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- Herausgeber: Packt Publishing
- Kategorie: Wissenschaft und neue Technologien
- Sprache: Englisch
Build optimized applications in Kotlin by learning how to make use of the standard library features the smart way
Key Features
- Get the most out of the Kotlin library to develop high-quality portable applications
- Explore the powerful support for data processing and I/O operations
- Discover ways to enhance your Android application development
Book Description
Given the verbosity of Java, developers have turned to Kotlin for effective software development. The Kotlin standard library provides vital tools that make day-to-day Kotlin programming easier. This library features the core attributes of the language, such as algorithmic problems, design patterns, data processing, and working with files and data streams.
The recipes in this book offer coding solutions that can be readily executed. The book covers various topics related to data processing, I/O operations, and collections transformation. We'll walk through effective design patterns in Kotlin and you'll understand how coroutines add new features to JavaScript.
As you make your way through the chapters, you'll learn how to implement clean, reusable functions and scalable interfaces containing default implementations. In the concluding chapters, we'll provide recipes on functional programming concepts, such as lambdas, monads, functors, and Kotlin scoping functions.
By the end of the book, you'll be able to address a range of problems that Kotlin developers face by implementing easy-to-follow solutions.
What you will learn
- Work with ranges, progressions, and sequences in use cases
- Add new functionalities to current classes with Kotlin extensions
- Understand elements such as lambdas, closures, and monads
- Build a REST API consumer with Retrofit and a coroutine adapter
- Discover useful tips and solutions for making your Android projects
- Explore the benefits of standard library features
Who this book is for
This book is for software developers who are familiar with Kotlin's basics and want to discover more advanced features and concepts, especially those provided by the Kotlin standard library. It's also ideal for experienced software developers who are familiar with the functional programming paradigm and other programming languages who want to switch to Kotlin. It will also help Java developers switch to Kotlin and integrate it into existing Java Virtual Machine (JVM) projects.
Das E-Book können Sie in Legimi-Apps oder einer beliebigen App lesen, die das folgende Format unterstützen:
Seitenzahl: 251
Veröffentlichungsjahr: 2018
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Kotlin Standard Library Cookbook
Copyright © 2018 Packt Publishing
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Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing or its dealers and distributors, will be held liable for any damages caused or alleged to have been caused directly or indirectly by this book.
Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.
Commissioning Editor: Richa TripathiAcquisition Editor: Chaitanya NairContent Development Editor: Akshada IyerTechnical Editor: Abhishek SharmaCopy Editor:Safis EditingProject Coordinator: Prajakta NaikProofreader: Safis EditingIndexer: Tejal Daruwale SoniGraphics: Jisha ChirayilProduction Coordinator: Aparna Bhagat
First published: July 2018
Production reference: 1260718
Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK.
ISBN 978-1-78883-766-8
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Contributors
About the author
Samuel Urbanowicz is an experienced software engineer skilled in mobile applications and backend development. A fan of modern programming languages, he has been using Kotlin since its beginning. He's always curious to dive into technologies. He is especially passionate about machine learning. Samuel believes that the Kotlin language has great potential for multiplatform development. He has work experience in both big corps and small start-ups. He is an active contributor to open source projects.
About the reviewer
Miłosz Pacholczyk is a software developer with 5 years of commercial experience in Java. He worked on B2B software used by leading manufacturers of automotive and construction industries. He graduated from the University of Warsaw.
Packt is searching for authors like you
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Table of Contents
Title Page
Copyright and Credits
Kotlin Standard Library Cookbook
Dedication
Packt Upsell
Why subscribe?
PacktPub.com
Contributors
About the author
About the reviewer
Packt is searching for authors like you
Preface
Who this book is for
What this book covers
To get the most out of this book
Download the example code files
Conventions used
Sections
Getting ready
How to do it…
How it works…
There's more…
See also
Get in touch
Reviews
Ranges, Progressions, and Sequences
Introduction
Exploring the use of range expressions to iterate through alphabet characters
Getting ready
How to do it...
How it works...
There's more...
See also
Traversing through ranges using progression with a custom step value
Getting ready
How to do it...
How it works...
See also
Building custom progressions to traverse dates
Getting ready
How to do it...
How it works...
Using range expressions with flow control statements
Getting ready
How to do it...
How it works...
There's more...
See also
Discovering the concept of sequences
Getting ready
How to do it...
How it works...
There's more...
See also
Applying sequences to solve algorithmic problems
Getting ready
How to do it...
How it works...
Expressive Functions and Adjustable Interfaces
Introduction
Declaring adjustable functions with default parameters
How to do it...
How it works...
See also
Declaring interfaces containing default implementations
Getting ready
How to do it...
How it works...
There's more...
See also
Extending functionalities of classes
Getting ready
How to do it...
How it works...
There's more...
Destructuring types
Getting ready
How to do it...
