Inserting XML layouts into DSL
Converting XML files into DSL
Showing Snackbar
Showing Toasts
Accessing views using synthetic properties
Accessing views of view groups using extension functions
10
Databases and Dependency Injection
Databases and Dependency Injection
Introduction
Using SQLite database in Kotlin
Creating database tables
Injecting dependencies in Kotlin
Reading data from database
Converting database cursor into list of objects
Using parseOpt for nullable object
Inserting data into database
Creating singletons in Kotlin
Using Dagger 2 with Kotlin
Using Butterknife with Kotlin
11
Networking and Concurrency
Networking and Concurrency
Introduction
How to fetch data over network
How to create data class in Kotlin
How to copy data class with modifications
How to parse JSON data from network to data class
How to download a file in Kotlin
How to use RxJava and Retrofit with Kotlin
How to make an endless list using RecyclerView
How to use Anko to run background tasks with Kotlin in Android
How to use coroutines to achieve multithreading
12
Lambdas and Delegates
Lambdas and Delegates
Introduction
Click listeners using lambdas
Using lazy delegate in Kotlin
Using the observable delegate
Using vetoable delegate
Writing your own delegates
Using the lateinit modifier
Working with SharedPreferences
Creating a chain of multiple lets in Kotlin
Creating global variables
13
Testing
Testing
Introduction
Unit testing Kotlin code
Unit testing with Mockito
Running instrumentation tests
Writing JUnit rules in Kotlin (@Rule)
Acceptance tests using Espresso Kotlin
Writing assertEquals in Kotlin
14
Web Services with Kotlin
Web Services with Kotlin
Introduction
How to run the application on Tomcat
Setting up dependencies for building RESTful services
How to create a REST controller
Creating the Application class for Spring Boot
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Index
Index

Working with delegated properties

Kotlin 1.1 brought many updates; one of the important ones was delegated properties. There are three types of delegated properties:

  • lazy: Lazy properties are the ones evaluated first and the same instance is returned after them, much like a cache
  • observable: The listener is notified whenever a change is made
  • map: Properties are stored in the map instead of in every field

 In this recipe, we will see how to work with these delegates. So let's get started.

Getting ready

We will be working on Android code, so we will require Android Studio 3.

How to do it...

Let's see a simple example of a delegated property:

  1. First, we will work with the lazy delegate property. Simply put, this delegate can suspend the object creation until we first access it. This is really important when you are working with heavy objects; they take a long time to be created—for example, when creating a database instance or maybe dagger components. Not only this, the result is remembered and the same...
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