Kotlin Programming Cookbook

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria

Buy this Book

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Buy this Book

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.

Title Page

Packt Upsell

Contributors

Preface

Free Chapter

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

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

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

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

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

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

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

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

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

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

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

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

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

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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Converting Java code to Kotlin and vice versa

The best part about Kotlin is its interoperability with Java. Also, with IntelliJ-based IDE, we can directly convert our Java code to Kotlin. In this recipe, we will see how to do it.

Getting ready

This recipe needs IntelliJ-based IDE installed, which compiles and runs Kotlin and Java.

How to do it...

Let's see the steps to convert a Kotlin file to a Java file:

In your IntelliJ IDE, open the Java file that you want to convert to Kotlin.
Note that it has a .java extension. Now, in the main menu, click on Code menu and choose the Convert Java File to Kotlin File option. Your Java file will be converted into Kotlin, and the extension will now be .kt.

Shown here is an example of a Java file:

After converting to Kotlin, this is what we have:

A Kotlin file can be converted into Java, but it's better if you can avoid it or find an alternative way to do it. If you have to absolutely convert your Kotlin code to Java, click on Tools | Kotlin | Show Kotlin Bytecode in the menu:

After clicking on Show Kotlin Bytecode, a window will open with the title Kotlin Bytecode:

Click on Decompile and a .java file will be generated, containing a decompiled Java bytecode from Kotlin code:

Yes, it has a lot of unnecessary code that was not present in the original Java code, but that is the case with decompiled bytecode. At the moment, this is the only way to convert Kotlin code to Java. Copy the decompiled file into a .java file and remove the unnecessary code.

How it works...

Kotlin is a statically-typed programming language that works on Java Virtual Machine and compiles into JVM compatible bytecode. This is the reason we can convert Java code to Kotlin and mix Java and Kotlin code together. This is also the reason why you can, in a way, get Java code back from Kotlin (although the output is not completely desired).

Kotlin Programming Cookbook

By : Aanand Shekhar Roy, Rashi Karanpuria

Kotlin Programming Cookbook

By: Aanand Shekhar Roy, Rashi Karanpuria

Overview of this book

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Getting ready

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How it works...