How it works...
There's more...
Returning multiple data
How to do it...
How it works...
There's more...
See also
Inlining parameters of closure type
Getting ready
How to do it...
How it works...
There's more...
Infix notations for functions
Getting ready
How to do it...
How it works...
There's more...
See also
Smart types checking with generic reified parameters
Getting ready
How to do it...
How it works...
Overloading operators
Getting ready
How to do it...
How it works...
There's more...
Shaping Code with Kotlin Functional Programming Features
Introduction
Working effectively with lambda expressions
Getting ready
How to do it...
How it works...
There's more...
Discovering basic scoping functions – let, also, apply
Getting ready
How to do it...
How it works...
See also
Initializing objects the clean way using the run scoping function
Getting ready
How to do it...
How it works...
There's more...
See also
Working with higher-order functions
How to do it...
How it works...
Functions currying 
Getting ready
How to do it...
How it works...
There's more...
Function composition
Getting ready
How to do it...
How it works...
Implementing the Either Monad design pattern
How to do it...
How it works...
There's more...
Approach to automatic functions memoization 
How to do it...
How it works...
There's more...
Powerful Data Processing
Introduction
Composing and consuming collections the easy way
Getting ready
How to do it...
How it works...
There's more...
See also
Filtering datasets
Getting ready
How to do it...
How it works...
There's more...
See also
Automatic null removal
How to do it...
How it works...
See also
Sorting data with custom comparators
Getting started
How to do it...
How it works...
There's more...
Building strings based on dataset elements
How to do it...
How it works...
There's more...
See also
Dividing data into subsets
Getting ready
How to do it...
How it works...
There's more...
See also
Data transformation with map and flatMap
How to do it...
How it works...
There's more...
Folding and reducing data sets
How to do it...
How it works...
There's more...
Grouping data
How to do it...
How it works...
There's more...
See also
Tasteful Design Patterns Adopting Kotlin Concepts
Introduction
Implementing the Strategy pattern
How to do it...
How it works...
There's more...
See also
Exploring the power of the Delegation pattern
Getting ready
How to do it...
How it works...
See also
Implementing delegated class properties
Getting ready
How to do it...
How it works...
There's more...
See also
Tracking state with the Observer pattern
How to do it...
How it works...
See also
Restricting property updates with the Vetoable delegate
How to do it...
How it works...
See also
Implementing the advanced Observer pattern by defining a custom property delegate
How to do it...
How it works...
See also
Working with the Lazy delegate
How to do it...
How it works...
See also
Implementing builders the smart way
Getting ready
How to do it...
How it works...
There's more...
See also
Friendly I/O Operations
Introduction
Reading the contents of a file
Getting ready
How to do it...
How it works...
See also
Ensuring stream closing with the use function
Getting ready
How to do it...
How it works...
Reading the contents of a file line by line
Getting ready
How to do it...
How it works...
See also
Writing the contents to a file
How to do it...
How it works...
See also
Appending a file
How to do it...
How it works...
Easy file copying
Getting ready
How to do it...
How it works...
Traversing files in a directory
Getting ready
How to do it...
How it works...
Making Asynchronous Programming Great Again
Introduction
Executing tasks in the background using threads
Getting ready
How to do it...
How it works...
See also
Background threads synchronization
Getting ready
How to do it...
How it works...
See also
Using coroutines for asynchronous, concurrent execution of tasks
Getting ready
How to do it...
How it works...
See also
Using coroutines for asynchronous, concurrent tasks execution with results handling
Getting ready
How to do it...
How it works...
There's more...
See also
Applying coroutines for asynchronous data processing
How to do it...
How it works...
See also
Easy coroutine cancelation
Getting ready
How to do it...
How it works...
See also
Building a REST API client with Retrofit and a coroutines adapter
Getting ready
How to do it...
How it works...
See also
Wrapping third-party callback-style APIs with coroutines
Getting ready
How to do it...
How it works...
See also
Best Practices for the Android, JUnit, and JVM UI Frameworks
Introduction
Clean and safe view-binding with the Android Extensions plugin
Getting ready
How to do it...
How it works...
There's more...
Applying coroutines for asynchronous UI programming on Android, JavaFX, and Swing
Getting ready
How to do it...
How it works...
There's more...
See also
Easy class serialization on Android using the @Parcelize annotation
Getting ready
How to do it...
How it works...
See also
Implementing a custom property delegate that provides lifecycle-aware values
Getting ready
How to do it...
How it works...
See also
Easy operations on SharedPreferences
Getting ready
How to do it...
How it works...
See also
Less boilerplate Cursor data parsing
Getting ready
How to do it...
How it works...
Mocking dependencies with the Mockito Kotlin library
Getting ready
How to do it...
How it works...
See also
Verifying function invocations
Getting ready
How to do it...
How it works...
Unit tests for Kotlin coroutines
Getting ready
How to do it...
How it works...
Miscellaneous
Introduction
Kotlin and Java interoperability
How to do it...
How it works...
Kotlin and JavaScript interoperability
Getting ready
How to do it...
How it works...
There's more...
Renaming generated functions
How to do it...
How it works...
There's more...
See also
Decompiling Kotlin code to Java and JVM bytecode
Getting ready
How to do it...
How it works...
Adding custom names for imports
How to do it...
How it works...
Wrapping complex type declarations with type aliases
Getting ready
How to do it...
How it works...
Expressive try…catch declarations
Getting ready
How to do it...
How it works...
There's more...
Safe type-casting 
How to do it...
How it works...
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Preface
The primary aim of Kotlin Standard Library Cookbook is to help you dive into advanced language concepts and features as fast as possible in a friendly way. It covers a wide range of general programming problems at varying difficulty levels, including design patterns, functional programming, data processing, and more. The book consists of recipes that present a specific problem and give a step-by-step explanation of how to approach it effectively. All the presented features of the standard library are well explained, allowing you to discover them with ease.
This book will help software developers switch to Kotlin with ease and integrate it seamlessly into the existing JVM and JavaScript projects. Examples included in the book can easily be implemented in your own projects. You can also get the ready-made solutions from the book's GitHub repository if you prefer to follow and test the recipes in your favorite IDE. Once you have completed the book, you should have expert knowledge and insight into the language's advanced concepts, allowing you to address your daily programming challenges efficiently.
Who this book is for
The book is ideal for those who are already familiar with the basics of Kotlin and want to discover how to effectively solve day-to-day programming problems with state-of-the-art solutions, utilizing advanced language and standard library features. Experienced programmers who are willing to switch to Kotlin from other languages, especially Java, Scala, and JavaScript, will find it helpful as well.
What this book covers
Chapter 1, Ranges, Progressions, and Sequences, presents the concept of Kotlin ranges and sequences. It shows how to approach common algorithmic problems by defining custom sequences and how to define ranges for custom classes.
Chapter 2, Expressive Functions and Adjustable Interfaces, shows how to approach designing functions and interfaces using the language's built-in features. The chapter explains how to implement clean, reusable functions, and scalable interfaces containing default implementations. The recipes also cover other features of the language, such as inlining closures, destructuring variables, reified type parameters, and other useful tips that help design more flexible and natural code.
Chapter 3, Shaping Code with Kotlin Functional Programming Features, shows how to solve real-life programming challenges by adopting state-of-the-art functional programming patterns. The chapter helps readers get familiar with Kotlin support for functional programming concepts provided by the standard library and the built-in language features.
Chapter 4, Powerful Data Processing, focuses on presenting standard library support for declarative style operations on collections. The included recipes present solutions to varying programming problems related to dataset transformations, reducing, or filtering. The chapter shows how to approach data processing operations practicing a functional programming style with the use of powerful functionalities built into the standard library.
Chapter 5, Tasteful Design Patterns Adopting Kotlin Concepts, presents the Kotlin-specific approach to implementing popular design patterns, including the Observer and Lazy delegates, Builder, Strategy, and more. Design patterns presented in the following chapter are backed by real-life examples that emphasize the benefits of the Delegation pattern.
Chapter 6, Friendly I/O Operations, presents useful extension functions available in the standard library that simplify the work with I/O operations. The chapter focuses on common use cases of read-write operations on files, working with streams and buffers, and the Kotlin approach to traversing files available in a specific directory.
Chapter 7, Making Asynchronous Programming Great Again, is an in-depth guide to asynchronous programming focusing on the Kotlin coroutines framework and its application in real-life situations. The chapter presents how to optimize and advance previous examples by executing parts of their code in the background in a non-blocking way. Here, you will also find a practical example of implementing an asynchronous REST client with the Retrofit library and the coroutines framework.
Chapter 8, Best Practices for the Android, JUnit, and JVM UI Frameworks, covers practical problems specific to the popular frameworks, among which Kotlin is the one used most often. In general, it will focus on Android platform-specific aspects and asynchronous UI programming with coroutines, both on Android and JVM frameworks such as JavaFX and Swing. It will also help you to write effective unit tests for the JVM platform using the JUnit framework. The recipes related to unit testing will also include more advanced topics, such as mocking dependencies with the Mockito Kotlin library and testing asynchronous code based on the coroutines framework.
Chapter 9, Miscellaneous, presents handy solutions to various problems and issues that Kotlin developers deal with on a daily basis.
To get the most out of this book
In order to learn from the book efficiently, you should follow the included recipes step by step and try to implement the solutions on your own. You can download the sample code from the book's GitHub repository athttps://github.com/PacktPublishing/Kotlin-Standard-Library-Cookbook and import it into IntelliJ IDEA and Android Studio. If you have any trouble, you can run and test each recipe instantly in the IDE.
Download the example code files
You can download the example code files for this book from your account at www.packtpub.com. If you purchased this book elsewhere, you can visit www.packtpub.com/support and register to have the files emailed directly to you.
You can download the code files by following these steps:
Log in or register at
www.packtpub.com
.
Select the
SUPPORT
tab.
Click on
Code Downloads & Errata
.
Enter the name of the book in the
Search
box and follow the onscreen instructions.
Once the file is downloaded, please make sure that you unzip or extract the folder using the latest version of:
WinRAR/7-Zip for Windows
Zipeg/iZip/UnRarX for Mac
7-Zip/PeaZip for Linux
The code bundle for the book is also hosted on GitHub at https://github.com/PacktPublishing/Kotlin-Standard-Library-Cookbook. In case there's an update to the code, it will be updated on the existing GitHub repository.
We also have other code bundles from our rich catalog of books and videos available at https://github.com/PacktPublishing/. Check them out!
Sections
In this book, you will find several headings that appear frequently (Getting ready, How to do it..., How it works..., There's more..., and See also).
To give clear instructions on how to complete a recipe, use these sections as follows:
Getting ready
This section tells you what to expect in the recipe and describes how to set up any software or any preliminary settings required for the recipe.
How to do it…
This section contains the steps required to follow the recipe.
How it works…
This section usually consists of a detailed explanation of what happened in the previous section.
There's more…
This section consists of additional information about the recipe in order to make you more knowledgeable about the recipe.
See also
This section provides helpful links to other useful information for the recipe.
Get in touch
Feedback from our readers is always welcome.
General feedback: Email [email protected] and mention the book title in the subject of your message. If you have questions about any aspect of this book, please email us at [email protected].
Errata: Although we have taken every care to ensure the accuracy of our content, mistakes do happen. If you have found a mistake in this book, we would be grateful if you would report this to us. Please visit www.packtpub.com/submit-errata, selecting your book, clicking on the Errata Submission Form link, and entering the details.
Piracy: If you come across any illegal copies of our works in any form on the Internet, we would be grateful if you would provide us with the location address or website name. Please contact us at [email protected] with a link to the material.
If you are interested in becoming an author: If there is a topic that you have expertise in and you are interested in either writing or contributing to a book, please visit authors.packtpub.com.
Reviews
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For more information about Packt, please visit packtpub.com.
Ranges, Progressions, and Sequences
In this chapter, we will cover the following recipes:
Exploring the use of range expressions to iterate through alphabet characters
Traversing
through ranges using progression with a custom step value
Building custom progressions to traverse dates
Using range expressions with flow control statements
Discovering the concept of sequences
Applying sequences to solve algorithmic problems
Introduction
This chapter will focus on explaining the advantages of range expressions and sequences. These powerful data structure concepts offered by the Kotlin standard library can help you to improve the quality and readability of your code, as well as its safety and performance. Range expressions provide a declarative way of iterating through sets of comparable types using for loops. They are also useful for implementing concise and safe control flow statements and conditions. The Sequence class, as a missing supplement to the Collection type, provides a built-in lazy evaluation of its elements. In many cases, using sequences can help optimize data-processing operations and make the code more efficient in terms of computation complexity and memory consumption. The recipes covered in this chapter are going to focus on solving real-life programming problems. Moreover, at the same time, they are also going to explain how those concepts work under the hood.
Exploring the use of range expressions to iterate through alphabet characters
Ranges, provided by the Kotlin standard library, are a powerful solution for implementing iteration and conditional statements in a natural and safe way. A range can be understood as an abstract data type that represents a set of iterable elements and allows iteration through them in a declarative way. The ClosedRange interface from the kotlin.ranges package is a basic model of the range data structure. It contains references to the first and last elements of the range and provides the contains(value: T): Boolean and isEmpty(): Boolean functions, which are responsible for checking whether the specified element belongs to the range and whether the range is empty. In this recipe, we are going to learn how to declare a range that consists of alphabet characters and iterate through it in a decreasing order.
How to do it...
Declare a decreasing range of alphabet characters:
'Z' downTo 'A'
2. Create a for loop to traverse the range:
for (letter in 'Z' downTo 'A') print(letter)
How it works...
As a result, we are going to get the following code printed out to the console:
ZYXWVUTSRQPONMLKJIHGFEDCBA
As you can see, there is also a downTo() extension function variant for the available Char type. We are using it to create a range of characters from Z to A. Note that, thanks for the infix notation, we can omit the brackets while invoking the function—'Z' downTo 'A'.
Next, we are creating a for loop, which iterates through the range and prints out the subsequent Char elements. Using the in operator, we are specifying the object that is being iterated in the loop—and that's it! As you can see, the Kotlin syntax for the for loop is neat and natural to use.
